Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (6): 1162-1175.doi: 10.11743/ogg20200605

• Petroleum Geology • Previous Articles     Next Articles

Characteristics and controlling factors of pore structures of various lithofacies in shales of Longmaxi Formation, eastern Sichuan Basin

Jianfeng Huo1(), Jian Gao2, Xiaowen Guo1,*(), Jizheng Yi3, Zhiguo Shu3, Hanyong Bao3, Rui Yang1, Tao Luo1, Sheng He1   

  1. 1. Key Laboratory of Tectonics and Petroleum Resources, Ministry of Education, China University of Geosciences(Wuhan), Wuhan, Hubei 430074, China
    2. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    3. Research Institute of Exploration and Development of Jianghan Oilfield Company, SINOPEC, Wuhan, Hubei 430223, China
  • Received:2018-06-27 Online:2020-12-28 Published:2020-12-09
  • Contact: Xiaowen Guo E-mail:hhuojianfeng@126.com;guoxw@cug.edu.cn

Abstract:

The eastern Sichuan Basin is one of the major shale gas producing areas in China.However, with gas being mostly found in the clay-rich siliceous shale, the silica-rich argillaceous and mixed argillaceous/siliceous shales in the Wufeng-Longmaxi formation have been largely neglected.This study focuses on pore structure features of the shales by comparing the structural features of diverse lithofacies and investigating their main controlling factors based on the lithofacies classification of the shale samples from the Longmaxi Formation by means of low pressure N2/CO2 gas adsorption, high pressure mercury intrusion, porosity measurement, XRD analyses, FE-SEM and so on.The results show that the organic-rich shales in the eastern Sichuan Basin can be divided to silica-rich argillaceous, mixed argillaceous/siliceous and clay-rich siliceous lithofacies with a porosity ranging from 2.62% to 5.65%.Pore volume of the shale reservoirs is primarily contributed by mesopores, accounting for 50% to 60% of the total, followed by micropores and macropores, accounting for 15% to 20% of the total; while the total specific surface area is mainly contributed by micropores and mesopores, accounting for 70% and 30% of total respectively.The pore development is chiefly controlled by the abundance of organic matters instead of the clay mineral content.Shale with high abundance of organic matters may contain less pores as it could not withstand intense compaction with its soft matrix.The organic-rich shale of silica-rich argillaceous and mixed argillaceous/siliceous lithofacies is high in porosity and shares the similar pore structure with most of the clay-rich siliceous shale, suggesting that the silica-rich argillaceous and mixed argillaceous/siliceous shales can also generate certain amount of nano-scaled pores for shale gas storage.

Key words: pore structure, organic pore, shale gas, Longmaxi Formation, Sichuan Basin

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