6th International Conference on Gas Hydrates


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* Schlumberger Trade Mark  1 WIRE-LINE LOGGING ANALYSIS OF THE 2007 JOGMEC/NRCAN/AURORA MALLIK GAS HYDRATE PRODUCTION TEST WELL  Tetsuya Fujii  , Tokujiro Takayama  , Masaru Nakamizu, Koji Yamamoto Technology & Research Center, Japan Oil, Gas and Metals National Corporation 1-2-2 Hamada, Mihama-ku, Chiba, 261-0025, JAPAN  Scott Dallimore, Jonathan Mwenifumbo, Fred Wright Geological Survey of Canada, Natural Resources Canada 9860 West Saanich Road, Sidney, BC V8L 4B2, CANADA  Masanori Kurihara, Akihiko Sato Japan Oil Engineering Company 1-7-3 Kachidoki, Chuo-ku, Tokyo, 104-0054, JAPAN  Ahmed Al-Jubori Schlumberger Canada Ltd. 525 3rd Ave SW, Calgary, AB, CANADA  ABSTRACT In order to evaluate the productivity of methane hydrate (MH) by the depressurization method, Japan Oil, Gas and Metals National Corporation and Natural Resources Canada carried out a full scale production test in the Mallik field, Mackenzie Delta, Canada in April, 2007.  An extensive wire-line logging program was conducted to evaluate reservoir properties, to determine production/water injection intervals, to evaluate cement bonding, and to interpret MH dissociation behavior throughout the production. New open hole wire-line logging tools such as MR Scanner, Rt Scanner and Sonic Scanner, and other advanced logging tools such as ECS (Elemental Capture Spectroscopy) were deployed to obtain precise data on the occurrence of MH, lithology, MH pore saturation, porosity and permeability. Perforation intervals of the production and water injection zones were selected using a multidisciplinary approach. Based on the results of geological interpretation and open hole logging analysis, we picked candidate test intervals considering lithology, MH pore saturation, initial effective permeability and absolute permeability. Reservoir layer models were constructed to allow for quick reservoir numerical simulations for several perforation scenarios. Using the results of well log analysis, reservoir numerical simulation, and consideration of operational constraints, a MH bearing formation from 1093 to 1105 mKB was selected for 2007 testing and three zones (1224-1230, 1238-1256, 1270- 1274 mKB) were selected for injection of produced water. Three kinds of cased-hole logging, RST (Reservoir Saturation Tool), APS (Accelerator Porosity Sonde), and Sonic Scanner were carried out to evaluate physical property changes of MH bearing formation before/after the production test. Preliminary evaluation of RST-sigma suggested that MH bearing formation in the above perforation interval was almost selectively dissociated (sand produced) in lateral direction. Preliminary analysis using Sonic Scanner data, which has deeper depth of investigation than RST brought us additional information on MH dissociation front and dissociation behavior.    Corresponding author: Phone: +81 43 276 9243  Fax +81 43 276 4062  E-mail: fujii-tetsuya@jogmec.go.jp  Present address: Research Center, Japan Petroleum Exploration Co., Ltd., 1-2-1 Hamada, Mihama-ku, Chiba, 261-0025, JAPAN   Proceedings of the 6th International Conference on Gas Hydrates (ICGH 2008), Vancouver, British Columbia, CANADA, July 6-10, 2008. * Schlumberger Trade Mark  2 Keywords: methane hydrates, production test, wire-line logging, perforation interval  INTRODUCTION The 2006-08 JOGMEC/NRCan/Aurora Mallik gas hydrate production research program is being conducted with a central goal to measure and monitor production response of a terrestrial gas hydrate deposit  to pressure draw down [1]. The Japan Oil, Gas and Metals National Corporation (JOGMEC) and Natural Resources Canada (NRCan) are funding the program and leading the research and development studies. Aurora College/Aurora Research Institute is acting as the operator for the field program. This paper reviews the extensive wire-line logging program, which was conducted to evaluate reservoir properties, to determine production/water injection intervals, evaluate cement bonding, and interpret methane hydrate (MH) dissociation behavior throughout the production test. Figure 1 shows the role and workflow of wire-line logging applied in the production well. In this paper, we mainly focused on the well log evaluation for MH bearing zone. Complimentary papers are also published in this volume describing technical details of open hole well log analysis [2], operations [3], geophysical monitoring techniques employed [4], porous media conditions [5] and production modeling trials [6].               Figure 1. Purpose and work flow of wire-line logging program applied in the Mallik 2L-38 (2007) production test well.   OPEN HOLE LOGGING Aurora/JOGMEC/NRCan Mallik 2L-38 production well was originally drilled to 1150m as a gas hydrate research and development well by Japan and Canada in 1998 [7]. The open hole section of the wellbore was re-occupied and a 311.15mm (12 1/4”) new hole section was advanced in 2007 from 1150m to 1310m (RKB). This well is referred to in this paper as Mallik  2L-38 (2007).  Objectives Open hole wire-line logging in the production test well (2L-38) was conducted for following objectives. (a) Determination of production test /water injection zone (perforation interval). (b) Evaluation of reservoir properties such as lithology, porosity, MH pore saturation, and permeability (initial, absolute) for MH bearing /water injection formation. (c) Construction of reservoir geological model for the production simulation.  Measurement items Table 1 shows the open hole wire-line logging program conducted in Mallik 2L-38 (2007). For precise evaluation of MH bearing formation properties, advanced wire-line logging tools such as APS *  (Accelerator Porosity Sonde), ECS *  (Elemental Capture Spectroscopy Sonde), and new logging tools such as MR Scanner * , Rt Scanner *  and Sonic Scanner *  were applied in this logging program in addition to conventional tools such as resistivity, FMI *  (Fullbore Formation MicroImager), CMR *  (Combinable Magnetic Resonance Tool), density, sonic and neutron, which were used in 1998 when Mallik 2L-38 was originally drilled  and  2002 when Mallik 5L-38 was drilled [8, 9]. Among these measurement items, effectiveness of conventional tools for MH bearing formation evaluation has been already confirmed [8, 9]. APS can measure formation porosity and sigma (a mineral's ability to absorb thermal neutrons, defined as its capture cross section) using nuclear reactions between epithermal neutrons, thermal neutrons and the formation. APS epithermal neutron porosity is insusceptible to lithology and formation salinity. Sigma is also used as a shale indicator and to calculate Vcl (clay volume) [10]. ECS is a neutron source tool based on spectral analysis of gamma-ray radiated from the formation. It’s used to evaluate lithology, Vcl, matrix density, sigma matrix, epithermal neutron matrix, thermal neutron matrix and absolute permeability by analyzing nine elements in the formation (H, Cl, Si,  O pen ho le Logging G eolog ical Form ation G as H ydrate C ased ho le Logging (1st) C em ent C asing C ased ho le Logging (2nd) Produ ction T est ? ? C asing  set, C em enting C em ent Evaluation W ell Log Analysis R eservoir S im ulation C andidates for perforation O K Perforation R eservoir Property C em ent Evaluation R eservoir Property C om parison (Sh, ph i, e tc)  * Schlumberger Trade Mark  3 Ca, Fe, S, Ti, Gd, K) [10]. In this project, it was mainly used for the absolute permeability evaluation. Sonic Scanner measures compressional, shear and stoneley waves. The tool is used to evaluate formation elastic/mechanical properties at multiple depths of investigation and acoustic anisotropy. The source of the acoustic anisotropy can be discriminated as to whether it is intrinsic or stress- induced [10]. These advanced sonic measurements enabled an increased understanding of both the MH characteristics and formation geomechanics. Rt Scanner is a triaxial induction tool that calculates vertical and horizontal resistivities (Rv, Rh) from direct measurements, while simultaneously solving for formation dip at any well deviation including anisotropic formations [10]. Its multiple depths of investigation in all three dimensions ensures that derived resistivities are a true 3D measurement. MR Scanner is the latest generation of magnetic resonance tools. It has the capability of recording multiple depths of investigation in a single pass. Its measurement sequence allows a profiled view of the reservoir fluids. Deeper and multiple depths of investigation make it easier to detect any data- quality problems associated with rugose boreholes, mudcake, and fluids in various hole sizes  [10].  Table 1. Open hole wire-line logging program in Mallik 2L-38 (2007). Run D ate D epth interval Logging too l pre-logging M arch 3, 2007 850-1121 AIT -T LD -H G N S-CM R-E M S #1 M arch 6, 2007 680-1276 G R-PPC-G PIT -E M S-H RLT -SP-Rt Scanner #2 M arch 6 and 7, 2007 680-1268 G R-PPC-H N G S-E CS-CM R-H G N S-H RM S-APS #3 M arch 9, 2007 680-1279 G R-PPC-Sonic Scanner-FM I #4 M arch 9, 2007 1296-1308 G R-H G N S-T LD -AIT -SP #5 M arch 9 and 10, 2007 850-1150 G R-M R Scanner-H G N S        Formal nomenclatures and applications A IT  (A rray In duction  Im age T ool): In duction  resistivity, SP, Rm A PS (A ccelerator  Porosity Son de): N eutron  porosity in dex, Form ation  sigm a C M R (C om bin able M agn etic Reson an ce T ool): T otal N M R porosity, N M R free-fluid porosity, Perm eability E C S (E lem en tal C apture Spectroscopy Son de): Lith ology fraction s, Form ation  elem en ts (Si, Fe, C a, S, T i, G d, C l, Ba, H) E M S (E n viron m en tal M easurem en t Son de): M ud resistivity, M ud tem perature, C aliper FM I (Fullbore Form ation  M icroIm ager): High -resolution  electr ical im ages G R (G am m a Ray): G am m a ray G PIT  (G en eral Purpose In clin om etry T ool): Boreh ole azim uth , deviation , T ool azim uth HG N S (High ly In tegrated G am m a Ray N eutron  Son de): G am m a ray, N eutron  porosity HN G S (Hostile N atural G am m a Ray Son de): G am m a ray HRLT  (High  Resolution  Laterolog A rray T ool): High  resolution  resistivity HRM S (High -Resolution  M ech an ical Son de): Bulk den sity, PE F, C aliper , M icroresistivity M R Scan n er (M agn etic Reson an ce Scan n er): T otal N M R porosity, N M R free-fluid porosity, Perm eability PPC  (Power Position in g C aliper  T ool): C aliper Rt Scan n er (T riaxial In duction  Scan n er): Rv, Rh , A IT  logs, SP, D ip, A zim uth Son ic Scan n er (A coustic Scan n in g Platform form s): D T p, D T s, Full waveform s, C em en t bon d quality waveform s SP (Spon tan eous Poten tial): Spon tan eous poten tial T LD  (T h ree-D etector  Lith ology D en sity): Lith ology den sity   Perforation intervals selection workflow The 2007  Mallik 2L-38 production well was advanced to 1310m (RKB) to allow for downhole gas/water separation and re-injection of produced water in the same well.  