Geological characteristics of continental shale oil and gas in Lower Jurassic Ziliujing Formation of Sichuan Basin
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    Abstract:

    The Jurassic Ziliujing Formation in the Sichuan Basin has two sets of organic- rich shale series, the Dongyuemiao Member and Da’anzhai Member, which are mainly lacustrine shale with siltstone and shale with shell limestone. Methods: Selecting rock core of the Lower Jurassic Ziliujing Formation in the Sichuan Basin for sedimentation, hydrocarbon resource and reservoir research, analyzing the inorganic pore development characteristics of different lithofacies and minerals, the organic pore development characteristics of different types of organic matter, the spatial configuration relationship between different types of pores and hydrocarbon generating substances, and the controlled shale gas occurrence capacity, the diagenesis and hydrocarbon generation processes at different evolutionary stages, and the jointly controlled pore evolution process, these provide reference for the sedimentation, hydrocarbon resource and reservoir research of terrestrial shale oil and gas, which has important reference value for exploring the enrichment mechanism of terrestrial shale oil and gas and guiding the exploration deployment of Jurassic terrestrial shale oil and gas in the Sichuan Basin. Results: Based on the assemblage characteristics of shale, shell limestone and siltstone, 3 types and 7 types of shale lithofacies assemblage are identified in the Lower Jurassic Ziliujing Formation. The organic matter abundance of the shale is medium, the organic matter types are mainly type II1 and type II2, the thermal evolution degree is medium, and oil and gas coexist. There are both inorganic pores and organic pores in shale reservoir space, and micro- fractures are developed locally. The relationship between the allocation of inorganic minerals and organic matter, and between organic matter and organic pores in the Ziliujing Formation shale controls the effectiveness of the source-reservoir allocation of the shale. At a higher evolution degree, the organic matter porosity increases with the increase of TOC, and the source-reservoir allocation relationship becomes better. The solid bitumen stored in the rigid mineral stable support lattice is large, and the number of organic pores inside is large and the pore size is large. The asphalt preserved under the unstable support lattice of clay minerals is long in shape, and the pore size of organic matter inside is small. Conclusions: Based on the evaluation results of the source-reservoir coupling conditions of different lithology of shale strata, the source-reservoir coupling conditions of shale are obviously better than that of interlayer. The high- quality shale with good source-reservoir coupling conditions is the sweet interval of shale oil and gas, in which clay shale is the best, shell gray shale is better, and silty shale is worse. The intercalations of shell limestone and siltstone have no hydrocarbon source conditions and poor reservoir conditions, and can only form near- source aggregation system with adjacent organic- rich shales.

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HU Zongquan, FENG Dongjun, LI Peng, WANG Qianru, LIU Zhongbao, WANG Ruyue, ZHAO Guowei.2023. Geological characteristics of continental shale oil and gas in Lower Jurassic Ziliujing Formation of Sichuan Basin[J]. Geological Review,69(6):2023060019.

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History
  • Received:August 07,2023
  • Revised:December 02,2023
  • Adopted:
  • Online: December 20,2023
  • Published: