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Basin analysis of Tertiary strata in the Pattani Basin Gulf of Thailand Chonchawalit, Anun 1993

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BASIN ANALYSIS OF TERTIARY STRATAIN THE PATTANI BASINGULF OF THAILANDbyANUN CHONCHAWALITM.Sc., Engineering Geology, Asian Institute of Technology, 1985A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinTHE FACULTY OF GRADUATE STUDIESDepartment of Geological SciencesWe accept this thesis as conformingto the required standardTHE UNIVERSITY OF BRITISH COLUMBIAJANUARY, 1993© ANUN CHONCHAWALITIn presenting this thesis in partial fulfilment of the requirements for an advanceddegree at the University of British Columbia, I agree that the Library shall make itfreely available for reference and study. I further agree that permission for extensivecopying of this thesis for scholarly purposes may be granted by the head of mydepartment or by his or her representatives. It is understood that copying orpublication of this thesis for financial gain shall not be allowed without my writtenpermission.Department of ^QA4 0i (A\^C\',\AUSThe University of British ColumbiaVancouver, CanadaDate^3- 1912DE-6 (2/88)ABSTRACTThe stratigraphic and structural evolution of the Pattani Basin, the most prolificpetroleum basin in Thailand, reflects the extensional tectonic regime of theContinental Southeast Asia. East-west extension, a product of the northwardcollision of India with Eurasia since the Early Tertiary, resulted in the formation of aseries of N-S trending sedimentary basins including the Pattani Basin. Subsidenceand thermal histories of the basin can generally be accounted for by nonuniformlithospheric stretching. The validity of nonuniform lithospheric stretching as amechanism for the formation of the Pattani Basin is confirmed by a reasonably goodagreement between the modeled and observed vitrinite reflectance at various depthsand locations. The amount of stretching as well as surface heat flow generallyincreases from the margin to the basin center. Crustal stretching factor variesfrom 1.3 at the basin margin to 2.8 in the center. Subcrustal stretching factor (8)ranges from 1.3 at the basin margin to more than 3.0 in the basin center. Thestretching of the lithosphere may have extended the basement rocks as much as 45 to90 km and have caused the upwelling of aesthenosphere resulting in high heat flow.The sedimentary succession in the Pattani Basin is divisible into synrift and post-riftsequences. The synrift sequence comprises three stratigraphic units: 1) Late Eoceneto Early Oligocene alluvial fan, braided river and floodplain deposits; 2) LateOligocene to Early Miocene floodplain and channel deposits; and 3) an EarlyMiocene regressive package comprises marine to nonmarine sediments. Depositionof the synrift sequences corresponded to rifting and extension which includedepisodic block faulting and rapid subsidence. Post-rift succession comprises: 1) anEarly to Middle Miocene regressive package of shallow marine sediments throughfloodplain and channel deposits; 2) a late Early Miocene transgressive package; andii3) a Late Miocene to Pleistocene transgressive succession. The post-rift phase ischaracterized by slower subsidence and decreased sediment influx. The present-dayshallow marine condition in the Gulf of Thailand is the continuation of this latesttransgressive phase.The dispersed organic matter in Tertiary strata is composed mainly of Type III andType IV kerogen with minor amounts of Type II kerogen. The organic matter ispredominantly detrital and continental in origin as evident from low HI and high (IIvalues, and maceral composition (mainly vitrinite). The variation in abundance oforganic matter occurs both within the stratigraphic units and across the units; thelowest TOC and HI occur in the high energy nonmarine deposits such as alluvial fanand braided stream deposits, whereas higher TOC and HI generally occur in lowenergy deposits.Prospective petroleum source rocks generally have low TOC and very lowhydrocarbon potential as defined by pyrolysis. The presence of numerouscommercial gas fields suggests either that the source rocks here, despite very lowgenetic potentials, are very effective in producing, migrating, and accumulatinghydrocarbon or higher quality source rocks occur within the basin but have not yetbeen reached by drilling. Mean activation energies (E 0) of the perspective sourcerocks range from 46.1 to 60.6 kcal/mol which agree well with the activation energiesrequired to break down carbon-oxygen and carbon-carbon bonds (40-70 kcal/mol).The dispersion of activation energies (crE) varies from 0.26 to 9.30% of the meanvalues (E0). Analyses of hydrocarbon generation history, using a chemical kineticmodel based on the Arrhenius equation, indicates, except for the youngest unit (unit1), the strata are either mature or overmature with respect to the oil window. Themain phase of hydrocarbon generation started at about 33-35 Ma.iiiTABLE OF CONTENTSABSTRACT^ iiTABLE OF CONTENTS^ ivLIST OF TABLES viiiLIST OF FIGURES^ ixACKNOWLEDGEMENT xvii1. INTRODUCTION^ 11.1 General Overview^ 11.2 Location of the study area 31.3 Data sources 31.4 Exploration history in the Gulf of Thailand^51.5 Purpose of study^ 52. REGIONAL GEOLOGY 72.1 Introduction^ 72.2 Present-day geologic setting^ 72.3 Tectonic elements 93. STRATIGRAPHY AND SEDIMENTOLOGY^ 123.1 Abstract^ 123.2 Introduction 143.3 Methods of study^ 143.4 Stratigraphic subdivision 193.4.1 Unit 6 203.4.2 Unit 5^ 303.4.3 Unit 4 353.4.4 Unit 3 443.4.5 Unit 2^ 533.4.6 Unit 1 603.5 Discussion 653.5.1 Synrift sedimentation^ 66a. Late Eocene to Early Oligocene(40-30 Ma) 66b. Late Oligocene to Early Miocene(30-24 Ma)^ 67c. Early Miocene (24-20 Ma)^683.5.2 Post-rift sedimentation 70iva. Late Early to Middle Miocene(20-15 Ma)^ 70b. Middle Miocene (15-12 Ma)^72c. Late Miocene to Pleistocene(12-0 Ma)^ 723.6 Summary and conclusions 764. TECTONIC EVOLUTION AND BASIN MODELLINGOF THE PATTANI BASIN, THE GULF OF THAILAND ^794.1 Abstract^ 794.2 Introduction 804.3 Methods of study^ 824.3.1 Geohistory analysis^ 82a. Decompaction 83b. Backstripping 87c. Eustatic correction^ 884.3.2 Basin forming modelling 884.4 Basin forming mechanism in the Pattani Basin^954.5 Timing of basin formation^ 954.6 Subsidence history 964.6.1 Total subsidence and burial history^1004.6.2 Tectonic subsidence^ 1024.6.3 Lithospheric stretching factors 1184.7 Thermal history^ 1234.7.1 Heat flow history^ 1234.7.2 Thermal history and present-daygeothermal gradients 1244.7.3 Vitrinite reflectance^ 1264.8 Discussion^ 1324.9 Summary and conclusions 1395. ORGANIC CHARACTERISTICS AND PETROLEUMSOURCE ROCK POTENTIAL OF TERTIARY STRATAIN THE PATTANI BASIN^ 1425.1 Abstract 1425.2 Introduction 1435.3 Methods of study^ 1445.4 Summary of Tertiary stratigraphyin the Pattani Basin 1495.5 General characteristics of organic matter^1585.5.1 Unit 6^ 1895.5.2 Unit 5 2365.5.3 Unit 4 2375.5.4 Unit 3^ 2395.5.5 Unit 2 240v5.5.6 Unit 1^ 2425.6 Discussion 2435.6.1 Origin of variation in organic matter^243a. Origin of organic matter 244b. Organic characteristics anddepositional environments^245c. Organic characteristics andmaturation^ 247d. Organic abundance andsedimentation rate 248e. Organic abundance and age^254f. Discussion^ 2585.6.2 Source rock considerations 2595.7 Summary and conclusions 2626. ORGANIC MATURATION ANDHYDROCARBON GENERATION^ 2666.1 Abstract^ 2666.2 Introduction 2686.3 Methods of study^ 2736.3.1 Kinetics and organicmaturation modelling^ 2736.3.2 Determination of kinetic parameters^2776.4 Summary of Tertiary stratigraphy and organiccharacteristics in the Pattani Basin^ 2826.5 Kinetic parameters of the potential source rocks^2866.5.1 Unit 6^ 2876.5.2 Unit 5 2876.5.3 Unit 4 2906.5.4 Unit 3^ 2906.5.5 Unit 2 2916.5.6 Unit 1 2916.6 Hydrocarbon generation modelling^ 2926.7 Discussion^ 3206.7.1 Variation of kinetic parameters 320a. Sample preparation vs. kineticdeterminations^ 320b. Type of organic matter vs. kineticvariation 322c. Depositional environmentvs. kinetic variation^ 323d. Degree of thermal maturation vs.kinetic variation 3246.7.2 Hydrocarbon generation history^3246.7.3 Hydrocarbon potential considerations 326vi6.7.4 Other considerations^ 3276.8 Summary and conclusions 3287. SUMMARY AND CONCLUSIONS^ 331REFERENCES^ 339APPENDIX A: BASIN FORMATION MODELLING ^348APPENDIX B: ORGANIC MATURATION MODELLING 356APPENDIX C: DETERMINATION OF KINETICPARAMETERS OF SOURCE ROCKS^363viiLIST OF TABLESTable 3.1 Stratigraphy and depositional environments of Tertiarystrata in the Pattani Basin^ 21Table 4.1 Thermo-physical parameters used in the lithosphericstretching model^ 101Table 4.2 Summary of crustal and subcrustal stretching factors,geothermal gradients, organic maturation gradients,and present-day heat flow in the Pattani Basin^119Table 4.3 Kinetic parameters used to model vitrinite maturation 130Table 5.1 Measured and calculated parameters derived fromRock-Eval/TOC analysis^ 146Table 5.2 Generalized characteristics of organic facies A-D ^150Table 5.3 Stratigraphy and depositional environments of Tertiarystrata in the Pattani Basin^ 155Table 5.4 Summary of organic geochemical characteristics ofTertiary stratigraphic units in the Pattani Basin^207Table 5.5 Summary of organic geochemical characteristics ofTertiary stratigraphic subunits in the Pattani Basin 207Table 6.1 Kinetic parameters of potential source rocks ofTertiary stratigraphic units in the Pattani Basin^288viiiLIST OF FIGURESFigure 1.1 Tertiary basins in the Gulf of Thailand ^ 2Figure 1.2 Location of well data used in this study 4Figure 2.1 Tectonic map of Southeast Asia 8Figure 2.2 Generalized W-E cross section of thePattani Basin^ 10Figure 3.1 Location map of the Pattani Basin^ 15Figure 3.2 Four characteristic gamma log motifs 17Figure 3.3 Diagram showing three common grain-size motifs^17Figure 3.4 Cenozoic palynological zones^ 18Figure 3.5 W-E stratigraphic section-1 23Figure 3.6 W-E stratigraphic section-2 23Figure 3.7 W-E stratigraphic section-3^ 24Figure 3.8 W-E stratigraphic section-4 24Figure 3.9 N-S stratigraphic section-5 25Figure 3.10 N-S stratigraphic section-6^ 25Figure 3.11 Typical log profiles of unit 6 27Figure 3.12 Isopach map of the stratigraphic unit 6 ^ 28Figure 3.13 Typical log profiles of unit 5^ 31Figure 3.14 Isopach map of the stratigraphic unit 5 32Figure 3.15 Typical log profiles of unit 4 36Figure 3.16 Isopach map of the stratigraphic unit 4 ^ 37Figure 3.17 Isopach map of unit 4's lower subunit 39Figure 3.18 Isopach map of unit 4's middle subunit 41Figure 3.19 Isopach map of unit 4's upper subunit^ 43Figure 3.20 Typical log profiles of unit 3^ 46Figure 3.21 Isopach map of the stratigraphic unit 4 47Figure 3.22 Isopach map of unit 3's lower subunit^ 48Figure 3.23 Isopach map of unit 3's middle subunit 50Figure 3.24 Isopach map of unit 3's upper subunit 52Figure 3.25 Typical log profiles of unit 2^ 55Figure 3.26 Isopach map of the stratigraphic unit 2 ^ 56Figure 3.27 Isopach map of unit 2's lower subunit 57Figure 3.28 Isopach map of unit 2's upper subunit 59Figure 3.29 Typical log profiles of unit 1^ 61Figure 3.30 Isopach map of the stratigraphic unit 4 ^ 62Figure 3.31 The regressive cycle of unit 4 69Figure 3.32 The regressive cycle of unit 3^ 71Figure 3.33 The transgressive cycle of unit 2 73Figure 3.34 Tectonic subsidence and sedimentation ofTertiary strata in the Pattani Basin ^ 74Figure 3.35 Schematic evolution of sedimentaryenvironments in the Pattani Basin 75Figure 4.1 Location of well data used in this study ^ 81ixFigure 4.2 W-E stratigraphic section-1 ^ 97Figure 4.3 W-E stratigraphic section-2 97Figure 4.4 W-E stratigraphic section-3 98Figure 4.5 W-E stratigraphic section-4^ 98Figure 4.6 N-S stratigraphic section-5 99Figure 4.7 N-S stratigraphic section-6 99Figure 4.8 Basin subsidence, heat flow history, and vitrinitereflectance at Ranong-1 well^ 103Figure 4.9 Basin subsidence, heat flow history, and vitrinitereflectance at Kung-1 well 103Figure 4.10 Basin subsidence, heat flow history, and vitrinitereflectance at Surat-1 well^ 104Figure 4.11 Basin subsidence, heat flow history, and vitrinitereflectance at Platong-8 well 104Figure 4.12 Basin subsidence, heat flow history, and vitrinitereflectance at Platong-1 well^ 105Figure 4.13 Basin subsidence, heat flow history, and vitrinitereflectance at Insea-1 well 105Figure 4.14 Basin subsidence, heat flow history, and vitrinitereflectance at Palcarang-1 well^ 106Figure 4.15 Basin subsidence, heat flow history, and vitrinitereflectance at Pladang-3 well 106Figure 4.16 Basin subsidence, heat flow history, and vitrinitereflectance at South Platong-2 well ^ 107Figure 4.17 Basin subsidence, heat flow history, and vitrinitereflectance at Trat-1 well^ 107Figure 4.18 Basin subsidence, heat flow history, and vitrinitereflectance at Dara-1 well 108Figure 4.19 Basin subsidence, heat flow history, and vitrinitereflectance at Erawan-12-1 well^ 108Figure 4.20 Basin subsidence, heat flow history, and vitrinitereflectance at Erawan-12-8 well 109Figure 4.21 Basin subsidence, heat flow history, and vitrinitereflectance at Satun-3 well^ 109Figure 4.22 Basin subsidence, heat flow history, and vitrinitereflectance at Jakrawan-2 well 110Figure 4.23 Basin subsidence, heat flow history, and vitrinitereflectance at Krut-1 well^ 110Figure 4.24 Basin subsidence, heat flow history, and vitrinitereflectance at Erawan-K-1 well 111Figure 4.25 Basin subsidence, heat flow history, and vitrinitereflectance at Baanpot-1 well^ 111Figure 4.26 Basin subsidence, heat flow history, and vitrinitereflectance at Baanpot-B-1 well 112Figure 4.27 Basin subsidence, heat flow history, and vitrinitereflectance at Jakrawan-1 well^ 112Figure 4.28 Basin subsidence, heat flow history, and vitrinitereflectance at Funan-1 well 113Figure 4.29 Basin subsidence, heat flow history, and vitrinitereflectance at Yala-2 well^ 113Figure 4.30 Basin subsidence, heat flow history, and vitrinitereflectance at Kaphong-3 well 114Figure 4.31 Basin subsidence, heat flow history, and vitrinitereflectance at Kaphong-1 well^ 114Figure 4.32 Basin subsidence, heat flow history, and vitrinitereflectance at Platong-5 well 115Figure 4.33 Basin subsidence, heat flow history, and vitrinitereflectance at South Platong-1 well^ 115Figure 4.34 Basin subsidence, heat flow history, and vitrinitereflectance at Satun-2 well^ 116Figure 4.35 Basin subsidence, heat flow history, and vitrinitereflectance at Satun-1 well 116Figure 4.36 Basin subsidence, heat flow history, and vitrinitereflectance at Erawan-12-9 well^ 117Figure 4.37 Basin subsidence, heat flow history, and vitrinitereflectance at Erawan-12-7 well 117Figure 4.38 Lateral variation of crustal lithosphericstretching ((3)^ 120Figure 4.39 Lateral variation of subcrustal lithosphericstretching (5) 121Figure 4.40 Lateral variation of total lithosphericstretching (c)^ 122Figure 4.41 Present-day surface heat flow (HFU) ^ 125Figure 4.42 Calculated present-day geothermalgradients (°C/km)^ 127Figure 4.43 Observed present-day organic maturationgradients (%Ro/km) 131Figure 4.44 Tectonic map of Southeast Asia and South Chinashowing the main fault patterns^ 134Figure 4.45 Structural map of the Gulf of Thailand 135Figure 5.1 Location of well data used in this study 151Figure 5.2 W-E stratigraphic section-1^ 152Figure 5.3 W-E stratigraphic section-2 152Figure 5.4 W-E stratigraphic section-3 153Figure 5.5 W-E stratigraphic section-4 ^ 153Figure 5.6 N-S stratigraphic section-5 154Figure 5.7 N-S stratigraphic section-6 154Figure 5.8 Rock-Eval pyrolysis result of Ranong-1 well^ 159xiFigure 5.9 Rock-Eval pyrolysis result of Kung-1 wellFigure 5.10 Rock-Eval pyrolysis result of Surat-1 wellFigure 5.11 Rock-Eval pyrolysis result of Platong-8 wellFigure 5.12 Rock-Eval pyrolysis result of Platong-1 wellFigure 5.13 Rock-Eval pyrolysis result of Insea-1 wellFigure 5.14 Rock-Eval pyrolysis result of Pakarang-1 wellFigure 5.15 Rock-Eval pyrolysis result of Pladang-3 wellFigure 5.16 Rock-Eval pyrolysis result of SouthPlatong-2 wellFigure 5.17 Rock-Eval pyrolysis result of Trat-1 wellFigure 5.18 Rock-Eval pyrolysis result of Dara-1 wellFigure 5.19 Rock-Eval pyrolysis result of Erawan-12-1 wellFigure 5.20 Rock-Eval pyrolysis result of Erawan-12-8 wellFigure 5.21 Rock-Eval pyrolysis result of Satun-3 wellFigure 5.22 Rock-Eval pyrolysis result of Jakrawan-2 wellFigure 5.23 Rock-Eval pyrolysis result of Krut-1 wellFigure 5.24 Rock-Eval pyrolysis result of Erawan-K-1 wellFigure 5.25 Rock-Eval pyrolysis result of Baanpot-1 wellFigure 5.26 Rock-Eval pyrolysis result of Baanpot-B-1 wellFigure 5.27 Rock-Eval pyrolysis result of Jakrawan-1 wellFigure 5.28 Rock-Eval pyrolysis result of Funan-1 wellFigure 5.29 Rock-Eval pyrolysis result of Yala-2 wellFigure 5.30 Rock-Eval pyrolysis result of Kaphong-3 wellFigure 5.31 Rock-Eval pyrolysis result of Kaphong-1 wellFigure 5.32 Rock-Eval pyrolysis result of Platong-5 wellFigure 5.33 Rock-Eval pyrolysis result of SouthPlatong-1 wellFigure 5.34 Rock-Eval pyrolysis result of Satun-2 wellFigure 5.35 Rock-Eval pyrolysis result of Satun-1 wellFigure 5.36 Rock-Eval pyrolysis result of Erawan-12-9 wellFigure 5.37 Rock-Eval pyrolysis result of Erawan-12-7 wellFigure 5.38 Modified Van Krevelen diagram for samples fromunit 6's lower subunitFigure 5.39 Modified Van Krevelen diagram for samples fromunit 6's upper subunitFigure 5.40 Modified Van Krevelen diagram for samples fromunit 5's lower subunitFigure 5.41 Modified Van Krevelen diagram for samples fromunit 5's upper subunitFigure 5.42 Modified Van Krevelen diagram for samples fromunit 4's lower subunitFigure 5.43 Modified Van Krevelen diagram for samples fromunit 4's middle subunitFigure 5.44 Modified Van Krevelen diagram for samples fromunit 4's upper subunit160161162163164165166167168169170171172173174175176177178179180181182183184185186187188190190191192193194195xiiFigure 5.45 Modified Van Krevelen diagram for samples fromunit 3's lower subunitFigure 5.46 Modified Van Krevelen diagram for samples fromunit 3's middle subunitFigure 5.47 Modified Van Krevelen diagram for samples fromunit 3's upper subunitFigure 5.48 Modified Van Krevelen diagram for samples fromunit 2's lower subunitFigure 5.49 Modified Van Krevelen diagram for samples fromunit 2's upper subunitFigure 5.50 Modified Van Krevelen diagram for samples fromunit l's lower subunitFigure 5.51 Modified Van Krevelen diagram for samples fromunit l's upper subunitFigure 5.52 Lateral distribution of TOC (%) of unit 5Figure 5.53 Lateral distribution of TOC (%) of unit 4Figure 5.54 Lateral distribution of TOC (%) of unit 3Figure 5.55 Lateral distribution of TOC (%) of unit 2Figure 5.56 Lateral distribution of TOC (%) of unit 5'slower subunitFigure 5.57 Lateral distribution of TOC (%) of unit 5'supper subunitFigure 5.58 Lateral distribution of TOC (%) of unit 4'slower subunitFigure 5.59 Lateral distribution of TOC (%) of unit 4'smiddle subunitFigure 5.60 Lateral distribution of TOC (%) of unit 4'supper subunitFigure 5.61 Lateral distribution of TOC (%) of unit 3'slower subunitFigure 5.62 Lateral distribution of TOC (%) of unit 3'smiddle subunitFigure 5.63 Lateral distribution of TOC (%) of unit 3'supper subunitFigure 5.64 Lateral distribution of TOC (%) of unit 2'slower subunitFigure 5.65 Lateral distribution of TOC (%) of unit 2'supper subunitFigure 5.66 Lateral distribution of QOM (mg HC/g TOC)of unit 5Figure 5.67 Lateral distribution of QOM (mg HC/g TOC)of unit 4Figure 5.68 Lateral distribution of QOM (mg HC/g TOC)of unit 3197198200202204206206208209210211212213214215216217218219220221222223224Figure 5.69 Lateral distribution of QOM (mg HC/g TOC)of unit 2^ 225Figure 5.70 Lateral distribution of QOM (mg HC/g TOC)of unit 5's lower subunit^ 226Figure 5.71 Lateral distribution of QOM (mg HC/g TOC)of unit 5's upper subunit 227Figure 5.72 Lateral distribution of QOM (mg HC/g TOC)of unit 4's lower subunit^ 228Figure 5.73 Lateral distribution of QOM (mg HC/g TOC)of unit 4's middle subunit 229Figure 5.74 Lateral distribution of QOM (mg HC/g TOC)of unit 4's upper subunit^ 230Figure 5.75 Lateral distribution of QOM (mg HC/g TOC)of unit 3's lower subunit 231Figure 5.76 Lateral distribution of QOM (mg HC/g TOC)of unit 3's middle subunit^ 232Figure 5.77 Lateral distribution of QOM (mg HC/g TOC)of unit 3's upper subunit 233Figure 5.78 Lateral distribution of QOM (mg HC/g TOC)of unit 2's lower subunit^ 234Figure 5.79 Lateral distribution of QOM (mg HC/g TOC)of unit 2's upper subunit 235Figure 5.80 Variation of TOC and HI withdepositional environments^ 246Figure 5.81 Variation of TOC and HI with organic maturation ^249Figure 5.82 Variation of TOC and HI with sedimentation rate 251Figure 5.83 Variation of TOC and HI with age^ 255Figure 5.84 Variation of mean sedimentation rate and TOCwith age^ 256Figure 5.85 Variation of genetic potential and QOM with age^260Figure 6.1 Location of well data used in this study^ 269Figure 6.2 W-E stratigraphic section-1^ 270Figure 6.3 W-E stratigraphic section-2 270Figure 6.4 W-E stratigraphic section-3 271Figure 6.5 W-E stratigraphic section-4^ 271Figure 6.6 N-S stratigraphic section-5 272Figure 6.7 N-S stratigraphic section-6 272Figure 6.8 Shift of Tmax with heating rate ^ 279Figure 6.9 Reaction rate profiles using different values ofdistribution of activation energies 279Figure 6.10 Activation energy of each stratigraphic unit^289Figure 6.11 The extent and rate of hydrocarbon generation atRanong-1 well^ 293Figure 6.12 The extent and rate of hydrocarbon generation atKung-1 well 293xivFigure 6.13Figure 6.14Figure 6.15Figure 6.16Figure 6.17Figure 6.18Figure 6.19Figure 6.20Figure 6.21Figure 6.22Figure 6.23Figure 6.24Figure 6.25Figure 6.26Figure 6.27Figure 6.28Figure 6.29Figure 6.30Figure 6.31Figure 6.32Figure 6.33Figure 6.34of hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonellof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonof hydrocarbonThe extent and rateS urat-1 wellThe extent and ratePlatong-8 wellThe extent and ratePlatong-1 wellThe extent and rateInsea-1 wellThe extent and ratePalcarang-1 wellThe extent and ratePladang-3 wellThe extent and rateSouth Platong-2 wThe extent and rateTrat-1 wellThe extent and rateDara-1 wellThe extent and rateErawan-12-1 wellThe extent and rateErawan-12-8 wellThe extent and rateSatun-3 wellThe extent and rateJakrawan-2 wellThe extent and rateKrut-1 wellThe extent and rateErawan-K-1 wellThe extent and rateBaanpot-1 wellThe extent and rateBaanpot-B-1 wellThe extent and rateJakrawan-1 wellThe extent and rateFunan-1 wellThe extent and rateYala-2 wellThe extent and rateKaphong-3 wellThe extent and rateKaphong-1 wellgeneration at294generation at294generation at295generation at295generation at296generation at296generation at297generation at297generation at298generation at298generation at299generation at299generation at300generation at300generation at301generation at301generation at302generation at302generation at303generation at303generation at304generation at304xvFigure 6.35 The extent and rate of hydrocarbon generation atPlatong-5 well^ 305Figure 6.36 The extent and rate of hydrocarbon generation atSouth Platong-1 well 305Figure 6.37 The extent and rate of hydrocarbon generation atSatun-2 well^ 306Figure 6.38 The extent and rate of hydrocarbon generation atSatun-1 well 306Figure 6.39 The extent and rate of hydrocarbon generation atErawan-12-9 well^ 307Figure 6.40 The extent and rate of hydrocarbon generation atErawan-12-7 well 307Figure 6.41 Calculated present-day reaction extent of unit 6'shydrocarbon generation^ 308Figure 6.42 Calculated present-day reaction extent of unit 5'shydrocarbon generation 309Figure 6.43 Calculated present-day reaction extent of unit 4'shydrocarbon generation^ 310Figure 6.44 Calculated present-day reaction extent of unit 3'shydrocarbon generation 311Figure 6.45 Calculated present-day reaction extent of unit 2'shydrocarbon generation^ 312Figure 6.46 Timing of main hydrocarbon generation phase ofunit 6^ 313Figure 6.47 Timing of main hydrocarbon generation phase ofunit 5 314Figure 6.48 Timing of main hydrocarbon generation phase ofunit 4^ 315Figure 6.49 Timing of main hydrocarbon generation phase ofunit 3 316Figure 6.50 Timing of main hydrocarbon generation phase ofunit 2^ 317Figure 6.51 The effect of sample preparation on kineticparameters 321Figure 6.52 Variation of kinetic parameters with depositionalenvironments^ 321Figure 6.53 Variation of kinetic parameters with organicmaturation 325xviACKNOWLEDGEMENTThe author is grateful to his thesis supervisor Dr. R.M. Bustin for direction, advice,support and patience throughout this study. The author gratefully acknowledges thefinancial support of the Canadian International Development Agency. The author isgrateful to Unocal Thailand Company for providing all the logistical data. Thanks arealso due to Dr. M.A. Barnes, Dr. W.C. Barnes, Dr. J.W. Murray, Dr. R.L. Chase,and Dr. G.E. Rouse of the University of British Columbia for their expertise andconsultation. Thanks are also extended to Dr. R.L. Braun of the Lawrence LivermoreNational Laboratory, California, for his consultation in kinetic modelling. Finally, Iam grateful to my wife Kwanjai Chonchawalit, without whose patience and moralsupport, this work would not have been possible.xvii1. INTRODUCTION1.1 GENERAL OVERVIEWThe Pattani Basin is a Tertiary depocenter located in the central part of the Gulf ofThailand (Figure 1.1) covering approximately 10,000 square kilometres. The basinis an intracratonic basin containing a succession of more than ten kilometres ofTertiary sedimentary rocks. The sequence is dominated by nonmarine and marginalmarine clastics, predominantly sandstone and shale. The origin of the Pattani Basinand other Tertiary basins in Thailand is related to the extensional tectonic regimedeveloped after the collision of the Indian and Eurasian plates.Tertiary basins, including the Pattani Basin, are the prime target for hydrocarbonexploration in Southeast Asia. Numerous oil and gas discoveries in these basinshave stimulated extensive exploration programs in the 1980's and 1990's, the mostactive of which is centered in the Pattani Basin. Although exploration andproduction activities in the Pattani Basin have been carried out for more than tenyears, there is very limited previous information available on source rocks andorganic maturation history (Achalabhuti and Oudom-Ugsorn, 1978; Chinbunchornet al., 1989). The present investigation attempts to study tectonic evolution,sedimentary history, and hydrocarbon potential of the Tertiary strata in the PattaniBasin. Tectonic evolution of this basin is studied in terms of possible mechanismsof basin formation, burial and thermal histories of the stratigraphic units. Theevaluation of hydrocarbon potential includes analysis of source rock properties andpotential, organic maturation and hydrocarbon generation histories.1Figure 1.1: Tertiary basins in the Gulf of Thailand. The basins show general N-S trendingalignment.2Various analytical techniques have been used in this study. Wireline log analysis,well cutting sample examination and paleontological data are used to interpretstratigraphy and depositional environments in the study area. Backstripping andgeohistory analyses are employed to restore the subsidence history of the basin.Models of basin formation and lithospheric stretching are used to predict thethermal history of the basin. Organic petrography is used to establish the degree oforganic maturation and the maturity framework of the strata. Rock-Eval pyrolysisand organic petrography are used to identify and characterize potential hydrocarbonsource rocks. Modelling of chemical kinetics is used to determine the timing andextent of hydrocarbon generation.1.2 LOCATION OF THE STUDY AREAThe study area encompasses the western flank of the Pattani Basin, Gulf ofThailand, between latitudes 8° 50'N and 10° 05'N and longitudes 101° 05'E and101° 45'E (Figure 1.2). The area covers approximately 5,000 square kilometresand lies in water 60-80 m deep. This area was chosen for study in order to enhanceour knowledge of geological evolution and hydrocarbon potential of economicallyimportant Tertiary strata in the Pattani Basin. The Pattani Basin is the mostprolific basin in Thailand, accounting for more than 80% of present-dayhydrocarbon production in the country.1.3 DATA SOURCESThe data and samples used in this study were provided by Unocal ThailandCompany. The data includes 2D seismic sections, rotary cutting samples, wirelinelogs, paleontological reports and other general geological information.3Surat-1Platong-5 00 0 Platong-10 Platong-8Ranong-10Yala-200^5^10 km0 Kaphong-3o Kaphong-10Kung-10 S. Platong-1Pakarang-10^Pladang-30^ 0Insea-1 0 S. Platong-200^Trat-1Satun-20Satun-1Dara-10Erawan-12-900 Satun-30Krut-1o Erawan-12-10 Erawan-12-8Erawan-12-70 Jakrawan-20^ 0Erawan-K-10Jakrawan-10Baanpot-1 o^ Funan-10Baanpot-B-1Figure 1.2: Location of well data used in this study41.4 EXPLORATION HISTORY IN THE GULF OF THAILANDPetroleum exploration in the Pattani Basin, the largest Tertiary basin in the Gulf ofThailand, began in the early 1970's (Nakanart, 1978). The first well, drilled in1971 by Continental Oil Company of Thailand, did not encounter hydrocarbons.The first discovery well was completed in 1972 by the Union Oil Company ofThailand. The discovery well encountered natural gas and condensate. Additionaldrilling and other exploration activities have been carried out since. The firstnatural gas production began in August, 1981, from Erawan field by UnocalThailand Company (Lian and Bradley, 1986). There have been more than 10natural gas and condensate fields found to date. Current production rates from 4fields, all located in the western flank of the Pattani Basin and operated by UnocalThailand, are approximately 3200 m 3/day of condensate and 15.6 million m 3/day ofgas (Chinbunchorn et al., 1989). Other fields are being prepared for furtherproduction.1.5 PURPOSE OF STUDYThe main purpose of this investigation is to establish the tectonic evolution,sedimentary history, and hydrocarbon generation of Tertiary strata in the PattaniBasin, Gulf of Thailand. In order to achieve the goals described above, this thesisis divided into four parts. The first part describes the stratigraphy andsedimentological evolution of Tertiary strata. The second part describes thetectonic evolution, subsidence and thermal histories, and possible formationmechanisms of the basin. A computer program, based on geohistory analysis (VanHinte, 1978; Angevine et al., 1990) and a nonuniform lithospheric stretching model(McKenzie, 1978; Hellinger and Sciater, 1983; Friedinger, 1988), is developed to5calculate decompacted burial and tectonic subsidence histories and to determine thehistory of heat flow of the basin. The third part evaluates the hydrocarbon sourcerock potential of the Tertiary strata. The fourth part deals with kinetic propertiesand organic maturation and histories of hydrocarbon generation of the stratigraphicunits. Two computer programs, based on the Arrhenius equation and thedistribution of the activation energies (Braun and Sweeney, 1987; Sweeney andBurnham, 1990) were developed to calculate kinetic parameters of the kerogen andto predict timing and extent of hydrocarbon generation respectively.Results from this integrated study may greatly improve our understanding of thegeological evolution of the Pattani Basin and provide a more accurate assessment ofhydrocarbon potential of the Tertiary strata in the Pattani Basin, as well as otherbasins of similar tectonic setting.62. REGIONAL GEOLOGY2.1 INTRODUCTIONThe regional geology of the Pattani Basin has been summarized by Achalabhuti andOudom-Ugsorn (1978) and Lian and Bradley (1986). The stratigraphy and historyof sedimentation have been studied by Woollands and Haw (1976), ASCOPE(1981), and Bunopas and Vella (1983). Tectonic elements and structural evolutionof the study area have been the subject of discussion by various authors (Molnarand Tapponnier, 1975; Bunopas and Vella, 1983; Hellinger and Sclater, 1983;Peltzer and Tapponnier, 1988; Ohnstad, 1989; Polachan and Sattayarak, 1989).This chapter summarizes current ideas on the regional geology and tectonicelements of Tertiary strata in the Gulf of Thailand.2.2 PRESENT-DAY GEOLOGIC SETTINGThe Gulf of Thailand basin is a northwest-trending reentrant into Sundaland, thesouthwestern most part of the Eurasian plate. It lies near the intersection of twomajor transcurrent fault systems (Figure 2.1). The first fault system, the NW-SEtrending Three Pagoda fault, runs along from the Burmese border through theThree Pagoda Pass and may extend along the northeastern part of the Gulf ofThailand. The second fault system, comprising the NNE-SSW trending PhangNga-Surat Thani and Ranong faults, cuts across the southern Thai Peninsula andextends into the western part of the Gulf. The displacement direction along bothfault systems has been described as left-lateral by some authors (Wilcox et al.,1973; Tapponnier et al., 1986) but as right-lateral by others (O'Leary and Hill,1989; Polachan and Sattayarak, 1989). The geological structures seen in Tertiary740°80°^ 120°Figure 2.1 Tectonic map of S.E. Asia and South China Sea showing the main fualt patterns andthe relative movement of crustal blocks in response to the collision of India with Eurasia8sections in the Pattani Basin and adjacent areas comprise a series of N-S trendingelongate grabens, half-grabens, and horsts. Further south, in the Malay basin,grabens and half grabens show a NW-SE trending (Figure 1.1).2.3 TECTONIC ELEMENTSGeological structures within the Pattani Basin, the largest basin in the Gulf ofThailand, and adjacent basins indicate a multitude of closely spaced N-S trendingnormal faults. Many of these normal faults transect Pre-Tertiary basementsuggesting a basement-involved extension. An idealized cross sectiondemonstrating a basement-involved extension is illustrated in Figure 2.2.The Pattani Basin is approximately 300 kilometres long and 50 to 80 kilometreswide. It is bounded to the west by the Ko Kra Ridge, to the east by the shallowCambodian Shelf, and to the southeast by the Narathiwat Ridge (Figure 1.1 andFigure 2.2). It is filled with Tertiary nonmarine fluvio-deltaic clastic sediments upto ten kilometres thick in the grabens and in places less than one kilometre thick onthe horsts. Drilling efforts have not reached basement in the deepest part of thebasin due to high temperature resulting from high geothermal gradients. The oldestsediments penetrated by drilling within the basin are Oligocene in age. Thestratigraphy in the basin can be broadly subdivided into 3 sequences: (1) preriftsequence: basement rocks that predate the formation of Tertiary basins; (2) synriftsequence: a sequence deposited during active rifting; and (3) post-rift sequence: asequence deposited after the cessation of rifting (Chinbunchorn et al., 1989).Geophysical surveys and drilling results show that the Pre-Tertiary basementcomprises diverse rocks of different ages including upper Paleozoic metamorphic,901! ne - L MiocenKo Kra RidgeM. - U. MioceneMiocene0km5 Cambodian ShelfEocene - OligocenePre-Tertiary Basement0^kmFigure 2.2: Generalized W-E cross section of the Pattani Basin (After ASCOPE, 1981)10clastic, and carbonate rocks, Mesozoic clastic rocks, and upper Paleozoic andMesozoic granites (Lian and Bradley, 1986).The dominant period of rifting of Pre-Tertiary basement lasted about 20 m.y. fromLate Eocene to Early Miocene (Hellinger and Sclater, 1983; Chinbunchorn et al.,1989). The synrift sequence consists predominantly of low-energy alluvial plainand lacustrine deposits with high-energy alluvial fan and braided stream deposits inthe lower part. The upper part of synrift sequence comprises mainly fluvialdeposits, delta-front deposits, and some ephemeral lacustrine deposits in the centralpart of the basin.The post-rift sequence, deposited during late Early Miocene to Quaternary time,comprises a transgressive succession beginning with mangrove swamp at the basewith minor nonmarine deposits and extends into the present-day shallow marineenvironment.113. STRATIGRAPHY AND SEDIMENTOLOGY3.1 ABSTRACTThe Pattani Basin is a N-S elongate rift basin which comprises part of the Tertiaryrift system in the Gulf of Thailand. The basin is of significant economicimportance as a major hydrocarbon province in Thailand. The sedimentaryevolution in this area is a response to rifting process which began in Late Eocene.The sedimentary succession is divided into synrift and post-rift sequences.Deposition of synrift sequences corresponds to rifting and extension of ContinentalSoutheast Asia which included episodic block faulting and rapid subsidence. Themain controlling factors of the sedimentary records of synrift sequences are highsubsidence rate and large sediment influx which are the direct result of rifting.Deposition of post-rift sequences, on the other hand, corresponds to a period ofrelatively slower subsidence and less sediment influx. Hence eustatic sea-levelfluctuation played a more important role in the resulting sedimentary records.The synrift sequence comprises three stratigraphic units. The basal unit representsLate Eocene to Early Oligocene nonmarine, alluvial fan and braided stream depositsin the lower part and floodplain-channel deposits in the upper part. The middlesynrift unit represents Late Oligocene to Early Miocene nonmarine, floodplain andchannel deposits in the lower part and mainly channel deposits in the upper part.The upper synrift unit comprises an Early Miocene regressive sequence in whichbasal prodelta to shallow marine sediments are overlain by distributary mouth bardeposits and beach ridge complexes which, in turn, are overlain by nonmarinefloodplain and meandering channel deposits. The first marine transgression in thePattani Basin occurred in the Early Miocene and may have been the result of rapid12subsidence due to an episode of block faulting and/or eustatic sea-level rise. Thefollowing regressive succession in the upper part of synrift sequence resulted whenthe deposition rate exceeded the rate of relative sea-level rise. Although notreached by drilling, a thick succession of synrift lacustrine deposits are believed tohave been deposited in the vicinity of the basin center throughout the early part ofthe rifting period.The post-rift succession comprises three stratigraphic units. The lower post-rift unitrepresents an Early to Middle Miocene regressive sequence similar to that of theupper synrift unit. The late Early Miocene transgression, which was probably theresult of a rapid eustatic sea-level rise, created a brief period of nondepositionduring which the rate of relative sea-level rise exceeded the rate of deposition. Asthe deposition rate slowly exceeded the rate of relative sea-level rise, a regressivesuccession resulted. The middle post-rift unit represents a Middle Miocenetransgressive succession which was probably the result of slow rise of relative sea-level and a decreasing amount of sediment supply. A rapid fall of relative sea-levelwhich resulted in subaerial exposure, intense oxidation, and possibly erosion of theMiddle Miocene sediments was probably the effect of eustatic sea-level fall at theend of the Middle Miocene. The upper post-rift unit represents a Late Miocene toPleistocene transgressive succession indicating a slow rise of eustatic sea-level, slowsubsidence, and decreasing amount of sediment influx. The present-day shallowmarine condition in the Pattani Basin is the continuation of the latest transgression.133.2 INTRODUCTIONThe Pattani Trough is the largest of a series of N-S trending rift basins in the Gulfof Thailand (Figure 3.1) containing more than ten kilometres of Tertiary sediments.The Tertiary basins in Thailand have striking geological similarities in origin andtectonic setting. The evolution of the Pattani Basin, thus, provides a general modelfor other basins in the area. Although the stratigraphy of the Pattani Basin has beenstudied by Woollands and Haw (1976); Achalabhuti and Oudom-Ugsorn (1978) andLian and Bradley (1986), these studies generally have considered regionalstratigraphy. The present investigation provides a somewhat more detaileddescription and interpretation of the sedimentary and stratigraphic development ofthe Tertiary strata in the Pattani Basin. This section describes and interprets thestratigraphic successions in terms of typical log profiles, thickness, faciesdistribution, and depositional environments. Data are from well logs, cuttingsamples, 2D seismic sections, and unpublished paleontology reports provided by theUnocal Thailand Company. The study area is located on the west flank of thePattani Basin which has been most extensively explored.3.3 METHODS OF STUDYThe stratigraphic correlation and sedimentological analysis in this study are basedmainly on wireline logs, cutting samples, and palynological data.The gamma-ray log patterns can be used to identify vertical sequence and log faciesbecause gamma-ray logs reflect clay content and grain-size profiles in clasticsequences. As vertical profiles of sediment grain-size are often environmentallydiagnostic in clastic rocks. Log signatures, combined with knowledge of the14Platong-1Pla ng-8Ranong-1Kung-1Yala-2 0^5^10kman-12-1Erawan-12-Eraw -12-7Eraw -K-1Baanpot-1Baanpot-B-1Figure 3.1: Location of well data used in this study. Numbers in the box indicate thecross sections shown in Figures 3.5 through 3.1015general depositional setting, the vertical distribution of glauconite (marine indicator)and carbonaceous detritus (winnowing index), are a powerful tool in diagnosingclastic environments (Selley, 1979). Figures 3.2, and 3.3 show typical logsignatures and their various combinations and interpretation. Environmentalinterpretation from wireline logs utilized in this study is based on Fisher (1969),Selley (1979), Galloway and Hobday (1983), Cant (1984) and Walker (1984).Drill-cutting samples were used to obtain the lithology of the strata.Micropaleontological data, where available, were used as a framework for agedetermination and, together with log signatures, for interpretation of depositionalenvironment. Because no core samples were available, lithologies and depositionalenvironments interpreted from wireline logs had to be calibrated with drill-cuttingsamples. Electric logs were also used as a secondary tool for correlation.Stratigraphic correlation in the deeper part of the basin, which is not reached bydrilling, utilized 2D seismic sections.Due to the laterally discontinuous sedimentation and close spacing of faults,correlation of individual marker horizons between wells is difficult. Sequencecorrelation was thus used in this study. The technique involves the recognition andmatching of distinctive patterns of sedimentary succession in logs rather than singlemarker beds (Cant, 1984).The predominance of nonmarine or marginal marine sediments rules out the use offoraminifera for age correlation and dating. Stratigraphic subdivision was thusmade by means of lithological association and palynomorph assemblages(Woollands and Haw, 1976; Ratanasthien, 1988; Scrutton and Tidey, 1974).Figure 3.4 shows the Cenozoic palynological subdivision of various geographic16GL .0CSUBMARINEFAN(TURBIDITE)Gamma RayA.P.I.Umt•O 100,..11.., IIGI.^CEDGE OF^DELTAICMARINEBARGamma RayA P.I.UndsO 100Gamma Ray^ Gamma RayA .P.I.Unots A.P.I.Unds0^100^ 0^100^GI.^GI.^Gl.