Porosity and Pore Networks in Tight Dolostone—Mudstone Reservoirs: Insights from the Devonian Three Forks Formation, Williston Basin, USA

Abstract

This study was performed to evaluate pore systems of reservoir lithofacies within the Devonian Three Forks Formation in the Williston Basin through micro-scale pore characterization. These lithofacies are from the Upper Three Forks section, which is a prominent drilling target within the Bakken-Three Forks Petroleum System. Samples from the Formation were examined by (1) physical core description, (2) petrographic thin section microscopy, (3) x-ray diffractometry (XRD) minerals analysis, (4) scanning electron microscopy (SEM), and (5) porosity measurements from helium porosimetry, nuclear magnetic resonance (NMR), gas adsorption and mercury intrusion porosimetry (MIP). These were done to provide better understanding of the local variations in pore structures and how such structures impact reservoir quality within the Three Forks Formation. Seven reservoir lithofacies were identified and described, including laminated lithofacies, massive dolostone, mottled dolostone, massive mudstone, mottled mudstone, mudstone conglomerates, and brecciated mudstone. Samples show a diverse variation in mineralogical composition, pore types, porosity, and pore-size distribution. Six types of pores were identified: interparticle, intercrystalline, intracrystalline, vuggy, microfractures, and mudstone microporosity. Dolostone-rich lithofacies have abundant dolomite and less siliciclastic minerals such as quartz, feldspar, and clays. They also have relatively low porosity and generally larger pore size. A general positive trend exists between porosity with clay minerals and feldspar, in contrast to a negative trend with dolomite, and no clear relationship with quartz content. Results from the gas adsorption analysis, NMR and MIP pore-size distribution confirm an abundance of macropores (>50 nm in diameters) in dolostone dominated lithofacies while other lithofacies generally have abundant mesopores (2–50 nm).

Keywords

dolostone / mudstone / porosity / pores / clay minerals / dolomite / lithofacies / bakken-three forks petroleum system / petroleum geology

References

Adeyilola A, Nordeng S, Onwumelu C, . Geochemical, Petrographic and Petrophysical Characterization of the Lower Bakken Shale, Divide County, North Dakota. International Journal of Coal Geology, 2020, 224(2): 103477

Akai T, Wood J M. Application of Pore Throat Size Distribution Data to Petrophysical Characterization of Montney Tight-Gas Siltstones. Bulletin of Canadian Petroleum Geology, 2018, 66 2 425-435

Baah D. Nano-Petrophysics of the Three Forks Formation in Williston Basin, North Dakota: [Dissertation], 2015, Arlington: University of Texas

Basan P B, Lowden B D, Whattler P R, . Pore-Size Data in Petrophysics: A Perspective on the Measurement of Pore Geometry. Geological Society, London, Special Publications, 1997, 122(1): 47-67.

Bazzell A. Origin of Brecciated Intervals and Petrophysical Analyses, the Three Forks Formation, Williston Basin, North Dakota, USA: [Dissertation], 2014, Golden: Colorado School of Mines, 140

Bernard S, Wirth R, Schreiber A, . Formation of Nanoporous Pyrobitumen Residues during Maturation of the Barnett Shale (Fort Worth Basin). International Journal of Coal Geology, 2012, 103(20): 3-11.

Berwick B. Depositional Environment, Mineralogy, and Sequence Stratigraphy of the Late Devonian Sanish Member (Upper Three Forks Formation), Williston Basin, North Dakota: [Dissertation], 2008, Golden: Colorado School of Mines

Bjørlykke K, Jahren J. Open or Closed Geochemical Systems during Diagenesis in Sedimentary Basins: Constraints on Mass Transfer during Diagenesis and the Prediction of Porosity in Sandstone and Carbonate Reservoirs. AAPG Bulletin, 2012, 96(12): 2193-2214.

