Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (1): 146-157.doi: 10.11743/ogg20210113

• Petroleum Geology • Previous Articles     Next Articles

Geological characteristics and enrichment pattern of Permian Mao 1 Member shale gas reservoirs at the southeastern margin of Sichuan Basin

Peixian Zhang(), Xipeng He, Quanfang Gao, Yuqiao Gao, Bin Sun, Xiao Cai, Guisong He, Zhiping Zhang, Nana Liu   

  1. Exploration and Production Research Institute of East China Oil & Gas Company, SINOPEC, Nanjing, Jiangsu 210019, China
  • Received:2020-06-16 Online:2021-02-28 Published:2021-02-07

Abstract:

To understand the shale gas reservoirs in the first member of the Permian Maokou Formation (Mao 1 Member) in the southeastern margin of Sichuan Basin (southeastern Sichuan Basin), we combined outcrop and core observation, mineralogical and geochemical data, thin section analysis and scanning electron microscopic results of argon ion beam cross sections, with logging and seismic attribute prediction techniques to study their sedimentary facies, source rocks, reservoir properties and types.The geological characteristics and gas enrichment pattern of the Mao 1 Member shale were revealed and summarized as: (1) The member is located in the relatively deep-water gentle slope of a carbonate platform and comprised of well-developed dark gray-gray black carbonaceous mudstone, calcareous mudstone, argillaceous limestone and bioclastic limestone.The carbonaceous and calcareous mudstone, among others, with relatively high TOC (0.5%-5.1%) and moderate thermal maturity (Ro: 2.0-2.3), are potential hydrocarbon source rocks with possible new-type atypical shale gas.(2) The reservoir space in the member including organic matter pores, dissolution pores, grain boundary fractures, and constricted fissures, may form a reservoir complex of "pore-fracture-network".The carbonaceous mudstone and calcareous mudstone are dominated by organic matter pores, clay mineral shrinkage cracks and bedding-parallel fractures, while argillaceous limestone and bioclastic limestone mainly develop dissolution pores, grain boundary fractures, contraction fissures and high-angle cracks.(3) The shale gas enrichment in the member can be generally described as "integrated continuous source-reservoir assemblages controlled dually by structures and fractures", and results in an estimated geological resource volume of more than 500 BCM continuously distributed in an area of more than 7 000 km2.It therefore has great exploration potential for shale gas.The research results are of great significance to improving the understanding of the new-type shale gas geology and guiding the shale gas exploration in southeastern Sichuan Basin.

Key words: geological characteristics, enrichment pattern, resource potential, Mao 1 Member, the Permian, shale gas, Southeast Sichuan Basin

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