Characteristics, Types, and Prospects of Geological Sweet Sections in Giant Continental Shale Oil Provinces in China

Abstract

“Sweet sections” in giant shale oil provinces are preferential fields that primarily support China to increase the reserves and production of continental shale oil. Based on the study of the geological conditions of shale oil in the continental basins in China, it was found that the shale stratum in major oil generation windows generally has higher degrees of oil and gas accumulation, and mostly contains oil. Hydrocarbon generation and reservoir capacities are the two key parameters for evaluating and optimizing favorable shale oil provinces. The evaluation index (volume of shale stratum multiplied by total organic carbon (TOC) multiplied by total porosity) for the giant continental shale oil provinces is also proposed. It is optimized that the Upper Triassic Chang 7 Member in the south-central Ordos Basin, Lower Cretaceous Qing 1 Member in the Gulong-Changling Sag in the Songliao Basin, Middle — Lower Permian in the Junggar Basin, Da’anzhai Member of the Ziliujing Formation of Lower Jurassic in the central and northern Sichuan Basin, and Paleogene oil-rich sag in the Bohai Bay Basin are the five giant continental shale oil provinces. The word “geological sweet sections” in continental shale oil provinces of China refers to favorable shale intervals which are relatively rich in oil, with superior physical properties, and more easily modified and developed commercially under applicable economic and technological conditions. After evaluation, there are mainly two types of “geological sweet sections” of giant continental shale oil developed onshore in China. One type of “geological sweet sections” is generally mudstone with optimal physical properties or a thin tight reservoir, to which the shale oil migrates a short distance. They are medium-to-high-mature zones with a thin sandy shale stratum in the Chang 7 Member in the Ordos Basin, mixed shale stratum in the medium-mature Lucaogou Formation in the Jimsar Sag, and multi-layered mixed Paleogene shale stratum in the Bohai Bay Basin. The other type of “geological sweet sections” is generally shale oil residing in various shale reservoir spaces. This type was developed in the Qing 1 Member in the Gulong Sag and Da’anzhai Member in the north-central Sichuan Basin. Free shale oil mainly occurs in shale, sandy-carbonate lamina, micro-lamella structure, and micro-fractures. Layers with lamina, lamination, and micro-fractures are generally shale oil “geological sweet sections.” Starting from field tests and the construction of the “geological sweet sections” in giant continental shale oil provinces, the shale oil industry has been rapidly developing and will become an important supplement to domestic oil production in China.

Keywords

continental shale oil / shale stratum / geological sweet section / source rock oil / micro-nano pore throats / laminae / lamination / free hydrocarbons / shale oil revolution / petroleum geology

References

[1] Cander, H., 2012a. Sweet Spots in Shale Gas and Liquids Plays: Prediction of Fluid Composition and Reservoir Pressure. In: AAPG Annual Convention and Exhibition, September 16–19, Singapore

[2] Cander, H., 2012b. What Are Unconventional Resources? A Simple Definition Using Viscosity and Permeability. AAPG Annual Convention and Exhibition, September 16–19, Singapore

[3] Chen D, Pang X Q, Wang Y W, . Palaeoenvironmental Periodisms of Middle Eocene Terrestrial Sediments in Bohai Bay Basin, Eastern China, and Their Implications for Organic Matter Accumulation. Marine and Petroleum Geology, 2020, 112(5044): 104060

[4] Chen X H, Chen L, Jiang S, . Evaluation of Shale Reservoir Quality by Geophysical Logging for Shuijingtuo Formation of Lower Cambrian in Yichang Area, Central Yangtze. Journal of Earth Science, 2021, 32 4 766-777

[5] Chen Z H, Jiang C Q. An Integrated Mass Balance Approach for Assessing Hydrocarbon Resources in a Liquid-Rich Shale Resource Play: An Example from Upper Devonian Duvernay Formation, Western Canada Sedimentary Basin. Journal of Earth Science, 2020, 31(6): 1259-1272.

[6] Cui B W, Chen C R, Lin X D, . Characteristics and Distribution of Sweet Spots in Gulong Shale Oil Reservoirs in Songliao Basin. Petroleum Geology & Oilfield Development in Daqing, 2020, 39: 45-55. (in Chinese with English Abstract)

[7] Dai J X, Ni Y Y, Gong D Y, . Geochemical Characteristics of Gases from the Largest Tight Sand Gas Field (Sulige) and Shale Gas Field (Fuling) in China. Marine and Petroleum Geology, 2017, 79(10): 426-438.

