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Stratigraphic, depositional and diagenetic controls on reservoir development, Upper Devonian Big Valley… Colborne, Jacqueline 2014

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STRATIGRAPHIC, DEPOSITIONAL AND DIAGENETIC CONTROLS ON RESERVOIR DEVELOPMENT, UPPER DEVONIAN BIG VALLEY FORMATION, SOUTHERN ALBERTA by Jacqueline Colborne B.A., Colgate University, 2011 A THESIS SUBMITTED IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF MASTER OF SCIENCE in The Faculty of Graduate and Postdoctoral Studies (Geological Sciences) THE UNIVERSITY OF BRITISH COLUMBIA (Vancouver) April 2014 © Jacqueline Colborne, 2014 ii Abstract The Upper Devonian Big Valley Formation in southern Alberta is a 10-m thick carbonate succession, unconformably overlain by organic-rich source rocks of the Exshaw Formation. The Exshaw Formation is part of a global continuum of mudrocks deposited under anoxic conditions, representing a distinct interval in Earth’s climatic, terrestrial and marine evolution, and the generation of prolific hydrocarbon source rocks worldwide. This thesis summarizes the stratigraphic, depositional and diagenetic controls on reservoir development of the Big Valley Formation and its relationship to the Exshaw Formation. Data analyses involved stratigraphic top picks and regional correlations in an 84 well-log database, core study, seismic interpretation, petrographic and carbon isotope analyses and petrophysical measurements. The availability of more core and wireline data as a result of recent exploration led to refining of the stratigraphic framework in the study area. The Big Valley Formation is redefined in this study to consist of two informal units: upper (open-marine) and lower hydrocarbon-bearing (peritidal) units. Based on lithofacies analyses, the peritidal unit more appropriately fits with the Big Valley Formation, rather than its current assignment to the underlying Stettler Formation. The peritidal unit consists of four lithofacies: subtidal shoal peloidal packstone-grainstone, mid-to-high intertidal microbial laminite and laminated dolomudstone and a local intraclastic breccia-laminite related to tidal drainage channels. Each lithofacies is laterally discontinuous, variably dolomitized and ranges from 0.5-to-2.0-m thick. iii In some areas the Big Valley Formation is up to 25-m thick, with >4-m of shoal deposits that have excellent reservoir properties. Thickened Big Valley areas are underlain by thinned evaporite beds, and have a similar orientation as an underlying NNW/SSE structural lineament. This relationship suggests basement-controlled high-angle block faulting and/or salt dissolution and collapse of underlying Devonian evaporite beds during Big Valley deposition. The complex interplay between deposition and diagenesis has influenced reservoir quality. Dolomitized peloidal packstone-grainstones have high intercrystalline porosity (>5%) and permeability values (>0.20 md). Reservoir potential of the microbial laminites is dependent on dolomitization and lack of anhydrite cement. Non-reservoir lithofacies show low petrophysical properties (<<0.00001-0.002 md) as the result of a lack of dolomitization and/or extensive cementation. iv Preface This thesis is an original study by the author, Jacqueline Colborne. Design of the research program was conducted by Jacqueline Colborne and supervisor Dr. R. Marc Bustin, with contributions from Dr. Kurt Grimm (committee member), Dr. Gerry Reinson from Reinson Consultants, Ltd. (Calgary, Alberta) and Mr. Nathan Bruder, staff geologist with Murphy Oil Ltd (Calgary, Alberta). Dr. James Murray, member of the supervisory committee, assisted in the editing of the body chapters; Chapter 2 and Chapter 3. This research was funded by Murphy Oil Company Ltd and NSERC. I was responsible for data collection and analyses for this research project. Cores were logged at the Energy Resources Conservation Board (ERCB) in Calgary, Alberta. Samples (pieces for thin section and plugs) were taken from the cores with written permission from the company well owners. Routine and special core analyses reports for all of the cored wells in the study area were obtained from the Alberta Energy Regulator (AER) from Calgary Alberta. These analyses were used to supplement the in-lab analytical work accomplished at the University of British Columbia. Rock samples were sent off to Calgary Rock Services Ltd. in Calgary, Alberta for thin section preparation and then returned back to the University of British Columbia for analyses. Dr. Kurt Grimm assisted in petrographic analyses. Access to two seismic lines was granted under an academic license, and analysis of the two lines was accomplished at Murphy Oil Ltd. (Calgary, Alberta). Isotope analyses on 8 samples were sent to the Pacific Centre for Isotopic and Geochemical Research (PCIGR) at The University of BritishColumbia. Janet Gabites acidified the samples with phosphoric acid in helium-flushed sealed vials and ran the analyses using the gas v bench and Delta Plus XL mass spectrometer. All of the analytical work was completed in the laboratories at The University of British Columbia, Department of Earth Ocean and Atmospheric Sciences. The research project was orally presented at the Canadian Society of Petroleum Geologists Core Conference in Calgary, Alberta in May, 2013. In addition to the oral presentations, three (5x 8 ft) posters were made, with three well cores from the study area displayed. The core conference is a platform for students and industry to share respective research. This research project won best student core presentation and display. Supervisor Dr. Marc Bustin, Dr. Gerry Reinson and Mr. Nathan Bruder were coauthors on this research project at the Core Conference. This research project was also orally presented at the Unconventional Resources Technology Conference in Denver, Colorado in August, 2013. I prepared the manuscripts for the publishable chapters (Chapter 2 and Chapter 3) with collaboration and manuscript edits from supervisor and committee members. vi Table of Contents ABSTRACT  ............................................................................................................................................................................... ii PREFACE  .............................................................................................................................................................................. iv TABLE OF CONTENTS ............................................................................................................................................................. vi LIST OF TABLES ..................................................................................................................................................................... viii LIST OF FIGURES ...................................................................................................................................................................... ix ACKNOWLEDGEMENTS ........................................................................................................................................................ xii CHAPTER 1: INTRODUCTION ............................................................................................................................................... 1 1.1 INTRODUCTION .................................................................................................................................................................................... 1 1.2 THESIS STRUCTURE ............................................................................................................................................................................ 3 CHAPTER 2: STRATIGRAPHY AND FACIES ANALYSIS, BIG VALLEY FORMATION, SOUTHERN ALBERTA . 4 2.1 INTRODUCTION .................................................................................................................................................................................... 4 2.2 METHODOLOGY ................................................................................................................................................................................... 7 2.3 TECTONIC SETTING ............................................................................................................................................................................. 8 2.4 REGIONAL STRATIGRAPHY .............................................................................................................................................................. 12 2.5 BIG VALLEY STRATIGRAPHY – STUDY AREA ................................................................................................................................ 15 2.6 LITHOFACIES ANALYSIS ................................................................................................................................................................... 17 2.6.1 Introduction ....................................................................................................................................................................... 17 2.6.2 Upper Stettler Formation ............................................................................................................................................. 18 2.6.3 Lower Big Valley Formation ....................................................................................................................................... 20 2.6.4 Upper Big Valley Formation ........................................................................................................................................ 37 2.7 EXSHAW FORMATION ....................................................................................................................................................................... 40 2.8 BIG VALLEY AND EXSHAW FORMATIONS: LOCALIZED OVER-THICKENED SECTION ............................................................. 42 2.9 DEPOSITIONAL AND STRATIGRAPHIC FRAMEWORK ................................................................................................................... 49 2.10 CONCLUSIONS .............................................................................................................................................................................. 57 vii CHAPTER 3: DEPOSITIONAL AND DIAGENETIC CONTROLS ON RESERVOIR DEVELOPMENT OF THE UPPER DEVONIAN BIG VALLEY FORMATION, SOUTHERN ALBERTA .................................................................. 60 3.1 INTRODUCTION .................................................................................................................................................................................. 60 3.2 GEOLOGIC SETTING AND STRATIGRAPHIC FRAMEWORK ........................................................................................................... 63 3.3 METHODOLOGY ................................................................................................................................................................................. 66 3.4 LOWER BIG VALLEY FORMATION: SEDIMENTARY LITHOFACIES AND PARAGENETIC HISTORY .......................................... 68 3.5 SUMMARY OF DIAGENETIC PROCESSES, PRODUCTS AND ENVIRONMENTS ............................................................................. 84 3.6 DIAGENETIC EVOLUTION: INFLUENCE ON PETROPHYSICAL PROPERTIES AND RESERVOIR QUALITY OF THE LOWER BIG VALLEY FORMATION .................................................................................................................................................................................... 88 3.6.1 Permeability and Effective Stress Relationships: Influence on Reservoir Quality ............................. 95 3.7 CONCLUSIONS .................................................................................................................................................................................... 97 CHAPTER 4: CONCLUSIONS ................................................................................................................................................ 99 REFERENCES .......................................................................................................................................................................... 103 APPENDIX A: CORE LOG DESCRIPTIONS ..................................................................................................................... 110 APPENDIX B: FORMATION TOP DATA BASE .............................................................................................................. 131 APPENDIX C: PETROGRAPHIC ANALYSES ................................................................................................................... 149 APPENDIX D: SEISMIC ANALYSES................................................................................................................................... 160 APPENDIX E: ISOTOPIC ANALYSES ................................................................................................................................ 162 APPENDIX F: X-RAY DIFFRACTION ................................................................................................................................ 164 viii List of Tables Table 2.1. Summary of the peritidal facies association of the lower Big Valley Formation. ........................................ 20 Table 3.1. Summary of the sedimentological details of the peritidal facies association ............................................... 69 Table 3.2. Summary of the paragenetic succession in each lithofacies of the lower Big Valley Formation.. ....... 75 ix List of Figures Figure 2.1. Generalized stratigraphic column for the Big Valley-Exshaw succession in the southern portion of the Alberta Basin, and WCSB framework during Late-Devonian-Early Mississippian time. ........................................ 5 Figure 2.2. Southern Alberta study area. .............................................................................................................................................. 6 Figure 2.3. Interpreted paleogeography of North America in Late Devonian time. ........................................................ 10 Figure 2.4. Model of the western margin of Canada during the Famennian stage.. ......................................................... 10 Figure 2.5. Structural elements of the Western Canada Sedimentary Basin and adjacent United States during Late Devonian-Mississippian times…. .................................................................................................................................................. 11 Figure 2.6. Stratigraphic correlations and nomenclature chart as proposed for this study. ....................................... 14 Figure 2.7. Well log picks using current nomenclature (left) versus proposed nomenclature (right).. ................. 16 Figure 2.8. Generalized lithofacies sequence for the Stettler, Big Valley and Exshaw formations ........................... 17 Figure 2.9. Core photographs of upper Stettler Formation…. ................................................................................................... 19 Figure 2.10. Cross-section illustrating the thickness trends of the Big Valley and Exshaw formations.. .............. 22 Figure 2.11. Core photographs of the peloidal packstone-grainstone (2a).. ...................................................................... 23 Figure 2.12. Composite grains within the peloidal packstone-grainstone (2a). ............................................................... 24 Figure 2.13. Thin section photomicrographs of the peloidal packstone-grainstone (2a) ............................................ 25 Figure 2.14. Core photographs of the microbial laminated dolostone (2b).. ...................................................................... 27 Figure 2.15. Thin section photomicrographs of the microbial laminated dolostone (2b).. ......................................... 28 Figure 2.16. Core photographs of the intraclastic breccia-laminite (2c)…. ......................................................................... 30 Figure 2.17. Thin section photomicrographs of the intraclastic breccia-laminite (2c)……….. .................................... 31 Figure 2.18. Core photographs of the laminated dolomudstone (2d). .................................................................................. 33 Figure 2.19. Thin section photomicrographs of the laminated dolomudstone (2d) ....................................................... 34 Figure 2.20. Core photograph and thin section photomicrographs of the upper Big Valley open marine lithofacies (1a).. .............................................................................................................................................................................................. 38 Figure 2.21. Gamma ray log signature and stratigraphic contacts of the Big Valley Formation and its relationship to the underlying Stettler Formation and overlying Exshaw Formation ................................................... 41 x Figure 2.22. Isopach maps of the Big Valley Formation and Stettler Formation. ............................................................. 43 Figure 2.23. Anomalously thick Big Valley succession ................................................................................................................. 44 Figure 2.24. Cross-section illustrates that the thickest accumulations of Exshaw and Big Valley formations occur where the underlying Stettler Formation is thinnest. ...................................................................................................... 45 Figure 2.25. Two-dimensional seismic image of the over-thickened Big Valley-Exshaw sections........................... 46 Figure 2.26. Cored section of over-thickened Big Valley Formation ...................................................................................... 47 Figure 2.27. Aeromagnetic map of southern Alberta with mapped structural lineaments. ........................................ 48 Figure 2.28. Depositional model proposed for the Big Valley Formation ............................................................................ 54 Figure 2.29. Processes and timing of formation of the ‘regional’, vs. the ‘local’ over-thickened Big Valley succession. ........................................................................................................................................................................................................ 55 Figure 2.30. Detailed sequence stratigraphic column .................................................................................................................. 56 Figure 3.1. Southern Alberta study area ............................................................................................................................................. 61 Figure 3.2. Rock fabric and reservoir quality flow chart. ............................................................................................................ 62 Figure 3.3. Upper Devonian-Lower Mississippian stratigraphic correlation and nomenclature charts. ............... 64 Figure 3.4. Informal nomenclature of the Stettler-Big Valley-Exshaw succession on well logs. ............................... 65 Figure 3.5. Ternary diagrams displaying bulk mineralogy of the lower Big Valley lithofacies .................................. 70 Figure 3.6. SEM backscatter image of detrital grains observed in the lower Big Valley Formation. ....................... 71 Figure 3.7. SEM Backscatter images and corresponding thin section photomicrographs of the peloidal packstone-grainstone (2a). ....................................................................................................................................................................... 