• C^C^I^I I I^REGRESSIVE^TIDAL^ SUBMARINE^FLUVIAL OR DELTAICBAR^SAND CHANNELRIDGEDISTAL SLOPEORCREVASSE SPLAYPROXIMALFigure 3.2: Four characteristic gamma ray log motifs. From left to right: thinly interbedded sand and shale;an upward coarsening profile with an abrupt upper sand-shale contact; a uniform sand with abrupt upperand lower contacts; and, furthest right, an upward fming sand-shale sequence wih an abrupt base. Noneof these is environmentally diagsnostic on its own. Coupled with data on their glauconite andcarbonaceous detritus content, however, they define the origin of many sand bodies. (After Selley, 1979)LogmotifGlauconiteand shelldebris(high-energymarine)TidalchannelTidal sandwaveRegressivebarrierbarGlauconite.shell debris,carbonaceousdetritus, andmica(dumpedmarine)Submarine channelProgradingsubmarinefanTurbiditcfill Grain flowfillCarbonaceousdetritus andmica(dumped)Fluvial ordeltaicchannelDeltadistributarychannelProgradingdelta orcrevassesplayFigure 3.3: Diagram showing the three common grainsize motifs seen on S.P. and gamma ray logs andhow, by combining these with the analysis of well samples, environmental interpretations of sandbodies can be made. (After Selley, 1979)17GEOLOGICALSUBDIVISION PALYNOLOGICAL SUBDIVISIONci) —0= gz =oN^LLccz^Luw Lo <<PANTROPICALZONEATLANTICZONECARIBBEANZONEBORNEOZONEw2 3EchitricolporitesSpinosusAlnipollenitesVerue Podocarpus7EchitricolporttesMcNeillyi DacrydiumtuE8UPPERMIDDLE18PachydermitesDiederlxiFlorschuetziaMeridlonalisFlorschuetziaLevipollLOWER26CrassoretitriletesVanraadshooveniGrimsdaleaMagnaclavataMultimaginiteeVanderhammeniMagnastrlatitesHowardiVerrutricolporitesRotundiporisPsiladiporiteeMinimusJandufouriaSeamrogiformisFlorschuetziatuzwM038CicatricosisporitesDorogensis Trilobatawztu8LuUPPER45VerrucatosporitesUsmensisMIDDLE49MonoporitesAnnulatusRetitricolporitesGularensisPsilatricolporltesOperculatusPsilagi ollffitesFig 3.4: Cenozoic palynological zones (Modified from Germeraad et al., 1968 and Ratanasthien, 1988)18zones (Germeraad et al., 1968). Based on the palynomorph assemblages of coniferand mangrove pollen present in Borneo and Pantropical zones, palynologicalsubdivisions are the Podocarpus floral zone (Quaternary), the Dacrydium floralzone (Pliocene), the Florschuetzia meridionalis floral zone (Middle to UpperMiocene), and the Florschuetzia levipoli floral zone (Lower to Middle Miocene).The Oligocene epoch is represented by the occurrence of the Florschuetzia trilobatafloral zone in Borneo and the Magnastriatites howardi in the Pantropical area. TheUpper Eocene epoch is marked by the occurrence of Verrucatosporites usmensis inthe Pantropical area.It is important to note that the palynology described above provides onlyapproximate dating and allows only broad correlations. A more detailedchronology is difficult to achieve because palynomorphs suitable for dating are fewand the index palynomorphs are facies-controlled to some extent, e.g. Florschuetziapollen is dispersed mainly by water (Woollands and Haw, 1976). The abundanceof unfossiliferous red beds further restricts dating and correlation to limitedintervals. Benthic foraminifera are present in some intervals, but are not age-diagnostic, and their use is therefore restricted to an indication of marginal marineenvironments.3.4 STRATIGRAPHIC SUBDIVISIONDue to rapid lateral variation of individual beds, detailed lithostratigraphiccorrelations based on electric logs are impossible. Correlation in this study istherefore based on the recognition and matching of distinctive log patterns ofsedimentary successions, which reflect broader and more widespread geologicalevents, rather than a single marker bed. Although 2D seismic sections exist, their19use is limited to confirming lateral continuity of stratigraphic sequences betweenwells and extrapolating stratigraphic units laterally from wells to non-penetratedareas in the deeper part of the basin. No interpretation of sequence stratigraphy hasbeen made in this study for the following reasons: first, the seismic sectionsavailable are of relatively poor quality; second, because the successions under studyare mainly nonmarine deposits with only minor marine influence; thus, thesequence boundary which is defined by the basinward shift of the sedimentaryfacies is very difficult to identify especially from the widely-spaced well data (VanWagoner, 1991).Six stratigraphic subdivisions can be recognized from subsurface data in the PattaniBasin. They are referred to here, from younger to older ages, as unit 1 throughunit 6. Units 6, 5, and 4 are interpreted to be synrift sediments, whereas units 3, 2,and 1 are regarded as post-rift. Figures 3.5 to 3.8 summarize stratigraphiccorrelation in four E-W sections in the study area whereas Figures 3.9 and 3.10summarize the stratigraphic correlation in two parts of a continuous north-southsection. Table 3.1 summarizes the stratigraphy and depositional environments ofTertiary strata in the study area.3.4.1 Unit 6Unit 6 is the oldest Tertiary sediment package encountered in this study. Onlythree wells located in the northwest corner of the basin completely penetrate thisunit. Its lower boundary, where penetrated, is marked by Pre-Tertiary basementrocks such as Cretaceous granite or Paleozoic and Mesozoic sediments. Thisboundary is clearly seen as a strong and continuous reflector in seismic sections.The upper boundary is marked by the sudden change from low gamma radiation in20Table 3.1: Stratigraphy and depositional environments of the Tertiary post-rift strata in the Pattani BasinUNIT SUBUNIT DEPOSITIONALENVIRONMENTSSEDIMENTARYSTRUCTURESLITHOLOGY RELATIVESEA-LEVEL+ -EUSTATICSEA-LEVELrise fall1 Upper Shallow marine Fine-grained Not available ''*z--4;7°-4Middle Interdistributary bayand/or crevasse splayGenerally fine-grained Dark greyclaystoneLongtermShorttermLower Distributary channelin the Coastal plainFining-upwardsequencesReddish brownclaystone andsandstone2 Upper Brackish swamp andmarginal marineGenerally fine-grainedwith some fining-upwardsequencesBrownish greyclaystone andsandstone Lower Dist channelsDistributaryand floodplainGenerally fine-grainedwith fining-upwardsequencesclaystone andsandstone3 Upper Meandering channel Fine-grained andfining-upward sequencesSandstone andminor claystoneMiddle Distributary mouth-barand beach-ridge complexCoarsening-upwardsequencesSandstone andclaystoneLower Prodelta and shallowmarineGenerally fine-grained Claystone andminor sandstoneTable 3.1: (continued): Stratigraphy and depositional environments of the Tertiary synrift strata in the Pattani BasinUNIT SUBUNIT DEPOSITIONALENVIRONMENTSSEDIMENTARYSTRUCTURESLITHOLOGY RELATIVESEA-LEVEL+ -EUSTATICSEA-LEVELrise fall4 Upper Upper delta plain andfloodplainGenerally fine-grainedwith fining-upwardsequencesClaystone andsandstone-4,LongtermShorttermMiddle Distributary mouth-barand beach-ridge complexCoarsening-upwardsequencesWhite sandstoneand minorclaystoneLower Prodelta and shallowmarineGenerally fine-grained brownish claystonewith coal partings5 Upper Nonmarine meanderingchannelFining-upwardsequencesBrownishsandstoneLower Meandering channeland floodplainGenerally fine-grainedwith fining-upwardsequencesRed claystoneand sandstone6 Upper Floodplain and channel Fine-grained andfining-upward sequencesSandstone andgreyish brownclaystoneLower Alluvial fan and braidedstreamCoarse-grained andpoorly sortedConglomerateand coarse-sand0-23-4-5 SURAT-1 PLATONG-8^PLATONG-1SECTION-1• WATER COLUMN 0 UNIT-1 0 UNIT-2 • UNIT-3 UNIT-4 0 UNIT-5 lI UNR-0........................................................................Figure 3.5: Stratigraphic section-1 W-E direction. See Figure 3.1 for the location of the section.KUNG-1RANONG-1SECTION-20-2-6-a INSEA-1 PAKARANG-1 PLADANG-3TRAT-1SOUTH PLATONG-2• WATER COLUM1 UNIT-IC) UNIT-20 UNIT4E1 UNIT-40 UNIT-50 UNIT4 .......^........ • • • .• .-• .....^..............................^• • .....................^• . ..........................................• ..Figure 3.6: Stratigraphic section-2 W-E direction. See Figure 3.1 for the location of the section.230-2-4-a-88-10 • WATER COLUMN 0 UNIT-1 0 UNIT-2• UNIT-3 FM UNIT-4 0 UNIT-5 0 UNIT43KRUT-1 ERAWAN-K-1 BMNPOT-1^BMNPOT-B-1 JAKRAWAN-1^FUNAN-1SECTION-3............^•^... ...• .......0-2-8• WATER COLUMN C UNIT-i I UNIT-2 • UNrr-3 0 UNIT-4 0 UNIT-5 0 UNIT-0ERAWAN-1 2-1 ERA WAN-1 2-8 SATUN-3^JAKRAWAN-2-8 DARA-1Figure 3.7: Stratigraphic section-3 W-E direction. See Figure 3.1 for the location of the section.SECTION-4Figure 3.8: Stratigraphic section-4 W-E direction. See Figure 3.1 for the location of the section.24PLATONG-5^PLATONG-1^SOUTH PLATONG-1^PLADANG-3^SATUN-2^SATUN-1YALA-2 KAPHONG-3 KAPHONG-10-2-4a_wa-a......... ..................................................................^.......-10III WATER COWAN^0 UNIT-1 0 UNIT-2• utar-3 0 utirr-4 0 UNIT-5 0 umr-6SECTION-5.........................................Figure 3.9: Stratigraphic section -6 N-S direction. See Figure 3.1 for the location of the sectionSECTION-60 ^I^a-2...............U4w -8a• ..-• .............................................. ....-8• WATER COLUMN^0 UNIT-1 0 UNIT-2• UNIT-3 5 &H1-4 0 UNIT-5 0 UNff-6-10ERAWAN-12-0 ERAWAN-12-1^ERAWAN-12-8 ERAWAN-12-7^ERAWAN-K-1 BAANPOT-1^BAANPOT-B-1SATUN 1Figure 3.10: Stratigraphic section-6 N-S direction. See Figure 3.1 for the location of the sectionthe upper part of unit 6 to high gamma radiation in the lower part of unit 5. Thissudden increase of gamma radiation marks the change in lithological associationfrom coarse-grained sediments of unit 6 to fine-grained sediments of unit 5.A typical composite log profile of unit 6 is shown in Figure 3.11. Surat-1 andRanong-1 wells encountered Cretaceous granite basement whereas Dara-1encountered Cretaceous sediments. The presence of Cretaceous sediments isevident from the distinct change in lithology from interbedded grey sandstone andshale of unit 6 to the underlying red shale of the basement and the sharp increase insonic velocity across this contact. The thickness of this unit varies from 150-350 min the western margin of the basin to as thick as 3000 m in the basin center (Figure3.12). Lithologically, unit 6 can be subdivided into lower and upper subunits.The lower subunit is laterally highly discontinuous. Its thickness varies from 60 mat Surat-1 well to less than 20 m thick at Ranong-1 well to nil at Dara-1 well. Atypical log profile of this subunit occurs in Surat-1 well between the depths of2715-2900 m (Figure 3.11). The subunit consists mainly of conglomerate at thebase and grades upward to very coarse- to coarse-grained, angular to subangularsandstone, minor siltstone and claystone. The basal conglomerate comprises quartzpebbles and clasts of quartzose and feldspathic granite. The subunit is barren ofany fossils.The presence of a fining-upward sequence of conglomerate and very coarse-grained, angular to subangular sandstone suggests the lower subunit was depositedin the alluvial fan and braided plain environments. The alluvial fan environment isbelieved to have developed in a restricted area during the initial phase of basinformation. Block faulting created a high relief topography which, in turn, induced26Figure 3.11: Typical log profiles of unit 6, showing coarse-grained alluvial fan deposits and braided stream deposits in the lowersubunit and fining-upward sequences of channel deposits of the upper subunit0^5^10kmYala-2 (961)0(30Kung-1 (351)000 . Platong-1 (1434)o S. atong-2 (1312)01 (2425),45, ^ o,0^ Trn-2 (1(2•455a an-10EDar -1 (130-9 (2410)0 Satun-3 (2959)0 Kaphong-3 (3569)Plato -5 0 9Ranong-10(198) 0Po la-8Sura 151500arang-1 (1678)°^Pladang-3 (1588)0^ 0I nsea-1 (60Saturawan-2 (1800)080raw -1(1769)0Funan-1(1281)Kaphong-1 (2623)ng-1 (1495)(1433)0 Er^-12-1(2 9)0an-12-8 37Er =w=,^2-7(3111)0J0Era^1 (2135)Baan o 0 (31 101 (30Krut-1(885)Figure 3.12: Isopach map of the stratigraphic unit 6 (contour interval = 500 m)28mass movement and rapid sedimentation (Nilsen, 1982). Because of limited data,the geometry and extent of the alluvial fan deposits are not known. Away from themarginal faults, the lower subunit was deposited in a braided alluvial plainenvironment. The occurrence of interbedded sandstone, siltstone and claystone inthe upper part of this subunit possibly indicates the transition from braided riverenvironment to that of meandering river with overbank and floodplain deposits(Cant, 1982).The upper subunit of unit 6 is approximately 80-300 m thick and thickens towardthe basin center. Typical successions of this subunit occur in Ranong-1 wellbetween the depths of 2320-2470 m which are shown in Figure 3.11. Log profileshows a series of fining-upward sequences with sharp contacts at the base andgradational contacts at the top. Each sequence is approximately 6-12 m thick.Sandstone beds at the base of the sequences are approximately 2-7 m thick. Thesubunit consists mainly of white to grey, fine- to medium-grained sandstone andreddish brown to grey brown claystone. Coal seams occur locally interbedding withfine-grained sediments. The palynological assemblages include only rare pollen andlack key fossils. The only microflora present in this interval is the fern spore,Verrucatosporites usmensis.The stacked fining-upward sequences, the presence of a fresh water fern spore,Verrucatosporites usmensis, and the oxidation of the sediments (evident by thereddish brown color) suggests the upper subunit was deposited in a fluvialfloodplain environment consisting of coarse-grained channel sediments and fine-grained overbank sediments. Uniformly fine-grained sediment intervals in thissubunit may indicate an ephemeral lacustrine environment further downslope fromthe alluvial fans.29The depositional history of unit 6 can be summarized as follows. At the initialstage of basin formation in this area, block faulting and rapid subsidence created ahigh-relief topography which led to the development of alluvial fan and alluvialplain environments. As the source areas were substantially eroded together withdecreasing subsidence rate, floodplain and ephemeral lacustrine environmentsprevailed.The presence of Verrucatosporites usmensis, a diagnostic species of the Pantropicalzone (Figure 3.4) suggests that the age of unit 6 is approximately Late Eocene(Germaraad et al., 1968; Ratanasathien, 1988).3.4.2 Unit 5Unit 5 directly overlies unit 6. Its lower boundary is marked by the change inlithological association from a series of fining-upward sequences in the upper partof unit 6 to uniformly fine-grained claystone that characterizes the lower part ofunit 5. The upper boundary of this unit is marked by the change in lithologicalassociation from coarse-grained sandstone interbedded with claystone in the upperpart of unit 5 to generally fine-grained claystone in the lower part of unit 4.The typical composite log profile of unit 5 is shown in Figure 3.13. Unit 5 wascompletely penetrated by four wells located in the northwestern and western marginof the basin. Seismic sections were used for correlation in areas where the unit wasnot penetrated by wells. Generally, the unit thickens toward the center of the basinand thins toward the eastern margin of the basin (Figure 3.14). A prominentdepocenter of this unit is located in the southern part of the study area. The30GA 2379 m RESIST 2794 m RESISTShaleSandstone.".•,•.•...•.•".•.•.•.•.....Lower subunit^ Upper subunit2538 m^ 2952 mSurat-1 Erawan-12-1Figure 3.13: Typical log profiles of unit 5, showing general fine-grained floodplain and channel deposits in the lower subunitand fining-upward sequences of channel deposits in the upper subunit0^5^10kmYala-2 (256)0o Kaphong-3 (682)Ranong-1 (442)00Kung-1 (250)0 S. Platong-1 (625)030°Pakar •-1 (584)Pladang- • (915)0^ ocooInsea-1 (368)^N^0 S. Platon 2 (1251)Eraw 12-7 (824)0Krut-1(433Jakrawan-2 (1088)00Erawan-K-1 (0Jakrawan-1(1281)0Funan-1(1068)Baanp(1817)E^(778)Dara-10^0 Satun-3 (1220)Erawan-12-1(1287)o Erawan-12-8 (1287)0 Kaphong-1 (663)Platong-5 0 368)o o Platong-1 (564)° P ong-8 (366)Surat-1(351)0Trat-1 (946)0Satun-2 (1159)0Satun-1 (1129)Figure 3.14: Isopach map of the stratigraphic unit 5 (contour interval = 500 m)32thickness varies from approximately 250-450 m in the northern and western marginof the basin to approximately 1300-1600 m in the depocenter in the south. Basedon lithological associations, unit 5 can be subdivided into lower and upper subunits.The lower subunit is approximately 90-200 m thick based on well data. Thethickness in the area not penetrated by wells is thought to increase toward thedepocenter in the central part of the basin. The typical log profile of this subunitoccurs in Surat-1 well between the depths of 2380-2560 m (Figure 3.13). A logprofile shows generally high gamma radiation with a few widely-spaced lowgamma-ray intervals in between. This log signature reflects mainly fine-grainedsediments and minor coarse-grained sediment interbeds. Coarse-grained sedimentinterbeds show a series of fining-upward sequences. These fining-upwardsequences, where present, are approximately 3-9 m thick. The subunit consistsmainly of red, reddish brown to brownish grey, noncalcareous claystone and red tobrown, mottled argillaceous siltstone. Sandstones are generally grey to brown incolor and fine- to medium-grained. The lower subunit contains very sparse pollenand lacks foraminifera. The only palynomorph encountered in this subunit isMagnastriatites howardi, fresh water palynomorph.The generally fine-grained nature of the lower subunit of unit 5, the absence ofmarine and brackish water indicators, and the presence of the fresh waterpalynomorph, Magnastriatites howardi suggest that this subunit was deposited in alow energy, fresh water floodplain environment. The presence of red beds maypossibly have been a result of the subsequent aerial exposure of the sediments, orrapid aerobic decomposition of plant materials which led to oxidation of sediments.A series of thin, fining-upward sandstone sequences represents small-scalemeandering channel deposits.33The upper subunit is approximately 90-300 m thick. A typical log profile of thissubunit occurs in the Erawan-12-1 well between the depths of 2790-3000 m (Figure3.13). The profile defines a stacked series of fining-upward sequences with sharpbasal and gradational upper contacts. The thickness of each of these sequencesvaries from 6 m to 12-15 m. Sandstone at the base of the sequences is 3 to 9 mthick. The subunit consists mainly of white to brown, fine- to medium-grainedsandstone. Siltstone and claystone are generally brown to red or yellow andnoncalcareous. The subunit contains very low palynomorph abundance.The series of well developed fining-upward sequences and the highly oxidizednature of the sediments, evident from their reddish color, suggest that the uppersubunit of unit 5 was deposited in a nonmarine meandering channel environment.The overall depositional environment of unit 5 is interpreted to be entirelynonmarine and can be summarized as follows. The base of unit 5 representsnonmarine floodplain deposits characterized by generally fine-grained overbanksediments. Small-scale meandering channel deposits are also present and arecharacterized by a series of widely-spaced, small-scale fining-upward sequences inthe fine-grained overbank deposits. These sediments were subsequently subaeriallyexposed and oxidized as evident from the occurrence of red beds. The upper partof unit 5 represents a change from low energy floodplain deposits into high energychannel-fill and point bar deposits. These high energy deposits are characterized bya predominance of thick, fining-upward sequences with minor interbeds of finer-grained sediments.34No age diagnostic fossil assemblages occur in this interval. The age of unit 5 isinterpreted to be Late Oligocene to Early Miocene because this unit directly overliesunit 6 of Late Eocene to Early Oligocene age and underlies unit 4 of Early Mioceneage.3.4.3 UNIT 4Unit 4 is a coarsening-upward regressive sequence. Its lower boundary is markedby an abrupt change in lithological association from a series of fining-upwardsequences in the upper part of unit 5 to generally fine-grained sediments in thelower part of unit 4. This boundary is a surface of nondeposition representing arapid rise of the relative sea-level (transgression). As the rate of depositionexceeded the rate of sea-level rise, a regressive sedimentary succession resulted.The surface of nondeposition is characterized by the sudden change from nonmarinechannel deposits of unit 5 to low energy shallow marine sediments of the lowersubunit of unit 4 in the vicinity of the basin center. Westward toward the basinmargin, this boundary is marked by a change from high energy channel deposits tolow energy floodplain deposits. The upper boundary of unit 4 is marked by asudden increase in gamma radiation which reflects a change in lithology fromcoarse-grained sandstone of upper unit 4 to relatively fine-grained claystone of unit3.A typical composite log profile of unit 4 is shown in Figure 3.15. This unitgenerally thickens from about 300 to 400 m in the north and west to about 1400 to2800 m in the depocenters (Figure 3.16). Two depocenters are recognized (Figure3.16). The smaller depocenter, located around the Pladang-3 well location,contains sediments up to 1400 m thick. The main depocenter of unit 4 is located35ShaleSandstoneLower subunit^ Middle subunit^ Upper subunitGR^2349 m RESIST^GR^2776 m RESIST^GR^1650 m RESIST2501 m^ 2934 m^ 1809 mPakarang-1 Baanpot-B-1 Ranong-1Figure 3.15: Typical log profiles of unit 4, showing general fine-grained shallow marine and prodelta deposits in the lower subunit,and coarsening-upward sequences of distributary mouth bar and beach ridge deposits in the middle subunit, and fining-upward sequences of nonmarine channel deposits of the upper subunitO 5^10kmYala-2 (392)00 Kaphong-3 (339)0^ Platong-8 (436)Surat-1O (363)Kung-1 (400)^500 S. Platong-1 (658)Pakar g-1 ( 7)P adang-3 (1479)0^ 0Insea-1 (338)^ o S. Platong-2 (915)o Kaphong-1 (313)Platong-5 0 (512)0 0 Platong-1 (439)Ranong-1 (281)^00O Trat-1 (854)Satun-2 (963)0Satun-1 (930)Erawan- 9 (381)Dara-1 (357) 00^0 Satun-3 (519)0 Erawan 12-1(338)0 Eraw -12-8 (2379)Krut- Erawan-12-7 (525)(817)rawan-2 (732)oErawan-K-1 (2278)an-1(702)0Baanpot-1 0 (7Q28)^unan-1(871)Baanpot-B-1 (2849)Figure 3.16: Isopach map of the stratigraphic unit 4 (contour interval = 500 m)37further south around the Erawan-K-1, Baanpot-1, and Baanpot-B-1 well locations.This southern depocenter contains sediments greater than 2800 m thick. Based onlithological associations, unit 4 can be subdivided into lower, middle, and uppersubunits.A typical log profile of the lower subunit occurs in Pakarang-1 well between thedepths of 2350-2500 m (Figure 3.15). The serrated, generally high-intensitygamma ray signature reflects the generally fine-grained sediments interbedded withthin, coarse-grained sediments. The thickness of this subunit varies from zero inthe western margin of the basin to more than 150 m toward the basin center (Figure3.17). The subunit consists mainly of brown grey to grey, noncalcareous to slightlycalcareous claystone and argillaceous siltstone and thin (generally less than 3 mthick) but closely-spaced white to light grey, fine- to medium-grained sandstone.Thin, widely-spaced carbonaceous partings are present throughout the interval. Acalcareous benthic foraminiferal assemblage is common in this interval. Thepredominant species are Ammonia nipponica and A. beccarii. Microflora and plantdebris are rare in this subunit. Where present, the palynomorph assemblagesinclude Florschuetzia semilobata, F. trilobata, F. levipoli, Crassoretitriletesvanraadshooveni, and Magnastriatites howardi.The lower subunit of unit 4 consists of shallow marine, prodelta sedimentsdeposited in a littoral to very shallow marine inner sublittoral environment. Suchan interpretation is based on the fine-grained nature of the sediments, the presenceof shallow marine foraminifera (Ammonia nipponica and A. beccarii), and theoccurrence of mixed fresh water palynomorphs (Magnastriatites howardi andCrassoretitriletes vanraadshooveni) and brackish water palynomorphs(Florachuetzia Trilobata and F. levipoli).38Yala-2 (0)00^5^10kmatong-8 (82)urat-1(61)150ng-1 (157)o Kaphong-3 (40)o Kaphong-1 (69)0^Platong-5 (52)Platong-1 (40)Ranon0 S. Platong-1 (NA)arang-1 (134)°^Pladang-3 (NA)0^ 0Insea-1 (0)^ 0 S. Platong-2 (NA)00^Trat-1 (NA)Satun-2 (NA)0Satun-1 (NA)rawan-12-9 (165)0150 ° Satun-3 (NA)o Erawan-1•50-12- (3400raw K- NABaanpot-1 0 (189)0Jakrawan-2 (NA)00Jakrawan-1(NA)0Funan-1(NA)134)(88)0Krut-1(NA)Baanpot-B-1 (NA)Fietgure 3.17: lsopach map of unit 4's lower subunit (contour interval = 50 m)39A typical log profile of the middle subunit occurs in Baanpot-B-1 well between thedepths of 2800-3000 m (Figure 3.15). The subunit consists mainly of white to lightgrey, fine- to medium-grained sandstone and grey to light grey and brownclaystone, siltstone interbeds and minor carbonaceous partings. The thickness ofthis subunit varies from zero in the western basin margin to more than 300 mtoward the depocenter in the south central part of the basin (Figure 3.18). The logprofile depicts a series of coarsening-upward sequences with gradational contacts atthe base and sharp contacts at the top. These sequences vary in thickness frommore than 30 m in the lower part of the section to approximately 10 m in the upperpart. The thickness of clean sandstone beds at the top of each sequence alsodecreases upward, ranging from as thick as 20 m in the lower part to about 2-7 min the upper part of the section. The subunit is characterized by the lack offoraminifera and the near absence of palynomorph and other plant debris.The middle subunit of unit 4 was deposited in a delta-front environment. Thisinterpretation is based on the very low palynomorph abundance and barren intervalsin this subunit, together with a series of coarsening-upward sequences and thelithological association of the underlying fine-grained prodelta deposits of the lowersubunit and the overlying nonmarine delta plain deposits of the upper subunit. Thedelta-front sediments of this subunit include both distributary mouth bar depositsand also, where the marine reworking process dominates, beach-ridge complexes(cf. Coleman and Prior, 1982; Miall, 1984).A typical log profile of the upper subunit of unit 4 occurs in Ranong-1 well betweenthe depths of 1620-1830 m (Figure 3.15). The log profile depicts a series of fining-40Platong-1 (183)ong-8 (0)Ranong-1 (0)0^0Kaphong-1 (131)Piston0 S. Platong-1 (NA)ang-1 (131)°^Pladang-3 (NA)0^ 0Insea-1 (0)00^Trat-1 (NA)Satun-2 (NA)0Satun-1 (NA)awan-12-9 (159)00 Satun-3 (NA)wan-12-1(67)wan-12-8 (95)0 S. Platong-2 (NA)2-7 (461)0Erawan-K-1 (NA)0Krut-1(NA)Jakrawan-2 (NA)00Jakrawan-1 (NA)0Baanpot-1 0 (336)^Funan-10 (NA)Baanpot-B-1 (317)Yala-2 (153)^ 0^5^100 km0 Kaphong-3 (122)Figure 3.18: Isopach map of unit 4's middle subunit (contour interval = 50 m)41upward sequences with sharp basal contacts and gradational upper contacts. Thesesequences vary in thickness from less than 3 m to as thick as 20 m. The thicknessof sandstone layers at the base of the sequences varies from less than 2 m toapproximately 15 m. This subunit consists mainly of interbedded light brown towhite sandstone and reddish brown to grey brown claystone. This subunit isthickest (more than 300 m thick) in the western margin of the basin and thins (lessthan 30 m thick) toward the basin center (Figure 3.19). This subunit contains verylow fresh water palynomorph abundance. It lacks both foraminifera and brackishwater palynomorphs. The only abundant palynomorph present is the fresh waterfern spore Magnastriatites howardi.The upper subunit of unit 4 was deposited in the supratidal floodplain environment.This interpretation is evident from the absence of marine foraminifera and brackishwater palynomorphs, the presence of the fresh water fern spore, Magnastriatiteshowardi, a series of fining-upward sequences and the presence of red beds. Theseries of sand-rich fining-upward sequences may be meandering channel deposits.The overall depositional environment of unit 4 is a coarsening-upward regressivesequence in which the coastline prograded gradually basinward, resulting innonmarine deposits superimposed upon the earlier shallow marine or marginalmarine deposits. The depositional history of this unit can be summarized asfollows. A rapid rise of relative sea-level at the end of unit 5 resulted in a surfaceof nondeposition (transgressive surface) on which unit 4 was deposited. The baseof the unit represents prodelta to shallow marine, inner sublittoral depositscharacterized by generally fine-grained sediments and minor sandstone interbeds,shallow marine foraminifera, and a mixture of both brackish and fresh waterpalynomorphs. Overlying these prodelta to shallow marine deposits are coarse-420^5^10kmYala-2 (239)0Ranong-1 (281)0Platong-5 oatong-1 (217)0 ng-8 (354)3000Kung-1 (2o S. Platong-1 (NA)(182)Pladang-3 (49)0^0Insea-1 (30o^Trat-1 (NA)Satun-2 (29)0Satun-1 (48)0 S. Platong-2 (NA)Dar0an-12-D (58)0 stun-3 (NA)rawan-12-1( 1)0 Erawan-12-8awan-12-7 (31)00 Jakrawan- (NA)/44 .4,an-1(NA)0Baanpot-1 0 (81)^Funan-10 (NA)Baanpot-B-1 (0)400Erawan-K-1 (458)0Kr(32o Kaphong-3 (177)Kaphong-1 (113)Figure 3.19: Isopach map of unit 4's upper subunit (contour interval = 100 m)43grained, high-energy distributary-mouth bar deposits and beach-ridge complexes,characterized by a series of coarsening-upward sequences and the absence of fossils.The upper part of the unit is nonmarine floodplain and meandering channeldeposits, as evident from the absence of foraminifera and brackish waterpalynomorphs, the occurrence of fresh water fern spores and red beds, togetherwith a series of fining-upward sequences within the generally fine-grainedsediments.Unit 4 correlates positively to the Florschuetzia levipoli zone from Borneo(Germeraad et al., 1968; Figure 15, p. 230-232). This is based on the occurrenceof F. levipoli and F. semilobata, which have first occurrence in the F. levipolizone, and the absence of F. meridionalis and Echitricolporites spinosus, with firstoccurrence in the F. meridionalis zone immediately above the F. levipoli zone. Theage of unit 4 is, therefore, identified precisely as Early Miocene.3.4.4 Unit 3Unit 3 is characterized by a generally coarsening-upward regressive sequencesimilar to unit 4. In unit 3, nonmarine deposits of the upper subunit lie on top ofdistributary mouth bar and beach ridge deposits of the middle subunit which, inturn, lie on top of prodelta and shallow marine deposits of the lower subunit. Thelower boundary of unit 3 is a surface of nondeposition, a result of rapid rise ofrelative sea-level. The upper boundary of unit 3 in the vicinity of the basin centeris marked by a change in lithological association, from a series of coarsening-upward sequences of a distributary mouth bar or beach ridge deposit of the middlesubunit of unit 3 into a series of fining-upward sequences of a floodplain-meandering channel deposit of unit 2. Near the basin margin, this boundary is44marked by a change from a series of fining-upward sequences of a meanderingchannel deposit of the upper subunit of unit 3 to generally fine-grained floodplaindeposits of unit 2.A typical composite log profile of unit 3 is shown in Figure 3.20. This unitgenerally thickens from 200-300 m in the northern and western margin toapproximately 1200-1400 m in the basin center (Figure 3.21). The likelydepocenter occurs at the south-central part of the basin (Figure 3.21). Based on thelithological associations, unit 3 can be subdivided into lower, middle, and uppersubunits.A typical log profile of the lower subunit occurs in Pladang-3 well between thedepths of 2380-2535 m (Figure 3.20). The serrated, generally high gamma ray logsignature reflects the generally fine-grained sediments interbedded with thin,coarse-grained sediments. This subunit's thickness varies from zero in the westernpart of the basin to more than 200 m toward the basin center (Figure 3.22). Thesubunit consists mainly of light grey to grey, calcareous claystone and siltstoneinterbedded with minor occurrences of coarsening-upward sandstone andcarbonaceous shales. Small calcareous benthic foraminifera are common. Themain species are Ammonia cf. beccarii and Pseudorotalia cf. yabei. Thepalynomorph assemblage encountered in this subunit includes Florschuetziasemilobata, F. levipoli, Crassoretitriletes vanraadshooveni, Verrumonoletesusmensis, and Discoidites boneensis. Other plant fragments are rare in this subunit.The lower subunit of unit 3 is interpreted as shelf to prodelta sediments which weredeposited in a littoral to shallow marine inner sublittoral environment. Thisinterpretation is based on the fine-grained nature of sediments, the occurrence of45Lower subunit Upper subunitMiddle subunit2117 mErawan-12-12538 mPladang-32455 mSouth Platong-1GR 2379 m RESIST 1958 m RESIST 2297 m RESISTIGRShaleSandstoneFigure 3.20: Typical log profiles of unit 3, showing general fine-grained shallow marine and prodelta deposits in the lower subunit,and coarsening-upward sequences of distributary mouth bar and beach ridge deposits in the middle subunit, and fining-upward sequences of nonmarine channel deposits of the upper subunit0^5^10kmYala-2 (352)0o Kaphong-3 (207)Sa0n-2 (535)0Satu -1 (390)0Insea-1 (244) S. Platong-2 (1088)7047 0Trat-1 (1244)Kung-1 (232)o S. Platong-1 (595)Pakarang-1 (338)°^Plad (433)Erawan-12-9Dara-1 (228) 000 Era`tq7^0 Era393)0 Satu (875)Erawan-12-700Erawan-K- (281)0Jakraw 1(1388)0Baanpot- 0 (534)^Funan-10 (810)Baanpot-B-1 (819)0Krut-1(871)Jakrawan-2 (1437)0Ranong-1 (299)00 Kaphong-1 (320)Platong-5 0 (305)o o Platong-1 (329)° Platong-8 (278)0Surat-1(232)Figure 3.21: Isopach map of the stratigraphic unit 3 (contour interval = 500 m)47Platong-5 0Platong-1 (119)Platong-8 (91)0urat(790Kung-1Yala-2 (0)00^5^10km0 Kaphong-3 (0)Kaphong-1 (0)eang-3 (311)0^ 0Insea-1 (0akarang-10o S. Platong-2 (NA)0Trat-1 (NA)Sa -2 (181)0Satun-1 (250)Krut-1(0)(92)° Satun-3 (244)Erawan-12-1(247)2-8 (159)0 S. Platong-1 (NA).p°ErawDara-1 (101)Erawan-1200Erawan-K-1looJakrawan-2 (122)0otip Jakrawan-1 (NA)0Baanpot-1^ Funan-1Baanpot-B-1 (323)^(NA)Ranong-1 (0)0Figure 3.22: Isopach map of unit 3's lower subunit (contour interval = 100 m)48shallow water foraminifera (Ammonia cf beccarii and Pseudorotalia cf. yabei),together with the presence of mixed fresh water palynomorphs (Crassoretitriletesvanraadshooveni, Verrumonoletes usmensis, and Discoidites boneensis). The rarecoarsening-upward sequences (3-10 m thick) may represent offshore bar deposits.A typical log profile of the middle subunit of unit 3 occurs in the Erawan-12-1 wellbetween the depths of 1950-2160 m (Figure 3.20). The log profile represents aseries of coarsening-upward sequences with gradational basal contacts and sharpupper contacts. Each of these coarsening-upward sequences is approximately 10-40m thick. Clean sandstone layers at the top of these sequences range from 3-12 mthick. The subunit consists mainly of fine- to coarse-grained, white sandstone andcalcareous claystone and siltstone interbeds and minor carbonaceous partings. Thethickness of this middle subunit varies from zero in the northwestern margin of thebasin to more than 200-300 m in the southern part of the basin (Figure 3.23). Twominor depocenters trending ENE-WSW are recognized in the southern part of thebasin (Figure 3.23). The palynomorph assemblage encountered in this subunitincludes Florschuetzia semilobata, Florschuetzia levipoli, Crassoretitriletesvanraadshooveni, Pinus sp., Dicolpopollis malesianus, and Magnastriatiteshowardi. Calcareous foraminifera encountered are Ammonia cf. beccarii andPseudorotalia cf yabei.The middle subunit was deposited in the distributary mouth bar and beach ridgeenvironments. Evidences for such an interpretation include a series of sand-rich,coarsening-upward sequences; the presence of shallow marine calcareousforaminifera; the mixed occurrences of fresh and brackish water palynomorphs;together with the lithological association of the underlying fine-grained shelf toprodelta deposits of the lower subunit and the overlying nonmarine coastal plain49Yala-2 (69)00^5^10km0Insea-1 (0) S. Platong-2 (NA)A000 Kaphong-3 (70)Kaphong-1 (214)(143)Platong-1 (149)ng-8 (0)PI0Surat-1(0). Platong-1 (92)Pakarang-1 (0)°^Plad 0)0Trat-1 (NA)2 (220)0an-12-9(117)a-1^)^0 200 00 Erawan-12-1(244)0^-12-8 (259)_ ..-• — — —EjaWin-12-7 (84) — -'(214)^..-^0^100,atun-3 (174)1Jakrawan-2 (137)(---—^0-........gsk ^____3001(342)0Baanpot-1 0 97)^Funan-10 (275)Baanpot-B-1 (298)Ranong-1 (0)00Kung-1 (0)Figure 3.23: Isopach map of unit 3's middle subunit (contour interval = 100 m)50deposits of the upper subunit similar to that of unit 4 (cf. Coleman and Prior, 1984;Miall, 1984).A typical log profile of the upper subunit of unit 3 occurs in South Platong-1 wellbetween the depths of 2290-2500 m (Figure 3.20). The log profile characterizes aseries of fining-upward sequences with sharp basal contacts and gradational uppercontacts. These sequences vary in thickness from less than 5 m to as thick as 20 m.The thickness of sandstone layers at the base of the sequences varies from 2 m toapproximately 13 m. The subunit consists mainly of interbedded light grey to lightbrown sandstone, siltstone, and brown grey claystone. The thickness of this subunitvaries from zero in the south central part of the basin center to as thick as 250-300m the western and southeastern basin margins (Figure 3.24). The subunit is barrenof any foraminifera and brackish water palynomorphs, but does include a fewspecimens of the fern spores Crassoretitriletes vanraadshooveni and Magnastriatiteshowardi.The upper subunit of unit 3 was deposited in a nonmarine, meandering channel andfloodplain environment. This interpretation is supported by the presence of a seriesof fining-upward sequences, the absence of marine foraminifera and brackish waterpalynomorphs, and the occurrence of fresh water fern spores, Crassoretitriletesvanraadshooveni and Magnastriatites howardi.The overall depositional environment of unit 3 displays a generally coarsening-upward regressive succession similar to unit 4, and can be summarized as follows.At the end of unit 4 deposition, rapid relative sea-level rise resulted in a surface ofnondeposition, at least in the central basin area. This surface marks the boundarybetween the stratigraphic unit 4 and unit 3. As the rate of deposition exceeded the51Yala-2 (284)09., o Kaphong-1 (107)atong-5 o)42)y6 Platong-1 (61)Platong-8 (187)0Surat-1(153)Kung-1ng-1 (473)0Insea-1 (244)Pakarang-1 (204)000^Trat-1 (NA)Satun-^34)0Satun-1 (79)Ranong-1 (299)0o Kaphong-3 (137)g-3 (122)00 S. Platong-2 (NA)0^5^10kmErawan-1^(85)Dara-1 (35) 00^0 Satun-3 (0)100^Erawan-12-1(0)Erawan-12-8 (0)Jakrawan-2 (0)0Krut-1(458)Era an-K-1 (70)J^1(85)10° 0Baanpo -1 0 (13'^'.9-' ,"Funan-1(305)Baanpot-B- (0)Figure 3.24: Isopach map of unit 3's upper subunit (contour interval = 100 m)52rate of relative sea-level rise, a regressive sedimentary package prograded. At thebase of unit 3 are prodelta to shallow-marine to inner sublittoral depositscharacterized by fine-grained sediments and minor sandstone interbeds, shallowmarine foraminifera and brackish water microfloral assemblages. Higher in thesection are coarse-grained, high energy distributary mouth bar and beach ridgedeposits. The deposits are characterized by a well developed series of sand-rich,coarsening-upward sequences, shallow marine foraminifera and mixed fresh andbrackish water microfloral assemblages. The upper portion of unit 3 representsnonmarine meandering channel and floodplain deposits characterized by the absenceof any marine and brackish water indicators, the presence of fresh water microfloraand a well developed series of fining-upward sequences.The presence of Florschuetzia semilobata, F. levipoli, Magnastriatites howardi, andCrassoretitriletes vanraadshooveni indicate that unit 3 is in the Florschuetzialevipoli Borneo zone which is equivalent to the Crassoretitriletes vanraadshooveniPantropical zone of Late Early-Middle Miocene (Germeraad et al., 1968; Scruttonand Tidey, 1974).3.4.5 Unit 2The lower boundary of unit 2 is marked by change from coarse-grained sandstoneof the upper part of unit 3 to fine-grained claystone of the lower part of unit 2.Unit 2 is bounded above by the Mid-Miocene unconformity. This unconformity isrecognized in the well logs by a sharp increase in sonic velocity downward acrossthe unconformity surface and by a change in color of cuttings from grey above theunconformity to brown or red below indicating oxidizing conditions prevailed53below the unconformity. In seismic sections, however, no angular relationship isevident across this surface.The typical composite log profile of unit 2 is shown in Figure 3.25. The unitthickens from 250-450 m in the western basin margin to more than 1000 m in thebasin (Figure 3.26). A small depocenter occurs in the vicinity of South Platong-2well in the central part of the basin which contains more than 1500 m of sediments(Figure 3.26). Based on lithological association, unit 2 can be subdivided intolower and upper subunits.A typical log profile of the lower subunit occurs in Surat-1 well between the depthsof 1310-1520 m (Figure 3.25). The log profile depicts a well developed series offining-upward sequences with sharp basal contacts and gradational upper contacts.The thickness of these sequences varies from 6 m to approximately 20 m.Sandstones at the top of the sequences are approximately 2-10 m thick. Thissubunit thickens toward the south (Figure 3.27). A prominent depocenter occurs inthe southwestern part of the study area which contains a sequence of sandstones andshales more than 800 m thick (Figure 3.27). The subunit consists mainly ofintercalations of white to light grey sandstone and mottled red, yellow to brownsiltstone and claystone. The subunit is barren of foraminifera and plant debris isscarce. Few palynomorphs consist of fresh water and locally, mixed fresh andbrackish water species.The lower subunit was deposited in a meandering channel-floodplain environment.This interpretation is based on the absence of marine foraminifera, rare occurrenceof plant debris and fresh water palynomorphs, the oxidation of the sediments,indicated by the mottled red to yellow siltstone and claystone, and the well54GR^1357 m RESISTLower subunit Upper subunitGR^1403 m RESIST1516 mSurat-11562 mBaanpot-B-1Figure 3.25: Typical log profiles of unit 2, showing general fining-upward sequences of nonmarine channel deposits in the lowersubunit and generally fine-grained marginal marine deposits and marsh complexes in the upper subunitShaleSandstone• :-:•:•:•:-:•:•• :.:.:.:•:•:•:..^...•.•.•.•.•.•.•.:•:-:-:•:•:•:•:Surat-1(474Kung-1 (317)o Kaphong-1 (806)Platong-5 0 (483)0 0 Platong-1 (616)0 latong-8 (397)0 S. Platong-1 (662)Pakaran -1 (457)Pladang-0Insea-1 (216)^ (1542)0rat-1 (934)Satun- (738)0Satun-1 (820)Erawan-12-9 (716)Dara-1 ('27) 00^0 Satun-3 (779)0 Erawan-12-1(589)0 Erawan-12-8 (669)Yala-2 (314)00^5^10 km0 Kaphong-3 (768)Ranong-1 (375)0rawan-12-7 (702)00Erawan-K-1 (822)0Jakrawan-1(775)0Baanpot-1 0 (705)^Funan-10Baanpot-B-1 (686)^(562)0Krut-1(249)Jakrawan-2 (599)0Figure 3.26: Isopach map of the stratigraphic unit 2 (contour interval = 500 m)560^5^10kmYala-2 (314)00 Kaphong-3 (207)400o S. Platong-1 (381)0Trat-1 (552)0-1(4 )Kung-1 (174+)0Insea-1 (226)akarang-1 (457) 5000 P:rang-3 (512)0 S. Platong-2 (512)n-2 (570)-1 (485)(481)Erawan-K-1 (82o 5o0Krut-(2Dara0^ 0 Satu -3 (581)rawan-12-1 32)0 Erawan-1 -8 (509)rawan-2 (332)00Baanpot 0 (5 unan-1Baanpot-B-1 (509) 49^0^ (299)0Surat-1(327)0o Kaphong-1 (290)tong-5 0 (281) Platong-1 (332)Platong-8 (293)Ranong-1 (375)0Figure 3.27: Isopach map of unit 2's lower subunit (contour interval = 100 m)57developed fining-upward sequences. Minor influence of brackish water is evidentfrom the local occurrence of brackish water palynomorphs. The oxidation of thesediments suggests that this subunit might have been periodically subaeriallyexposed.A typical log of the upper subunit of unit 2 occurs in Baanpot-B-1 well between thedepths of 1400-1590 m (Figure 3.25). The profile is characterized by a generallyhigh gamma ray count with minor intercalations of small fining-upward sequences.The subunit consists mainly of reddish brown to grey brown claystone and siltstonewith minor light brown sandstone interbeds. This subunit thickens from zero in thewestern margin of the basin to more than 300 m at the basin center (Figure 3.28).A probable depocenter of this subunit was recognized in the north central part ofthe basin in the vicinity of the Kaphong-3 and Kaphong-1 wells where up to 500 mthick succession of sediments occurs (Figure 3.28). The subunit is barren offoraminifera and contains abundant plant debris and palynomorphs. Dominantbrackish water palynomorphs include Florschuetzia meridionalis, F. levipoli, andZonocostites ramonae (Rhizophora sp.).The upper subunit of unit 2 was deposited in a brackish water swamp environment.This interpretation is supported by the presence of fine-grained sediments, abundantplant debris and brackish water palynomorphs. The reddish color of the sedimentsindicates subaerial exposure leading to intense oxidation of exposed sediments.The overall depositional environment of unit 2 was a transgressive phase in whichnonmarine sediments were initially deposited, followed by brackish water, marginalmarine deposits. The depositional history of unit 2 can be summarized as follows.At the base of unit 2 are nonmarine meandering channel-floodplain deposits58Yala-2 (0)0$0°Kaphong-3 (561)Kaphong-1 (516)203)Ranong-1 (0)^ o Platong-1 (284)0^ latong-8 (104)0 S. Platong-1 (281)ang-3 (235)0^0Insea-1 (0)^ o S.^tong-2 (203)Pak0Trat-1 (382)0tun-1 (336)e°0an-12-9 (256)00 Satun-3 (218)awan-12-1 (158)0 Erawan-12-8 (160)-12-7 (275)Jakrawan-2 (267)00Jakrawan-1(311)0Baanpot-1 0 (202) Funan-1(264)Baanpot-B-1 (177)0Krut-1(0)Eraw^(0)0^5^10kmFigure 3.28: Isopach map of unit 2's upper subunit (contour interval = 100 m)59characterized by a series of strongly oxidized, fining-upward sequences, thepresence of fresh water palynomorphs, and the absence of marine indicators. Localbrackish water deposits contain brackish water palynomorphs. In the upper part ofunit 2 are the marginal marine deposits characterized by fine-grained sediments,abundant plant debris and brackish water microflora. Subaerial exposure of thesediments of unit 2 led to intense oxidation resulting in the marked reddish color.The presence of Florschuetzia meridionalis, F. levipoli, and Zonocostites ramonae(Rhizophora sp.), along with the absence of Pliocene palynomorphs, indicate thatunit 2 is in the Florschuetzia meridionalis Borneo zone of Middle to Late Mioceneage (Germaraad et al., 1968).3.4.6 Unit 1Unit 1 encompasses the interval from the Mid-Miocene unconformity to thepresent-day sea bed (approximately 60-80 m subsea elevation). Due to the lack ofcutting samples and well log data at shallower depths, only the lowermost part ofthe unit is discussed here.A typical composite log profile of unit 1 is shown in Figure 3.29. The thickness ofthis unit varies from about 800-850 m in the western basin margin to as thick as1300-1400 m in the basin center (Figure 3.30). No prominent depocenter isrecognized. Lithologically, the lower part of unit 1 can be subdivided into 2subunits.A typical log profile of the lower subunit occurs in Baanpot-1 well between thedepths of 1220-1370 m (Figure 3.29). The profile is characterized by a series of60..•.•.'.•.•.'