[8] Dai J X, Zou C N, Liao S M, . Geochemistry of the Extremely High Thermal Maturity Longmaxi Shale Gas, Southern Sichuan Basin. Organic Geochemistry, 2014, 74: 3-12.

[9] Dong T, Harris N B, Knapp L J, . The Effect of Thermal Maturity on Geomechanical Properties in Shale Reservoirs: An Example from the Upper Devonian Duvernay Formation, Western Canada Sedimentary Basin. Marine and Petroleum Geology, 2018, 97: 137-153.

[10] Hackley P C, Cardott B J. Application of Organic Petrography in North American Shale Petroleum Systems: A Review. International Journal of Coal Geology, 2016, 163(8): 8-51.

[11] Han Y J, Horsfield B, Curry D J. Control of Facies, Maturation and Primary Migration on Biomarkers in the Barnett Shale Sequence in the Marathon 1 Mesquite Well, Texas. Marine and Petroleum Geology, 2017, 85(24): 106-116.

[12] Han Y J, Mahlstedt N, Horsfield B. The Barnett Shale: Compositional Fractionation Associated with Intraformational Petroleum Migration, Retention, and Expulsion. AAPG Bulletin, 2015, 99(12): 2173-2202.

[13] Hao F, Zou H Y, Lu Y C. Mechanisms of Shale Gas Storage: Implications for Shale Gas Exploration in China. AAPG Bulletin, 2013, 97(8): 1325-1346.

[14] 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.

[15] Hu S Y, Zhao W Z, Hou L H, . Development Potential and Technical Strategy of Continental Shale Oil in China. Petroleum Exploration and Development, 2020, 47(4): 877-887.

[16] Hu Z Q, Wang R Y, Liu Z B, . Source-Reservoir Characteristics and Coupling Evaluation of Lacustrine Shale Gas in the Lower Jurassic, Sichuan Basin. Earth Science Frontiers, 2020, 28(1): 261-272. (in Chinese with English Abstract)

[17] Huang H, Chen J Y, Deng Y L, . Types and Influencing Factors of Pores in Chang 7 Continental Shale Matrix of South Ordos Basin. Journal of Xi’an Shiyou University (Natural Science Edition), 2017, 32(5): 42-48. (in Chinese with English Abstract)

[18] Huo J, He J X, Gao Y, . Difficulties and Countermeasures of Shale Oil Development in Lucaogou Formation of Jimsar Sag. Xinjiang Petroleum Geology, 2019, 40(4): 379-388. (in Chinese with English Abstract)

[19] Huo Z P, Hao S B, Liu B, . Geochemical Characteristics and Hydrocarbon Expulsion of Source Rocks in the First Member of the Qingshankou Formation in the Qijia-Gulong Sag, Songliao Basin, Northeast China: Evaluation of Shale Oil Resource Potential. Energy Science & Engineering, 2020, 8(5): 1450-1467.

[20] Jarvie, D. M., 2011. Unconventional Oil Petroleum Systems: Shales and Shale Hybrids. AAPG International Conference and Exhibition, April 10–13, Houston

[21] Jarvie D M. Shale Resource Systems for Oil and Gas: Part 2-Shale-Oil Resource Systems. In: Breyer, J. A., ed., Shale Reservoirs-Giant Resources for the 21st Century. AAPG, 2012, 97: 89-119.

[22] Jia C Z. Breakthrough and Significance of Unconventional Oil and Gas to Classical Petroleum Geology Theory. Petroleum Exploration and Development, 2017, 44(1): 1-10.

[23] Jiang Z, Zhang D X, Zhao J L, . Experimental Investigation of the Pore Structure of Triassic Terrestrial Shale in the Yanchang Formation, Ordos Basin, China. Journal of Natural Gas Science and Engineering, 2017, 46(1): 436450

[24] Jiao F Z, Zou C N, Yang Z. Geological Theory and Exploration & Development Practice of Hydrocarbon Accumulation Inside Continental Source Kitchens. Petroleum Exploration and Development, 2020, 47 6 1147-1159.

[25] Jin C Z, Dong W B, Bai Y F, . Lithofacies Characteristics and Genesis Analysis of Gulong Shale in Songliao Basin. Petroleum Geology & Oilfield Development in Daqing, 2020, 39(3): 35-44. (in Chinese with English Abstract)

[26] Jin Z J, Bai Z R, Gao B, . Has China Ushered in the Shale Oil and Gas Revolution. Oil & Gas Geology, 2019, 40(3): 451-458. (in Chinese with English Abstract)

[27] Johnston C T. Probing the Nanoscale Architecture of Clay Minerals. Clay Minerals, 2010, 45(3): 245-279.

[28] Kang Y S, Rao Q, Zhao Q, . Exploration and Development Potential of the Low-Maturity Continental Shale Gas in the Fuxin Basin. Natural Gas Industry B, 2019, 6(5): 435-443.

[29] Krooss B M, Brothers L, Engel M H. Geochromatography in Petroleum Migration: A Review. Geological Society, London, Special Publications, 1991, 59(1): 149-163.

[30] Lei W Z, Chen D X, Zhang R, . Lithological Combination Types and Characteristics of Continental Shale Strata in the Second Sub-Member of Da’anzhai in Central Sichuan. Earth Science, 2021, 46(10): 3657-3672. (in Chinese with English Abstract)

[31] Li S Z, Liu W B, Wang D D, . Continental Shale Oil Geological Conditions of China and the United States. Geological Review, 2017, 63(S1): 39-40

[32] Liu B, Yan M, Sun X D, . Microscopic and Fractal Characterization of Organic Matter within Lacustrine Shale Reservoirs in the First Member of Cretaceous Qingshankou Formation, Songliao Basin, Northeast China. Journal of Earth Science, 2020, 31(6): 1241-1250.

[33] Liu K Q, Wang L, Ostadhassan M, . Nanopore Structure Comparison between Shale Oil and Shale Gas: Examples from the Bakken and Longmaxi Formations. Petroleum Science, 2019, 16(1): 77-93.

[34] National Technical Committee for OilGas Standardization Geological Evaluation Methods for Shale Oil: GB/T-2020, 2020, Beijing: Standards Press of China (in Chinese)

[35] Pan S Q, Horsfield B, Zou C N, . Statistical Analysis as a Tool for Assisting Geochemical Interpretation of the Upper Triassic Yanchang Formation, Ordos Basin, Central China. International Journal of Coal Geology, 2017, 173: 51-64.

[36] Pang F, Zhang Z H, Zhang J F, . Progress and Prospect on Exploration and Development of Shale Gas in the Yangtze River Economic Belt. Earth Science, 2020, 45(6): 2152-2159. (in Chinese with English Abstract)

[37] Pollastro, R. M., Roberts, L. N. R., Cook, T. A., 2010. Geologic Assessment of Technically Recoverable Oil in the Devonian and Mississippian Bakken Formation. Assessment of Undiscovered Oil and Gas Resources of the Williston Basin Province of North Dakota, Montana, and South Dakota, Chapter 5/7

[38] Qian K R, He Z L, Liu X W, . Intelligent Prediction and Integral Analysis of Shale Oil and Gas Sweet Spots. Petroleum Science, 2018, 15(4): 744-755.

[39] Qiu Z, Tao H F, Lu B, . Controlling Factors on Organic Matter Accumulation of Marine Shale across the Ordovician-Silurian Transition in South China: Constraints from Trace-Element Geochemistry. Journal of Earth Science, 2021, 32(4): 887-900.

[40] Sarg J F. The Bakken-An Unconventional Petroleum and Reservoir System, 2012, Denver: Office of Fossil Energy, Colorado School of Mines

[41] Shen J, Xue B, Wu J L, . Lake Sedimentation and Environmental Evolution, 2010, Beijing: Science Press (in Chinese)

[42] Shi J Y, Jin Z J, Liu Q Y, . Lithofacies Classification and Origin of the Eocene Lacustrine Fine-Grained Sedimentary Rocks in the Jiyang Depression, Bohai Bay Basin, Eastern China. Journal of Asian Earth Sciences, 2020, 194: 104002

[43] Slatt R M, O’Brien N R. Pore Types in the Barnett and Woodford Gas Shales: Contribution to Understanding Gas Storage and Migration Pathways in Fine-Grained Rocks. AAPG Bulletin, 2011, 95(12): 2017-2030.