Perforation intervals for the water injection and production zones were selected using a multidisciplinary approach by considering the reservoir properties of MH bearing zones interpreted from well log analysis, productivity and water injectivity predicted from quick reservoir numerical simulation, cement bonding conditions, and operational constraints. Figure 2 shows the work flow applied in the determination of the perforation intervals in 2L-38 (2007).                 Figure 2. Work flow for the determination of perforation intervals in 2L-38 (2007).  D ata (P D S ,  LAS ,  D LIS : 4G B ) P roduction  P ro files  (G as, W ater) W ell Log Analysis, G eological in terpretation, Construction of Com posite Log E quations,  P aram eters Reservoir M odel Construction (Layering) Extraction of Candidates for Perforation In terval (P roduction zone, W ater in jection zones) V sh, P hi, S h , k V sh, P hi, S h , k Determ ination of Perforation In terval (Zone A, W ater In jection zones) G un Length, Float collar, e tc Reservoir S im ulation  Constraint on O peration Layer m odel D epth In terva ls O pen H ole W ire -line Logging (2L -38) Preparation of W ell Log Analysis V sh: V olum e of shale P hi: P orosity S h: H ydrate satu ration k : P erm eability  * Schlumberger Trade Mark  4 Well log analysis in the production zone (a) Well log analysis method Figure 3 shows an example of composite chart of 2L-38 (2007) derived from the open hole wire-line logging data in one of the MH bearing zones (zone A). Technical details of these open hole well log analysis are also described in [2].    For the basis of reservoir model construction, volume of shale (Vsh), effective porosity (PhiE), hydrate pore saturation (Sh), initial effective permeability (Kint), and absolute permeability (Ka) were analyzed using the logging data. Vsh was evaluated using natural gamma ray log (GR, T2 column in Figure 3) through following equation with GR response in clean sand (GRclean) and shale interval (GRshale). Vsh = (GR-GRclean)/(GRshale-GRclean) (1) PhiE was evaluated based on density porosity (PhiD, T4 column in Figure 3), together with Vsh correction using following equations. PhiE = PhiD (1-Vsh)  (2) PhiD = (ρma-ρb)/ (ρma-ρf)  (3) ρma: matrix density (2.65 g/cm 3  was used) ρb : bulk density (g/cm 3 ) ρf  : fluid density (1.0 g/cm 3  was used) Sh was estimated using the combination of total CMR porosity (TCMR, T4 column in Figure 3) and PhiD through DMR (Density-Magnetic- Resonance) method [11, 12] using following equation. Sh = (PhiD-TCMR)/PhiD  (4) Estimation results were shown in T6 column in Figure 3. Kint was estimated by analyzing CMR log using both SDR (Schlumberger-Doll Research) method (KSDR, [13]) and Timur-Coates method (KTIM, [14]), with following equations and parameters. KSDR (md) = C*TCMR 4 *T2LM 2   (5) C: mineralogy constant (4000 D/s 2 = 4 md/s 2  [15]) T2LM: T2 logarithmic mean (milli-seconds) KTIM (md) = a*TCMR 4 *(FFV/BFV) 2   (6)  a: constant (10,000 was used) TCMR: Total NMR porosity FFV: NMR Free Fluid Volume BFV: NMR bound Fluid Volume Generally, KTIM shows higher value than KSDR using above constants (T7 column in Figure 3). We used KSDR for initial effective permeability input as base case, mainly because the number of uncertain parameter is smaller than KTIM. Ka was evaluated using both empirical model constructed by JOE (Ka_JOE) [6] and model derived from ECS (Ka_ECS) [16]. Ka_JOE is based on the well log calibration results using actual core samples from Mallik 5L-38 and it is the function of PhiE, Vsh, and Sh [6]. On the other hand, Ka_ECS is mainly governed by weight fraction of clay, which is based on core database of mineralogy and chemistry measured on 400 samples [16]. Both permeability evaluations were shown in T7 column in Figure 3. These two models show discrepancy in shaley intervals, which is attributed to the difference in correction method for shale volume. We used Ka_JOE for the base case because it is based on actual Mallik core samples, while Ka_ECS was used for sensitivity analysis.  (b) Criteria for selection of  perforation interval for production well We have picked up candidates for the perforation interval based on the results of geological interpretation, well log analysis mentioned above, and the following criteria (Table 2) suggested by Japan Oil Engineering Company (JOE)/AIST, based on the past reservoir simulations. (a) Sandy formations: identified mainly from the gamma-ray log curve. (b) High initial effective permeability (rough measure is higher than 0.5 md):  evaluated from CMR log (Figure 3, column T7). (c) Moderate degree of MH pore saturation (rough measure is around 60 %): Evaluated from CMR and density logs (Figure 3, column T6). 60 % is a preferable MH saturation figure in terms of dissociation efficiency, because if the MH saturation is too high, then the initial effective permeability becomes too low. (d) Enough vertical distance from the top of the water bearing zone (rough measure is more than 5 m): Evaluated from resistivity and CMR logs. The top of the water bearing zone was interpreted to be around 1,112 mKB (Figure 3). The objective was to avoid water production (coning) by depressurization. (e) Existence of a seal formation between water bearing zones.  * Schlumberger Trade Mark  5 By considering the above criteria and other geological features such as fracture distribution (FMI, Figure 3, column T8 and T9), coal layers (Sonic, Density, ECS), we extracted four possible candidates for the production zone as shown in Figure 3 (Red bar).                                    Track No. Parameters Units Comments T1 Depth mKB KB=11.8mMSL T2 GR, SP, Caliper, etc API, mV, cm, etc T3 Resistivity (HRLT) ohm.m T4 Porosity (φd_sand, TCMR, φPef, φd_ECS, etc) fraction φd_ECS is slightly larger than φd_sand [2] T5 Sw (Ro/Rt, Indonesian Eq, DW model) fraction Indo and DW are almost the same T6 Sh from CMR (quick look (overlay) and DMR) fraction Both models have similar output T7 Permeability (KSDR, KTIM, Ka_ECS, Ka_JOE) fraction Technical details are also described in [2] T8 FMI (Static image) degree T9 Dip data from FMI degree Fracture dips were classified by confidence level. T10 DT-slow, DT-fast, slow-fast us/ft Difference of slowness between fast and slow [2]. T11 X-line energy (max, min) Fast azimuth  Anisotropy T12 Delta-T us/ft Hydrate saturation [2].  Figure 3.  An example of the composite chart of 2L-38 (2007) open hole logging data in a MH bearing zone (zone A) and extracted perforation candidates.  Extracted cand idates for perfora tion R esistiv ity Porosity H ydrate Satura tion (CM R log)Perm eability FM I (S tatic) Absolu te  k (ECS log、 JO E M odel) φ d (Sand) φ N (CNL) φ d (ECS) In itial k (NM R log) Depth (m K B ) H ydrate CMR Free  F luid CMR Capilla ry BoundCMR Small Pore Top of W ater bearing zone (1112m KB) G R Sonic Scanner 1 2 4 3 T1 T2 T3 T4 T5 W ater Saturation (resistivity) T6 T7 T8 T9 Dip data (FM I) T10 T11 T12 Perforated Interval(1093 -1105m K B ) 5 6 φ N (APS) Perforation  scenarios applied in pre -sim ula tion Extracted from well log  analysis Additional case for sensitivity analysis  * Schlumberger Trade Mark  6 Table 2.  Criteria for determining the production zone (zone A) and the tools used for evaluation.  Measurement Items Critaria Tools for decision Log analysis method (a) Lithology of sediments Sandy layer GR, HNGS, ECS, (Cuttings)  (b) Initial effective permeability > 0.5md CMR, MR Scanner SDR (Kenyon, 1992) (KSDR) [13] Timur&Coates (KTIM) [14] (c) MH pore saturation Around 60% CMR, Resistivity DMR method  [11, 12] (d) Vertical distance from water bearing zone > 5m Resistivity, CMR (e) Existence of seal formation between water bearing formation GR, HNGS, ECS  Quick reservoir simulation Based on four candidate intervals for perforation (Figure 3) and reservoir layered model constructed reflecting the above well log analysis, JOE/AIST carried out a quick reservoir numerical simulation for the determination of perforation interval (pre- simulation). For this reservoir simulation, MH21- HYDRES (MH21 Hydrate Reservoir Simulator) [17, 18] was used. This simulator is able to deal with three-dimensional, five-phase, four- component problems [17, 18]. Reservoir layer model was constructed for the simulation input based on the well log analysis results already mentioned above. Detail parameters and settings of the model are described in [6]. Besides four perforation candidates extracted from the well log analysis, two additional scenarios were assumed for sensitivity analysis. Therefore, the simulation was conducted assuming totally six perforation scenarios (Figure 3, 4). Figure 4 shows an example of simulated production performances for 5 days. The solid lines show the predicted gas production rates, while the dashed lines show the predicted water production rates. 3 MPa was assumed as a bottom hole pressure in all the cases.  Gas production of 1,000- 3,000 m 3 /d and water production of 10-40 m 3 /d were predicted. It was anticipated that if the perforation interval is shorter like Cases 2 (5 m) and 4 (3 m), the production rates should be lower. It was also simulated that if there wasn’t an enough vertical distance from the top of water bearing zone as shown in case 6 (4 m), water coning could happen at an early stage (in this case, within 2.5 days). Considering the conditions of (1) higher gas production rate and (2) lower water production rate, it was concluded that Case 3 is the most preferable.  Case Perforation interval (mKB) Case 1 1099 - 1105 Case 2 1093 - 1098 Case 3 1093 - 1105 Case 4 1078 - 1081 Case 5 1078 - 1098 Case 6 1099 - 1108  Figure 4. Prediction of production test performance by JOE for the determination of perforation interval.    