76 Figure 3.8. SEM backscatter images and corresponding thin section photomicrographs of the microbial laminite (2b) .................................................................................................................................................................................................... 77 Figure 3.9. Early stage diagenetic events............................................................................................................................................ 78 Figure 3.10. Thin section photomicrographs of the intraclastic breccia-laminite (2c). ................................................ 79 Figure 3.11. SEM back scatter images and thin section photomicrographs of evaporite cement............................. 80 Figure 3.12. SEM backscatter image and thin section photomicrographs of pyrite grains. ......................................... 81 Figure 3.13. Insoluble hydrocarbon rich residue pressure solution seams. ....................................................................... 81 Figure 3.14. Thin section photomicrographs of pyrobitumen lined pore space. .............................................................. 82 Figure 3.15. Cored section of over-thickened Big Valley Formation. ..................................................................................... 83 xi Figure 3.16. Total bulk mineralogy data of the peloidal packstone-grainstone lithofacies and corresponding porosity values. .............................................................................................................................................................................................. 90 Figure 3.17. Total porosity for each lithofacies of the lower Big Valley Formation. ....................................................... 91 Figure 3.18. Pore size distributions of the peloidal packstone-grainstone (2a) ............................................................... 92 Figure 3.19. Pore size distribution of the microbial laminites (2b)........................................................................................ 93 Figure 3.20. Thin section photomicrographs of the lower Big Valley lithofacies with porosity and permeability data at reservoir condition. ...................................................................................................................................................................... 94 Figure 3.21. Variations in the permeability of the peloidal packstone-grainstone (2a), microbial laminite (2b) and laminated dolomudstone (2d) lithofacies with increased effective stress. ................................................................ 96 xii Acknowledgements The work of this study is the reflection of many people’s endless support and guidance. Firstly, thank you to my advisor Marc Bustin who gave me the opportunity and support to pursue grad school at UBC. I am grateful to Murphy Oil Ltd., who provided financial support for this project and direction for the study. Special thanks for the support I received from staff geologist Nathan Bruder. From the beginning, committee member Kurt Grimm provided significant insight to help shape the outcome of this project. Your passion for teaching and knowledge of carbonate systems took this project to a further level, my sincerest thanks for all of your help. Many thanks to Jim Murray who took an active interest during the editing process. I am forever grateful for your time, guidance and mentorship.  I am especially thankful to have met Gerry Reinson during this study. With his vast knowledge and teaching ability, Gerry selflessly provided substantial guidance and support throughout the entire duration of the project. I not only received direction from the best, I also acquired a great mentor and friend.  I am extremely appreciative of the support and friendship of my friends and colleagues in the geology department. This project would not be what it is without your suggestions and recommendations. Specifically, thank you to Erik Munson, who from the beginning of my grad school career has supported me in countless ways, offering perspective and insight on many levels. Additionally, I am very grateful of the friendships outside of UBC that have assisted me through this journey.  Further thanks to my parents, David and Dana Colborne and my siblings, Katie, Joe and Marnie, who have seen me through each one of my endeavors. Every day you inspire me to work my hardest, and realize that anything is achievable through perseverance. xiii Dedication To my friends and family1 Chapter 1: Introduction 1.1 Introduction Reservoir development of the Upper Devonian Big Valley Formation in southern Alberta has been investigated, examining the stratigraphic, depositional and diagenetic controls on hydrocarbon-bearing reservoirs. Conventional exploration for liquid hydrocarbons from the Big Valley Formation began in the 1970’s in southern Alberta. Recent exploration and horizontal drilling techniques applied to the carbonates of the Big Valley Formation is a result of the prolific production of the statigraphically equivalent (in part) Bakken-Three Forks petroleum system of the Williston Basin. However, successful production from the Big Valley Formation in southern Alberta occurs locally, with overall inconsistent regional production. The most significant vertical well has produced over 250,000 barrels of oil since initial production in 1979, with some recently drilled horizontal wells showing promising production results. Localized reservoir development in southern Alberta is a result of the complex interplay between stratigraphic, depositional and diagenetic controls on hydrocarbon reservoirs of the Big Valley Formation. Previous works on the Big Valley-Exshaw succession in Alberta established a regional stratigraphic framework (Andrichuk, 1954; Andrichuk and Wonfor, 1954; Beales, 1956; Wonfor and Andrichuk, 1956; Morrow and Geldsetzer, 1988; Moore, 1989; Richards, 1989; Richards et al., 1991; Caplan and Bustin, 1994, 1998; Smith et al., 1995; Johnston et al., 2010). Increased drilling activity during the last five years in southern Alberta has led to more available data to refine the stratigraphic framework, and provide the first detailed 2 characterization of Big Valley reservoir development in southern Alberta, needed for successful future exploration and drilling. 3 1.2 Thesis Structure This thesis is presented in two separate stand-alone papers. The first paper (Chapter 2) deals with the stratigraphy and sedimentology of the Big Valley Formation and the second paper (Chapter 3) deals with diagenesis and reservoir quality of the Big Valley Formation. 4 Chapter 2: Stratigraphy and Facies Analysis, Big Valley Formation, southern Alberta 2.1 Introduction The Upper Devonian Big Valley Formation in southern Alberta is a tight-oil carbonate reservoir, overlain by widespread organic-rich source rocks of the Exshaw Formation (Figure 2.1). Renewed exploration and development of the Big Valley-Exshaw succession in southern Alberta is a result of prolific production from the (in part) stratigraphic equivalent Three Forks-Bakken petroleum system in the Williston Basin (recoverable oil estimates of 7.38 BBL, Gaswirth et al., 2013). Successful production from the Big Valley Formation in southern Alberta occurs locally, with overall inconsistent regional production. The most significant vertical well in the study area has produced over 250, 000 bbl since initial production in 1979, with some recently drilled horizontal wells showing promising results. Localized reservoir development in southern Alberta is a result of complex stratigraphic and depositional controls on the hydrocarbon reservoirs of the Big Valley Formation. Due to recent industry activity in the Big Valley-Exshaw succession in southern Alberta, new core and wireline data have become available to refine the stratigraphic framework and characterize the stratigraphic and depositional setting of potential hydrocarbon-bearing reservoirs in southern Alberta (Figure 2.2). 5 Figure 2.1. Generalized stratigraphic column for the Big Valley-Exshaw succession in the southern portion of the Alberta Basin, and WCSB framework during Late-Devonian-Early Mississippian time (after Halbertsma, 1994; Smith and Bustin, 2000). 6 Figure 2.2. Southern Alberta study area, showing the well control and locations of cores examined. 49°57´36῎N/ 113°32´56῎W 49°57´21῎N/ 112°50´22῎W 49°15´40῎N/ 112°50´1῎W 49°15´48῎N/ 113°32´49῎W 7 2.2 Methodology Four hundred and fifty metres of core from 21 wells, and logs from 84 wells were used to construct stratigraphic cross-sections and isopach maps throughout the southern Alberta study area. Well log signatures from cored wells were correlated to log signatures from uncored wells to determine stratigraphic relationships between the Stettler Formation, informal lower and upper units of the Big Valley Formation, and the lower, middle and upper parts of the Exshaw Formation. In addition, two-dimensional seismic lines were interpreted. Detailed core descriptions and sampling of the 21 wells were accomplished at the Energy Resources Conservation Board in Calgary Alberta. Lithofacies were interpreted based on lithology, sedimentary structures and biological criteria. Both productive and nonproductive lithofacies were sampled to determine the variable depositional and diagenetic properties responsible for reservoir quality. In addition to core observations, detailed descriptions of the Big Valley Formation lithofacies included examining one hundred and twenty-six thin section slides prepared with a double carbonate stain mixture of Alizarin Red S and Potassium Ferricyanide, which aid in the identification of calcite, ferroan calcite and ferroan dolomite. Eight whole-rock samples were prepared for carbon isotope analyses using the gas bench and a Delta Plus XL mass spectrometer. 8 2.3 Tectonic Setting The Upper Devonian-Lower Mississippian strata of the Western Canada Sedimentary Basin (WCSB) consist of a thick succession of shelf, ramp and basinal strata deposited in a semi-arid, epeiric seaway on the western convergent margin of ancestral North America (Richards, 1989; Figure 2.3). In the Late Devonian, the western margin of ancestral North America was an unstable ramp cut by extensional faulting and flexural loading from convergent tectonism of the Antler orogeny in the western United States (Richards, 1989; Johnston et al., 2010; Figures 2.4, 2.5). Antler orogenics in the United States influenced sediment depositional patterns in southern Alberta, resulting in low-frequency base level changes (Smith and Bustin, 2000). The Antler magmatic arc acted as an oceanographic barrier on the proto-pacific side of ancestral North America, preventing coastal upwelling of nutrients which provided for the accumulation landward of shelf carbonates (Whalen, 1995). The main basinal tectonic elements impacting on the deposition and accumulation of Upper Devonian-Lower Mississippian strata, were the westward dipping cratonic platform, the Prophet Trough and the Peace River Embayment (Figure 2.5). The Prophet Trough originated in the Late Devonian as the result of plate convergence along the western margin of North America during Antler tectonism. The Prophet Trough extends southward to the Antler Foreland basin of the western United States (Douglas et al., 1970; Richards, 1989; Richards et al., 1994). In Mississippian time, the Peace River Embayment of northwestern Alberta and northeastern British Columbia opened into the Prophet Trough as an unstable, fault-controlled re-entrant into the western cratonic platform. Regional subsidence of the Peace River Embayment coupled with block faulting resulted in the 9 deposition of a thick Carboniferous succession in the embayment (Douglas et al., 1970; Richards et al., 1994). In southern Alberta, Exshaw deposition and accumulation was influenced by structural movements in the adjacent Williston Basin which initiated the realignment of the WCSB margins. The Alberta Basin was eventually isolated from the Williston Basin through extensive uplift of the Sweet Grass Arch (Douglas et al., 1970; Richards, 1989; Caplan and Bustin, 1998; Smith and Bustin, 2000; Figure 2.5). 10 Figure 2.3. Interpreted paleogeography of North America in Late Devonian time with the approximate location of the paleo-equator (Golonka et al., 1994). The southern Alberta study area is located at 15°S in a semi-arid environment at the southern end of the Alberta Basin, a sub-basin situated on the NW margin of the Williston Basin (see Figure 5) (modified from Blakey, 2011). Figure 2.4. Model of the western margin of Canada during the Famennian stage. The Antler magmatic arc had a profound impact on the western margin of the ancestral North American craton (from Richards, 1989).  11 Figure 2.5. Structural elements of the Western Canada Sedimentary Basin and adjacent United States during Late Devonian-Mississippian times (modified from Richards et al., 1994). 12 2.4 Regional Stratigraphy The stratigraphy of the Upper Devonian-Lower Mississippian succession in central and western Alberta was established by earlier workers through outcrop and subsurface studies (i.e.: Andrichuk, 1954; Andrichuk and Wonfor, 1954; Beales, 1956; Wonfor and Andrichuk, 1956; Macqueen and Sandberg, 1970; Morrow and Geldsetzer, 1988; Moore, 1989). In southern Alberta, more recent subsurface stratigraphic studies of the Wabamun -Exshaw succession and their stratigraphic equivalent formations in the Williston Basin include Richards et al., (1991); Caplan and Bustin, (1994, 1998); Smith et al., (1995); Meijer Drees and Johnston, (1996); Smith and Bustin, (2000); and Johnston et al., (2010). The Upper Devonian lower Costigan Member and the upper part of the Morro Member of the Palliser Formation outcrop in the Rocky Mountains, and are correlated in the subsurface with peritidal and supratidal carbonate-evaporites of the Stettler Formation (Figure 2.6). Deposition of the Stettler Formation occurred on an epeiric platform in southern Alberta, and is correlated to the east in southern Saskatchewan as the Torquay Formation (Christopher, 1961; Meijer Drees and Johnston, 1994; Richards et al., 1994; Caplan and Bustin, 1998; Peterhansel and Pratt, 2008). Stratigraphically, the Torquay Formation correlates to the Three Forks Formation in Montana and North Dakota (Sandberg and Hammond, 1958). Previous authors interpret the contact between the peritidal-supratidal evaporite deposits (Stettler) and the overlying open-marine limestones (Big Valley) as a major erosional unconformity, resulting from uplift and exposure, prior to basin-wide transgression (Wonfor and Andrichuk, 1956; Richards et al., 1991). The open-marine limestone of the upper Costigan member in the Rocky Mountains is considered equivalent 13 to the Big Valley Formation in southern Alberta (Richards et al., 1994; Caplan and Bustin, 1998, and Figure 2.6). This open- marine limestone unit is less than 2-m thick, extending eastward into Saskatchewan as argillaceous, pyrite-rich, lime-mudstones (Christopher, 1961). The Pronghorn Member in North Dakota consists of restricted marine dolomites overlain by locally preserved open-marine limestones, thought to be equivalent in part to the Big Valley Formation (Skinner et al., 2013; Figure 2.6). The open-marine limestones of the Big Valley Formation are sharply overlain by a pyritized lag deposit which forms the base of the black-organic-rich mudrocks of the lower Exshaw Formation (Macqueen and Sandberg, 1970). In this study the overlying Exshaw-lower Banff interval is informally divided into three parts, comprised of lower, middle and upper Exshaw members. This informal division is based on the similar tripartite gamma ray signature that is present in the three members of the Bakken Formation in the Williston Basin (Stoyles et al., 2011). The lower organic-rich Exshaw member is gradationally to sharply overlain by bioturbated siltstone and silty carbonate mudstones of the middle Exshaw member, which in turn is overlain by organic shale of the upper Exshaw or lower Banff Formation (Figure 2.6; Caplan and Bustin, 1998; Smith and Bustin, 2000; Johnston et al., 2010). The organic-rich members of the Bakken and Exshaw-lower Banff formations represent a distinct interval in Earth’s Late Devonian climatic, terrestrial and marine evolution, where widespread oceanic anoxic events deposited prolific hydrocarbon-source rocks worldwide (Caplan and Bustin, 1999). These organic-rich deposits in the Western Canada Sedimentary Basin and Williston Basin are economically important as source and reservoir beds. 14 Figure 2.6. Stratigraphic correlations and nomenclature chart as proposed for this study relative to contiguous areas. 15 2.5 Big Valley Stratigraphy – Study Area In the study area, the stratigraphic succession (Stettler, Big Valley, Exshaw) is lithologically more similar to stratigraphic equivalent units in the Williston Basin, than to the Wabamun-Exshaw succession in the foothills and central plains of Alberta (Figure 2.6). The Big Valley Formation has been divided into an informal lower (peritidal unit) and an informal upper (shallow open-marine) unit. This informal revision deviates from published literature, which considers the peritidal dolomites as part of the upper Stettler Formation (eg. Wonfor and Andrichuk, 1956; Richards, 1989; Richards et al., 1991; Meijer Drees and Johnston, 1996; Johnston et al., 2010). In the study area, the peritidal unit more appropriately fits within the Big Valley Formation, because of its visibly distinct contact with the underlying evaporitic succession both on well logs, and in cores (Figure 2.7). The sharp contact between the peritidal unit and evaporite unit suggests that a significant depositional break occurred at this stratigraphic level. This lithological contact is distinct on gamma ray and resistivity logs throughout the study area. Accordingly, the top of the Stettler Formation is shifted downward as shown in Figure 2.7. The contact between the peritidal unit and overlying open-marine unit is a distinct change in color and lithological composition, and the units herein are considered to be genetically related (Figure 2.8). The informal stratigraphy proposed here for the Big Valley Formation more appropriately correlates with stratigraphic divisions existing in Saskatchewan, North Dakota and Montana. Comparable basin configurations of the southern Alberta sub-basin and the Williston Basin led to the deposition of lithologically similar units (Figure 2.6). The upper Big Valley correlates with the Big Valley Formation in Saskatchewan, part of the Three Forks Formation in Montana, and the Pronghorn Member in North Dakota.16 Figure 2.7. Well log picks using current nomenclature (left) versus proposed nomenclature (right). The upper Big Valley consists of shallow marine nodular mudstones and wackestones, and the lower Big Valley of peritidal dolomitic mudstones, packstones, grainstones and algal laminites. The Stettler Formation contact (red line) is shifted down to the sharp notch where nodular-mosaic anhydrites and lesser evaporitic dolomites dominate. 17 2.6 Lithofacies Analysis 2.6.1 Introduction The cores examined included the sequence from the upper Stettler through to the lower Banff; however, the main focus of this paper is the Big Valley Formation. The generalized lithofacies sequence and bounding stratigraphic units are shown in Figure 2.8. The bounding stratigraphic units are discussed to provide context to the sequence stratigraphic framework proposed. Figure 2.8. Generalized lithofacies sequence for the Stettler, Big Valley and Exshaw formations in the study area. 18 2.6.2 Upper Stettler Formation The Stettler Formation is an evaporitic succession underlying the Big Valley Formation. The evaporitic unit consists of variable textures of enterolithic anhydrite separated by millimeter-thick, dark organic-rich, microbial mats, nodular to interbedded anhydrite with minor dolomite laminae and algal stromatolite beds (Figure 2.9). The contact between the Stettler and the overlying peritidal carbonate unit of the lower Big Valley Formation is sharp to erosive and regionally distinct on all well logs in the study area (Figure 2.21F). The contact is marked by nodular to interbedded anhydrite sharply overlain by peritidal dolomite deposits, suggesting that a significant shift in sedimentation was initiated by sea level transgression. 