Bottjer R J, Sterling R, Grau A, . Robinson J W, LeFever J A, Gaswirth S B, . Stratigraphic Relationships and Reservoir Quality at the Three Forks-Bakken Unconformity, Williston Basin, North Dakota. The Bakken-Three Forks Petroleum System in the Williston Basin, 2011, Denver: Rocky Mountain Association of Geologists

Carvajal-Ortiz, H., Gentzis, T., Xie, H., 2019. High-frequency (20 MHz) NMR and Modified Rock-Eval Pyrolysis Methods as an Integrated Approach to Examine Producibility in Kerogen-Rich Source-Reservoirs. In: Unconventional Resources Technology Conference, Denver, Colorado, 22–24 July 2019 (1861–1877). Unconventional Resources Technology Conference (URTeC); Society of Exploration Geophysicists

Chalmers G R L, Bustin R M. The Organic Matter Distribution and Methane Capacity of the Lower Cretaceous Strata of Northeastern British Columbia, Canada. International Journal of Coal Geology, 2007, 70(1/2/3): 223-239.

Chalmers G R L, Marc Bustin R. On the Effects of Petrographic Composition on Coalbed Methane Sorption. International Journal of Coal Geology, 2007, 69(4): 288-304.

Chalmers G R L, Ross D J K, Bustin R M. Geological Controls on Matrix Permeability of Devonian Gas Shales in the Horn River and Liard Basins, Northeastern British Columbia, Canada. International Journal of Coal Geology, 2012, 103(6): 120-131.

Chalmers G R, Bustin R M, Power I M. Characterization of Gas Shale Pore Systems by Porosimetry, Pycnometry, Surface Area, and Field Emission Scanning Electron Microscopy/transmission Electron Microscopy Image Analyses: Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig Units. AAPG Bulletin, 2012, 96(6): 1099-1119.

Choquette P W, Cox A, Meyers W J. Characteristics, Sistribution and Origin of Porosity in Shelf Solostones; Burlington-Keokuk Formation (Mississippian), US Mid-Continent. Journal of Sedimentary Research, 1992, 62(2): 167-189

Choquette P W, Pray L C. Geologic Nomenclature and Classification of Porosity in Sedimentary Carbonates. AAPG Bulletin, 1970, 54: 207-250.

Christopher J E. Transitional Devonian-Mississippian Formations of Southern Saskatchewan, 1961, Saskatoon: Saskatchewan Department of Mineral Resources

Clark, A. J., 2009. Determination of Recovery Factor in the Bakken Formation, Mountrail County, ND. SPE Annual Technical Conference and Exhibition, New Orleans, October 4–7, 2009. https://doi.org/10.2118/133719-stu

Clarkson C R, Haghshenas B, Ghanizadeh A, . Nanopores to Megafractures: Current Challenges and Methods for Shale Gas Reservoir and Hydraulic Fracture Characterization. Journal of Natural Gas Science and Engineering, 2016, 31: 612-657.

Clarkson C R, Solano N, Bustin R M, . Pore Structure Characterization of North American Shale Gas Reservoirs Using USANS/SANS, Gas Adsorption, and Mercury Intrusion. Fuel, 2013, 103: 606-616.

Coates G R, Xiao L Z, Prammer M G. NMR Logging Principles and Applications, Halliburton Energy Services Publication, 1999, Golden: Colorado School of Mines

Curtis M E, Cardott B J, Sondergeld C H, . Development of Organic Porosity in the Woodford Shale with Increasing Thermal Maturity. International Journal of Coal Geology, 2012, 103: 26-31.

Dechongkit, P., Prasad, M., 2011. Recovery Factor and Reserves Estimation in the Bakken Petroleum System (Analysis of the Antelope, Sanish and Parshall Fields). Presented at the SPE Canadian Unconventional Resources Conference, Calgary. https://doi.org/10.2118/149471-ms

Deng H C, Hu X F, Li H A, . Improved Pore-Structure Characterization in Shale Formations with FESEM Technique. Journal of Natural Gas Science and Engineering, 2016, 35(1): 309-319.