Free gas indication While not conclusive, examination of the Vp/Vs ratio from 1998 sonic log in Mallik 2L-28 well suggested a thin free-gas-bearing interval just below the lower most hydrate bearing zone [8]. In order to investigate the possibility of existence of fee gas layer, we checked open hole logging data. Free gas layers are usually identified by the separation between density porosity (DPHI) and neutron porosity (NPOR) curves in well log data (DPHI>NPOR, Figure 3). We also utilized density porosity derived from the ECS log (DPHI.ECS) and 2 kinds of neutron porosity derived from the APS log for more precise analysis (APSC in Figure 3 is neutron porosity with shallower depth of investigation). As a result of overlaying these density and neutron porosity logs, we did not see 0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 0 12 24 36 48 60 72 84 96 108 120 Tim e (hours) G a s  R a te  ( m 3 /d ) 0 10 20 30 40 50 60 70 80 90 100 W a te r  R a te  ( m 3 /d ) C ase 1.1  (G as) C ase 1.2  (G as) C ase 1.3  (G as) C ase 1.4  (G as) C ase 1.5  (G as) C ase 1.6  (G as) C ase 1.1  (W ater) C ase 1.2  (W ater) C ase 1.3  (W ater) C ase 1.4  (W ater) C ase 1.5  (W ater) C ase 1.6  (W ater) C ase 1 C ase 2 C ase 3 C ase 4 C ase 5 C ase 6 1 3 2 4 5 6 1 3 2 4 5 6  * Schlumberger Trade Mark  7 any significant gas indication within the surveyed interval (820 to 1270 mMSL) (Figure 3). We also compared Vp/Vs obtained from Sonic Scanner this time with Vp/Vs obtained from sonic log in 1998, as shown in Figure 5. We could not find significantly low Vp/Vs interval around the top of water bearing zone like 2L-38 (1998), which suggests no significant gas bearing layer.                       Figure 5. Comparison of Vp, Vs, and Vp/Vs between obtained in 2007 and 1998, respectively. (a) comparison of Vp and Vs. (b) comparison of Vp/Vs. Considering the KB hight (11.8mMSL), perforated interval 1093-1105 mKB (2007) is 1081-1093 mMSL, while the top of water bearing zone 1112 mKB (2007) is 1100 mMSL.  Determination of perforation intervals Considering the reservoir properties of MH bearing zones derived from well log analysis, gas productivity and water injectivity predicted from reservoir numerical simulation, cement bonding condition, and operational constraints such as perforation gun lengths (6m base) and time constraints, we selected the following perforation intervals. (a) Production test zone (A zone) 1093-1105 mKB (12m continuous, Case 3 in Figure 4) (b) Produced water injection zone        1224-1230, 1238-1256, 1270-1274 mKB   CASED HOLE LOGGING  There were two main objectives for undertaking cased hole logging in Mallik 2L-38 (2007). The first objective was cement evaluation, which is important for the optimization of well completion such cement volume estimation, and confirmation of monitoring cable location. The second objective was to evaluate physical property changes (MH dissociation behavior) of hydrate bearing formations throughout the production test. In this paper, we will focus on the second objectives and related study results.  Measurement items For the cement bond evaluation in 2L-38 (2007), we used new logging tools such as the Isolation Scanner * , in addition to conventional evaluation tools such as CBL-VDL (Sonic Scanner). Both tools were used simultaneously to confirm the exact location and distribution of the monitoring cables for safe perforation. In the Mallik 2002 project, CHFR *  (Cased Hole Formation Resistivity) was used for the evaluation of MH dissociation [9]. However we could not use the CHFR in this project due to the presence of a plastic coating (yellow jacket) behind the casing, which was installed for electrical resistivity monitoring purpose [4]. For that reason, we used RST (Reservoir Saturation Tool), APS (Accelerator Porosity Sonde), and Sonic Scanner for MH dissociation evaluation instead. Table 3 shows the cased hole wire-line logging program conducted in Mallik 2L-38 (2007).  Table3.  Cased hole wire-line logging program in Mallik 2L-38 (2007). R un D ate Logging tool M ode D epth (mK B) C BL-VD L 30-1273 C oncise 850-1273 USI 850-1273 IBC 30-1273 2 M arch 23-24, 2007 APS-G R -C C L 850-1273 3 M arch 24, 2007 R ST (S igma, C /O )-G R -C C L 820-1270 C BL-VD L 850-1195 R AD 850-1193 BAR S 850-1193 APS 850-1208 2 April 8-9, 2007 R ST (S igma)-G R -C C L Sigma only 850-1206 3 April 9, 2007 Isolation Scanner-G R -C C L IBC , USI 1040-1209 G R G amma R ay C C L C asing C ollar Locator After T est Before T est Sonic Scanner-Isolation Scanner -G R -C C L 1 Sonic Scanner -APS -G R -C C L 1 M arch 23, 2007 April 7-8, 2007      RST is a saturation evaluation tool that uses a minitron instead of a chemical neutron source. It utilizes two kinds of reactions between atoms in 0 10 00 20 00 30 00 40 00 50 00 1 070 108 0 109 0 11 00 1 110 112 0 11 30 D ep th (m MS L ) V p  o r V s  ( m /s e c ) V p  (20 07 ) V s  (20 07 ) V p  (19 98 ) V s  (19 98 ) Perforation interval (a) Top of w ater bearing  zone 1 .0 2 .0 3 .0 4 .0 1 070 108 0 10 90 1 100 1 110 112 0 11 30 D ep th (m MS L ) V p /V s  ( fr a c ti o n ) V p/V s (2007) V p/V s (1998) Top of w ater bearing  zonePerforation interval (b) G as ind ication  * Schlumberger Trade Mark  8 the formation and fast neutrons, i.e. neutron capture and inelastic scattering. RST sigma is the measurement of the gamma-ray count (capture gamma-ray) emitted from atoms excited by the neutron capture reaction, which can give us information about fluid saturation [19]. Pure water and carbon (oil, MH) have similar neutron capture sections, while chlorine is more reactive with neutron and has a larger cross section. Therefore, RST sigma can be an indicator of salinity change in formation water. An outline of APS and Sonic Scanner has already been described in previous sections of this paper. These cased hole logging measurements were utilized for the analysis of physical property changes throughout the production test.  RST results Figure 6 shows some differences in the RST and APS log responses between before and after the production test. Depth of investigation of RST is 10 in (25.4 cm) [10], and the detector faces the inner surface of casing during logging. Taking into consideration the difference between the inner diameter of casing and the borehole diameter, the actual depth of investigation of RST is about 19 cm from open hole wall (Figure 7). Black dashed lines and red solid lines in Figure 6 show the depth plot of parameters before and after the production test, respectively. The area within the red box is the production (perforated) interval. Throughout the production test, some changes in the log response where noticed, such as a significant selective decrease in inelastic scattering signal (T1), a selective increase in thermal decay signal (T4), and a selective increase in RST sigma (T5), in the perforated interval. A small change in the same parameters just 1m above and 3m below the perforated interval was noticed too, but to a lesser degree. We also recognized that above parameters in high MH saturation intervals just below the perforated interval (1108-1112 mKB) did not change throughout the production. These results suggest that MH bearing formations at the perforated interval was almost selectively dissociated / sand produced in a lateral direction. That suggests the possibility of water invasion from water bearing zones behind casing (water coning) is small, because formation water inversion would have caused MH dissociation, and these parameters would have changed as a result.  APS results Figure 6 (right) shows the difference in APS outputs before and after the production test. Actual depth of investigation from the open hole wall is about 11cm when considering the casing diameter (Figure 7). Generally speaking, repeatability of the ASP curves was much poorer than the RST, and that was the case when overlaying two passes of the same descent in hole. The major factor causing that is the relatively small depth of investigation compared to the open hole size. In spite of these difficulties, we were able to recognize a selective increase in neutron porosity (APSC, T6) between before and after the production test in the perforated interval.  Sonic Scanner results After the processing and re-picking we recognized the following velocity changes in P-wave (Compressional) and S-wave (Shear) from the Sonic Scanner, which has a deeper depth of investigation than APS and RST (P-wave: 20-40 cm from borehole wall, S-wave: 30-60 cm from borehole wall, in this case, Figure 7), in the perforated interval [20]. (1) P-wave, which was detected before the production test, could not be detected in the lower part of the perforated interval after the test (indicating gas existence) (Figure 7, right). (2) S-wave velocity at the lower part of the perforated interval decreased to the velocity level of a water bearing zone (Figure 7, right). This velocity decreased happened in the zone of with higher initial effective permeability suggested from the CMR log (middle of Figure 7).  DISCUSSION As discussed in the previous section, the following changes in RST and APS response were recognized in perforated interval (1093-1105 mKB), in spite of the relatively shallower depth of investigation (about 19cm and 11cm from open hole wall, respectively) (Figure 6 and 8). (1) Selective increase in RST sigma and APS, which corresponds to the number of chlorine atoms and hydrogen atoms, respectively. (2) Selective decrease in the inelastic scattering, which corresponds to the number of carbon atoms. The increase in RST sigma can be a reflection of an increase in formation salinity (chloride atoms  * Schlumberger Trade Mark  9 number), i.e. replacement of MH bearing formation behind casing by well bore fluid (Brine@KCl 5 %) or formation water. There are three possible replacement scenarios; (1) into the sand pore space, (2) cavity space, or (3) a combination of both. However, from the RST data alone we can not distinguish these scenarios. We also need to consider about not only fluid movement, but also sediment movement (grain rearrangements) induced  by sanding. Clearly there are a number of complex considerations to be evaluated.  Based on the observations and analysis above, following interpretation on MH dissociation process could be possible as one hypothesis (Figure 9). (1) MH bearing sands are composed of a relatively robust frame work before the production test. (2) When depressurizing, MH’s dissociated and the robust MH bearing sand layers (frame work) broke down and caused a decrease in the shear stiffness. Methane gas, dissociated water, and sand grains were released and discharged into the well bore. (3) After the production test (when the pump was stopped), MH and sand grains were replaced by formation water or borehole fluid (suggested from the increase in RST sigma, and APSC). P- wave was not excited after the test because of residual gas (suggested from shear slowness of Sonic Scanner).  On the other hand, it is difficult to assume that there are large cavities between the cement and formation considering that S-wave was transmitted to the formation and detected by the Sonic Scanner. Therefore, all we could suggest at present stage might be selective porosity increase by hydrate dissociation and sanding, and residual gas existence.  