[44] Sun H Q. Exploration Practice and Cognitions of Shale Oil in Jiyang Depression. China Petroleum Exploration, 2017, 22(4): 1-14. (in Chinese with English Abstract)

[45] Sun J B, Sun H B, Zhao Q P, . Geological Characteristics and Exploration Potential Evaluation of Chang 7 Lacustrine Shale Oil in Yanchang Formation, Fuxian Area, Ordos Basin. China Petroleum Exploration, 2018, 23(6): 29-37. (in Chinese with English Abstract)

[46] Sun L D. Gulong Shale Oil. Petroleum Geology & Oilfield Development in Daqing, 2020, 39(3): 1-7. (in Chinese)

[47] Tinnin, B., Bello, H., McChesney, M., 2016. Multi-Source Data Integration to Predict Well Performance: Eagle Ford Sweet Spot Mapping. International Conference and Exhibition, April 3–6, Barcelona

[48] Wan T, Liu H X. Exploitation of Fractured Shale Oil Resources by Cyclic CO₂ Injection. Petroleum Science, 2018, 15(3): 552-563.

[49] Wang L, Zeng W T, Xia X M, . Study on Lithofacies Types and Sedimentary Environment of Black Shale of Qingshankou Formation in Qijia-Gulong Depression, Songliao Basin. Natural Gas Geoscience, 2019, 30 1125-1133. (in Chinese with English Abstract)

[50] Wang P X, Liu C L. Research Methods of Paleolimnology in Petroliferous Basins, 1993, Beijing: China Ocean Press (in Chinese)

[51] Wang X J, Yang Z F, Guo X G, . Practices and Prospects of Shale Oil Exploration in Jimsar Sag of Junggar Basin. Xinjiang Petroleum Geology, 2019, 40(4): 402-413. (in Chinese with English Abstract)

[52] Wang X Z, Zhang L X, Li Z T, . Pore Type Classification Scheme for Continental Yanchang Shale in Ordos Basin and Its Geological Significance. Oil & Gas Geology, 2016, 37(1): 1-7. (in Chinese with English Abstract)

[53] Wang Y F, Zhai G Y, Liu G H, . Geological Characteristics of Shale Gas in Different Strata of Marine Facies in South China. Journal of Earth Science, 2021, 32(4): 725-741.

[54] Wang Y H, Liang J P, Zhang J Y, . Resource Potential and Exploration Direction of Gulong Shale Oil in Songliao Basin. Petroleum Geology & Oilfield Development in Daqing, 2020, 39(3): 20-34. (in Chinese with English Abstract)

[55] Wu T H, Zhao J L, Zhang W, . Nanopore Structure and Nanomechanical Properties of Organic-Rich Terrestrial Shale: An Insight into Technical Issues for Hydrocarbon Production. Nano Energy, 2020, 69: 104426

[56] Wu Z R, He S, Han Y J, . Effect of Organic Matter Type and Maturity on Organic Matter Pore Formation of Transitional Facies Shales: A Case Study on Upper Permian Longtan and Dalong Shales in Middle Yangtze Region, China. Journal of Earth Science, 2020, 31(2): 368-384.

[57] Xiao Q L, He S, Yang Z, . Petroleum Secondary Migration and Accumulation in the Central Junggar Basin, Northwest China: Insights from Basin Modeling. AAPG Bulletin, 2010, 94(7): 937-955.

[58] Xiong F Y, Jiang Z X, Chen J F, . The Role of the Residual Bitumen in the Gas Storage Capacity of Mature Lacustrine Shale: A Case Study of the Triassic Yanchang Shale, Ordos Basin, China. Marine and Petroleum Geology, 2016, 69(1): 205-215.

[59] Yang H, Li S X, Liu X Y. Characteristics and Resource Prospects of Tight Oil and Shale Oil in Ordos Basin. Acta Petrolei Sinica, 2013, 34(1): 1-11. (in Chinese with English Abstract)

[60] Yang H, Zhang W Z. Leading Effect of the Seventh Member High-Quality Source of Yanchang Formation in Ordos Basin during the Enrichment of Low-Penetrating Oil-Gas Accumulaton: Geology and Geochemistry. Geochimica, 2005, 34(2): 147-154. (in Chinese with English Abstract)

[61] Yang Z, He S, Li Q Y, . Geochemistry Characteristics and Significance of Two Petroleum Systems near Top Overpressured Surface in Central Junggar Basin, NW China. Marine and Petroleum Geology, 2016, 75(7): 341-355.

[62] Yang Z, Hou L H, Tao S Z, . Formation and “Sweet Area” Evaluation of Liquid-Rich Hydrocarbons in Shale Strata. Petroleum Exploration and Development, 2015, 42(5): 609-620.

[63] Yang Z, Li Q Y, Qi X F, . A New Possible Giant Hydrocarbon Generated Formation: The Upper Triassic Source Rock in Southwestern Junggar Basin, NW China. Marine and Petroleum Geology, 2017, 88(4): 575-586.

