Fine-grained rock fabric facies classification and its control on shale oil accumulation: a case study from the Paleogene Kong 2 Member, Bohai Bay Basin

Abstract

Lacustrine shale oil resources in China are abundant, with remarkable exploration breakthroughs being achieved. Compared to marine shale oil in North America, efficient exploration of lacustrine shale oil is more difficult; thus, selecting favorable layer and optimization zone for horizontal wells is more important. In this study, based on systematic coring of approximately 500 m fine-grained deposits of the Kong 2 Member, combining laboratory tests and log data, source rock geochemistry and reservoir physical properties, the favorable rock fabric facies for oil accumulation was analyzed and classified. First, the dominant lithologic facies, organic facies, and bed combination facies were determined based on mineral composition from logging, total organic content (TOC), and sedimentary structure. Secondly, 10 fabric facies were classified by combining these three facies, with 4 fabric facies were found to have high TOC content, high total hydrocarbon, and strong fluorescence features, indicating good shale oil enrichment. Thirdly, the distribution of the upon good fabric facies was identified to be located at the top of the Kong 2 Member, with evidences of seismic resistivity inversion, thermal maturity, structure depth, and strata thickness. And the favorable facies were found to be stably distributed lateral at the area of about 100 km². High oil flow has been detected at this layer within this area by several wells, including horizontal wells. The exploratory study of fabric facies classification and evaluation provides a new research idea for lacustrine shale oil exploration and effectively promotes breakthroughs in lacustrine shale oil exploration in Bohai Bay Basin.

Keywords

fabric facies / fine grained deposits / lithologic facies / organic facies / Bohai Bay Basin

References

[1] Akinyemi S A, Adebayo O F, Nyakuma B B, Adegoke A K, Aturamu O A, OlaOlorun O A, Adetunji A, Hower J C, Hood M M, Jauro A (2020). Petrology, physicochemical and thermal analyses of selected cretaceous coals from the Benue Trough Basin in Nigeria. Int J Coal Sci Technol, 7(1): 26–42

[2] Chen S, Zhang S, Wang Y, Tan M (2016). Lithofacies types and reservoirs of paleogene fine-grained sedimentary rocks dongying sag, Bohai Bay Basin, china. Pet Explor Dev, 43(2): 218–229

[3] Cui J, Zhu R, Mao Z, Li S (2019). Accumulation of unconventional petroleum resources and their coexistence characteristics in Chang 7 shale formations of Ordos Basin in central China. Front Earth Sci, 13(3): 575–587

[4] Fu J H, Deng X Q, Chu M J, Zhang H F, Li S X (2013). Features of deepwater Lithofacies, Yanchang Formation in Ordos Basin and its petroleum significance. Acta Sedimentology Sinica, 5: 928–938

[5] Geng S (2013). Study on shale mineral component content model in Luojia area. Petroleum Geology and Recovery Efficiency, 1: 24–27

[6] Gu J, Huang Y J, Wang C (2010). Mudstone lithofacies in the Cretaceous Qingshankou Formation of Well Sk I, Songliao Basin, Northeastern China. China Mining Magazine, 19: 161–165

[7] Jarvie DM, Hill RJ, Ruble T E, Pollastro R M. (2007) Unconventional shale-gas systems: the Mississippian Barnett Shale of north-central Texas as one model for thermogenic shale-gas assessment. AAPG Bulletin 91: 475–499

[8] Jia C Z, Zou C N, Li J Z, Li D H, Zheng M (2012). Assessment criteria, main types, basic features and resource prospects of the tight oil in China. Acta Petrol Sin, 3: 343–350

[9] Jin Z, Sun Y, Yang L (2001). Influences of deep fluids on organic matter of source rocks from the Dongying Depression, East China. Energy Exploration & Exploitation, 19(5): 479–486

[10] Li S Z, Suo Y H, Zhou L H, Dai L M, Zhou J T, Zhao F M, Lu Y, Pu X G, Lou D, Wu Q, Jiao Q (2011). Pull-apart basins within the North China Craton, structural pattern and evolution of Huanghua Depression in Bohai Bay Basin. Journal of Jilin University (Earth Science Edition), 5: 1362–1379

[11] Li Y, Wang Z, Pan Z, Niu X, Yu Y, Meng S (2019b). Pore structure and its fractal dimensions of transitional shale: a cross section from east margin of the Ordos Basin, China. Fuel, 241: 417–431

[12] Li Y, Gao X, Meng S, Wu P, Niu X, Qiao P, Elsworth D (2019a). Diagenetic sequences of continuously deposited tight sandstones in various environments: a case study from upper Paleozoic sandstones in the Linxing area, eastern Ordos Basin, China. AAPG Bull, 103(11): 2757–2783

[13] Li Y, Yang J, Pan Z, Meng S, Wang K, Niu X (2019c). Unconventional natural gas accumulations in stacked deposits: a discussion of Upper Paleozoic coal-bearing strata in the east margin of the Ordos Basin, China. Acta Geol Sin, 93(1): 111–129