CONCLUSIONS We obtained valuable new data about MH bearing formations and hydrate occurrence from open hole wire-line logging. Based on the logging data and production numerical simulation results, we determined the production (zone A) and water injection intervals of 2L-38 (2007) as below. (a) Production interval: 1093-1105 mKB (Total 12m, continuous) (b) Water injection interval: 1224-1230, 1238- 1256 and 1270-1274 mKB Three cased-hole logging services, RST, APS and Sonic Scanner were carried out to evaluate physical property changes of the MH bearing formation throughout the production test. At the perforation interval of the MH bearing formation (1093 – 1105 mKB) we noticed a selective dissociation (sand production) in the lateral direction. It was also suggested that neutron porosity was increased and shear stiffness of the formation frame work was decreased, and small amount of gas was remained.  FUTURE WORKS In the future, the following studies are necessary. A. Borehole seismic data (BARS) analysis by Sonic Scanner to investigate and detect MH dissociation front. B. Integrated analysis/interpretation of dissociation front using RST, APS and Sonic Scanner data, taking into consideration both sanding volume and the amount of produced gas (mass balance). C. Investigation of borehole wall shape change behind casing using other logging data such as Isolation Scanner. D.  Three dimensional analysis on heterogeneity of MH bearing formation using Rt Scanner and Sonic Scanner.  ACKNOWLEDGEMENTS The methane hydrate research program has been carried out by the MH21 research consortium consisting of JOGMEC, AIST, and ENAA, with financial support from METI. We would like to thank METI, JOGMEC, NRCan, and Aurora Research Institute (Aurora) for giving their permission to publish this report. We would also like to thank Schlumberger for the significant effort to acquire precious wire-line logging data under extreme severe conditions and for the strong support with our well log analysis.  REFERENCES  [1] Yasuda, M., Dallimore, S.R., The task force for production testings; MH21 Research Consortium for Methane Hydrate Resources in Japan,  Summary of the Methane Hydrate Second Mallik Production Test (2007), Journal of the Japanese Association for Petroleum Technology Vol. 72, No. 6 (Nov., 2007), p603-607 (Japanese). [2] Murray, D., Fujii, T., Dallimore, S.R., Developments in Geophysical Well Log Acquisition and interpretation in gas hydrate saturated  * Schlumberger Trade Mark  10 Reservoirs, in Proceedings of the VIth International Conference on Gas Hydrates, Vancouver, B.C. July 6-11, 2008. [3] Numasawa, M., Dallimore, S.R., Yamamoto, K., Yasuda, M., Imasato, Y., Mizuta, T., Kurihara, M., Masuda, Y., Fujii, T., Fujii, K., Wright, J. F., Nixon, F.M, Cho, B., Ikegami, T., Sugiyama, H., Objectives and Operation Overview of the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test;  in Proceedings of the VIth International Conference on Gas Hydrates, Vancouver, B.C. July 6-11, 2008. [4] Fujii, K., Cho, B., Ikegami, T., Sugiyama, H., Imasato, Y., Dallimore, S.R. and Yasuda, M., Development of a monitoring system for the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test Program;  in Proceedings of the VIth International Conference on Gas Hydrates, Vancouver, B.C. July 6-11, 2008. [5] Dallimore S.R., Wright  J. F., Nixon  F. M, Kurihara, M., Yamamoto K., Fujii , T, Numasawa M., Yasuda , M., Imasato Y. 2008.  Geologic and porous media factors affecting the 2007 Produciont response characteristics of the JOGMEC/NRCan/Aurora gas hydrate production research wellt;  in Proceedings of the VIth International Conference on Gas Hydrates, Vancouver, B.C. July 6-11, 2008. [6] Kurihara, M, Masuda, Y., Funatsu, K., Ouchi, H., Yasuda, M., Yamamoto, K., Numasawa, M., Fujii, T. Narita, H., Dallimore, S.R. and Wright, J.F., Analysis of the JOGMEC/NRCan/Aurora Mallik Gas Hydrate Production Test through Numerical Simulation;  in Proceedings of the VIth International Conference on Gas Hydrates, Vancouver, B.C. July 6-11, 2008. [7] Dallimore, S..R., Uchida, T. and Collett, T.S. 1999.  Scientific results from JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well, Mackenzie Delta, Northwest Territories, Canada, Geological Survey of Canada, Bulletin 544, 403p. [8] Collett, T.S., R.E. Lewis, S.R. Dallimore, M.W. Lee, T.H. Mroz, and T. Uchida, Detailed evaluation of gas hydrate reservoir properties using JAPEX/JNOC/GSC Mallik 2L-38 gas hydrate research well downhole well-log displays, GSC Bulletin 544, p295-311, 1999. [9] Collett, T.S., Lewis, R.E., and Dallimore S.R., JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate production research well downhole well-log and core montages, GSC Bulletin 585, 2005. [10] Schlumberger, Wireline Services Catalog 2007. [11] Freedman, R., Minh, C.C., Gubelin, G., Freeman, J.J., McGuiness, T., Terry, B. and Rawlence, D. , Combining NMR and Density Logs for Petrophysical Analysis in Gas-Bearing Formations, Paper II, presented at 39th SPWLA Symposium, 1998. [12] Akihisa, K., Tezuka, K., Senoh, O. and Uchida, T., 2002, Well log evaluation of gas hydrate saturation in the MITI-Nankai-Trough well, offshore south-east Japan, SPWLA 43 rd  Annual Logging Symposium, Oiso, Japan, Paper BB.s [13] Kenyon, W.E., 1992. Nuclear