19 Figure 2.9. Core photographs of upper Stettler Formation. A. Characteristic textures of sabkha-salina environments, enterolithic (en) anhydrite layers separated by laminoid dark organic-rich microbial mats (06-13-009-25W4, 2453.0 m). B. Laminated to disrupted dololaminite (dol.micr) with nodular anhydrite (03-034-005-24W4, 2380.10 m). C. Stromatolitic oncoids (onc) and laminites within the anhydrite (06-13-009-25W4, 2454.5 m). D. Bedded to-nodular (nod) anhydrite with thin mm-scale dolomicrite interlayers (11-35-005-25W4, 2423.25 m).  20 2.6.3 Lower Big Valley Formation The lower Big Valley is normally less than 7-m thick across most of the study area (Figure 2.10), and consists of a peritidal facies assemblage which is divided into four main, variably hydrocarbon-stained and dolomitized lithofacies: peloidal packstone-grainstone; microbial laminite; laminated dolomudstone; and intraclastic breccia-laminite (Table 2.1). Table 2.1. Summary of the peritidal facies association of the lower Big Valley Formation. 21 2.6.3.1 Peloidal packstone-grainstone (Lithofacies 2a) The defining characteristics of this lithofacies are listed in Table 2.1. Peloidal packstone-grainstones are a brown, finely crystalline to coarse recrystallized lithofacies (Figure 2.11). Grains are mainly peloids with minor rounded ooids, and composite grains that consist of irregular to elongated algal intraclasts (Figure 2.12). This lithofacies is generally dolomitized with rare preservation of calcareous depositional fabrics. The more calcareous peloidal grainstones are calcite cemented with low porosity. In contrast, the variably dolomitized deposits are partially to fully replaced by well-developed euhedral to subhedral dolomite crystals, which results in intercrystalline pore space (Figure 2.13). Some pore space reduction is the result of pyrobitumen lined pore walls, calcite spar, and pressure solution processes. This lithofacies is normally 0.5 to 2.0-m thick, however in over-thickened Big Valley sections (discussed in section 2.9) the peloidal packstone-grainstone attains up to 8-m in thickness, forming the main hydrocarbon-bearing reservoir. 22 F igure 2. 10. C ross - s e c tion i l l us tra ting the  thic k ne s s  trends of the  B ig Va l le y a nd E xs ha w forma tio ns  in the  s tudy a re a . The B ig Va l le y F orma tion is ge ne ra l l y l e s s  tha n 10 m thic k  a c ross  the  s tudy a re a .  23 Figure 2.11. Core photographs of peloidal packstone-grainstone, lithofacies 2a. Lithofacies 2a is the main reservoir producing interval of the lower Big Valley Formation. A. Buff-brown peloidal grainstone with pinpoint porosity (pp) (04-24-007-22W4, 1823.5 m). B. Firm ground (dashed line) between the clotted peloidal packstone and the microbial laminated dolostone (facies 2b (11-35-005-25W4, 2418.66 m). C. Calcite cement (calc) creates a clotted fabric (11-35-005-25W4, 2418.33 m). D. Heavily oil stained, partially recrystallized peloidal packstone (09-07-005-25W4, 2835.30 m).  A B C D pp Calc lithofacies 2b 1 1 1 1 24 F igure 2.1 2. C o mpos i te  g ra ins  w ithin  pe l oida l  pa c k s ton e - gra ins tone  ( l ithofa c ie s  2a ) . A. C omposi te  gra i n c ons ist s  of e pisode s  o f a ggra da ti on  a nd  e rosion ( a rro w)  ( 09 - 0 7 - 0 0 5 - 25W 4, 2833.50 m, PPL  x5) B. Irre gul a r to e l onga te  s ha pe d a l ga l intra c l a s ts  (a rrow) , ha ve  inc l ude d qua rtz gra i ns  ( qtz) ( 09 - 0 7 - 0 0 5 - 25W 4, 2833.50  m, PPL x 2) .  A B qtz  qtz 25 A B C D ISP InG IG Figure 2.13. Thin section photomicrographs of peloidal packstone-grainstones, (lithofacies 2a) of the lower Big Valley Formation.  A. Calcareous peloidal grainstone with calcite cement (white arrow) and subsequent partial replacement of calcite with coarse, clear euhedral dolomite rhombs (08-30-008-23W4, 2210.69 m, PPL x 10). B. Relict peloidal grains (arrow) in a dolomitized fabric (09-07-005-25W4, 2834.0 m, PPLx 10). C. Dolomitized peloidal packstone with isopachous dolomite rim cement (ISP), high intergranular (IG) and intragranular porosity (InG) (04-33-007-22W4, 2389.0 m, PPL x5). D. Sub-to euhedral coarse dolomite rhombs replacing calcite, with rare preservation of original fabric. Pyrobitumen occludes secondary intercrystalline porosity (arrow) (06-13-009-25W4, 2445.18 m, XPL x10).  26 2.6.3.2 Microbial laminite (Lithofacies 2b) Microbial laminites are olive-gray to brown, finely crystalline microbial laminated dolostones (Table 2.1; Figure 2.14). Individual laminae vary from millimetre to centimetre in thickness and often have a crenulated fabric. Minor components such as peloidal grains are bound between laminar mats. Anhydrite pseudomorphic crystals (after gypsum) occur along the laminar planes, and displacive anhydrite occurs between some layers (Figure 2.15). Dessication features, uplifted microbial layers, and minor fenestral fabric are common sedimentary structures. Microbial laminites are pervasively dolomitized, with pore space reduction the result of anhydrite infill of fenestral and intercrystalline pore space This lithofacies is 0.5 to 2.0-m thick, and is a secondary reservoir facies in the lower Big Valley Formation (Table 2.1). 27 Figure 2.14. Core photographs of microbial laminated dolostone, lithofacies 2b. A. Cyclical laminite displays crenulate texture of dark gray wispy microbial mat material (11-35-005-25W4, 2416.31 m). B. Teepee structure (arrow) is indicative of subaerial exposure during hydration and dessication cycles combined with thermal contraction and expansion which caused upturning and displacement of the sediment, a common sedimentary feature in the tidal flat zone (Assereto and Kendall, 1977).  C. Micro-fault offsets microbial laminae. Anhydrite pseudomorphs, replaced after gypsum (arrow) are trapped within the microbial material (04-24-007-22W4, 1820.9 m). D. Bituminous microbial dolostone with thick sediment accumulation between microbial material. Interstitial anhydrite pseudomorph growth (arrow) occurs between the laminae along with trapped intraclastic debris (11-35-005-25W4, 2419.3 m). A B C D 1 1 1 1 28 F igure 2.1 5. Thi n s e c tion  p hotomic r ogra phs  of mic ro bi a l  l a mina te d dol ostone s , l ith o fa c ie s  2b o f the  l o we r B ig  V a l l e y F orma tion. A . A l ga l  ma t  with  c re nul a te  te xture  ( a rrow)  ( 09 - 0 7 - 0 0 5 - 25W 4 , 2834.60 m, P PL  x20) B.  W ispy  mic robia l  ma t wit h intra c l a s ts  ( I) . C oa rse re pl a c e me nt e uh e dra l  dol omite  rho mbs  ( a r ro w) inc re a s e  inte rc rys ta l l ine  ( IC )  por o s ity  ( 11 - 3 5 - 0 0 5 - 24W 4,  241 6.0 m,  PPl  x1 0) . C . W e a k  pre s e rva ti on o f de po s iti ona l  fa bric  due  to dol o mitiz a tio n. Infil l e d fe ne s tra l  por osity  ( F P)  with a nhy dri te  c e me nt ( A )  ( 0 4 - 3 3 - 0 0 7 - 22W 4, 2393.0 m, P PL  x20).  D . Hyd r oc a rbo n - s ta ine d s tyol ite s  ( S )  a nd s utu re d  gra i n c o nta c ts  ( 1 6 - 2 7 - 1 1 - 22W 4, 1799.0  m, PPL  x 10) .  IC A  B  C  D  S  I C A FP  I  29 2.6.3.3 Intraclastic breccia-laminite (Lithofacies 2c) This lithofacies consists of an olive-gray, fine-grained matrix with buff-brown angular to subangular intraclasts (Table 2.1; Figure 2.16). Intraclasts are variable in size and are more porous than the surrounding matrix. Micro-cross stratification features are common sedimentary structures. Facies 2c is pervasively dolomitized, with coarse dolomite cement precipitated around the micritized intraclastic grain rims. Pore space reduction resulted from anhydrite and non-ferroan calcite cement filling primary pore space between grains, with supplemental space filled with pyrobitumen (Figure 2.17). This local lithofacies is less than 0.5-m thick and often truncates the laminated dolomudstones (2d). Intraclastic breccia-laminites are not a hydrocarbon-bearing reservoir facies. 30 Figure 2.16. Core photographs of intraclastic breccia-laminite, lithofacies 2c of the lower Big Valley Formation. A. Matrix and intraclast material are variably oil stained, note styolites (s) between intraclasts, evidence of pressure solution compaction (08-21-11-22W4, 1813.43 m). B. Porous, oil-stained intraclasts within a tight argillaceous dolomitized matrix (16-31-11-23W4, 2057.23 m). C. Argillaceous matrix with variably sized algal intraclasts (I). Note lack of stratification (03-34-005-24W4, 2369.21 m). D. Slumping of soft sediment (01-02-006-26W4, 2890.6 m).  A B C D slumping I oil staining oil stained intraclasts S 1 1 1 1 31 Figure 2.17. Thin section photomicrographs of intraclastic breccia-laminites, lithofacies 2c of the lower Big Valley Formation.  A. Pyrobitumen (pybit)-stained algal intraclasts (06-30-008-23W4, 2235.63 m, PPL x2) B. Non-ferroan coarse calcite cement, late stage anhydrite cement (A) and pyrobitumen (pybit) occluding intercrystalline porosity (8-03-009-26W4, 2696.22 m, PPL x5) C. Preserved intergranular (IG) porosity due to dolomitization(04-33-007-24W, 2386.0 m, PPL x2). D. High intergranular (IG) and intragranular (InG) porosity. Isopachous (ISP) dolomite rim cement truncates into void spaces between intraclasts (16-31-11-22W4, 2050.16 m, PPL x20).  Disrupted pybit A B C D InG IG IG Calc pybit A ISP 32 2.6.3.4 Laminated dolomudstone (Lithofacies 2d) This lithofacies is a buff to dark brown laminated dolomudstone composed of a very fine-grained dolomite with minor peloidal grains and microbial laminae (Table 2.1, Figure 2.18). Pore space reduction is the result of anhydrite infill of fenestral and intercrystalline pore space and chemical pressure solution compaction (Figure 2.19). Laminated dolomudstones range from 0.5 to 2.0-m thick, and are commonly truncated by the overlying local deposits of the intraclastic breccia-laminite lithofacies (Figure 2.18B). 33 Figure 2.18. Core photographs of laminated dolomudstone, lithofacies 2d of the lower Big Valley Formation. A. Cross-laminated dolomudstone (arrow) (11-35-005-25W4, 2418.36 m). B. Locally truncated by intraclastic breccia-laminite (lithofacies 2c) (03-34-005-24W4, 2369.55 m). B A lithofacies 2c dolomudstone, 2b cross-laminated 1 1 34 A B C D FP A Py S Figure 2.19. Thin section photomicrographs of laminated dolomudstones, lithofacies 2d of the lower Big Valley Formation. A. Late stage anhydrite cement (A) infilling interpreted dessication cracks and fenestral porosity (03-34-005-24W4, 2375.75 m, XPL x5). B. Laminated dolomudstone with calcite laminae and styolites (S). Opaque grains are widely dispersed pyrite (16-27-11-22W4, 1798.22 m, XPL x2).  C. Late stage anhydrite cement infilling fenestral porosity (FP) (06-30-008-23W4, 2236.0 m, PPL x2). D. Laminated dolomudstone with pyrite (py) (08-30-008-23W4, 2220.50 m, XPL x5).  S 35 2.6.3.5 Peritidal Facies Association The lower Big Valley Formation is interpreted to be peritidal, based on the association of four tidally-influenced lithofacies (Table 2.1). The peloidal packstone-grainstone lithofacies (2a) is interpreted as a high energy subtidal shoal deposits. This interpretation is based on the presence of well sorted peloidal grains, minimal amount of interstitial mud, presence of ooids and the lack of preserved bioturbation structures. Microbial laminated dolostones (lithofacies 2b) and laminated dolomudstones (lithofacies 2d) are interpreted as mixed tidal flat deposits. The wavy laminites are cryptalgal, formed by the trapping and binding of sediment by blue-green algae mats (Schieber et al., 2007). The cryptalgal laminae are deformed around sulfate crystals by intrasediment displacive growth of the evaporite minerals within this semi-arid environment. The microbial dolostones and laminated dolomudstones were periodically both hydrated and subaerially exposed, resulting in formation of mud cracks and teepee structures. Variable carbonate sediment thicknesses between microbial layers, is related to variable sediment accretion time, governed by tidal flat inundation or exposure. Lithofacies 2b and 2d display fenestral pore space, characterized by irregular discontinuous partings that remain open or filled by anhydrite. This is interpreted as a product of periodic wetting and drying higher on the tidal flat. Intraclastic breccia-laminites (lithofacies 2c) are interpreted to be remnants of ephemeral tidal drainage channels on the tidal flats. The porous brecciated algal clasts are supported by an argillaceous matrix which commonly displays microscale-cross- stratification, indicative of currents influencing sediment deposition. The local occurrence of lithofacies 2c is attributed to high tides cutting channels into the tidal flat, dependent on season and storm activity. 36 The peritidal lithofacies succession primarily consists of stratigraphic couplets of metre-scale intertidal and subtidal deposits, represented respectively by the peloidal packstone-grainstones (2a) and the microbial-laminated dolostones (2b), (Figures 2.11, 2.14). The contacts between lithofacies 2a and 2b are vertically gradational. The subtidal-intertidal couplets are interrupted locally by laminite (2c) and laminated dolomudstone (2d) lithofacies. In peritidal successions, lateral discontinuity, thickness variations and the absence of an apparent stratigraphic pattern results from variations in autocyclic tidal processes that lead to a spatial mosaic of sediment production and deposition (Pratt, 2010). The contact between the peritidal carbonates and the overlying open-marine limestones (upper Big Valley) is distinct and marked in cores by change in color and lithologic composition. On well logs, a low gamma ray response is only identifiable when the limestone reaches thicknesses of 2-m or more, whereas thicknesses under 2-m are difficult to detect. This contact is interpreted to represent drowning of the tidal flats, as continued platform subsidence allowed for the sea to advance (Figure 2.21E and Christopher 1961). In areas where the upper Big Valley has eroded beneath the Exshaw, the peritidal succession is unconformably overlain by a granular transgressive lag at the base of the lower Exshaw member. The lag is less than 3-cm thick, characterized by an abundance of pyritized fragments, phosphate grains and mudstone clasts (Figure 2.21D). 37 2.6.4 Upper Big Valley Formation 2.6.4.1 Nodular Limestone-Wackestone (Lithofacies 1a) The upper Big Valley Formation averages less than 2-m thick, except where it has eroded beneath the mudrocks of the lower Exshaw member. The upper Big Valley Formation consists of one lithofacies (1a) a nodular, olive green to gray argillaceous, very fine-grained limestone with variable bioclast composition. The bioclastic components are crinoid and brachiopod fragments with minor gastropods and ostracodes (Figure 2.20). Both lime-mudstones and wackestones are poorly sorted with bioclasts heterogeneously distributed through the rock. Some bioclasts show erosion of their hard substrate by pitted surfaces. Bioturbation is common throughout; no primary stratification is preserved. The upper Big Valley mainly consists of calcite with minor dolomite replacement. Quartz grains dispersed throughout the lithofacies account for less than 5% of the total grain composition. Authigenic pyrite occurs as both framboidal grains and euhedral crystals, and is disseminated throughout. 38 Figure 2.20. Core photograph and thin section photomicrographs of the upper Big Valley open marine lithofacies. A. Argillaceous, nodular brachiopod lime wackestone (03-34-0075-24W4, 2363.6 m). B. Bioturbated lithofacies with fibrous and pitted brachiopod bioclasts (b). Coarse, euhedral, non-ferroan replacement dolomite rhombs are present (arrow) (16-27-11-22W4, 1793.35 m, PPL x10). C. Poorly sorted ostracod bioclasts (o) and brachiopod fragments (b) in a lime-wackestone and crinoid fragments (c) (16-27-11-22W4, 1793.35 m, PPL x20).  A B C o b c 1 39 2.6.4.2 Shallow Open-Marine Facies Association The upper Big Valley Formation is interpreted as open-marine deposits, based on the occurrence of a nodular lime mudstone to-wackestone lithofacies (1a), which consists mainly of crinoid and brachiopod fragments. This bioclast composition consists of sessile suspension feeders that are less specialized, fast growing, resistant to environmental stresses and represent deposition in a mesotrophic environment (Peterhansel and Pratt, 2008). Some bioclast surfaces are eroded, which suggest nutrient-triggered bioerosion of the hard substrate by other organisms (Peterhansel and Pratt, 2001). The high argillaceous content and lower biodiversity of the limestones suggests a depositional environment characterized by slow sedimentation rates, increased nutrient supply and oxygen-reduced conditions (Peterhansel and Pratt, 2008). The open-marine limestones, when present, are unconformably overlain by a less than 3-cm thick, granular transgressive lag consisting of pyritized fragments, phosphate grains and mudstone clasts at the base of the organic-rich mudrocks of the lower Exshaw (Figure 2.21D). 40 2.7 Exshaw Formation The Exshaw Formation averages less than 7-m thick throughout the study area, locally is up to 17-m thick and is divided into three informal members (Figures 2.6, 2.8). The lower Exshaw is a fine grained, brown to black organic-rich laminated mudrock containing disseminated pyrite and phosphatized nodules. The contact between the lower Exshaw and middle Exshaw is distinct (Figure 2.21C) and is marked by a significant change in sediment composition from an organic-rich mudrock to a silty carbonate mudstone. The biogenic component is mainly crinoid ossicles and brachiopod shell fragments. The middle Exshaw is overlain by a less than 2-cm thick, coarse grained transgressive lag on top of a burrowed firm ground, marking the base of the upper Exshaw. The lag consists of pyritized nodules, fossil debris, lime-mudstone clasts and phosphate grains (Figure 2.21B). The upper Exshaw is similar to the lower Exshaw, consisting of dark brown to black organic shale and contains rare crinoid fragments, phosphate and pyrite grains. 41 Figure 2.21. Gamma ray log signature and stratigraphic contacts of the Big Valley Formation and its relationship to the underlying Stettler Formation and overlying Exshaw Formation. A. Erosive contact between lower Banff and underlying upper Exshaw shale (9-07-005-25W4, 2828.6 m). B. Granular transgressive lag on burrowed firm ground at the top of silty crinoidal wackestone of the middle Exshaw (9-07-005-25W4, 2830.5 m). C. Distinct contact between silty dolomitic mudstone of the middle Exshaw and the underlying organic-rich shale of the lower Exshaw (9-07-005-25W4, 2832.7 m). D. Granular transgressive lag between lower Exshaw shale and brachiopod-crinoid wackestone of the upper Big Valley Formation (11-36-007-23W4, 1952.2 m). E. Distinct contact between upper Big Valley and subtidal shoal facies of the lower Big Valley Formation (4-33-007-24W4, 2391.5 m). F. Distinct contact between the lower Big Valley peritidal deposits and Stettler Formation, marked by detrital nodular anhydrite and laminated dolomite clasts (16-24-005-24W4, 2718.0 m). 