.:•:•:•:•:•:•:•:ShaleSandstoneLower subunit Upper subunitGR^1220 m RESIST GR 1129 m RESIST1373 mBaanpor-11287 mSouth Platong-1Figure 3.29: Typical log profiles of unit 1, showing general fining-upward sequences of nonmarine channel deposits at the baseand generally fine-grained marginal marine deposits at the top of lower subunit and fine-grained shallow marine depositsin the upper subunito Kaphong-1 (1302)Platong-5 0 (1157)o o Platong-1 (1242)Surat-10^(1070)Kung-1 (1106)Ranong-1 (856)0 ° Platong-8 (1166)0 S. Platong-1 (1445)Pakaran•1 (1229)°^Pladang-3 (1419)0^ 0Insea-1 (803)^ 0 S. PI n.9-2 (1467)TisoTrat-1 (1317)Sa -2 (1384)0atun-1 (1507)Yala-2 (1235)00^5^10 km0 Kaphong-3 (1307)Erawan-12- (1264)Dena-1^1) 0^0 0 Satun-3 (1450)0 Erawan -1(1283)0 Erawan- -8 (2379)1^Erawan-12-7 (1176)Krut-(970)° Jakrawan-2 (1493)0^ 0-Erawan-K-1 (2135)oJakraw^1489)0Funan-1(1351)0Baanpot-1 0 (1325)0Beanpot-B-1 (1335)Figure 3.30: Isopach map of the stratigraphic unit 1 (contour interval = 400 m)62interbedded coarsening- and fining-upward sequences in the lower part and morefine-grained intervals in the upper part. Due to the lack of data in the upper part ofthis subunit, no isopach map was made. This subunit consists mainly ofinterbedded fine- to very fine-grained sandstone and grey to grey brown claystoneand siltstone. Carbonaceous partings are common. The subunit contains abundantplant debris and palynomorphs. The predominant brackish water assemblageincludes Florschuetzia meridionalis, Zonocostites ramonae (Rhyzophora sp.), andSpinizonocolpites echinatus (Nypa sp.). The subunit also contains arenaceousforaminifera such as Miliammina telemaquensis.The lower subunit was probably deposited in distributary channel environments in acoastal plain based on a series of fining- and coarsening-upward sequences,brackish water palynomorphs and foraminifera. The upper part of this subunit wasprobably deposited in a lower delta plain or interdistributary bay where there wasmore influence of brackish water and marine processes. This interpretation is basedon a series of fining-upward sequences which are overlain by fine-grainedsediments, and the presence of brackish water palynomorphs and foraminifera.A typical log profile of the middle subunit of unit 1 occurs in South Platong-1 wellbetween the depths of 1100-1340 m (Figure 3.29). The serrated, generally highgamma ray log signature reflects fine-grained sediments interbedded with thin,coarse-grained sediments. Small-scale coarsening- and fining-upward sequenceslocally occur. No isopach map was constructed for this subunit because of the lackof constraint in the upper boundary. The subunit consists mainly of grey to darkgrey claystone, siltstone and minor coarsening-upward sandstone and coal.Fragments of limestone also occur. The subunit contains abundant arenaceousforaminifera and palynomorph assemblages. Arenaceous foraminifera encountered63include Miliammina cf telemaquensis and M. sp. These are the typical brackishwater foraminifera. The palynomorph assemblage, also typical of brackish water,includes Zononcostites ramonae, Florschuetzia meridionalis, Avicennia sp., andSpinizonocolpites echinatus (Nypa sp.).The middle subunit was deposited in interdistributary bay environments. Thisinterpretation is supported by the abundance of brackish water foraminifera andpalynomorphs, the generally fine-grained sediments, and the presence of coalinterbeds. Locally high concentrations of plant debris and palynomorphs mayindicate proximity to distributary systems. The presence of small-scale coarsening-and fining-upward sequences may indicate crevasse splay and channel depositswhich built into interdistributary bays.Based on mud log data, the interval stratigraphically higher than the sectiondescribed above, consists mainly of dark-grey to black clay and claystone withminor coal and sandstone interbeds. These lithologies together with the fact that thearea is now approximately 60-80 m below sea-level suggest that the uppermost partof unit 1 was deposited in a lower delta plain and prodelta to shallow marineenvironments. This unit may, however, possibly have been exposed during thePleistocene glaciation.Arenaceous foraminifera such as Miliammina cl telemaquensis and M. sp., andpalynomorphs Florschuetzia meridionalis, Zonocostites ramonae, andSpinizonocolpites echinatus suggest that the lower part of unit 1 is in theMiliammina paleontological zone and in the Florschuetzia meridionalis floral zone.The presence of fossils described above and the absence of Pliocene floral elementssuggest that the lower part of unit 1 is of Late Miocene age.64The overall depositional environment of unit 1 shows a transgressive phase in whichshallow marine sediments prograded onto nonmarine or marginal marine deposits.The depositional history of unit 1 is summarized as follows. The base wasdeposited in a distributary channel environment in a coastal plain characterized by aseries of interbedded coarsening- and fining-upward sequences. Brackish water,interdistributary bay deposits subsequently overlaid the coastal plain deposit,evident by the abundance of brackish water foraminifera and palynomorphassemblage. The upper part of unit 1 is a shallow marine deposition characterizedby dark-grey to black clay and claystone.3.5 DISCUSSIONThe stratigraphy of the Tertiary succession in the Pattani Basin is a response to thetectonic evolution of the Gulf of Thailand. Figure 3.34 shows temporal variation ofthe average rates of tectonic basement subsidence and decompacted sedimentation.The rate of tectonic subsidence and decompacted sedimentation rates werecalculated using decompaction and backstripping analyses (cf. Van Hinte, 1978;Friedinger, 1988; Angevine et al., 1990). The subsidence was at a maximumduring the Late Eocene to Early Oligocene interval and has generally decreasedwith time. The maximum rate of sedimentation occurred during the Early Mioceneand Middle Miocene. The dominant period of rifting in the Pattani Basin lastedabout 20 m.y. from Late Eocene (40 Ma) to Early Miocene (20 Ma) time and wascharacterized by episodic normal faulting, rapid subsidence, and high topographicrelief (Chinbunchorn et al., 1989). After the rifting, a period of tectonicquiescence ensued and is characterized by relatively slow thermal subsidence.Based on tectonic characteristics of the study area, the Tertiary stratigraphy in the65Pattani Basin comprises two phases of sedimentation: synrift and post-rift. Thesynrift phase is characterized mainly by nonmarine sediments of unit 6 and unit 5,and a broad regressive sedimentary package of unit 4. The post-rift phase ischaracterized by a regressive (unit 3) and two transgressive sedimentary units (unit2 and unit 1). The stratigraphy of Tertiary strata of this area is summarized inTable 3.1. The schematic sedimentary evolution of the Pattani Basin is summarizedin Figure 3.35 and is discussed below.3.5.1 Synrift Sedimentationa. Late Eocene to Early Oligocene (40-30 Ma)In the Earliest Tertiary, the Gulf of Thailand probably was elevated above sea level(Achalabhuti and Oudom-Ugsorn, 1978). The shoreline of the ancestral Gulf Basinwas several hundred kilometres south of its present position. The initial phase ofbasin formation probably began in Late Eocene (Hellinger and Sclater, 1983;Chinbunchorn et al., 1989) when the area was subjected to an extensional tectonicregime of block faulting (Figure 3.35A) and rapid subsidence which created hightopographic relief and high sediment influx into the basin (Figure 3.34). Rapidsubsidence and high sediment supply led to the development of alluvial fan andalluvial plain deposits (Figure 3.35A). Due to limited available data, thedistribution of the alluvial fan deposits cannot be documented here. However, it ismost likely that the fan deposits, especially the coarse-grained proximal facies, wereconcentrated along the edge of the basin margin, whereas relatively finer-grained,braided stream deposits of the distal facies were concentrated farther toward thebasin center. A narrow restricted depocenter in the south of the study area, andprobably another in the north, (Figure 3.12) may have been the site of lacustrine66deposition. Similar conditions also existed in the narrow grabens of the PhitsanulokBasin, northern Thailand where approximately 2000 m of Oligocene to Miocenesynrift lacustrine sediments occur (Burri, 1989; Chinbunchorn et al., 1989).Alluvial fan environments may have predominated until the end of the Eocene afterwhich the source areas were substantially eroded, and depositional environments ofthe Pattani Basin changed from alluvial fans and braided streams to floodplains.Hence, Early Oligocene sediments are predominantly floodplain depositscharacterized by generally fine-grained sediments with an occasional series offining-upward sandstone representing meandering channel deposits. Lacustrinedeposition, characterized by uniformly fine-grained sediments and coal interbeds,occurred locally mainly in the areas away from the basin edges. It is believed thatthick lacustrine sediments were being deposited in the restricted narrow area in thebasin center (Burn, 1989; Chinbunchorn et al., 1989).b. Late Oligocene to Early Miocene (30-24 Ma)In the Late Oligocene, the Pattani Basin subsided at a lower rate and consequentlyhad a lower sedimentation rate than during Early Oligocene (Figure 3.34). Riftingand block faulting continued but with less intensity. A depocenter in the southernpart of the basin suggests higher subsidence and sedimentation rates in that area.Sedimentation in the Pattani Basin was purely nonmarine (Figure 3.35B). Fluvialsandstone and claystone interbeds characterize a series of fining-upward sequencesand the occurrence of fresh water palynomorphs suggest that channel deposition wastypical of this synrift phase of basin in-filling. The change from fine-grainedsediments in the lower subunit to coarser-grained sediments in the upper subunitprobably reflects greater sediment influx which possibly resulted from more activefaulting at the end of this time interval. Such episodic block faulting is common67during the rifting stage of basin formation (Allen and Allen, 1990). During thisinterval, the contemporary shoreline was tens of kilometres southeast of the PattaniBasin.c. Early Miocene (24-20 Ma)A rapid marine transgression from the end of the Late Oligocene to the EarlyMiocene (end of unit 5) is indicated by a sudden change from nonmarine floodplaindeposits in the upper part of unit 5 to prodelta and shallow marine deposits in thelower part of unit 4. This transgression was caused by a rapid rise of relative sea-level during the early part of Early Miocene which, in turn, was the result ofepisodic block faulting and graben formation. Episodic block faulting is evidentfrom an increase in subsidence rate during this time interval (Figure 3.34). Therapid increase in water depth temporarily created a surface of nondeposition, atleast in the vicinity of the basin center, which marks the boundary betweenstratigraphic units 5 and 4. This transgression marks the first marine influence inthe Pattani Basin. Following this, the rate of deposition exceeded the rate ofwater-depth increase, creating a broad regressive sedimentary succession. Theregressive succession is characterized by fine-grained, prodelta to shallow marinesediments at the base overlain by a series of coarsening-upward distributary mouthbar and beach ridge deposits which, in turn, are overlain by a series of fining-upward sequences and red beds of floodplain-channel deposits. The updip limit oflittoral to shallow marine sediments of the lower subunit of unit 4 (Figure 3.31)approximates the position of the shoreline in the early part of the Early Miocene.Marine influence in this area probably originated from the South China Sea to theeast. As regression proceeded, nonmarine sediments progressively prograded overearly shallow marine sediments, and the shoreline progressed toward the southeast.68Yala-2^ 0^5^100 kmPladang-30Insea-1^ ? o S. Platong-20o^Trat-1Satun-i0I^Satury1Erawan-12-9De,ra-1^0 0 atun-3Erawan-12-10 Erawan-12-8'....trzwien-12-7Krut-1JakrawaN2/ 0Pakarang-10,swan-K-1^ ./J5krewan-10Baanpot-1 0^Funan-1Baanpot-B-1Ranon94• —.•o Kaphong-3o Kaphong-1••' Platong-5 0o Platong-1°^Platong-80 S. Platong-1Kung-1Surat-1N.Figure 3.31: The regressive cycle of unit 4. Arrows indicate direction of advancing shoreline.69The distance between the updip limit of the littoral to shallow marine sediments ofthe lower subunit of unit 4 and the downdip limit of nonmarine deposits of theupper subunit of unit 4 (Figure 3.31) approximates the amount of regression withinthe Early Miocene interval.3.5.2 Post-rift SedimentationBy the end of unit 4 sedimentation, the Pattani Basin became tectonically quiescent.Subsequent evolution of the basin was essentially governed by relatively slow, post-rift thermal subsidence and sediment loading. Although faulting still occurredlocally, fault density decreased substantially.a. Late Early to Middle Miocene (20-15 Ma)After the Early Miocene (the end of unit 4, about 20 Ma), another rapidtransgression occurred in the Pattani Basin (Figure 3.35C). This transgression isrecorded by a sudden change from nonmarine floodplain deposits in the upper partof unit 4 to prodelta and shallow marine deposits in the lower part of unit 3. Thesurface of nondeposition which marks the boundary between stratigraphic units 4and 3 is the result of rapid rise in relative sea-level. This rapid rise may have beendue more to a rapid rise of global eustatic sea-level (Hag et al., 1988) and lowsedimentation rate rather than tectonic subsidence, because post-rift subsidence isrelatively slow and continuous (Figure 3.34). As the rate of deposition exceededthe rate of relative sea-level rise, a coarsening-upward regressive sedimentarypackage resulted (Figure 3.32). The updip limit of the prodelta and shallow marinedeposits of the lower subunit of unit 3 indicates that late Early Miocenetransgression was less extensive in the northwestern part of the basin. The downdip70Yala-200^5^10 km0 Kaphong-3Kaphong-1•Platong-5• ••—••• •. 0 Platong-1/0,••^Platong-80^ •.Surat-10Kung-1 /'/.0Insea-1^\0^I^0^Trat-1/ Satun-2iSatunA1i^ .. -(..... ......•^Erawan-124/* ..Dara-1^o •0 o Satun-3i^f•%. ,i‘Erawan-12-1\^ -.. ^Erawan-12-8.. ‘...• --...**a.Jakrawjan-20Erawan-K-1I APir Jakrawan-10Baanpot-1 1^Funan-10Baanpot-B-1Ranong-1Erawan-12-7Krut-1 •■•^ -•-•-•^00 S. Platong-2Figure 3.32: The regressive cycle of unit 3. Arrows indicate direction of advancing shoreline.71limit of nonmarine deposits of the upper subunit of unit 3 suggests that during theMiddle Miocene (about 15 Ma) marine influence was restricted to a small area inthe south-central part of the basin (Figure 3.32).b. Middle Miocene (15-12 Ma)During the Middle Miocene, minor basin-margin faulting continued, but with muchless intensity. Continued fault movement, although local, is evident from relativelyhigh tectonic subsidence rate (Figure 3.34). A progressive decrease in subsidenceand sedimentation rates toward the end of this time interval led to a progressiveincrease in relative sea-level, i.e. transgression. This Middle Miocene transgressioninvolved brackish water with marginal marine sediments slowly prograding overearly nonmarine sediments. As a result, the contemporary shoreline advancedlandward toward the northwest of the Gulf of Thailand. The amount oftransgression can be approximated from the distance between the downdip limit ofnonmarine sediments of the upper subunit of unit 3 and the updip limit of brackishwater, marginal marine sediments of the upper subunit of unit 2 (Figure 3.33).Subsequently, a Late Middle Miocene transgression extended further to the north,but less to the west, than the earlier transgression (Figure 3.32 and 3.33). A rapideustatic sea-level fall at the end of Middle Miocene (Haq et al., 1988) led to rapidregression and subaerial exposure, intense oxidation, and possibly erosion ofMiddle Miocene sediments (unit 2) in the study area. The shoreline at the end ofunit 3 sedimentation was probably located further to the east of the study area.720Baanpot-1 0^ Funan-10Baanpot-B-10Insea-10^IKrut-1 k Erawan-12-70^*\\^Jakrawan-2....-... '‘..Erawn-K•1^.c/**Ci AV^..---..a; 0.1 Jakrawan-1tPakarang-1b1.ii.^0 S. Platong-2i 00^Trat-1/^Satun-2i/^Nq ^,-10Satun.-!I ... •i^Erawan-124Da4a-1c).•'^o Satun-3A^!.\ \Erawan-12-1•S,Erawan-12-8...Pladang-30Yala-2 0^5^10 km0 Kaphong-30 Kaphong-1—..Platong-5 00^0 0 Platong-1Ranong-1 Platong-80Kung-10 S. Platong-1Surat-1Figure 3.33: The transgressive cycle of unit 2. Arrows indicate direction of advancing shoreline.730.30.0 ^-40 -30^-20^-10^0Age (Ma)Tectonic subsidence SedimentationFigure 3.34: Tectonic subsidence (solid line) and decompacted sedimentation(dashed line) rates74Coastal sediments floodplainShallow marineOpen manne shelfDCBraided river system Alluvial plainRiver systemFlood basinLake BLate Oliocene (:::24 Ma)Marine sedimentsFloodplain-channel sedimentsMiddle Miocene (^--15 Ma)Lacustine sedimentsAlluvial fan and braided-stream sediments Basement rocksEILL2IL:.1Present-dayt%(‘Alluvial fanFigure 3.35: Schematic evolution of sedimentary environments of the Pattani Basin. (A) Late Eocene: after the formation of basin by extension.Alluvial fan and braided stream sedimentation is dominant. (B) Late Oligocene: most basement highs were eroded, extensive floodplaindeveolp. (C) Middle Miocene: extensive low- gradient floodplain passed southward to shallow marine during transgression. (D) Present-day condition: estasblishment of shallow marine condition which may have started in the Late Miocene.c. Late Miocene to Pleistocene (12-0 Ma)After the Middle Miocene, the Pattani Basin was subjected to slow subsidence andsedimentation (Figure 3.34). Slow subsidence, decreasing sediment influx togetherwith eustatic sea-level rise (Haq et al., 1988) caused a slow rise in relative sea-leveland hence transgression (Figure 3.35D). A broad transgressive succession (unit 1)is characterized by basal nonmarine, distributary channel deposits overlain by fine-grained, brackish water, interdistributary bay deposits and marsh and swampcomplexes which, in turn, are overlain by fine-grained, prodelta to shallow marinedeposits. The shoreline advanced westward and northward to the present-daylocation (Figure 3.35D).3.6 SUMMARY AND CONCLUSIONSRifting, as well as other tectonic processes, plays a major role in controlling therate and amount of subsidence and the amount of sediment supply into asedimentary basin. The rate and amount of basin subsidence, together with theamount of sediment influx generally dictated the sedimentary record developed inthe study area, especially during the rifting phase and early part of the post-riftphase. Fluctuation in eustatic sea-level played a major role in controlling thesedimentary record in the latter part of the post-rift phase, during which subsidenceand sediment supply rates were reduced significantly. The sedimentary history inthe Pattani Basin, and the Gulf of Thailand in general, is a response to rifting whichbegan in Late Eocene. The sedimentary succession in the Pattani Basin can bedivided, based on the rifting process, into synrift and post-rift sequences. Threefactors controlling the sedimentary records are evident in the Pattani Basinstratigraphy: (1) basin subsidence, (2) sediment supply and (3) sea-level fluctuation.76The effect of basin subsidence and sediment supply were probably greatest duringthe rifting phase and the early part of post-rift phase, characterized by blockfaulting and high topographic relief. In contrast, sea-level fluctuation probablyplayed a more important role in the later part of post-rift phase, characterized byrelatively slow and continuous subsidence.The synrift stratigraphy comprises three stratigraphic units (units 6, 5, and 4). Thebasal unit (unit 6) represents Late Eocene to Early Oligocene (40-30 Ma)nonmarine sediments of alluvial fan, braided stream environments in the lower partand flood-plain deposits in the upper part. Lacustrine deposits were probablydeposited in the vicinity of the basin center throughout this interval. The overlyingunit (unit 5) represents Late Oligocene to Early Miocene (30-24 Ma) nonmarinefloodplain-channel sediments in the lower part and coarse-grained channel depositsin the upper part. The uppermost succession of the synrift sequences (unit 4)represents an Early Miocene (24-20 Ma) broad regressive sedimentary package inwhich the basal prodelta to shallow marine sediments were overlain by distributary-mouth bar deposits and beach-ridge complexes. In turn, these were overlain bynonmarine floodplain and meandering channel deposits at the top. The depositionof the synrift sequence corresponded to the rifting and extension of the continentalSoutheast Asia which induced episodic block faulting and rapid subsidence. Thesedimentary record of synrift sequences is the response to high subsidence rate andhigh sediment influx which were a direct result of rifting. The first marinetransgression in the Pattani Basin in the Early Miocene might have been the resultof rapid subsidence due to the episode of block faulting and the rise in eustatic sea-level. The following broad regressive succession in unit 4 resulted when the rate ofdeposition exceeded the rate of relative sea-level rise.77The post-rift stratigraphy comprises stratigraphic units 3, 2, and 1. The first post-rift unit (unit 3) represents an Early to Middle Miocene regressive sedimentarypackage, in which the basal prodelta and shallow marine sediments were overlainby distributary mouth bar deposits and beach complexes. These, in turn, areoverlain by nonmarine floodplain and meandering channel deposits. The post-riftphase marks a slower subsidence rate, hence the amount of sediment influx andeustatic sea-level fluctuation played an important role in the resulting sedimentaryrecord. Late Early Miocene transgression, which was probably the result of rapideustatic sea-level rise, created a short period of nondeposition during which the rateof relative sea-level rise exceeded the rate of deposition. As the rate of depositionslowly exceeded the rate of relative sea-level rise, a broad regressive sedimentarysuccession resulted. The transgressive succession of unit 2 (Middle Miocene, 15-12Ma) was the result of the slow rise of relative sea-level and progressive decreasingsediment supply, probably from a lowering of source areas toward the end of thistime interval. The rapid fall of relative sea-level, resulting in subaerial exposure,intense oxidation, and possible erosion of the Middle Miocene sediments, wasprobably the effect of the global eustatic sea-level fall at the end of MiddleMiocene. The uppermost transgressive succession of unit 1 (Late Miocene toHolocene, 12-0.01 Ma) was the result of a slow rise in relative sea-level, probablya result of a slow rise in eustatic sea-level, slow subsidence, and decreasingsediment supply. The present-day shallow marine condition in the Pattani Basinand throughout the Gulf of Thailand is the continuation of the latest transgressivephase.784. TECTONIC EVOLUTION AND BASIN MODELLINGOF THE PATTANI BASIN, THE GULF OF THAILAND4.1 ABSTRACTSubsidence and thermal histories of the Pattani Basin have been investigated using anonuniform lithospheric stretching model. The predicted heat flow history is usedto calculate the degree of organic maturation, in this case: vitrinite reflectance. Thevalidity of the model is verified by comparing the calculated vitrinite reflectancewith the measured values.The opening of the Pattani Basin is related to a northward collision of Indiansubcontinent with Eurasia in the Eocene. The penetration of India into Eurasiacaused clockwise rotation of Southeast Asia, resulting in an increasingly obliquesubduction of the Indian Ocean plate beneath the western edge of Southeast Asia.The oblique subduction changed the stress field in Southeast Asia from one ofconvergence to one with a strike-slip component which led to right-lateralmovement on NW-SE fault systems and left-lateral movement on NE-SW conjugatefault systems. The E-W extension associated with the right-lateral fault systemscaused crustal thinning and lithospheric stretching in Thailand. This, in turn,induced the formation of N-S trending sedimentary basins along an old Triassic-Jurassic suture zone and the similar NNW-SSE tectonic trends which are the weakzones in the lithosphere.The nonuniform lithospheric stretching model is generally consistent with theobserved geological constraints in the Pattani Basin. The amount of lithosphericstretching and surface heat flow generally increase from the basin margin to the79basin center. The crustal lithospheric stretching factor ((3) ranges from 1.3-1.4 atthe basin margin to 2.6-2.8 in the center. The subcrustal stretching factor (8) variesfrom 1.3 at the basin margin to 3.0 in the basin center. Generally, the amount ofsubcrustal stretching is greater than that of crustal stretching, except in areas with agreat thicknesses of synrift sediments, where the amount of crustal stretching isgreater than that of subcrustal stretching. Such areas might have been affected bythe pre-existing basement topography prior to rifting.The lithospheric stretching in the Pattani Basin may have extended the basement asmuch as 45 to 60 km and have caused the passive upwelling of the hotaesthenosphere, resulting in high surface heat flow (1.9-2.5 HFU) and highgeothermal gradient (45-60°C/km).4.2 INTRODUCTIONRecent advances in understanding the mechanisms of basin formation have madepossible quantitative basin modelling, based on known physical principles. Twoprocesses believed to create sedimentary basins are flexure of the lithosphere inresponse to surface loading by overthrusts (Beaumont, 1981; Jordan, 1981) andthinning of the lithosphere by stretching (McKenzie, 1978). Tertiary basins in theGulf of Thailand, having a series of normal faults, horsts, grabens, and half grabenstructures, are thought to have been initiated by continental rifting and lithosphericstretching (Bunopas and Vella, 1983; Hellinger and Sclater, 1983). This chapterapplies the modified McKenzie's kinematic lithospheric stretching model(McKenzie, 1978; Hellinger and Sclater, 1983; Allen and Allen, 1990) to predictsubsidence and thermal histories of the Pattani Basin (Figure 4.1). The predictedheat flow history is used to calculate the degree of organic maturation and the80Platong-1Pia • ng-8Ranong-1Yala-2 0^5^10kmI nsea-1Trat-1an-12-1Erawan-1 2Baanpot-1Baanpot-B-1Figure 4.1: Location of well data used in this study. Numbers in the box indicate thecross sections shown in Figures 4.2 through 4.781timing and location of hydrocarbon generation (Turcote and McAdoo, 1970;Royden et al., 1980; Issler and Beaumont, 1987). The validity of the model is thenassessed by comparing the calculated thermal maturation index, in this study:vitrinite reflectance, with the measured values.4.3 METHODS OF STUDY4.3.1 Geohistory AnalysisThe total amount of subsidence in sedimentary basins is the sum of the true tectonicsubsidence and the subsidence due to sediment loading. The total subsidencehistory of a sedimentary basin can be analyzed from outcrop sections, well data,and seismic sections using the technique referred to as "Geohistory analysis" byVan Hinte (1978).Geohistory provides a true picture of subsidence and sediment accumulation ratesthrough time by making three corrections to the present (observed) stratigraphicthickness. The three corrections are decompaction, paleobathymetry, and eustaticsea-level fluctuations. Decompaction is applied to the observed stratigraphicthickness in order to remove the progressive effects of rock volume changes withtime due to the progressive loss of porosity with depth. Paleobathymetry, the waterdepth at the time of deposition, is used to determine the position of a stratigraphiclayer relative to a datum such as present-day sea-level. Eustatic sea-levelfluctuation data is used to remove the effect of changes in paleosea-level relative toa datum such as today's sea-level.82True tectonic subsidence is obtained only after the removal, from the totalsubsidence, of the subsidence due to the sediment load and after corrections forvariations in water depth and eustatic sea-level fluctuations. The common approachfor removing the effect of sediment loading is by assuming a simple Airy's localisostatic model in which the sedimentary units can be removed (backstripped), andthe basin is allowed to isostatically rebound (Steckler and Watts, 1978; Angevine etal., 1990). The true tectonic subsidence obtained from backstripping can be used ininterpreting the mechanisms of basin formation.The following sections describe the methods of decompaction, backstripping, andcorrections for paleowater depth and eustatic sea-level changes used in this study inorder to obtain the total subsidence and the true tectonic subsidence, respectively.a. DecompactionThe purpose of decompaction is to remove progressive effects of rock volumechange with time and depth due to the progressive loss of porosity during burial.Assuming, for clastic sediments, no significant chemical diagenesis, volume ofgrains does not change during burial (Van Hinte, 1978). Volume of pore space,however, decreases with time and depth of burial. The original thickness (To) isrelated to the present-day thickness (T,,) as follows (Van Hinte, 1978; Sclater andChristie, 1980):0-0)T T —^" "°^1-00 (4.1)83Where 00 is the original porosity at time of deposition. 7,, and 0. are present-day(observed) thickness and porosity of the stratigraphic unit, respectively. Severalporosity-depth functions for various lithologies have been proposed (Sclater andChristie, 1980; Baldwin and Butler, 1985). For normally compacted sediments theporosity-depth function can be either exponential or linear (Ruby and Hubbert,1960; Sclater and Christie, 1980; Friedinger, 1988) according to the followingequations:0(Z) = 00 exp(—cz)^ (exponential)^(4.2)or0(z) = 00 - CZ^ (linear)^(4.3)Where 0(z) is the porosity at depth z. Variables 00 and c are surface porosity andcompaction coefficient, respectively, and are controlled by lithological properties ofthe sediment layer.The thickness of a sediment layer at any time in the past can be calculated bymoving the layer up along an appropriate porosity-depth curve. This exercise isequivalent to sequentially removing overlying sediment layers and allowing thesediment layer of interest and underlying layers to decompact. If a sediment layerbetween depth z1 (top) and z2 (bottom) moves up to the surface, z; (new top)becomes zero and the new bottom depth Z2 can be calculated using (Sclater andChristie, 1980; Friedinger, 1988):84•^0z2 —z2 + z, — z, +--2-exp(— z )c+--Lklexp(—cz, )— exp(—cz;)-exp(—cz; )1 = 0or in case of a linear-depth porosity function:2 ^2z2 + 2- (1 - 00 )Z2 - - [k +Z; (1 - 0° -I--2 Z;)] = 0C^Cwherek = (z2 — zi )Ll— 930 + —c . (z2+ zi)The depth z; then becomes the new top (z,) for the underlying layer. When thisprocedure is applied successively from top to bottom of the sedimentary column,the decompacted subsidence history of each sediment layer in a stratigraphic columncan be determined.The rate of sediment-fill, Rp for the topmost layer, after each backstrippingexercise, of thickness z; (where z, = 0) can be calculated using the equation:R — z2f - AzA twhere A, = t 2 —t,^ (4.6)Where t, and t2 are the ages of top and base boundaries of the layer, respectively.(4.4)(4.5)85The rate Rf thus calculated, however, still does not fully represent the sedimentationprocess. Thicker units, due to their heavier loads, are subject to more compactionand have lower initial porosity than thinner units (Van Hinte, 1978). A true rate ofsediment-mass accumulation, Ra, for each top layer corrected for self-compactionof the sediments is, therefore, calculated by:RaA,(1– 0° )+-[1–exp(–cRaA,^= 0^(exponential)^(4.7)or2 n 2z, (linear)fc;^+— = 0^ (4.8)cA,The new mean porosity of each decompacted sediment layer, 0,, is calculatedusing:exp(–cz, – exp(–cz0, =^ (exponential)^(4.9)– zior= 0° – 5-(z;^ (linear)^(4.10)The new mean density of each decompacted sediment layer, p„ is calculated using:P, = 0,P. +0 – 0,)Pg^ (4.11)86n [43iP. + ( 1— (OP g E ^z.]=►(4.12)Where p„, and pg are the densities of water and the sediment grains, respectively.The new mean density of the total sediment column, p„ is:Where 0, and z; are the mean porosity and decompacted thickness, respectively, ofthe ith sediment layer, and S is the total decompacted thickness of individualsediment column at the time of interest.b. BackstrippingThe total subsidence calculated from decompaction described in the previous sectionincludes the contribution of all factors that affect the subsidence of the basin:tectonics, sediment load, sea-level changes, and paleowater depth. In a studyoriented toward interpreting tectonic processes responsible for the basin formation,the effect of subsidence caused by loading during deposition needs to be removed(Allen and Allen, 1990; Angevine et al., 1990).The backstripping technique (Steckler and Watts, 1978) is used to remove the effectof sediment loading on the total subsidence by assuming a simple Airy's localisostatic model in which the sedimentary units are removed and replaced by water,and the basin is allowed to isostatically rebound.The tectonic subsidence of the basement, Y, is given by (Steckler and Watt, 1978):87Y_ S(Pm —PS +Wdpm _ pw (4.13)Where S is the decompacted thickness of a sediment column, Wd the water depth attime of sediment deposition, pn, the mean density of mantle, pw the mean density ofwater, and ps the mean density of a sediment column.c. Eustatic correctionEquation 4.13 is used for cases in which the eustatic sea-level fluctuation is notconsidered. If the magnitude of sea-level change is known, then equation 4.13 canbe rewritten to give a more accurate true tectonic subsidence of the basin as:Y = S( Pm — Pc)+T, ASL( PwP„, — P.^P„,— P,,, (4.14)Where ASL is the eustatic sea-level change relative to the present-day sea-level.ASL is positive for a sea-level rise and negative for a sea-level fall.4.3.2 Basin Forming ModellingThe true tectonic subsidence obtained from backstripping analysis is very importantin characterizing structural style and determining the mechanism causing theoccurrence and development of the sedimentary basins. Intracratonic rift basins andAtlantic-type continental margins are extensional basins believed to have beeninitiated by lithospheric stretching. The lithospheric stretching model, first88quantified by McKenzie (1978), can be used to predict subsidence of such basins(Royden and Keen, 1980; Sclater and Christie, 1980; Wood, 1982; and Hellingerand Sclater, 1983).McKenzie (1978) proposed the uniform lithospheric stretching model in which theextension of crustal and subcrustal continental lithosphere are identical. In themodel, a rapid extension of continental lithosphere causes lithospheric thinning andpassive upwelling of hot aesthenosphere to maintain isostatic balance. This liftingstage is associated with block faulting and initial subsidence or uplift. Followingrifting, the attenuated region slowly subsides over a period of time due to thermalcontraction and thickening of the lithosphere as it cools. The overall tectonicsubsidence is amplified by sediment and water loading. McKenzie's model assumesthat rifting is an instantaneous event and that the amount of lithospheric extension,0, is uniform with depth in the lithosphere, but 0 varies laterally.Royden and Keen (1980) proposed the dike-intrusion model in which fracturing oflithosphere and intrusion of dense ultramafic mantle materials into the crust areassumed. Addition of dense ultramafic material to light crustal rocks results ininitial subsidence associated with block faulting. The relatively slow post-riftsubsidence is controlled by a decreasing thermal anomaly. Hellinger and Sclater(1983) modified McKenzie's model by proposing the non-uniform lithosphericextension model in which the amount of thinning of the crust is different from thatof the subcrustal lithosphere. The amount of crustal lithospheric stretching is 0whereas that of subcrustal lithospheric stretching is S. Friedinger (1988) combinedthe three models outlined above and provided a modelling technique for calculatingsubsidence and heat flow history of the sedimentary column formed by rapidextension of the lithosphere.89Initial or synrift, fault-controlled, subsidence or uplift (Si) caused by instantaneouslithospheric stretching is the difference between subsidence due to isostaticcompensation of denser mantle material (E) and the thermal expansion oflithosphere (T, Friedinger, 1988):E S =^—Tpm ( 1—aTm )— pw (4.15)WhereE=(Pm pc)tc.(1--)(1 Tmatc)fi^2aT. Trnaap.[(1_1) + (1,2 211(1 1— )]2 o^a^a fl8Where (3 and 5 are crustal and subcrustal lithospheric stretching factors,respectively. p,„ pm , and pc are densities of water, mantle and lithospheric crust,respectively. 71, is the pre-rift thickness of the crust. a and a are thermal expansioncoefficient and thickness of lithosphere. T. is the temperature of upper mantle.The surface of the crust is assumed to lie at sea-level before extension, to subsidebelow sea-level after extension (Si > 0) and then to be water-loaded. In the casewhere the surface rises above sea-level after extension (Si < 0), p,„ should bereplaced by zero (air density).90As time elapses (t ---> ao) the thermal perturbation within the lithosphere graduallydecays; thermal contraction due to the cooling of the lithosphere induces post-rift orthermal subsidence. In order to predict the cooling of the lithosphere after rifting,the heat flow variation through time must be known. To simplify the calculation, itis assumed that lateral temperature gradients are much smaller than verticaltemperature gradients; that is, heat is conducted upwards in a vertical directiononly. If a is the lithosphere's thickness, z is the elevation above the finalequilibrium depth and T(Z) is the temperature at depth z, the boundary conditionsare:T(z) = 0^at^z = 0T(z) = TM^at^z = aThe one-dimensional unsteady state heat flow is:8T_ kl52TSt^8z 2 (4.16)Where k is the diffusity of both crustal and subcrustal materials. The secondderivative gives the curvature of the geotherm as it relaxes to its pre-stretchinggradients.The temperature at any depth and time, Trz,0 is made up of a steady-statecomponent, sw, and an unsteady-state component, u(z,0 (Allen and Allen, 1990):Tz,„^s(,) + u(z.,)^ (4.17)91Where,s(z) = Tn,(1-1au(2t) = E Xn exp( --n t)t )n=0^ rwitha2=7/2kODXn =(^t(fl— 5) sin {nit 1-1+ Ssinafi )(1 a) (1 icafi j^8nit'Where n is an integer which expresses the order of the harmonic of the Fouriertransform; t and k are the thermal-time constant and thermal diffusity of thelithosphere.The surface heat flux (Q) at time t after the end of rifting is given by Fourier's law:Q(0 = Q,{1+2E[Xn exp( —n 2t / r)]}^ (4.18)n=192Where Q, is the equilibrium heat flux:Q. T K= a (4.19)where K is the mean thermal conductivity of the lithosphere and Q,. is the internalheat created by radioactive decay within the lithosphere.The elevation, zo, above the final equilibrium depth to which the upper surface ofthe lithosphere subsides at time t is (Friedinger, 1988):4aap„,T,,,^{x(2.+1)z(l) =^P.);r2 _cl x (21 n +1)2 exp[—(2m+1) 2 t / r, ^ (4.20)The water-loaded thermal subsidence, S o, is obtained:S(1) = z(0) — z(,)^ (4.21)The total tectonic subsidence is the sum of initial (synrift) and thermal (post-rift)subsidences. The total lithospheric extension (c), including both crustal ((3) andsubcrustal (5) extension is:ae= ^t, + (a — tc )8(4.22)93Assuming that heat flux is independent of depth within the sediment column andneglecting deep water circulation of pore water, the temperature, Ta), at depth z isgiven by (Andrews-Speed et al., 1984):T = 7' +—z(z)^K (4.23)Where To) is the temperature at the sediment surface, Q is the heat flux conductedvertically upwards through the sediment column, K is the mean thermalconductivity of sediments which is (Woodside and Messmer, 1961):K = 41(1'4^ (4.24)Where 0 is the porosity of the sediment column, Kb and Kg are the thermalconductivities of pore water and sediment grains, respectively.The temperature, T(,), at a given depth z within the nth layer from the surface of thesediment column is (Friedinger, 1988):T – T +Q[-±-(Z(z)^0^K,(4.25)Where di and Ki are the thickness and thermal conductivity of each individual layerfrom top to bottom. K„ is the mean thermal conductivity of the sediment column.94A basin modelling program using the concepts described above is included in acomputer disk at the end of this thesis. This program is used to calculatedecompacted total and tectonic subsidences and predict thermal history of asedimentary basin formed by non-uniform lithospheric stretching. Appendix Adescribes how to run the program.4.4 BASIN FORMING MECHANISM IN THE PATTANI BASINThe extensional nature of the Tertiary basins in the Gulf of Thailand has beendocumented (Bunopas and Vella, 1983; Hellinger and Sclater, 1983; and manyothers) but the controlling tectonic regime responsible for the origin of these basinshas been a subject of discussion. Tapponnier et al. (1982), Pelzer and Tapponnier(1988), and Ohnstad (1990) related this extension to the extrusion of a portion ofIndochina away from India as the Indian plate collided with the Eurasian plate.Bunopas and Vella (1983) related the Tertiary extension and rifting in the Gulf ofThailand and onshore Thailand to back-arc spreading accompanying the subductionof the Indian plate beneath Continental Southeast Asia along the Java Trench andAndaman-Nicobar Island chain. Polachan and Sattayarak (1989) consideredTertiary basins in Thailand as transtensional basins whose development is related toright-lateral simple shear along the NW-SE fault system.4.5 TIMING OF BASIN FORMATIONThe proposed initiation of Tertiary basins, including the Pattani Basin, took placefrom as early as Late Cretaceous to as late as Early Tertiary. Woollands and Haw(1976) pointed out that deposition of Tertiary sediments and facies distribution inthe restricted basins were tectonically controlled, and suggested that the95intracratonic basins in the Gulf of Thailand were formed during Late Mesozoic toEarly Tertiary by block faulting which occurred along earlier N-S and NNE-SSWtectonic trends of a Triassic-Jurassic suture zone. Tapponnier et al. (1982), Knoxand Wakefield (1983), and Bunopas and Vella (1983) suggested Early Tertiary asthe time of basin formation. Ohnstad (1990) suggested that the basins were formedin Early Tertiary time, no later than Oligocene.Tertiary stratigraphy in the Pattani Basin is summarized in Figure 4.2 throughFigure 4.7. Stratigraphic analysis of sedimentary successions in the Pattani Basin(chapter 3) suggests that the onset of rifting of the Pattani Basin coincided withdeposition of the oldest synrift sediments (Late Eocene to Early Oligocene,approximately 40 Ma) penetrated by drilling. These strata (units 6, 5 and 4)unconformably overlie a basement comprising Mesozoic sedimentary rocks andgranite. Rifting associated with extensive normal faults lasted approximately 20million years (Chinbunchorn et al., 1989). After the middle of the Early Miocene(the base of unit 3) major tectonic activity ceased and the area gradually subsided.The base of unit 3 marks the break between the highly faulted synrift sedimentarysuccessions (units 6, 5 and 4) and the post-rift sedimentary successions (units 3, 2and 1).4.6 SUBSIDENCE HISTORYIn order to determine the history of subsidence of the Pattani Basin, the sedimentcolumns from thirty wells were decompacted and backstripped using the basinmodelling concept described in the previous section. Tectonic subsidence thusobtained was then used to determine the crustal and subcrustal lithosphericstretching factors, 0 and 5, respectively. The lithospheric stretching factors were96SURAT-1RANONG-1^ KUNG-1. ........ ................ ..... • •...............^........... „__ WATER COLL1AI10 UNIT-10 UNIT-2  UNIT4111 UNIT-40 UNIT40 UNIT4SECTION-10-1................-2• WATER COLUMN 0 UNIT-1 0 UNIT-2 • UNIT-3 • UNIT-4 0 UNIT-5 0 UNIT4PLATONQ-8^PLATON:3-1-5Figure 4.2: Stratigraphic section-1 W-E direction. See Figure 4.1 for the location of the section.SECTION-a0...-2........................E 48-aPAKARANG-1 PLADANG-3 SOUTH PLATONG-2^TRAT-1-8 INSEA-1Figure 4.3: Stratigraphic section-2 W-E direction. See Figure 4.1 for the location of the section.97DARA-1 ERA WAN-1 2-1^ERAWAN-12-80-2-4-a-8-10 • WATER COLUMN 0 UNIT-1 0 UNIT -2• UNIT-3 0 UNIT-4 0 UNIT-5 Cl UN1T49KRUT-1 ERAWAN-K-1 BAANPOT-1^BAANPOT-B-1 JAKRAWAN-1^FUNAN-1SECTION-3.....0-2..............................0-a• WATER COLUMN 0 UNIT-1 El uNrr-2 U UNIT-3 E3 uturr-4 0 UNIT-5 C3 UNT4 .................................SATUN-3^ JAKRAWAN-2-8Figure 4.4: Stratigraphic section-3 W-E direction. See Figure 4.1 for the location of the section.SECTION-4Figure 4.5: Stratigraphic section-4 W-E direction. See Figure 4.1 for the location of the section.98PLATONG-5^PLATONG-1^SOUTH PLATONG-1^PLADANG-3^SATUN-2^SATUN-1YALA-2 KAPHONG-3 KAPHONG-10-2..........-4-6 ..............-8-10................. •-•111 WATER COLLIMN^0 UNIT-1 0 UNIT-2 UNIT-3 13 UNIT-4 0 UNIT-5 0 UNIT-8ERAWAN-12-8^ERAWAN-12-7^ERAWAN-K-10BAANPOT-B-1BAANPOT-1ERAWAN-12-9 ERAWAN-12-1SATUN-1SECTION-50......................................• -•--- • •^.................................................................• ..................... ........^..... •• .........^...-2U 4-6w.....^...-8 WATER COLUMN^UNIT-1 0 UNIT-2 UNI1-3 El 138T-4 D UNIT-5 0 UNITE-10Figure 4.6: Stratigraphic section-6 N-S direction. See Figure 4.1 for the location of the sectionSECTION-6Figure 4.7: Stratigraphic section-6 N-S direction. See Figure 4.1 for the location of the sectionII.......... .....further employed to determine the history of heat flow and temperature and present-day geothermal gradients.The validity of the lithospheric stretching model used in this study can be tested bycomparing the level of organic maturation predicted by the model and that observedin the field. Because the chemical composition and reflectivity of vitrinite changewith time and temperature, the vitrinite reflectance provides an important boundarycondition to constrain the predicted time-temperature history of any stratigraphicunit. Verification of the lithospheric stretching model used in this study is,therefore, carried out by comparing predicted and measured vitrinite reflectance, anorganic maturity indicator, at various depths and locations.4.6.1 Total Subsidence and Burial HistoryData from wells located in the Pattani Basin (Figure 4.1) are used to studysubsidence. Ages, present-day depths, and lithological data of each stratigraphiclayer needed for decompaction and backstripping are obtained from well data(Figure 4.2 through Figure 4.7). The depths to basement and the depths to deeperstratigraphic unit boundaries where they were not penetrated by wells weredetermined from seismic cross sections.Physical parameters such as surface porosity, compaction coefficient, porosity-depth function, grain density, and thermal conductivity for each lithology are listedin Table 4.1 (from Sclater and Christie, 1980).^Lithologies of differentstratigraphic units are obtained from well log data.^Physical and thermalparameters of the lithosphere and other parameters necessary for modelling were100Table 4.1: A list of Thermo-physical parameters used in the lithospheric stretchingmodel (After Sclater & Christie, 1980; Issler & Beaumont, 1987)1. Water layerI Density of sea water^ 1.03 g/cm32. Sedimentary layerLithology Sandstone Shale Shaly sandstoneSurface porosity (%) 49 63 56Compaction constant(x10-5 cm-')0.27 0.51 0.39Matrix densitycm-3(g^)2.65 2.72 2.68Matrix thermal conductivity(mcal cm-' sec-1 °C)9.6 5.5 7.53. Lithosphere and mantlePre-rift thickness of crust 35 kmThickness of lithosphere 125 kmThermal expansion coefficient of lithosphere 3.3 x10-5/°CThermal conductivity of lithosphere 7.5 mcal/cm sec °CThermal-time constant of lithosphere 62.8 m.y.Density of lithosphere 2.8 g/cm3Density of mantle 3.3 g/cm3Temperature of mantle 1350 °C101obtained from the studies of Parsons and Sclater (1977), Issler and Beaumont(1987), and Friedinger (1988).Total subsidence and decompacted burial histories of the basement rocks and allother stratigraphic layers at well locations are displayed in Figures 4.8 through4.37.4.6.2 Tectonic SubsidenceBy subtracting the sediment loading effect from the total subsidence, the tectonicsubsidence of basement through time at each well location is acquired. Because theentire Tertiary sediment column in the Pattani Basin was deposited in fluvio-deltaicto shallow marine environments, it is assumed that sedimentation of all strata tookplace at sea-level and thus eustatic sea-level fluctuation was not considered. It isfurther assumed that there was no basement topography prior to rifting. Thetectonic subsidence histories at each well location are displayed in Figure 4.8through Figure 4.37.The comparison of total and tectonic subsidence curves at well locations (Figure 4.8through Figure 4.37) indicates that the effect of sediment loading accounted for upto 50% of the total subsidence. The tectonic subsidence curves also indicate that, ingeneral, most of the subsidence took place from 40 Ma to 20 Ma. Subsidencewhich occurred after 20 Ma was considerably smaller and more gradual.102Figure 4.8: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Ranong-1 well01^03 OS 1 069198-35 .30 -15^-20^-IS399)598)• 1 0 0-18^-16^-14^.12^-10^.8^-649. 