magnetic resonance as a petrophysical measurement, Nuclear Geophysics, 6 (2): 153-171. [14] Stambaugh, B.J., NMR tools afford new logging choices, Oil & Gas Journal; Apr 17, 2000; 98, 16; Platinum Periodicals p 45-52. [15] Kleinberg, R.L., Flaum, C., Griffin, D.D., Brewer, P.G., Malby, G.E., Peltzer, E.T., and Yesinowski, J.P., 2003, Deep sea NMR: Methane hydrate growth habit in porous media and its relationship to hydraulic permeability, deposit accumulation, and submarine slope stability: Journal of Geophysical Research, Vol. 108, No. B10, 2508. [16] Herron, M.M., Herron, S.L., Grau, J.A., Seleznev, N.V., Phillips, J., Sherif, A.E, Farag, S., Horkowtiz, J.P., Neville, T.J., Hsu, K., Real-Time Petrophysical Analysis in Siliciclastics From the Integration of Spectroscopy and Triple-Combo Logging, SPE Annual Technical Conference and Exhibition, San Antonio, Texas, 2002(SPE 77631). [17] Kurihara, M., Ouchi, H., Inoue, T., Yonezawa, T., Masuda, Y., Dallimore, S.R., and Collett, T.S., Analysis of the JAPEX/JNOC/GSC et al. Mallik 5L-38 gas hydrate thermal-production test through numerical simulation, In: S.R. Dallimore & T.S. Collett (Eds), Scientific Results from the Mallik 2002 Gas Hydrate Research Well Program, Mackenzie Delta, Northwest Territories, Canada., Geological Survey of Canada, Bulletin 585, 2005. [18] Masuda,Y., Konno, Y., Iwama, H., Kawamura, T., Kurihara, M., Ouchi, H., Improvement of Near Wellbore Permeability by Methanol Stimulation in a Methane Hydrate Production Well, Proceedings of 2008 Offshore Technology Conference, Houston, Texas, U.S.A., 2008 (OTC 19433). [19] Schlumberger, Introduction to cased hole logging (C.5), RST Reservoir Saturation Tool. [20] Inamori, T., Fujii, T., Takayama, T., Saeki, T., Yamamoto, K., A trial of monitoring of the methane hydrate-production test by sonic well  * Schlumberger Trade Mark  11 logging data, Abstracts of Japan Geoscience Union Meeting 2008, Makuhari, Japan.                         Track No Logging Tool Parameters T1 RST WINR (Weighted Inelastic Ratio) T2 IRAT (Near/Far Inelastic Ratio) T3 TRAT (Near/Far Capture Ratio) T4 TPHI (Thermal Decay Porosity) T5 SIGMA (Formation Sigma (Neutron Capture Cross Section) ) T6 APS APSC (Near/Array Corrected Sandstone Porosity) T7 SIGF  (Formation Capture Cross Section) T8 ENFR (Dead Time Corrected Near/Far Count Rate Ratio)  Figure 6. RST and APS change throughout the production test (Zone A).                 Figure 7. Vertical resolutions and depth of investigations (DOI) of applied cased hole logging tools. 1100 1110 1090 Depth (m KB ) Top of W ater Bearing Zone (around 1112m KB) Perforated In terval (1093 -1105m K B ) 1080 C R ST (Fast N eutron Source) AP S (Therm al Neutron S ource) HC C l C l H C l Ine lastic Scattering N eutron Capture W eighted N ear/Far N ear/Far C ross Section Therm al D ecay C ross Section N eutron C apture C :  D ecrease C l:  Increase H :  Increase T1 T2 T3 T4 T5 T6 T7 T8 APS DOI 7 in (17.8cm ) APS O D: 3.625 in (9.21cm ) 6.6cm R ST O D: 1.71 in (4.34cm ) 50cm RST DOI 10 in (25.4cm ) Sonic Scanner O D: 3.625 in (9.21cm ) Sonic Scanner DO I (P-Slowness) 30-50cm Sonic Scanner DO I (S-Slowness) 45-67cm Casing O D 9-5/8 in (24.45cm ) Hole size 14 in (35.56cm ) O uter D iameters (O D ) Casing ID 8.835 in (22.44cm ) 18.8cm 11.2cm 6.6cm 36.8cm 54.1cm O D of M onitoring Cable C lam p 12 in (30.5cm ) In  general, Sonic Scanner flexural wave can see form ation away from  borehole wall 2 to 3 tim es of borehole d iam eter. 8.84inch*2to3=45to67cm Pla in  view of borehole S P 32-54  cm45-67  cm 17-37  cm30-50  cm< 1.82mSonic Scanner 18.8 cm25.4 cm38.1 cmR ST 11.2 cm17.8 cm35.6 cmAPS C asing and annulus0.6 in (1.52cm ) Isola tion Scanner D O I from 14” O pen hole w all D O I from Tools Vertical R esolution Tool N am e Schlum berger (2007): W ire line Services C ata log [5 ] C ementP S M odes of w ave Frequency T-R  d istance Assum ption: 9-5/8 in casing is  loca ted at the center o f 14 in hole  * Schlumberger Trade Mark  12                               Figure 8.  MH bearing formation properties from open hole logs, and the change in cased hole logging response throughout the production test in Zone A, Mallik 2L-38 (2007)                    Figure 9. Possible interpretation of MH bearing formation property changes based on RST, APS, Sonic Scanner, and sanding information. O pen H ole  Log C ased Hole  Log P erforation In terval (1093-1105m KB) R esistiv ity. P orosity H ydrate Satura tion (C M R  log) Permeability R ST SIG M A (C l) APS Porosity (H ) Com pressional S lowness (1/Vp) Share S lowness (1/Vs) S onic S canner Before After A fter After Test B efore  Test Absolu te  k (ECS log、 JO E M odel) φ d (Sand) φ N (CNL) φ d (ECS) φ N (APS) In itial e ffective  k (CM R log) Depth (m KB) H ydrate CM R Free  F luid CM R Capilla ry BoundCM R Small Po re Top  o f W ater Zone (around  1112m KB) G R O pen H ole P S (1) B efore S+M H+FW (2) Production S+FW S+FW S+M H+FW S+M H+FW (3) After S+W S+W S+M H+W S+M H+W D O I of R ST S+W S+W W ater M ethane G as H 2 O + K C l(5% ) Sand G rainM H D O I of APS S+FWS+FW S+M H+FW S: Sand,   FW : Form ation W ater,   BW : Borehole W ater,    M H: M ethane Hydrate,   G : M ethane G as S+FW FW S+FW G G S+FW BW BW D O I of Sonic  Scanner PS P S PS P S 0.5 m R esidual G as


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