Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (6): 1265-1280.doi: 10.11743/ogg20210603

• Petroleum Geology • Previous Articles     Next Articles

Hydrothermal dolomitization and its role in improving Middle Permian reservoirs for hydrocarbon accumulation, Sichuan Basin

Shuangjian Li1,2(), Tianbo Yang3, Yueqing Han1,2, Ping Gao3, Yujin Wo1, Zhiliang He2,4   

  1. 1. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    2. Structural Geology and Reservoir Laboratory, Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    3. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
    4. SINOPEC, Beijing 100728, China
  • Received:2020-07-28 Online:2021-12-28 Published:2021-12-16

Abstract:

The Middle Permian in the Sichuan Basin hosts various types of hydrothermal dolomites that are important to oil and gas exploration. Their mechanisms and occurring models as well as their contribution to reservoir quality enhancement have been the focus of study for years but a consensus is yet to be reached. This paper summarizes the mechanisms and their role in shaping reservoirs through detailed mineralogical, petrographic and geochemical analyses of hydrothermal dolomites from typical locations in the Sichuan Basin. The results show that the hydrothermal dolomitization in the Middle Permian of the Sichuan Basin is mainly related to contemporaneous fault activities and has no obvious correlation with the lithology and lithofacies of surrounding rocks. According to the relationship between hydrothermal dolomites and surrounding rocks, the hydrothermal dolomitization possibly occurs in three models: (1) hydrothermal dolomitization from modification of grain-beach facies, mainly occurring in the Qixia Formation of western and central Sichuan Basin and has no significant contribution to the improvement of reservoirs; (2) hydrothermal dolomitization from modification of karstified limestone, mainly occurring in the Maokou Formation of central Sichuan Basin and is insignificant in contributing to reservoir quality enhancement; and (3) hydrothermal dolomitization from modification of tight limestone, mainly occurring in the Maokou Formation of eastern Sichuan Basin and has contributed greatly to reservoir property improvement. Fault-related fractures, residual dissolution pores and dolomite intercrystalline pores constitute most storage space in reservoirs with hydrothermal dolomitization. Compared with reservoirs with relatively good initial physical properties, the reservoirs with poor initial physical properties are even more significant in terms of quality enhancement after hydrothermal dolomitization and relevant structural activities.

Key words: hydrothermal dolomite, reservoir, Qixia Formation, Maokou Formation, Middle Permian, Sichuan Basin

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