首页|Development characteristics and controlling factors of fractures in lacustrine shale and their geological significance for evaluating shale oil sweet spots in the third member of the Shahejie Formation in the Qikou Sag,Bohai Bay Basin

Development characteristics and controlling factors of fractures in lacustrine shale and their geological significance for evaluating shale oil sweet spots in the third member of the Shahejie Formation in the Qikou Sag,Bohai Bay Basin

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Natural fractures are critical for shale oil and gas enrichment and development.Due to the extremely high heterogeneity of shale,the factors controlling the formation of internal fractures,especially hori-zontal fractures,remain controversial.In this study,we integrate thin section analysis and micro-computed tomography(CT)data from several lacustrine shale samples from the third member(Es3)of the Shahejie Formation,Qikou Sag,Bohai Bay Basin,to assess the fractures in detail.The goal is to reveal the development characteristics,controlling factors,and geological significance for evaluating sweet spots in a shale oil play.The fractures in the Es3 contain high-angle structural and horizontal bed-parallel fractures that are mostly shear and extensional.Various factors influence fracture development,including lithofacies,mineral composition,organic matter content,and the number of laminae.Struc-tural fractures occur predominantly in siltstone,whereas bed-parallel fractures are abundant in lami-nated shale and layered mudstone.A higher quartz content results in higher shale brittleness,causing fractures,whereas the transformation between clay minerals contributes to the development of bed-parallel fractures.Excess pore pressure due to hydrocarbon generation and expulsion during thermal advance can cause the formation of bed-parallel fractures.The density of the bed-parallel and structural fractures increases with the lamina density,and the bed-parallel fractures are more sensitive to the number of laminae.The fractures are critical storage spaces and flow conduits and are indicative of sweet spots.The laminated shale in the Es3 with a high organic matter content contains natural fractures and is an organic-rich,liquid-rich,self-sourced shale play.Conversely,the siltstone,massive mudstone,and argillaceous carbonate lithofacies contain lower amounts of organic matter and do not have bed-parallel fractures.However,good reservoirs can form in these areas when structural fractures are present and the source,and storage spaces are separated.

FracturesDevelopment characteristicsControlling factorsShale oilSweet spot

Xu Zeng、Tao Yang、Jian-Wei Feng、Cong-Sheng Bian、Ming Guan、Wei Liu、Bing-Cheng Guo、Jin Dong

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Research Institute of Petroleum Exploration and Development,China National Petroleum Corporation,Beijing,100083,China

College of Geosciences,China University of Petroleum(Beijing),Beijing,102249,China

Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum(Beijing),Beijing,102249,China

Research Institute of Petroleum Exploration and Development,China National Petroleum Corporation,Beijing 100083,China

School of Earth Sciences,China University of Petroleum,Qingdao,266400,Shandong,China

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CNPC Prospective Basic Science and Technology Special ProjectScience and Technology Cooperation Project of the CNPC-SWPU Innovation Alliance

2023ZZ082020CX050103

2024

10.1016/j.petsci.2023.10.029

石油科学(英文版)
中国石油大学（北京）

石油科学(英文版)

EI
影响因子：0.88
ISSN：1672-5107
年,卷(期)：2024.21(2)
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