Dow W G. Application of Oil Correlation and Source-Rock Data to Exploration in Williston Basin: Abstract. AAPG Bulletin, 1974, 58: 1253-1262.

Du Y, Fan T L, Machel H G, . Genesis of Upper Cambrian-Lower Ordovician Dolomites in the Tahe Oilfield, Tarim Basin, NW China: Several Limitations from Petrology, Geochemistry, and Fluid Inclusions. Marine and Petroleum Geology, 2018, 91(2): 43-70.

Dumonceaux G M. Stratigraphy and Depositional Environments of the Three Forks Formation (Upper Devonian), Williston Basin, North Dakota: [Dissertation], 1984, Fargo: University of North Dakota

Dunn K J, Bergman D J, LaTorraca G A. Nuclear Magnetic Resonance: Petrophysical and Llogging Applications, Handbook of Geophysical Exploration, 2002, New York: Pergamon

Franklin A, Sarg J F. Sedimentology and Ichnofacies, Uppermost Three Forks Formation (Fammenian), Williston Basin, North Dakota and Montana—A Storm Dominated Intrashelf Basin. The Sedimentary Record, 2017, 15(2): 4-12.

Gantyno A A. Sequence Stratigraphy and Microfacies Analysis of the Late Devonian Three Forks Formation, Williston Basin, North Dakota and Montana, U. S. A.: [Dissertation], 2011, Golden, Colorado: Colorado School of Mines

Gao F L, Song Y, Li Z, . Lithofacies and Reservoir Characteristics of the Lower Cretaceous Continental Shahezi Shale in the Changling Fault Depression of Songliao Basin, NE China. Marine and Petroleum Geology, 2018, 98(4): 401-421.

Gao H, Li H Z. Determination of Movable Fluid Percentage and Movable Fluid Porosity in Ultra-Low Permeability Sandstone Using Nuclear Magnetic Resonance (NMR) Technique. Journal of Petroleum Science and Engineering, 2015, 133(3): 258-267.

Gao Z Y, Hu Q H. Estimating Permeability Using Median Pore-Throat Radius Obtained from Mercury Intrusion Porosimetry. Journal of Geophysics and Engineering, 2013, 10(2): 025014

Garcia-Fresca B, Pinkston D, Loucks R G, . The Three Forks Playa Lake Depositional Model: Implications for Characterization and Development of an Unconventional Carbonate Play. AAPG Bulletin, 2018, 102 8 1455-1488.

Gharechelou S, Daraei M, Amini A. Pore Types Distribution and their Reservoir Properties in the Sequence Stratigraphic Framework: A Case Study from the Oligo-Miocene Asmari Formation, SW Iran. Arabian Journal of Geosciences, 2016, 9(3): 194

Chalmers, G., Bustin, R. M., Power, I. M., 2009. A Pore by any Other Name would be as Small: the Importance of Meso- and Microporosity in Shale Gas Capacity. AAPG Datapages, Search and Discovery Article 90090. AAPG Annual Convention and Exhibition, Denver, Colorado, June 7–10, 2009 URL. http://www.searchanddiscovery.com/abstracts/html/2009/annual/abstracts/chalmers.html (last accessed on 16/02/2014)

Droege L A. Sedimentology, Facies Architecture, and Diagenesis of the Middle Three Forks Formation—North Dakota, USA: [Dissertation], 2014, Fort Collins: Colorado State University

Gherabati S A, Hamlin H S, Smye K M, . Evaluating Hydrocarbon-in-Place and Recovery Factor in a Hybrid Petroleum System: Case of Bakken and Three Forks in North Dakota. Interpretation, 2019, 7 3 T607-T624.

Handy L L. Determination of Effective Capillary Pressures for Porous Media from Imbibition Data. Transactions of the AIME, 1960, 219(1): 75-80.