110000-055.10.2 5-0^970 ^1 965$t 9551 950I 1 9459401 9351 933 ^1-1 5•1SI -2)-29-20-36^.30^.25^-20^-15^-10^-5699 194040^63^80^100^120^140P1838.6. l89.er8091'0100-05-IS-I 5E .106 .15-30-35-90-455020 1E0^ISO^200Ranong-1(3 ^1.4 5 =1.8-2-18^-16^.14^-12^-10^-8^-6309 830ISO 180 270140^60^BO^103^120^14001000■10,1010.00ur. (I c )Kung-10=1.4 a=1.8Figure 4.9: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Kung-1 well^970 ^I 965 ^(950 ^^1 1 955 ^I 950 ^^I I INS ^1940 ^935 ^( 93320^-IS^-100^-35^-33^-25^-2080•829)10318360^ao^133^1 27^140Pres2-6. germs.. (o)2 2502 200I^2 103 ^•20 -113^-16 •12^-to^-630.04140Surat-1= 1.5 5 = 2.1Figure 4.10: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Surat-1 well0205 40BO-l5120I 532 20-1 0-15-25.30353160-2550•40 -2009.0.116040 10360^BO^160^20^1406504 505050'0• rc)-16^• 6^-14^-12^-to^-13^-6.2. MalPlatong-813 =1.8 5 = 2.8Figure 4.11: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Platong-8 well-20^.15^-1047CW00-05•1 0•1.20-2- 30-35-4 0093no160200 325022 4502 4602E 23501 3002 2502 200Tecto266 4‘9646694e65-40 -30^-25^.20^-'5^-10^-500-05 —I -20e -25 1041(0 183 20040^60^80^150^120^140pra...414ry torporaufsec)22 2502 2002 1501 21332 050-oo.0•04.100-05-IC-Is-20"Z.g-25.30-3.40-4 5.^^2 OCO ^-20 .18^-162 302^03^05Flo(%)Platong-1f3 ^1.9 .3 = 2.8Figure 4.12: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Platong-1 well.18^-16^•14^.12^.10^.8^-6^-4^-2N.C.)•15 • 1 0 -5 000-0 5E -20l -1 5I .2 0.2 5-35^-30^.25^-20A0 ,4 1,40- 30,0^I 561 ^1 5601 560seeI ,t! 1 556  I 557 ^I 557 ^556 ^-2002^03^00#2)56)Insea-10=1.3 6=1.3Figure 4.13: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Insea-1 wella-25^.20^-15^-10^-6^0510•296)00.1 0.2 0-30g40^60^SO^IGO^120^140Prosan.lay wryer...Cc)-40-50-607020160 180105Pladang-30=2.2 8=2.4Figure 4.15: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Pladang-3 well000 0-05 --05 40•1 0 ^ •1 0 44   40Te4C 43nic 40616360446 •1 5 120-20 ^ .1'^-20 66.6.66,v:   f-25 ^ r -25 160-30 ^ 3 -3 0-35 ^ -3 5 ^  ^2003 -40 ^ .4 0.4 5 ^'5:------ 240'0.40 .as -10^ -00^35^-30^-25 -20 -15 .10 -5 0442.1640 A911 14.4•1Pakarang-10=1.9 s =2.7Figure 4 14 . Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Palcarang-1 wellrosmi-by layoralt.(•c)2 5002 4502 4032.350- 23502 2502-20^-16^-IS^-14^.12^-10^-8^-6,0•14•410-30^-25^-20^-IS^-10^-5AP• PAO-25^.20^-'S^.10^-5.40•114.135023502 250I 2 2002 150^2150 ^.20 •18.^.16^.14^-12^.10..4* (.4-2Resant-day Nrrp■eure r e)00• -304090120I60200 g72403200106- 28^-15^-14^-12^-10^-5^-6505 PO60^60^120^120^140004441144ay 2sm4,44.150•40 1E0 120 203250210323502 3032 250I 2 2032I502 1002 05005 2 3 5 1002^0300 0040-I 0 ^ 90-20 .20 ^, ^  120Pe.Tec00nic .03 f 160^-30 ^^.10 ^.30.,0 --r 293.50 ^ 3g -50 , 240 1--60 ^ 'r°5013084d0n 290-70 ^ -70 —   320-80-40 50-0,^-35^-33^-15^ -15^-10-35^-30^-25^-20^ .10^-5VOW 595 8./South Platong-213=2.4 8=2.8Figure 4.16: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at South Platong-2 well1 6•115I -20-22120 183 20040^83^50^03^ITO^140ft MOH.; larrporesr.(0)00f -30-4.03g -60416^-1631003CCO2930E 29301 2 703I 2 BOO25402 400233D-20 -12^.10^-0058(644)'frat-113 2.7 8 = 3.6Figure 4.17: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Trat-1 well30^-25^-20^-15^-105C33,•193160240 E60 40^.9.04i;;:•107202^03•la.30^-25^.20A9* MO0 40^03^BO^120^120^14006444166.4..64■08.4 (I a)102 1E0-20^•113^.16 -12^-10A90,40132.1201 1102 1032 MO/ 0301 2 0702 0E02 05000140-(0-I S-202520 ,Ro(%)Dara-113 = 1.4 5 =2.0Figure 4.18: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Dara-1 well-1 4.1 6.23-2 261.41644v•Isalwrn- 1 6 .12^-10^4^-62 650^2 MO ^^2 550 ^E^2603 ^^1 2 450 ^1 2 400 ^2 350 ^2 303 ^2 250 ^-20 10000^80^ICO^(20^1401.4444*-41.,441.400,01'6)1E0 2030020 6-31)-30^-25^.20^-15^•1069.14.40)Erawan-12-113=2.1 8=2.8Figure 4 19* Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Erawan-12-1 well10800-20 ^I - 03 -4 0-so -40BO120160200240200-30^-25^-20^-15.23 (Mal70 0^BUM. SY!.,,1;0111061:0 103100 220.12^-10^-12213*02^03 05 102^2 303 ^2 200 ^^2 2 zoo ^^2 240 ^2 220 ^^1520 ^1180 ^2 1802„^1• I6-20g -22-2 4-26-2300 ,40^60^BO^1CO^120^$40Presers-632 rorproutoErawan-12-8p=2.1 s =2.1Figure 4 202 Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Erawan-12-8 well40^53^BO^700^120^140177532145/507347537•rel1E0 103 200Satun-3p = 2.6 6 = 2.8Figure 4.21: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Satun-3 well2 500002 453 ^052 403 ^-1 01350 ^ -152 MO ^-202 250 ^2200 ^2150 ^-30700-352 -20^ -72^-10^-6^9 -0010925602 5002 450E 2 4322 3502 3332 250•16 -12^.10^-1334.8•8120240^90^90^100^120^140^163^183Pres411-0991.9orattmers10 0-I 0-2 01 -10A -SO-60-70'°-40^-35 -20^-15950SW-33^-25^-20^-15^-10.39 04191Jakrawan-213 = 2.4 8 = 2.9Figure 4.22: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Jakrawan-2 well00020E 30I-40SO60204080120160200240 ,121032000-0505l- -202. -25-30-3 500-0$r -15-204 -2Tectaltellhocime^-3 5 ^^40 ^-4 $40^ -25^-20^-IS^-1019701960 ^1 450 ^1910 ^1933 ^I 1 920 ^1 910 ^900 ^1690 ^11360 ^1 670 ^-20 -IS-10^5-35^-30^-25^-20• 95154)40so160240Pres.►awenswan...1Krut-113= 1.7 8 = 2.1Figure 4.23: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Krut-1 well110-35-35^-30^-25^-20^-15^-104414 (MO-25^-20^-15A9• PAWErawan-K-1(3=2.2 8=1.5Figure 4.24: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Erawan-K-1 well0 0 00 40803 20^-10 ^^-2 0    I -30 ^ dome. -30 ^ 60yv-e0 ^ -4 0 8o919ure0 ^-50340 ^240-70         14adcknfilkoce ^ 280-B0 ^ 3200163 20010^60^BO^'CO^120^110Pronni-elay twadraumr.)30-35-305202 0152 0102 015E 2 000I 19951 NO1905-12^-10^-^.6104 1.4.)980-20^-180005-1 0-15-20g -25^2 115 ^2 110 ^2 106 ^E 2 100 ^• 025 ^I 2 COO ^2006 ^20n ^2 075 ^2 070 ^-20 -I8^-IS -12^-10^4^4/451919)00-2 0Team* sebskYnce-e0▪ 40 ^^I 40 ^-100 ^-12 0.40bed subskilme.-25^-20^ -1009•049.)Figure 4.25: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Baanpot-1 wellBaanpot-13=2.8 8=1.510^BO^BO^103^120^140Prosard-ftv ...Mae re)2031E0111404040-1B -14^-12^-10^43^.6^-4^-2409 0401E0 1BD 21:040^6D^00^100^120^1404141.4.4.5 0103002020009401 935  -051 930      .1 0925 ^ •11 920 -201 915 ^ -25910 ^ .30906         -3 51900 ^ J01 80520Baanpot-B-113 = 2.8 8 = 1.5Figure 4.26: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Baanpot-B-1 well2.16^.16^.14^.12^-10^-820•0.00Jakrawan-113 = 2.4 8 = 2.5Figure 4.27: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Jakrawan- I well2 750 002 700     -052 650 ^2 .1 0E - 15 ; 2.550 ^ g -202 500^2 450 ^2 400 ^-20-25303 52a ISO 11. 20240^CO^83^103^120^140035002 ■230.201200093160240320-30i -40I -50-60-70-06 -330 -26^-20^.15/42.049)-1000•1 0-20^...30 ••••••••••714.4,0saf^I -40 ^'.?Pf."7^3 -SD .60 . ^ -.70 - 11.•60 ^^10 -35-25^-20^-IS^-10A9•14A.). • -112Yala-213 = 1.6 6=2.2Figure 4.30: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Yala-2 well-18^-16 -10^-8^-6Funan-113 = 2.1 5= 3.0Figure 4.28: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Funan-1 well2 503 00450 ^ -052 420 ^2 330 ^ E^$2 330 ^ 0RCS2 250 52 200 ^ -30,42•1.812.150 ^2 10020183 18300•211-303-40•5080-40^35^ -25^-20^-15^-10898 (LW40^60^03^103^120^140Rosen.. 2.4:4.44884( . 0)cuni3-Isr 0)2200^2 160 ^2 103 ^2^x 2 140 ^2.120 ^2103 ^2 000 ^2 0302 ^-10^-840•0•48)1132 1402 1201COE 2043 -la^-16^-14^.12^-10^-0^-640.(648)^I 2 050 ^1 2 040 ^2 020 ^2 GOD ^3 NO ^-20 0Figure 4.30: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Kaphong-3 well160 153 253-70.40-200440698)30 -25 -75 -10 000-ID-20-393 -403-50-60g00-05-I 0-1 5-25-30-4 0520^40^60^80^104^120^140lenpwateKaphong-3(3 =2.2 5 = 2.140so120160200240 .0290.16^.14^-32^-10^-a^-6^-44)^2020 ^2 750 ^2 703 ^f 2 650 ^-1, 2 !CO ^2 550 ^I 2 503 ^2 450 ^2 400 ^2 35020^Figure 4.31: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Kaphong-1 wellId) 1E0 3:093160 94240 ars32040^03^130^104^120^1407688.505 040441•(3)Kaphong-10=2.2 8=3.000-06-30-15-20.25.3020114South Platong-113=2.1 6=33Figure 4 33 . Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at South Platong-1 well00^%^1%^120^140^160^ 2%Proserlmla/14/.44ature (c)24%2 80027%21. 2200I 2.503224%2 2002o^ 18^-16^-14^-12^-10^4^4^.4^.2-6 -22 505 3 1002^031E0 26040^60^80^110^120^140Pros...day 14romrature re)Volk.)Platong-53=1.6 8=2.1Figure 4.32: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Platong-5 well-35 -25^-20^-15^-10^-509•03*)-351 2-1 6-2 0-2 22 1202 1102%^f 22000.0 ^^2 070 1 24%^2050 ^^O 040 ^2 030 ^2^-20^18^16^14^1200 00- 1 0TNO313104ay.1 -304040120160200 5,240 Ba -40 •-5 0 • ..230•6 0_4°^ -35-60 .0^ -33^-25^-20^-15^-10V• WO-35^-30^-25^-20^-IS^-10^-5%•W)11510330^50^BO^103^120^140Preen-ay lerrostMoo C41Satun-1= 2.4 8 = 2.6Figure 4.35: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Sawn-1 well103 180 20340^60^03^103^120^140R66444-41, ienvoroute (c)12 4002 3502 3030F.. 2 2502 2036^.16^.14^-12^-10^-B^-6N. PAO^250 ^2 100 ^2 0932a^Satun-213 = 2.2 =2.8Figure 4.34: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Satun-2 well-30^-25^.20^-15^-10BP 04614080120I00200 e210 B1 30 Bori4446.-46Isolwrn :-60 ^-60 67000r-350.10040SO120L -313 ^ 160I -40 - 1i17 mi.^ 2003g -50 20;--320-35 -30 -25 .20-15 .10.9.0A0116Erawan-12-90 =2.1 6=2.1Figure 4.36: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Erawan-12-9 wellErawan-12-713=2.1 6= 1.9Figure 4.37: Basin subsidence, burial, heat flowhistory, geothermal gradients, andcalculated and measured vitrinitereflectance at Erawn-12-7 well.12^-10^-0^-6404 PO40^83^83^132^120^140^180^ 20341,1r0/02 3402 33D2 3202 3102 3202 290• 2 2602 2702 2832 2502 240-35 -25^-20^-IS86 9 (.0le0183-100 0E -20I -301 .1 0-50-60• 012 3032 260f 2 260-16^-16^-14^.12^-10^-6^-6 40^60^60^120^120^110Resent-day torrpsrature r^3 2 240 ^^2 220 ^^2 203 ^2 100 ^2 1602o^:3120160260;-..----r--30^-25^-20^-15^• 10^-0070)610)-3070-408;0840003 -4.01174.6.3 Lithospheric Stretching FactorsCrustal and subcrustal stretching factors Ws and 5, respectively) at well locations canbe determined by best-fitting the observed basement's tectonic subsidence with thetotal (initial and thermal) tectonic subsidence predicted from nonuniformlithospheric stretching model.For the purpose of computation, rifting in the Pattani Basin is assumed to havestarted approximately 40 Ma (Late Eocene) and lasted until about 20 Ma (middleEarly Miocene) and thermal subsidence took place afterward. Thus the extensionalor rifting phase lasted about 20 million years. This was probably long enough tocause some heat loss during rifting. Jarvis and McKenzie (1980), however, foundthat as long as rifting times were not more than 20 million years in duration, thelithospheric stretching model, assuming instantaneous rifting, was a reasonableapproximation. The basement underlying unit 6 comprises Paleozoic and Mesozoicmetamorphosed sedimentary rocks and Mesozoic plutonic rocks. Any compactionthat occurred in these Paleozoic and Mesozoic rocks is assumed to have terminatedprior to the Late Eocene rifting phase. The surface of these rocks is therefore takenas a reference surface for calculating the basement subsidence.The values of crustal and subcrustal stretching factors (13 and 5) and thecorresponding correlation coefficients at well locations are shown in Figure 4.8through Figure 4.37 and are summarized in Table 4.2. The lateral distributions ofcrustal and subcrustal stretching factors (0 and 5) and the total lithosphericattenuation (c) in the Pattani Basin are shown in a series of maps in Figure 4.38,Figure 4.39, and Figure 4.40, respectively.118Table 4.2: Summary of crustal and subcrustal stretching factors, geothermal gradients,organic maturation gradients, and present-day heat flow at well locations in thePattani BasinWELL 13 5EGEOTHERM.GRADIENT(°C/Ian)Ro.GRADIENT(log %Ikm)HEATFLOW(11FU)Ranong-1 1.4 1.8 1.67 36 0.23 1.93Kung-1 1.4 1.8 1.67 39 0.20 1.93Surat-1 1.5 2.1 1.89 46 0.29 2.16Platong-8 1.8 2.8 2.42 52 0.37 2.20Platong-1 1.9 2.8 2.47 46 0.28 2.00Insea-1 1.3 1.3 1.30 28 0.17 1.56Pakarang-1 1.9 2.7 2.42 52 0.28 2.19Pladang-3 2.2 2.4 2.34 51 0.26 2.13S.Platong-2 2.4 2.8 2.68 50 0.38 2.08Trat-1 2.7 3.6 3.29 58 0.37 2.32Dara-1 1.4 2.0 1.79 40 0.28 2.05E-12-1 2.1 2.8 2.56 56 0.31 2.27E-12-8 2.1 2.1 2.10 52 0.31 2.17Satun-3 2.6 2.8 2.74 51 0.27 2.10Jakrawan-2 2.4 2.9 2.74 51 0.28 2.11Krut-1 1.7 2.1 1.97 40 0.07 1.87E-K-1 2.2 1.5 1.65 44 0.33 1.98Baanpot-1 2.8 1.5 1.72 48 0.32 2.07Baanpot-B-1 2.8 1.5 1.72 42 0.37 1.90Jakrawan-1 2.4 2.5 2.47 63 0.31 2.42Funan-1 2.1 3.0 2.68 50 0.30 2.10Yala-2 1.6 2.2 1.99 49 0.24 2.07Kaphong-3 2.2 2.1 2.13 45 0.36 1.99Kaphong-1 2.2 3.0 2.72 59 0.43 2.35Platong-5 1.6 2.1 1.93 46 0.49 2.02S.Platong-1 2.1 3.5 2.95 56 0.38 2.24Satun-2 2.2 2.8 2.60 49 0.31 2.06Satun-1 2.4 2.6 2.54 48 0.29 2.01E-12-9 2.1 2.1 2.10 52 0.34 2.17E-12-7 2.1 1.9 1.95  55 0.36 2.2413 is a crustal lithospheric stretching factor5 is a subcrustal lithospheric stretching factorE is a total attenuation of lithosphere1190Satun-2 (2to^0Trat-1 (2.7)0Erawan-K- (2.2)Jakrawan-2 (2.4)0Yala-2 (1.6)0Kaphong-3 (2.2)0 Kaphong-1 (2.2)Rat ng-5 0 (1 6)0^atong-1 (1.9)Raton 8 (1.8)S at-11.5)ev^0 S. Platong-1 (2.1)0Kung-1 (1.4)Ranong-1 (1.4)0Pakarang- (1.9)0^Pladang-3 (2.2)0^ 0Insea-1 (1.3)^ o S. Platong-2 (2.4)0^5^10km0Satun- (2.4)1)0 Satun-3 (2.8)-12-1(2.1)an-12-8 (2.1)Erawan-12- (2.1)0Dara-00Krut-1(1.7)Era(1.4)an-12-90 Eraw0 Er0Jakrawan-i (2.4)0^Baanp•-1 0 (2.8)^Funan-10 (2.1)npot-^(2.8)Figure 4.38: Lateral variation of crustal lithospheric stretching (beta)120Yala-2 (2.2)00^5^10kmarang-1 (2.0 PIadang-0(2.42-9 (2.1)0 Satun-3 (2.8)12-1(2.8)-8 (2.1)-7(1.9) .°O E rawErawan-12akra000Erawan-K-1 (1.5)-2 (2.9)0 Kaphong-3 (2.1)Kaphong-1 (3.0)-1 (3.5)0Insea- (1.3) o S. laton -2 (2.8)00^Trat-1 (3.6)Satin- (2.8)0Satun-1 (2.8)00Jakr an-1 .5)Baanpot-1 0 (1.5)^Fun- -10 (3.0)Baanpot-B-1 (1.5)0ut-1Erawan-(2.0) 0P 1)atong-1 (2.8)P tong-8 (2.8).8)0Kung-1 (tong-5 0 (000Surat 1(2.Ranong-1 (1.8)0•0Figure 4.39: Lateral variation of subcrustal lithospheric stretching (delta)121Ranong-1 (1.7)0Yala-2 (2.0)00 1<aphong-3 (2.1)Kaphong-1 (2.7)Platong-5 •^.9)Platong-1 (2.5)latong-8 (2.4)CoSng-1 (3.0)Pakarang-1 (2.4)Pladang- (2.3)atong-2 (2.7)0Trat-1 (3.3)n-2 (2.8)-1 (2.5).1)0 Satun-3 (2.7)0 Erawan-12-1(2.8)0 Era -4-12-8 (2.1)an-12-90Erawan-12-7 (2.0)^20Erawan-K-1 (1.7)akrawan-2 (2.7)0Jakra^-1(2.5)0Baanpot-1 0 (1.7)^unan-10 .7)Baanpot-B-1 (1.7)'2..Kung-1 (351)Krut-1(2.0)0^5^10km0Insea-1Figure 4.40: Lateral variation of total lithospheric stretching factor (epsilon)122The distribution of total lithospheric stretching, 6, (Figure 4.40) indicates thatlithospheric stretching generally increases from the basin margin (e.g. Ranong-1,Kung-1, and Insea-1 wells) toward the basin center (e.g. South Platong-1, Trat-1,Satun-3, and Jakrawan-2 wells). In general, subcrustal lithospheric stretching isgreater than crustal lithospheric stretching. In some locations in the basin center,however, crustal lithospheric stretching is greater than subcrustal stretching. Thesewells include Erawan-K-1, Baanpot-1, Baanpot-B-1, Kaphong-3, and Erawan-12-7.This can be rationalized because these wells contain very thick synrift sedimentcolumns. Thick synrift sediments indicate that synrift subsidence is large becausecrustal thinning or stretching has a much greater effect on initial subsidence thansubcrustal stretching. A greater amount of crustal thinning is, therefore, requiredto accommodate such thick synrift sediments.4.7 THERMAL HISTORY4.7.1 Heat flow HistoryUtilizing the lithospheric stretching factors summarized in section 4.6.3, it ispossible to predict heat flow history of the Pattani Basin. Before making anyprediction of the heat flow history, however, some assumptions must be made inregard to the background heat flux prior to extension and the heat generated byradioactive decay within the earth's crust. Following McKenzie (1978) andHellinger and Sclater (1983), an original background heat flux of 0.8 HFU(pcal/cm2 sec) is assumed for the Pattani Basin. It is further assumed thatradioactivity in the study area contributed about 0.2-0.4 HFU (p.cal/cm 2 sec) to thesurface heat flow and that this value should be divided by the factor to give the123post-extensional contribution. Thermo-physical properties of sediments and thoseof lithosphere and mantle are listed in Table 4.1.Figure 4.8 through 4.37 show that surface heat flow histories at each well locationgenerally decreased with time since the end of rifting. The present-day surface heatflows calculated from the model described in section 4.6.3 at different welllocations are shown in Figure 4.41. The predicted present-day surface heat flowvaries approximately from 1.6 to 2.4 HFU. These values generally agree with themeasured present-day values reported by Matsubayashi and Uyeda (1979) andRutherford and Qureshi (1980) which range approximately from 1.9 to 2.5 HFU.The surface heat flow in the study area is high compared to the earth's average heatflow of 1.4 to 1.6 HFU because the Pattani Basin is a rifted intracratonic basin, lessthan 25 Ma old. Rifting and consequent upwelling of hot aesthenosphere materialelevated the heat flow, which subsequently decreased exponentially with time(McKenzie, 1978). In a "standard" lithosphere, the heat flow reachesapproximately 1/e of its originally elevated value after 62.8 million years (thethermal-time constant of the lithosphere, t; McKenzie, 1978; Hellinger and Sclater,1983; Allen and Allen, 1990). At this time (62.8 million years after the cessationof rifting), the dependency of heat flow on the stretching factors is insignificant,and surface heat flow of the area returns to a normal value which is about 1.4 to1.6 HFU.4.7.2 Temperature History and Present-dayGeothermal GradientsIf the thermal conductivity of the sediments is known as a function of time,124Ranong-1 (1.9)0^ Plaat-1tong-1 (2.0)g-8 (2.2)0 0Su0Insea-1 (1.8)Pakar g-1 (2.2)PISSg-3 (2.10o S. P0tun-2 (20n-i (21)0)ong-2 (2.1)0Trat-1 (2.3)0 Erawan-12-1(2.3)0 Erawan-12-8 (2.2)12-7(2.2)Jakrawan-2 (2.1)0-K- (2.0)0Jakraw -1(2.4)2.20Baanpot- 0 (2.1) zo^Funan-1(2.1)Baanpot-B-1 1.9)0Krut-1(1.9) EraErawP -5 o (• •Yala-2 (2.1)00^5^10km2.0 0 Kaphong-3 (2.0)2.22k4aphong-1 (2,4)0Kung-1 (1..2)O S. Platong-1 (2.2)awan-12-9 (2.2)Dar0-1 (2.1) OSatun-3 ( .1 )Figure 4.41: Present-day surface heat flow (contour interval = 0.2 HFU)125temperatures at any given depth and time since deposition can be calculated fromthe heat flow history. Relevant thermo-physical properties of sediments such asthermal conductivity of grains and porosity are listed in Table 4.1. The thermalconductivity of pore water is assumed to be 1.43 mcal/cm sec °C (Friedinger,1988). For the purpose of computation and lack of reliable measurement, surfacetemperature during deposition of all stratigraphic layers is assumed to be 10 °C.Temperature histories at well locations displayed as isotemperature lines andpresent-day geothermal gradients, based on the above consideration, are shown inFigure 4.8 through Figure 4.37. The lateral distribution of the calculated present-day geothermal gradients is shown in a map in Figure 4.42. In general, thegeothermal gradients increase from 36 to 40 °C/km in the basin margin to 58 to 60°C/km at the basin center. The lowest calculated geothermal gradient is in Insea-1well location which has the lowest lithospheric stretching factors ((3 = 5 = 1.3).The calculated geothermal gradients agree well with the measured present-daygeothermal gradients in this area which range from 45 to 60 °C/km (Rutherford andQureshi, 1981).4.7.3 Vitrinite ReflectanceGiven burial history and temperature history, the degree of thermal maturation ofany individual stratigraphic layer can be predicted. Because it is an indicator oforganic thermal maturity, vitrinite reflectance is widely used in an integrated basinanalysis and the exploration for oil and gas (Hunt, 1979; Tissot and Welte, 1984;Waples, 1985; and many others).126Yaia-2 (49)00^5^10kmPI ong-5 0O 00urat-(40)PI0Kung-1 (39)atong-i (46)g-8 (52)Ranong-1 (36)0an• 1 (52)S0S n-2 (49)0tun-1 49)0 rawan-12-8 (52)• 45Baanpot-B-1 (42)Kaphong-3 (45)Kaphong-1 (59)0 S. Platong-1 (56)0I nsea-1 (28)Pladang-3 (51)0S. P ng-2 (50)0Trat-1 (58)ra^.9 (521 40) Satun-3rawan-12-1(58)12-7 (55)•Erawan-Baanpot-1 unan-1(50)Dar00Krut-1(40) Jakrawan-2 (51)00Jakraw 1(63)55Figure 4.42: Calculated present-day geothermal gradients (contour interval = 5°C/km)127Various models that simulate vitrinite maturation fall into four categories (Sweeneyand Burnham, 1990): (1) models that describe vitrinite maturation solely as afunction of temperature (Price, 1983; Barker and Pawlewicz, 1986); (2) models thatincorporate time as a rule of thumb (Hood et al., 1975; Bostick et al., 1978); (3)models that describe vitrinite reflectance as an Arrhenius first-order chemicalreaction with a single activation energy (Middleton, 1982; Antia, 1986; Wood,1988); and (4) models that describe vitrinite reflectance as an Arrhenius first-orderchemical reaction with a single activation energy, but with the activation energyitself as a function of temperature (Lerche et al., 1984; Armagnac et al., 1989).The limitation of these models, as pointed out by Sweeney and Burnham (1990), isthat they are all empirical.Larter (1988) described vitrinite maturation with parallel Arrhenius first-orderreactions with a Gaussian distribution of activation energies. Larter's model uses aGaussian distribution of activation energies, with a mean value of 44.5 kcal/moleand a standard deviation of 7 per cent to calculate the decrease of phenol yield withmaturity during pyrolysis. Phenol yield, in turn, correlates linearly with vitrinitereflectance. The limitation of Larter's model is that correlation can be made onlyover the range of phenol reaction which is equivalent to the vitrinite reflectance of0.45 to 1.6 %Ro.Burnham and Sweeney (1989), and later Sweeney and Burnham (1990), proposed avitrinite maturation model that integrates chemical kinetic equations over time andtemperature to account for the elimination of water, carbon dioxide, methane, andhigher hydrocarbons from vitrinite. The resulting composition of vitrinite is, then,used to calculate vitrinite reflectance via correlation between elemental composition128and reflectance. The model uses a single pre-exponential factor with the activationenergy distribution. Table 4.3 lists the activation energies, stoichiometric factors,and a pre-exponential factor used to model vitrinite maturation. The model can beused to calculate vitrinite reflectance ranging from 0.3 to 4.7 %Ro.The vitrinite maturation model proposed by Burnham and Sweeney (1989) was usedin this study to calculate vitrinite reflectance at the boundaries of all stratigraphicunits. The modeled vitrinite reflectances were then compared with the measuredvalues obtained from well cutting samples to verify the validity of the lithosphericstretching model used to predict heat flow history of the basin. The plots ofcalculated and measured vitrinite reflectances at well locations are shown in Figure4.8 through Figure 4.37. The lateral distribution of the Ro-gradients (%Ro/km) isplotted in the map shown in Figure 4.43.In general, the measured and modeled vitrinite reflectance values agree reasonablywell, considering the uncertainties involved in both modelling and measuring thevitrinite reflectance, as well as uncertainties in geological parameters. The poorestagreement between modeled and measured vitrinite reflectance occurs in Krut-1well (Figure 4.23) where the measured vitrinite reflectances are more or lessconstant (about 0.6 %Ro) with depth. This might be due to variation in organicfacies rather than abnormal thermal history. Jones (1987) showed that a constantlylow vitrinite reflectance profile (about 0.6 %Ro) to the depth of nearly 2500 m wasdue to the dominance of fine-grained, oxidized detrital vitrinite that had areflectance of 0.6 %Ro when deposited and matured very slowly. Such a situationmight also be the case for the erratic vitrinite profile encountered in Krut-1 wellwhere most of the sediments are substantially oxidized. The computed vitrinitereflectances seem to be too low in Insea-1 well (Figure 4.13) and slightly too high129Table 4.3: A list of pre-exponential factor, activation energies, and stoichiometric(influential) factors used to model vitrinite maturation (After Sweeney andBurnham, 1990)Pre-exponential factor (A) = 1.00E+13 /secStoichiometricFactorActivation Energy(kcal/mol)00.0300 34.0000.0300 36.0000.0400 38.0000.0400 40.0000.0500 42.0000.0500 44.0000.0600 46.0000.0400 48.0000.0400 50.0000.0700 52.0000.0600 54.0000.0600 56.0000.0600 58.0000.0500 60.0000.0500 62.0000.0400 64.0000.0300 66.0000.0200 68.0000.0200 70.0000.0100 72.00130Yala-2 (0.24)0o Kaphong-1 (0.43)(0.49)Platong-1 (0.28)Platong-8 (0.37)Ranong-1 (0.23)00Trat-1 (0.37)0(0.28) 0 un-3 (0.27)0 Kaphong-3 (0.38)0Kung-1 (0o S. Platong-1 (0.38)0Insea-1 (0.17)arang-1 (0.28)°^Pladang-o.28)o S. Platong-2 (0.38)-2 (0.31)1 (0.29)12-9 (0.34)o Erawan-12-1(0.31)0 Erawan-12-8 (0.31)w -12-7 (0.38)Jakrawan-2 (0.28)0Krut-1(0.07)1 (0.33)(41%Baanpot-1^0.32)pot-B-1 (0.37)0^5^10km0Figure 4.43: Observed present-day organic maturity gradients (contourinterval= 0.05 %Ro/km)131in Trat-1 well (Figure 4.17). These variations may be caused by the differencebetween assumed and true heat flows within the earth's crust. The thermal historyof the basin is controlled by radiogenic heat generation as well as by the upwellingof the hot aesthenosphere. Heat generated by the upwelling of the aesthenospherecan be modeled as described earlier, whereas heat from radioactive decay wasassumed. Errors in the assumed values could lead to the discrepancies betweenpredicted and measured heat flow histories and the local erratic vitrinite reflectanceprofiles.4.8 DISCUSSIONThe tectonic regime responsible for the origin of the Tertiary basins in Thailand hasbeen a subject of discussion. Bunopas and Vella (1983) related extension andrifting in the Gulf of Thailand and onshore Thailand to back-arc spreading behindthe subduction of the Indian plate beneath Southeast Asia along the Java Trench andAndaman-Nicobar Island chain. However, most back-arc basins develop a fewhundred kilometres behind the subduction zone (Karig, 1971; Taylor and Karner,1983) whereas Tertiary basins in Thailand are located approximately 1000 to 1500km behind the subduction zone mentioned above. It is also unclear whethersubduction even occurs along the Andaman-Nicobar Island chain. Subduction alongthe Java Trench may become strike-slip motion along the Andaman-Nicobar Islandchain (Ohnstad, 1989; Polachan and Sattayarak, 1989). These arguments make theback-arc tectonic regime less likely to be the responsible mechanism for theformation of Tertiary basins in Thailand.Molnar and Tapponnier (1975), Tapponnier et al. (1982), and Ohnstad (1989)suggested that development of Tertiary basins in Thailand is related to the132northward progressive collision of India with Eurasia since 40-50 Ma. Thisresulted in the eastward and southward extrusion of Indochina and portions ofeastern China along left-lateral, strike-slip faults such as the Red-River and Altyn-Tagh faults (Figure 4.44). The left-lateral motion of the fault systems in SoutheastAsia interpreted from this model do not correspond with the present-day right-lateral motions (Allen et al., 1984; Le Damn et al., 1984; Tapponnier et al., 1986),although the India-Eurasia collision zone continues. The contrasting evidencesuggests that this geologic model may not be valid for the development of theTertiary basins in Thailand.Polachan and Sattayarak (1989) related the development of Tertiary basins inThailand to the progressive northward collision of India with Eurasia since theEocene. Penetration of India into Eurasia caused clockwise rotation of SoutheastAsia, resulting in increasingly oblique subduction of the Indian Ocean plate beneaththe western edge of Southeast Asia. This led to the right-lateral movement on majorNW-SE faults such as Red River, Mae Ping, Three Pagodas and Sumatra faults(Figure 4.44). Polachan (1988) and Polachan and Sattayarak (1989) related thefault distribution to the strain ellipsoid during right-lateral motion in the Gulf ofThailand (Figure 4.45), and suggested that E-W extension could develop duringright-lateral movement on the NW-SE Three Pagodas faults, and left-lateralmovement on the conjugate NE-SW Ranong and Klong Marui faults. This model issupported by paleomagnetic analyses of Cenozoic rocks in Thailand, indicating anearly 25° clockwise rotation of Western Thailand from Indochina (McCabe et al.,1988); the right-lateral movement of major fault systems in Southeast Asia; and theN-S trending extensional basins in Thailand. The origin and tectonic setting of thePattani Basin and other Tertiary basins in Thailand are, in general, comparable tothat of Late Tertiary basins along the western margin of the Basin and Range13380° 120°South ChinaSea40°Figure 4.44 Tectonic map of S.E. Asia and South China Sea showing the main fualt patterns andthe relative movement of crustal blocks in response to the collision of India with Eurasia134GULF OF THAILANDTranstenelonal Dextral Shear99°^ 103°Figure 4.45: Structural map of the Gulf of Thailand. Showing relationship between strike-slip faults and the development of N-S trending (After Polachan & Sattayarak, 1989).9°8°10°135Province in western Nevada. The N-S trending extensional basins in westernNevada are characterized by a series of N-S trending normal faults associated with aNW-SE strike-slip fault system (Link et al., 1985). High heat flow in Tertiarybasins in Thailand and volcanism in the western margin of the Basin and RangeProvince are closely related to mechanical thinning of the lithosphere andconsequent upwelling of the hot aesthenosphere.The E-W extension, which was the result of the oblique subduction of the IndianOcean plate beneath the western edge of Southeast Asia, caused the lithosphericstretching and crustal thinning, which led to the passive upwelling of the hotaesthenosphere in Central Thailand and the Gulf of Thailand. Ohnstad (1989)modeled the Bouguer gravity anomaly and suggested an elevated lithosphere-aesthenosphere boundary in the Tertiary basins in the Gulf of Thailand. High heatflow in the Tertiary basins in Thailand also supports the crustal thinning model.Geohistory analysis of well data from the Pattani Basin has shown that the observedsynrift and post-rift subsidences can generally be accounted for by simple E-Wextension causing crustal and subcrustal lithospheric thinning. The present studyalso verifies the validity of nonuniform stretching model as a mechanism formodelling the formation of the Pattani Basin. Values predicted by the model forthe maturity index, vitrinite reflectance, compared well with the observed values.From these observations and from the stratigraphic analysis carried out in chapter 3,the Tertiary tectonic and stratigraphic evolution of the Pattani Basin is interpretedbelow.At the beginning of the Tertiary, most of the Gulf of Thailand probably waselevated above sea-level (Achalabhuti and Oudom-Ugsorn, 1978). Extension in136Continental Southeast Asia was initiated during Late Eocene both along an oldTriassic-Jurassic suture zone between the Indochina plate in the east and theBurmese-Thai plate in the west, and along other similar N-S and NW-SE trendingweak zones (Burri, 1989; Chinbunchorn et al., 1989). During this primary periodof extension, which lasted about 20 m.y., faulting and graben formation werecommon and probably episodic. A series of N-S and NW-SE trending, fault-controlled, half grabens and grabens developed in the proto-Gulf of Thailand.These faults may have extended the underlying basement by as much as 90 km.The crust underwent brittle failure, producing isostatic fault-controlled subsidencewithin the graben area. The main extensional area might have been in the south-central part of the study area where the Late Eocene and Early Oligocenedepocenters are located (Figure 3.11 and Figure 3.12). Following the riftingphase, the post-rift thermal subsidence was characterized by a slower rate ofsubsidence and the absence of major fault movement.The result of the stratigraphic analysis described in detail in chapter 3 suggests thatthe Tertiary sedimentary succession in the Pattani Basin is generally consistent withthe tectonic evolution predicted by the lithospheric stretching model. The synriftbasins were dominated by coarse-grained alluvial fan and braided stream depositsalong syndepositional faults at the basin margins and by fine-grained lacustrinedeposits further from the faults in the basin center (stratigraphic unit 6). Thesesediments unconformably overlie the Paleozoic and Mesozoic basement. As theextension abated, the area subsided more slowly, and sediments gradually changedupward into nonmarine floodplain and channel deposits (stratigraphic unit 5). Abrief and rapid transgression during the Early Miocene (at the base of stratigraphicunit 4) might have been the result of an episode of normal faulting and grabenformation leading to rapid subsidence of the basin. After faulting, the rate of137subsidence declined, leading to a decrease in the rate of relative sea-level rise and,as a consequence, the occurrence of a regressive sedimentary succession of thestratigraphic unit 4.Fault movement decreased toward the end of the rifting phase in Early Miocene(about 20 Ma), after which a post-rift thermal subsidence took place more slowlyuntil the present-day.The post-rift sediments comprise a regressive sequence in the lower part of thesuccession (stratigraphic unit 3) and two transgressive cycles in the upper part(stratigraphic units 2 and 1). Because of the relatively slow post-rift subsidence,the regressive and transgressive cycles in the post-rift sedimentary succession areattributed to variations in sediment supply and eustatic sea-level change during thistime interval.In general, the amount of total lithospheric stretching increases from the basinmargin to the basin center (Figure 4.40). The crustal lithospheric stretching factors((3) range from 1.3-1.4 at the basin margin to 2.6-2.8 in the basin center (Figure4.38). These values are, however, affected by basement topography and probablyreflect local changes in crustal thickness which are difficult to constrain duringmodelling. The crustal stretching factors ((3) obtained from the model should,therefore, be considered as approximations. The subcrustal lithospheric stretchingfactors (8) range from 1.3 at the basin margin to more than 3.0 in the basin center(Figure 4.32). The total (crustal and subcrustal) lithospheric stretching factors (c)range from 1.3-1.6 at the basin margin to more than 2.5 in the basin center (Figure4.33). Generally, the subcrustal lithospheric stretching factors are greater than thecrustal lithospheric stretching factors. In areas with great thickness of synrift138sediments such as those containing the Erawan-K-1, Baanpot-1, and Baanpot-B-1wells, however, crustal stretching is greater than subcrustal stretching. These areasmight have been affected by basement topography prior to rifting.The amount of lithospheric stretching may have extended the underlying basementas much as 90 km. This amount of extension agrees reasonably well with the 85km basement extension in the Gulf of Thailand calculated from the modelling of theBouguer gravity anomalies by Ohnstad (1989).High geothermal gradients (45-60°C/km) and high surface heat flow (1.9-2.5 HFU)observed in the study area and in other Tertiary basins in Thailand can generally beaccounted for by the lithospheric stretching model. The geothermal gradients andpresent-day surface heat flow predicted from a non-uniform lithospheric stretchingmodel range from 36°C/km to 63°C/km and from 1.6 HFU to 2.5 HFU,respectively. High geothermal gradients and high heat flow can be attributed to theupwelling of hot aesthenosphere. This is evident from the modelling of Bouguergravity anomalies by Ohnstad (1989) which suggested that the lithosphere-aesthenosphere boundary in the Gulf of Thailand is shallow. High geothermalgradients still exist in the Gulf of Thailand probably because the area is relativelyyoung and still in thermal disequilibrium, in which thermal decay due to theelevated aesthenosphere has not been complete.4.9 SUMMARY AND CONCLUSIONSThe collision of India with Eurasia which has been continuing since Eocene timehas caused clockwise rotation of Southeast Asia, resulting in increasingly obliquesubduction of the Indian Ocean plate beneath the western edge of the Continental139Southeast Asia. This led to the right-lateral movement on the major NW-SE faultsystem and left-lateral movement on the conjugate NE-SW faults in Thailand,which together induced the E-W extensional tectonic regime in the Gulf of Thailandand adjacent areas. Such a tectonic regime is comparable to that of Late Tertiary,NW-SE strike-slip related basins in the western margin of the Basin and RangeProvince in western Nevada.The resulting E-W extension caused continental rifting and crustal thinning resultingin the development of a series of N-S trending Tertiary basins in the Gulf ofThailand and onshore Thailand.Due to the large amount of subsidence during the rifting phase, the sedimentarysignature of the synrift deposits in the Pattani Basin was controlled mainly by itstectonic subsidence. Because of the relatively slow and small amount of subsidenceduring the post-rift phase, the transgressive and regressive cycles in the post-rift,sedimentary succession in the study area might have been the result of variations insedimentary supply and eustatic sea-level fluctuation.The amount of lithospheric stretching as well as the surface heat flow in the PattaniBasin generally increased from the basin margin to the basin center.Subcrustal stretching was generally greater than crustal stretching, except in theareas with a great thickness of synrift sediments where crustal stretching is greaterthan subcrustal stretching.140The lithospheric stretching in the Pattani Basin may have extended the basementrocks by as much as 45 to 90 km, and may have promoted the upwelling of hotaesthenosphere resulting in high surface heat flow.The high present-day surface heat flow and geothermal gradients suggest that thePattani Basin and other Tertiary basins in the Gulf of Thailand are still in theelevated and disequilibrium thermal condition. Apparently, thermal decay from theupwelling of the aesthenosphere has not yet been completed.1415. ORGANIC CHARACTERISTICS AND PETROLEUMSOURCE ROCK POTENTIAL OF TERTIARY STRATAIN THE PATTANI BASIN, THE GULF OF THAILAND5.1 ABSTRACTRock-Eval pyrolysis and organic petrography have been used to evaluate theorganic characteristics and petroleum source rock potential of Tertiary strata in thePattani Basin. Average total organic carbon (TOC) contents are generally low tomoderate (0.2 to 1.4%). Dispersed organic matter in the Pattani Basin consistsmainly of Type III and Type IV kerogen with minor amount of Type II kerogen. Itis composed chiefly of the macerals vitrinite, with minor inertinite and liptinite.Geochemical and petrological studies indicate a predominantly terrestrial anddetrital source of organic matter throughout the Tertiary strata.The variation in abundance and character of organic matter occurs both within andacross the stratigraphic units. Within each stratigraphic unit, the lowest TOC andHI (hydrogen index) occur in high energy deposits such as alluvial fan and braidedstream deposits; higher TOC and HI generally occur in low energy deposits.Across the stratigraphic units, TOC and HI generally increase in progressivelyyounger strata. The abundance of organic matter within sediments is the combinedresult of organic input into sediments and degree of organic preservation. LowTOC and HI values in high energy nonmarine deposits reflect both low amount oforganic input, and of a low state of preservation. Higher TOC and HI in lowenergy floodplain and interdistributary bay deposits, on the other hand, may reflectboth proximity to marsh complexes, which could be sources of organic matter, andalso a high degree of organic preservation which is common in fine-grained142sediments. The variation in abundance and character of organic matter in sedimentsboth within and across the stratigraphic units is, therefore, controlled mainly by thedepositional environments within which organic matter was deposited. The effectof sedimentation rate on the abundance of organic matter in the study area isapparent only in the relatively high TOC units (0.6-2.2%, unit 1). In units withlow TOC (less than 0.5%), indigenous variation of TOC within the sediments hasgreater effect than sedimentation rate. A strong negative correlation between TOCand sedimentation rate in organic-rich unit 1 indicates the effect of elastic dilutionon organic input with increased rate of sedimentation. A weak correlation betweenTOC and degree of organic maturation may also reflect the original variation ofTOC from place to place within the stratigraphic unit and across the units ratherthan a true relationship between TOC and degree of organic maturation.Source rocks of Tertiary strata in the Pattani Basin have very low hydrocarbonpotential as defined by pyrolysis. The presence of a number of commercial gasfields suggests that either the source rocks here, despite very low genetic potential,are very effective in producing, migrating, and accumulating hydrocarbons, or thepresence of higher quality source rocks within the basin which have not beenreached by drilling, or a combination of both factors.5.2 INTRODUCTIONRecent studies of modern and ancient sediments have revealed that allochthonousorganic matter derived from terrestrial sources also comprises a major source of oiland gas, especially in nonmarine and deltaic settings (Compaz and de Matharel,1978; Snowdon, 1980; Thomas, 1982; Bustin, 1988). The origin, distribution, andcharacter of allochthonous organic matter have an important influence on the143volume and character of hydrocarbon generated. In the Pattani Basin (Figure 5.1),natural gas and condensate are produced from nonmarine and marginal marineTertiary strata. Subsurface exploration and development provide geochemical andgeological data to evaluate the factors controlling the distribution and deposition ofsource rocks in nonmarine and deltaic settings.In this chapter, abundance and types of organic matter in Tertiary strata in thePattani Basin are described, the factors controlling such abundance andcharacteristics are interpreted, possible petroleum source rocks are identified, andtheir regional extents are outlined. In particular, this chapter documents thevariation in the abundance of organic matter with depositional environments, ages,sedimentation rates, and degree of organic maturation.5.3 METHODS OF STUDYThe petroleum source rock characteristics of more than four thousand well cuttingsamples were determined by Rock-Eval pyrolysis (Espitalie et al., 1975). Cuttingsamples were sieved and the <2 mm (-10 mesh) portion was washed to removewater-soluble drilling mud contaminants. Shale fragments in the samples werehand-picked by the help of binocular microscope and were crushed and pulverizedwith a centrifugal grinding mill to approximately 170 (80 mesh) particles.Sample sizes used for Rock-Eval pyrolyses were 100 mg for samples containing lessthan 3% total organic carbon (TOC), and 5 to 50 mg for samples containing morethan about 3% TOC. Organic-rich shale or coal fragments in cutting samples werealso hand-picked for vitrinite reflectance measurements and organic petrography.144Interpretation of Rock-Eval pyrolysis data in this study is based on parameters andtheir experimental limits documented by Espitalie et al. (1985) and Peters (1986).Table 5.1 summarizes the measured and calculated parameters derived from Rock-Eval/TOC analysis. The measured S 1 value represents the amount of hydrocarbonspre-existing in the rock since deposition plus those already generated in thesubsurface. The S2 value represents the amount of hydrocarbons being generatedduring pyrolytic degradation of the kerogen. The S3 value represents the amount ofcarbon dioxide being generated during pyrolysis. It is a measure of the oxygencontent in the kerogen. The TOC value is used to indicate organic richness of thesediments being analyzed. The S i +S2 value indicates the hydrocarbon (HC)potential (Genetic Potential; Tissot and Welte, 1984). The (S i +S2)/TOC ratioexpresses the relative quality of organic matter (QOM). The 5 2/S3 ratio is used toindicate the types of product (oil or gas) that will be generated from source rocks atthe oil window (a degree of organic maturation (DOM) equivalent to 0.6 %Ro,Peters, 1986). The QOM is a measure of the type of OM and thermal maturity;high ratios indicate immature to mature hydrogen-rich strata. A significant spreadin the QOM, which cannot be related to variations in the DOM or type of organicmatter (OM), is considered to reflect the effects of migration of hydrocarbons intoor out of the strata (Espitalie et al., 1985). Depletion of S 1 and S2 values iscommon in oxidized OM (Peters, 1986). Thus, the QOM of some samples doesnot closely reflect the regional variation in petroleum potential of a particularhorizon.The hydrogen index (peak S2 normalized for TOC content, HI) and oxygen index(peak S3 normalized for TOC content, 0I), when interpreted in concert withmaturation data can be used to define the type of organic matters (Espitalie et al.,1985). Type I OM refers to kerogen with an HI value > 600 mg HC/g TOC,145Table 5.1: Measured and calculated parameters derived from Rock-Eval/TOC analysis1. Measured parameters:Si Hydrocarbons generated