[64] Yang Z, Tang Z X, Li G H, . Optimization of Enrichment Plays, Evaluation of Sweet Area & Section and Application of Key Technologies for the Continental Shale Strata Oil in China. Acta Geoligica Sinica, 2021, 95(8): 2257-2272. (in Chinese with English Abstract)

[65] Yang Z, Zou C N. “Exploring Petroleum Inside Source Kitchen”: Connotation and Prospects of Source Rock Oil and Gas. Petroleum Exploration and Development, 2019, 46(1): 181-193.

[66] Yang Z, Zou C N, Hou L H, . Division of Fine-Grained Rocks and Selection of “Sweet Sections” in the Oldest Continental Shale in China: Taking the Coexisting Combination of Tight and Shale Oil in the Permian Junggar Basin. Marine and Petroleum Geology, 2019, 109(12): 339-348.

[67] Yang Z, Zou C N, Wu S T, . Formation, Distribution and Resource Potential of the “Sweet Areas (Sections)” of Continental Shale Oil in China. Marine and Petroleum Geology, 2019, 102(12): 48-60

[68] Yergin D. The Quest: Energy, Security, and the Remaking of the Modern World, by Daniel Yergin. Quantitative Finance, 2012, 12(12): 1787-1789.

[69] Yuan W, Liu G D, Xu L M, . Main Controlling Factors for Organic Matter Enrichment in Chang 7 Member of the Yanchang Formation, Ordos Basin. Oil & Gas Geology, 2019, 40(2): 326-334. (in Chinese with English Abstract)

[70] Zhang B, Yan D T, Drawarh H J, . Formation Mechanism and Numerical Model of Quartz in Fine-Grained Organic-Rich Shales: A Case Study of Wufeng and Longmaxi Formations in Western Hubei Province, South China. Journal of Earth Science, 2020, 31(2): 354-367.

[71] Zhang P F, Lu S F, Li J Q, . Broad Ion Beam-Scanning Electron Microscopy Pore Microstructure and Multifractal Characterization of Shale Oil Reservoir: A Case Sample from Dongying Sag, Bohai Bay Basin, China. Energy Exploration & Exploitation, 2020, 38(3): 613-628.

[72] Zhang P L, Xu Y B, Meng Q T, . Sequence Stratigraphy and Geochemistry of Oil Shale Deposits in the Upper Cretaceous Qingshankou Formation of the Songliao Basin, NE China: Implications for the Geological Optimization of in situ Oil Shale Conversion Processing. Energies, 2020, 13(11): 2964

[73] Zhao W Z, Hu S Y, Hou L H, . Types and Resource Potential of Continental Shale Oil in China and Its Boundary with Tight Oil. Petroleum Exploration and Development, 2020, 47 1 1-11.

[74] Zhi D M, Tang Y, Yang Z F, . Geological Characteristics and Accumulation Mechanism of Continental Shale Oil in Jimsar Sag, Junggar Basin. Oil & Gas Geology, 2019, 40(3): 524-534. (in Chinese with English Abstract)

[75] Zhou H T, Li D Y, Liu X T, . Sweet Spot Prediction in Tight Sandstone Reservoir Based on Well-Bore Rock Physical Simulation. Petroleum Science, 2019, 16(6): 1285-1300.

[76] Zou C N, Yang Z, Wang H Y, . “Exploring Petroleum Inside Source Kitchen”: Jurassic Unconventional Continental Giant Shale Oil & Gas Field in Sichuan Basin, China. Acta Geologica Sinica, 2019, 93(7): 1551-1562. (in Chinese with English Abstract)

[77] Zou C N, Liu K Y, Zhu R K. Preface for the Special Issue of Formation and Enrichment of Tight (Shale) Oil Resources in Chinese Continental Basins. Journal of Asian Earth Sciences, 2019, 178 1-2.

[78] Zou C N, Yang Z, Cui J W, . Formation Mechanism, Geological Characteristics and Development Strategy of Nonmarine Shale Oil in China. Petroleum Exploration and Development, 2013, 40(1): 15-27.

[79] Zou C N, Yang Z, Tao S Z, . Continuous Hydrocarbon Accumulation over a Large Area as a Distinguishing Characteristic of Unconventional Petroleum: The Ordos Basin, North-Central China. Earth-Science Reviews, 2013, 126(6): 358-369.

[80] Zou C N, Yang Z, Zhu R K, . Geologic Significance and Optimization Technique of Sweet Spots in Unconventional Shale Systems. Journal of Asian Earth Sciences, 2019, 178(5): 3-19.