Hinai A A, Rezaee R, Esteban L, . Comparisons of Pore Size Distribution: A Case from the Western Australian Gas Shale Formations. Journal of Unconventional Oil and Gas Resources, 2014, 8: 1-13.

Hu J G, Tang S H, Zhang S H. Investigation of Pore Structure and Fractal Characteristics of the Lower Silurian Longmaxi Shales in Western Hunan and Hubei Provinces in China. Journal of Natural Gas Science and Engineering, 2016, 28(1): 522-535.

Hu Q H, Zhang Y X, Meng X H, . Characterization of Micro-Nano Pore Networks in Shale Oil Reservoirs of Paleogene Shahejie Formation in Dongying Sag of Bohai Bay Basin, East China. Petroleum Exploration and Development, 2017, 44(5): 720-730.

Hu, Q. H., 2018. Quantifying Effective Porosity of Oil and Gas Reservoirs. In: 2018 International Conference and Exhibition, Cape Town, November 4–7. https://doi.org/10.1306/70376hu2018

Islam M A. Diagenesis and Reservoir Quality of Bhuban Sandstones (Neogene), Titas Gas Field, Bengal Basin, Bangladesh. Journal of Asian Earth Sciences, 2009, 35(1): 89-100.

James N P, Jones B. Origin of Carbonate Sedimentary Rocks, 2015, Chichester: John Wiley and Sons

Jiang F, Chen D, Chen J, . Fractal Analysis of Shale Pore Structure of Continental Gas Shale Reservoir in the Ordos Basin, NW China. Energy & Fuels, 2016, 30(6): 4676-4689.

Jiang F, Chen D, Wang Z, . Pore Characteristic Analysis of a Lacustrine Shale: A Case Study in the Ordos Basin, NW China. Marine and Petroleum Geology, 2016, 73: 554-571.

Kenyon W E. Nuclear Magnetic Resonance as a Petrophysical Measurement. Nuclear Geophysics, 1992, 6(2): 153-171

Kenyon W E. Petrophysical Principles of Applications of NMR Logging. The Log Analyst, 1997, 38(02): SPWLA-1997-v38n2a4

Klaver J, Desbois G, Littke R, . BIB-SEM Pore Characterization of Mature and Post Mature Posidonia Shale Samples from the Hils Area, Germany. International Journal of Coal Geology, 2016, 158: 78-89.

Kleinberg R L. Utility of NMR T2 Distributions, Connection with Capillary Pressure, Clay Effect, and Determination of the Surface Relaxivity Parameter P2. Magnetic Resonance Imaging, 1996, 14(7/8): 761-767.

Kleinberg R L, Farooqui S A, Horsfield M A. T1/T2 Ratio and Frequency Dependence of NMR Relaxation in Porous Sedimentary Rocks. Journal of Colloid and Interface Science, 1993, 158(1): 195-198.

Ko L T, Loucks R G, Milliken K L, . Controls on Pore Types and Pore-Size Distribution in the Upper Triassic Yanchang Formation, Ordos Basin, China: Implications for Pore-Evolution Models of Lacustrine Mudrocks. Interpretation, 2017, 5(2): SF127-SF148.

Ko L T, Loucks R G, Ruppel S C, . Origin and Characterization of Eagle Ford Pore Networks in the South Texas Upper Cretaceous Shelf. AAPG Bulletin, 2017, 101(3): 387-418.

Kuila U, Prasad M. Specific Surface Area and Pore-Size Distribution in Clays and Shales. Geophysical Prospecting, 2013, 61(2): 341-362.