42 2.8 Big Valley and Exshaw Formations: Localized Over-Thickened Section The Big Valley Formation is usually 10-m thick across the study area (Figure 2.10), but is locally up to 25-m thick (Figures 2.22, 2.23). Isopach maps and cross-sections of the Big Valley Formation indicate that localized areas of Big Valley and Exshaw Formation ‘thicks’ occur where the underlying Stettler Formation is thinner (Figures 2.22, 2.24). The over-thickened areas are resolvable in 2-d seismic, as semi-circular shaped depressions (Figure 2.25). In cores of the over-thickened Big Valley sections, the peritidal packstone-grainstone lithofacies attains thicknesses of 4 to 8-m (Figure 2.26). Overlying these thick shoal units, are brecciated limestones. An aeromagnetic map (Figure 2.27) of southern Alberta indicates the presence of a NNW-SSE basement structural lineament traversing the study area (Lyatsky et al., 2005). This lineament corresponds to the trend of over-thickened zones. This linear structural trend, along with the relationship of the concomitant thinning of Stettler evaporites and increased Big Valley-Exshaw thicknesses are attributed to the dissolution of Stettler and stratigraphically lower salt beds during Big Valley and Exshaw time. The mapped NW/SE structural lineament, inferred from Lyatsky et al, (2005) as a basement-controlled high-angle block fault, may have acted as a conduit for interstratal fluids to dissolve salt from the evaporite beds underlying the Big Valley Formation. A similar trend in the Williston Basin shows that several of the most prolific and thickest Bakken-Three Forks petroleum reservoirs are related to basement fault systems and/or dissolution of older evaporite beds overlying the basement faults and occurring simultaneously with fault movements (Wright et al. 1994; Sonnenberg and Pramudito, 2009). 43 The lower Big Valley shoal deposits are thought to fill the increased accommodation space resulting from localized salt dissolution. The brecciated limestones may be representative of the open-marine upper Big Valley unit that accumulated in the topographic ‘lows’, and represent sink-hole ‘karstification’ processes (discussed further section 2.10). Figure 2.22. Isopach maps of the Big Valley Formation (left) and Stettler Formation (right) A. This map highlights the irregular over thickened localized areas, as well as the thickness trend oriented NNW-SSE. B. This map illustrates to some degree that where the Big Valley Formation is thickest, the Stettler Formation is thinner. T4 T11 R 22 R 26 44 Figure 2.23. Anomalously thick Big Valley succession (~25 m) contrasts with regional thickness trends illustrated in Figure 10. 45 Figure 2.24. Cross-section utilizing the upper Exshaw as datum, illustrates that the thickest accumulations of Exshaw and Big Valley formations occur where the underlying Stettler Formation is thinnest. 46 F igure 2. 25. Two- d ime ns io na l  s e is mic  ima ge  of the  over- thic k e ne d B ig Va l l e y  s e c tions  in the  1 4 - 2 1 - 0 0 4 - 25W 4 we l l . This we l l  a ppe a rs  to ha ve be e n dril l e d o n the  fl a nk  of a n ove r - thic k e ne d s e mi - c irc ul a r fe a ture . The  fe a ture  is a b out 5 75 m in d ia me te r ( wi t h pe rmiss io n of C onoc o Phil l ips C a na da  L imite d).  47 Figure 2.26. Cored section of over-thickened Big Valley Formation (04-33-007-24W4). The peritidal shoal deposits attain thicknesses of >4 metres. Overlying these thick shoal units are karsted, open marine Big Valley deposits. 48 F igure 2 . 27 . A e roma g ne tic  ma p of s outhe r n A l be rta  wit h ma ppe d s truc tu ra l  l ine a me nts , inte r pre te d to be  ba s e me nt - c ont rol l e d high - a ngl e  bl oc k fa ul t s  ( L ya tsk y e t a l ., 2005) . A  ma ppe d N N W / SSE  fa ul t (or s truc tura l  l ine a me nt) un de r the  s tudy a re a  al igns  wi th s e ve ra l  ove r - thick e ne d we l ls. E a c h of the s e  we l l s  is unde r l a in by th in ne d De vonia n e v a porite  be ds. This s ug ge s ts  c onte mpo ra ne ous  ba s e me nt c ontr ol  due  to  hi gh - a ngl e  bl oc k fa ul ting, with sa l t diss ol utio n a nd  c ol l a pse  oc c urring  a l ong the  t re nd.   49 2.9 Depositional and Stratigraphic Framework The Big Valley Formation is the primary focus of this study; however, in order to present both a depositional and stratigraphic model, the Big Valley must be considered in context within the overall bounding stratigraphic succession. Depositional-model interpretations for both the Big Valley regional lithofacies sequence, and the locally ‘anomalous’ over-thickened sequence are given in Figure 2.28 and Figure 2.29. Figure 2.30 presents a sequence stratigraphic interpretation for the entire upper Stettler to lower Banff succession. The block diagram in Figure 2.28 illustrates the upper Stettler/ lower Big Valley sequence as a low-gradient ramp setting of an epeiric shelf. The upper Stettler evaporites are characterized by nodular and enterolithic anhydrite beds, stromatolites and microbial mat interlayers (Figures 2.8, 2.9). The textures observed in the Stettler Formation are characteristic of modern day marginal marine sabkhas and salina environments deposited on a shelf-margin platform, such as in the Persian Gulf (James et al., 2010; Kendall, 2010). The Stettler evaporites attain thicknesses well over 100 metres (Figure 2.24), leading to the theory that most of the lower Stettler sequence might better fit the basin-centre evaporite model of which there is no modern analogue (Kendall, 2010). Both Handford and Loucks (1993) and Kendall (2010) consider shelf-margin platform evaporites to indicate highstand conditions. It is proposed that the upper Stettler evaporites record deposition in a highstand setting (Figure 2.30). The sharp contact in cores and on logs regionally marks a sequence boundary (SB) between the upper Stettler evaporites and the transgressive peritidal lithofacies assemblage of the lower Big Valley Formation. 50 The lower Big Valley Formation forms a transgressive systems tract (TST) within which peritidal lithofacies are laterally discontinuous, and varying in thickness from 0.5 to 2-m thick. This autocyclic variability is interpreted to result from localized aggradation and lateral shifting of lithofacies. Local sediment accumulation occurs until high-tide level is reached and then tidal forces will shift sedimentation to a new area, resulting in a spatial mosaic of sediment production and deposition (Pratt and James, 1986; Pratt, 2010). Usually, the peritidal deposits of the lower Big Valley Formation are collectively less than 7-m thick, whereas in local areas, increased accommodation space due to salt dissolution and subsidence, allowed accumulation of up to 15-m of the peritidal succession. Deposition of the peritidal sequence generally culminates in a deepening upward trend resulting in the deposition of subtidal shoal lithofacies beneath the upper Big Valley Formation, as interpreted in cores. The contact between the lower Big Valley and the upper Big Valley displays a distinct change in color and lithological composition, from peritidal dolomites(2a) to open-marine, crinoid-brachiopod, muddy limestones (1a). This contact is a flooding surface (FS), resulting from an increased rate of sea level rise in response to basin-wide continuous platform subsidence, as demonstrated by Christopher (1961) for the Torquay Formation in the Williston Basin. Convergence on the western margin of ancestral North America supports a compressional origin for the subsidence of the basin which initiated sea level transgression and Big Valley open-marine deposition. During deposition of the Big Valley open-marine limestones, extensive colonization of vascular land plants increased weathering rates and nutrient supply to the coastal settings (Algeo et al., 1995). The mesotrophic carbonate assemblage of the Big Valley Formation reflects the nutrient-enriched system which continued during the deposition of the organic-rich 51 Exshaw Formation, also discussed by Christopher (1961) for the apparent similarity in the environment of deposition between the Big Valley Formation and the organic-rich lower Bakken member of the Williston Basin. Throughout the study area, the open-marine limestones of the upper Big Valley are usually less than 2-m thick, and overlie the peritidal facies assemblage which is generally less than 7-m thick. In local areas (Figures 2.23, 2.24, 2.25), salt dissolution and resultant subsidence led to the deposition of a thick (up to 10-m) open-marine package on top of an over-thickened peritidal succession (up to 15-m; Figure 2.29). Subsequent base level drop resulted in subaerial exposure and karstification of the open-marine facies in over-thickened local areas. Subaerial exposure of the open-marine Big Valley carbonates placed the Big Valley sediments in the vadose zone. Carbon isotope exchange between the enriched 13C Big Valley sediments and the 13C depleted vadose water resulted in 13C depletion of both the over-thickened (-8.75 13C) and normal (-2.24 13C) open-marine carbonate deposits. These carbon isotope values are in the range for oxidized carbon, indicating the influence of soil carbon dioxide within the vadose zone (Goldstein et al., 1991; Yang, 2001). Basin-wide transgression then ensued which eroded much of the thin regional upper Big Valley deposits while preserving the thick, now-collapsed, karsted succession. The transgression terminated the Big Valley sequence and resulted in a marked change in depositional conditions basin-wide. Continued vascular land plant colonization supplied an abundance of nutrients to the system, as well as climatic cooling and a mini-glaciation in the Southern Hemisphere led to an increased overturn of nutrients to the surface waters, stimulating primary production (Algeo et al., 1995; Caplan and Bustin, 52 1999). Increased primary production eventually led to benthic anoxia and the deposition of globally continuous black mudrocks. This bio-event is the Hangenberg extinction, and is identified by the unconformable maximum flooding surface (MFS) that separates the upper Big Valley Formation from the condensed section of the organic-rich lower Exshaw mudrocks (Caplan and Bustin, 1999). The entire lower Banff- Exshaw succession was deposited in a low-gradient epeiric shelf basin that became partially isolated and depositionally restrictive on two separate episodes. Basement tectonic activity is thought to be the cause of the temporal changes in shelf-basin configuration from southwestern Alberta into southeastern Saskatchewan (Smith and Bustin, 2000). The lower Banff-Exshaw interval is interpreted as two TST-HST sequence sets (Figure 2.30). Deposition of the black organic-rich lower Exshaw shale occurred during the first TST, and provided a record of the low sedimentation rates and restriction of water circulation in the environment. Nutrient influx to the depositional system, rather than over-deepening of the basin, is thought to have resulted in the anoxic water conditions (Algeo et al., 1995; Caplan et al., 1996; Smith and Bustin, 2000). The middle Exshaw member is a silty carbonate mudstone with biogenic carbonate fragments. Burrowing organisms redistributed and destroyed organic matter, resulting in low total organic carbon content, as reflected by the light grey color (Macqueen and Sandberg, 1970). This member was deposited in an unrestricted open epeiric shelf in the distally located portion of the HST. The distal HST (toe) deposits record initial sedimentation following the maximum flooding surface at the top of the lower Exshaw. Following middle Exshaw deposition, sedimentation of black, organic-rich upper Exshaw shale records return to a partially 53 isolated shelf-basin during the second TST. At the top of the upper Exshaw, a maximum flooding surface characterized by shale rip-up clasts and disseminated pyrite marks maximum marine transgression on the shelf (Posamentier and Allen, 1999; Abouelresh, 2013). The erosive contact marks the beginning of net regression during the HST, where rate of sediment supply overwhelmed sea level rise and resulted in progradation of the lower Banff Formation. 54 Figure 2.28. Depositional model proposed for the Big Valley Formation in the study area. 55 Figure 2.29. Processes and timing of formation of the ‘regional’, vs. the ‘local’ over-thickened Big Valley succession. 56 Figure 2.30. Detailed sequence stratigraphic column with core photographs from the Stettler, Big Valley and Exshaw formations. 57 2.10 Conclusions The conclusions of this study are:  The stratigraphic succession (Stettler, Big Valley, and Exshaw formations) in thestudy area is lithologically more similar to the stratigraphic equivalent Three Forks and Bakken formations in the Williston Basin and the northwestern United States, than to the Wabamun-Exshaw succession in the foothills and central plains of Alberta. Comparable basin configuration of the southern Alberta sub-basin and the Williston Basin led to the deposition of the lithologically similar units.  The Big Valley Formation has been informally divided into two depositionallyrelated units: an open-marine nodular limestone and a lower partially dolomitized peritidal carbonate. In published literature, the peritidal interval is assigned to the upper part of the underlying Stettler Formation. Based on lithofacies analyses, it is proposed that the peritidal unit more appropriately fits with the Big Valley Formation. The contact between the evaporites and overlying peritidal unit is sharp to erosive and readily mappable on well logs and in cores.  The lower Big Valley Formation consists of a peritidal facies assemblage which isdivided into four, each 0.5 to 2.0-metres thick, variably hydrocarbon-stained lithofacies: peloidal packstone-grainstone, microbial laminite, laminated dolomudstone, and intraclastic breccia-laminite. The peloidal packstone-grainstone lithofacies (2a) is interpreted to have been deposited in a high energy subtidal shoal environment, based on the abundance of peloidal grains and lack of bioturbation structures. Microbial laminated dolostones (lithofacies 2b) and laminated dolomudstones (lithofacies 2c) are interpreted as mixed tidal flat deposits, that 58 were periodically both hydrated and subaerially exposed, resulting in the formation of dessication structures and intrasediment displacive growth of evaporite minerals. Locally occurring, intraclastic breccia-laminites (lithofacies 2c) are interpreted to be remnants of ephemeral tidal drainage channels on the tidal flats, where the matrix commonly displays micro-scale-cross-stratification, indicative of hydraulic influence on sediment deposition. The contact between the peritidal assemblage and the upper Big Valley Formation is marked by a distinct color and composition change. The Upper Big Valley Formation is interpreted to be open-marine and consists of one lithofacies, a nodular, argillaceous limestone with variable crinoid and brachiopod composition.  The lower Big Valley Formation was deposited in a low-gradient ramp setting of anepeiric shelf, and forms a transgressive systems tract (TST), where the peritidal lithofacies are laterally discontinuous, and varying in thickness. Deposition of the peritidal sequence generally culminates in a deepening upward trend resulting in the deposition of subtidal shoal lithofacies beneath the upper Big Valley Formation. The contact between the lower Big Valley and the upper Big Valley displays a distinct change in color and lithological composition, from peritidal dolomites (2a) to open-marine, limestones (1a). This contact is a flooding surface (FS), resulting from an increased rate of sea level rise in response to basin-wide continuous platform subsidence (Christopher, 1961). Subsequent base level drop resulted in subaerial exposure, and karstification of the open-marine facies in over-thickened local areas. Basin-wide transgression eroded much of the thin regional upper Big Valley deposits while preserving the thick, now-collapsed, karsted succession. The 59 transgression terminated the Big Valley sequence and resulted in a drastic change in depositional conditions basin-wide, eventually resulting in deposition of the Exshaw Formation.  Hydrocarbon production from the Big Valley Formation occurs from the peritidaldeposits. The main hydrocarbon reservoir lithofacies is the dolomitized peloidal packstone-grainstone (2a). Successful production of the Big Valley Formation has occurred locally in southern Alberta, where the most significant oil producer is the vertical 10-30-008-23W4 well, which has yielded over 250,000 barrels of oil since initial production in 1979. The Big Valley Formation is normally less than 10-m thick, but locally can be up to 25-m thick as shown in the 10-30 well. The over-thickened parts have 4 to 8-m of porous oil-stained peloidal packstone-grainstone deposits. In such thickened areas, the overlying Exshaw Formation also displays increased thicknesses of up to 17-m. These localized over-thickened zones appear to align along a possible NNW/SSE trend which follows a similar orientation of a basement structural lineament treading through the study area. This linear structural trend of over-thickened deposits may have resulted from basement controlled high-angle block faulting and/or salt dissolution and collapse of underlying Devonian evaporite beds. Dissolution would have started at the time of lower Big Valley deposition and extended into Exshaw time. This relationship is observed from concomitant thinning of underlying Stettler evaporites associated with increases of Big Valley and Exshaw thicknesses. 60 Chapter 3: Depositional and Diagenetic Controls on Reservoir Development of the Upper Devonian Big Valley Formation, southern Alberta 3.1  Introduction  Recent industry interest in the Devonian-Mississippian (Big Valley-Exshaw) succession in southern Alberta (Figure 1) is the result of successful hydrocarbon production of the, in part, stratigraphic equivalent Three Forks-Bakken petroleum system in the Williston Basin. Increased activity in southern Alberta has resulted in the availability of more core logs to examine the complex interplay between depositional and diagenetic controls on reservoir development of the Big Valley Formation. In this study the relationship between depositional rock fabric, diagenetic phases and reservoir quality of each lower Big Valley lithofacies was determined (Figure 3.2). This study compliments the previous work of Colborne et al., (2014), which determined the stratigraphic and depositional controls on hydrocarbon-bearing Big Valley reservoirs. Together, these works provide the first detailed characterization of Big Valley reservoir development in southern Alberta. 61 Figure 3.1. Southern Alberta study area showing the well control, location of cores examined and the producing wells 62 Figure 3.2. Rock fabric is the product of various sedimentary and diagenetic processes that determine pore-size distribution and petrophysical parameters that control reservoir quality (modified from Lucia, 1995). 63 3.2 Geologic Setting and Stratigraphic Framework In Devonian-Carboniferous time, the Western Canada Sedimentary Basin was located at low paleolatitudes and experienced semi-arid climatic conditions (Richards, 1989). During the Late Devonian, the Big Valley Formation was deposited on a NW/SE trending carbonate ramp in an epeiric shelf setting. The carbonate platform was affected by flexural loading and stresses from western convergent tectonic activity of the Antler magmatic arc with ancestral North America (Root, 2001). The Alberta cratonic platform, the Prophet Trough and the Peace River Embayment were the main tectonic controls that impacted deposition and accumulation of the Big Valley Formation (Douglas et al., 1970). In published literature, the Big Valley Formation is considered to consist of an open-marine limestone unit that is underlain by peritidal dolomites and supratidal evaporites of the Stettler Formation. Previous authors interpret the contact between the dolomite -evaporites of the Stettler Formation and overlying open-marine limestones of the Big Valley Formation as a major erosional unconformity (Andrichuk and Wonfor, 1954; Richards et al., 1991). The availability of more recent data has led to the refinement of the stratigraphic framework as presented in this study (Figure 3.3). A previous study (Colborne et al., 2014), based on lithofacies and petrographic analyses, informally divided the Big Valley Formation into two genetically related units; an informal lower peritidal unit and an informal upper open-marine unit. The peritidal unit, considered in published literature as part of the upper Stettler Formation, is here more appropriately placed within the Big Valley Formation, because the contact between the Stettler evaporites and overlying peritidal dolomites is sharp both on well logs and in core (Figure 3.4; Colborne et al., 2014). 