at less than 300°CS2 Hydrocarbons generated during Rock-Eval pyrolysis, from 300-600°CS3 Organic CO9 generated during Rock-Eval pyrolysisTmax Temperature of maximum rate of hydrocarbon evolution duringpyrolysisTOC Total Organic Carbon = (S 1 +S2) plus organic CO2 generatedfrom combustion of OM at 600°C after pyrolysis2. Calculated parameters:S 1 +S9 Hydrocarbon potential or Genetic potentialS1/(S1 +S9) Production Index (PI) or Transformation ratio; maturity indexS2/S' Organic typing parameter; high value means hydrogen-rich OMHI Hydrogen Index = (S7*100)/TOC; organic typing parameterOI Oxygen Index = (S3*100)/TOC; organic typing parameterQOM Quality of Organic matter = (Si+S2)/TOC; organic typing andmaturity indicator, subject to migration146whereas Type II kerogen is defined by HI values ranging from 300 to 600 mg HC/gTOC, assuming a DOM equivalent to 0.6 %Ro (Espitalie et al., 1985). Relativelylow HI values (<300 mg HC/g TOC) define Type III kerogen. (Espitalie et al.,1985). Type I and Type II OM comprise oil and gas prone kerogen, whereas TypeIII kerogen is mostly gas prone (Tissot and Welte, 1984). Some recent studiessuggest that Type III OM can contain 10 to 20% liptinite or resinite in a vitrinitematrix and thus may act as effective oil prone source rocks (Snowdon, 1980;Powell and Snowdon, 1983; Snowdon, 1987). Other studies (Lewan and Williams,1987; Link, 1988) argue that resinite or liptinite in a vitrinite matrix contribute onlyminor components to conventionally sourced crude oil and are not likely sources ofcommercial oil deposits.The DOM can be approximated from the production index, defined as S I/(S I +S2)ratio, (PI or Transformation Ratio, Tissot and Welte, 1984) and the temperature ofmaximum HC evolution during pyrolysis (Tmax). In general, PI and Tmax valuesof <0.1 and 435°C, respectively, indicate immature OM (Peters, 1986). The oilzone starts at 435°C for both Type II and Type III OM, whereas the wet gas zonestarts at about 450°C for the type II OM but not until 465°C for Type III OM(Espitalie et al., 1985). Overmature OM is defined by Tmax values of >465°Cfor Type III OM, and >450° to 455°C for Type II OM. Tmax of Type I OM is,for the most part, independent of the DOM, and generally ranges from 460° to470°C (Link, 1988).For all types of OM, PI values between approximately 0.1 and 0.4 define the oilzone and the PI value increases to 1.0 when the HC generation capacity of thekerogen is exhausted (Peters, 1986). The PI value best illustrates the DOM byplotting PI versus depth (Espitalie et al., 1977; 1985). Anomalously high PI values147may indicate HC accumulation whereas anomalously low values may indicatedepletion (Espitalie et al., 1985). In general, Tmax values cannot be determined asaccurately if S2 yields are less than 0.2 mg HC/g rock (Espitalie et al., 1985).In order to assess the potential of petroleum source rocks, the regional distributionof organic richness, type, facies and maturity have to be examined. Organicrichness is best determined as the average TOC content across the thickness of apotential source horizon rather than considering organic richness as a measure ofOM concentrated in a discrete sample. Tertiary stratigraphic succession in thePattani Basin is subdivided into units and subunits based on the lithologicalassociation and palynological assemblages. Average TOC content, HC potential(S 1 +S2) and QOM [(S 1 +S2)/TOC] have been calculated across the thickness ofeach unit and subunit at different well locations. Variations within the units andsubunits, where detectable, are also described. In this way, regional evaluation ofeach unit and subunit can be discussed by considering how parameters differ andtheir combined effects on potential hydrocarbon source rocks.Also described in this chapter is the relationship between the characteristics ofdispersed organic matter and depositional environment, stratigraphic age, anddegree of organic maturation. The organic characteristics of sediments aredescribed in terms of kerogen type (Espitalie et al., 1985) and organic faciesproposed by Jones and Demaison (1982) and Jones (1987) which defined an organicfacies as "a mappable subdivision of a designated stratigraphic unit, distinguishedfrom the adjacent subdivisions on the basis of the character of its organicconstituents, without regard to the inorganic aspects of the sediments". Jones(1987) stressed that the definition of the term "facies", in organic facies, describeda specific body of rock with lateral and vertical extent and not the organic148constituents present in the rock itself. The distribution of organic facies isdetermined by the origin of organic remains, the time spent in an oxidizingenvironment prior to deposition, and the redox potential prevailing near thesediment surface in early diagenetic environments (Jones, 1987).Jones (1987) classified sedimentary organic facies into seven facies namely, A, AB,B, BC, C, CD, and D. The primary basis of the classification is the generatingcapacity for petroleum per unit of TOC at a vitrinite reflectance of about 0.5 %Ro.Therefore, the H/C ratio as well as HI and OI ratio of the kerogen are the primarydiscriminants between different facies (Durand, 1980; Hutton et al., 1980; Jones,1987). Although based on certain combinations of factors that often occur together,the boundaries between different facies are arbitrary. Table 5.2 illustrates somegeneralized geochemical and microscopic characteristics of the seven organic faciesrecognized by Jones (1987).5.4 SUMMARY OF TERTIARY STRATIGRAPHYIN THE PATTANI BASINTertiary strata in the Pattani Basin are subdivided into 6 stratigraphic units (Figure5.2 through Figure 5.7), based on lithological association and palynomorphassemblages. The stratigraphy and sedimentology of the strata, which have beendescribed in detail in chapter 3, are summarized in this section (Table 5.3).The stratigraphic and structural evolution of the Pattani Basin reflects the rifting ofContinental Southeast Asia during the Tertiary. The geodynamic model for theformation of the Pattani Basin involves stretching of the continental lithosphere andcrustal thinning, with an initial phase of rapid, fault-controlled subsidence, followed149Table 5.2: Generalized characteristics of organic facies A-D (After Jones,1987)OrganicfaciesH/C atRo=0.5%HydrogenIndexOxygenIndexDominant organic matterA > 1.45 >850 10-30 Algal; amorphousAB 1.35-1.45 650-850 20-50 Amorphous; minor terrestrialB 1.15-1.35 400-650 30-80 Amorphous; commonterrestrialBC 0.95-1.15 250-400 40-80 Mixed; some oxidationC 0.75-0.95 125-250 50-150 Terrestrial; some oxidationCD 0.60-0.75 50-125 > 150 Oxidized; reworkedD <0.60 <50 >200 Highly oxidized; reworked150Platong-1Pla • ng-8Ranong-1an-12-1Erawan-12Eraw6Eraw -K-1Baanpot-1Baanpot-B-1Yala-2^ 0^5^10kmFigure 5.1: Location of well data used in this study. Numbers in the box indicate thecross sections shown in Figures 5.2 through 5.7151RANONG-1 KUNG-1 SURAT-1 PLATONG^ PLATONG-1SECTION-1• WATER COLUMN 17.3 UNIT-1 0 UNIT-2 • UNR.3 t2 UNIT-4 0 UNIT•15 0 UMT4Figure 5.2: Stratigraphic section-1 W-E direction. See Figure 5.1 for the location of the section.0-1-28 -3-4-5...........^.......0-2t8-8SECTION-2........................... • •^........... •.• WATER COLONIC] UNIT-10 UNIT-211 UNIT-3 E1 UNIT-40 UNIT-50 UNIT4I•• .......... • ................PAKARANG-1 PLADANG-3 SOUTH PLATONG-2^TRAT-1INSEA-1Figure 5.3: Stratigraphic section-2 W-E direction. See Figure 5.1 for the location of the section.152DARA-1 ERAWAN-1 2-1 ERAWAN-1 2-8 SATUN-3^JAKRAWAN-20-2-a-80-2-4-a-80-10KRUT-1 ERAWAN-K-1 BAANPOT-1^BAANPOT-B-1 JAKRAWAN-1^FUNAN-1SECTION-3• WATER COLUMN 0 UNIT-1 UNIT-2 • UNIT-3 • UNIT-4 0 UNIT-5 0 UNIT-0... .................... ........Figure 5.4: Stratigraphic section-3 W-E direction. See Figure 5.1 for the location of the section.SECTION-4Figure 5.5: Stratigraphic section-4 W-E direction. See Figure 5.1 for the location of the section.• WATER COLUMN 0 UNIT-1 0 UNIT-2• UN1T-3 UNIT-4 0 UN1T-5 a UNIT-01530-2L0-8-10PLATONG-5^PLATONG-1^SOUTH PLATONG-1^PLADANG-3^SATUN-2^SATUN-1YALA-2 KAPHONG-3 KAPHONG-1ERAWAN-1243^ERAWAN-12-7^ERAWAN-K-1 BAANPOT-B-1BAANPOT-1SATUN-1 ERAWAN-12-O ERAWAN-12-1SECT1ON-5.... ......^:::....."^............. ..........................................^ ..................... ..........^ ...........IIII....^....• WATER COLUIAN^0 UNIT-1 0 UNIT-2• LW-9 IS UNIT-4 0 LW-5 0 UNIT-6Figure 5.6: Stratigraphic section-5 N-S direction. See Figure 5.1 for the location of the sectionSECTJON-6Figure 5.7: Stratigraphic section-6 N-S direction. See Figure 5.1 for the location of the section• WATER COLUMN^0 UNIT-1 0 UNIT-2• UNIT-9 IS 1NIT-4 0 LW-5 0 U111-60-2-8-10.... ................................ ....... ...............Table 5.3: Stratigraphy and depositional environments of Tertiary strata in the PattanibasinUNIT SUBUNIT DEPOSITIONENVIRONMENTSSEDIMENTARYSTRUCTURESLITHOLOGY1 Upper Shallow marine Fine-grained Not availableMiddle Interdistributary bayand/or crevasse channelGenerally fine-grained Dark grey claystoneLower Distributary channel in acoastal plainFining-upwardsequencesReddish brownclaystone andsandstone2 Upper Brackish swamp andmarginal marineGenerally fine-grainedwith some fining-upward sequencesBrownish greyclaystone andsandstoneLower Distributary channels andfloodplainFining-upwardsequences and fine-grainedSandstone andclaystone3 Upper Nonmarine meanderingchannelFining-upwardsequences and fine-grainedSandstone andminor claystoneMiddle Distributary mouth bar andbeach ridge complexCoarsening-upwardsequencesSandstone andclaystoneLower Prodelta and shallowmarineGenerally fine-grained Claystone andminor sandstone155Table 5.3 (Continued): Stratigraphy and depositional environments of Tertiary strata inthe Pattani basinUNIT SUBUNIT DEPOSITIONENVIRONMENTSSEDIMENTARYSTRUCTURESLITHOLOGY4 Upper Upper delta plain andfloodplainGenerally fine-grainedwith fining-upwardsequencesclaystone andsandstoneMiddle Distributary mouth bar andbeach ridge complexCoarsening-upwardsequencesWhite sandstoneand minor claystoneLower Prodelta and shallowmarineGenerally fine-grained brownish claystonewith coal partings5 Upper Nonmarine meanderingchannelFining-upwardsequencesbrownish sandstoneLower Meandering channel andfloodplainGenerally fine-grainedand fining-upwardsequencesRed claystone andsandstone6 Upper Floodplain and channel Fine-grained andfining-upwardsequencesSandstone andgreyish brownclaystoneLower Alluvial fan and braidedstreamCoarse-grained andpoorly sortedConglomerate andcoarse-sand156by a subsequent phase of slow, post-rift, thermal subsidence. The rifting phasewhich lasted about 20 m.y. (from Late Eocene to Early Miocene) was recorded insynrift sediments which comprise two nonmarine sedimentary successions(stratigraphic units 6 and 5) and one regressive package (stratigraphic unit 4). Thefollowing post-rift phase comprises one regressive sedimentary package (unit 3) andtwo transgressive successions (unit 2 and unit 1).The stratigraphic unit 6, Late Eocene to Early Oliocene age, is characterized bycoarse-grained, alluvial fan and braided stream sediments in the lower subunit andfine-grained, floodplain-channel deposits in the upper subunit. Unit 5, LateOligocene to Early Miocene age, is characterized by fine-grained, floodplaindeposits in the lower subunit and somewhat coarser-grained, meandering channeldeposits in the upper subunit. A brief transgression which occurred at the end ofunit 5 deposition (early part of Early Miocene) caused a short period ofnondeposition which marked the boundary between unit 5 and unit 4. Thesucceeding sedimentary succession (unit 4, Early Miocene age) represents acoarsening-upward regressive sequence which is characterized by fine-grained,prodelta to shallow marine deposits in the lower subunit; coarse-grained,distributary mouth bar deposits and beach complexes in the middle subunit; andcoarse- to fine-grained, nonmarine floodplain-meandering channel deposits in theupper subunit.By the end of sedimentation of unit 4 (Early Miocene, about 20 Ma), the PattaniBasin became tectonically quiescent, its post-rift thermal subsidence was slow. Thesedimentation was controlled mainly by the amount of sediment influx and eustaticsea level fluctuation. The post-rift sediments comprise one regressive sedimentarypackage (unit 3) and two transgressive packages (units 2 and 1). A brief and rapid157transgression occurred again at the base of unit 3 (Early Miocene, about 20 Ma)and caused a brief period of nondeposition which marked the boundary betweenunit 4 and unit 3. A coarsening-upward regressive succession of unit 3 (Early toMiddle Miocene age), which followed a brief transgression, is characterized byfine-grained, prodelta to shallow marine-shelf deposits in the lower subunit; coarse-grained, distributary mouth bar deposits and beach complexes in the middlesubunit; and coarse- to fine-grained, nonmarine floodplain-meandering channeldeposits of the upper subunit. Unit 2 (Middle Miocene age) represents a broadtransgressive succession which is characterized by coarse-grained, nonmarinemeandering channel and floodplain deposits in the lower subunit and fine-grainedinterdistributary bay complexes and marginal marine deposits in the upper subunit.At the end of Middle Miocene, a rapid regression occurred in the Pattani Basin,probably as a result of rapid eustatic sea level fall, causing subaerial exposure,oxidation, and probable minor erosion of unit 2 sediments. Unit 1 (Late Mioceneto Pleistocene age) records the latest transgressive succession and is characterizedby the basal coarse-grained, nonmarine, distributary channel deposits of the lowersubunit; fine-grained, brackish water, interdistributary bay deposits and marsh andswamp complexes of the middle subunit; and fine-grained, prodelta to shallowmarine deposits of the upper subunit.5.5 GENERAL CHARACTERISTICS OF ORGANIC MATTERThe abundance and type of organic matter in different stratigraphic units andsubunits are described in this section. Classification of organic facies and organicmatter types are based on the concepts of Tissot and Welte (1984) and Jones(1987), respectively. Rock-Eval log diagrams of well samples are shown in Figure5.8 to Figure 5.37. The modified Van Krevelen diagrams (HI versus ()I plots) of158159480440TRIM-1600Ranong-1-1600-1400-1400Lr-1800- -1800I-2000-2000-2200 •-2200-2400- -24000^0.5^1^I5TO (%)2^ 25525382Si 461 4521a.^4200 852200Figure 5.8: Rock-Eval pyrolysis of Ranong-1 well1200Kung-1er• .Ili1200-1400iF--1400• •al:1800•w■ • -1800CI..II%1•1800 ^ -18001giI•I.-2000i20002200milt1.....-rS..Is _el-.-2400• -240010. •>IP ••2800 0^1.3^2 8^0^2^0^45^9^0^ICO 200 300^0^08 12^420^450 4802800TOC (%) 52 52/53 HI 51451.02) Tm.Figure 5.9: Rock-Eval pyrolysis log of Kung-1 well16016121.3^26^0^12^ SO^600^0^OSTOC (%) S2 02/S3^ N SIASI.S21r r--2000 CfL-2400-2600-1200■I —1400 -1600••••U. -1800'U.••••■ EQ ■ -2200-2400I .-2800Figure 5.10: Rock-Eval pyrolysis log of Surat-1 well46. 0Tmmc460-1200-1400-1600-1800Surat-111,120^1.8^3 6^0TOC (%)■■■ ■• •• ff■■Platong-832F10^20 050260 S 10142)Figure 5.11: Rock-Eval pyrolysis log of Platong-8 well-1000.1200- -1400-1600S-1800••••■•420^450Trroo(-2000-240016221222260 520Platong-1Oil^1.6^0TCC (1 )Figure 5.12: Rock-Eval pyrolysis log of Platong-1 well163lnsea-1•■-1000-1200-1400EQ1800-18002^ 0^17^34S1 S2/S30 04^08^42031/(31.32)1.7^3.4^0TOC (%)14070HI TrroxFigure. 5.13: Rock-Eval pyrolysis log of Insea-1 well164Pakarang-1■■I0^ 0^2 5^0^3TOC (%)^ 32 02/53Figure 5.14: Rock-Eval pyrolysis log of Pakarang-1 well165Pladang-3Figure 5.15: Rock-Eval pyrolysis log of Pladang-3 well1400.1600—1800-2400• •ti•-2000■ms ■•■45005^430S1451.32)440Imax166S2 S2/S3 12240^0^06S1/(SItS2)0^1TOC (%)0 26 52 120IY 430■■■■■■•■•■■■ •■■••• •■■■■••••■■•Tow■440-2200-2000• 8001800South Platong-2Figure 5.16: Rock-Eval pyrolysis log of South Platong-2 well167-1800-18000^04^04^430S143142)0TOC (%)1 5 130F1132L4WSJTrat-1-2400440TmmFigure 5.17: Rock-Eval pyrolysis log of Trat-1 well168S2 S2/S3180HI0^05Sl4S1.$21Eg27-1400-1300■■■ •UN■■■■■■■■■■ ■   ■ma a-1000Eg■ I■■-2200-2400340 300 sio sio seoTrim■Dara-1Figure 5.18: Rock-Eval pyrolysis log of Dara-1 well169Erawan-12-1-1400 IP -1400■-1600 -1600..VI■•-1800■-1800 -2000i-2000-2200 - y■--„..•22004I-ag-2400■-2400 ga2.■ ■ ■■^■■ ■■ ^■-2600 ■ asI^1-2600-t1I ■ ■^■■ ■ril ■i-2800 I -28001■4 . •ii.-3009ii ■■^71■^■  „,^el ■-3200r^• ,■ aa■-3400• ji,W■0^0.8^1.8^0^11^22^0^17^ 110 220^ Oa 12^360 300 420 460 460TOO (%) S2 S033 HI 01451.02) Imo(Figure 5.19: Rock-Eval pyrolysis log of Erawan-12-1 well170170^0^05^420^450^400S1(Si.S2) Trne4Erawan-12-8-1400-1000-.1000EiQ-2200-2400•S2S3Figure 5.20: Rock-Eval pyrolysis log of Erawan-12-8 well17152TOO (%)-1800-1800-2000-2200-2100-28000^0.8^16^0^+2■■■■■. 11■If■■?1i■■■■-2400-2200-1800-1800■Satun-329^0^10352/S3440^480Trnax04^00^420SI1Si.S2)Figure 5.21: Rock-Eval pyrolysis log of Satun-3 well172Jakrawan-2053 21 aS21502BTOO (%) S2/S3 S1451.52)Figure 5.22: Rock-Eval pyrolysis log of Jakrawan-2 well•-1400—1600-1$00S-2200•O.2400430 45044.0Trim173Figure 5.23: Rock-Eval pyrolysis log of Krut-1 wellKrut-116S2320.8^1TOC (%)200^0^060253^ HI S1431.52)•-2600460- -2200-2400-2000- -1600-1800EQ12^400 420 440Trtax-1200-1400-1600-1800QE-2400-2600-1200-1400f-2000-2200174Erawan-K-1I1400)--1400)(C.- 41800 11° 1 gilli18004'•/ i-1800- ) --11110i.".I[4U•2000 E2.■-2200 -112200■)• •2400 -. ■ --2400■fn.1^..i: ■-28002800 -l• 8-28000 1^2 0 2 0 8 0-200^400^0^05^420^440^480^480TOC (%) S2^S2/S3^HI SI8S1.S2) TmaxFigure 5.24: Rock-Eval pyrolysis log of Erawan-K-1 well175Baanpot-1 • -1400.0-1800■ ■  ■ 4•••II --1600• -2000•• •• •••• ill.■ 0• ■▪^     ■■■ •IC■1 —2400 g-2600■• •■-3000•-320015 3$2/0304$1(31.321400 440 480TomFigure 5.25: Rock-Eval pyrolysis log of Baanpot-1 well176Baanpot-B-1- -1400- -1600-1800■■ • - -2200-2400•-30002^0^13^26^ f4^24TOC (%) S2 SO/SOFigure 5.26 Rock-Eval pyrolysis log of Baanpot-B-1 well08Sl4S1.S2)440 480 620Tmex177Jakrawan-1-1200-1400-1800-1800EiQ-2000-2200Sf•■-2400■I-2800■I-2900•08^12^440^480S1481.S2) Tmax2^4^0^4TOC (%) S2^ S2/S3Figure 5.27: Rock-Eval pyrolysis log of Jakrawan-1 well178Funan-1440Tmsx0S140 1 .S2)08^400--1400- -1600-2200■■-1600EQI■-240026S2/S3Figure 5.28: Rock-Eval pyrolysis log of Funan-1 well10014-1400-1600-1800Eg-2200-2400 -0^1.1^22^0^13TOC(%) S2179Yala-2•■■■• -2400440Trmx0^0.5^1^0^0 5^0^06TCC (%) S2 S2/53Figure 5.29: Rock-Eval pyrolysis log of Yala-2 well203^0^0651451.52)-1400• ••-1600■•-1 800180Kaphong-3440Iowa•■•▪ ■■IC II■■■ ■ ■■• •▪ •■•■-1400 -1600-1800-2000-2200-28000^0.9^0.8^04^06TOC (%) S1 52/S3Figure 5.30: Rock-Eval pyrolysis log of Kaphong-3 well3EQ-2400- -1400- -1600- -1600- -2000-2200-2400-2800-2000181-1400Kaphong-1- -1400•r5....-1600 • • 1800.444—... II■■rirIII-1800 ■ -1800■)> •1 $1-2000 (••.••■I -2400 - --2400 1i •ZMa gr-2600 1 • -2800IIit14di ill-2800■4.  i -3000■ti^ir.Iol    --3200•111 0^05^1^15^0^04^08^12^1 6^0^1^2^o^100^200^0^05^420^450^450^510TOO (%) S2 0263 IS SI4SI.S2) TrntocFigure 5.31: Rock-Eval pyrolysis of Kaphong-1 well182-1400-1600.1600••440Tmax06S1461.S2)12^420Platong-50^0.6^12^06^12^ 1TOO (%) S2 S253Figure 5.32: Rock-Eval pyrolysis log of Platong-5 well160■•I^ .up•■■■■■•▪ ••-2200-2400■-2600-2000 t183South^ tonc-1600-1800•EQ■■■-2400-2600••0^0.7^14^0^11^22^0^13^2670C (IC) S2 0253Figure 5.33: Rock-Eval pyrolysis log of South Platong-1 well440Tmax04St(S 1 ....82)-1600  -1800-2400-2600  184Satun-2r0^ 0 8^1^14^26^ 36TCC C/4 S2 SZS3Figure 5.34: Rock-Eval pyrolysis log of Satun-2 well—1800- -1800mr•■■■ig■■■■-2400■••■I• ■S14S1 4S2)03 440Tmex1850^03^06^42061491.94440Tmsx-1600 -1900-2000-2200-2400-2800■•-2900Satun-1Figure 5.35: Rock-Eval pyrolysis log of Satun-1 well186200149C0Erawan-12-9-1400-1400-1600-1600-1800' ■■■-2000-2000a-2200-2400-2400-2600-2800I4-10Trnioc-28003962/S3680^0.9^1 .8^0^09TOC(%) S2Figure 5.36: Rock-Eval pyrolysis log of Erawan-12-9 well-280048005S18S19S2)-1800187-1400Erawan-12-7-- -1400•Ci —-1600 -180011111' Mil-1600 I ■ --18001111°. 5/Iti-2000t: k:2. 1-2200111111"■t-2400 $ii -2400■  ;11"  "1 ■■■ •-2000•la mill1 -26°°••-2800 • ■ ► -MO•• ■a0 1S^3^25^ 0^37^71 0 200 100^0^08 12 420 440^480^480TOC (%) 02 02/03 10 S1(01■02) TrnctFigure 5.37: Rock-Eval pyrolysis log of Erawan-12-7 well188different subunits are shown in Figure 5.38 through Figure 5.51. Table 5.4 andTable 5.5 summarize the classification of specific stratigraphic units and subunits,respectively. The lateral variation of organic richness (TOC) for specificstratigraphic units and subunits are shown in Figure 5.52 through Figure 5.65. Thelateral variation of the relative quality of organic matter (QOM, [S 1 +S2]/TOC) isshown in Figure 5.66 through Figure 5.79.5.5.1 Unit 6Only a few samples from four wells located in the western part of the basin marginwere available for study. Because of limited data, maps showing lateral variationsof organic matter in unit 6 were not constructed. This unit is organically lean. Theoverall average TOC content of unit 6 is 0.20% with the HI value of 80 mg HC/gTOC, the OI of 204 mg CO2/g TOC, and the QOM of 1.6 mg HC/g rock (Table5.4). Organic characteristics of lower and upper subunits are described below.The lower subunit, which is characterized by alluvial fan and braided streamdeposits, is very lean in organic matter. It contains about 0.07 %TOC with HIvalue of 9 mg HC/g TOC, OI value of 247 mg CO 2/g TOC and QOM value of0.13 mg HC/g rock (Table 5.5). The organic matter of this subunit comprisesorganic facies D (Type IV OM, Figure 5.38). The maceral composition of thissubunit is dominated by vitrinite.The upper subunit, which is characterized by a series of channel and floodplaindeposits, contains approximately 0.22 %TOC with HI value of 87 mg HC/g TOC,01 value of 199 CO2/g TOC and QOM value of 1.82 mg HC/g rock (Table 5.5).This organic matter consists mainly of organic facies CD and D (Type III-IV and189Figure 5.38: Hydrogen index vs. oxygen index for samples from unit 6's lower subunit.UNIT-8LOWER SUBUNITinnsRanong-1n • 2Typo IITypo IVMOM0.11010011MUNITELONER SUBUNITType ISLrat-1n •Typo IIsv-Typo IIIoxvoet• moex.29Typo H■• l• • r,,,o1•.^. 10, 'ID^ID^SD0.01101011NY•UNIT-8UPPER SUBUNITTypeDare-1n•14Figure 5.39: Hydrogen index vs. oxygen index for samples from unit 6's upper subunit.190Yela-2Type IUNIT-5LONER SUBUNITTypose^leyOSIODDI IOUUNIT-5LOWER SUBUNITTN.PII110119-fn• 2TYPAToe e •So^210PXolibmierfUNIT-5LOWER SUBUNIT^Ranong-1n • NITypo^■^Typo III^up ^I TO^SoTypo IUNIT-5LOWER SUBUNIT^Insee-12Tn.Typo!!!^ Ka.^Is,carom •Rec„„,Type IUNIT-5LOWER SUBUNIT^Dare-1n•10Type D•• •^•rt owType IIf>oalDeo NenFigure 5.40: Hydrogen index vs. oxygen index for samples from unit 5's lower subunit.191UNIT-5UPPER SUBUNITType IPlalang-En • 6ptl1909091010.Tyr.Type IIIType IUNITSUPPER SUBUNIT Platcog-1n • 691^19^ZO^7,9Orre0.11199UNITSUPPER SUBUNRType IYale-2n • 6TypoTYp 16SO^ZOCanOOMOCCUNITSUPPER SUBUNITTYPOTypo IIIP_% ■Dare-1n • IITyraTyp• I1111UNIT-5UPPER SUBUNITTypo IlErawan-12-n• 26Type III09919■1190(ZO 9 XOOZIODI MCCZOFigure 5.41: Hydrogen index vs. oxygen index for samples from unit 5's upper subunit.192Type IPlato g-'n • 5UNIT4LONER SUBUNITTVG*Erawan-12-n • 3UNIT4LOWER SUBUNITUNIT4LOWER SUBUNITTypoKaphong-1n • 7Typo IITYE. I*1100.01510 "INType.in 10)^'10^20^303t01.0010•KgKaphong-:UNIT-4LOWER SUBUNITTyq ITway I n • 18■^Type,<00.0010/0/2Tn.277^712,0:0520. MIXLOWER SUBUNITUNIT-4^Erawan-12-Type IIIsiOxV001,100•2UNIT4LOWER SUBUNITTyq IBaanpot-B-n • INW IIT5157 III• ■ •.100^10^20^200:.0601.004Figure 5.42: Hydrogen index vs. oxygen index for samples from unit 4's lower subunit.193Satun-2• • 3UNIT,*Type ^NICOLE SUBUNITTypesPakarang-'n • 11UNIT4L1COLE SUBUNITTyroType IS•13300.0 .003UNIT4Type,^1.ZIOLE SUBUNITTyro03061004 DOISn • 17UNIT4NICOLE SUBUNIT.0 ,KaPh009411.301-3Type IIMIX0^20.1001 BMXTypo 3■ iirphip00004 SOOFigure 5.43: Hydrogen index vs. oxygen index for samples from unit 4's middle subunit.194Renonvn • 31UNIT-4TYPeI^UPPER SUBUNIT.0,UNI14^Satan?Typ ^UPPER SUBUNIT n • 5Figure 5.44: Hydrogen index vs. oxygen index for samples from unit 4's upper subunit.Typo IIX■^KO^ X0^2:003,0. MOVETypo NX00.00/ MUUNIT-4Typo I^UPPER SUBUNITJalvawans.n • 2TypTypo NIIO^240.11,1 1 01e(195rata-2n • 26TypalTy, 61—111, NI aUNIT-4UPPER SUBUNIT Kaphong- ,n   13UNIT4Ty,. ,^UPPER SUBUNITUNIT4UPPER SUBUNITTyne 11-Satan-2n . 3no.TypalUNIT4UPPER SUBUNITType IITY. INSatan-1n • 6•• • on.^Y0^1,0 Ma SD OD Ico ■ S. ZO AOWrIf.1.111017 110.131911110VUNIT4Tvp. ,^UPPER SUBUNITErawan-12-n. sTypo 11Ty,* IN.^..^I lo^ZO^2 3CKVOMMIXFigure 5.44 (cont.): Hydrogen index vs. oxygen index for samples from unit 4 s upper subunit.Typo V Type IITypo .■ 411---- •10>^19^X0^MOOrKIN DON196n gUNITSLONER 9JOUNITiv, IFigure 5.45: Hydrogen index vs. oxygen index for samples from unit 3's lower subunit.Ty,.0:enaat seec197198Ty, IJakrawan-■n • 15UNIT-351 POLE SUBUNIT17   •UNIT-3Typa l^MCOLE SUBUNITTip..UNIT3Tyre^MOUE SUBUNITTypo 11KO4.0    MYYela-2n SNp. •Tyre 11• ^a■K.^3,0^TOOVA. 04.1Figure 5.46: Hydrogen index vs. oxygen index for samples from unit 3'smiddle subunit.Figure 5.46 (cont.): Hydrogen index vs. oxygen index for samples from unit 3's middle subunit.UNIT4 south memouCO.E SUBUNITType I^n • 1,1Tyq II1p^1 socontIPPOPTypo 1.11ti MI..^2.199Figure 5.47: Hydrogen index vs. oxygen index for samples from unit 3's upper subunit.Ranong-1n • 32UNIT-3Typo^UPPER SUBUNITTypoErawan-K-n • 7UNITSyip, '^UPPER SUBUNITUNIT-3TYpoI^UPPER SUBUNITso,Typo IITrat-1• 2Typo IIIUNIT-3Typol^UPPER SUBUNITTypo IIDara-1n • 501■.0^190110101 MODZO 110011•00/1•10011SOUNITSUPPER SUBUNITType 1 Jakrawan-,n • 6NE MI 01071•01 o/001kTypo IP310^101IONp1 a,^NO^NO▪ 03110011 NUMTypo IUNIT-3UPPER SUBUNIT Kaptiong4n • 10Typo*ZO• TYPO in0,0^101^310canao•sameUNITSTyp.,^UPPER SUBUNITTap.Kaphong-n • 12Typo MIZO100^151^310OZW301UNIT-3UPPER SUBUNITTyplTOM*TyP•• Ilo^ZO^2110▪ C0■100111001PI/SW*194n • 16200Figure 5.47 (cont.): Hydrogen index vs. oxygen index for samples from unit 3's upper subunit.201Surat-1n .38UNIT2LONER SUBUNITPlatong.8n • nUNIT-2LOWER SUBUNITTypo Ir Typo II■°stolen OenUNIT2K 1^LOWER SUBUNITiyTy. 11Ranong.1n • 2Typo INKO,Ko^ISO^ID^210Ozrann NOVTypo 11100 111I l)-^X0^TMOXYGInn oCIXFigure 5.48: Hydrogen index vs. oxygen index for samples from unit 2's lower subunit.202UNIT2LOWER SUBUNITKO,TIE. IIKaphong-3n   20Type IIIMN. SUNIT2Typ l^LOWER SUBUNITTypo IIKaphong-1o   31Typo IIIIMPMAIN SPYre KID^1500M061 01:11re 211,1TypoUNIT2LONER SUBUNIT Platong-5n • 17Type IIairOr100114011XUNIT2 South Platong-1Ty^LONER SUBUNITp. , n • 4060Typo100^1100:(106111001Figure 5.48 (cont.): Hydrogen index vs. oxygen index for samples-from unit 2's lower subunit.203Typo IUNIT-2UPPER SUBUNIT Erawan-12-8n • 169^90^19^20Ca100090tUNIT.2UPPER SUBUNITTypo ITypo II911^1 9oxrpod ooNEYPladeng-9n • 26Figure 5.49: Hydrogen index vs. oxygen index for samples from unit 2's upper subunit.204Figure 5.49 (cont.): Hydrogen index vs. oxygen index for samples from unit 2s upper subunit.205Typ. IPladang-3• 9UNITALOWER SUBUNITFigure 5.50: Hydrogen index vs. oxygen index for samples from unit l's lower subunit.UNITATygl^LONER SUBUNITBaanpot-B-1n • 5Type IIType IIIOrrt101110017UNIT-1Typed^LOWER SUBUNITJaIQawan-1n•19Type IITYE* InCANOCII.00CFigure 5.51: Hydrogen index vs. oxygen index for samples from unit 1's middle subunit.206Table 5.4: Summary of organic geochemical characteristics of Tertiary stratigraphicunits in the Pattani basinUNIT TOC HI OI HC-P QOM S1 S2 S31 1.41 122 71 2.20 1.39 0.22 1.98 0.842 0.54 99 274 0.83 1.44 0.16 0.66 0.613 0.36 85 232 0.46 1.30 0.13 0.33 0.404 0.33 87 187 0.50 1.44 0.19 0.31 0.365 0.24 83 181 0.45 1.60 0.20 0.25 0.286 0.20 80 204 0.48 1.61 0.24 0.24 0.24*TOC is the total organic carbon (%)HI is the hydrogen indexOI is the oxygen indexHC-P is the hydrocarbon potential = s, +s 2QOM is the quality of organic matter = (s 1 +s2)/TOCTable 5.5: Summary of organic geochemical characteristics of Tertiary stratigraphicsubunits in the Patani basinUNIT SUBUNIT TOC HI OI HC-P QOM S1 S2 S31 Middle 1.47 127 73 2.42 1.64 0.21 2.21 0.92Lower 1.37 127 65 2.05 1.49 0.26 1.80 0.732 Upper 0.81 120 131 1.31 1.57 0.20 1.11 0.72Lower 0.43 91 312 0.64 1.49 0.15 0.50 0.543 Upper 0.29 80 316 0.37 1.28 0.10 0.27 0.39Middle 0.39 88 191 0.49 1.31 0.14 0.35 0.41Lower 0.44 98 137 0.57 1.34 0.16 0.41 0.444 Upper 0.36 89 204 0.55 1.39 0.20 0.34 0.41Middle 0.35 82 155 0.49 1.37 0.20 0.29 0.42Lower 0.32 82 112 0.52 1.56 0.22 0.30 0.285 Upper 0.25 94 191 0.52 1.93 0.25 0.27 0.29Lower 0.24 75 190 0.40 1.46 0.17 0.23 0.326 Upper 0.22 87 199 0.50 1.82 0.25 0.26 0.24i Lower 0.07 9 223 0.01 0.13 0.00 0.01 0.11*TOC is the total organic carbon (%)HI is the hydrogen indexOI is the oxygen indexHC-P is the hydrocarbon potential = s, +s2QOM is the quality of organic matter = (s 1 +s2)/TOC2070Trat-1 (NA)0Satun-2 (NA)0Satun-1 (NA)Yala-2 (0.19)00 Kaphong-3 (0.27)phong-1 (0.20). 8)Platong-1 (0.18)Ranon0Kung-1 (0.44)0 Surat-10.100 atong-8 (0.33)0Insea-1 (0.070 S. Platong-1 (NA)g-1 (0.23)Pladang-3 (NA)00 S. Platong-2 (NA)PlatongErawan-12-9 (NA)1 (0.25) 0 0 Satun-3 (NA)Erawan-12-1 (0.25)0 Erawan-12-8 (0.34)Eraw -12-7(0,23)0Jakrawan-2 (NA)00Jakrawan-1(NA)0Baanpot-1 0 (NA)^Funan-10 (NA)Baanpot-B-1 (NA)0Krut-1(NA)0Erawan-K-1 (NA)0^5^10kmFigure 5.52: Lateral distribution of TOC (%) of unit 5208o Kaphong-1 (0.26)Platong-5 0 '.22)0.25 0 0 Platong-1 (0.38)° -1 Platong-8 (0.41)(0.18)0ng-1 (0.84)Ranong-1 (0.000 S. Platong-1 (NA)Pakarang-1 (0.32)0 Pladang-3 (0.29)00 S. Platong-2 (NA)00^Trat-1 (NA)Satun-2 (0.33)0Insea-1 (0.13)0Satu 1 (0.24)rawan-12-9 (0.45)(0.25) o^0 Satun-3 (NA)0 2-5^0 Erawan-12-1(0.39)0 Erawan-12-8 (0.45)0Krut-1(0.39) Erawan-1^•.34)00Erawan-K-1 (0.51)Jakrawan-2 (NA)00Jakrawan-1(NA)0Baanpot-1 0 (0.61)^Funan-10 (NA)Baanpot-B-1 (0.53)Yala-2 (0.09)00^5^10 km0 Kaphong-3 (0.20)Figure 5.53: Lateral distribution of TOC (%) of unit 42090^5^10kmYaia-2 (0.11)0Sa n-2 (0.25)0Satun-1 (0.28)0 Kaphong-3 (0.13)Ranong-1 (0.13)0^0.250 Kaphong-1 (0.13)Platong-5 0 (0.17)Platong-1 (0.23)Platong-8 (0.35)0Surat-10^(0.27)Kung-1 (0.41)0. 50^0 S. Platong-1 (0.28)0Insea-1 (0.2rawan-12-9 .44)Dara-1 '.21) 00^0 Satun-3 (0.20)0.54)0.81)0rawan-K-1 (0.80)Pakarang-10 0.53)2 (NA)0Trat-1 (0.41)akrawan-2 (0.22)00.250 0.50Jakrawan-1 (0 .88)Erawan- 2-7 (0.39)0Krut-1(0.29)0n • of-1 0 0.80)^Funan-10 (0.78)Baanpot-B-1 (0.41)Figure 5.54: Lateral distribution of TOC (%) of unit 32100^5^10kmYaia-2 (0.48)00swan-K-1 (0.84)Jakrawan-2 (0.80)00 Kaphong-3 (0.15)Ranong-1 (0.83)0o \Kaphong-1 (0.26)Platong-6 0 (0.44)0 0 Platong-1 (0.45)Plat ng-8 (0.71)0Kung-1Platong-1 (0.42)1.00adang-3 (1.37)0^ 0Insea-1 (0.00^Trat-1 (0.69)tun-2 (0.55).42)2)0 Satun-3 (0.57)0 Erawan-12-1(0.64)0 Erawan-12-8 (0.81)0Erawan-12-7 (0.64)00Jakrawan-1 (0.72)0Baanpot-1 0 0 . • ;(0.63)Funan-1Baanpot-B-1 (•43)0.50Pakarang 100 S. Platong-2 (0.62)0.25ErawDara-10Krut-(0.07)Figure 5.55: Lateral distribution of TOC (%) of unit 2211o Kaphong-1 (0.21)Platong-5 0 (0.30)O 0 Platong-1 (0.15)° Platong-8 (0.44)Surat-1(0.04)Yaia-2 (0.17)00^5^10 km/1"0 Kaphong-3 (0.40)Ranong-1 (0 •9)00Kung-1 (0.O S. Platong-1 (NA)akarang-1 0.30)0 Pladang-3 (NA)0^ 0Insea-1 (0.07)^ o S. Platong-2 (NA)0O Trat-1 (NA)Satun-2 (NA)0Satun-1 (NA)Erawan-12-9 (NA)a-1 (0.25) 0^O Satun-3 (NA)0 Erawan-12-1(NA2379)0 Erawan-12-8 (NA)Erawan-12-7 (NA)0OErawan-K-1 (NA)0Jakrawan-1 (NA)0Baanpot-1 0 (NA)^Funan-10 (NA)Baanpot-B-1 (NA)0Krut-1(NA)Jakrawan-2 (NA)0Figure 5.56: Lateral distribution of TOC (%) of unit 5's lower subunit2120^5^10kmYala-2 (0.21)00 S. Platong-1 (NA)phong-3 (0.24)Ranong-1 (0.07)0 0 Platong-8 (0.27)at-10^(0.15)Kung-1 (0.38)0^phong-1 (0.18)Platong-5 0 (0.25)Platong-1 (0.15)Pakaran -1 (0.21)0 Pladang-3 (NA)0^ 0Insea-1 (NA)^ 0 S. Platong-2 (NA)00^Trat-1 (NA)Satun-2 (NA)cr0Satun-1 (NA)CYEra an-12-9 (0.44)-1 (0.28) 00 Satun-3 (NA)0 Er an-12-1(0.31)0 Erawan-12-8 (0.34)Erawan-12-7 (NA)00Krut-1(NA)Jakrawan-2 (NA)00Erawan-K-1 (NA)0Jakrawan-1(NA)0Baanpot-1 0 (NA)^Funan-10 (NA)Baanpot-B-1 (NA)Figure 5.57: Lateral distribution of TOC (%) of unit 5's upper subunit213Yala-2 (NA)00^5^10 kmKaphong-3 (0.28), ^• Kaphong-1 (0.28)^....................-"^Platong-5 0 (0. 0)0 0^atong-1 (0.21)Ranor3i.1.17A^0. 5/50 •^-1 Platong-8 (0.27)(0.13)\^0ng-1 (0.75)0 S. Platong-1 (NA)Pak:^g-1 (0.18)0^Pladang-3 (NA)1^ 0(NA)awan-12-9 (0.38)Dira-1 (N4) 00 Erawan-12-1(0.37)0 Erawan-12-8 (0.37)1<r ut0-1^ trawlan-1 -7 (0.28)(NA) 0 Jakrawan-2 (NA)/ 0 cY^ 0,Flrawa.n-K-1 (NA)0Jakrawan-1 (NA)0Baanpot-1 0 (NA)^Funan-10 (NA)Baanpot-B-1 (NA)0Insea-1 0 S. Platong-2 (NA)00^Trat-1 (NA)Satun-2 (NA)0Satun-1 (NA)0 Satun-3 (NA)Figure 5.58: Lateral distribution of TOC (%) of unit 4's lower subunit214^02.5Krut-1^Erawan-12-7 .34)^(0.33) 00.5°rawan-K-1 (NA)Baanpot-1 0 (0.76)0Baanpot-B-1 (0.53)Jakrawan-2 (NA)00Jakrawan-1(NA)0Funan-1(NA)Yala-2 (0.12)00^5^10 km0 Kaphong-3 (0.18)Ranong-1 (NA)0430 Kaphong-1 (0.33)Platort-5 0 0.15)0 Platong-1 (0.31)latong-8 (NA)....tura/Kung-1 (NA)0 S. Platong-1 (NA)\^P. arang-1 (0.30)\ °^Pladang-3 (NA)0^\ 0Insea-1 (NA) \^ 0 S. Platong-2 (NA)0i^0^Trat-1 (NA)i Satun-2 (0.32)Ii^ 0i Satun-1 (0.27)ik^rawan-12-9 (0.44)Dark-1 (^00 N•, ° Satun-3 (NA)\i^-12-1(0.41)...-... an-12-8 (0.39)•Figure 5.59: Lateral distribution of TOC (%) of unit 4's middle subunit215Pakarang-1 (0.48)°^Pladang-3 (0.29)0^ 0Insea-1 (NA) ? o S. Platong-2 (NA)i^00 , Trat-1 (NA)S n-2 (0.33)Eraw 12-7 (0.38)JakrawaN2 (0.52)oi/o,J0kfitwan-1 (NA)Baanpot-1 0 (ow'^Funan-1))* (NA)Baanpot-B-1 (NA)0Krut-1(0.48) 0050 0Erawan-K-1 (0.51)Eraw^(013)Dar 1 (0.25) atun-3 (0.18)0 raw^2-00.40)0 Erawan-12-5A52)Yala-2 (0.08)00^5^10 km0 Kaphong-3 (0.19)o Kaphong-1 (0.19)Platong-5 0 •. 3)Ranong-1 (0.07) • 5^o 0 Platong-1 (0.47)o^ atong-8 (0.44)0.500 -,....____^(0.19)ung-1 (0.58)0 S. Platong-1 (NA)o ,Satun11 (0.24)0.25^iFigure 5.60: Lateral distribution of TOC (%) of unit 4's upper subunit216Yala-2 (NA)00^5^10 km0 Kaphong-3 (NA)0Kung-1 ..(i<JA)Kaphong-1 (NA)Platong-51 . 0 latong-1 (0.28)/' t-1 Platong-8 (0.28)(0. 5)Ranong-1 (NA)00 S. Platong-1 (NA)Pakar/0Insea-1 (NA)/Dara-1(NA)Erawan0Erawan-K-1 (IAA)Baanpot-1 p (NA)0Baanpot-B-1 (0rawan-2 (0.17)00„250. 500 O. 7*Jakrawan-r(0.97)0Funan-1(NA).53)g-3 (0.38)0 S. Platong-2 (NA)0 500tun-2 (NA)0atun-1 (0.23)2-7(0.0Trat-1 (NA)(0.50)0 Satun-3 (0.21)-1(0.81)-8 (0.87)Figure 5.61: Lateral distribution of TOC (%) of unit 3's lower subunit217Erawan-12- 0.48)0Erawan-K-1 (0.BaanpoJakrawan-2 (0.22)0Jakrawan-1(0.57)0Funan-1(0.97)0Kwt-1(0.41Baanpot-B-1 (0.29)Yala-2 (0.08)00^5^10 kmo Kaphong-3 (0.15)Ranong-1 (NA)00 Kaphong-1 (0.14)Plato\v-5 0 (0.24)\ o 0 Platong-1 (0.23)Surat-V: Platong-8 (NA)0^(NA)Kung-1 (NA)0 S Platong-1 (0.21)Pakarang-1 (NA) \°^Pladark-3oSaSatun-3 (0.18)o Era an-12-1(0.48)E wan-12-8 (0.44)0Insea-1 (NA)Figure 5.62: Lateral distribution of TOC (%) of unit 3's middle subunit2180^5^10kmYala-2 (0.11)0o Kaphong-3 (0.11)Ranong-1 (0.13)00 Kaphong-1 (0.12)Platong-5 0 (0.10)0.2^o o Platong-1 (NA)° Platong-8 (0.38)Surat-1(NA)0Kung-1 (0.40)00^Trat-1 (0.30)Satun-2 (0.30)0Satun-1 (0.38)Er an-124 (0.30)Dara-1 (0. • ) 9. i^0 Satun-3 (NA)Erawan-12-1(NA)'Q,Erawan-12-8 (NA)Erawan-12-7 (a:34)Jakrawan-2 (NA)0Erawan-K-1 (0.34)0Jakrawan-1(0.54)0Funan-1(0.80)0Kr(0.0 S. Platong-1 (0.27)Pakarang-1 (0.32)°^Pladang-3 (NA)0^ 0Insea-1 (NA)Baanpot-1 f (0.50)0Baanpot-B-1 (NA)0 S. Platong-2 (NA)Figure 5.63: Lateral distribution of TOC (%) of unit 3's upper subunit2190^5^10kmYala-2 (0.4.8)00 Kaphong-3 (0.09)Ranong-1 (0.83)0o Kaphong-1 (0.07)Platong-5 0 0.39)Platong-1 (NA)ng-8 (0.89)0Kung-1 (0.88)0 .S0 ..%*P0Insea-1 (NA)S. Platong-1 (0.35)0,*Te-(1.37)S. Platong-2 (0.42)00^Trat-1 (0.82)Satun-2 (0.38)0Satun-1 (0.41)Erawan- 2-9 (0.23)arDa-1 (NA)0^ 0 Satun-3 (0.47)2-1(0.18)12-8 (0.54)0Jakrawan-2 (0.44)01(0.59)0(0.40)^Funan-1(0.41)Baanpot-B-1 (0.24)Krut-1(0.07)Figure 5.64: Lateral distribution of TOC (%) of unit 2's lower subunit220Yala-2 (NA)^ 0^5^10kmNcvcIa Kaphong-3 (0.18)(t(Ei1^in.^cid o^phong-1 (0.38)(0.48)Ranong-1 (NA) "-0^along-1 (0.82)a S. Platong-1 (0.53)'N.Pak .tan0Insea-1 (NA)(0.86)0Satun-1 (0.44)Era an-12-9 (0.51)Data-1 (NA) 0C0^iKrum \ Er^-12-7 (1.24)(NA)^0 Jakrawan-2 (0.80)C^ 0.Erawir-K-1 (NA)I^IP ^Baanpot-1 Funan-1(0.87)Baanpot-B-1 (1.00)o Pla ng-8 (0.82)/** Surat-1(NA)oKung-1 (0.84)00 Satun (0.91)-1(NA)0 Erawan- -8 (1.01)0Jakrawan-1(0.90)0Figure 5.65: Lateral distribution of TOC (%) of unit 2's upper subunit2210 Satun-3 (0.91)an-12-1(1.90)eb• 0^0 rawan-12-8 (1.24)tiEraw 12-7 (0.89)Jakrawan-2 (0.80)00Krut-1(NA)0Erawan-K-1 (NA)0Jakrawan-1(NA)0Baanpot-1 0 (NA)^Funan-10Baanpot-B-1 (NA)^(NA)Yala-2 (0.97)00^5^10 km0 Kaphong-3 (0.88)Ranong-1 (0.42)00 Kaphong-1 (1.38)Platon -5 0 (2.49)o Platong-1 (1.49)01.0^Platong-8 (2.21)0 S. Platong-1 (NA)1 (1.83)Pladang-3 (NA)0^ 0Insea-1 0 S. Platong-2 (NA)00^Trat-1 (NA)25)^ tun-2 (NA)Figure 5.66: Lateral distribution of QOM (mg HC/g rock) of unit 52220^5^10kmYala-2 (0.74)00 Kaphong-3 (0.51)0 Kaphong-1 (1.30)Platon -5 0 (1.78)0 Platong-1 (1.14)Ranong-1 (0.36)^ 2.0•rat-111 Platong-8 (2.59)0^(0.79Kung-1 (1.28)0 S. Platong-1 (NA),Pakarang-1 (1.35)°^Pladang-3 (1.80)0^ 0Insea-1 (0.51)^ o S. Platong-2 (NA)0o^Trat-1 (NA)1.0^ n-2 (1.20)1 (0.85)Erawan- -9 (2.58)Dara-1 (2.69) 00^0 Satun-3 (NA)0 awan-12-1(2.22)0 Erawan-12-8 (1.82)0ut-12.0Erawan-12-7 (1.33)00Erawan-K-3.0 0Jakrawan-1(NA)2.0 0BaarcV.-o—(1.01)^Funan-1(NA)Jakrawan-2 (NA)0A.0^oBaanpot-B-1 (0.57)Figure 5.67: Lateral distribution of QOM (mg HC/g rock) of unit 42230^5^10kmYala-2 (1.09)00 Kaphong-3 (2.11)Kaphong-1 (2.11)o S. Platong-2 (NA)arang-1 (1.18)°^Pladang (1.90)0^ 0Insea-1 (0.55)S0tun-1 (0.85)Dara01Erawan- 2-9(0.85) 0.20)o Satun-3 (0.97)0Baanpot-1Baanpot-B-1 (0.90)0Erawan-K-1 1.38)(1.50)rawan0S. Platong-1 (1.00)0O Trat-1 (0.77)S tun-2 (0.98)Erawan-12-7 (2.38)0OJakrawan-1(0.42)0Funan-1(0.95)Krut-1(1.82)0o Erawan-12-1(1.13)rawan-^)Ranong-1 (0.91)0Platong-5^(3.00)o o Platong-1 (1.80)Surat-10^(0.31)Kung-1 (0.99)° Platong-8 (1.48)Figure 5.68: Lateral distribution of QOM (mg HC/g rock) of unit 32240^5^10kmYala-2 (1.02)0Ranong-1 (0.57)01.5^0 S. Platong-1 (1.44)0arang-1 (1.68)° Pladang- • (1.91)oInsea-1 ( .74)^ o S. Platong-2 (1.17)0Satan-1 (1.18)Erawan-12 9 (1.84)Dara-1 (NA) 00^0 Satun-3 (1.18)an-12-1(1.44)awan-12-8 (2.94)-12-7 (1.40)^1.50Erawan-K-10Jakrawan-1(1.08)0Baanpot-1 o .28)^Funan-1(1.04)Baanpot-B-1 (1.48)0Jakraw0 -2 (1.72)2.00Krut-1(2.65)00^Trat-1 (0.85)n-2 (1.43)1o^(0.72)Kung-1 (1.20)o Kaphong -3 (1.14)' 2.0/o Kaphong-1 (2.21)Platong-^(1.43)Platong-1 (1.32)1.0^Platong-8 (1.32)Figure 5.69: Lateral distribution of QOM (mg HC/g rock) of unit 22250^5^10kmYala-2 (1.05)0phong-3 (0.99)Kaphong-1 (1.31)Platon.^ (2.08)lRanong-1 (0.67)^ atong-1 (0.63)0^ Platong-8 (1.68)143)0 S. Platong-1 (NA)Pakarang-1 (1.47)0^Pladang-3 (NA)0o S. Platong-2 (NA)00^Trat-1 (NA)Satun-2 (NA)0Satun-1 (NA)12-9 (NA)Data Satun-3 (NA)00 0 Erawan-12-1(1.33NA)c? 0 Erawan-12-8 (NA)0Kung-1 (1.54)0I nse ■ Erawan-12-7 (NA)00Erawan-K-1 (NA)0Krut-1(NA)Jakrawan-2 (NA)00Jakrawan-1 (NA)0Baanpot-1 0 (NA)^Funan-1(NA)Baanpot-B-1 (NA)Figure 5.70: Lateral variation of QOM (mg HC/g rock) of unit 5's lower subunit226Kaphong-3 (0.57)0Surat-10^(1.87)Kung-1 (1.48)o Kaphong-1 (1.45)2.53)o Platong-1 (1.83)latong-8 (2.48)Ranong-1 (0.93)00I nsea-1 (NA)0 S. Platong-1 (NA)Pakarang-1 (1.33)°^Pladang-3 (NA)00 S. Platong-2 (NA)0Satin-1 (NA)12-9(2.52)0 Satun-3 (NA)rawan-12-1(3.14)Erawan-12-8 (123)1=2tT'ODara0Yala-2 (0.91)00^5^10 km00^Trat-1 (NA)Satun-2 (NA)Erawan-12-7 (NA)00Erawan-K-1 (NA)0Jakrawan-1(NA)0Baanpot-1^(NA)^Funan-1Baanpot-B-1 (NA)^(NA)0Krut-1(NA)Jakrawan-2 (NA)0Figure 5.71: Lateral variation of QOM (mg HC/g rock) of unit 5's upper subunit2271.00 Kaphong-3 (0.87)..•2 0 0 Kaphong-1 (1.02)Ranon5p4.1NA)Surat-1(0.72)Platong-1 (0.82)tong-8 (2.91)1)0 S. Platong-1 (NA)0Satun-1 (NA)Erawan 2-9(2.92)DAra-1 (NA) 0 0 Satun-3 (NA)1:20awan-12-1 (2.36)0 Erawan-12-8 (1.79)Yala-2 (NA)00^5^10 km0Insea-1 (NA)Pakarang-1 (0.87)°^Pladang-3 (NA)00 S. Platong-2 (NA)0^ Trat-1 (NA)Satun-2 (NA)0^• ,Krut-1^•Erawfm-12-7 (1.29)(NA) i 0/i.- 0,Errawan-K-10NP^Jakrawan-1 (NA)0Baanpot-1 0 (NA)^Funan-10 (NA)Baanpot-B-1 (0.87)Jakrawan-2 (NA)0Figure 5.72: Lateral variation of QOM (mg HC/g rock) of unit 4's lower subunit228Yala-2 (1.02)00^5^10 kmRanong-1 (NA)0..ef..Kung-1 (NA)0 S. Platong-1 (NA)rVPakaran -1 (2.42)Pladang-3 (NA)0^ 0^Insea-1 (NA) \^ o S. Platong-2 (NA)0Trat-1 (NA)Satun-2 (1.05)oSatun-1 (0.63)Erawan-1 9 (2.88)Dart-1 (NA) cp0^0 Satun-3 (NA)O0 Kaphong-3 (0.38)0 Kaphong-1 (1.49)PIatont-5 0 (1.40)! 0 0 Plato g-1 (1.34)Platong-8 (NA)SyIrs11510Krut-1(1.54)o awan-12-1(2.28)Erawan-12-8 (1.17)Erawan-12-7 (1.44)00^ Jakrawan-2 (NA)0Erawan-K-1 (NA)0Jakrawan-1 (NA)0Baanpot-1 0^4)^Funan-1Baanpot-B-1 (0.57)^(NA)Figure 5.73: Lateral variation of QOM (mg HC/g rock) of unit 4's^middle subunit229Yala-2 (0.81)00^5^10 km0 Kaphong-3 (0.88).......^ 0 Kaphong-1 (1.22)oRaton 7..)0 (1.88)0 ^Platong-1 (1.04)Ranong-1 (0.33) 0^ ni Platong-8 (3.25)S at-1^0^ 0.88)0 \ •Kung-1 (1.11)0 s. Platong-1 (NA)Pakarang-1 (1.53)°^Pladang-3 (1.82)0^ 0Insea-1 (NA)^ 0 S. Platong-2 (NA)0-2 (1.19)—toSa ns1 (0.88)0Trat-1 (NA)E wan-12-9 (1.98)Dara-1 (2.^00 atun-3 (1.08)0 Er^-12-1(4..84)0 rawan-12-6(t.88)...0^ ...Eraw 12-7 (1.39)^...Krut-^(2.01)^00Erawan-K-1 (1.53)JakrawaN2 (0.81)i/9/4*f/wan-i(NA)1., ...^0Baanpot-1 0 (1.54)-^Funan-11:)*^ (NA)Baanpot-B-1 (NA)Figure 5.74: Lateral variation of QOM (mg HC/g rock) of unit 4's upper subunit230Yala-2 (NA)00^5^10kmo Kaphong-3 (NA),o Kaphong-1 (NA)Platong-5 9/ (NA)Ranong-1 (NA)^ o Platong-1 (1.80)/..e0^^ 0^Platong-8 (1.88)urat0 / (0.5Kung-1 ..(NA)0 S. Platong-1 (NA)(1.21)Pladang-3 (1.81)00 S. Platong-2 (NA)0Trat-1 (NA)NA)0Insea-1tun-3 (1.08)o Erawan-12-1(1.13)o Erawan-12-8 (1.85)0Er an-12-7 (1.72)rawan-2 (1.95)00Erawan-K-1 (i4A)Baanpot-1 p (NA)^Funan-1o (NA)Baanpot-B-1 (0.78)Krut-(NA)0 7.0Jakrawan-1(0.42)0Figure 5.75: Lateral variation of QOM (mg HC/g rock) of unit 3's lower subunit231Yala-2 (1.15)0....'oKaphong-3 (1.02)k.Plato\v-5 00 0° \Surat-1. Pla0^(NA) ‘1Kung-1 (NA)phong-1 (1.77)ng-1 (1.60)(NA)Ranong-1 (NA)0S. Platong-1 (0.84)0Insea-1 (NA) 0 S. Platong-2 (NA)\Pakarang-1 (NA) \I° Pladar)-3 (NA)P'.,'/'/(k00^Trat-1 (0.82)Satun-2 (0.83)...\eo,.00a n-1 (0.93).52)0 Satun-3 (1.25)-12-1(1.11)2-8 (2.55)0Jakrawan-2 (1.23)1.0^°Era^1.28)0Jakrawan-1(0.48)0Baanpot-1 0 I .81)^Funan-1Baanpot-B-1 (1.00)^(0.75)Krut-1(1.81)0^5^10kmFigure 5.76: Lateral variation of QOM (mg HC/g rock) of unit 3's ^middle subunit232•^0Kung-1 (1.85)2.0/0 Kaphong-1 (2.21)Platong-5^'.96)Platong-1 (NA)Surat-1 Platong-8 (1.28)(NA)Ranong-1 (0.640Yala-2 (1.07)00^5^10 km0 Kaphong-3 (0.65)0 S. Platong-1 (1.12)Pakarang-1 (1.10)°^Pladang-3 (NA)0^ 0Insea-1 (NA)^ 0 S. Platong-2 (NA)00^Trat-1 (0.92)Satun-2 .10)0Satin-1 (1.07)Erawan- 24 (1 .68)Dara-1 2.05)0 Satun-3 (NA)Erawan-12-1(NA)15^'Qs Erawan-12-8 (NA)0Krut-1^Erawan-12-7(1.39)  00^\^Jakrawan-2 (NA)Erawan-K-1 .58)Baanpot-1 0^ unan-10 (1.19)Baanpot-B- (NA)0rawan-1(0.49)0Figure 5.77: Lateral variation of QOM (mg HC/g rock) of unit 3's upper subunit2330^5^10kmYala-2 (1.00)0Kung-1 (1.34)0 S. Platong-1 (1.48)0Insea-1 (NA) . Platong-2 (1.51)0Trat-1 (1.18)Ranong-1 (0.74)00 Kaphong-3 (0.70)0 Kaphong-1 (2.24)Platong-5 0 112)atong-1 (NA)Platong-8 (1.45)00Surat-1(1.39)Er^(1.88)Dara-1 (NA)00 Satun-3 (1.24)(1.21)1.5^ 3.20)2.00Krut-1(2.05)rawan-2 (1.48)0Eraw0x:2^Jakrawan (1.14)0Baanp Funan-10^ (0.91)Baanpot-B-1 (1.41) ,,c?Figure 5.78: Lateral variation of QOM (mg HC/g rock) of unit 2's lower subunit234Ranong-1 (F '•• ^0Platong-8 (1.12)0 Surat-1Yala-2 (NA)0 Kaphong-3 (1.40)Kaphong-1 (1.44)......Platong-5 0^.88)1 .5 o o Platong-1 (1.40)0Satun-1 (1.14)0^5^10km0^(NA)\^Kung-1 (1.27)1.5atong-1 (1.82)Pakaiang-1 (NA)Pladan -3 (1.70ErawData-1 (NA) 0■^o Erawan-12-1° Erawan-12-8 (1.58)0Krut-1 \ Erawan-12-7 (2.43)(NA)^0Erawan-K-1 (NA)Baanpot-1 0 . )0Baanpot-B-1 (1.42)0Insea-1 (NA)0(1.85)12-9 (1.88)0 Satun-3 (1.31)2 (2.03)0Trat-1 (1 .30)an-1(1.52)0Funan-1(1.29)Jakraw -2 (2.21)0Figure 5.79: Lateral variation of QOM (mg HC/g rock) of unit 2's upper subunit235IV OM, Figure 5.39). This subunit contains mainly vitrinite and minor amounts ofliptinite and inertinite. The vitrinite includes eu-ulminite, telocollinite andvitrodetrinite. The liptinite includes liptodetrinite and sporinite; the inertinite groupincludes semifusinite.5.5.2 Unit 5The TOC content of unit 5 ranges from less than 0.10% to about 0.44% (Figure5.52) with an average value of 0.24% (Table 5.4). In general, the TOC content ofthis unit increases from the basin margin toward the basin center (Figure 5.52).The QOM of this unit varies from less than 0.5 mg HC/g rock to more than 5.1 mgHC/g rock (Figure 5.66) with an average value of 1.60 mg HC/g rock (Table 5.4).The organic characteristics of lower and upper subunits are described below.The lower subunit of unit 5 is characterized by generally fine-grained claystone andminor interbeds of sandstone of the nonmarine floodplain deposits. The sedimentsin this subunit are partly oxidized due to their aerial exposure during and afterdeposition. The TOC content of this subunit varies from less than 0.1 % to about0.45% (Figure 5.56) with an average TOC of 0.24% (Table 5.5). The QOM ofthis subunit varies from 0.46 to 5.3 mg HC/g rock (Figure 5.70) with an averageQOM of 1.46 mg HC/g rock (Table 5.5). This subunit contains mainly organicfacies CD and D (Type III and Type IV OM, Figure 5.40). A mixture of organicfacies BC and C (Type II-III OM) occurs in Kung-1 well. The maceralcomposition of this subunit is mainly vitrinite (including telinite, collinite, eu-ulminite, and corpohuminite) and minor liptinite (including cutinite and resinite).236The upper subunit of unit 5 is characterized by a series of fining-upward sequencesof highly oxidized, nonmarine channel-fill and point bar deposits. Its TOC contentranges from less than 0.1 % to about 0.44% (Figure 5.57) with an average TOC of0.25% (Table 5.5). The TOC content generally increases toward the basin center(Figure 5.57). The QOM varies from 0.9 to about 5.3 mg HC/g rock (Figure5.72) with an average QOM of 1.93 mg HC/g rock (Table 5.5). This subunitcontains mainly organic facies C, CD, and D (Type III and Type IV OM, Figure5.41). A single sample in Surat-1 well with a very high HI value (> 600 mg HC/gTOC) may be from drilling mud contamination. The maceral composition of thissubunit is mainly vitrinite (attrinite, collinite, and telocollinite).5.5.3 Unit 4The TOC content of unit 4 ranges from less than 0.1 % at the western margin of thebasin to more than 0.5% at the basin center in the south-central part of the studyarea (Figure 5.53). The QOM varies from 0.36 mg HC/g rock to about 3.7 mgHC/g rock (Figure 5.67) with an average value of 1.44 mg HC/g rock (Table. 