Kulke H. Kulke H. Nigeria. Regional Petroleum Geology of the World. Part II: Africa, America, Australia and Antarctica, 1995, Berlin: Gebrüder Borntraeger

Lai J, Wang S, Zhang C S, . Spectrum of Pore Types and Networks in the Deep Cambrian to Lower Ordovician Dolostones in Tarim Basin, China. Marine and Petroleum Geology, 2020, 112(1): 104081

Lang D J, Shang G H, Lü C Y, . Experiment and Application of NMR in Carbonate Reservoir Analysis: An Example from Tahe Oilfield. Oil and Gas Geology, 2009, 30 3 363-369. (In Chinese with English Abstract)

Lawal L O, Adebayo A R, Mahmoud M, . A Novel NMR Surface Relaxivity Measurements on Rock Cuttings for Conventional and Unconventional Reservoirs. International Journal of Coal Geology, 2020, 231 103605

LeFever J A, Nordeng S H. Three Forks Formation. North Dakota. Geological Survey Newsletter, 2008, 35(2): 4-5

LeFever J A, Martiniuk C D, Dancsok E F, . Petroleum Potential of the Middle Member, Bakken Formation, Williston Basin. Sixth International Williston Basin Symposium, 1991, Tulsa: AAPG Datapages, Inc.

LeFever J A, LeFever R D, Nordeng S H. Role of Nomenclature in Pay Zone Definitions—Three Forks Formation, North Dakota, 2013, Bismarck: North Dakota Geological Survey Geologic Investigations

Lewis, R., Singer, P., Jiang, T., et al., 2013. NMR T₂ Distributions in the Eagle Ford Shale: Reflections on Pore Size. In: SPE Unconventional Resources Conference-USA. Woodlands, April 10–12, 2013

Li Q, Jiang Z X, Hu W X, . Origin of Dolomites in the Lower Cambrian Xiaoerbulak Formation in the Tarim Basin, NW China: Implications for Porosity Development. Journal of Asian Earth Sciences, 2016, 115 557-570.

Lønøy A. Making Sense of Carbonate Pore Systems. AAPG Bulletin, 2006, 90(9): 1381-1405.

Loucks, R. G., Handford, C. R., 1992. Origin and Recognition of Fractures, Breccias, and Sediment Fills in Paleocave-Reservoir Networks. In: Candelaria, M. P., Reed, C. L., eds., Paleokarst, Karst Related Diagenesis and Reservoir Development: Examples from Ordovician-Devonian Age Strata of West Texas and the Mid-Continent. Permian Basin Section-SEPM Publ 92–33, Midland

Loucks R G, Reed R M, Ruppel S C, . Morphology, Genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale. Journal of Sedimentary Research, 2009, 79(12): 848-861.

Loucks R G, Reed R M. Scanning-Electron-Microscope Petrographic Evidence for Distinguishing Organic-Matter Pores Associated with Depositional Organic Matter versus Migrated Organic Matter in Mudrock. Gulf Coast Assoc. Geol. Soc. J., 2014, 3: 51-60.

Loucks R G, Reed R M, Ruppel S C, . Morphology, genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale. J. Sediment. Res., 2009, 79: 848-861.

Loucks R G, Ruppel S C, Wang X, . Pore Types, Pore-Network Analysis, and Pore Quantification of the Lacustrine Shale-Hydrocarbon System in the Late Triassic Yanchang Formation in the Southeastern Ordos Basin, China. Interpretation, 2017, 5(2): SF63-SF79.

Lucia F J. Petrophysical Parameters Estimated from Visual Descriptions of Carbonate Rocks: A Field Classification of Carbonate Pore Space. Journal of Petroleum Technology, 1983, 35(3): 629-637.

Lucia F J. Seewald K, Sundeen D. Lower Paleozoic History of the Western Diablo Platform of West Texas and South-Central Mexico. the Geologic Framework of the Chihuahua Tectonic, 1970, Midland: West Texas Geol. Soc.

Lucia F J. Rock-Fabric/Petrophysical Classification of Carbonate Pore Space for Reservoir Characterization. AAPG Bulletin, 1995, 79: 1275-1300.

Ma B Y, Hu Q H, Yang S Y, . Multiple Approaches to Quantifying the Effective Porosity of Lacustrine Shale Oil Reservoirs in Bohai Bay Basin, East China. Geofluids, 2020, 1: 1-13.