64 Figure 3.3. Upper Devonian-Lower Mississippian stratigraphic correlation and nomenclature chart for the southern Alberta study area and adjacent areas (as proposed by Colborne et al., 2014). 65 Figure 3.4. Big Valley Formation is divided into an informal lower peritidal unit and an upper open-marine unit. Stettler Formation is shifted down to where a decrease in gamma ray and high resistivity reading indicates where the evaporites begin (Colborne et al., 2014). 66 3.3 Methodology The lithologic and diagenetic controls on reservoir development are based on the analysis of twenty-one cores and well logs from 84 wells. The cored wells were described and sampled at the Energy Resources Conservation Board (ERCB) in Calgary, Alberta. Lithofacies of the lower Big Valley Formation were determined by differences in lithology, sedimentary structures, and biological criteria as described by Colborne et al., 2014. Fourteen of the twenty-one cored wells were sampled for reservoir and non-reservoir lithologies, to determine depositional and diagenetic controls on reservoir development. Petrographic analyses were undertaken on one hundred and twenty-six thin section slides, prepared with double carbonate stain of Alizarin Red S and Potassium Ferricyanide to aid in the identification of calcite, dolomite and non-ferroan calcite and dolomite. Seventeen polished rock-billet samples were analyzed under scanning electron microscope to further document the relationship between rock fabric and diagenetic phases. To semi-quantitatively determine the bulk mineralogy of the lithofacies, ninety-eight smear mount samples were run using X-Ray Diffraction and the Rietveld method (Rietveld, 1967). Petrophysical data include porosity and permeability analyses from 280 Big Valley Formation samples, obtained from standard core analysis reports from the Alberta Resource Conservation Board in Calgary Alberta. In-lab petrophysical analyses include total porosity of 50 reservoir and non-reservoir samples, determined using skeletal density measurements from helium pycnometry and bulk density measurements from mercury immersion. 67 Mercury porosimetry was conducted on thirty-five samples of reservoir and non-reservoir lithologies, to determine relationships between pore size distributions and reservoir properties. Thirteen core plugs were taken from six cored wells for permeability measurements. Hydrocarbon residue was extracted from the plugs using a toluene-ethanol solution mixture in a soxhlet apparatus; after extraction the plugs were dried for 24 hours at 110°C. The plugs were analyzed in a flow-through permeameter using nitrogen gas at reservoir conditions. All analytical work was completed in the laboratories at The University of British Columbia, Department of Earth Ocean and Atmospheric Science. 68 3.4 Lower Big Valley Formation: Sedimentary Lithofacies and Paragenetic History Reservoir development of the lower Big Valley Formation is challenging because of the stratigraphic and depositional controls on reservoir occurrence as discussed by Colborne et al., 2014. The lower Big Valley Formation is normally less than 7-m thick across most of the study area, but locally occurs up to 15-m thick. Four lithofacies, each varying from 0.5 to 2.0-m thick, laterally discontinuous and variably dolomitized, were identified in the lower peritidal unit: peloidal packstone-grainstone (occurs up to 8-m thick in local, over-thickened areas; Figure 3.15), microbial laminite, laminated dolomudstone and intraclastic breccia-laminite. Lithologic description and depositional environment of these lithofacies are summarized in Table 3.1 (Colborne et al., 2014). The mineralogy of the lower Big Valley lithofacies consists mainly of calcite and dolomite (65-100%), with minor ferroan dolomite and variable quantities of anhydrite, quartz, feldspars, clays and pyrite (Figures 3.5, 3.6). All analyses on the lower Big Valley lithofacies include the over-thickened areas. 69 Table 3.1. Summary of the sedimentological details of the peritidal facies association of the lower Big Valley Formation. 70 Figure 3.5. Ternary diagrams displaying bulk mineralogy of the lower Big Valley lithofacies. Lower Big Valley peritidal deposits are predominantly dolomitized, with minor undolomitized intervals. Minor clay, feldspar and quartz grains are dispersed throughout. 71 Figure 3.6. SEM backscatter image of detrital grains observed in the lower Big Valley Formation and confirmed by elemental analysis. A. Euhedral quartz grain (white arrow) surrounded by dolomite rhombohedra (black arrow) (08-03-009-26W4, 2696.22 m, mag. 400x). B. Feldspar grains (arrow), disseminated pyrite (pyr) and anhydrite cement (A) within a clotted fabric (08-21-11-22W4, 1821.69 m, mag. 400x). C. Pyritized grain (arrow) within a euhedral- to subhedral dolomitized fabric (06-21-005-25W4, 2707.32 m, mag. 250x). D. Orthoclase (orth) grain entrained in clotted fabric (bottom right). Smaller feldspar grains dispersed throughout fabric (arrow) (08-30-008-23W4, 2210.69 m, mag. 800x). orth pyr AA A B C D orth 72 Each of the lower Big Valley lithofacies has recorded a moderately different diagenetic history, documenting the interplay between deposition and diagenesis, and the impact of both on reservoir quality fabrics. A paragenetic sequence and the relative timing of diagenetic events were determined from fabric relationships observed by petrographic and SEM/BSE analyses. Due to likely contemporaneous formation of some phases, a definitive diagenetic sequence is not always differentiable, however identification between early and late stage diagenesis is possible (Table 3.3). Physical and biological processes inherently altered the lower Big Valley lithofacies. The peloidal and intraclast grains were enveloped and encrusted by microbial films, and subjected to repeated algal borings, resulting in the formation of micritized envelopes (Figure 3.10). Early dessication features and fenestral pore space are evident in the intertidal lithofacies (2b, 2d), and were subjected to later cementation (Figures 3.8, 3.11). Early authigenic euhedral pyrite was precipitated and commonly trapped between microbial mat layers, and preserved by dolomitization (Figure 3.12B). In the depositionally preserved calcareous fabrics of the peloidal packstone-grainstone (2a), a non-ferroan, coarse calcite spar fills intergranular space between peloidal grains. Closely associated with the calcite spar, a prismatic microcrystalline calcite cement also occurs between the peloidal grains (Figures 3.7B, 3.9A). The spar and cement are early in the diagenetic history, as they do not occur in dolomitized deposits. Dolomite occurred as several early replacement and cement phases, diagenetically overprinting much of the four lithofacies. Partial dolomite replacement occurs as euhedral rhombs, which partially replace peloidal grains and pore filling calcite spar in the calcareous fabrics of the peloidal packstone-grainstone lithofacies (Figure 3.7B). A later 73 partial dolomite replacement phase occurs in the intraclastic laminite lithofacies (2c), however a distinct relationship to other late diagenetic processes is not clear (Figure 3.9B). Dedolomitization occurred after early partial dolomite replacement, identified by rhombohedral pseudomorphs of dolomites that entirely consist of equicrystalline anhedral calcite (Figure 3.9B). Calcitization of dolomite crystals is rarely observed in the calcareous fabrics of the peloidal packstone-grainstones (2a). Complete dolomitization of the peloidal packstone lithofacies has resulted in a mosaic of planar sub-to euhedral crystals. The depositional rock fabric of this lithofacies is partially to completely obliterated, with relict peloidal grains rarely observed in some samples. In contrast, complete dolomitization of the other peritidal lithofacies has resulted in diagenetic rock fabrics that partially to completely mimic the original carbonate rocks (Figures 3.8B, 3.12B, 3.13B, 3.14B). Partial to complete dissolution of grain interiors formed intragranular and moldic pore space in the intraclastic laminite lithofacies (2c). Micritic envelopes retain the shape of the relict intraclasts (Figure 3.10A, C). Close relationship of dolomite fabrics to the selectively dissolved grains, suggests penecontemporaneous dolomitization after dissolution in the intraclastic laminities (2c). Following dolomitization, the micritic envelopes served as a substrate for the clear isopachous dolomite cement to precipitate. Sharp contacts occur between the micritized intraclast grains and the cement. Continued precipitation of dolomite cement partially to completely filled void space (Figure 3.10). Precipitation of the dolomite is interpreted as early diagenetic, occurring before significant compaction of the surrounding sediment (Kaldi and Gidman, 1982). 74 Mechanical compaction is reflected by the close packing of peloidal grains in the peloidal packstone-grainstones (Figure 3.7B); in addition to some fractured micritized rims in the intraclastic laminites (Figure 3.10B). The intraclast grains are able to mainly resist mechanical compaction, because of early dolomite cement precipitation (Figure 3.10B). Open fenestral and intercrystalline pore space in the mid-to-high intertidal microbial laminites and laminated dolomudstones were potentially filled by late circum-granular anhydrite cement. Distribution of the anhydrite cement is uneven throughout the previously dolomitized fabric (Figure 3.11). Intraclastic laminites (2c) show some anhydrite cementation, however anhydrite infill was not pervasive or not readily preserved in this lithofacies (Figure 3.10C). The subtidal depositional setting of the peloidal packstone-grainstone prevented this lithofacies from evaporitic cementation. A coarse, non-ferroan calcite spar fills remnant secondary pore space between grains in the intraclastic laminite lithofacies (2c). Calcite spar is scarce, but when present is lined with pyrobitumen (Figure 3.10D). The close relationship to late hydrocarbon migration provides evidence that the calcite spar is the final precipitated carbonate phase in the lower Big Valley lithofacies. Pressure solution is evident in all of the four lithofacies by sutured dolomite crystals, interpenetrated grain contacts and styolites. Styolites cut across diagenetic fabrics and are usually hydrocarbon stained, resulting from later hydrocarbon migration through these pathways (Figure 3.13). 75 Table 3.2. Summary of the paragenetic succession in each lithofacies of the lower Big Valley Formation, as recognized from petrographic analyses. 76 Figure 3.7. SEM Backscatter images and corresponding thin section photomicrographs of lithofacies 2a. A. Clotted fenestral dolostone, with relict peloidal grains (p), and feldspar grains (arrow) (08-30-008-23W4, 2210.69 m, mag. 200x). B. Calcareous peloidal grainstone with calcite spar (calc spr) infilling primary intergranular pore space, with partial replacement by euhedral dolomite rhombs (dol). Red stained areas of calcite visible in the dolomite crystals may be evidence of dedolomitization (arrow)(08-30-008-23W4, 2210.69 m, PPL x 10) C. Planar, euhedral dolomite crystals create secondary intercrystalline porosity (arrow) (06-13-009-25W4, 2245.18 m, mag. 200x) D. Sub to euhedral coarse dolomite rhombs replace calcite. Bitumen lines secondary intercrystalline pore space (arrow) (6-13-009- 25W4, 2445.18 m, XPL x10).  p calc spr dol A B C D 77 B A C DA p Figure 3.8. SEM backscatter images and corresponding thin section photomicrographs of dolomite fabric and enhanced secondary porosity of lithofacies 2b. A. SEM image of intercrystalline porosity between dolomite crystals, some pore space is filled by anhydrite cement (arrow). Complete dolomitization has retained partial preservation of the microbially controlled depositional fabric (black arrow) (16-27-11-22W4, 1798.89 m, mag. 1800x) B. Microbial laminite with peloid grains (arrows). Well-developed intercrystalline porosity is a result of dolomitization (8-30-008-23W4, 2216.98 m, PPL, x10). C. Well-developed interconnected euhedral dolomite rhombs. Late stage evaporite cement fills intercrystalline pore space (A) (03-34-005-24W4, 2368.0 m, mag. 1600x). D. Intragranular porosity of a peloidal grains, (p) in a dolomitized fabric that has been partially cemented with anhydrite cement (arrows) (6-21-005-2707.32 m, XPL, x10).  78 Figure 3.9. A. Composite grains with pore filling, circumgranular microcrystalline calcite cement (micro calc) between peloidal grains (p). Pressure solution seams around some of the grains (arrows) (09-07-005-25W4, 2833.50 m, PPL x5). B. Replacement of euhedral dolomite rhomb with anhedral calcite (arrow); dedolomitization is a locally observed occurrence in the lower Big Valley lithofacies (01-25-11-22W4, 2441.80 m, PPL x10).  A B micro. calc micro. calc p calc 79 Figure 3.10. Thin section photomicrographs of intraclastic laminite lithofacies (2c). A. Growth of clear, equant isopachous dolomite cement. Relict intraclast grain shape is preserved by dolospar fringe (arrow). Dolomite crystals are uniform and inclusion free. (16-31-11-23W4, 2057.23 m, PPL x10). B. Preserved micritized rims outline relict intraclast (I) grain, grain interiors were more soluble. Mechanical compaction evident by fractured rim (arrow) C. Intragranular porosity within intraclast (arrow). Anhydrite cement fills secondary pore space (A), (16-31-11-23W4, 2057.23 m, PPL x20). D. Late stage, non-ferroan calcite cement fills remnant pore space. Generation of calcite cement (calc) predates hydrocarbon emplacement (pybit), (08-03-009-26W4, 2696.22 m, PPL x10).  B A AI B C D pybit. dol calc I p 80 F igure 3 .11 . SEM  ba c k  s c atte r  ima ge s  a nd c or re s pon ding thi n s e c tion ima ge  of pore  fil l ing l a te  s ta ge  e va porite  c e me nt. A &B . F e ne s tr a l pe l o ida l  fa bric  re pl a c e d by e uh e dra l  dol omite  a nd the n p a rtia l l y c e me nte d with l a te  sta ge  a nhy drite  c e me nt ( a rro w) ( 8 - 2 1 - 1 1 - 22W 4, 1820.43  m , ma g. 100x, P PL , x10 ) . Pe r me a bil ity pa thwa ys  duri ng t ime  of e va porite  c e me nta tio n a re  indic a te d by whe re  th e  l a te s ta ge  ce me nt infil l s  the ope n po re  s pa c e . C &D . Sha r p fro nt be twe e n e va pori te  c e me nt a nd d ol o mite  ( a rro ws ) , biofil m s t ruc ture s  c oul d pr ote c t dol omitiz e d fa bric  f ro m l a te  s ta ge  c e me nta tion pr oc e s s e s  ( 8 - 0 3 - 0 0 9 - 26W 4, 2696.22 m, ma g. 25 0x, PPL , x 10 ) .  A  B C  D 81 A B Figure 3.13. A. Insoluble hydrocarbon rich residue pressure solution seams in the over-thickened peloidal packstone lithofacies (04-33-007-24W4, 2393.0 m, PPL x10). B. Pressure solution seam in the microbial dolostone lithofacies, also hydrocarbon stained (16-31-11-23W4, 2053.85 m, PPL x10). A B Figure 3.12. SEM backscatter image and thin section photomicrographs of pyrite grains in the lower Big Valley Formation. A. Disseminated pyrite in a fully dolomitized fabric (arrow) (03-34-005-24W4, 2368.0 m, mag. 800x) and; B. Opaque euhedral pyrite grains in a microbial dolostone (16-31-11-22W4, 2051.38 m, XPL x5). 82 F igure 3.1 4. Thin s e c tio n photomic rog ra phs  of pyro b itume n l ine d  po r e  s pa c e  in  l ithofa c ie s  2a  a nd 2 b of  t he  l owe r B ig Va l l e y F orma tion A. Pyro bitume n l ine d pore  r im s , pa rtia l l y to ful l y oc cl ude s  pore  s pa c e  in the  pe l oida l  pac k s tone  l ithofa c ie s , found in a n ove r - thic k e ne d we l l  ( a rrow)  ( 06 -3 0 - 0 0 8 - 23W 4, 26962.22  m, PPL x10). B. W e l l  de vel ope d, e uh e dra l  dol omite  c rys ta l s , re pl a c ing initia l  de positiona l  fa bric . M ic ro bia l  s truc ture  a t c e ntre  of pho to is bitu me n l i ne d ( a r row) ,  with  in te rc rys ta l l ine  p ore  s pa c e  pa rtia l l y to a l most  ful l y occ l ude d  ( 08 - 0 3 - 0 0 9 - 26W 4, 2696.22  m.  X PL  x5).  A B  83 Figure 3.15. Cored section of over-thickened Big Valley Formation (04-33-007-24W4). The peritidal shoal deposits attain thicknesses of >4 metres. Overlying these thick shoal units are karsted, open marine Big Valley deposits (Colborne et al., 2014). 84 3.5 Summary of Diagenetic Processes, Products and Environments The diagenetic phases documented in the lithofacies of the lower Big Valley Formation record a variety of conditions that range from initial deposition through to later burial. Various biological and physical processes influenced insitu production, distribution and deposition of the biologically produced carbonate grains in the peritidal environment. Peloidal grains in the lithofacies of the lower Big Valley Formation are thought to have varied origins. In the peloidal packstone-grainstone (2a), the peloidal grains are spherical to ovoid and are thought to be fecal in origin, produced by burrowing organisms (Figure 3.7B). In the mid to-high intertidal lithofacies the peloids occur as aggregates and are thought to be microbially induced (automicritic peloids) (Figure 3.11D; Chafetz, 1986), or are left ungrouped and are thought to be caused by calcification of microbial mats that eventually disintegrate and are winnowed into peloids under increased energy conditions (Figure 3.8B/D; Kazmierczak, 1996). The primary sediments deposited on the tidal flats were periodically both hydrated and subaerially exposed. This resulted in dessication features and minor fenestral porosity that was later subjected to infill by evaporitic cement. Synsedimentary reworking of intraclasts by storm activity and tidal currents resulted in brecciation of the intraclastic laminities that were deposited within ephemeral tidal channels (Figure 3.10; Scholle and Ulmer-Scholle, 2003) The occurrence of early calcite spar in the calcareous peloidal packstone-grainstone is the product of aggrading neomorphism. The former micritic matrix between the peloidal grains are recrystallized and altered to coarse microsparite (Figure 3.7B). This process occurred during early lithification of the calcareous sediment (Bathurst, 1975) 85 Possible models for early pervasive dolomite formation in a semi-arid depositional environment include; sulfate reduction and seepage refluxion. The sulfate reduction model is based on evidence from modern carbonate environments, as observed in the hypersaline lakes of the Coorong region of South Australia, a genetic link is shown to exist between microbial organisms and dolomite precipitation (Compten, 1988; Wright, 1997, 1999, 2005). Sulfate reducing bacteria facilitate dolomite precipitation through consumption of organic matter, which increases the pH of the pore waters (Wright 1999; Teal et al., 2000; Lith et al., 2003). In the lower Big Valley Formation, widespread dolomitization is in close association with microbial activity on the tidal flat. Occurrence of authigenic pyrite in the lower Big Valley lithofacies further suggests that during consumption of organic matter, sulfate was reduced and sulfide was released into the pore waters and able to combine with dissolved iron in the system to initiate pyrite precipitation (Figure 12; Schieber, 2007). The other viable alternative is the seepage-refluxion model, which requires evaporation of tidal flat waters to increase Mg:Ca ratios, needed for dolomitizing fluid (Rameil, 2008). Evaporation results in a density contrast between the saline brines and underlying marine pore waters, resulting in the sinking of the brines, and dolomitization of the underlying carbonate sediments. Textural and dolomite crystal size variability’s in the Big Valley lithofacies could indicate proximity of the deposits to the brine source as discussed in a study by Wahlman (2010) on peritidal carbonates. Further evaporation of the marine pore waters at the surface on the tidal flat could account for the precipitation of authigenic anhydrite cement, as observed in the high tidal flat deposits of the microbial laminites and dolomudstones. 