[14] Li Y, Yang J, Pan Z, Tong W (2020). Nanoscale pore structure and mechanical property analysis of coal: an insight combining AFM and SEM images. Fuel, 260: 116352

[15] Macquaker J H S, Adams A E (2003). Maximizing information from fine-grained sedimentary rocks: an inclusive nomenclature for mudstones. J Sediment Res, 73(5): 735–744

[16] Macquaker J H S, Keller M ADavies S J (2010) Algal blooms and “marine snow”: mechanisms that enhance preservation of organic carbon in ancient fine-grained sediments: Journal of Sedimentary Research, 80: 934–942

[17] Pu X G, Han W Z, Zhou L H, Chen S Y, Zhang W, Shi Z N, Yang F, Liu S (2015). Lithologic characteristics and geological implication of fine-grained sedimentation in Ek2 high stand system tract of Cangdong Sag, Huanghua Depression. China Petroleum Exploration, 5: 30–40

[18] Pu X G, Zhou L H, Han W Z, Zhou J S, Wang W G, Zhang W, Chen S Y, Shi Z N, Liu S (2016). Geologic features of fine-grained facies sedimentation and tight oil exploration: a case from the second Member of Paleogene Kongdian Formation of Cangdong Sag, Bohai Bay Basin. Pet Explor Dev, 43(1): 26–36

[19] Ren J Y, Liao Q J, Lu G C, Fu L X, Zhou J Y, Qi P, Shi S S (2010). Deformation framework and evolution of Huanghua Depression, Bohai Gulf. Geotectonica et Metallogenia, 4: 461–472

[20] Slatt R M (2007). Introduction to the petroleum geology of deepwater setting. In Weimer P and Slatt RM, eds. Introduction to the Petroleum Geology of Deepwater Setting. AAPG Bull, 57: 1–18

[21] Wang Y, Wang X J, Song G Q, Liu H, Zhu D, Zhu D, Ding J, Yang W, Yin Y, Zhang S, Wang M (2016). Genetic connection between mud shale lithofacies and shale oil enrichment in Jiyang Depression, Bohai Bay Basin. Pet Explor Dev, 43(5): 759–768

[22] Wang Y S, Li Z, Gong J Q (2013). Discussion on an evaluation method of shale oil and gas in Jiyang depression, a case study on Luojia area in Zhuanhua Sag. Acta Petrol Sin, 1: 83–91

[23] Yang Y T, Zhang J C, Wang X Z, Cao J Z, Tang X, Wang L, Yang S Y (2012). Source rock evaluation of lacustrine shale gas, A case study of Chang 7 of Mesozoic Yanchang Formation in Xiasiwan area of Yanchang. Journal of Northeast Petroleum University, 4: 10–17

[24] Yang Z, Hou L H, Tao S Z, Cui J W, Wu S T, Lin S H, Pan S Q (2015). Formation conditions and “sweet spot” evaluation of tight oil and shale oil. Pet Explor Dev, 42(5): 555–566

[25] Zhang S, Chen S Y, Cui S L, Gong W L, Yu J Q, Yan J H, Shao P C, Liu Y. (2014) Characteristics and types of fine grained sedimentary rocks lithofacies in semi-deep and deep lacustrine, Dongying Sag. Journal of China University of Petroleum 5: 9–17

[26] Zhao X Z, Pu X G, Han W Z, Zhou L H, Shi Z N, Chen S Y, Xiao D Q (2017). A new method for lithology identification of fine grained deposits and reservoir sweet spot analysis: a case study of Kong 2 Member in Cangdong sag, Bohai Bay Basin, China. Pet Explor Dev, 44(4): 524–534

[27] Zhao X Z, Zhou L H, Pu X G, Han W Z, Jin F M, Xiao D Q, Shi Z N, Deng Y, Zhang W, Jiang W Y (2019). Exploration breakthroughs and geological characteristics of continental shale oil: a case study of the Kongdian Formation in the Cangdong Sag, China. Mar Pet Geol, 102: 544–556

[28] Zhao X Z, Zhou L H, Pu X G, Jin F M, Han W Z, Xiao D Q, Chen S Y, Shi Z N, Zhang W, Yang F (2018). Geological characteristics of shale rock system and shale oil exploration breakthrough in a lacustrine basin: a case study from the Paleogene 1st submember of Kong 2 Member in Cangdong sag, Bohai Bay Basin, China. Pet Explor Dev, 45(3): 377–389

[29] Zhao Z Z, Du J H (2012) Tight Oil and Gas. Beijing: Petroleum Industry Press: 125–143 (in Chinese)

Acknowledgments

This research is supported by PetroChina Major Science and Technology Project “Research and Application of Key Technology for Efficient Reservoir Increase and Stable Production in Dagang Oil and Gas Field” (2018E-11). We extend gratitude to the PetroChina Dagang Oilfield Company for providing data and granting permission to publish this paper. The authors also thank Professor Yan J. H. for their constructive comments.

RIGHTS & PERMISSIONS

2021 Higher Education Press