Mastalerz M, Schimmelmann A, Drobniak A, . Porosity of Devonian and Mississippian New Albany Shale Across a Maturation Gradient: Insights from Organic Petrology, Gas Adsorption, and Mercury Intrusion. AAPG Bulletin, 2013, 97(10): 1621-1643.

Meissner, F. F., 1991. Petroleum Geology of the Bakken Formation Williston Basin, North Dakota and Montana. In: Demaison, G., Murris, R. J., American Association of Petroleum Geologists, Tulsa

Milliken K L, Rudnicki M, Awwiller D N, . Organic Matter-Hosted Pore System, Marcellus Formation (Devonian), Pennsylvania. AAPG Bulletin, 2013, 97(2): 177-200.

Moore C H, Heydari E. Burial Diagenesis and Hydrocarbon Migration in Platform Limestones: A Conceptual Model Based on the Upper Jurassic of the Gulf Coast of the USA. AAPG Bull., 1993, 77: 213-229.

Moore C H, Druckman Y. Burial Diagenesis and Porosity Evolution, Upper Jurassic Smackover, Arkansas and Louisiana. AAPG Bulletin, 1981, 65(4): 597-628

Murphy E C, Nordeng S H, Junker B J, . North Dakota Stratigraphic Column. North Dakota Geological Survey, Bismarck Nesheim, T. O., 2019. Examination of Downward Hydrocarbon Charge within the Bakken-Three Forks Petroleum System-Williston Basin, North America. Marine and Petroleum Geology, 2009, 104(3): 346-360

Norbisrath J H, Eberli G P, Laurich B, . Electrical and Fluid Flow Properties of Carbonate Microporosity Types from Multiscale Digital Image Analysis and Mercury Injection. AAPG Bulletin, 2015, 99(11): 2077-2098.

Nordeng S H, LeFever J A. Three Forks Formation Log to Core Correlation, 2009, Bismarck: North Dakota Geological Survey Geologic Investigation

Nordeng S H. The Bakken Petroleum System: An Example of a Continuous Petroleum Accumulation. DMR Newsletter, 2009, 36(1): 21-24

Pires L O, Winter A, Trevisan O V. Dolomite Cores Evaluated by NMR. Journal of Petroleum Science and Engineering, 2019, 176(1–4): 1187-1197.

Rezaee R, Saeedi A, Clennell B. Tight Gas Sands Permeability Estimation from Mercury Injection Capillary Pressure and Nuclear Magnetic Resonance Data. Journal of Petroleum Science and Engineering, 2012, 88/89(4): 92-99.

Ross D J K, Bustin R M. Characterizing the Shale Gas Resource Potential of Devonian — Mississippian Strata in the Western Canada Sedimentary Basin: Application of an Integrated Formation Evaluation. AAPG Bulletin, 2008, 92(1): 87-125.

Ross D J K, Bustin R M. The Importance of Shale Composition and Pore Structure Upon Gas Storage Potential of Shale Gas Reservoirs. Marine and Petroleum Geology, 2009, 26(6): 916-927.

Roth S, Biswal B, Afshar G, . Continuum-Based Rock Model of a Reservoir Dolostone with Four Orders of Magnitude in Pore Sizes. AAPG Bulletin, 2011, 95(6): 925-940.

Rouquerol J, Avnir D, Fairbridge C W, . Recommendations for the Characterization of Porous Solids (Technical Report). Pure and Applied Chemistry, 1994, 66(8): 1739-1758.

Saller A H, Budd D A, Harris P M. Unconformities and Porosity Development in Carbonate Strata: Ideas from a Hedberg Conference. AAPG Bulletin, 1994, 78(6): 857-872

Sandberg C A, Hammond C R. Devonian System in Williston Basin and Central Montana. AAPG Bulletin, 1958, 42: 2293-2335.