86 Several diagenetic phases in the lower Big Valley Formation are thought to have been initiated by meteoric waters on the tidal flats. Beginning with dedolomitization (Figure 3.9B), this process is the replacement of dolomite with calcite under the influence of oxidizing meteoric waters, occurring at or near the surface of deposition (Adams et al., 1984). Further, during early burial of the intraclastic laminite lithofacies, dilution of the marine pore fluids with meteoric waters is thought to have initiated the dissolution of highly soluble (high-magnesium calcite) intraclast grain interiors, whereas the micritized envelopes were preserved (Figure 3.10). Preservation of peloidal grains in the intraclastic laminite lithofacies infers that the peloidal grains consisted of chemically stable, low-magnesium micrite, and were able to survive dilution of the marine pore waters (Figure 3.10B; Kaldi and Gidman, 1982). Dolomite formation in the intraclastic laminites may have occurred penecontemporaneously with the dissolution of high-magnesium intraclast grains, as the magnesium required for dolomite precipitation became available (Folk and Land, 1975; Kaldi and Gidman, 1982). The crystal morphology of the isopachous dolospar cement is indicative of precipitation in the meteoric phreatic zone, under continued dilution by freshwaters. The equant dolomite crystals are uniform and inclusion free, evidence that the dolospar is a diagenetic cement and not a mimetic texture of a precursor calcite cement (Kaldi and Gidman, 1982). The uniform truncation of the dolomite cement (Figure 3.10), suggests that the interstitial pore fluids became undersaturated with carbonate species and cement growth was subsequently terminated (Choquette and Hiatt, 2008). Precipitation of the late, local calcite spar is thought to have occurred during moderate burial of the intraclastic laminites. A local chemistry change of the pore fluids 87 may have caused nearby dissolution of metastable carbonate, which resulted in precipitation of the calcite spar. 88 3.6 Diagenetic Evolution: Influence on Petrophysical Properties and Reservoir Quality of the lower Big Valley Formation Lithofacies distribution and petrophysical properties varies laterally and vertically through the lower Big Valley Formation. The reservoir quality is determined by the interplay of depositional and diagenetic controls that have varied through space and time. Secondary intercrystalline pore space in the main hydrocarbon-bearing peloidal packstone-grainstone lithofacies is a product of fabric-destructive dolomitization. The dolomite crystals occur as a mosaic of euhedral to subhedral crystals which range from 20 to 40 μm, and mainly obliterate the precursor limestone texture. An increase in total bulk dolomite mineralogy in the peloidal packstone-grainstone directly correlates with increase in porosity (Figure 3.16A). Dolomitized peloidal packstone-grainstones show a unimodal pore size distribution from 0.3-5 μm with 8% average porosity, and a range of 0.2-0.7 md permeability (Figures 3.17, 3.18, 3.20). The preserved calcareous fabrics of the peloidal packstone-grainstone lithofacies shows that an increase in total bulk calcite percentage results in porosity decrease (Figure 3.16B). Calcareous fabrics show no dominant pore size distribution, the result of calcite spar filling intergranular pore space. These non-reservoir quality fabrics average <2% porosity values and permeability values of <<0.00001 md (Figure 3.20). A secondary reservoir lithofacies is the microbial laminite, which consists of fine-grained depositional fabrics that are preserved by fabric-retentive dolomite crystals. The replacive dolomite crystals are anhedral to subhedral and are less than 20 μm. The distribution of anhydrite cement in the dolomitized fabric affects the petrophysical properties. The pore size distribution reflects the impact of unevenly distributed cement 89 that partially occludes the intercrystalline and fenestral pore space (Figure 3.19). Microbial laminites that were pervasively dolomitized but not extensively cemented show similar petrophysical properties of the dolomitized peloidal packstone-grainstones: a unimodal pore size distribution between 0.4-4 μm, porosity values under 8%, and permeability values of 0.2 md (Figures 3.17, 3.19, 3.20). In contrast, anhydrite cemented microbial laminites show a unimodal pore size distribution between 0.001-0.1 μm, suggesting that the anhydrite cement entirely filled the larger, more interconnected pores (0.1-4 μm). Anhydrite cementation decreases porosity values to less than 5% and permeability to <0.002md (Figure 3.20). Non-reservoir lithofacies include the laminated dolomudstones and the intraclastic laminites. The dolomudstones have low intercrystalline porosity, partly filled with anhydrite cement which results in low permeability values of <0.0002 md (Figure 3.20). Moldic and intragranular porosity in the intraclastic laminites are the dominant pore spaces. The moldic pore space is partially to fully filled by dolomite cement that has precipitated around the intraclast grains. The heterogeneity in the pore space results in a range of porosity values from 3 to 8%, and low permeability values (<0.00001 md) (Figure 3.20). 90 Figure 3.16. Total bulk mineralogy data of the peloidal packstone-grainstone lithofacies and corresponding porosity values. A. Positive linear relationship between increase in dolomite percentage and increase in porosity. B. Negative linear relationship between increase in calcite percentage and increase in porosity. 0246810121416180 20 40 60 80 100 120Calcite Content (%)Porosity (%)Porosity vs. Calcite PercentageB 0246810121416180 20 40 60 80 100 120Dolomite Content (%)Porosity (%)Porosity vs. Dolomite PercentageA91 Figure 3.17. Box and whisker plot of porosity (helium) for each lithofacies of the lower Big Valley Formation. Main reservoir lithofacies of the peloidal packstone-grainstones have the highest average porosity values. Followed by a secondary reservoir lithofacies of the microbial laminites. Non-reservoir lithofacies of intraclastic laminites and laminated dolomudstones show seemingly high porosity values for non-reservoir quality rocks.  92 Figure 3.18. The calcareous peloidal packstone-grainstones exhibit no dominant pore size distribution. In comparison, dolomitized peloidal packstone-grainstone samples display a unimodal pore size distribution from 0.3 to5 μm, and higher porosity values.  00.0010.0020.0030.0040.0050.0060.0070.001 0.01 0.1 1 10 100 1000Incremental Pore Volum (mL/g)Mean Pore Diamater (µm)16-27 1798.8914-5 2835.8411-35 2418.2011-35 2415.878-30 2214.758-30 2210.696-30 2232.954-33 2389.74-33 2389.04-33 2388.01-2 2896.31-2 2888.9Peloidal Packstone, 2acalcareous fabric dolomitized fabric calcareous rock fabric (no dominant pore size distribution) dolomitized rock fabric (unimodal pore size distribution) 93 Figure 3.19. Pore size distribution of microbial laminites. Less cemented samples show a unimodal pore size distribution between 0.1 and 4 μm. Pervasively cemented samples show a unimodal pore size distribution between 0.001 and 0.1 μm, suggesting that the anhydrite cement entirely cemented the large 0.1-4 μm pores. pervasive cementation less cemented less cemented pervasive cementation 94 Figure 3.20. Thin section photomicrographs of the four lithofacies with corresponding porosity and permeability data at reservoir condition.  95 3.6.1 Permeability and Effective Stress Relationships: Influence on Reservoir Quality The permeability of reservoir and non-reservoir lithofacies of the lower Big Valley Formation was measured at varying effective stresses, to determine the sensitivity of permeability to change in effective stress. Permeability of the main reservoir lithofacies, peloidal packstone-grainstone (2a), is largely insensitive to changes in effective stress up to and exceeding reservoir effective stress (25-30 MPa, Figure 3.21). Permeability of reservoir lithofacies (2a) decreases by less than an order of magnitude over the range of effective stresses tested. The lack of sensitivity to changes in effective stress of the peloidal packstone-grainstone likely occurs because of early dolomitization. The fine-grained microbial laminite lithofacies (2b) is more stress sensitive than the peloidal packstone-grainstone, as permeability decreases by an order of magnitude with a range of effective stress from 12–46 MPa. A non-reservoir lithofacies, the laminated dolomudstone (2d), is not stress sensitive, however overall permeability is 2 to 3 orders of magnitude lower than the peloidal packstone-grainstones (2a). 96 Figure 3.21. Variations in the permeability of the peloidal packstone-grainstone (2a), microbial laminite (2b) and laminated dolomudstone (2d) lithofacies with increased effective stress. Shaded red area is effective stress at reservoir conditions. 97 3.7 Conclusions The results of this study are summarized in the following conclusions:  Interplay of depositional and diagenetic controls has influenced potential reservoirquality of each lithofacies. The four lithofacies of the lower Big Valley Formation provide a collective record of the diagenetic phases that have contributed to the depositional fabrics and include; several dolomitization processes, cementation, solution, chemical compaction and hydrocarbon migration.  Petrographic and petrophysical analyses indicate that the main reservoir lithofaciesof the lower Big Valley Formation is the dolomitized peloidal packstone-grainstone. Depositional fabric is mainly obliterated by dolomitization, which results in well-developed secondary intercrystalline porosity. Average porosity is under 8% with permeability values between 0.2 to 0.7 md. The permeability of the peloidal packstone-grainstone is largely insensitive to change in effective stress.  Secondary reservoir lithofacies is the microbial laminites, where reservoir potentialis dependent on pervasive dolomitization and the absence of anhydrite cement. Reservoir-quality microbial laminites have >5% porosity values and permeability values around 0.2 md. Non-reservoir microbial laminites show porosity values less than 5% and permeability values <<0.002 md. Permeability of the microbial laminites is more stress-sensitive than the peloidal packstone-grainstone (2a).  Pore size distributions of reservoir rock fabrics of the peloidal packstone-grainstones and microbial laminites are similarly affected by dolomitization. Dolomitized packstone-grainstones show a unimodal pore size distribution between 98 0.3 and 5 μm, and less anhydrite cemented microbial laminites have a unimodal pore size distribution of 0.1 to 4 μm.  Depositionally preserved calcareous fabrics of the peloidal packstone-grainstonesare non-reservoir quality lithologies. Reduction of primary intergranular pore space by calcite spar and lack of any diagenetically enhanced secondary pore space has resulted in average porosity values of <2% and permeability values of <<0.00001 md.  Intraclastic laminites have a complex diagenetic history that results in a non-reservoir quality rock. Moldic-pore space created by selective grain dissolution is completely isolated by dolomite rim cement or fully occluded by other diagenetic phases, shown by low permeability values (<<0.0001 md).  The laminated dolomudstones are fine-grained dolomitized lithologies that average<5% porosity. These dolomudstones have limited intercrystalline pore space, and when present is generally filled by anhydrite which result in low permeability values (0.00028md)  Predicting reservoir development of the lower Big Valley Formation is difficult,where prediction of the generally thin, laterally discontinuous lithofacies makes them an elusive target for exploration. However, in local areas an abundance of pervasively dolomitized peloidal packstone-grainstone deposits occur up to 8-m thick. These areas provide an attractive target for future exploration success of the lower Big Valley Formation. 99 Chapter 4: Conclusions The stratigraphic, depositional and diagenetic controls on reservoir development of the Big Valley Formation in southern Alberta were examined. Apart from more recent subsurface stratigraphic studies of the (Stettler-Big Valley-Exshaw) succession in southern Alberta, (Richards et al., 1991; Caplan and Bustin, 1994, 1998; Smith et al., 1995; Meijer Drees and Johnson, 1996; Smith and Bustin, 2000; and Johnston et al., 2010), no published work has been done on reservoir development of the Big Valley Formation in southern Alberta. A review of the studies main conclusions and their implications on reservoir development are discussed below, with directions for future research. Increased industry activity in southern Alberta resulted in more core, well and seismic data to refine the stratigraphic framework in the study area, and develop depositional and stratigraphic models for the Big Valley Formation in southern Alberta. The Big Valley Formation consists of two depositionally related units: an upper (open-marine) unit and a lower (peritidal) unit. It is proposed in this study that the peritidal unit more appropriately fits with the Big Valley Formation, rather than with current assignment to the underlying Stettler Formation, because the contact between the Stettler evaporites and overlying peritidal unit is sharp and mappable on well logs and in core throughout the study area. The informal stratigraphy for the Big Valley Formation more appropriately correlates with stratigraphic divisions in Saskatchewan, North Dakota and Montana, because of similar configurations of the southern Alberta sub-basin and Williston Basin. The lower Big Valley is divided into four lithofacies associated with deposition in a peritidal environment: subtidal shoal peloidal packstone-grainstone, mid-to-high intertidal 100 microbial laminite and laminated dolomudstone and local intraclastic breccia-laminite related to tidal drainage channels. These lithofacies each vary from 0.5 to 2.0-m thick, are laterally discontinuous and variably dolomitized. The main reservoir lithofacies is the peloidal packstone-grainstone and the secondary reservoir is the microbial laminite. The absence of a stratigraphic pattern in the lower Big Valley lithofacies is the result of autocyclicity in the peritidal environment. Local sediment accumulation occurs until high-tide level is reached and then tidal forces shift sedimentation to a new area, resulting in a spatial mosaic of sediment production and deposition (Pratt and James, 1986; Pratt, 2010). The inability to predict the areal distribution of each lithofacies is a challenge for reservoir development. In local areas the Big Valley Formation is over-thickened, occurring up to 25-m thick and contains >4-m of peloidal packstone-grainstone lithofacies. These isolated areas form the most productive reservoir of the Big Valley Formation and include the 10-30-008-23W4 well, which has produced over 250, 000 barrels of oil since 1979. A NNW/SSE thickening trend follows a similar orientation of a mapped structural lineament in the study area. This linear structural trend of over-thickened deposits along with the relationship of concomitant thinning of Stettler evaporates, may have resulted from dissolution of Stettler Formation and/or older Devonian salt beds. The mapped structural lineament may have propagated into evaporite beds underlying the Big Valley Formation and acted as a conduit for interstratal fluids to dissolve salt from the evaporite beds starting at lower Big Valley deposition. Future exploration of the Big Valley Formation should investigate the spatial order of these over-thickened areas, where seismic analyses would aid in resolving their occurrence. 101 Depositional models that account for both the Big Valley regional and local thickened sequences were derived and discussed in context with the stratigraphic framework. In local areas, starting at the time of lower Big Valley deposition, dissolution of underlying evaporite beds and subsidence increased the accommodation space available for the peritidal deposits to accumulate. Initial deposition of the overlying upper Big Valley Formation is marked by a distinct change in color and lithologic composition from peritidal dolomites to open-marine limestones. The contact represents a flooding surface resulting from sea level rise in response to continued basin-wide platform subsidence as documented by Christopher (1961) for the Torquay Formation in the Williston Basin. In local areas of salt dissolution and subsidence, overlying the thickened peritidal succession are thick open-marine deposits. A base level drop occurred at the end of Big Valley deposition in the Williston Basin (Caplan and Bustin, 1994; Smith and Bustin, 2000) and is thought to have also resulted in subaerial exposure of the open-marine lithofacies, and karstification of the thickened deposits in southern Alberta. Following subaerial exposure, a basin-wide transgression eroded much of the regional upper Big Valley, while preserving the thick, collapsed karsted sequence. The transgression resulted in deposition of the organic-rich Exshaw Formation, and marks a distinct interval in Earth’s climatic and terrestrial evolution. In the Late Devonian, prevalent upwelling and increased primary production resulted from climatic cooling and a mini-glaciation in the Southern Hemisphere, as well as increased nutrient input due to extensive colonization of vascular land plants. These significant climatic and terrestrial changes led to global oceanic-anoxic events and the deposition of hydrocarbon source rocks worldwide (Caplan and Bustin, 1999). 102 Complex interplay between depositional and diagenetic controls has influenced the potential reservoir quality of each lithofacies. Pervasive dolomitization of fine-grained peloidal packstone-grainstones resulted in well-developed intercrystalline porosity (>5%) and permeability values (>0.20 md). Reservoir potential of the microbial laminites is dependent on dolomitization and lack of anhydrite cement. Non-reservoir lithologies include calcareous fabrics of the peloidal packstone-grainstone, intraclastic laminite and the laminated dolomudstone. 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Journal of Sedimentary Research, v. 71, p. 778-789. 