5.4).The organic characteristics of each subunit are described below.The lower subunit of unit 4 is characterized by generally fine-grained claystone andsiltstone interbedded with thin sandstone of the prodelta to shallow marine deposits.Its TOC content varies from less than 0.20% at the basin margin to about 0.3 to0.5% toward the basin center (Figure 5.58) with an average TOC content of 0.32%(Table 5.5). The QOM increases from less than 0.5 mg HC/g rock to more than2.0 mg HC/g rock (Figure 5.72) with an average QOM of 1.56 mg HC/g rock(Table 5.5). This subunit contains mainly organic facies CD and D (Type III andType IV OM, Figure 5.42). Vitrinite (collinite) is the main maceral of this subunit.237The middle subunit of unit 4 is characterized by a series of coarsening-upwardsequences representing distributary mouth bar deposits and beach ridge complexes.The TOC content of this subunit increases from less than 0.15% in the northern andwestern parts of the study area to about 0.7% in the southern part (Figure 5.59)with an average TOC of 0.35% (Table 5.5). The QOM, in contrast, increases fromabout 0.6 mg HC/g rock in the south to more than 2.4 mg HC/g rock in thewestern part of the study area (Figure 5.73). The main organic constituents of thissubunit are facies D and CD (Type IV and Type III OM, Figure 5.43). Vitrinites,including collinite and eu-ulminite, are the main macerals in this subunit.The upper subunit of unit 4 is characterized by a series of fining-upward sequencesand interbedded claystones of nonmarine channel and floodplain deposits. TheTOC content generally increases from less than 0.2% in the northern and westernparts of the study area to about 0.7% in the southern and central parts with anaverage value of 0.36% (Figure 5.60). The highest QOM value in the northernpart occurs in Platong-8 well location (3.2 mg HC/g rock) and decreasesnorthwestward to less than 0.3 mg HC/g rock and eastward to about 1.0 mg HC/grock (Figure 5.74). In the south, the QOM generally increases from less than 0.9mg HC/g rock in the basin center to more than 2.4 mg HC/g rock to the west(Figure 5.74). The main organic constituents of this subunit are facies D and CD(Type IV and Type III OM, Figure 5.44). A mixture of organic facies BC and C(Type II OM) is found in Platong-8 and Krut-1 wells. Microscopic analysis ofkerogen shows abundant vitrinite (collinite and telocollinite) and inertinite(fusinite), with minor amounts of sporinite.2385.5.4 Unit 3The TOC content of unit 3 varies from about 0.5% to 0.8% in the west central partof the basin to less than 0.25% toward the west and east (Figure 5.54) with anaverage value of 0.44% (Table 5.5). Its QOM value shows a similar trend to TOC;it is highest (about 2.0 mg HC/g rock) in the south central part of the study areaand decreases to less than 1.0 mg HC/g rock northwestward and to about 0.9 mgHC/g rock eastward (Figure 5.68) with an average value of 1.34 mg HC/g rock(Table 5.5). Organic characteristics of each subunit are described below.The lower subunit of unit 3 is characterized generally by fine-grained, calcareoussediments interbedded with thin, coarse-grained shallow marine deposits. The TOCcontent of this subunit shows a NNW-SSE trend from relatively higher TOC values(about 0.9%) in the west-central part of the study area to lower values bothwestward and eastward to less than 0.2% (Figure 5.61), with an average TOCcontent of 0.44% (Table 5.5). The QOM value of this subunit generally increasesfrom about 0.5 mg HC/g rock in the west to more than 1.8 mg HC/g rock in thecentral part of the study area (Figure 5.75), with an average value of 1.34 mg HC/grock (Table 5.5). The main organic constituents of this subunit are facies CD andD (Type III and Type IV OM, Figure 5.45). The organic facies C and CD (TypeII-III OM) also occur in Erawan-12-8 well location. The kerogen type is dominatedby vitrinites (desmocollinite, eu-ulminite, and collinite) and inertinite(semifusinite), with minor amounts of liptinite (cutinite).The middle subunit of unit 3 is characterized by a series of coarsening-upwardsequences representing distributary mouth bar deposits and beach ridge complexes.239The TOC content is very low (about 0.2%) in the north, and higher (more than0.5%) in the central part of the basin (Figure 5.62). A NW-SE trend of relativelyhigh TOC (0.4 to 0.7%) occurs in the south (Figure 5.62). Overall, the averageTOC content of this subunit is 0.39% (Table 5.5). This unit shows a complexQOM trend especially in the southern part of the study area (Figure 5.76). Ingeneral, however, the QOM values of this subunit range from 0.8 to 2.5 mg HC/grock with an average QOM of 1.31 mg HC/g rock (Table 5.5). The main organicconstituents of this subunit are facies D and CD (Type IV and Type III OM, Figure5.46). A mixture of organic facies C and CD (Type II-III OM) occurs in Erawan-12-8 and Erawan-12-9 well locations. The kerogen types are mainly vitrinites(telinite and collinite) and subordinate liptinites (resinite and cutinite).The upper subunit of unit 3 is characterized by a series of fining-upward sequencesand fine-grained sediments of nonmarine meandering channel and floodplaindeposits. The TOC content of this subunit generally increases toward the east fromabout 0.1 % in the northern and western parts of the study area to about 0.6% in thesoutheastern part (Figure 5.63), with an average TOC content of 0.29% (Table5.5). The QOM varies from less than 0.5 mg HC/g rock to about 2.1 mg HC/grock (Figure 5.77), with an average QOM of 1.28 mg HC/g rock (Table 5.5). Thissubunit consists mainly of organic facies D and CD (Type IV and Type III OM,Figure 5.47). Vitrinites (telocollinite and eu-ulminite) are the main maceralcomponents of this subunit.5.5.5 Unit 2Unit 2 is characterized by two relatively high TOC areas (about 0.8% in thenorthwest and about 0.6% in the east), separated by a NNE-SSW trending low240TOC region (Figure 5.55), with an average TOC of 0.54% (Table 5.4). The QOMvalues range from less than 0.7 mg HC/g rock to more than 2.0 mg HC/g rock(Figure 5.69), with an average QOM of 1.44 mg HC/g rock (Table 5.4). Theorganic characteristics of each subunit are described below.The lower subunit of unit 2 is characterized by a well developed, equally-spacedseries of fining-upward sequences of highly-oxidized, nonmarine meanderingchannel-floodplain deposits. In the northern part of the study area, the lowersubunit is characterized by a NW-SE trending high TOC region (about 0.8 to 1.3%TOC) flanked by low TOC areas (less than 0.3%) in the northeast and southwest(Figure 5.64). Further south, this subunit is characterized by an area of relativelyhigh TOC (0.4-0.5%), flanked by lower TOC areas in the northeast and southwest(Figure 5.64). The average TOC content of the lower subunit is 0.43% (Table5.5). The QOM in the northern part of the study area generally increases from lessthan 1.0 mg HC/g rock in the northwestern basin margin to about 2.2 mg HC/grock in the basin center (Figure 5.78). Further south, a high QOM region (about1.8-3.2 mg HC/g rock) is flanked by low QOM areas (approximately 1.2-1.3 mgHC/g rock) in the east and west Figure 5.78). The average QOM value of thislower subunit of unit 2 is 1.49 mg HC/g rock (Table 5.5). The subunit containsmainly organic facies C, CD, and D (Type Type III OM, and Type IV OM,Figure 5.48). Vitrinite (collinite) is the main maceral component.The upper subunit of unit 2 is characterized by generally fine-grained sediments ofmarsh complexes to marginal marine deposits. The TOC content of this subunitgenerally decreases from more than 0.8% in the west to less than 0.5% toward thebasin center (Figure 5.65) with an average TOC content of 0.81% (Table 5.5).The QOM, similar to that of TOC, generally decreases basinward from about 2.0241mg HC/g rock to less than 1.5 mg HC/g rock (Figure 5.79), with the average QOMof 1.57 mg HC/g rock (Table 5.5). This subunit contains mainly organic facies CD(Type III OM) and a mixture of organic facies C and CD (Type OM, Figure5.49). Microscopic analysis of organic matter shows abundant vitrinites (textiniteand collinite) with minor liptinites (sporinite and cutinite).5.5.6 Unit 1Due to limited information from this unit, maps showing lateral variation of organicmatter of this unit were not made. The average TOC content of this unit is 1.41%and an average QOM value is 1.39 mg HC/g rock (Table 5.4). The organiccharacteristics of each subunit are described below.The lower subunit of unit 1 is characterized by a series of fining-upward sequencesand fine-grained sediments of nonmarine to brackish water, coastal plain deposits.The TOC content ranges from 1.33 to 1.45% with an average TOC of 1.37%(Table 5.5). QOM values vary from 1.20 to 1.66 mg HC/g rock with an averageQOM of 1.49 mg HC/g rock. The main organic constituents of this subunit are amixture of organic facies C and CD (Type II-III OM, Figure 5.50). The dominantmaceral is vitrinites (textinite and collinite), with lesser amounts of liptinite(cutinite) and inertinite (sclerotinite).The middle subunit of unit 1 is characterized generally by fine-grained sedimentsinterbedded with coal stringers representing brackish water interdistributary baydeposition. The TOC of the middle subunit ranges from 0.85 to 2.08%, average1.47% (Table 5.5). The QOM of this subunit varies from 0.96 to 2.04 mg HC/grock with an average QOM of 1.64 mg HC/g rock. This subunit contains mainly242organic facies BC, C and CD (Type II and Type III OM, Figure 5.51). The mainmaceral composition determined from reflected white light examination isdominated by vitrinite (textinite and collinite) with minor amounts of liptinite(cutinite).The upper subunit of unit 1 is characterized by fine-grained sediments of shallowmarine deposition. No samples from this interval are available.5.6 DISCUSSION5.6.1 Origin of Variation in Organic MatterFactors that control the abundance of organic matter in sediments include organicinputs, sedimentation rates, degree of preservation of organic matter afterdeposition, and degree of organic maturation. Depending on the combination ofthese factors, the organic carbon content and characteristics in sediments will varysignificantly. It is very important to note that using any one of the factors may notexclusively explain the variation in organic characteristics in the sediments becauseas one factor changes, other factors might also change. This section documents thesource, character, and factors affecting the distribution of organic matter. In orderto examine the influence of geology on the variation of organic characteristics ofthe Tertiary strata in the Pattani Basin, various diagrams of organic propertiesversus geological factors such as depositional environments, sedimentation rates,and age were prepared.243a. Origin of Organic Matter:The dispersed organic matter in the Tertiary sediments in the Pattani Basin iscomposed mainly of Type III (organic facies C and CD) and Type IV (organicfacies D) kerogen with minor mixtures of Type II and Type III kerogen. Theorganic matter is characterized by relatively low HI and high OI values. Themaceral composition of the organic matter is consistent in all units with vascularplant sources. The dominant maceral component of all studied samples is vitrinite(collinite, eu-ulminite, and textinite) with minor amounts of inertinite (semifusiniteand sclerotinite) and liptinite (sporinite and cutinite).Because most of the Tertiary stratigraphic units in the Pattani Basin were depositedin nonmarine to marginal marine environments, the dispersed organic matter in thesediments was probably of detrital, and continental in origin. The detrital andcontinental origin of the sedimentary organic matter is supported by thepredominant occurrence of Type III-Type IV kerogen, combined with the presenceof vitrinite, liptinite, and especially sporinite and cutinite, which were derived fromvascular plants, accompanied by relatively low HI and high CH values of thekerogen (Tissot and Welte, 1984; Bustin, 1988). The detrital organic matter wassupplied to the depositional sites mainly by the river systems that also fed elasticsediments to the areas and hence was mainly allochthonous. Autochthonous andhypautochthonous origins are also evident from the presence of interbedded coalsand carbonaceous partings in many stratigraphic units.244b. Organic Characteristics and Depositional EnvironmentsVariations of TOC and HI in different stratigraphic units with respect todepositional environments are shown in Figure 5.80.For almost all stratigraphic units, both the TOC and HI increase from high energynonmarine environments to lower energy marginal marine or shallow marineenvironments (Figure 5.80), although the mean TOC contents and HI values differfor different stratigraphic units. The lowest TOC and HI (0.07% and 9 mg HC/gTOC, respectively) occur in high energy, alluvial fan and braided stream depositsof the lower subunit of unit 6. The highest TOC (1.47%) occurs in fine-grainedshallow marine deposits of the middle subunit of unit 1. The highest HI (120-127mg HC/g rock) occurs floodplain deposits in the lower subunit of unit 1 andprodelta to shallow marine deposits of the upper subunit of unit 2 and the middlesubunit of unit 1.The very low TOC of alluvial fan and braided stream sediments of the lowersubunit of unit 6 can be explained by the fact that the subunit consists of coarse-grained sediments deposited in a high energy environment. Under such aerobicpromoting conditions, low quantities of organic input and low degrees ofpreservation resulted. A low organic supply reflects less vegetation hence aminimal source of organic matter for the subunit. Free circulation of watercontaining dissolved oxygen would be common in such an aerobic environment,resulting in intense destruction of organic matter by oxidation.Higher TOC and HI in floodplain deposits may reflect the proximity to swampcomplexes, hence, sources of organic matter. Fine-grained sediments in floodplain2451.50.50.0Unit-6 Unit-5 Unit-4* GUnit:3 Unit-2 UXnit-115012060i— 90EiEE 60I3001^2^3^4^5^ 1^2^3^4^5Depositional environments Depositional environmentsFigure 5.80: Variation of TOC (%) and HI (mg HC/g TOC) v.s. depositional environment ofdifferent stratigraphic units. 1. Alluvial fan and braided stream sediments; 2. Channeldeposits; 3. Floodplain deposits; 4. Distributary mouth bars; 5. shallow marine deposits.(n = 4500).246deposits would further enhance the degree of organic preservation because the fine-grained sediments would quickly form a closed environment. In such confinement,there would be no replenishment of oxygen, anaerobic conditions would be rapidlyestablished, and hence the rate of destruction of organic matter was reduced (Tissotand Welte, 1984).TOC content in river mouth bar deposits and beach complexes in this study is ashigh as that in floodplain deposits. Such a similarity may reflect a balance betweenthe degree of organic preservation and the effect of dilution of mainly allochthonousorganic matter by rapid sedimentation.The highest TOC and HI in this study occur in interdistributary bay and shallowmarine deposits, especially in units 2 and 1. This may be the result of both highorganic input and high degree of organic preservation. High organic input mayreflect the proximity to sources of organic matter such as marsh and peat swampenvironments. A high degree of organic preservation may be the result of the fine-grained nature of the sediments and the transgressive nature of the stratigraphicunits. This would prevent easy circulation of free oxygen, and thus reducingoxidation of organic matter.c. Organic Characteristics and MaturationThe relations of organic maturation with both the abundance and characteristics oforganic matter in sediments can be assessed by comparing maps of TOCdistribution (Figure 5.52 through Figure 5.55) with maps of organic maturation, inthis case, the extent of hydrocarbon generation (Figure 6.41 through Figure 6.44).They can also be noted by plots of TOC and HI versus maturity indices, as247expressed by the extent of hydrocarbon generation and vitrinite reflectance (Figure5.81).The TOC values of most strata do not conform with the isomaturation lines. Ingeneral, there is a weak positive correlation between degree of organic maturationand TOC and HI. Such a weak correlation might be fortuitous, and simply be theresult of natural variations in TOC from place to place within the same stratigraphicunit and variations across the unit. A weak positive correlation between HI anddegree of organic maturation also indicates that the sediments in the deeper, thusmore mature, part of the basin are richer in organic content and pyrolysis yield thanthose in the shallow part.d. Organic Abundance and Sedimentation RateThe variation in TOC with sedimentation rate is shown in Figure 5.82.Sedimentation rates, corrected for sediment compaction, were calculated usinggeohistory analysis described in chapter 4. Relationships between sedimentationrate and organic abundance on the scale of the unit were made because the ageconstraint available did not permit the relation to be lowered to the subunit scale.Except for unit 6 and unit 1, the correlation coefficient between sedimentation rateand TOC is very poor (r2 < 0.10, Figure 5.82). In units 6 and 1, TOC generallydecreases as sedimentation rate increases (Figure 5.82). In general, the TOC versussedimentation rate relationship is poor (Figure 5.82). The sedimentation rate in thestudy area is very high compared to that of marine sedimentation, with thedecompacted sedimentation rate ranging from about 0.02 km/m.y. to more than 0.9km/m.y. (Figure 5.82). High sedimentation rates such as these are a commoncharacteristic of sediments deposited in deltaic environments such as the Tertiary2481.0 1.5Ro (%)25 300.5 200.040^60^80^100Generation ectent (%)0^20• • ••0.6 0.6Unit-6 and Unit-5 Unit-6 and Unit-50.5 ^ 0.5 ^  •  0.4 ^ 0.4 ^7 • •0.3 - 0.3 ^0•o • • ••0.2 - • 0.2 ^ •0.1 ^•  0.1 ^• •• •0.020^40^60^80^100Generation extent (%)^U^  ^a  e^a^ ^a ^1 o -  - a    • Unit-2 and Unit-1•      ^  IL  al ^ •  •20^40-^60Generation extent (%)80^100^0.50 0^0.3^0.6^0.9^1.2^1.5^1.8Re (%)Figure 5.81: Variation of TOC v.s. degree of organic maturation of different stratigraphic units0.5 -01.00.87 0.60.40.20.03.02.53.025ao1.51.0Unit-4 and Unit-3• •  • asaw^ • •    usviUAs •••- a•• Unit-2 and Unit-1249Unit12 end Unit-1■ ■■• • •00 0.3^0.6^0.9^1.2^1.5^1 8150y▪ 100 NE ^a ^di II• 1r ■^■■^•^■ •Unit-2 and Wnit-1^■20^40^60•■ ■■^■ ■• ■^M-ao^100200 200150 ^ Unit-6 and Unit-5 •150 ^Unit-6 and Unit-5• ■■ ■■ ■■^•2 100 ^ y 100 ^■ ■■■ • ■ ■■T  ■^■50 ^ so • A. ■ •■ ■0 00 20 40^60^80 100 0.5^1.0^1.5^20 Z5 300.0Generation octant (%) Ro (%)200Unit-4 and Unit-3 Unit-4 and Unit-3150 ^ ■  150 ^Era •FI ■■ ■ •• ■^■ ■ ■100 --•^■ ■■ ^111 ^   ^ ^ g 100 ^  %^am ■NZ■•• ■^■ ill• ■ ■ iv '^■■ ■ ■so50UM• , • • 1 W ••■ • ■■ ■■20^ao^60^80^100Genefation anent (%)■00^0.5^1.0^1.5^2.0^2.5^30Ro (%)Genendion octant (%)^ Ro (%)Figure 5.81 (Continued): Variation of HI v.s. degree of organic maturation of differentstratigraphic units250•■ ■■■•■■■■0.400.10^0.20^0.30Decompected sedimentation rate (Iogry)■ Unit-20.000.07^0.00^0.05^0.10^0.15^0.20^0.25^0.30^aasDecompected sedimentation rate (lonimy)1.000.800.600.400.200.00  ^0.600.00^0.20^0.40^0.60^0.80 0.00^0.10^0.11^0.12^0.13Deoompated sedimentation rate (ionirry) Decompacted sedimentation rate (lon^ny)0.500.400.300.200.100.000.02^0.03^0.04^005^0.06Decompacted sedimentation rate (IcYmy)0.000.000.14Figure 5.82: Variation of TOC (%) v.s. sedimentation rate (km/my) of different stratigraphic units0.700.600.507 0.400 0.300.200.10o.00a 00^0.20^0.40^0.60^0.80Deconvected sedimentation rate (la^na)1.000.350.300.250.200 0.150.100.051.000.807 0.600.400.202.202001.801.601.401.201.000.80■• • ■me   • • mil' •■■^  ■ ■■•Unit-3^■^■HIMIL ▪ •^-111^ ■ ▪ •   g11(251Unit-1■•■■ ■■■• ■200■■ •1 50• 100500.00 0.10^0.20^0.30^0.40Deconpaoted sedimentation rate (Icr^my)0.800.20^0.40^0.60Ceoompened sedimentation one Nye*•■■ ■0.03^0.04^aos^aosDeo:ape:trod sedimentation rate (Iari/my)•o aoo^0.05^0.10^0.15^0.20^025^0.30Decornpected sedimentation rate (Ion/my)150100035■200150 ^■ Wnit-2N g.• •g 100 ^• • ■  ■ ■•50 ^• 11 ^Figure 5.82 (Continued): Variation of HI (mg HC/g TOC) v.s. sedimentation rate (km/my) ofdifferent stratigraphic units0.00^0.20^0.40^060^0.80^1.00Decompected sedimentation rate (lm/my)sit■ ■• Unit-415010050150g 100^L..^0.10^all 0.12^0.13^0.14Decompacted sedimentation rate (IcrWmy) Unit-5•0.09Unit-3■^ILA^•■^  r^• •■ ■ ■ • is•252Niger Delta, where the undecompacted sedimentation rate ranges between 0.07-0.70 km/m.y. (Bustin, 1988).The relationship between sedimentation rates and TOC has been studied by variousauthors. Toth and Lerman (1977) and Muller and Suess (1979) suggested that inareas of mainly primary autochthonous production, organic matter content generallyincreases with sedimentation rate due to rapid burial. Ibach (1982) carried out thestudy on DSDP cores of ancient marine sediments, and suggested that at slowsedimentation rates, TOC content increases with sedimentation rate due to greaterpreservation of organic matter with more rapid burial which prevents oxidation.Above a critical sedimentation rate (0.021 km/m.y. for siliceous sediments and0.041 km/m.y. for black shale), the TOC content decreases with increasingsedimentation rate due to dilution by mineral matter. The relationship betweenallochthonous organic matter and sedimentation rate was documented, thoughindirectly, by both Meybeck (1982) and Bustin (1988). Meybeck (1982) studied thetotal organic carbon transport in rivers, and pointed out that, although the totalparticulate organic carbon content increases with river discharge, total suspendedmatter concentration increases more rapidly with increasing discharge. This resultsin an absolute increase in TOC, but a decrease in TOC content relative to thevolume of sediment transported. Bustin (1988), based on his study on the dispersedorganic matter in the Niger Delta, suggested, in the semi-quantitative terms, thatTOC content decreases with increasing sedimentation rate due to increased dilutionby mineral matter.Compared to the study of other ancient marine sediments, the sedimentation rate ofTertiary sediments in the Pattani Basin is much higher than the criticalsedimentation rates proposed by Ibach (1982). The TOC of Tertiary sediments in253the Pattani basin, except for unit 1, is very low (less than 1.0%, Figure 5.82). Forthose units with low TOC, there is no correlation between sedimentation rate andTOC. Such results indicate that in the units with low TOC, indigenous variation ofTOC within the sediments has greater effect on TOC than the sedimentation rate.By contrast, in the unit with high TOC (more than 0.6-2.2%, unit 1), there is astrong negative correlation between TOC and sedimentation rate. Such a resultsuggests that in organic-rich sediments, sedimentation rate has greater control onTOC. A decrease in TOC with increasing sedimentation rate in unit 1 may be theresult of clastic dilution of the organic input.e. Organic Abundance and AgeThe variation in abundance and characteristics of organic matter in the Pattani Basinis closely correlated with the age of strata. Younger strata have higher TOC andgenerally higher HI (Figure 5.83) and the increases occur in almost all sedimentaryfacies (Figure 5.80). The variation of TOC and HI with age is greater than thevariation within strata of the same age but among different sedimentary facies(Figure 5.80). The strong correlation between the age of strata and TOC and HImust be an indication of: (1) factors controlling either the relative availability oforganic matter, such as organic supply, or the preservation of organic matter, suchas sedimentation rate, organic maturation or both such as depositional environment;(2) changes in main plant types; and (3) changes in paleoclimate.The fact that there is no significant correlation between organic maturation and theabundance of organic matter in sediments suggests that an increase in TOC contentin younger strata cannot be accounted for by the decreasing degree of organicmaturation of younger strata. Figure 5.84 shows the variation in mean254200150C.-i0i-cn2 100cneI500-40^-30^-20^-10Age (Ma)02.01.50.50.0-40^-30^-20^-10Age (Ma)0Figure 5.83: Variation of TOC (%) and HI (mg HC/g TOC) v.s. age (n = 4500)255TOC Sedimentation rateO^__,__0C1 0.3Ea)f.z..c 0.20ta)Ei-5 0.1u")0.0Age (Ma)Figure 5.82: Variation of sedimentation rate and TOC with age0.4-40^-20-30 -1 0 0 00.41.21.6256sedimentation rates and mean TOC for strata of different ages. It can be seen thatalthough the mean TOC contents increase in younger strata, the sedimentation ratevaries considerably with age. This relationship suggests that, for nonmarine anddeltaic deposits in general, sedimentation rate cannot be used exclusively to predictorganic abundance in sediments.The increase in TOC and HI contents in younger strata may, in part, be related toorganic preservation. The sedimentary environment in the study area has evolvedfrom totally nonmarine (units 6 and 5) to regressive sequences (units 4 and 3) andfinally to transgressive sequences (unit 2 and 1). If the production of organicmatter remained constant throughout the Tertiary, the TOC in sediments woulddepend upon the ability of a depositional site to preserve it. In nonmarineconditions, organic matter is unstable and quickly oxidized and decomposedbecause of aerial exposure. Low TOC values found in units 6 and 5 are the resultof such a highly oxidizing condition. In the case of regressive units 4 and 3, of allthe organic matter deposited, only that in the prodelta and shallow marine sedimentsin the lower subunits was relatively better preserved. These were least aeriallyexposed, thus subjected to less oxidation and less destruction. In contrast, theorganic matter mainly deposited in nonmarine sediments in the higher subunits, wasmainly oxidized from aerial exposure. The highest TOC's were found intransgressive sequences (units 2 and 1), probably reflecting higher degrees ofpreservation, resulting from the fine-grained nature of sediments, and thesubsequent transgression which prohibited, or at least reduced, oxidation. Theother important aspect of depositional environments on the abundance of organicmatter in sediments is the relative distance from sources. Greater proximity to asource of organic matter such as marsh and peat swamp complexes of the middleand upper subunits of units 2 and 1 may have resulted in higher autochthonous257organic input into these two youngest strata, thereby contributing to the higher TOCcontents.The increase in TOC and HI in younger strata in the Pattani Basin may, therefore,suggest that younger strata have more favorable depositional environments fororganic input and preservation.Other contributors to the progressive change in TOC with time include variations inthe paleoclimate and changes in plant types. During the Tertiary, the flora evolvedand the availability and type of organic matter probably changed. The progressiveevolution of mangrove flora is marked by the disappearance of the Pinus sp. andthe appearance of Rhyzophora sp. during the Early Miocene, and the appearance ofNypa sp. in the Late Miocene. Significant climate changes in Thailand during theTertiary have not been documented, however, the appearance of Nypa-type pollenhas been considered the result of more seasonal climate and increasing temperatures(Germeraad et al., 1968). The consequence of factors such as the evolution ofmangrove flora and minor paleoclimate fluctuations that may have occurred remainslargely unknown. Such factors probably did not play an important role indetermining TOC content independent of depositional environment and/orsedimentation rate.f. DiscussionOf all the parameters influencing the abundance and types of the organic matter inthe study area, the most prominent parameter is depositional environment. Hence,changes in organic characteristics both within and across the stratigraphic units aremainly the result of changes in depositional environments. Within the stratigraphic258units, the abundance of organic matter generally increases from high energynonmarine to low energy marine subunits. Across the stratigraphic units, anincrease in TOC and HI values in progressively younger strata also reflects the shiftfrom high energy nonmarine environment to low energy marine environments.Effects of sedimentation rate and the degree of organic maturation on organiccharacteristics in the study area is not distinct. Such an ambiguous result,especially in the units with low TOC, may be the result of original variation ofTOC within the sediments rather than the effect of sedimentation rate or the degreeof organic maturation.5.6.2 Source Rock ConsiderationsThe general evaluation of hydrocarbon potential in the Tertiary strata in the PattaniBasin, in terms of maturation history, tectonic history, and possible trap formation,is discussed in chapters 4 and 6. This section will focus on the hydrocarbon sourcequality of the sediments available for analysis.Lateral distributions of QOM of different stratigraphic units and subunits are shownin Figure 5.66 through Figure 5.79. Figure 5.85 shows the variations ofhydrocarbon potential (or Genetic Potential, S 1 +S2) and QOM (quality of organicmatter, S 1 +S2/TOC) for different strata of different ages. The variations of geneticpotential values in the stratigraphic units 6, 5, 4, and 3 are very similar to eachother, varying from less than 0.1 to 1.5 mg HC/g rock with an average value ofapproximately 0.5 mg HC/g rock. Unit 2 shows higher genetic potential whichranges from 0.1 to 2.8 mg HC/g rock with an average value of 0.8 mg HC/g rock.The highest genetic potential value in the study area occurs in stratigraphic unit 1,2595.0 6.05.04.0rn0, 3.0C 3.0E2n 2.0aL0a 1.01.00.0-40 -10-3000 2.0■■■■■U■■UIU ■-30^-20^-10Age (Ma)C5-o 4.0rn-20Age (Ma)■•U•■^■Figure 5.85: Variation of Genetic potential (mg HC/g rock) and QOM (mg HC/g TOC) v.s. age(n = 4500)260ranging from 0.8 to 4.3 mg HC/g rock with an average value of 2.2 mg HC/grock.While the genetic potential of the Tertiary strata in the Pattani Basin increases inyounger strata, the QOM variation shows a minor decreasing trend toward youngerrocks, from 1.6 mg HC/g rock in unit 6 to 1.4 mg HC/g rock in unit 1 (Figure5 . 85).It is evident that all stratigraphic units, except unit 1, which is immature withrespect to the oil generation window, have very low hydrocarbon source potentialsas measured by pyrolysis. Synrift sediments (units 6, 5, and 4) and early post-riftsediments (unit 3) contain very low TOC (less than 0.4%), very low HI (between80-90 mg HC/g TOC), very low genetic potential (less than 0.5 mg HC/g rock),and low QOM (between 1.3 to 1.6 mg HC/g rock). Based on a conventionaldefinition of hydrocarbon source rocks (Tissot and Welte, 1984; Waples, 1985),these sediments cannot be considered as source rocks at all. Although Unit 2 hasTOC of 0.5% and HI of 100 mg HC/g TOC, it also has very low genetic potential(about 0.8 mg HC/g rock) and low QOM (1.4 mg HC/g rock). Unit 1, on theother hand, has the highest hydrocarbon source potential with TOC content of1.4%, HI value of 122 mg HC/g TOC, genetic potential of 2.2 mg HC/g rock, andQOM of 1.4 mg HC/g rock. This unit is immature relative to the oil generationwindow. The variation in HI, genetic potential, and QOM values of all samples inthe study area may represent variations in source rock quality, but may also be dueto the mineral matrix absorption effect (Espitalie et al., 1985). The mineral matrixabsorption effect results in the suppression of the pyrolysis yield, particularly insamples with low TOC (less than 2-3%) and high clay content. Such a condition isgenerally the case for Tertiary sediments in the study area.261The fact that the Pattani Basin is a producing basin suggests that: either sourcerocks have been very effective at an overall lower organic matter quality thangenerally considered necessary; or higher quality source rocks, possibly at depths,and have not been reached by drilling, are present in the basin; or a combination ofboth factors. The potential source rocks in the Pattani Basin, despite their very lowoil generating potential, may represent an enormous volume of low quality sourcebeds, which together with interbedded sandstones throughout the succession, wouldfunction as highly effective carrier beds during migration. In addition, the rapidsubsidence rate and high heat flow, resulting in rapid hydrocarbon generation, mayalso have facilitated creating commercial hydrocarbon accumulations. Suchconditions are not unique. Bustin (1988) studied the source rock characteristics ofthe Niger Delta sediments and suggested that despite very low oil generatingpotential of the source rocks, a combination of favorable intercalation of sourcebeds and carrier beds which provides excellent drainage for hydrocarbon migration,together with the rapid rate of maturation, may have helped in creating commercialoil accumulations. The synrift and possibly post-rift lacustrine deposits, whichwidely occur in other Tertiary basins in Thailand, are believed to occur in thecenter of the Pattani Basin as well (Gibling, 1988; Burri, 1989; Chinbunchorn etal., 1989). These lacustrine sediments may possibly be the source rockscontributing a major part of hydrocarbons to the commercial gas fields.5.7 SUMMARY AND CONCLUSIONSThe dispersed organic matter in Tertiary strata in the Pattani Basin is composedmainly of Type III (organic facies CD) and Type IV (organic facies D) kerogenwith minor amounts of mixed Type II and Type III (organic facies C and CD)262kerogen. Because of the nonmarine and marginal marine nature of the sediments,the presence of low HI and high OI values, and the types of organic matter(primarily vitrinite), the organic matter found in these sediments is interpreted to bepredominantly of detrital and continental origin.The variation of organic characteristics of the sediments occurs both within andacross the stratigraphic units. Within each stratigraphic unit, the lowest TOC andHI values occur in the high energy nonmarine deposits such as alluvial fan andbraided stream deposits in unit 6, whereas low energy deposits such as floodplaindeposits of unit 6 normally contain higher TOC and HI values. The increase inTOC content and HI value in the sediments also occurs from nonmarine floodplaindeposits to shallow marine and interdistributary bay deposits. Across thestratigraphic units, TOC and HI generally increase in progressively younger strata.The abundance of organic matter within the sediments is the combined result oforganic input into the sediments plus the degree of organic preservation. HigherTOC and HI values in floodplain deposits, for example, may reflect proximity toswamp complexes, thus, sources of organic matter. Fine-grained sediments furtherenhance the degree of organic preservation by the rapid development of ananaerobic condition within the sediment column which reduces oxidation, hencedestruction, of organic matter. The variation of abundance and characteristics oforganic matter in the sediments both across and within the stratigraphic units is,therefore, controlled, in large part, by the depositional environments within whichthe organic matter was deposited.A weak positive correlation between TOC and HI and degree of organic maturationin the study area may reflect the natural variation in TOC from place to place263within the same stratigraphic unit and across the units rather than a true relationshipbetween TOC and HI and maturation.The general increase in TOC in progressively younger strata may reflect morefavorable sedimentary facies for organic matter of younger strata. No significantcorrelation occurs between maturity parameters, such as the extent of hydrocarbongeneration and vitrinite reflectance, nor the abundance and type of organic matter.The sedimentation rate, corrected for compaction, of the Tertiary strata in thePattani Basin varies from 0.02 km/m.y. to more than 0.9 km/m.y. Such a highsedimentation rate is quite common in the Tertiary deltaic deposits such as theNiger Delta (Bustin, 1988), and it is considerably higher than the sedimentation rateof ancient marine sediments (Ibach, 1982). A very weak correlation between TOCand sedimentation rate in all units, except unit 1, is the result of variable TOCwithin and across the units. A negative correlation between TOC and sedimentationrate in unit 1 may be the result of elastic dilution of the organic input. It is,however, important to point out that to use the sedimentation rate alone to predictthe organic abundance might be misleading. Other factors, such as the types ofplant and/or animal organic; the proximity to sources of organic matter; and thedepositional environments can also have influence on the organic input andpreservation, hence, the abundance of organic matter in the sediments.Source rocks of the Tertiary strata in the Pattani Basin represent an end member interms of source rock composition and properties. The source rocks contains mainlyType III, Type IV and a relatively small amount of Type II kerogens, and havevery low hydrocarbon potential as defined by pyrolysis (Tissot and Welte, 1984).The presence of numbers of commercial gas fields suggests that either the source264rocks here, despite very low genetic potential, have been very effective inproducing, migrating, and accumulating the hydrocarbon or the presence of higherquality source rocks within the basin which have not been reached by drilling, or acombination of both factors.2656. ORGANIC MATURATION ANDHYDROCARBON GENERATION6.1 ABSTRACTThe kinetic parameters of potential source rocks and the extent and timing ofhydrocarbon generation in Tertiary strata in the Pattani Basin have beeninvestigated. Kinetic parameters of source rocks were determined from Rock-Evalanalyses of whole rock samples or kerogens at multiple heating rates using a linearregression technique based on the assumption of a Gaussian distribution ofactivation energies with some mean value (E0) and standard deviation (crE). Theextent and timing of hydrocarbon generation were predicted using a chemicalkinetic model proposed by Sweeney and Burnham (1990), based on known burialand thermal histories, and kinetic properties of the stratigraphic units.The mean activation energies of the source rocks in the Pattani Basin, ranging from46 to 61 kcal/mol, coincide generally well with the activation energies required tobreak down carbon-oxygen and carbon-carbon bonds (40 to 70 kcal/mol). Thedispersion of activation energies ranges from 0.26 to 9.30% of the mean value (E 0).The kinetic parameters derived from kerogen samples are not much different fromthose derived from whole rock samples of the same sediments. Such results suggestthat, at least for sediments with high TOC, either whole rock samples or kerogenscan be used to determine the kinetic parameters of the source rocks. Fororganically lean sediments, whole rock samples should be used to modelhydrocarbon generation because the effect of matrix adsorption may becomesignificant. Notable variation of activation energies within the same type ofkerogen in all samples may reflect the variability of chemical composition of266kerogen. It, therefore, cannot be assumed that activation energies depend only onkerogen type.Depositional environments seem to have no influence on the value of meanactivation energies (E0) but show a weak influence on their dispersion (o-E). Largedispersions of activation energies (°E) correspond to high energy sediments,whereas low dispersions (o-E) correspond to low energy sediments. Such resultssuggest that depositional environment may have an effect, at least in part, on aredistribution and the oxidation of organic matter and the variation of its activationenergy dispersion (o-E) within sediments. A weak correlation occurs betweenkinetic parameters (mean activation energies and their dispersion) and the degree ofthermal maturation. This correlation may reflect the original variation of kineticproperties of organic matter rather than the effect of maturation. By using adistribution of activation energies, kinetic parameters of organic matter areindependent of degree of organic maturation.Most of the stratigraphic units in the Pattani Basin, except that of the youngest unit(unit 1), are either mature or overmature with respect to the oil window. The mainphase of hydrocarbon generation began at about 33-35 Ma and has continued to thepresent. A relatively early generation (about 5-7 m.y. after deposition) is attributedto the area's high geothermal gradients and rapid sedimentation-hence high heatingrate for the sediments. Low mean activation energy in some stratigraphic units alsoenhanced early generation.The presence of good, although laterally discontinuous, reservoir rocks, theadjacent occurrences of source and reservoir rocks, and the structural and267stratigraphic traps in the study area are the key factors that made the Pattani Basin aprolific hydrocarbon basin.6.2 INTRODUCTIONKnowledge of the degree and timing of maturation of organic matter is important inhydrocarbon exploration. In particular, modelling of organic maturation historyprovides details on the timing of hydrocarbon generation relative to the tectonicevolution of a sedimentary succession. In the Pattani Basin, Gulf of Thailand(Figure 6.1), a thick succession of Tertiary strata is preserved (Figure 6.2 throughFigure 6.7). The succession was penetrated and studied by exploration wells andby geophysical surveys. No equivalent sequences crop out onshore. Although thearea has been active in terms of hydrocarbon exploration and production since1970's, there is very limited documentation in terms of the degree of organicmaturation or timing of hydrocarbon generation (Lian and Bradley, 1986;Achalabhuti and Oudom-Ugsorn, 1978; Chinbunchorn et al., 1989). The presentinvestigation is one of the first attempts to determine the extent and history oforganic maturation as well as hydrocarbon generation in this area.In this study, a chemical kinetic model is used to predict the degree of organicmaturation and the extent and timing of hydrocarbon generation. The inputinformation needed for the model includes burial and thermal histories of thesedimentary successions, and the chemical kinetic properties of the included organicmatter. Burial history of any stratigraphic layer within a sedimentary basin,corrected for compaction, can be acquired by backstripping analysis of the welldata. Because thermal history and paleotemperatures are controlled by the basalheat flow history, which in turn reflects the lithospheric mechanics and heat268Platong-1Pla • ng-8Ranong-1Yala-2 0^5^10kman-12-1Erawan-12Baanpot-1Baanpot-B-1Figure 6.1: Location of well data used in this study. Numbers in the box indicate thecross sections shown in Figures 6.2 through 6.7269...-a INSEA-1 SOUTH PLATONG-2^TRAT-1PAKARANG-1 PLADANG-3SECTION-IFigure 62: Stratigraphic section-1 W-E direction. See Figure 6.1 for the location of the section.0• WATER COLUMN 0 UNIT-1 0 UNIT-2 IN UNIT-3 UNIT-4 0 UN1T-6 0 UNIT-0-1...-2.3-4-5 RANONG-1KUNG-1 SURAT-1 PLATONG-8^ PLATONG-1SECTION-20-28...... ^ .^ .................................................................................... •............. • ...........^......• WATER COLUMMO UNIT-10 UNIT-2N UNIT-3D UNIT-40 UNIT-50 UNIT-0 ...... •^...^..... • ....^..Figure 6.3: Stratigraphic section-2 W-E direction. See Figure 6.1 for the location of the section.2700-2-8a.8-10 • WATER COLUMN 0 umr.1 0 UNIT-2• UNIT4 0 UNIT-4 0 UNIT-8 0 UNIT-SKRUT-1 ERAWAN-K-1 BAANROT-1 BMNPOT-B-1 JAKRAWAN-1^FUNAN-1SECTION-3• , = =, -• •^..0-2....................^.....^. ........... ...8• WATER COLUMN 0 UNIT-1 El UNIT-2 • UNIT-3 0 UNIT4 0 UNIT4 C3 UNIT-21ERAWAN-12-1 ERAWAN-12-8 SATUN-3^ JAKRAWAN-2-8 DARA-1Figure 8.4: Stratigraphic section-3 W-E direction. See Figure 8.1 for the location of the section.SECTION-4Figure 8.5: Stratigraphic section-4 W-E direction. See Figure 8.1 for the location of the section.271BAANPOT-1^E3AANPOT-B-1ERAWAN-12-1^ERAWAN-12-8^ERAWAN-12-7^ERAWAN-K-1SATUN-1 ERAWAN-12-0PLATONG-5^PLATONG-1^SOUTH PLATONG-1^PLADANG-3^SATUN-2^SATUN-1YALA-2 KAPHONG-3 KAPHONG-1SECTION-5..................^............^ .............. ............... ......... .......0-2........-8.......^• •..................^•^.-a■ WATER COLUMN^0 UNT-2■ UNIT-3 ■ UNIT-4 0 UNTd 0 UNT-6-10Figure 6.6: Stratigraphic section-6 N-S direction. See Figure 6.1 for the location of the sectionSECTION-6Figure 6.7: Stratigraphic section-6 N-S direction. See Figure 6.1 for the location of the section0-2 .................................................................-4 .......w -60-8■ WATER COWAN^0 UNIT-1 0 UNIT-2-10 ■ UNIT-3^sp UNIT-4^0 UNIT-5 0 UNT-6......................... .................... ..........................