Sonnenberg, S. A., 2017. Sequence Stratigraphy of the Bakken and Three Forks Formations, Williston Basin, USA. In: AAPG Rocky Mountain Section Annual Meeting, Billings, June 25–28

Sonnenberg S A, Gantyno A, Sarg R. Petroleum Potential of the Upper Three Forks Formation, Williston Basin, USA, 2011, Houston: AAPG Annual Convention and Exhibition April 10–13

Topór T, Derkowski A, Ziemiański P, . The Effect of Organic Matter Maturation and Porosity Evolution on Methane Storage Potential in the Baltic Basin (Poland) Shale-Gas Reservoir. International Journal of Coal Geology, 2017, 180(32): 46-56.

Wang G W, Li P P, Hao F, . Dolomitization Process and Its Implications for Porosity Development in Dolostones: A Case Study from the Lower Triassic Feixianguan Formation, Jiannan Area, Eastern Sichuan Basin, China. Journal of Petroleum Science and Engineering, 2015, 131: 184-199.

Wang S, Javadpour F, Feng Q H. Confinement Correction to Mercury Intrusion Capillary Pressure of Shale Nanopores. Scientific Reports, 2016, 6: 20160

Wang X, Jiang Z, Jiang S, . Full-Scale Pore Structure and Fractal Dimension of the Longmaxi Shale from the Southern Sichuan Basin: Investigations Using FE-SEM, Gas Adsorption and Mercury Intrusion Porosimetry. Minerals, 2019, 9(9): 543

Wardlaw N C. Pore Geometry of Carbonate Rocks as Revealed by Pore Casts and Capillary Pressure. AAPG Bulletin, 1976, 60 2 245-257

Wardlaw N C, Taylor R P. Mercury Capillary Pressure Curves and the Interpretation of Pore Structure and Capillary Behaviour in Reservoir Rocks. Bulletin of Canadian Petroleum Geology, 1976, 24(2): 225-262

Washburn E W. Note on a Method of Determining the Distribution of Pore Sizes in a Porous Material. Proceedings of the National Academy of Sciences, 1921, 7(4): 115-116.

Washburn K E, Birdwell J E. Updated Methodology for Nuclear Magnetic Resonance Characterization of Shales. Journal of Magnetic Resonance, 2013, 233 17-28.

Woody R E, Gregg J M, Koederitz L F. Effect of Texture on Petrophysical Properties of Dolomite: Evidence from the Cambrian-Ordovician of Southeastern Missouri. AAPG Bulletin, 1996, 80(1): 119-131

Xie Z H, Gan Z. Value of 20 Mhz NMR Core Analysis for Unconventional Mudstones. SPWLA 59th Annual Logging Symposium, 2018, London: Society of Petrophysicists and Well-Log Analysts

Xiong J, Liu X J, Liang L X. Experimental Study on the Pore Structure Characteristics of the Upper Ordovician Wufeng Formation Shale in the Southwest Portion of the Sichuan Basin, China. Journal of Natural Gas Science and Engineering, 2015, 22(1): 530-539.

Yang R, He S, Yi J Z, . Nano-Scale Pore Structure and Fractal Dimension of Organic-Rich Wufeng-Longmaxi Shale from Jiaoshiba Area, Sichuan Basin: Investigations Using FE-SEM, Gas Adsorption and Helium Pycnometry. Marine and Petroleum Geology, 2016, 70: 27-45.

Yuan Y J, Rezaee R. Comparative Porosity and Pore Structure Assessment in Shales: Measurement Techniques, Influencing Factors and Implications for Reservoir Characterization. Energies, 2019, 12(11): 2094

Zargari S, Canter K L, Prasad M. Porosity Evolution in Oil-Prone Source Rocks. Fuel, 2015, 153 6 110-117.

Zhang J Z, Li X Q, Xie Z Y, . Characterization of Microscopic Pore Types and Structures in Marine Shale: Examples from the Upper Permian Dalong Formation, Northern Sichuan Basin, South China. Journal of Natural Gas Science and Engineering, 2018, 59(3): 326-342.