110 Appendix A: Core Log Descriptions111 112  113 114 115 116 117 118 119 120 121  122  123  124  125  126  127  128  129  130   131  Appendix B: Formation Top Data Base132   UWI Kelly Bushing (m) Formation Top Pickᵻ Depth (m) 100/05-13-004-22W4/00 1109.50 Upper Exshaw -676.00   Middle Exshaw -677.00   Lower Exshaw -680.50   Big Valley -683.50   Big Valley Marine -683.50   Big Valley Peritidal -684.20   Stettler -688.80     100/03-32-004-23W4/00 1094.70 Upper Exshaw -1116.00   Middle Exshaw -1117.30   Lower Exshaw -1121.30   Big Valley -1125.80   Big Valley Marine -1125.80   Big Valley Peritidal -1126.80   Stettler -1135.70     100/14-21-004-25W4/00 1120.50 Upper Exshaw -1724.50   Middle Exshaw -1730.70   Lower Exshaw -1731.50   Big Valley -1735.50   Big Valley Marine -1735.50   Big Valley Peritidal -1738.00   Stettler -1765.60     100/13-07-004-25W4/00  Upper Exshaw -2934.30   Middle Exshaw -2936.50   Lower Exshaw -2940.50   Big Valley -2941.20   Big Valley Marine -2941.20   Big Valley Peritidal -2941.50   Stettler -2947.50     100/03-34-005-24W4/00 1096.40 Upper Exshaw -1263.10   Middle Exshaw -1263.60   Lower Exshaw -1267.20   Big Valley -1267.20   Big Valley Marine -1267.20   Big Valley Peritidal -1268.75 133 UWI Kelly Bushing (m) Formation Top Pickᵻ Depth (m) Stettler -1275.10 100/11-35-005-24W4/00 1104.50 Upper Exshaw -1301.50 Middle Exshaw -1304.35 Lower Exshaw -1306.00 Big Valley -1307.50 Big Valley Marine -1307.50 Big Valley Peritidal -1308.99 Stettler -1322.43 100/14-05-005-25W4/00 1099.80 Upper Exshaw -1730.20 Middle Exshaw -1730.74 Lower Exshaw -1732.89 Big Valley -1733.56 Big Valley Marine N/A Big Valley Peritidal -1733.56 Stettler -1741.50 100/06-21-005-25W4/00 1058.20 Upper Exshaw -1644.60 Middle Exshaw -1644.80 Lower Exshaw -1646.60 Big Valley -1648.00 Big Valley Marine -1648.00 Big Valley Peritidal -1649.00 Stettler -1654.80 100/06-35-005-25W4/00 1056.40 Upper Exshaw -1335.10 Middle Exshaw -1336.10 Lower Exshaw -1341.60 Big Valley -1342.60 Big Valley Marine -1342.60 Big Valley Peritidal -1343.20 Stettler -1353.60 100/16-02-005-26W4/00 1066.50 Upper Exshaw -1891.00 Middle Exshaw -1891.50 Lower Exshaw -1892.70 Big Valley -1893.50 Big Valley Marine -1893.50 Big Valley Peritidal -1894.80 134  UWI Kelly Bushing (m) Formation Top Pickᵻ Depth (m) 100/11-14-005-26W4/00 1058.00 Lower Exshaw -1919.80   Big Valley -1920.50   Big Valley Marine -1920.50   Big Valley Peritidal -1921.00   Stettler -1921.70     100/07-08-006-22W4/00 990.30 Upper Exshaw -818.20   Middle Exshaw -818.70   Lower Exshaw -821.70   Big Valley -826.70   Big Valley Marine -826.70   Big Valley Peritidal -827.20   Stettler -833.70     100/06-16-006-22W4 975.10 Upper Exshaw -832.90   Middle Exshaw -838.90   Lower Exshaw -841.90   Big Valley -843.90   Big Valley Marine N/A   Big Valley Peritidal -843.90   Stettler -860.90     100/06-23-006-22W4 969.50 Upper Exshaw -794.50   Middle Exshaw -799.70   Lower Exshaw -801.50   Big Valley -803.50   Big Valley Marine -803.50   Big Valley Peritidal -804.40   Stettler -818.60     100/06-22-006-23W4 1004.70 Upper Exshaw -1192.00   Middle Exshaw -1193.80   Lower Exshaw -1196.30   Big Valley -1196.80   Big Valley Marine -1196.80   Big Valley Peritidal -1197.50   Stettler -1204.30     100/15-12-006-24W4 1038.20 Upper Exshaw -1193.30   Middle Exshaw -1194.10 135  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1197.10   Big Valley -1198.00   Big Valley Marine -1198.00   Big Valley Peritidal -1199.10   Stettler -1204.30     100/04-21-006-24W4 1065.40 Upper Exshaw 1303.60   Middle Exshaw 1304.60   Lower Exshaw 1306.60   Big Valley 1307.60   Big Valley Marine N/A   Big Valley Peritidal 1307.60   Stettler 1315.60     100/09-14-006-25W4 1058.10 Upper Exshaw 1474.90   Middle Exshaw 1475.40   Lower Exshaw 1476.90   Big Valley 1477.90   Big Valley Marine N/A   Big Valley Peritidal 1477.90   Stettler 1485.10     100/01-02-006-26W4 1045.10 Upper Exshaw 1837.90   Middle Exshaw 1838.20   Lower Exshaw 1839.90   Big Valley 1840.90   Big Valley Marine N/A   Big Valley Peritidal 1840.90   Stettler 1851.10     100/08-19-006-26W4/00 1139.40 Upper Exshaw 2046.50   Middle Exshaw 2047.10   Lower Exshaw 2050.10   Big Valley  2050.60   Big Valley Marine N/A   Big Valley Peritidal 2050.60   Stettler 2059.10     100/04-24-007-22W4 937.60 Upper Exshaw 863.90   Middle Exshaw 866.40 136  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw 871.10   Big Valley 876.70   Big Valley Marine N/A   Big Valley Peritidal 876.70   Stettler 897.60     100-05-18-007-23W4 1016.00 Upper Exshaw 1229.50   Middle Exshaw 1232.00   Lower Exshaw 1238.50   Big Valley 1239.50   Big Valley Marine N/A   Big Valley Peritidal 1239.50   Stettler 1247.40     100/12-28-007-23W4 1014.80 Upper Exshaw 1136.70   Middle Exshaw 1139.70   Lower Exshaw 1141.70   Big Valley 1142.70   Big Valley Marine N/A   Big Valley Peritidal 1142.70   Stettler 1152.20     100/11-36-007-23W4 957.70 Upper Exshaw 989.70   Middle Exshaw 989.00   Lower Exshaw 993.80   Big Valley 994.80   Big Valley Marine 994.80   Big Valley Peritidal 995.50   Stettler 1004.55     100/03-22-007-24W4 1016.40 Upper Exshaw 1345.10   Middle Exshaw 1345.60   Lower Exshaw 1346.60   Big Valley 1347.60   Big Valley Marine 1347.60   Big Valley Peritidal 1348.60   Stettler 1358.60     100/03-32-007-24W4 964.70 Upper Exshaw 1407.80   Middle Exshaw 1408.30 137  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw 1412.30   Big Valley 1412.80   Big Valley Marine 1412.80   Big Valley Peritidal 1413.30   Stettler 1420.30     100/04-33-007-24W4 967.50 Upper Exshaw 1392.90   Middle Exshaw 1394.10   Lower Exshaw 1405.31   Big Valley 1406.10   Big Valley Marine 1406.10   Big Valley Peritidal 1412.40   Stettler 1428.00     100/10-21-007-25W4/00 997.30 Upper Exshaw -1590.20   Middle Exshaw -1591.20   Lower Exshaw -1595.10   Big Valley -1596.70   Big Valley Marine N/A   Big Valley Peritidal -1596.70   Stettler -1604.90     100/05-30-007-25W4/00 1047.40 Upper Exshaw 1707.10   Middle Exshaw 1708.00   Lower Exshaw 1709.60   Big Valley 1710.40   Big Valley Marine 1710.40   Big Valley Peritidal 1710.80   Stettler 1719.60     100/06-26-007-26W4/00 1099.90 Upper Exshaw -1821.60   Middle Exshaw -1822.20   Lower Exshaw -1824.60   Big Valley -1826.60   Big Valley Marine -1826.60   Big Valley Peritidal -1828.80   Stettler -1841.60     100/06-10-008-22W4/00 848.80 Upper Exshaw -887.40   Middle Exshaw -888.70 138  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -891.20   Big Valley -893.50   Big Valley Marine -893.50   Big Valley Peritidal -895.30   Stettler -904.70     100/06-29-008-22W4/00 933.60 Upper Exshaw -999.00   Middle Exshaw -834.60   Lower Exshaw -838.60   Big Valley -840.40   Big Valley Marine -840.40   Big Valley Peritidal -842.20   Stettler -849.90     100/16-30-008-22W4/00 930.50 Upper Exshaw -828.50   Middle Exshaw -829.90   Lower Exshaw -834.00   Big Valley -835.50   Big Valley Marine -835.50   Big Valley Peritidal -836.60   Stettler -844.50     100/09-09-008-23W4/00 1001.90 Upper Exshaw -1118.60   Middle Exshaw -1119.60   Lower Exshaw -1121.60   Big Valley -1122.60   Big Valley Marine N/A   Big Valley Peritidal -1122.60   Stettler -1133.10     100/10-20-008-23W4/00 995.20 Upper Exshaw -1148.80   Middle Exshaw -1149.80   Lower Exshaw -1152.80   Big Valley -1153.80   Big Valley Marine -1153.80   Big Valley Peritidal -1154.90   Stettler -1162.40     100/10-23-008-23W4/00 959.30 Upper Exshaw -1029.40   Middle Exshaw -1031.20 139  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1033.70   Big Valley -1035.20   Big Valley Marine N/A   Big Valley Peritidal -1035.20   Stettler -1042.90     100/06-28-008-23W4/00 994.80 Upper Exshaw -1213.70   Middle Exshaw -1215.20   Lower Exshaw -1217.20   Big Valley -1218.70   Big Valley Marine N/A   Big Valley Peritidal -1218.70   Stettler -1226.20     100/08-30-008-23W4/00 990.80 Upper Exshaw -1212.25   Middle Exshaw -1212.78   Lower Exshaw -1217.48   Big Valley -1218.12   Big Valley Marine -1218.12   Big Valley Peritidal -1218.45   Stettler -1231.30     100/06-30-008-23W4/00 1018.10 Upper Exshaw -1182.40   Middle Exshaw -1183.90   Lower Exshaw -1192.10   Big Valley -1198.40   Big Valley Marine -1198.40   Big Valley Peritidal -1199.80   Stettler -1218.90     100/10-30-008-23W4/00 1012.80 Upper Exshaw -1194.90   Middle Exshaw -1197.70   Lower Exshaw -1207.20   Big Valley -1212.70   Big Valley Marine -1212.70   Big Valley Peritidal -1214.10   Stettler -1237.70     100/13-35-008-23W4/00 942.10 Upper Exshaw -886.90   Middle Exshaw -887.40 140  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -889.90   Big Valley -890.50   Big Valley Marine -890.50   Big Valley Peritidal -891.50   Stettler -900.90     100/10-13-008-24W4/00 1050.00 Upper Exshaw -1180.90   Middle Exshaw -1181.90   Lower Exshaw -1183.00   Big Valley -1183.50   Big Valley Marine -1183.50   Big Valley Peritidal -1184.20   Stettler -1191.50     100/10-22-008-24W4/00 969.90 Upper Exshaw -1215.60   Middle Exshaw -1216.30   Lower Exshaw -1218.60   Big Valley -1220.10   Big Valley Marine -1220.10   Big Valley Peritidal -1220.70   Stettler -1226.80     100/10-36-008-24W4/00 970.00 Upper Exshaw -1215.00   Middle Exshaw -1215.30   Lower Exshaw -1217.00   Big Valley -1217.50   Big Valley Marine -1217.50   Big Valley Peritidal -1218.10   Stettler -1225.50      1013.00 Upper Exshaw 1641.50   Middle Exshaw 1643.20 100/02-18-008-25W4/00  Lower Exshaw 1650.75   Big Valley -1652.10   Big Valley Marine N/A   Big Valley Peritidal 1652.10   Stettler 1664.00     100/06-35-008-25W4/00 944.70 Upper Exshaw -1447.60   Middle Exshaw -1448.10 141  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1453.10   Big Valley -1456.60   Big Valley Marine N/A   Big Valley Peritidal -1456.60   Stettler -1465.10     100/06-26-008-26W4/00 971.30 Upper Exshaw -1715.20   Middle Exshaw -1716.20   Lower Exshaw -1717.70   Big Valley -1718.70   Big Valley Marine -1718.70   Big Valley Peritidal -1719.70   Stettler -1725.70     100/03-08-009-24W4/00 962.70 Upper Exshaw -1426.30   Middle Exshaw -1428.80   Lower Exshaw -1432.30   Big Valley -1434.30   Big Valley Marine N/A   Big Valley Peritidal -1434.30   Stettler -1440.30     100/02-17-009-24W4/00 952.30 Upper Exshaw    Middle Exshaw    Lower Exshaw -1243.90   Big Valley -1265.90   Big Valley Marine N/A   Big Valley Peritidal -1265.90   Stettler -1274.70     100/14-05-009-24W4/00 951.00 Upper Exshaw -1325.00   Middle Exshaw -1326.00   Lower Exshaw -1332.00   Big Valley -1831.70   Big Valley Marine N/A   Big Valley Peritidal -1831.70   Stettler -1838.80     100/16-07-009-24W4/00 946.20 Upper Exshaw -1368.50   Middle Exshaw -1369.50 142  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1372.00   Big Valley -1373.00   Big Valley Marine N/A   Big Valley Peritidal -1373.00   Stettler -1380.00     100/06-17-009-24W4/00 958.60 Upper Exshaw -1277.40   Middle Exshaw -1278.90   Lower Exshaw -1282.60   Big Valley -1283.60   Big Valley Marine -1283.60   Big Valley Peritidal -1284.00   Stettler -1291.90     100/10-17-009-24W4/00 961.90 Upper Exshaw 1247.10   Middle Exshaw 1248.10   Lower Exshaw 1255.80   Big Valley 1259.60   Big Valley Marine 1259.60   Big Valley Peritidal 1260.10   Stettler -1278.40     100/16-19-009-24W4/00 943.00 Upper Exshaw -1336.00   Middle Exshaw -1337.50   Lower Exshaw -1341.20   Big Valley -1342.20   Big Valley Marine N/A   Big Valley Peritidal -1342.20   Stettler -1351.80     100/06-32-009-24W4/00 955.20 Upper Exshaw -1329.80   Middle Exshaw -1331.80   Lower Exshaw -1338.30   Big Valley -1340.00   Big Valley Marine -1340.00   Big Valley Peritidal -1340.00   Stettler -1348.00     100/16-35-009-24W4/00 961.70 Upper Exshaw -1143.30   Middle Exshaw -1144.30 143  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1148.30   Big Valley -1149.30   Big Valley Marine N/A   Big Valley Peritidal -1149.30   Stettler -1158.30     100/06-02-009-25W4/00 952.00 Upper Exshaw -1457.50   Middle Exshaw -1458.00   Lower Exshaw -1461.50   Big Valley -1462.50   Big Valley Marine -1462.50   Big Valley Peritidal -1463.30   Stettler -1469.50     100/06-13-009-25W4/00 950.60 Upper Exshaw -1416.90   Middle Exshaw -1417.90   Lower Exshaw -1419.90   Big Valley -1420.90   Big Valley Marine -1420.90   Big Valley Peritidal -1422.50   Stettler -1441.90     100/08-03-009-26W4/00 960.40 Upper Exshaw -1729.10   Middle Exshaw -1729.10   Lower Exshaw -1731.60   Big Valley -1733.10   Big Valley Marine -1733.10   Big Valley Peritidal -1734.20   Stettler -1739.10     100/16-23-009-26W4/00 965.20 Upper Exshaw -1628.30   Middle Exshaw -1630.10   Lower Exshaw -1634.80   Big Valley -1635.80   Big Valley Marine N/A   Big Valley Peritidal -1635.80   Stettler -1643.30     100/08-26-009-26W4/00 942.00 Upper Exshaw -1637.60   Middle Exshaw -1638.50 144  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Lower Exshaw -1638.90   Big Valley -1640.00   Big Valley Marine N/A   Big Valley Peritidal -1640.00   Stettler -1650.50     100/13-33-009-26W4/00 978.20 Lower Exshaw -1743.00   Big Valley -1744.00   Big Valley Marine -1744.00   Big Valley Peritidal -1745.10   Stettler -1750.80     100/16-06-010-22W4/00 933.40 Upper Exshaw -905.50   Middle Exshaw -906.50   Lower Exshaw -909.50   Big Valley -910.50   Big Valley Marine -910.50   Big Valley Peritidal -911.50   Stettler -919.00     100/08-11-010-22W4/00 931.00 Upper Exshaw -789.00   Middle Exshaw -790.50   Lower Exshaw -791.00   Big Valley -792.00   Big Valley Marine -792.00   Big Valley Peritidal -793.70   Stettler -804.00     100/16-32-010-24W4/00 964.80 Upper Exshaw -1192.50   Middle Exshaw -1194.20   Lower Exshaw -1200.70   Big Valley -1201.60   Big Valley Marine -1201.60   Big Valley Peritidal -1202.40   Stettler -1209.70     100/03-31-010-25W4/00 0.00 Upper Exshaw -1484.60   Middle Exshaw -1486.10   Lower Exshaw -1492.10   Big Valley -1493.60 145  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Big Valley Marine N/A   Big Valley Peritidal -1493.60   Stettler -1500.60     100/13-01-010-26W4/00 994.30 Upper Exshaw N/A   Middle Exshaw N/A   Lower Exshaw -1592.70   Big Valley -1593.60   Big Valley Marine -1593.60   Big Valley Peritidal -1594.10   Stettler -1602.05     100/04-10-010-26W4/00 999.20 Upper Exshaw -1679.30   Middle Exshaw -1679.80   Lower Exshaw -1683.50   Big Valley -1684.20   Big Valley Marine N/A   Big Valley Peritidal -1684.60   Stettler -1690.80     100/01-12-010-26W4/00 998.10 Upper Exshaw -1539.40   Middle Exshaw -1539.90   Lower Exshaw -1545.90   Big Valley -1546.90   Big Valley Marine -1546.90   Big Valley Peritidal -1547.50   Stettler -1555.10     100/08-15-010-26W4/00 1015.00 Upper Exshaw -1603.50   Middle Exshaw -1605.00   Lower Exshaw -1609.20   Big Valley -1610.80   Big Valley Marine -1610.80   Big Valley Peritidal -1611.70   Stettler -1617.10     102/13-35-010-26W4/00 987.50 Upper Exshaw -841.50   Middle Exshaw -842.10   Lower Exshaw -844.50   Big Valley -844.70 146  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Big Valley Marine -844.70   Big Valley Peritidal -846.00   Stettler -855.50     100/05-08-011-22W4/00 1014.40 Upper Exshaw -832.10   Middle Exshaw -833.10   Lower Exshaw -838.50   Big Valley -841.20   Big Valley Marine N/A   Big Valley Peritidal -841.20   Stettler -854.70     100/08-20-011-22W4/00 992.60 Upper Exshaw -839.80   Middle Exshaw -840.40   Lower Exshaw -841.90   Big Valley -842.20   Big Valley Marine N/A   Big Valley Peritidal -842.80   Stettler -855.60     100/14-20-011-22W4/00 996.70 Upper Exshaw -847.90   Middle Exshaw -849.10   Lower Exshaw -850.90   Big Valley -851.70   Big Valley Marine -851.70   Big Valley Peritidal -852.50   Stettler -861.80     100/08-21-011-22W4/00 985.20 Upper Exshaw -819.80   Middle Exshaw -821.30   Lower Exshaw -823.30   Big Valley -824.00   Big Valley Marine -824.00   Big Valley Peritidal -824.35   Stettler -835.10     100/08-22-011-22W4/00 975.50 Upper Exshaw -812.00   Middle Exshaw -813.50   Lower Exshaw -815.50   Big Valley -816.00 147  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Big Valley Marine -816.00   Big Valley Peritidal -816.60   Stettler -825.50     100/16-27-011-22W4/00 965.20 Upper Exshaw -823.10   Middle Exshaw -823.70   Lower Exshaw -825.20   Big Valley -826.40   Big Valley Marine -826.40   Big Valley Peritidal -826.51   Stettler -836.30     100/06-35-011-22W4/00 981.60 Upper Exshaw -1410.00   Middle Exshaw -1410.90   Lower Exshaw -1416.40   Big Valley -1417.40   Big Valley Marine N/A   Big Valley Peritidal -1417.40   Stettler -1426.40     100/15-01-011-23W4/00 1001.60 Upper Exshaw N/A   Middle Exshaw N/A   Lower Exshaw -991.80   Big Valley -993.60   Big Valley Marine -993.60   Big Valley Peritidal -994.80   Stettler -1010.10     100/16-05-011-23W4/00 986.60 Upper Exshaw -1080.10   Middle Exshaw -1080.60   Lower Exshaw -1088.40   Big Valley -1089.40   Big Valley Marine -1089.40   Big Valley Peritidal -1089.80   Stettler -1099.40     100/06-12-011-23W4/00 996.50 Upper Exshaw -962.10   Middle Exshaw -962.70   Lower Exshaw -966.20   Big Valley -967.50 148  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Big Valley Marine -967.50   Big Valley Peritidal -968.40   Stettler -979.00     100/14-31-011-23W4/00 969.80 Upper Exshaw -1114.20   Middle Exshaw -1114.70   Lower Exshaw -1121.90   Big Valley -1124.20   Big Valley Marine -1124.20   Big Valley Peritidal -1126.20   Stettler -1137.20     100/16-31-011-23W4/00 975.40 Upper Exshaw -1045.60   Middle Exshaw -1044.60   Lower Exshaw -1054.10   Big Valley -1058.10   Big Valley Marine -1058.10   Big Valley Peritidal -1058.90   Stettler -1077.40     100/14-32-011-23W4/00 980.00 Upper Exshaw -1007.00   Middle Exshaw -1007.70   Lower Exshaw -1014.00   Big Valley -1016.00   Big Valley Marine -1016.00   Big Valley Peritidal -1016.40   Stettler -1025.50     100/12-06-011-24W4/2 962.20 Upper Exshaw -1386.80   Middle Exshaw -1387.30   Lower Exshaw -1397.80   Big Valley -1398.80   Big Valley Marine -1398.80   Big Valley Peritidal -1399.70   Stettler -1409.80     100/01-28-011-24W4/00 962.80 Upper Exshaw -1252.50   Middle Exshaw -1253.00   Lower Exshaw -1260.20   Big Valley -1263.10 149  UWI Kelly Bushing (m) Formation Top Pick Depth (m)   Big Valley Marine -1263.10   Big Valley Peritidal -1265.10   Stettler -1269.60     100/16-23-011-25W4/00 974.20 Upper Exshaw -1619.40   Middle Exshaw -1621.00   Lower Exshaw -1626.00   Big Valley -1626.80   Big Valley Marine -1626.80   Big Valley Peritidal -1627.20   Stettler -1634.80     100/06-11-011-26W4/00 993.50 Upper Exshaw 1570.50   Middle Exshaw 1573.50   Lower Exshaw -1580.70   Big Valley -1582.70   Big Valley Marine -1582.70   Big Valley Peritidal -1584.00   Stettler -1589.70     100/01-25-011-26W4/00 993.00 Upper Exshaw -1434.00   Middle Exshaw -1436.80   Lower Exshaw -1444.00   Big Valley -1447.80   Big Valley Marine -1447.80   Big Valley Peritidal -1449.65   Stettler -1453.29 Table B.1. Formation top picks.  150  Appendix C: Petrographic Analyses151  Figure C.1. A. Brachiopod fragment with biogenic quartz growth infill (16-27-11-22W4, 1793.35 m, PPL, x 2). B. Crinoid fragments, with biogenic quartz growth and a shepherd’s hook trilobite (arrow) (16-27-11-22W4, 1793.35 m, XPL, x10).C. Crinoid fragments dispersed within a non-ferroan calcite matrix with partial replacement dolomite rhombs (16-27-11-22W4, 1793.35 m, PPL, x10). D. Ostracod valve with sparry calcite infill and opaque pyrite rhombs (08-30-008-23W4, 2009.50 m, XPL, x10).  A B C D 152  Figure C.2. Thin section photomicrographs of lithofacies 2a, peloidal packstone-grainstone. A. Planar fabric comprised of euhedral dolomite crystal. Pyrobitumen lines most of the secondary intercrystalline pore space (01-25-11-26W4, 2443.30m PPL, x20). B. Relict peloidal grains under cross polars (09-007-25W4, 2835.30 m, XPL, x5).C. Well-developed secondary intercrystalline porosity between the euhedral dolomite rhombs. (16-27-11-22W4, 1799.32 m, PPL, x20). D. Peloidal grains rimmed with coarse dolomite spar, high intercrystalline porosity (06-30-008-23W4, 2235.63 m, PPL, x10). B D A C 153  B D A C Figure C.3. Thin section photomicrographs of calcareous peloidal packstone grainstones. A. Calcareous depositional fabric of the peloidal packstone-grainstone. Some of the grains are aggraded into one another, with neomorphic calcite spar separating other grains (08-30-008-23W4, 2210.08 m, XPL, x5. B. Partial replacement dolomite rhombs replace some peloid grains and micrite. C. Few peloidal grains within the micrite matrix with partial ferroan replacement rhombs. Hydrocarbon stained pressure solution seams cross cut the depositional fabric (03-34-005-24W4, 2365.5 m, XPL, x20).D. Peloidal grains and ostracod fragments in the calcareous fabric. Large ostracod carapace in the centre of photomicrograph (08-30-008-23W4, 2212.0 m, PPL, x20). 154   B D C A Figure C.4. Thin section photomicrographs of lithofacies 2b, microbial dololaminites. A. Crenulated microbial laminae with gypsum pseudomorphs grown along bedding planes, no preservation of primary fabric (06-13-009-25W4, 2245.15 m, XPL, x2). B. Inclusion-rich dolomite crystals (06-21-005-25W4, 2707.92 m, XPL, x20). C. Hydrocarbon stained pressure solution seams, with pyrobitumen lined intercrystalline pore space (04-33-007-22W4 2235.93 m, PPL, x2). D. Elongated fenestral pores infilled with anhydrite cement. Pyrobitumen partially lines to fully occludes intercrystalline porosity (08-03-009-26W4, 2696.22 m, XPL, x10).  A C 155  A B C D Figure C.5. Thin section photomicrographs of lithofacies 2b, microbial dololaminites. A. Crenulated microbial laminae with secondary intercrystalline porosity ( 08-21-11-22W4, 1815.81 m, PPL, x2). B. Dessication features and fenestral pore space infilled with anhydrite cement (09-07-005-25W4, 2835.60 m, XPL, x10). C. Anhydrite filled fenestral pore space with partial open intercrystalline porosity (08-21-11-22W4, 1821.69 m, PPL, x2). D. Entrained mud clast within the microbial material. Quartz and gypsum crystals trapped between the mat (08-21-11-22W4, 1821.46 m, PPL, x2) Mud clast entrained in microbial material and with gypsum and quartz crystals 156  Figure C.6. Thin section photomicrographs of lithofacies 2c, intraclastic breccia-laminites. A. Porous coated algal grains, enhanced by solution. Pyrobitumen partially fills pore space (06-13-009-25W4, 2444.10 m, PPL, x5). B. Complex pore space; evolution of pore space affected by solution, dolomitization, dolomite cementation and hydrocarbon emplacement (06-13-009-25W4, 2444.10 m, PPL, x10). C. Coated grains with multiple episodes of reworking and encrustation (16-31-11-23W4, 2057.60 m, PPL, x2). D. High primary and secondary interparticle and secondary intraparticle porosity. Coarse non-ferroan euhedral dolomite crystals terminate into or fully occludes pore space (16-31-11-23W4, 2057.60 m, PPL, x10).  