Oil & Gas Geology ›› 2025, Vol. 46 ›› Issue (1): 211-229.doi: 10.11743/ogg20250115

• Petroleum Geology • Previous Articles     Next Articles

Sedimentary evolution and hydrocarbon exploration potential of platform-margin zones in the upper sub-member of the 2nd member of the Middle Permian Maokou Formation, eastern Sichuan Basin

Yue MU1(), Xiucheng TAN1,2(), Bing LUO3,4, Minglong LI1, Fabo XU4, Juanzi YI4, Yonghong WU4, Wenjie YANG1, Jie GUO1, Di XIAO1,2   

  1. 1.Key Laboratory of Carbonate Reservoirs,CNPC,Chengdu,Sichuan 610500,China
    2.State Key Laboratory of Oil and Gas Reservoir Geology and Exploitation,Southwest Petroleum University,Chengdu,Sichuan 610500,China
    3.Research Institute of Exploration and Development,Southwest Oil & Gasfield Company,PetroChina,Chengdu,Sichuan 610051,China
    4.Chongqing Gas Field,Southwest Oil & Gasfield Company,PetroChina,Chongqing 400707,China
  • Received:2024-08-11 Revised:2024-12-16 Online:2025-02-28 Published:2025-03-03
  • Contact: Xiucheng TAN E-mail:17830338219@163.com;tanxiucheng70@163.com

Abstract:

Platform-margin zones in the upper sub-member of the 2nd member of the Maokou Formation (also referred to as the Mao 2 Member) in the Sichuan Basin exhibit enormous hydrocarbon exploration potential, with constant breakthroughs having been made in the central to northwestern Sichuan Basin. However, the distribution pattern of platform-margin zones in the eastern Sichuan Basin remains unclear due to limited studies. Focusing on the eastern Sichuan Basin, we conduct sub-layer division and correlation, investigate the distribution and evolutionary pattern of the platform-margin zones therein, and propose hydrocarbon play fairways. The results indicate that the upper sub-member of the Mao 2 Member in the eastern Sichuan Basin exhibits two fourth-order eustatic cycles, as evidenced by lithologic assemblages and logs. Based on this finding, the upper sub-member can be divided into sub-layers 1 and 2. Both sub-layers consist of the sedimentary systems of rimmed carbonate platform facies, with major sedimentary subfacies including platform-margin shoals, inter-shoal lagoons, intra-platform shoals, and semi-restricted seas. The platform-margin zones in both sub-layers show similar distribution patterns, with platform-margin shoals along the Linshui-Fengdu and Dazhu-Zhongxian platform-margin zones spreading in the NW-SE direction. During the deposition of sub-layer 1, platform-margin shoals in both platform-margin zones display pronounced differentiation, separated by banded inter-shoal lagoons. During the deposition of the sub-layer 2, platform-margin shoals display lateral migration and an expanded planar distribution area, manifesting a contiguous development in the eastern part. The superimposition of penecontemporaneous karstification and dolomitization on platform-margin shoals is identified as the main cause of the formation of high-quality reservoirs. The Linshui-Fengdu and Dazhu-Zhongxian platform-margin zones are favorable for reservoir development, while slope-troughs and inter-shoal lagoons emerge as favorable areas for source rock development. The platform-margin shoals along the Dazhu-Zhongxian platform-margin zone exhibit great hydrocarbon exploration potential, serving as a new hydrocarbon play fairway.

Key words: play fairway, platform margin, sedimentary evolution, carbonate rocks, Maokou Formation, eastern Sichuan Basin

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