^..............generation from radioactive sources within the earth's crust (McKenzie, 1978;Allen and Allen, 1990), thermal history of a rifted intracratonic basin formed bylithospheric stretching can be estimated from the amount of crustal and subcrustallithospheric stretching ((3 and 5 factors respectively; Hellinger and Sclater, 1983).Thermal history of the Tertiary strata in the Pattani Basin is estimated using anonuniform lithospheric stretching model described in chapter 4.6.3 METHODS OF STUDY6.3.1 Kinetics and Organic Maturation ModellingHydrocarbon generation, organic maturation as well as other chemical reactions ofnatural materials are rate-controlled, thermocatalytic processes. These processesare essentially controlled by a time-temperature relationship. The simplest form ofthe chemical kinetics is a first order reaction, where the instantaneous rate ofconversion of component x to component y is proportional to the amount of thereactant x as follows (Lerche, 1990; Sweeney, 1990):dx dy =– — = —dt k^T'x (6.1)The dependence of chemical reaction rates upon temperature, km , is commonlyexpressed by the Arrhenius equation (Waples, 1985; Allen and Allen, 1990):k = Ae E°IRT^ (6.2)273Where k is the reaction rate, A is a pre-exponential factor (it is the maximum valuethat can be reached by k when given an infinite temperature, sec -1), Ea is theactivation energy of the reaction (it is the energy barrier over which molecules mustpass before a chemical reaction can occur, kcal/mol), R is the universal gas constant(1.987 cal/mol K-'), and T is the absolute temperature (K).Once the kinetic parameters and thermal history of a sedimentary succession havebeen determined, the extent of reaction is determined by integrating equation (6.1)over the temperature range expressed by thermal history. Lopatin (1971) andWaples (1980) proposed the rule-of-thumb estimate for hydrocarbon maturity usingthe time-temperature index (171) based on the assumption that the reaction rate ofkerogen maturation doubles with every 10°C increase.A single first order reaction described in equation 6.2 is sufficient for the chemicalreaction involving a single component. Kerogen is, however, a mixture of complexorganic and inorganic components. The evolution of kerogen during maturationincludes a complex set of chemical reactions such as progressive elimination offunctional groups and of the linkages between nuclei. A wide range of compoundsis formed during the thermal evolution of organic matter, including water, carbondioxide, medium to low molecular weight hydrocarbons, etc. Hence a single firstorder reaction is insufficient to describe the variety of complex chemical processesoccurring over a wide range of temperatures during organic maturation. Juntgenand Klein (1975), Burnham and Sweeney (1989), and Sweeney (1990) have pointedout that hydrocarbon generation involves the simultaneous occurrences of manydistinct chemical reactions, and that the overall rate of hydrocarbon generationshould depend upon the sum of the rates of all simultaneous reactions that producehydrocarbon molecules. Braun and Burnham (1987), Sweeney et al. (1987), and274Burnham et al. (1987) proposed that the hydrocarbon generation reaction kineticscan be better described in terms of a distributed activation energies model, in whichthere is an infinite number of channels for hydrocarbon production, but with anenergy weighting per channel. For the ith component of the reaction with a time-dependent temperature To, the extent of the reaction can be calculated as (Sweeneyand Burnham, 1990):, = —x, A exp[—E, / RT() ]dtanddx^dx,dt^dtThe amount of unconverted organic matter remaining in the ith reaction is describedby:,^_^ (6.5)0and the fraction of reactant converted (oil generated, if oil generation kinetics areused) is (Sweeney, 1990):F= 1— = 1 —xo(6.3)(6.4)(6.6)275Where x0  is the initial concentration of component i, x0 is the initial concentrationof the total reactant, and fi values are the stoichiometric, or weighting, coefficientsfor the simultaneous reaction components.The amount of reactant converted (F) can be calculated by dividing the time-temperature history into a series of constant heating rate segments (Braun andBurnham, 1987; Sweeney, 1990; Sweeney and Burnham, 1990). Hi is a heatingrate between times j and j-/ as:(T — TH = ^ti-1/The extent of reaction of the ith component at time j is:x. = 1— exp(—x0,Where(6.7)(6.8)(6.9)and276I. = Ti A exp(--L-)RTi 1 2^ +b,( El. ) +b2RT.^RT.(6.10)Where al = 2.334733, a2 = 0.250621, b1 = 3.330657, and b2 = 1.681534 (Braunand Burnham, 1987; Sweeney, 1990; Sweeney and Burnham, 1990).Provided that the activation energy distributions are known, the technique describedabove can be used to calculated the extent of reaction of any chemicaltransformation. An organic maturation program used to predict the extent ofhydrocarbon generation and vitrinite reflectance of a sedimentary layer is includedin a computer disk at the end of this thesis. Appendix B describes how to run theprogram.6.3.2 Determination of Kinetic ParametersAlthough the concept that petroleum generation as a kinetic process is wellestablished (Juntgen and Klein, 1975; Tissot and Welte, 1984), determining kineticparameters for quantitative prediction has been elusive because of the complexity ofboth the maturation processes and organic matter precursors. It is often found thatfitting a single first order reaction to experimental data gives an activation energymuch smaller than can be attributed to a chemical reaction (Connan, 1974; Waples,1985). Braun and Burnham (1987) have shown that the presence of a distributionof activation energies caused the effective activation energy, or Waples' (1985)277"pseudo-activation energy", determined by simple kinetic analysis to be much lowerthan the true average value, and that ignoring even a small distribution would causeproblems in extrapolating the reaction rate obtained from the laboratoryenvironment to the geologic temperatures.The actual distributed activation energy parameters can be determined by usingnonlinear regression to decouple the effects of time and temperature over the wholeextent of the reaction. Because of the large amount of computation power requiredto determine the distributed activation energy parameters using multiple nonlinearregression, Braun and Burnham (1987) proposed a simpler technique using linearregression based on the assumption of a simple Gaussian distribution of theactivation energies with some mean value (E0) and a standard deviation (o-E). Braunand Burnham (1987) further showed that a very good agreement occurred betweenthe kinetic parameters determined by multiple nonlinear regression and thosedetermined by linear approximation.For a single first order reaction, the kinetic parameters E0 and A can be determinedfrom a shift in T x with heating rate (Van Heek et al., 1968). T x is thetemperature at which the maximum amount of hydrocarbons is generated duringpyrolysis. Thus, from the linear plots of ln(1-1, / Tr,;ax ) versus 1000 / T, in Figure6.8, Eo can be obtained from the slope and A from the intercept using equation:E0  +in (AR)7:,21 a x^RT^E,(6.11)2781.4^1.6^1.8^2.0^2.2^2.4^261000/Tmax (/K)Figure 6.8: Shift of Tmax with heating rate used to determine values of Eo (fromslope) and A (from the intercept) for different values of •gE (After Braun& Burnham, 1987)16CIE (% of Eo200^300^400^500^600^700Temperature (°C)Figure 6.9: Reaction rate profiles generated at a heating rate of 10 °C/Minby using a distribution of activation energies, Eo = 52.44 kcal/mol andcrE = 0-16 % of Eo (After Braun & Burnham, 1987)279As shown in Figure 6.8, even for a wide dispersion of activation energies (o-E), thelinear regression technique, assuming a Gaussian distribution of activation energiesoutlined above, is a good method for determining E0 and an approximate value ofA. This technique is consistent with the fact that the activation energy distributionbroadens the reaction profile without substantially shifting T (Figure 6.9; Braunand Burnham, 1987). An approximate value of oE can be determined from the ratioAT, / AT of the temperature width of the reaction rate profile (AT„, measured fromRock-Eval analysis pyrogram) to that calculated from the linear regressionparameters (AT). AT„ is directly obtained from the measured reaction rate profile(full width at half-height). The so called "full width at half-height" of thetemperature is determined from measuring, from the Rock-Eval pyrolysis rateprofile, the difference in temperature at half the maximum rate of hydrocarbongeneration during pyrolysis. AT can be calculated from the simple kineticparameters (E0 and A) determined in the first step. That is, TmaX when crE =0 mustfirst be calculated from:In I/4o^E0 = 0ART: RTn. (6.12)Then AT, can be calculated from the approximate rate equation by iterative solutionfor two values of T on both sides of the T in the reaction profile at whichdr (Braun and Burnham, 1987) where:dt = a5(—d t)T280dx A exp[ —E, exprE0)  ART 2](it^RT^RT ) H,,E, (6.13)Then the value of 0E can be calculated from (Braun and Burnham, 1987):^1.1^0.66crE =^3 ^30 + 2. 8 8p — 1.12P P (6.14)Where(52.4) 2 (AT,)P=E,^AT (6.15)The accurate value of A corrected for the effect of dispersion (aE) can be calculatedfrom the equation: A= Aapprox 1 — 0.4 1— exp 2.5 (6.16)The relationship of AT, / ET and aE depends on heating rate, but the dependence isrelatively small over the range of most laboratory experiments (Braun andBurnham, 1987). A Lotus 1-2-3 template file, Eo.wkl, using a linearregression/correlation approach delineated above to determine the kineticparameters (E0, A, and o-E) from Rock-Eval analyses of a potential source rock isincluded in a computer disk at the end of this thesis. Appendix C describes how torun the program.2816.4 SUMMARY OF TERTIARY STRATIGRAPHY ANDORGANIC CHARACTERISTICS IN THE PATTANI BASINThis section comprises a review of stratigraphy and organic characteristics of theTertiary sediments in the Pattani Basin. Detailed descriptions of the stratigraphyand organic characteristics of these sediments are given in chapters 3 and 5,respectively.The stratigraphic and structural evolution of the Pattani Basin reflects the rifting ofthe Continental Southeast Asia during Tertiary. The geodynamic model for theformation of the Pattani Basin involves stretching of the continental lithosphere andcrustal thinning, with an initial phase of rapid, fault-controlled subsidence, followedby a subsequent phase of slow, post-rift, thermal subsidence. The rifting phase,which lasted about 20 m.y. (from Late Eocene to Early Miocene), was recorded inthe synrift sediments which comprise two nonmarine sedimentary successions(stratigraphic units 6 and 5) and one regressive package (stratigraphic unit 4). Thefollowing post-rift phase comprises one regressive sedimentary package (unit 3) andtwo transgressive successions (unit 2 and unit 1).Stratigraphic unit 6, of Late Eocene to Early Oligocene age, is characterized bycoarse-grained, alluvial fan and braided stream sediments in the lower subunit andfine-grained, floodplain-channel deposits in the upper subunit. The lower subunit ispractically barren of organic matter; its TOC content ranges from 0.03% to 0.1%with an average value of 0.07 %. Its QOM value ranges from 0.08 to 0.14 mgHC/g TOC, with an average value of 0.13 mg HC/g TOC. The kerogens whichoccur in this unit are mainly Type IV kerogen (or organic facies D, based on Jones'282(1987) classification of sedimentary organic matter). The TOC content of the uppersubunit of unit 6 ranges from 0.04 to 0.33%, with an average value ofapproximately 0.22%. Its QOM ranges from 0.9 to 0.33 mg HC/g TOC, with anaverage value of 1.82 mgHC/g TOC. This upper subunit contains mainly of TypeIII-IV OM (organic facies CD and D).Stratigraphic unit 5, of Late Oligocene to Early Miocene age, is characterized byfine-grained, floodplain deposits in the lower subunit and somewhat coarser-grained, meandering channel deposits in the upper subunit. The TOC content ofthe lower subunit ranges from less than 0.1 % to 0.45%, with an average TOCcontent of 0.24%. Its QOM value ranges from 0.46 to 5.3 mg HC/g TOC, with anaverage QOM value of 1.46 mg HC/g TOC. The kerogens which occur in thissubunit are mainly Type III and Type IV OM with minor amounts of mixed TypeOM. The TOC content of the upper subunit of unit 5 varies from 0.1 % to0.44%, with an average value of 0.25%. The QOM value of this subunit variesfrom 0.9 to 5.3 mg HC/g TOC, with an average value of 1.93 mg HC/g TOC.The kerogens which occur in this subunit are Type II-III OM (organic facies C).A brief transgression occurred at the end of unit 5 deposition (early part of EarlyMiocene) and caused a brief period of nondeposition marking the boundary betweenstratigraphic units 5 and 4. The following sedimentary succession (unit 4-EarlyMiocene age) represents a broad regressive cycle characterized by fine-grained,prodelta to shallow marine deposits in the lower subunit; coarse-grained,distributary mouth bar deposits and beach complexes in the middle subunit; andcoarse- to fine-grained nonmarine, floodplain-meandering channel deposits in theupper subunit. The TOC content of the lower subunit varies from about 0.2% to0.5%, with an average value of 0.32%. The QOM value of this subunit varies283from 0.5 to 2.0 mg HC/g TOC, with an average value of 1.56 mg HC/g TOC.The organic constituents of the lower subunit are mainly Type III (facies CD) andType IV (facies D) OM. The TOC content of the middle subunit varies from0.15 % to 0.7%, with an average value of 0.35 %. The QOM value of this subunitvaries from 0.6 to 2.4 mg HC/g TOC, with an average QOM value of 1.37 mgHC/g TOC. The main organic constituents of the middle subunit are Type IV andType III (facies D and CD) OM. The TOC content of the upper subunit of unit 4varies from 0.2% to 0.7%, with an average value of 0.36%. The QOM value ofthis subunit varies from 0.3 to 2.4 mg HC/g TOC, with an average value of 1.39mg HC/g TOC. The main organic constituents are Type III-IV OM (facies CD andD) and Type II OM (facies BC and C).Following deposition of unit 4 (Early Miocene-about 20 Ma), sedimentation in thePattani Basin was in response to tectonic quiescence; subsidence was relativelyslow. The sedimentary signatures were controlled mainly by the amount ofsediment influx and the eustatic sea level fluctuation. Post-rift sediments compriseone regressive sedimentary package (unit 3) and two transgressive packages (units 2and 1). A brief and rapid transgression occurred again at the base of unit 3 (EarlyMiocene-about 20 Ma) and caused a short period of nondeposition marking theboundary between unit 4 and unit 3. The regressive succession of unit 3 (Early toMiddle Miocene), that followed the brief transgression, is characterized by fine-grained, prodelta to shallow marine-shelf deposits in the lower subunit; coarse-grained, distributary mouth bar deposits and beach complexes in the middlesubunit; and coarse- to fine-grained, nonmarine, floodplain-meandering channeldeposits of the upper subunit. The TOC content of the lower subunit of unit 3varies from 0.2% to 0.9%, with an average TOC content of 0.44%. The QOMvalue of this subunit varies from 0.5 to 1.8 mg HC/g TOC, with an average QOM284value of 1.34 mg HC/g TOC. The organic constituents of this subunit are Type IIIand Type IV OM (organic facies CD and D respectively) with minor amounts ofType II-III OM. The TOC content of the middle subunit varies from 0.2% to0.9%, with an average TOC content of 0.39%. The QOM value of this subunitvaries from 0.8 to 2.5 mg HC/g TOC, with an average QOM value of 1.31 mgHC/g TOC. The organic constituents of this subunit are Type III and Type IV OM(organic facies CD and D respectively) with minor amount of Type II-III OM. TheTOC content of the upper subunit of unit 3 varies from 0.1 % to 0.6%, with anaverage TOC value of 0.29%. The QOM of this subunit ranges from 1.0 to 2.0 mgHC/g TOC, with an average QOM of 1.28 mg HC/g TOC. This subunit containsmainly Type IV and Type III OM (organic facies D and CD).Stratigraphic unit 2 (Middle Miocene) represents a transgressive successioncharacterized by coarse-grained, nonmarine, meandering channel deposits in thelower subunit, and fine-grained interdistributary bay complexes and marginalmarine deposits in the upper subunit. The TOC content of the lower subunit of unit2 varies from 0.2% to 1.3%, with an average TOC content of 0.43%. Its QOMvalue ranges from 1.0 to 3.2 mg HC/g TOC, with an average QOM of 1.49 mgHC/g TOC. This subunit consists mainly of Type Type III, and Type IVOM (organic facies C, CD, and D). The TOC content of the upper subunit rangesfrom 0.2% to 1.4%, with an average TOC content of 0.81%. The QOM value ofthis subunit varies from 1.3 to 2.4 mg HC/g TOC, with an average value of 1.57mg HC/g TOC. This subunit consists mainly of Type III OM (facies CD) and amixture of Type II-III OM (organic facies C and CD).At the end of the Middle Miocene, a rapid regression occurred in the Pattani Basin,probably as a result of a rapid eustatic sea level fall, causing subaerial exposure,285oxidation, and probably minor erosion of stratigraphic unit 2. Following this briefregression is a transgressive sedimentary package of unit 1 (Late Miocene toPleistocene age). Unit 1 is characterized by basal coarse-grained, nonmarine,distributary channel deposits of the lower subunit; fine-grained, brackish water,interdistributary bay deposits and marsh and swamp complexes of the middlesubunit; and fine-grained, prodelta to shallow marine deposits of the upper subunit.The TOC content of the lower subunit of unit 1 varies from 1.33% to 1.45%, withan average value of 1.37%. The QOM value of this subunit varies from 1.20 to1.66 mg HC/g TOC, with an average value of 1.49 mg HC/g TOC. The mainorganic constituents of this subunit are a mixture of Type II-III OM (organic faciesC and CD). The TOC content of the middle subunit varies from 0.85% to 2.08%,with an average TOC content of 1.47%. The QOM value of this subunit rangesfrom 0.96 to 2.04 mg HC/g TOC, with an average QOM value of 1.64 mg HC/gTOC. This subunit consists mainly of Type II and Type III OM (organic faciesBC, C and CD). The organic characteristics of the upper subunit of unit 1 are notdescribed here because the samples are not available.6.5 KINETIC PARAMETERS OF THE POTENTIALSOURCE ROCKSThe potential hydrocarbon source rocks (high HC potential and high TOC content)of each stratigraphic unit in the Tertiary strata in the Pattani Basin, Gulf ofThailand, were identified from Rock-Eval analysis. Rock-Eval pyrolyses wereconducted on whole rock samples at a series of heating rates equal to 5, 25, and 50°C/min (cycle 4, 1, and 2 of Rock-Eval II instrument respectively). The values ofT and the corresponding heating rates, together with the temperature width of theRock-Eval reaction rate profile (full width at half-height), were used as input to the286Lotus 1-2-3 program, Eo.WK1, to determine the kinetic parameters (A, E0, and adfollowing procedures outlined earlier. The output of the Eo.WK1 program is a pre-exponential factor (sec-1 ) and a series of activation energies (cal/mol) and theircorresponding stoichiometric, or weighting factors. This output file can be useddirectly as an input file for the organic maturation modelling program described insection 6.2.1 to calculate hydrocarbon generation and organic maturation historiesof the sedimentary strata of interest.Table 6.1 and Figure 6.10 list the kinetic parameters (A, E0, and o-E) for thepotential hydrocarbon source rocks of the subunits of each stratigraphic unit atdifferent locations.6.5.1 Unit 6The lower subunit of stratigraphic unit 6 is practically non-organic. The kineticparameters of the fine-grained, floodplain deposits of the upper subunit of unit 6were represented by samples from Ranong-1 well. The main organic matteroccurring in this subunit is Type III-IV kerogens. The kinetic parameters of theupper subunit is characterized by a pre-exponential factor (A) of 1.97x10 12 sec-1 , amean activation energy (E0) of 46.7 kcal/mol, and a dispersion (o-E) of 3.67% ofE0.6.5.2 Unit 5Nonmarine channel and floodplain deposits of the lower subunit of unit 5, whichcomprise mainly Type III-IV kerogens and a mixture of Type II-III kerogens, arecharacterized by a variation of kinetic parameters. Its pre-exponential factors range287Table 6.1: Kinetic parameters for potential source rocks of Tertiary stratigraphic unitsin the Pattani basinUNIT SUBUNIT WELLA(/sec)E.(kcal/mol)crE(% Eo)1 Lower Funan-1 2.08E+16 58.19 3.54Pladang-3 1.08E+ 16 58.45 3.452 Upper Kaphong-1 1.76E+13 48.89 2.60Platong-5 3.05E+14 52.65 1.75Pladang-3 2.64E + 16 59.15 3.68E-12-1 3.73E+ 13 49.63 0.26Funan-1 1.80E+14 52.11 1.44Lower Kaphong-1 2.82E+13 52.20 5.05Platong-5 2.49E+15 55.77 2.62Pladang-3 1.79E+ 15 55.12 4.10Funan-1 7.34E + 13 50.88 3.743 Upper Kaphong-1 1.26E+ 13 51.28 3.78E-12-1 1.01E+15 54.53 2.24Funan-1 1.55E +14 52.22 4.32Middle Kaphong-1 1.13E+ 16 59.83 5.63Funan-1 4.27E+14 55.10 4.64Lower E-12-1 7.55E+15 58.08 4.07Pladang-3 3.15E+12 47.29 5.524 Upper Platong-5 3.84E + 13 51.07 3.72Middle Pladang-3 2.45E+12 46.11 3.52E-12-1 2.15E+14 54.87 7.66Lower Kaphong-1 1.39E+16 60.63 6.225 Upper Kaphong-1 9.41E+14 57.42 5.70Platong-5 1.15E + 14 51.94 9.30E-12-1 3.36E +15 50.81 6.47Lower Kaphong-1 1.01E+13 51.25 6.12Platong-5 1.73E+14 52.15 5.06E-12-1 2.77E+14 55.87 5.106 Upper Ranong-1 1.97E+12 46.70 3.67*A is the pre-exponential factorEo is the mean activation energyaE is the standard distribution of activation energies288Figure 6.10: Mean activation energy of each stratigraphic unit289from 1.01x10 13 to 2.77x1014 sec-1 , its mean activation energies vary from 51.2 to55.9 kcal/mol, and its dispersions vary from 5.06 to 6.12% of E0. The fine-grained, floodplain deposits of the upper subunit of stratigraphic unit 5, containingmainly Type II-III OM, are kinetically characterized by pre-exponential factorsranging from 9.41x10 14 to 3.36x1015 sec-1 , mean activation energies varying from50.8 to 57.4 kcal/mol, and dispersions ranging from 5.70 to 9.30% of E0.6.5.3 Unit 4Floodplain deposits of the lower subunit of unit 4, containing Type III and Type IVkerogens, are kinetically characterized by a pre-exponential factor of 1.39x10 16sec-1 , a mean activation energy of 53.4 kcal/mol, and a dispersion of 6.22% of E 0.The marginal marine, beach and distributary mouth bar deposits of the middlesubunit, containing mainly Type IV and Type III kerogens, are characterized bypre-exponential factors ranging from 2.45x10 12 to 2.15x1014 sec-1 , mean activationenergies ranging from 46.1 to 54.9 kcal/mol, and dispersions varying from 3.52 to7.66% of E0. A pre-exponential factor of the shallow marine deposits of the uppersubunit of unit 4, containing mainly Type III-IV OM and Type II OM, is 3.84x 10 13sec-1 , with a mean activation energy of 51.1 kcal/mol, and a dispersion of 3.72% ofE0.6.5.4 Unit 3Nonmarine floodplain deposits of the lower subunit of unit 3, containing mainlyType III OM and Type IV OM with minor amount of Type II-III OM, arekinetically characterized by pre-exponential factors ranging from 3.15x10 12 to7.55x10 15 sec-1 , mean activation energies varying from 47.3 to 58.1 kcal/mol, and290dispersions ranging from 4.07 to 5.52% of E0. The marginal marine, beach anddistributary mouth bar deposits of the middle subunit of unit 3, containing mainlyType III-IV OM and minor Type II-III OM, are marked by pre-exponential factorsvarying from 4.27x10 14 to 4.27x1016 sec-1 , mean activation energies varying from55.1 to 59.8 kcal/mol, and dispersions ranging from 4.64 to 5.63% of E0. Theshallow marine deposits of the upper subunit of unit 3 contain mainly Type IV andType III OM, and are marked by pre-exponential factors ranging from 1.26x10 13 to1.01x1015 sec-1 , mean activation energies varying from 51.3 to 54.5 kcal/mol, anddispersions ranging from 2.24 to 4.32% of E 0.6.5.5 Unit 2Nonmarine channel and floodplain deposits of the lower subunit of stratigraphic unit2 contain a mixture of Type Type III and Type IV OM, and are kineticallycharacterized by pre-exponential factors ranging from 2.82x10 13 to 2.49x1015 sec-1 ,mean activation energies varying from 52.2 to 55.8 kcal/mol, and dispersionsranging from 2.62 to 5.05% of E0. The shallow marine deposits of the uppersubunit of unit 2, which contain mainly a mixture of Type III and Type II-HI OM,are marked by pre-exponential parameters varying from 1.76x 10 13 to 2.64x 1016sec-1 , mean activation energies ranging from 48.9 to 59.6 kcal/mol, and dispersionsranging from 0.26 to 3.68% of E0.6.5.6 Unit 1No samples were available from the upper and middle subunits of stratigraphic unit1. Hence, only nonmarine, floodplain deposits of the lower subunit containing amixture of type II-III OM were used to determine the kinetic parameters. Pre-291exponential factors of the lower subunit vary from 1.82x10 16 to 2.08x 1016 sec-1 ,mean activation energies range from 58.2 to 58.4 kcal/mol, and dispersions rangefrom 3.45 to 3.54% of E0.6.6 HYDROCARBON GENERATION MODELLINGThe extent and rate of hydrocarbon generation through time since deposition ofeach stratigraphic unit at different well locations are predicted using an organicmaturation model outlined in section 6.3.1. The inputs needed for this maturationmodel are thermal and burial histories and the kinetic parameters of thestratigraphic unit of interest. The burial and thermal histories of each stratigraphicunit are obtained by the backstripping analysis and lithospheric stretching modellingdescribed in chapter 4. The kinetic parameters for the potential hydrocarbon sourcerocks used here were derived from the kinetic modelling described in section 6.2.2and are shown in Table 6.1. The kinetic parameters for calculating vitrinitereflectance are shown in Table 4.3 (Sweeney and Burnham, 1990). Because thereis no age constraint within the stratigraphic units, the maturation history modellingof the stratigraphic units was carried out at the basal boundaries of the units. Thispractice results in the earliest possible time of thermal maturation of each unitbecause the base of the unit is buried longer and to a greater depth, and henceexperienced higher temperatures than the top of the unit.The extents and the rates of hydrocarbon generation at different well locations areshown in Figure 6.11 through Figure 6.40. Figure 6.41 through Figure 6.45 are aseries of maps of the present-day extents of hydrocarbon generation in eachstratigraphic unit. Figure 6.46 through Figure 6.50 are a series of maps showingtiming of main hydrocarbon generation phase (reaction extent = 40%) of each2921C07:025ICS25502510075.2510050Th251007550261 03Th5025943Unit-2-5- 15 -10-33^25Unit-41Thiit-5Ranong-1 wellHydrocarbon generation historyRanong-1 wellHydrocarbon generation rate history2a ^18 , 2 ..I_Init106 ^97 18 ^,2 ..1.1nit-,206 ^92 , 82 -.Unit-306 ^92 18 ^1 .2 __Unit..06 ^92 18 ^, 2 -- Unit,506 ^2 1812 ..tInit-6)6 ^0940^-35 a0 -2S .,n ..ls .1n c AFigure 6.11: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Ranong-1 wellKung-1 wellHydrocarbon generation historya ^: ..Unit-.1 5 ^_Unit-2 5_Unit-ao ^Unit-4Unit?  ..Unit-6   .1,^-10Kung-1 wellHydrocarbon generation rate history24 ^1, 8, ..1.1nitd 06 ^22 1 8 .,2 _1Init,208 ^22 la 12 --ilnitg. ^as ^92le unit06 ^92 1 e .,, ..unit-506 ^97 18 ^,, ..Unit-636 ^30.,111251Th5025Figure 6.12: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Kung-1 well293Surat-1 well^ Surat-1 wellHydrocarbon generation history^Hydrocarbon generation rate history7s5025103So Unit-250 00Z Unit-3c 100 ^.QsoTh Unit-4cc^25 ^1039015-33^-25^-20^-15^-10^5^0484125^100 ^75„Unit-^25 ^^90 2 .1 ^nit,l.06 ^92 nit-0 6 ^92 nit,306 ^92 to ^,^nit. ^06 nit-506 ^22 8 ^2 Unit-606 ^'^ 3 -30 25 -20 -15 -10 5010a)Figure 6.13: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Surat-1 wellPlatong-8 wellHydrocarbon generation history,00 ..^nu7.10,2^0 ^_0 ^o^nit-40 5 ..Unit, 5 ^5 _Unit. ^5 _^.Platong-8 wellHydrocarbon generation rate history240 6  nit-928  111t-2 ^0692  nit-06‘2 ^1 nit ^0692  nit-5^06 ^2 ^,6 ^ ., 2 rut-6^D6 ^ ._..0 044 6,.........."10 35^33 25 20 15 -10 5104.1Figure 6.14: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Platong-8 well.4294Platong-1 wellHydrocarbon generation rate historyPlatong-1 wellHydrocarbon generation history-15loo75,025-40^.33^-25^-2006.1.21.Figure 6.15: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Platong-1 wellUnit-11005025..Unit-2^ 1CO759,2510050Th250025°5Th1007350252 4 ^18 i 2 -"Iliad_06 ^97 18 ^I , -1111a7206 ^97 18 ^12^t.T ^06 99 ^18 2 -Una06 ^-... 129 16 ^^11=7506 ^ _am._92 1 8 T r^:12 ---1.41-a, lill06 ^411h.lib■-004,-25 20 -15^-10 -5-5 0-10Insea-1 wellHydrocarbon generation history0 ^: ..Unitn1.5 ^0so ....Unit-25 ^0.0Tnu,0 ^^: -.Unit-4-.Unitut-425 ^0 10so ..Unit,-.55 ^10 ,05, ..Unit- ^2 ^210^35^30^-25^-20^-10^.5^0Insea-1 wellHydrocarbon generation rate history24 ^16 , 2 ..1.1nitd06 ^29 18 ^,, ..Unit-206 ^97 :: ..Unit-306 ^92 113 ^i2  -Unit..06 ^29 1 8 ^1.2 ..unit-506 ^92 l o ^1, .-LIttit.-606 ^-."--io^,55 30 -25 -15 -10 -51111015Figure 6.16: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Insea-1 well29550Pakarang-1 wellHydrocarbon generation history12Pakarang-1 wellHydrocarbon generation rate history1CO ^nit-.124 ^19 . Unitd.^25 ^ 06 ^100 92 16 ^755, ^Unit!.  12 Unit,2^25 ^ 06 ^-a?. ICS 92 50 nit-3 12,e ^..Unit-3^a)CCV0 6 ^00 ^ 92 4cttTs nit-4 Unit ^a)cc 25 ^ 5.100 0 97 ^5750 Unit-5I=,2e .13)C 06 ^'''.111 11 m400 ^ 92 75 ,e ^5025 ^ 06 ^-40^a5 33 25 -20 .15 .10 -5 0 0 .35 .25 -20 .15 -10 090.1 someFigure 6.17: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Pakarang-1 wellsoPladang-3 wellHydrocarbon generation historyPladang-3 wellHydrocarbon generation rate history25 ^nit-124 ^tutd^25 ^ 06 ^25 92 So06 ^100 ^ 9275 Unit73 16 ^nit,3^40tC.2(NIwa)06 ^Ico ^nit-492 nit ^CC25 ^ 06 ^100 92  27.712 nit-5^25 ^ 06 ^100 92 I S ^755° ^ nit-6^25    06 ^940 .30 .25 -20 -15 -10 -5 0 004 -25 20 -15 .70Figure 6.18: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Pladang-3 well296-10 5 0Trat-1 wellHydrocarbon generation historyTrat-1 wellHydrocarbon generation rate historySouth Platong-2 well^ South Platong-2 wellHydrocarbon generation history Hydrocarbon generation rate historyFigure 6.19: The extent of hydrocarbon generation (%) and generation rate (%/sec) at South Platong-2 well100 ^ 24 ^50 nit-1^ .Unit406 ^,00 ^ 22 50 Unit-2^ 12 Unit,225 ^ 06 ^,co 92 .Unit73^ 1218 ^Unit-325 ^ ;.3.' 06 ^(I)c 0 92 (.) nit-4 Lixi 19 ^Unit ^cr. 1213: 06 ^c120 ^ 227550 Unit;i5 .4.z.2"P 12I ^.-Unit-525 ^ 61).C 06 ^520   22 LB ^so nit-6 1225    06 ^94.0 -35 -25 -20 -15 -10 0040 25 -33 -25 -20SO I.,A so„50 ^25 ^nit-12418120624181206921812 06222525 ^Unit-20,3 25 ^100 .52 Unn-4 WX112CC 25 ^ 0 6100Unit-  .Q15 ,81225    06103    921850 n. 1225    06Unit-1Unit,2-3)^-25^ -15^-10Rico*40 0040 -36 -25 -200 -10UnitUnit-5^Figure 6.20: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Trat-1 well297Dara-1 wellHydrocarbon generation history1 2Dara-1 wellHydrocarbon generation rate history100 ^an 12 4 ^1 8 . Unit425 ^ 06 ^92 50 ..Unit-2 111 8 ^..Unit-225 ^ 06 ^e_ •100 92 1 8 ^7550 ^Unit-3 4.13 Unit-30' 6 ^C 100 ^ 92 .Q5075 Unit-4 X12 Unit ^a)25 ^ 06 ^100 22 75 ^ 1 ^50 225 ^ 06 ^92 507518 ^Unit-625 ^ 06 ^5.440^-20 20 -25 -10 -5 00,a 20 -25-20 -10 -5Figure 6.21: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Dara-1 wellErawan-12-1 wellHydrocarbon generation historyUnit-110075SO251007550Unit-UnitUnit-21C075251200230 -25 -15 -10 -5Erawan-12-1 wellHydrocarbon generation rate history1224 ^1 8 06 ^Unit.71.24 1218 ^Unit-206 ^92 1 218 ^.Unit-3;3'2 08 ^92 2to ^Unit ^06 ^9205 ..Unit-5C 08 ^27 1 ^1206 ^0 040 30 -25 .20 5Figure 6.22: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Erawan-12-1 well298Erawan-12-8 well^ Erawan-12-8 wellHydrocarbon generation history Hydrocarbon generation rate history2 4 ^nit-0692.Unit-20692.Unit3^069.Unit-4 069nit-5^0692012^06 ^004°^Figure 6.23: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Erawan-12-8 well10137550251037,5025940it--25^-20.55 -5 -5-25 -10100755025Z52^103755025a) nC.g25Crmt.100755025..Unit-.122i6Es^12• 06CCD100755025100755025• 755025c• 100.225CC100755025Satun-3 wellHydrocarbon generation historySatun-3 wellHydrocarbon generation rate history2411206Unit-1Unit-Unit-3^92Unit-411206o 940Figure 6.24: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Satun-3 wellUnit-2Unit1206o..Unit-1CO755,25940 -5 0-25 .209.1.40 .35 .30 -20&a.m.-10-10--99.S.S."%."•■9216120692t61.202 06299.Uatt.,2^1120618• 0• 1 6Unit-30-5 -5-35 -25-30 -150%3^30^25Jakrawan-2 well^ Jalcrawan-2 wellHydrocarbon generation history Hydrocarbon generation rate history2.Unitd.9292_Unit ^• 1C07550▪ 25Gl co.4o 50• 2cr^25Unit-4ICO50251087:025181206nit-1Unit-2^1COUnit-5• 16, 20O 9225100nit-6-33^-25^-20^ -10^.509.1.4-5-20 -15 .10-30 -25-3575251 B1206Unit-Figure 6.25: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Jakarawan-2 well50Krut-1 wellHydrocarbon generation history12Krut-1 wellHydrocarbon generation rate historynit,1^2.4 ^113 Unitd25 ^ 06 ^100 92Unit-2 (-3 1.2,6 ^Unit-225 ^ 0 06 ^o.t108UnIt7.3 ^o ^I92181 2rn Unit-32, 06 ^Ico ^ r 92 .450 111174^ X 121$ ^Unit 25 ^ 06 ^CC100 El 92 5075 ^ 01218 ^Unit, 25 ^ 06 ^100 92 so nit-6   12 -Unit-625    06 ^Figure 6.26: The extent of hydrocarbon generation (%) and generation rate (cc/sec) at Krut-1 well300Erawan-K-1 wellHydrocarbon generation historyErawan-K-1 wellHydrocarbon generation rate history100 ^nit-.1 12 Unit4^06 ^25 ^50 .Unit-2 12B ^Unit,2^25 ^ 06 ^1108 92 d 50 Unit- 12219 ^25 ^ 06 ^c0 C100 9 o4r:(Ti5a)Cc5075 ^25 nit-4 LLIX(1)Chit-4^1CO ^,e ^50 Unit-5^cCD01 6 ^Oo    9 8 ^1225   ^--Unit-6A06 ^gee 00.025^-20^ -10 -5 0 -35^-33 -25 -20 -10 -5Figure 6.27: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Erawan-K-1 well1035075251007550251005025Unit-4..Unit-125n251C07:025-51005025g40 -25 -10-2011.1.61Baanpot-1 wellHydrocarbon generation historyBaanpot-1 wellHydrocarbon generation rate history2 4 ^2 ..linitd.06 ^92 ,8 ^2 -- Unit,206 ^92 1 8 ^1 2 --IInit.,306 ^92 le ^, _Unit..06 ^22 le ^1 2 ._Unit,506 ^92 le ^1 2 --Unit- ^06^-- - ^' 940^-35 -10 -75 ,r0 -Is .10C.4CCFigure 6.28: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Baanpot-1 well30124101206Unit I.Unit. Unit-1100755025Baanpot-B-1 wellHydrocarbon generation historyBaanpot-B-1 wellHydrocarbon generation rate history1005025• 1007550C ,00.25▪ 50asa 3CC10075502510g7'55,252401812060040Unit--35 -25 -20 -10-30 -10 0 -35 5Uniti,_6. ^1 8120692a)^181 6'0cv92• 1812a)S1 06• 92ro^06a) 920:37^18Unit-4Una-5^Figure 6.29: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Baanpot-B-1 well..Unit-2Unit- Unit-3^Jakrawan-1 wellHydrocarbon generation historyJakrawan-1 wellHydrocarbon generation rate history100 ^ 24 ^nit-1 1218 Unit ^06 ^100 ^ 92Unit-2 1218 ^25 ^ 06 ^ 1.G^10075 ^Unit-3(,)1292 Unit-3^cv 06 ^92Unit-4 X 1152 Unit. ^cc^25n ^ CD 06 ^1CO 92 m Unit-50ro e ^Unit-5^25 ^a)06 ^42 nit 1218 ^3    06 ^9,0 0040-30 -25 -20 -15 - 10 -5 0 -35 -25 20sot. N1•1•61Figure 6.30: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Jakrawan-1 well302Funan-1 well Funan-1 well1812 Unit,2^Hydrocarbon generation history^Hydrocarbon generation rate history100 ^122 , ^16 ..Unit-125 ^ 06 ^100 92.Untt7.2^ 121 ^..Unit-225 ^ 06 ^,c0 97 12 Unit-2325 ^ 06 ^CDc 92 .4 7s ^Unit-4 X1218 ^Unit ^25 ^ 0 ^CtCO 92.4Unit-3^ 18 ^Unit-525 ^ co1 6200,co 92 ^25 ^^nit-6   128 Unit-625    06 ^940 -25 -15 .10 -5 0 0% -33 25 20 -15 -10 -5 0 1101 Ke01.1Figure 6.31: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Funan-1 wellYala-2 wellHydrocarbon generation historyYala-2 wellHydrocarbon generation rate historyUnit-1100755025041120692092Unit,3• as• 92.0 t ^92Urut,5^10375502510375502518113.)12^ 100Th25Unit • 1206. Unit-21007525IP^,61213)C 06Unit-5^10025080( 921612080%5 -5-1525 -10-10-33 -25 .33Figure 6.32: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Yala-2 wellUnit-6303940 00,0-25^-20.01W-10^0 -30^-25^-20PaPalKaphong-1 wellHydrocarbon generation history Kaphong-1 wellHydrocarbon generation rate historyKaphong-3 wellHydrocarbon generation history12Kaphong-3 wellHydrocarbon generation rate history100 ^nit-1 2s ^..Unit-125 ^ 06 ^00 5075 ^..Unit-21.225 ^ 06 ^22 di w nn, 8218 ^Unit, 25 ^ 0 6 ^CDc0.1100 92 .gT.;CD5025 ^nit-4 a) 1 118 06 ^Unit CC100 C 92 7550 Unitn5   01 Unit-5^25    10S' ^C O6 ^(5 92 4MMINI417:0 ^nit^121 8 ^ai06 ^Figure 6.33: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Kaphong-3 wellFigure 6.34 The extent of hydrocarbon generation (%) and generation rate (%/sec) at Kaphong-1 well-30 -200.1.4do.15 10 5:^Ind 8 ..Unit-2 3 ^nit,3nit ^Unit-5^Unit-1100Co..Unit-5'Co755025..Unit-425G 100 75CDC 100.g2CC^251005025940 -15 -10-30^-25.1,1n2009g 0120600.304Platong-5 well^ Platong-5 wellHydrocarbon generation history^Hydrocarbon generation rate history.Unit410025103502510050254131C025nit-nit-4Unit-.5^1005035^-31:1^25^20^-15^-10^3^04.1111.1co15925252o2 4 ^,812 ".1.Init,106 ^92 1B ^,2 ..linit,2.. ^92 1 8 ^1 2 --Unit5306 ^92 ,8 ^.,.2 _Unit ^06 ^92 18 ^12 "-Unit-606 ^92 18 ^12 --Uilit,656 ^......55.5...3 945^-35 -33 -25 -20 -15 -10 -5 0Figure 6.35: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Platong-5 wellSouth Platong-1 wellHydrocarbon generation history0 ^nit-15 ^.5 ..Unit-25 ^0o Unit-35 ^0o Unit-4o ^0 Unit,50 ^5 Unit, ^5 ^D40^38 30 25 20 0South Platong-1 wellHydrocarbon generation rate history24 ^:: ..1111/L1^08 ^92 ,e ^,,..1.1nit,2^06 ^■92 18 ^12 ..1Init,3^08 ^-4..-,...1/4...'....■22le .t,. ^1206 ^22 18 ^1.2 __Iinit75^06 ^92 le ,2 .Iln08 ^‘^6ilVt00J0^35 33 -25 -20 .15^.10asCCFigure 6.36: The extent of hydrocarbon generation (%) and generation rate (%/sec) at South Platong-1 well305Satun-2 well^ Satun-2 wellHydrocarbon generation history^Hydrocarbon generation rate historyFigure 6.37: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Satun-2 well2 4 ^18 12 -14Inittl^06 ^92 , e ,, ..linit,2^06 ^92 ,e ,, __Unit,3^06 ^_.4.80.......44■44.92 , e ^12 -- Unit .. ^0 6 ^rm."...''%. ._92 1e ,, ..Unit ,5^08 ^92 ,e ^1 2 --Unit, 6 ^06 ^Allib■0 940-30 -25 -20^- 15 -10 .5^0nit-120100..Unit..-2*eft^100^75 ^t so nit-(1 25 ^c 100 ^nit-4 a)•^25 ^CC100a100nit-6So3940 -25^-20^-1581418.1-10^-533Satun-1 wellHydrocarbon generation history: ..Unitr.1^0 ^: --unit-25 ^0 50 ..Unitn35 , ^aso --Unit-4 5 .D ^sr, _Unit? ^5 ; _Unit- •Satun-1 wellHydrocarbon generation rate history24 ^808  nit-1^22e nit-2^069218 nit-3^08■' ^8 ^ .nit ^08 .1.■044%,92, nit-5^O6 ^2 ^,e1 nn ^. ^0 0,0 25 20^15 10 5^080O0C01e ,08Figure 6.38: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Satun-1 well306Erawan-12-9 wellHydrocarbon generation historyUnit-1100501085550310815502510075Unit-2Unit-3Unit502575502510850940Unit-5.10-35^-30^-25^-20^-15CONErawan-12-9 wellHydrocarbon generation rate history^2.4 ^^0.6 ^..Unit-1 ^9:2 ^1.8 ^,, .nit7B. ^O. ^i nit73^0.Ei2Le nit-4^0.62:2nit-5^0.51.81 .D.13DO -25 -20 -15 -105 044 ow2CDCDC0a(.7Figure 6.39: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Erawan-12-9 wellErawan-12-7 wellHydrocarbon generation history. ^0 ^nit-1nit-2 2  5/0 ^7Unit-3Unit-4 Unit-5 _Unit  .1^-10Erawan-12-7 wellHydrocarbon generation rate history2.4 ^1.8 ^.tut-1o.e ^9:2s ^Unit-2 0.8 ^91 ^::..Unit73o.e ^9.2 :82 .^.nit-4^0.0:: ..Unit-5. ^2 --./I 1.8 ^120.6 ^0.-40^35^30^.25^-20^-15^-10^-5^05210191C475SC101755021750050Figure 6.40: The extent of hydrocarbon generation (%) and generation rate (%/sec) at Erawan-12-7 well3070^5^10kmYala-2 (100)00o Kaphong-1 (100)Platong-5 0 (100)Ranong-1 (89)^ 0 0 Platong-1 (100)0 Surat-1 Platong-8 (100)(100)1 Er an-12-9 (100)Dara-1 (94) °0^0 Satun-3 (100)100^0 Erawan-12-1 (100)0 Erawan-12-8 (100)0 Kaphong-3 (100)Kun -1 (99)0 S. Platong-1 (100)ang-1 (100)° Pladang-3 (100)00 S. Platong-2 (100)00^Trat-1 (100)Satun-2 (100)0Satun-1 (100)Erawan-12-7 (100)00Erawan-K-1 (100)0Krut-1(100)0Insea-1 (47)Jakrawan-2 (100)00Jakrawan-1 (100)0Baanpot-1 0 (100)^Funan-10 (100)Baanpot-B-1 (100)Figure 6.41: Calculated present-day reaction extent of unit 6's hydrocarbon generation (%)308Yala-2 (68)075Plat g-5 0 (9 )0 o P tong-1 (99)0 Plato -8 (96)0K ng-1 (58)0 E. Platong-1 (100)ang-1 (100)0 Pladang-3 (100)00 S. Platong-2 (100)00^Trat-1 (100)Satun-2 (100)0Satun-1 (100)(98)0 Satun-3 (100)0 Erawan-12-1(100)0 Erawan-12-8 (100)0Insea-1urat-1(88)Erawan-12-7 (100)00Erawan-K-1 (100)Krut-(58)1000 Kaphong-1 (100)0 Kaphong-3 (91)Ranong-1 (42)0Jakrawan-2 (100)0'0Jakrawan-1 (100)0Baanpot-1 0 (100)^Funan-1Baanpot-B-1 (100)^(100)0^5^10kmFigure 6.42: Calculated present-day reaction extent of unit 5's hydrocarbon generation (%)309Yala-2 (20)00^5^10km50 0 Kaphong-1 (74)PI - - ng-5 00urat-(59)400Kung-1 (34)Ranong-1 (18)00 o Platong-1 (81)Platong-8 (78)0Insea-1 (9)Dara-0 tun-3 (94)Era an-1 -9(69)(21^0 Os(70)0 awan-12-10 rawan-120rawan- (99)Jakrawan-2 (100)00 Kaphong-3 (29)0 S. Platong-1 (100)-1 (100)Pladang-3 (100)00 S. Platong-2 (100)00^Trat•1 (100)Satun-2 (100)0atun-1 (100)Eraw 12-7 (780oe^Jakrawan-1(100)0Baanpot-1 o (100)^Funan-1(100)Baanpot-B-1 (100)0Krut-1(45)4)Figure 6.43: Calculated present-day reaction extent of unit 4's hydrocarbon generation (%)310Ranong-1 (6)0Platong-5 00 00 PISurat-1(5)0Kung-1 (1)^ri.(3(7atong-1 (14)-8 (11)onYala-2 (10)00^5^10 km0 Kaphong-3 (17)Kaphong-1 (81)•NO°S. Platong-1 (100)Pak ang-1 (84° Plad g-3 (98)0Insea-1 (00 S. Platong-2 (100)00^ Trat-1 (100)Satun-2 (Dara-100Krut-1(2)0Satun-1 (9Eraw -1 9 (52)00 Satu -3 (94)wan-12-1(65)awan-12-8 (51-7(48)rawan-2 (100)0^ 0 59.Eraw0Jak awan-1 00)3^0Baanpot-1 • (80)^Funan-10 (57)Baanpot-B-1 (86)0 Er0Eraw0-K-1 22)Figure 6.44: Calculated present-day reaction extent of unit 3's hydrocarbon generation (%)311Yala-2 (6)00^5^10km0Trat-1 (87)Surat-1(0)0 Pla n -8 (3)0Satu -20Satu (59)012-9 (100)0 Satun-3 (100)Erawan-12-1(100)0 Erawan-12-8 (100)0 Kaphong-3 (24)0 Kaphong-1 (68)Platong-5 0Ranong-1 (0)00Kung-1 (0)0^atong-1 (6)S. Platong-1 (67)Pakarang-00Insea-1 (0)-3 (58)0 S. Platong-2 (98)-12-7 (100)Jakrawan-2 (76)Jakra an-11(100)0unan-1(57)Dara-00Krut-1(0)Baanpot-1Baanpot-B- (57)Figure 6.45: Calculated present-day reaction extent of unit 2's hydrocarbon generation (%)3120^5^10kmYala-2 (-21.8)06 0 Kaphong-3 (-34.7)Daro Kaphong-1 (-35.5)O (-21.8)PlatoRanong-1 (-7.7)0o o Platong-1 (-30.4)tong-8 (-31.0)0ung-1 (-10.5)0Surat-(-14.• S. Platong-1 (-32.8)ang-1 (-32.2)°^Pladang-3 (-31.5)S. Platong-2 (-31.1)0Insea-100o Trat-1 (-35.6)stun-2 (-31.3)0Satun-1 (-33.7)an-12-9 (-34.8)0O Satun-3 (-35.1)0 Erawan-12-1 (-32. 8)Erawan-12-8 (-33.8)Erawan-12-7 (-34.9)00Erawan-K-1 (-31.2)Krut-1(-22. Jakrawan-2 (-33.0)00Jakrawan-1(-33.5)0Baanpot-1 0 (-33.4)^Funan-10 (-30.4)Baanpot-B-1 (-32.8)Figure 6.46: Timing of main hydrocarbon generation phase (reaction extent=40%)of unit 6 (Ma)313o Kaphong-1 (-15.7)(-9.9)o o Platong-1 (-13.3)Platong-8 (-11.3)Ranong-1 (-0.3)00^5^10kmYala-2 (-4.7)00Kung- (-2.3)0 Kaphong-3 (-10.4)o S. Platong-1 (-20.8)-14.4)Pladang-3 (-22.2)0o S. Platong-2 (-23.5)0Insea-10atun-2 (-22.7)0tun-1 (-22.1)0Trat-1 (-23.9)Jakrawan-2 (-20.4)00Jakrawan- (-22.3)0Funan-1(-19.2)Dara-o-5Erawan-K-1 (-21.7)Baanpot-B-1 (-22,4)12.1)0 Satun-3 (-20.1)wan-12-1(-19.4)12-8 (-18.2)Eraw -12-7(-1.10^0Baanpot-1 0 (-22.5)00Krut(-4.5)Figure 6.47: Timing of main hydrocarbon generation phase (reaction extent=40%)of unit 5 (Ma)314Yala-2 (-)00^5^10kman-12-7 (-7.6)o Kaphong-3 (-)Ranong-1 (-)0o Kaphong-1 (-7.0)Platong-5^(-5.0)o o Platong-1 (-7.13)° Pla•g-8 (-6.1)0Kung-1Su -1-3.1)0 S. Platong-1 (-17.7)(-11,7)Pladang-3 (-20.4)0^ 0Insea-1 (-)0o^Trat-1 (-20.1)Satun-2 (-18.4)0tun-1 (-19.9)o S. Platong-2 (-19.2)Dara-1 (-)0rawan- -0 (-6.0atun-3 (-13.2)0).2)0 Eraw -12-10Erawan-K-1 (-18.8)Jakrawan-2 (-18.4)0^(t)0Jakraw 1 (-1 6.13)0Baanpot-1 0 (-20.4)^Funan-10 (-11.8)Baanpot-B-1 (-20.3)Figure 6.48: Timing of main hydrocarbon generation phase (reaction extent=40%)of unit 4 (Ma)315-3 (-8.9)-9 (-1 .2)O SaErawan-1Dara-1 (-)^00r an-12-7 (-0Erawan-K-1Baanpot-1 0 (-2.2)0Baanpot-B-1 (-2.8)0Krut-1(-)2)0Funan-1(-4.0)Jakrawan-2 (13.0)00 Era0 12-1(-2.awan-120Ranong-1 (-)00Kung-1 (-)A0O S. Platong-1 (-12.5)arang-1 (-8.° Plad: g-3 (-9.9)o S. Platong (-14,7)0O 1 Trat-1 (-15.8)S n-2 (-10.5)'76.0Satun- (-9.8)0Insea-1 (-)Platong-5 0 (-)o o Platong-1 (-)0 Platong-8 (-)Surat-1(-)^"5Yala-2 (-)00^5^10 kmo Kaphong-3 (-)o Kaphong-1 (-3.2)Figure 6.49: Timing of main hydrocarbon generation phase (reaction extent=40%)of unit 3 (Ma)3160Insea-1 (-) o S. Platong-2 (-9.4)NI 0o^Trat-1 (-8.0)Satun-2 (-0.0 Kaphong-3 (-)o Kaphong-1 (-3.4)Ranong-1 (-)00Kung-1 (-)o S. Platong-1 (-2.7)Pakarang-1 (-)°^Plad^(-1.5)0Satun-1ErawDara-1 (-)0Erawan-12-1(-0^an-12-8-12-7 (-3.5)2 (-3.1)0Erawan-K-1 (-0.9)1)0Baanpot-1 0 (-2.2)^Funan-10 (-1.5)Baanpot-B-1 (-1.5)2-9 (-3.1)atun-3 (-)0Krut-1^Era(-)Platong-5 0 (-)0 o Platong-1 (-)o Platong-8 (-)Surat-1(-)YaJa-2 (-)00^5^10 kmFigure 6.50: Timing of main hydrocarbon generation phase (reaction extent=40%)of unit 2 (Ma)317stratigraphic unit. The maps of stratigraphic unit 1 are not shown here because theunit is immature with respect to the main hydrocarbon generation phase at all welllocations in the study area.The present-day maturation level of the stratigraphic unit 6 (Figure 6.41) indicatesthat in most parts of the basin, this unit is overmature (reaction extent = 100%)with respect to the oil window, except in the western part of the basin where theunit is still in the oil window. The main hydrocarbon generation phase (= 40%hydrocarbon generation extent) of this unit started from as early as 35 to 36 Ma inthe basin center to as late as less than 1 Ma at the basin margin (Figure 6.46). Thepeak hydrocarbon generation rates occurred from about 35 Ma in the basin center tothe present-day at the basin margin (Figure 6.11 through Figure 6.40).The present-day maturation level of stratigraphic unit 5 (Figure 6.42) indicates thatthis unit is overmature (reaction extent = 100%) in the south and central part of thebasin. In the northern and western part of the basin, this unit is still within the oilwindow. In the western-most area, immediately west of the Insea-1 and Dara-1wells, unit 5 is still immature (reaction extent < 25%). The main phase ofhydrocarbon generation (= 40% hydrocarbon generation extent) started from about24 to 22 Ma in the basin center to as late as 3 Ma at the western margin (Figure6.47). The peak hydrocarbon generation rates of this unit occurred from 22 Ma inthe basin center to the present-day at the basin margin (Figure 6.11 through Figure6.40).The present-day maturation level of the stratigraphic unit 4 (Figure 6.43) suggeststhat this unit is overmature (reaction extent = 100%) with respect to the oil windowin the central and south central parts of the basin. The degree of maturation of this318unit decreases westward and northwestward toward the basin margin. This unit isstill within the oil generation window in the northern and western parts of the basin.It is immature in the western-most margin of the basin. The main phase ofhydrocarbon generation began from 20 Ma in the basin center to 2-3 Ma at thebasin margin (Figure 6.48). The peak generation rates of unit 4 started from about19 Ma in the basin center to the present-day at the margin.The present-day level of maturation of the stratigraphic unit 3 (Figure 6.44)indicates that this unit is overmature (reaction extent = 100%) with respect to theoil window in the central part of the basin. It is within the oil window in the westcentral, north central, and southeastern parts of the basin. It is immature in thewestern and northern parts of the basin (Figure 6.44). The main phase ofhydrocarbon generation started from 16 Ma in Trat-1 well in the basin center to thepresent-day in the area more to the west (Figure 6.49).The present-day level of maturation of the stratigraphic unit 2 (Figure 6.45)suggests that this unit is overmature with respect to the oil window in a small areain the south central part of the basin. From this area, the degree of maturationdecreases outward in every direction. This unit is still within the oil generationwindow in a narrow band extending from the north central to the south central andsoutheastern parts of the basin. It is still immature in much of the western part ofthe basin. The main hydrocarbon generation phase started from 6 to 9 Ma in thecentral part of the basin to about 1 Ma in the mature zone in the west central area.In many locations the generation rates have not yet reached the peak level.319Stratigraphic unit 1 is immature with respect to the oil generation window in alllocations in the study area. The present-day maturation level of this unit suggeststhat less than 3% of kerogen has been converted to hydrocarbons.6.7 DISCUSSION6.7.1 Variation of Kinetic ParametersThe characteristics of the kinetic parameters of each stratigraphic unit and thepossible influence of sample preparation, kerogen types, and depositionalenvironments on the kinetic parameters of the sediments are examined in thissection.a. Sample preparation vs. kinetic determinationsThe effect of sample preparation, i.e. whole rock sample vs. kerogen, indetermining kinetic parameters using Rock-Eval pyrolysis has been a subject ofdiscussion. Espitalie et al. (1980) reported that organically lean, gas prone, clasticsediments were most likely to be affected by the mineral matrix during pyrolysis.Burnham and Sweeney (1989) suggested that kinetic differences between wholerock and kerogen samples of an organically rich sediment were negligible becausethe mineral matrix interferences were minimal. In order to test the effect of sampletype on kinetic parameters, both the whole rock sample and the kerogen ofsediments containing 1.0-1.5% TOC were analyzed. Mean activation energies (E0)of kerogens are slightly higher than those of the whole rock samples, whereas thereis no significant difference in their dispersions (aE, Figure 6.51). The slight32040 45 50 55 60 65 70 75^ 4^6^8Activation energy: Whole rock (kcal/mol) Distribution of act. energy: Whole rock (% Eo)Figure 6.51: The effect of sample preparation (whole rock v.s. kerogen) on kinetic parametersFigure 6.52: Variation of kinetic parameters v.s. depositional environment. 2. Channel deposits;3. Floodplain deposits; 4. Distributary mouth bars; 5. Shallow marine deposits.es 100We■ 860■ III■ ■ ..aCa• • .E^655-^• ■13es^4Ir---------als 11 "5■ ■50 ■as■ ■ ••■4.002 3 4 5Depositional environments2^3^4^5Deposkional environments321difference in kinetic parameters of whole rock samples and kerogens may be theresult of mineral matrix interference as suggested by Espitalie et al. (1980).Espitalie et al. (1980) indicated that, during pyrolysis some minerals, such as illite,retain heavy hydrocarbons ( > C 15) generated from kerogen. The trapped heavyhydrocarbons ( > C 15) may be subsequently cracked at higher temperatures. Such aphenomenon may increase the value of T ., hence affecting the value of meanactivation energy and its dispersion. Such a result suggests that, for a sedimentwith high TOC, either a whole rock sample or kerogen can be used for modellinghydrocarbon generation. For organically lean sediments, whole rock samples shouldbe used for hydrocarbon generation modelling because the effect of mineral matrixinterference may become significant.b. Type of organic matter vs. kinetic variationMean activation energies of the Tertiary strata in the Pattani Basin, Gulf ofThailand, which mainly contain Type III OM and a mixture of Type II-III OM,generally range from 46.1 to 60.6 kcal/mol (Table 6.1; Figure 6.10). This rangeof values coincides reasonably well with the activation energies required to breakdown carbon-oxygen and carbon-carbon bonds (40 to 70 kcal/mol; Tissot andWelte, 1984; Waples, 1985). Because organic matter in the Pattani Basin is mainlyType III OM and a mixture of Type II and Type III OM, it is impossible tocompare the kinetic parameters between different types of organic matter in thestudy area. It is, however, possible to compare the results from this study withthose of others such as Tissot and Welte (1984) and Burnham et al. (1987). Themean activation energy of the Tertiary strata in the study area is comparable withthat of Type II and Type III source rocks in Paris Basin, France and Duoala Basin,Cameroon respectively (about 50-60 kcal/mol; Tissot and Welte, 1984), although322the dispersions of activation energies are different because this study assumes aGaussian distribution of activation energies, whereas Tissot and Welte's (1984)study employed a discrete distribution. The kinetic parameters of Tertiary strata inthe study area compare reasonably well with those of whole rock samples andextracted kerogen containing Type I and Type II OM studied by Burnham et al.(1987). This study and the study of Burnham et al. (1987) show that meanactivation energies of kerogen and source rocks, regardless of the type of OM, aresufficiently variable that one cannot assume that activation energies depend only onkerogen type. Such a variation may reflect the difference in chemical compositionof kerogen.c. Depositional environment vs. kinetic variationMean activation energies (E0) of organic matter deposited in different depositionalenvironments in the study area extend over almost the same interval (45-60kcal/mol, Fig 6.52). There is no correlation between depositional environment andmean activation energies. The dispersion of activation energies (o-E) is, however,slightly higher in nonmarine and coarse-grained beach and distributary mouth bardeposits than in fine-grained shallow marine and interdistributary bay deposits(Figure 6.52). This relationship may relate to grain-size distribution of sedimentswhich, in turn, relate to the energy regime during deposition. Interdistributary bayand shallow marine sediments were deposited under uniform and low energyenvironments, resulting in uniform organic matter distribution and thus lowervariation in activation energies and lower CIE values. Nonmarine channel,floodplain and coarse-grained beach and distributary mouth bar sediments, on theother hand, were deposited under high energy and often laterally discontinuous323environments, resulting in highly variable sediments and organic matter, which inturn resulted in a higher variation of activation energies and higher o-E values.d. Degree of thermal maturation vs. kinetic variationA weak negative correlation occurs between degree of organic maturation and meanactivation energies (E0) of organic matter in the study area (Figure 6.53). Thedispersion of activation energies (o-E), on the other hand, shows a positivecorrelation against degree of organic maturation (Figure 6.53). Such correlationsmay indicate the original variation of kinetic properties of organic matter, due tothe difference in kerogen composition, rather than the effect of maturation. This isbecause kinetic parameters (A, E0, and QE) of the hydrocarbon generation processare independent of the degree of thermal maturation, and represent a wide range ofsimultaneous reactions occurring during maturation (Braun and Burnham, 1987).The effective activation energy, which is actually the activation energy of theremaining material, however, increases with the degree of pre-reaction (maturity) ascan be seen from the increasing T x with thermal maturation. This phenomenoncan be explained by the fact that at low maturity, only reactions with low activationenergies occur, and as the maturity increases, those reactions with low activationenergies gradually continue to completion, yielding reactions with higher activationenergies. The effective activation energy of the reaction, which is an average ofthose high activation energies, is, therefore, relatively higher in more maturesamples.6.7.2 Hydrocarbon Generation HistoryAs noted earlier that hydrocarbon generation modelling of all stratigraphic units was32480 10020^40^80Generation extent (ti,)0.5 1.0 1.5Ro (%)20 25 a o■Esi.••▪ • -••lo• ■■a ^•■ ■10 ^6 a ^2 ^a0 ^0-a ■^al^ ^AL.■• •111-1—■■—____11—20^40^80^80^100Generation Went (%)Figure 6.53: Variation of kinetic parameters v.s. degree of organic maturation325carried out at their basal boundaries; hence, the timings of generation obtained fromthis study reflect the earliest possible times of generation for these units. Comparedto most other basins, hydrocarbon generation in the Pattani Basin is relatively early.The relatively early hydrocarbon generation in most stratigraphic units (generally 5-7 m.y. after deposition or 35-33 Ma in the basin center) is attributed mainly to highgeothermal gradients and rapid deposition of sediments, especially in the basincenter. Rapid sedimentation and rapid burial combined with high geothermalgradients resulted in rapid temperature increase and consequently rapid and earlyhydrocarbon generation of a stratigraphic unit. This rapid hydrocarbon generationis characterized by a narrow and high reaction rate profile (Figure 6.11 throughFigure 6.40). Relatively later and slower hydrocarbon generation occurring in thebasin margin, on the other hand, was caused by lower geothermal gradients,relatively slow sedimentation and burial-hence slow temperature increase and slowgeneration rate. This slow generation rate is characterized by a broad and lowreaction rate profile (Figure 6.11 through Figure 6.40). The other cause of rapidhydrocarbon generation especially in unit 6 is its low activation energy (46.7kcal/mol). Such a low activation energy indicates that unit 6 would generatehydrocarbon at lower temperatures and hence earlier than units with higheractivation energy.6.7.3 Hydrocarbon Potential ConsiderationsThe present-day maturation levels of all the Tertiary stratigraphic successions in thePattani Basin suggest that most of the stratigraphic units except unit 1 are eithermature or overmature with respect to the oil window. Hydrocarbon generationstarted as early as 33-35 Ma and lasted until the present-day. There is no doubt thatany potential source rocks in this area would have generated or still are generating326hydrocarbons. The quality of the source rocks is, however, questionable. All thesamples available for this study show very low TOC contents (in average, less than0.4% in units 6, 5, 4, and 3, and about 0.5% in unit 2) and low genetic potentials(less than 1.0 mg HC/g rock). Almost all samples have genetic potentials less thangenerally considered necessary for accumulation of commercial hydrocarbondeposits (Tissot and Welte, 1984). The fact that the Pattani Basin is one of theproducing basins suggests either the source rocks here, despite very low geneticpotential, are very effective in producing, migrating, and accumulatinghydrocarbons. Alternatively, it indicates the presence of higher quality sourcerocks within the basin that have not been reached by drilling, or a combination ofboth factors.6.7.4 Other ConsiderationsIn the Pattani Basin, hydrocarbons are currently produced from reservoir packagesof channel, beach, and distributary mouth bar sandstones of middle and uppersynrift sequences (Lian and Bradley, 1986; Chinbunchorn et al., 1989). Theporosity of these sandstones ranges from 15 to 30% at depths above 2700 m (Lianand Bradley, 1986). Below this depth, sandstones are generally too tight to bereservoirs. Reservoir rocks of good quality are also likely present in coarse-grainedalluvial fan and braided channel sediments on the flanks of the basin as well aschannel sandstones of the post-rift sequences. All reservoirs encountered in thePattani Basin are, however, generally small, with rapid horizontal and verticalchanges in qualities such as thickness, facies and porosity (Lian and Bradley, 1986).The reservoirs here are also highly compartmentalized due to high fault density.327The potential seals in the Pattani Basin are fine-grained claystones and shales offloodplain, interdistributary bay and shallow marine deposits. Floodplainclaystones may be laterally discontinuous, and hence may not be good seals. Incontrast, interdistributary bay and shallow marine shales are likely to be morelaterally extensive, hence make better seals. Clay smear-controlled fault-seals arealso one of the main sealing mechanisms in the study area (Burri, 1989).In an extensional rift basin such as the Pattani, structural traps are the majortrapping mechanism. The traps include tilting fault blocks, faulted and rolloveranticlines. However, stratigraphic traps such as pinch-out sandstone bodies are alsobelieved to play an important role in the accumulation of commercial hydrocarbondeposits in the Pattani as well as other Tertiary basins in Thailand. Timing of trapformation relative to petroleum generation and migration is very important in theformation of commercial hydrocarbon deposits. If traps predate migration, the areawill be productive. High sedimentation rates in the study area might have createdearly seals, which together with block faulting during rifting, might have resulted inthe occurrence of traps predating hydrocarbon migration.6.8 SUMMARY AND CONCLUSIONSBy using a simple linear regression/correlation technique, kinetic parameters of akerogen such as a pre-exponential factor (A) , the mean activation energies (E 0) ,and the dispersions of the activation energies (o-E) can be determined from theRock-Eval analyses of kerogen at multiple heating rates.Mean activation energies (E0) of the potential Tertiary source rocks in the PattaniBasin range from 46.1 to 60.6 kcal/mol, which coincide reasonably well with the328activation energies required to break down carbon-oxygen and carbon-carbon bonds(40 to 70 kcal/mol). The dispersions of the activation energies (aE) range from0.26 to 9.30% of the mean values.Kerogen type, as defined by Rock-Eval pyrolysis, includes a wide range ofactivation energies. A wide range of activation energies may reflect differences inthe chemical composition of kerogen. The depositional environments of thesediments have no influence on the values of mean activation energies, but show aweak influence on the dispersion of the activation energies. In general, highactivation energy dispersions (aE) correspond to sediments deposited under a highenergy regime, whereas low activation energy dispersions (aE) correspond tosediments deposited under a low energy regime. Such results indicate that theenergy regime hence the depositional environment may have an effect on aredistribution of organic matter and the variation of its activation energy dispersion(aE) within sediments.In the study area, the degree of organic maturation shows a weak negativecorrelation with mean activation energies (E0) but a positive correlation with thedispersion of activation energies (o-E). Such correlations may reflect the originalvariation of kinetic parameters of organic matter, due to difference in the kerogencomposition, rather than the effect of degree of organic maturation. The kineticparameters of organic matter in sediments are independent of the degree of organicmaturation. The effective activation energy of a sample, which is actually theaverage activation energy of the remaining material, increases with the degree ofthermal maturation because at high maturity levels, reactions with lower activationenergies are already complete; the effective activation energy of the remaining329material, therefore, represents only those reactions with high activation energies.The result is a higher effective activation energy in a more mature sample.Compared to other basins, hydrocarbon generation in the Pattani Basin is relativelyearly, about 5-7 m.y. after deposition. This early generation is attributed to thearea's high geothermal gradients and rapid sedimentation, and hence high heatingrates for the stratigraphic successions. In some stratigraphic units (unit 6), lowmean activation energy also enhanced early generation. Most of the stratigraphicunits in the Pattani Basin, except the youngest unit (unit 1), are either mature orovermature with respect to the oil window. The main phase of hydrocarbongeneration began at about 33-35 Ma and will continue into the future.Although most samples available for this study are very lean in TOC content andhave low genetic potentials, the fact that the area is a producing one suggests thateither the poor hydrocarbon potential of the sediments is offset by the great volumeof low-yield source rocks, good migration and drainage enhanced by interbeddedsandstones, or the presence of unsampled good quality source rocks in the basin.The possible source rocks may be the synrift and post-rift lacustrine and marinedeposits which are not reached by drilling.The presence of good, although laterally discontinuous, reservoir rocks, thejuxtaposition of source and reservoir rocks, and structural and stratigraphic traps inthe study area are the key factors that made the Pattani Basin a prolific hydrocarbonbasin.3307. SUMMARY AND CONCLUSIONSThe Pattani Basin, the Gulf of Thailand, is filled with Tertiary and Quaternarysediments. The basin formed during the Early Tertiary as a result of extensionalrifting related to the collision of India with Eurasia. Stratigraphic correlations andsedimentology were carried out based on wireline logs, seismic sections, andbiostratigraphic data. Subsidence and thermal histories of the basin were predictedbased on the lithospheric stretching model (McKenzie, 1978; Hellinger and Sclater,1983). Source rock potential and characteristics were made based on Rock-Evalpyrolysis data and organic petrography. Hydrocarbon generation histories ofdifferent strata were calculated based on a chemical kinetic model of organicmaturation (Sweeney and Burnham, 1990; Sweeney, 1990).The extensional origin of the Pattani Basin has a major effect on the subsequentgeologic and stratigraphic evolution. The opening of Tertiary basins in ContinentalSoutheast Asia, including the Pattani Basin, is related to collision of the northwardmoving Indian subcontinent with Eurasia in the Eocene. The penetration of Indiainto Eurasia caused clockwise rotation of Southeast Asia, resulting in anincreasingly oblique subduction of the Indian Ocean plate beneath the western edgeof Southeast Asia. This, in turn, changed the stress field of the region from one ofconvergence to one with a major component of strike-slip movement. The change instress field led to right-lateral movement on major NW-SE fault systems, and left-lateral movement on conjugate NE-SW fault systems. The resultant strain ellipsoidindicates the E-W extension associated with right-lateral fault systems. The E-Wextensional tectonic regime included lithospheric stretching and crustal andsubcrustal thinning in Thailand, which led to the occurrence of N-S trending331sedimentary basins along an old Triassic-Jurassic suture zone, which is the weakestzone in the local lithosphere.The stretching of the lithosphere caused rifting in the Continental Southeast Asia aswell as in the proto-Pattani Basin. Synrift and post-rift subsidence, analyzed usinggeohistory analysis and basin modelling, can generally be accounted for by simpleextension causing a nonuniform, crustal and subcrustal lithospheric thinning. Thevalidity of the nonuniform lithospheric stretching as a mechanism responsible forthe formation of the Pattani Basin is confirmed by a reasonably good agreementbetween the modeled and observed vitrinite reflectance values (one of the maturityindices) at various depths and locations. The amount of lithospheric stretching aswell as surface heat flow in the Pattani Basin generally increases from the basinmargin to the basin center. The crustal stretching factor ((3) ranges from 1.3-1.4 atthe basin margin to 2.6-2.8 in the center. The subcrustal stretching factor (5) variesfrom 1.3 at the basin margin to more than 3.0 in the basin center. Generally, theamount of subcrustal stretching is greater than that of crustal stretching except inareas with great thicknesses of synrift sediments where the amount of crustalstretching is greater than that of subcrustal stretching. Such areas might have beenaffected by the pre-existing basement topography prior to rifting.The stretching of the crust across the Pattani Basin may have been as much as 45 to90 km (13 = 1.3-2.8), and may have caused passive upwelling of hotaesthenosphere, resulting in high surface heat flow. Because the Pattani Basin isrelatively young (less than 20 m.y. after rifting), it still has elevated thermalgradients and is in thermal disequilibrium, as is evident from its high present-daysurface heat flow (1.9-2.5 HFU) and high geothermal gradient (45-60°C/km).332Rifting has been the major control of the rate and amount of subsidence and theamount of sediment supply into the Pattani Basin. The rate and amount of basinsubsidence, the sediment influx, and the fluctuation in the eustatic sea level duringdeposition has, in turn, dictated the sedimentary signatures recorded in the studyarea. The sedimentary succession in the Pattani Basin is divided into synrift andpost-rift sequences. The synrift sequence comprises three stratigraphic units. Thebasal unit comprises Late Eocene to Early Oligocene nonmarine, alluvial fan andbraided stream deposits in the lower part and floodplain deposits in the upper part.The middle synrift unit comprises Late Oligocene to Early Miocene nonmarine,floodplain-channel deposits in the lower part and coarse-grained channel deposits inthe upper part. The upper synrift succession comprises an Early Miocene,regressive sequence, in which basal prodelta to shallow marine sediments areoverlain by distributary mouth bar deposits and beach ridge complexes. These, inturn, are overlain by nonmarine floodplain and meandering channel deposits.Deposition of the synrift sequences was synchronous with extension of ContinentalSoutheast Asia, which was accompanied by episodic block faulting and rapidsubsidence. The main characteristics of the synrift sequence are a high rate ofsubsidence and a large influx of sediment supply, both the direct result of rifting.The first marine transgression in the Pattani Basin in the Early Miocene might havebeen a result of rapid subsidence due to block faulting and/or a eustatic rise in sealevel. The following regressive succession in the upper part of the synrift sequenceresulted when the rate of deposition exceeded the rate of relative sea level rise.Beyond the reach of drilling, a thick succession of synrift lacustrine deposits arebelieved to have been deposited in the center of the basin throughout the early partsof the rifting period.333The post-rift succession also comprises three stratigraphic units. The lower post-riftunit is an Early to Middle Miocene regressive sequence in which basal prodelta andshallow marine sediments are overlain by distributary mouth bar and beach ridgecomplexes which, in turn, are overlain by nonmarine floodplain and channeldeposits. The post-rift phase coincided with a slower subsidence rate and adecreasing sediment influx. Hence, eustatic sea level fluctuations had a moreimportant affect on sedimentation. A late Early Miocene transgression, which wasprobably the result of a rapid eustatic sea level rise, created a brief period ofnondeposition during which the rate of relative sea level rise exceeded the rate ofdeposition. Later, as the rate of deposition slowly exceeded the rate of relative sealevel rise, a broad regressive sedimentary succession prograded. The middle post-rift unit represents a Middle Miocene transgressive succession that was probably theresult of a slow rise of relative sea level and a decreasing amount of sedimentsupply due to lowering of source areas. Rapid fall of relative sea level resulted insubaerial exposure, intense oxidation, and possibly erosion of the Middle Miocenestrata, and was probably the result of eustatic sea level fall at the end of the MiddleMiocene (Haq et al., 1988). The upper post-rift unit is a Late Miocene toPleistocene transgressive succession indicating a slow rise of relative seal level.This was probably caused by a slow rise in eustatic sea level, slow subsidence, anda decreasing sediment supply. The present-day shallow marine condition in thePattani Basin is the continuation of the latest transgressive phase.The dispersed organic matter in Tertiary strata in the Pattani Basin is composedmainly of Type III and Type IV kerogens with minor amounts of mixed Type II-IIIkerogens. Due to the nonmarine and marginal marine features of the sediments, thepresence of low HI and high OI values, and the type of organic matter (mainlyvitrinite), the organic matter found in these sediments is interpreted to be334predominantly of detrital and continental origin. Variation of organiccharacteristics occurs both within and across stratigraphic units. Within eachstratigraphic unit, the lowest TOC and HI occur in high energy nonmarine depositssuch as alluvial fan and braided stream deposits, whereas higher TOC and HIgenerally occur in low energy deposits. TOC and HI values also increase fromnonmarine deposits to interdistributary bay and shallow marine deposits. TOC andHI generally increase in progressively younger strata. The abundance of organicmatter within sediments is the result of the combination of organic input intosediments and degree of organic preservation. Higher TOC and HI values infloodplain and interdistributary bay deposits may reflect the proximity to marshcomplexes, a source of organic matter. Fine-grained sediments further enhance thedegree of organic preservation by the rapid development after deposition ofanaerobic conditions that reduce oxidation and the destruction of organic matter.The variation of abundance and characteristics of organic matter in the basin was,therefore, controlled, in large part, by depositional environments. A generalincrease in TOC and HI with decrease in age may reflect an increasing degree ofpreservation and/or increasing proximity to sources of organic matter as the basinaged.A very weak correlation between TOC and HI and the degree of organic maturation(extent of hydrocarbon generation and vitrinite reflectance) in sediments in thestudy area can be explained by the original variation in TOC and HI from place toplace within the same stratigraphic unit and across the units.Sedimentation rate, corrected for compaction, of Tertiary strata in the Pattani Basinranges from 0.023 km/m.y. to more than 1.2 km/m.y. Such high sedimentationrates are common in Tertiary deltaic deposits and are much higher than those of335marine sediments. The effect of sedimentation rate on the abundance of organicmatter in nonmarine and deltaic deposits in the study area is apparent only in unitscontaining relatively high TOC (e.g., 0.6-2.2%, unit 1). In the units with lowTOC (less than 0.5%), original variation of TOC within the sediments has a greatereffect than sedimentation rate. A strong negative correlation between TOC andsedimentation rate in unit 1 indicates the effect of clastic dilution of organic input assedimentation rate increases.Source rocks of Tertiary strata in the Pattani Basin represent an end member interms of composition and properties. The source rocks here contain mainly TypeIII, Type IV kerogens, and minor amounts of mixed Type II-III kerogen and havevery low hydrocarbon potential as defined by pyrolysis (Tissot and Welte, 1984).Numerous commercial gas fields in the basin suggest that either the source rockshere, despite very low genetic potential, are very effective in producing, migrating,and accumulating hydrocarbons, or the presence of higher quality source rockswithin the basin which have not been reached by drilling, or a combination of bothfactors.Kinetic parameters of source rocks in Tertiary strata in the Pattani Basin in terms ofa pre-exponential factor (A) , mean activation energies (E 0) , and the dispersions ofthe activation energies (QE)) were determined from Rock-Eval analyses of wholerock samples at multiple heating rates using a linear regression/correlationtechnique. The mean activation energies of the potential source rocks vary from46.1 to 60.6 kcal/mol, and coincide reasonably well with the activation energiesrequired to break down carbon-oxygen and carbon-carbon bonds (40 to 70kcal/mol). The dispersion of activation energies (ok) ranges from 0.26 to 9.30% ofthe mean value (E 0) .336The effects of sample preparation on kinetic determination were studied bycomparing kinetic parameters derived from whole rock and kerogen samples of thesame sediments. The results suggest that, for sediments with high TOC, eitherwhole rock samples or kerogen can be used for modelling hydrocarbon generation.For organically lean sediments, whole rock samples should be used to modelhydrocarbon generation because the effect of matrix adsorption may becomesignificant.Comparison of activation energies of source rocks in the study area with otherareas, indicates that activation energies are sufficiently variable that one cannotsafely assume that they depend only on the kerogen type. Such a variation mayreflect difference in the chemical composition of kerogen. Depositionalenvironments have no influence on the value of mean activation energies (E0) butshow a weak influence on their dispersions (o-E). In general, wide dispersions ofactivation energies (crE) correspond to sediments deposited under a high energyregime, whereas narrow activation energy dispersions (o-E) correspond to sedimentsdeposited under a low energy regime. Such results suggest that the depositionalenvironment may have an effect on redistribution of organic matter and thus on thevariation of its activation energy dispersion (ok) within sediments. By using adistribution of activation energies, kinetic parameters of the organic matter insediments are independent of the degree of organic maturation. The effectiveactivation energy, which is the average activation energy of the remaining material,increases with the degree of thermal maturation because at high maturity levels,reactions with low activation energies have already occurred, and the effectiveactivation energy of the remaining material, therefore, is for those reactions withhigh activation energies. The result is a higher effective activation energy in a337more mature sediment. The apparent correlation between degree of organicmaturation and kinetic parameters of organic matter in the study area may reflectthe original variation of the kinetic properties of organic matter rather than theeffect of degree of maturation.Most of the stratigraphic units in the study area, except the youngest unit (unit 1),are either mature or overmature with respect to the oil window. The main phase ofhydrocarbon generation began about 33-35 Ma and will continue into the future. Arelatively early hydrocarbon generation (about 5-7 m.y. after deposition) isattributed to high geothermal gradients and rapid sedimentation and burial, andhence high heating strata. 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Haw, 1976, Tertiary stratigraphy and sedimentation inthe Gulf of Thailand, Presented at the Offshore South Fast Asia Conference,SEAPEX Program, paper 7.347APPENDIX ABASIN FORMATION MODELLINGThe basin formation modelling program used in this study to predict subsidence, theamount of crustal and subcrustal lithospheric stretching, and heat flow of the basinis based on a modified McKenzie's lithospheric stretching model, in which the crustis thinned by different amounts from that of subcrustal lithosphere (Hellinger andSclater, 1983; See detail in CHAPTER 4). The model first decompacts theobserved (present-day) thickness to calculate the subsidence history, then backstripsall the overlying sedimentary layers to calculate tectonic subsidence of the basementof the basin (Van Hinte, 1978; Allen and Allen, 1990). The program subsequentlyuses a nonuniform lithospheric stretching model to calculate tectonic subsidencehistory at different amounts of stretching (Hellinger and Sclater, 1983; Friedinger,1988). The modeled tectonic subsidence is then used to best-fit the tectonicsubsidence obtained from backstripping. When the best-fitted model is obtained,the program subsequently uses the crustal and subcrustal stretching factors ((3 and 5respectively) to calculate surface heat flow and temperature histories of the basin.This program requires two input files. The first input file contains thermo-physicalproperties of the lithosphere, crust, and sediments; and the modelling parameters.The second input file contains well information such as depth, lithology,paleobathymetry, and age of the stratigraphic units. The output from the programincludes decompacted subsidence of the stratigraphic units, basement subsidence,crustal and subcrustal lithospheric stretching factors (0 and 5), surface heat flowand temperature history of the basin. The format of input and output files is shownas follows.348FIRST INPUT FILE: EXAMPLE.IN1'EXAMPLE-1 EHFU = 1.2 NONUNIFORM STRETCHING'^Line 10,1.03,3.33^ Line 23^ Line 3'SH',0.63,0.51,2.72,5.5,'E'^ Line 4'SD',0.49,0.27,2.65,9.6,'E' Line 5'SS',0.56,0.39,2.68,7.5,'E'^ Line 63.3,1.2,1350.0,125.0,35.0,62.8,2.8,7.5^ Line 71.3,1.8,0.1,2.0,2.4,0.1,20^ Line 810^ Line 940,80,120,160,200,10^ Line 10Line 1:^Well name in single quotation marksLine 2:^1st number is 0 when the datum is sea floor or1 when the datum is sea level2nd number is sea water density (g/cm)3rd number is mantle density (g/cm)Line 3:^Numbers of lithologies present in the study areaLine 4-6: 1st input is the lithology in single quotation marks2nd input is the surface porosity (decimal point)3rd input is the compaction constant (x10-5cm-1)4th input is the grain density (g/cm3)5th input is the grain's thermal conductivity(mcal/cm sec °C)6th input is the type of porosity-depth functionin single quotation marks349E when it is exponentialL when it is linearLine 7^1st input is thermal expansion coefficient oflithosphere (x10-5/ °C)2nd input is the equilibrium heat flow (HFU)3rd input is temperature of mantle (°C)4th input is thickness of lithosphere (km)5th input is pre-rift thickness of crust (km)6th input is thermal-time constant (m.y.)7th input is density of mantle (g/cm)8th input is thermal conductivity of lithosphere(mcal/cm sec °C)Line 8:^1St input is the lower limit of 02nd input is the upper limit of 03rd input is the increment of 04th input is the lower limit of 55th input is the upper limit of 66th input is the increment of 67th input is the time when thermalcooling started (m.y.)Line 9:^numbers of isotemperature lines to be calculatedmaximum = 10Line 10: 1st to 5th input are values of temperature to becalculated (°C)6th input is surface temperature (°C)350SECOND INPUT FILE: EXAMPLE.IN2'EXAMPLE-1 THE GULF'^ Line 17^ Line 20.0,0.073,'SH',0.0,0.0^ Line 312.0,1.143,'SS',0.0,0.0 Line 415.0,1.617,'SS',0.0,0.0^ Line 520.0,1.848,'SS',0.0,0.0 Line 624.0,2.211,'SS',0.0,0.0^ Line 730.0,2.562,'SS',0.0,0.0 Line 840.0,2.898,'SS',0.0,0.0^ Line 9Line 1:^well name in quotation marksLine 2:^numbers of stratigraphic unit including basementLine 3-9: 1st input is the age of upper boundary of thestratigraphic unit (Ma)2nd input is the present depth below sea level (km)3rd input is the lithology in quotation marks4th input is the paleowater depth (km)5th input is the eustatic sea level change compare tothe present day sea level (km)OUTPUT FILE: EXAMPLE.OUT****LITHOSPHERIC STRETCHING BASIN MODELLING****WELL-NAME: EXAMPLE-1 THE GULF351EXAMPLE-1 THE GULF^DECOMPACTED COLUMNS (DEPTHS IN REFERENCETO SEA FLOOR ):40.0 30.0 24.0 20.0 15.0 12.0 0.00.00 0.00 0.00 0.00 0.00 0.00 0.00**** 0.54 0.55 0.54 0.34 0.63 1.07**** 1.01 1.01 0.83 0.90 1.54**** 1.42 1.26 1.33 1.78**** 1.66 1.72 2.14**** 2.09 2.49**** 2.83EXAMPLE-1 THE GULF(BASEMENT DEPTH IN REFERENCE TO SEA FLOOR ):1 2 3 4 5 6 740.0-30.0 1.847 0.505 0.543 0.054 0.350 0.03540.0-24.0 1.916 0.463 1.007 0.063 0.619 0.03940.0-20.0 1.970 0.430 1.419 0.071 0.839 0.04240.0-15.0 1.999 0.413 1.655 0.066 0.957 0.03840.0-12.0 2.048 0.383 2.085 0.075 1.163 0.04240.0-00.0 2.111 0.350 2.825 0.071 1.498 0.038column 1: Time interval (m.y.)column 2: Density of sedimentary columncolumn 3: Porosity of sedimentary columncolumn 4: depth to basement (km)352column 5: Total subsidence (km)column 6: Unloaded basement depth (km)column 7: Subsidence rate (km/m.y.)EXAMPLE-1 THE GULFBASEMENT SUBSIDENCE IN REFERENCE TO SEA FLOORAND SEDIMENTATION :1 2 3 4 5 6 7 8 9 1040.0-30.0 .543 .054 .350 .035 .543 .543 .577 .577 SS30.0-24.0 .463 .077 .269 .045 .547 .091 .581 .097 SS24.0-20.0 .412 .103 .220 .055 .542 .136 .575 .144 SS20.0-15.0 .236 .047 .119 .024 .343 .067 .356 .071 SS15.0-12.0 .431 .144 .205 .068 .625 .208 .670 .223 SS12.0-00.0 .740 .062 .335 .028 1.070 .089 1.286 .107 SScolumn 1: Time interval (m.y.)column 2: Basement subsidence (km)column 3: Subsidence rate (km/m.y.)column 4: Tectonic subsidence (km)column 5: Tectonic subsidence rate (km/m.y.)column 6: Sedimentary layer thickness (km)column 7: Sediment accumulation rate (km/m.y.)column 8: Initial layer thickness (km)column 9: Sediment supply rate (km/m.y.)column 10: Lithology353EXAMPLE-1 THE GULF^BEST-FITTING MODEL:DIFFERENCE MODEL/OBSERVATION ^0.05CRUSTAL STRETCHING (BETA) ^ 1.500SUBCRUSTAL STRETCHING (DELTA) ^2.100TOTAL LITHOSPHERE ATTENUATION ^1  888INITIAL SUBSIDENCE^ 0  994START OF RIFT-PHASE 40.000START OF THERMAL COOLING ^ 20.000PRESENT-DAY SURFACE HEAT FLOW^2.159EQUILIBRIUM HEAT FLOW OFLITHOSPHERE ^ 1.200EXAMPLE-1 THE GULF^BEST-FITTED MODEL:ISOTHERMS (IN KM) BELOW SEA FLOOR1 2 3 4 5 6 7 8 9 1019.0 1.0 0.020 1.01 2.25 0.43 1.10 2.17 3.51 4.8415.0 5.0 0.099 1.09 2.25 0.43 1.10 2.02 3.35 4.6812.0 8.0 0.162 1.16 2.25 0.44 1.10 1.89 3.11 4.4500.0 20.0 0.417 1.41 2.16 0.40 0.93 1.66 2.58 3.88column 1: Time before present (Ma)column 2: Elapsed time after the end of rifting (m.y.)column 3: Thermal subsidence (km)column 4: Total tectonic subsidence (km)column 5: Surface heat flow (HFU)354column 6: Depth at which subsurface temperature = 40°C (km)column 7: Depth at which subsurface temperature = 80°C (km)column 8: Depth at which subsurface temperature = 120°C(km)column 9: Depth at which subsurface temperature = 160°C (km)column 10: Depth at which subsurface temperature = 200°C (km)TO RUN THIS PROGRAM:1. Insert a computer disk containing the "BASIN" program in to thecomputer drive2. Type "BASIN" then press ENTER3. Type 1st input file name (Thermo-physical properties and modelparameters file) e.g. "EXAMPLE.IN1" then press ENTER4. Type 2nd input file name (Well information file)e.g. "EXAMPLE.IN2" then press ENTER5. Type name of the output file e.g. "EXAMPLE.OUT"then press ENTER355APPENDIX BORGANIC MATURATION MODELLINGThe organic maturation modelling program used in this study to predict the extentof hydrocarbon generation through time and the vitrinite reflectance is based on thechemical kinetic model of Braun and Burnham (1987) and Sweeney (1990). Thisprogram proposes that chemical reaction kinetics for natural materials such ashydrocarbon generation can be better described by models using a distribution ofactivation energies (See detail in CHAPTER 6). The program requires two inputfiles. The first file contains time-temperature history of the stratigraphic unit ofinterest. The second input file contains the unit's kinetic parameters. This programalso requires one more input file containing the kinetic parameters for vitrinite, butthis input file will be read automatically without the user's input. The output fromthe program includes the extent and rate of hydrocarbon generation through time,the corresponding vitrinite reflectance value, and the Tmax value if the sample ispyrolyzed. The format of input and output files is shown as follows.FIRST INPUT FILE: EX.IN3^ Line 1'Time-Temp Model-1'^ Line 25^ Line 3^0.000 10.000^ Line 42.000 20.000 Line 57.000 40.000^ Line 610.000 60.000 Line 712.000 66.000^ Line 8356'Time-Temp Model-2'^ Line 94^ Line 10^0.000 10.000^ Line 114.000 40.000 Line 1214.000 80.000^ Line 1326.000 140.000 Line 14'Time-Temp Model-3'^ Line 154^ Line 160.000 10.000^ Line 179.000 20.000 Line 1811.000 40.000^ Line 1912.000 54.000 Line 20Line 1:^Number of the time-temperature historymodels to be runLine 2:^Name of the 1st model in single quotation marksLine 3:^Number of time-temperature pairs for the modelLine 4-8: 1st input is time after deposition (m.y.)2nd input is the corresponding temperature (°C)Line 9: As Line 2Line 10: As Line 3Line 11-14: As line 4-8And ^ > So on...357SECOND INPUT FILE: KIN.ARR17^ Line 14.2964E+14^ Line 20.000068 46765.8847^ Line 30.000441 47536.8015 Line 40.002242 48307.7183^ Line 50.008866 49078.6351 Line 60.027310 49849.5519^ Line 70.065512 50620.4687 Line 80.122393 51391.3855^ Line 90.178081^52162.3023 Line 100.201792 52933.2191^ Line 110.178081^53704.1359 Line 120.122393 54475.0527^ Line 130.065512 55245.9695 Line 140.027310 56016.8863^ Line 150.008866 56787.8031 Line 160.002242 57558.7199^ Line 170.000441 58329.6367 Line 180.000068 59100.5535^ Line 19Line 1:^Number of influential factor-activation energy pairsLine 2:^Pre-exponential factor (sec 1)Line 3-19: Pt input is the influential or weighing factor2nd input is the corresponding activationenergy (cal/mol)358OUTPUT FILE: EX.OUTFor Model # 1For the Time-Temp Model-1Time^Temp(my)^(°C)OilgenwellGenrate %Ro Conrate0.00^10.0 0.00 0.00E+00 0.20 0.00E+001.00^15.0 0.00 0.11E-23 0.23 0.34E-152.00^20.0 0.00 0.47E-23 0.23 0.32E-153.00^24.0 0.00 0.15E-22 0.24 0.38E-154.00^28.0 0.00 0.44E-22 0.25 0.25E-155.00^32.0 0.00 0.13E-21 0.26 0.21E-156.00^36.0 0.00 0.37E-21 0.27 0.35E-157.00^40.0 0.00 0.53E-20 0.29 0.37E-158.00^46.0 0.00 0.98E-20 0.30 0.42E-159.00^53.3 0.00 0.26E-19 0.31 0.48E-1510.00^60.0 0.00 0.12E-18 0.33 0.67E-1511.00^63.0 0.00 0.23E-18 0.34 0.30E-1512.00^66. 0.00 0.45E-18 0.36 0.32E-15Rock-Eval Tmax = 394.5 °CFor Model # 2For the Time-Temp Model-2 wellTime^Temp(my)^(°C)Oilgen Genrate %Ro Conrate0.00^10.0 0.00 0.00E+00 0.20 0.00E+001.00^17.5 0.00 0.23E-23 0.23 0.34E-153592.00 25.0 0.00 0.19E-22 0.24 0.61E-153.00 32.5 0.00 0.15E-21 0.26 0.37E-154.00 40.0 0.00 0.10E-20 0.27 0.69E-155.00 44.0 0.00 0.28E-20 0.29 0.44E-156.00 48.0 0.00 0.74E-20 0.30 0.24E-157.00 52.0 0.00 0.19E-19 0.31 0.34E-158.00 56.0 0.00 0.48E-19 0.32 0.43E-159.00 60.0 0.00 0.12E-18 0.34 0.34E-1510.00 64.0 0.00 0.29E-18 0.35 0.28E-1511.00 68.0 0.00 0.69E-18 0.36 0.40E-1512.00 72.0 0.00 0.16E-17 0.38 0.50E-1513.00 76.0 0.00 0.36E-17 0.40 0.41E-1514.00 80.0 0.00 0.81E-17 0.42 0.30E-1515.00 85.0 0.00 0.21E-16 0.44 0.46E-1516.00 90.0 0.00 0.54E-16 0.46 0.59E-1517.00 95.0 0.00 0.13E-15 0.49 0.47E-1518.00 100.0 0.01 0.28E-15 0.52 0.49E-1519.00 105.0 0.02 0.58E-15 0.56 0.66E-1520.00 110.0 0.05 0.11E-14 0.60 0.53E-1521.00 115.0 0.09 0.18E-14 0.63 0.35E-1522.00 120.0 0.16 0.28E-14 0.66 0.44E-1523.00 125.0 0.27 0.37E-14 0.69 0.44E-1524.00 130.0 0.39 0.44E-14 0.72 0.35E-1525.00 135.0 0.54 0.46E-14 0.75 0.45E-1526.00 140.0 0.68 0.42E-14 0.80 0.54E-15Rock-Eval Tmax = 415.0 °C360For Model # 3For the Time-Temp Model-3 wellTime Temp Oilgen Genrate %Ro Conrate(MY) (°C)0.00 10.0 0.00 0.00E+00 0.20 0.00E+001.00 11.1 0.00 0.34E-24 0.22 0.35E-152.00 12.2 0.00 0.47E-24 0.23 0.10E-153.00 13.3 0.00 0.66E-24 0.23 0.87E-164.00 14.4 0.00 0.92E-24 0.23 0.98E-165.00 15.6 0.00 0.13E-23 0.24 0.11E156.00 16.7 0.00 0.18E-23 0.24 0.11E-157.00 17.8 0.00 0.25E-23 0.24 0.12E-158.00 18.9 0.00 0.34E-23 0.24 0.11E-159.00 20.0 0.00 0.47E-23 0.25 0.99E-1610.00 30.0 0.00 0.75E-22 0.25 0.29E-1511.0 40.0 0.00 0.10E-20 0.27 0.77E-1512.00 54.0 0.00 0.30E-19 0.30 0.74E-15Rock-Eval Tmax = 394.5 °CTO RUN THE PROGRAM:1. Insert a computer disk containing "BASINMAT" program in to acomputer drive2. Type "BASINMAT" then press ENTER3. Type 1st input file name (Time-Temperature file)e.g. "EX.IN" then press ENTER4. Type 2nd input file name(source rock's kineticparameter file) e.g. "KIN.ARR" then press ENTER3615. Type name of the output file e.g. "EX.OUT" thenpress ENTER6. Type time-step increment (m.y.) e.g. "1.0" then press ENTERthis number must be able to divide the time inputin Time-Temp file and result in integer number362APPENDIX CDETERMINATION OF KINETIC PARAMETERSA LOTUS 1-2-3 template file, Eo.wkl, used in this study to determine the kineticparameters such as a pre-exponential factor (A), mean activation energy (E0), and astandard deviation of the activation energies (o-E) from the Rock-Eval analyses of apotential source rock is based on a linear regression/correlation technique of Braunand Burnham (1987) which assumed a simple Gaussian distribution of activationenergies (See detail in CHAPTER 6). The program requires input data from threeRock-Eval analyses of a sample at different heating rates. The format of input datais shown as follows.INPUT DATA: For the Eo.wkl template fileEo.wk IDetermine a distribution ofactivation energies usingRock-Eval pyrolysisSAMPLE I.D.: RE-LAB STANDARD < = = = Cell B7REMARK:^write any remark here! < = = = Cell B8INPUTRUN #^HEATING RATE Tmax(°C/min)^(°C)3631 Cell B15 = = > 5 410 < = = = Cell C152 Cell B16= = > 25 441 < = = = Cell C163 Cell B17= = > 50 451 < = = = Cell C17CORRESPONDING HEATING RATE AT (FWHH)VALUES OF = = >^(°C/min)^(°C)Cell B22= = >^25^51.2 < = = = Cell C22Regression output should be in cell E25  Cell B7: Sample I.D.Cell B8: Any remarks on the sampleCell B15: Heating rate of a first run pyrolysis (°C/min)Cell C 15: A corresponding Tmax obtained froma first run pyrolysis (°C)Cell B16: Heating rate of a second run pyrolysis (°C/min)Cell C16: A corresponding Tmax obtained froma second run pyrolysis (°C)Cell B17: Heating rate of a third run pyrolysis (°C/min)Cell C17: A corresponding Tmax obtained froma third run pyrolysis (°C)Cell B22: Heating rate of any run of pyrolysis (°C/min)Cell C22: A temperature width at half the height of a pyrolysisprofile whose heating rate corresponds tothat used in Cell B22 (°C)364OUTPUT: From the Eo.wkl template fileOUTPUTFREQUENCY FACTOR (A)^=^7.5316E+13^/secACTIVATION ENERGY (E0) =^51200.45 cal/molSTANDARD DEVIATION (aE) = 3.57^%APPROXIMATED DISCRETE VALUESOF ACTIVATION ENERGIES:STOICHIOMETRICFACTORSACTIVATIONENERGIES (cal/mol)0.000068 43881.56970.000441 44796.42950.002242 45711.28930.008866 46626.14900.027310 47541.00880.065512 48455.86860.122393 49370.72830.178081 50285.58810.201792 51200.44790.178081 52115.30770.122393 53030.16743650.065512 53945.02720.027310 54859.88700.008866 55774.74670.002242 56689.60650.000441 57604.46630.000068 58519.3260TO RUN THIS TEMPLATE FILE:1. Call up the LOTUS spread sheet program2. Retrieve a template file "Eo.WK1" from the disk3. Type in input data described above e.g.-sample I.D. in cell B7-remarks in cell B8-heating rate and a corresponding Tmax in cells B15 and C15-heating rate and a corresponding Tmax in cells B 16 and C 16-heating rate and a corresponding Tmax in cells B17 and C17-heating rate and a corresponding FWHH in cell B22 and C224. Use the LOTUS menu to execute linear regression with the output of aregression go to cell E25, after which all kinetic parameters are automaticallycalculated5. Use the LOTUS menu to print a block of cells P55.. Q73 to a text file whichwill be readily used as an input file (e.g. KIN.ARR in Appendix B) forhydrocarbon generation modelling.366

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