C D B A 157  B A Figure C.7. Thin section photomicrographs of lithofacies 2d, laminated dolomudstones. A. Fenestral pore space filled with anhydrite cement (08-21-11-22W4, 1820.43, PPL, x2). B. Small quantity of microbial mat material included in the laminated dolomudstones (16-27-11-22W4, 1796.64 m, XPL, x2).  158   Figure C.8. SEM images of diagenetic rock fabric. A. High secondary intercrystalline porosity within the peloidal packstone-grainstone lithofacies, the peloidal grains display a clotted texture within the diagenetic fabric (06-13-009-25W4, 2245.18 m). B. Microbial precipitates may also display a similar clotted texture as the peloidal packstones. Patchy distribution of late stage anhydrite cement in the fenestral fabric of the microbial dololaminite facies (08-03-009-26W4, 2696.22 m). C. Disseminated framboidal pyrite (06-21-005-25W4, 2707.92 m). D. Dolomite rhomb growth within open pore space (08-03-009-26W4, 2969.22 m). A B C D 159         A B Figure C.9. SEM images of anhydritecement phase within fenestral fabric of the microbial dolostone. A. Patchy distribution of late stage pore-filling anhydrite cement, within the dolomitized rock fabric (16-27-11-22W4, 1798.89 m). B. Different dolomite phases are observed from rhomb size, as well as one phase of rhomb growth appears to have occurred after emplacement of late stage anhydrite cement (06-21-005-25W4, 2707.32 m). 160  Appendix D: Seismic Analyses  161  Figure D.1. Over-thickened 10-30-008-23W4 has produced over 250, 000 barrels of oil since 1979. The semi-circular depression is not highly resolvable in two-dimensional seismic (permission granted from Bonavista Energy). 162  Figure D.2. Interpreted structural lineaments below overthickened well 10-30-008-23W4 (granted permission from Bonavista Energy) 163  Appendix E: Isotopic Analyses 164  Figure E.1. Carbon and oxygen isotope analyses on the Big Valley Formation. Carbon values for the open-marine Big Valley Formation are in the range for oxidized carbon. Heavy oxygen isotopes may indicate climatic shifts during Big Valley deposition.  165  Appendix F: X-Ray Diffraction and Petrophysical Analyses166  XRD Analyses Well/ Depth (m)  Calcite Dolomite Anhydrite Quartz Ortho Muscovite Illite-Smectite Pyr 4-33(2377.24) 86.75 3.48 2.63 7.15 x x x x 4-33(2377.90) 89.33 1.01 7.65 2.01 x x x x 4-33(2380.10) 61.51 x 36.97 1.52 x x x x 4-33(2381.30) 5.85 74.13 6.68 9.42 x 2.47 x 0.45 4-33(2381.57) 3.18 81.65 0.73 10.28 x 3.36 x 0.81 4-33(2382.0) 3.17 81.69 0.71 10.27 x 2.36 2.3 0.8 4-33(2386.20) 0.88 85.09 2.1 6.15 x 5.39 x 0.39 4-33(2386.30) 1.82 71.15 0.15 12.5 8.03 2 4.92 6.24 4-33(2389.0) 0.17 89.32 0.82 7.22 x  2.47 x 4-33(2389.7) 0.16 90.88 3.89 4.55 x  x 0.28 4-33(2391.0) x 60.07 x 8.91 5.09  1.55 1.55 4-33(2393.0) x 88.87 2.15 4.04 x 3.56 x 1.37 8-21(1812.44) 0 68.97 0 25.38 5.52  x x 8-21(1815.33) 1.32 84.86 2.28 6.56 x 4.97 x x 8-21 (1815.81) 6.93 80.82 4.92 6.56 x 4.97 x x 8-21 (1816.27) 37.48 50.13 1.8 4.11 x 0 6.48 x 8-21 (1817.49) 0.66 72.41 14.17 11.36 x 1.4 x x 8-21 (1818.30) 1.63 90.4 0.28 7.2 x 1.3 x x 8-21 (1821.69) 0.74 86.57 3.59 4.86 x 2.24 2.24 x 8-21(1820.36) 5.43 60.13 31.76 2.68 x x x x 8-21(1820.43) 6.47 68.02 16.02 4.81 x 2.68 2 x 1-2(2887.0) 0.14 96.03 1.64 2.2 x x x x 1-2(2888.9) 32.57 51 14.96 1.47 x x x x 1-2(2892.0) 0.16 92.18 6.18 1.49 x x x x 1-2(2892.45) 0.16 89.27 6.88 3.69 x x x x 1-2(2896.3) x 59.52 36.15 1.2 x x x 2.6 1-25 (2440.5) 68.27 7.83 21.5 2.4 x x x x 1-25(2441.8) 88.38 3.74 5.53 2.36 x x x x 1-25(2443.3) 12.93 81.95 1.14 3.98 x x x x 1-25(2444.5) 4.5 80.74 2.58 6.59 x  5.59 x 3-34(2365.5) 85.37 7.86 0.65 3.35 x 2.77 x x 3-34(2368.0) 4.23 89.38 4 2.39 x x x x 3-34(2375.5) 1.81 60.1 24.13 6.06 x  7.9 x 6-21 (2707.32) 0.19 76.36 13.79 9.66 x x x x 6-21(2707.9) 0.11 77.55 21.49 0.86 x x x x 6-30(2220.0) 85.84 1.17 x 4.96 x  4.73 0.92 6-30(2221.25) 84.04 1.54 1.16 3.96 2.3 x x 0.39 6-30(2222.78) x 95.69 3.32 0.95 x x x x 6-30(2222.92) x 96.94 x x x x x x 167  Well/ Depth (m)  Calcite Dolomite Anhydrite Quartz Ortho Muscovite Illite-Smectite Pyr 6-30(2224.35) 9.24 73.49 x 7.93 x 9.28 x x 6-30(2226.0) 1.48 29.14 11.14 58.24 x x x x 6-30(2228.36) 4.04 71.25 5.85 9.93 x  6.8 1.62 6-30(2230.17) 1.03 92.41 3.23  3.13 x x x 6-30(2230.74) 1.3 72.9 2.83 10.48 x 7.48 x x 6-30(2231.21) 1.26 85.73 4.05 4.27 x 4.69 x x 6-30(2232.95) 0.44 96.41 0.49 2.66 x x x x 6-30(2233.75) 0.94 94.57 0.8 3.69 x x x x 6-30(2235.63) 0.61 94.41  3.32 1.66 x x x 6-30(2235.93) 2.76 63.98 22.59 5.22 x 5.46 x x 6-30(2236.08) 0.66 83.83 10.52 2.7 x 2.29 x x 6-30(2236.67) 0.56 91.46 6.84 1.15 x x x x 6-30(2237.76) x 96.63 1.51 1.5 x x x x 6-30(2239.61) 2.61 83.36 1.11 7.33 x 5.6 x x 6-30(2240.16) 0.47 92.81 2.95 3.78 x x x x 6-30(2245.13) 0.25 88.3 10.33 1.12 x x x x 6-30(2250.19) 0.26 87.65 10.82 1.27 x x x x 8-03(2696.22) 2.32 87.38 3.11 7.19 x x x x 8-03(2697.56) x 82.87 4.3 3.6 x  6.02 2.02 8-03(2697.68) x 72.68 0.48 9.12 8.46  7.28 2.08 8-03(2702.15) 4.83 74.47 14.33 3.93 x 2.44 x x 8-30(2210.08) 48.07 45.45 5.24 1.24 x x x x 8-30(2210.69) 38.27 58.24 2.71 0.83 x x x x 8-30(2211.50) 92.57 4.05 0.67 2.72 x x x x 8-30(2212.0) 92 4.49 1.05 2.49 x x x x 8-30(2214.75) 63.42 4.71 29.21 2.84 x x x x 8-30(2215.0) 7.74 74.45 6.2 2.91 x  8.6x x 8-30(2217.50) 1.88 82.03 0.84 6.72 x 8.52 x x 8-30(2218.0) 0.9 90.57 0.25 4.38 x 3.9 x x 8-30(2220.50) 0.85 86.03 0.08 6.38 x 6.66 x x 8-30(2221.50) 1.37 80.32 0.08 10.43 x  7.92 x 8-30(2228.75) 9.84 82.77 5.36 2.03 x x x x 11-35(2415.87) 90.31 6.72 0.88 2.21 x x x x 11-35(2418.30) 1.35 87.47 7.83 3.37 x x x x 11-35(2420.43) x 72.97 10.11 6.37 5.38  3.97 1.16 11-35(2421.83) x 30.45 45.83 10.56 5.75 2.68 5.0 0.84 11-35(2423.35) x 15.47 80.04 4.24 x x x x 16-27(1793.35) 65.54 21.42 1.59 6 x 5.79 x x 16-27(1795.0) 3.81 87.9 0.93 4.85 x 2.56 x x 16-27(1795.50) 0.59 91.89 1.01 3.37 x 3.15 x x 168  Well/ Depth (m)  Calcite Dolomite Anhydrite Quartz Ortho Muscovite Illite-Smectite Pyr 16-27(1796.0) 0.41 96.14 0.7 2.75 x x x x 16-27(1796.50) x 95.5 0.93 3.5 x x x x 16-27(1796.64) 2.03 69.72 12.88 3.92 x 2.0 8.13 1.13 16-27(1798.22) 1.07 79.4 0.93 4.72 x 13 x 0.9 16-27(1798.49) 0.7 87.65 0.26 5.79 x  4.97 0.67 16-27(1798.89) x 91.41 5.71 2.24 x x x 0.55 16-27(1799.32) 0.25 78.63 19.26 1.86 x x x x 16-27(1799.63) 0.35 77.16 7.03 10.35 x 5.12 x x 16-31(2042.30) x 78.28 0.28 10.16 3.03  7.49 1.76 16-31(2049.47) 0.75 89.53 6.02 3.02 x x x x 16-31(2049.86) 0.44 93.54 0.62 3.94 x 1.41 x x 16-31(2050.46) x 87.84 1.04 5.96 x 5.22 x x 16-31(2052.47) x 97.25 0.3 2.46 x x x x 16-31(2052.72) x 93.63 0.35 3.79 x 2.26 x x 16-31(2052.90) x 95.74 1.96 2.28 x x x x 16-31(2053.14) x 89.82 1.41 2.96 x  5.85 x 16-31(2053.52) x 98.23 0.34 1.44 x x x x 16-31(2053.85) 0.7 86.42 1.69 4.99 x  5.99x 0.9 16-31 (2054.96) 0.99 82.72 0.44 9.48 x 2.0 4.37 x Table F.1. X-ray diffraction data of the Big Valley Formation.169  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 1a* 4-33-007-24 2378.94 2.69 2.73 1.3 1a 4-33-007-24 2380.10 2.70 2.75 1.6 1a* 4-33-007-24 2380.53 2.51 2.82 10.7 1a* 4-33-007-24 2381.17 2.61 2.83 7.8 1a* 4-33-007-24 2381.32 2.61 2.81 7.0 1a* 4-33-007-24 2381.44 2.60 2.80 7.1 1a* 4-33-007-24 2381.72 2.63 2.79 5.8 1a* 4-33-007-24 2382.10 2.68 2.78 3.6 1a* 4-33-007-24 2382.97 2.69 2.78 3.5 1a* 4-33-007-24 2384.05 2.71 2.80 3.2 1a* 4-33-007-24 2385.30 2.67 2.79 4.4 1a* 4-33-007-24 2385.57 2.66 2.80 5.0 1a* 4-33-007-24 2385.91 2.62 2.79 6.2 1a* 4-33-007-24 2386.15 2.68 2.78 3.4 1a* 4-33-007-24 2386.41 2.70 2.80 3.8 1a* 4-33-007-24 2386.70 2.65 2.81 5.6 1a* 6-30-008-23 2220.84 2.64 2.70 2.4 1a* 6-30-008-23 2221.24 2.69 2.72 1.0 1a* 6-30-008-23 2221.42 2.76 2.78 1.0 1a* 6-30-008-23 2221.87 2.57 2.71 5.0 1a* 6-30-008-23 2222.01 2.71 2.77 2.3 1a* 6-30-008-23 2222.52 2.63 2.69 2.3 1a* 6-30-008-23 2222.92 2.65 2.71 2.3 1a* 6-30-008-23 2223.28 2.71 2.77 1.9 1a* 6-30-008-23 2223.38 2.63 2.70 2.5 1a* 6-30-008-23 2223.80 2.54 2.72 6.6 1a* 6-30-008-23 2224.01 2.66 2.71 2.1 1a* 6-30-008-23 2224.21 2.79 2.81 0.8 1a* 6-30-008-23 2224.31 2.61 2.80 6.6 1a* 6-30-008-23 2225.01 2.60 2.80 7.1 1a* 6-30-008-23 2225.80 2.57 2.80 8.0 1a* 6-30-008-23 2226.16 2.56 2.64 2.8 1a* 6-30-008-23 2226.31 2.62 2.78 5.5 1a* 6-30-008-23 2226.66 2.09 2.80 3.9 1a* 6-30-008-23 2229.30 2.72 2.78 2.3 1a* 6-30-008-23 2229.66 2.70 2.79 3.4 1a* 6-30-008-23 2230.50 2.51 2.82 11.1 1a* 6-30-008-23 2230.67 2.51 2.84 11.7 1a* 6-30-008-23 2230.97 2.61 2.83 7.5 1a* 6-30-008-23 2231.08 2.62 2.83 7.3 170  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 1a* 6-30-008-23 2231.30 2.70 2.78 2.7 1a* 6-30-008-23 2232.30 2.71 2.78 2.7 1a* 8-30-008-23 2216.98 2.70 2.80 7.0 1a* 8-30-008-23 2217.64 2.58 2.82 4.6 1a* 8-30-008-23 2218.21 2.71 2.80 7.1 1a* 8-30-008-23 2218.71 2.92 2.79 4.3 1a 16-31-11-23 2050.73 2.76 2.85 1.4 1a 16-31-11-23 2051.25   6.5 1a 16-31-11-23 2051.37 2.65 2.81 5.1 1a 16-31-11-23 2051.65  2.79 10.5 1a 16-31-11-23 2051.76 2.64 2.81 6.1 1a 16-31-11-23 2053.56 2.78  0.9 2a 3-34-005-24 2367.69 2.61 2.85 8.5 2a 3-34-005-24 2367.93 2.64 2.86 7.9 2a 3-34-005-24 2368.14 2.65 2.86 7.3 2a 3-34-005-24 2368.32 2.64 2.86 7.7 2a 3-34-005-24 2368.49 2.58 2.85 9.4 2a 11-35-005-24 2415.80 2.69 2.79 3.7 2a 11-35-005-24 2418.20 2.66 2.87 7.4 2a 9-07-005-25 2833.52 2.68 2.74 2.4 2a 9-07-005-25 2840.70 2.77 2.92 5.2 2a 9-07-005-25 2835.84 2.62 2.82 7.2 2a 9-07-005-25 2839.89 2.72 2.87 5.3 2a 6-21-005-25 2707.00 2.65 2.84 6.8 2a 6-21-005-25 2707.25   11.1 2a 6-21-005-25 2707.45 2.71 2.84 4.4 2a 11-14-005-26 2979.80 2.65 2.80 1.2 2a 6-16-006-26 1819.23 2.71 2.82 3.9 2a 6-16-006-26 1819.38 2.63 2.80 5.9 2a 6-16-006-26 1819.59 2.59 2.80 7.5 2a 6-16-006-26 1819.84 2.53 2.79 9.3 2a 6-16-006-26 1820.02 2.51 2.81 10.8 2a 6-16-006-26 1820.18 2.52 2.78 9.6 2a 6-16-006-26 1820.48 2.55 2.81 9.3 2a 6-16-006-26 1820.74 2.56 2.83 9.4 2a 1-02-006-26 2886.97 2.62 2.83 7.3 2a 1-02-006-26 2887.15 2.80 2.87 2.0 2a 1-02-006-26 2887.47 2.44 2.84 14.1 2a 1-02-006-26 2887.75 2.56 2.85 10.3 2a 1-02-006-26 2887.88 2.43 2.82 13.6 171  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2a 1-02-006-26 2888.10 2.60 2.86 9.0 2a 1-02-006-26 2888.28 2.54 2.86 11.2 2a 1-02-006-26 2888.51 2.55 2.85 10.6 2a 1-02-006-26 2888.75 2.69 2.86 5.7 2a 1-02-006-26 2888.90 2.78 2.93 5.1 2a 1-02-006-26 2895.75 2.72 2.86 5.2 2a 1-02-006-26 2896.00 2.78 2.85 2.5 2a 1-02-006-26 2896.18 2.81 2.87 1.8 2a 1-02-006-26 2896.30 2.81 2.94 4.6 2a 1-02-006-26 2896.44 2.81 2.87 2.2 2a 1-02-006-26 2896.62 2.80 2.80 2.6 2a 1-02-006-26 2896.79 2.66 2.87 7.3 2a 1-02-006-26 2896.91 2.63 2.83 6.9 2a 8-19-06-26 3213.61 2.67 2.85 6.2 2a 8-19-06-26 3213.91 2.68 2.87 6.8 2a 8-19-06-26 3214.21 2.65 2.88 8.0 2a 8-19-06-26 3214.49 2.68 2.88 6.7 2a 8-19-06-26 3215.04 2.65 2.88 7.9 2a 4-24-007-22 1823.10 2.84 2.89 1.8 2a 4-24-007-22 1823.65 2.60 2.84 8.4 2a 4-24-007-22 1823.90 2.62 2.81 6.7 2a 11-36-007-23 1953.20 2.68 2.69 0.5 2a 11-36-007-23 1953.50 2.64 2.71 2.5 2a 11-36-007-23 1953.70 2.62 2.70 3.0 2a 11-36-007-23 1954.00 2.61 2.69 3.0 2a 11-36-007-23 1954.25 2.47 2.71 9.1 2a 11-36-007-23 1954.60 2.61 2.81 7.0 2a 11-36-007-23 1955.00 2.68 2.70 0.6 2a 11-36-007-23 1955.40 2.67 2.69 0.8 2a 11-36-007-23 1955.70 2.65 2.68 1.4 2a 11-36-007-23 1955.90 2.65 2.69 1.8 2a 11-36-007-23 1956.25 2.66 2.70 1.4 2a 11-36-007-23 1965.50 2.66 2.68 0.9 2a 11-36-007-23 1956.70 2.62 2.68 2.1 2a 11-36-007-23 1956.90 2.67 2.70 1.0 2a* 4-33-007-24 2385.40 2.73 2.86 4.8 2a* 4-33-007-24 2387.15 2.59 2.80 7.8 2a* 4-33-007-24 2387.16 2.61 2.83 7.9 2a* 4-33-007-24 2387.66 2.56 2.81 8.9 2a* 4-33-007-24 2387.86 2.68 2.83 5.6 172  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2a* 4-33-007-24 2388.00 2.49 2.89 13.7 2a* 4-33-007-24 2388.07 2.61 2.82 7.3 2a* 4-33-007-24 2388.43 2.66 2.79 4.8 2a* 4-33-007-24 2388.66 2.64 2.84 6.9 2a* 4-33-007-24 2388.93 2.55 2.83 9.9 2a* 4-33-007-24 2389.00 2.57 2.86 9.9 2a* 4-33-007-24 2389.28 2.65 2.82 6.1 2a* 4-33-007-24 2389.29 2.65 2.86 7.3 2a* 4-33-007-24 2389.70 2.61 2.90 10.0 2a* 4-33-007-24 2389.73 2.67 2.83 5.8 2a* 4-33-007-24 2390.14 2.60 2.84 8.6 2a* 4-33-007-24 2391.07 2.41 2.85 15.5 2a* 4-33-007-24 2391.37 2.40 2.85 16.0 2a* 4-33-007-24 2391.60 2.69 2.86 6.1 2a* 4-33-007-24 2391.75 2.72 2.86 4.9 2a* 4-33-007-24 2392.10 2.73 2.86 4.5 2a* 4-33-007-24 2392.53 2.51 2.84 11.7 2a* 4-33-007-24 2393.01 2.48 2.85 13.1 2a* 4-33-007-24 2393.00 2.51 2.86 12.2 2a* 4-33-007-24 2393.55 2.51 2.82 11.0 2a* 4-33-007-24 2393.80 2.65 2.86 7.5 2a* 4-33-007-24 2394.18 2.45 2.85 13.9 2a* 4-33-007-24 2394.69 2.55 2.85 10.9 2a 6-30-008-23 2226.00 2.60 2.85 8.6 2a* 6-30-008-23 2233.43 2.50 2.84 11.8 2a* 6-30-008-23 2233.73 2.70 2.84 5.2 2a* 6-30-008-23 2234.23 2.61 2.84 8.0 2a* 6-30-008-23 2236.00 2.68 2.88 6.5 2a* 6-30-008-23 2236.26 2.57 2.84 9.8 2a* 6-30-008-23 2236.47 2.56 2.83 9.5 2a* 6-30-008-23 2236.90 2.50 2.85 12.2 2a* 6-30-008-23 2237.02 2.57 2.85 9.8 2a* 6-30-008-23 2237.20 2.44 2.84 14.2 2a* 6-30-008-23 2237.42 2.60 2.85 8.7 2a* 6-30-008-23 2237.60 2.47 2.84 13.3 2a* 6-30-008-23 2237.79 2.60 2.83 8.2 2a* 6-30-008-23 2237.98 2.56 2.85 10.1 2a* 6-30-008-23 2239.96 2.87 2.85 6.3 2a* 6-30-008-23 2240.13 2.71 2.86 5.2 2a* 6-30-008-23 2240.48 2.69 2.88 5.9 173  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2a* 6-30-008-23 2240.61 2.61 2.84 8.0 2a* 6-30-008-23 2240.80 2.75 2.85 4.4 2a* 6-30-008-23 2240.90 2.65 2.85 7.1 2a* 6-30-008-23 2239.61 2.75 2.95 6.6 2a* 8-30-008-23 2210.00 2.60 2.72 0.6 2a 8-30-008-23 2210.69 2.60 2.75 5.6 2a* 8-30-008-23 2212.93 2.64 2.70 0.8 2a* 8-30-008-23 2214.45 2.13 2.70 1.6 2* 8-30-008-23 2214.75 2.64 2.80 5.9 2a 6-13-009-25 2444.00 2.51 2.82 11.0 2a 6-13-009-25 2444.20 2.57 2.84 9.5 2a 6-13-009-25 2444.42 2.51 2.83 11.4 2a 6-13-009-25 2444.60 2.53 2.84 11.0 2a 6-13-009-25 2444.91 2.51 2.83 11.2 2a 6-13-009-25 2445.17 2.61 2.81 7.0 2a 8-03-09-26 2695.00  2.82 2.8 2a 8-03-09-26 2695.23 2.71 2.84 4.8 2a 8-03-09-26 2695.53 2.71 2.82 4.0 2a 8-03-09-26 2695.78 2.66 2.80 4.7 2a 8-03-09-26 2695.94 2.71 2.82 4.0 2a 8-03-09-26 2696.25 2.62 2.79 6.2 2a 8-03-09-26 2696.22 2.72 2.85 4.4 2a 8-21-11-22 1816.27 2.72 2.81 3.4 2a 8-21-11-22 1818.30 2.72 2.89 5.9 2a 16-27-11-22 1793.35 2.70 2.89 6.5 2a 16-27-11-22 1795.00 2.63 2.88 8.7 2a 16-27-11-22 1798.89 2.71 2.77 2.4 2a 16-27-11-22 1799.32    2a 16-31-11-23 2054.00 2.74 2.90 5.4 2a 16-31-11-23 2054.17 2.66 2.81 6.4 2a 16-31-11-23 2054.37  2.84 7.1 2a 16-31-11-23 2054.44 2.67 2.85 6.0 2a 16-31-11-23 2055.21 2.61 2.79 8.5 2a 16-31-11-23 2055.37  2.84 9.6 2a 16-31-11-23 2055.45 2.62 2.85 8.1 2a 16-31-11-23 2055.69  2.83 7.4 2b 3-34-005-24 2370.15 2.67 2.79 4.5 2b 3-34-005-24 2370.37 2.67 2.79 4.3 2b 3-34-005-24 2370.53 2.68 2.80 4.3 2b 11-35-005-24 2420.43 2.76 2.86 3.7 174  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2b 9-07-005-25 2834.60 2.71 2.85 5.2 2b 9-07-005-25 2839.29 2.72 2.89 5.6 2b 9-07-005-25 2840.90 2.69 2.89 6.8 2b 6-21-005-25 2708.60 2.73 2.80 2.5 2b 6-21-005-25 2711.00 2.87 2.88 0.1 2b 11-14-005-26 2980.01 2.66 2.80 1.0 2b 6-16-006-22 1825.09 2.63 2.86 8.2 2b 6-16-006-22 1825.41 2.76 2.84 3.1 2b 6-16-006-22 1825.77 2.68 2.85 6.1 2b 6-16-006-22 1826.00 2.76 2.83 7.7 2b 6-16-006-22 1826.30 2.61 2.78 6.3 2b 6-16-006-22 1826.64  2.83 8.1 2b 1-02-006-26 2889.95 2.70 2.77 2.3 2b 1-02-006-26 2891.36 2.58 2.81 8.3 2b 1-02-006-26 2892.00 2.65 2.91 9.1 2b 1-02-006-26 2892.10 2.66 2.81 5.6 2b 1-02-006-26 2892.32 2.56 2.80 8.8 2b 1-02-006-26 2892.45 2.48 2.91 14.9 2b 1-02-006-26 2892.58 2.57 2.81 8.6 2b 1-02-006-26 2892.91 2.62 2.83 7.3 2b 1-02-006-26 2894.85 2.61 2.80 6.6 2b 1-02-006-26 2894.90 2.66 2.89 7.8 2b 8-19-006-26 3212.87 2.73 2.88 5.1 2b 8-19-006-26 3213.08 2.67 2.86 6.7 2b 8-19-006-26 3213.31 2.72 2.88 5.7 2b 4-24-007-22 1820.90   6.9 2b 4-24-007-22 1822.65 2.64 2.72 3.0 2b 4-24-007-22 1822.90 2.88 2.96 2.5 2b 4-24-007-22 1824.30 2.66 2.82 5.6 2b 4-24-007-22 1824.60 2.75 2.83 2.9 2b 4-24-007-22 1825.00   5.4 2b 4-24-007-22 1827.90 2.67 2.86 6.6 2b 4-24-007-22 1828.20 2.65 2.85 6.9 2b 4-24-007-22 1828.35 2.76 2.86 3.7 2b 4-24-007-22 1828.60 2.63 2.85 7.7 2b 4-24-007-22 1829.00 2.68 2.85 6.0 2b 11-36-007-23 1957.10 2.68 2.74 2.0 2b 11-36-007-23 1957.30 2.70 2.71 0.1 2b 11-36-007-23 1957.45 2.68 2.70 0.9 2b 11-36-007-23 1958.40   8.4 175  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2b 11-36-007-23 1958.60   8.0 2b 11-36-007-23 1958.80   8.1 2b 11-36-007-23 1959.20 2.65 2.82 6.1 2b 8-30-008-23 2217.50 2.58 2.82 8.6 2b 8-30-008-23 2221.21 2.73 2.87 4.9 2b* 6-30-008-23 2232.64 2.58 2.84 9.3 2b* 6-30-008-23 2232.94 2.68 2.84 5.5 2b* 6-30-008-23 2232.95 2.67 2.89 7.6 2b* 6-30-008-23 2233.25 2.71 2.83 3.9 2b* 6-30-008-23 2233.89 2.69 2.83 4.7 2b* 6-30-008-23 2234.51 2.68 2.85 5.9 2b* 6-30-008-23 2234.87 2.72 2.83 3.9 2b* 6-30-008-23 2235.28 2.68 2.84 5.6 2b* 6-30-008-23 2235.71 2.71 2.84 4.8 2b* 6-30-008-23 2236.61 2.64 2.86 7.4 2b* 6-30-008-23 2236.67 2.66 2.86 6.9 2b* 6-30-008-23 2238.34 2.69 2.83 5.2 2b* 6-30-008-23 2238.57 2.64 2.86 7.6 2b* 6-30-008-23 2238.81 2.67 2.65 6.5 2b 6-13-009-25 2445.80 2.74 2.81 2.5 2b 6-13-009-25 2446.10 2.76 2.80 1.6 2b 6-13-009-25 2447.16 2.72 2.80 2.9 2b 8-21-11-22 1815.81 2.48 2.86 13.2 2b 8-21-11-22 1821.46 2.74 2.88 4.7 2b 8-21-11-22 1821.69 2.76 2.88 4.4 2b 16-27-11-22 1796.64 2.71 2.87 5.6 2b 16-31-11-23 2050.00 2.73 2.88 5.3 2b 16-31-11-23 2050.63   3.4 2b 16-31-11-23 2053.99 2.78 2.81 0.9 2b 16-31-11-23 2055.88 2.75 2.83 2.5 2b 16-31-11-23 2056.03  2.85 5.6 2b 16-31-11-23 2057.23 2.52 2.88 12.4 2b 16-31-11-23 2062.95  2.84 2.8 2c 3-34-005-24 2368.96 2.64 2.82 6.4 2c 3-34-005-24 2369.16 2.69 2.78 3.4 2c 3-34-005-24 2369.73 2.73 2.83 3.5 2c 6-16-006-22 1821.33 2.67 2.81 5.2 2c 6-16-006-22 1821.84 2.68 2.82 4.8 2c 6-16-006-22 1822.41 2.74 2.84 3.5 2c 6-16-006-22 1822.94 2.74 2.78 1.4 176  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2c 6-16-006-22 1823.48 2.76 2.78 0.7 2c 6-16-006-22 1823.79  2.83 3.6 2c 6-16-006-22 1823.93 2.76 2.78 0.8 2c 6-16-006-22 1828.90 2.63 2.84 8.2 2c 6-16-006-22 1829.24 2.66 2.82 4.7 2c 6-16-006-22 1829.62 2.71 2.83 4.1 2c 6-16-006-22 1830.02 2.73 2.81 2.7 2c 6-16-006-22 1830.38 2.74 2.84 3.5 2c 6-16-006-22 1830.54 2.73 2.81 3.1 2c 6-16-006-22 1830.88 2.69 2.83 5.0 2c 6-16-006-22 1831.46 2.71 2.83 4.3 2c 6-16-006-22 1831.86 2.70 2.84 5.0 2c 6-16-006-22 1832.44 2.53 2.84 10.8 2c 6-16-006-22 1832.91 2.62 2.84 7.8 2c 4-24-007-22 1826.65   4.7 2c 4-24-007-22 1826.85 2.90 2.92 0.8 2c 4-24-007-22 1827.15 2.87 2.92 1.5 2c 4-24-007-22 1827.60 2.68 2.89 7.3 2c 6-30-008-23 2235.63 2.67 2.73 5.1 2d 6-30-008-23 2239.08 2.77 2.85 2.8 2d 6-30-008-23 2239.28 2.75 2.82 2.6 2d 6-30-008-23 2239.49 2.73 2.79 2.2 2d 6-30-008-23 2241.08 2.77 2.83 2.0 2c 16-31-11-23 2052.72 2.75 2.80 1.8 2c 16-31-11-23 2055.16 2.74 2.87 4.6 2c 16-31-11-23 2057.60 2.62 2.91 9.8 2c 16-31-11-23 2056.25 2.45 2.83 13.6 2c 16-31-11-23 2056.38  2.85 8.9 2c 16-31-11-23 2056.49 2.61 2.84 8.0 2c 16-31-11-23 2056.69 2.55 2.82 9.6 2c 16-31-11-23 2056.86  2.85 13.6 2c 16-31-11-23 2056.95 2.58 2.84 9.3 2c 16-31-11-23 2057.11 2.67 2.81 4.7 2c 16-31-11-23 2057.38  2.82 6.6 2c 16-31-11-23 2057.51 2.79 2.83 1.3 2d 8-30-008-23 2220.50 2.73 2.86 4.5 2d 6-16-006-22 1826.75 2.67 2.83 6.4 2d 6-16-006-22 1827.03 2.66 2.82 2.4 2d 6-16-006-22 1827.51  2.78 8.5 2d 6-16-006-22 1827.63 2.72 2.84 3.3 177  Facies Well Sample Depth Bulk Density (g/mL) Skeletal Density (g/mL) Porosity (%) 2d 6-16-006-22 1828.09 2.70 2.84 5.4 2d 6-16-006-22 1828.65 2.68 2.83 2.7 2d 6-16-006-22 1833.19 2.68 2.86 6.3 2d 6-16-006-22 1833.69 2.64 2.82 6.3 2d 6-16-006-22 1834.27 2.58 2.80 8.0 2d 16-31-11-23 2053.79 2.78 2.81 0.7 Table F.2. Petrophysical analyses. 

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