Oil & Gas Geology ›› 2021, Vol. 42 ›› Issue (1): 1-15.doi: 10.11743/ogg20210101

• Petroleum Geology • Previous Articles     Next Articles

Differential occurence of shale gas in the Permian Longtan Formation of Upper Yangtze region constrained by plate tectonics in the Tethyan domain

Zhiliang He1,2,3(), Haikuan Nie1,2,4, Shuangjian Li4, Guangxiang Liu4, Jianghui Ding4, Ruikang Bian4, Zhiyuan Lu5   

  1. 1. State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development, Beijing 100083, China
    2. Key Laboratory of Shale Oil and Gas Exploration & Production, SINOPEC, Beijing 100083, China
    3. Department of Science and Technology, China Petroleum & Chemical Corporation, Beijing 100728, China
    4. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    5. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2020-12-01 Online:2021-02-28 Published:2021-02-07

Abstract:

Great success has been achieved in marine shale gas exploration and development worldwide.Exploration in marine-terrestrial transitional and terrestrial shales has also been active in China but a large scale commercial development is yet to come.Based on the analysis of the controlling effect of the Permian plate tectonics on the formation and distribution of prototype basins and organic-rich shales in South China, we explored the petrographic, geochemical and mineral assemblages as well as reservoir characteristics of the Longtan Formation shale in the Sichuan Basin.In comparison to typical shale formations of similar sedimentary settings that are under commercial development elsewhere, we clarified the occurrence features and resource prospect of marine shale gas in the formation.The main conclusions are as follows: (1) Under the influence of the subduction of the Qinling and Jinshajiang (ocean) blocks and other tectonic events such as the Emei taphrogeny, multiple rift basins were developed in both the center and edge of the Yangtze platform and a set of continental-transitional-marine sedimentary system was also deposited by the subsequent intensive tectonic-sedimentary differentiation.(2) The organic-rich Longtan Formation in the Sichuan Basin can be lithologically categorized into three types: the mud-shale intercalated with limestone intervals of deep-water shelf facies, sandstone-mudstone-limestone interbeds of shallow-water shelf facies and mud-shale intercalated with coal beds of tide flat-lagoon facies.(3) The Longtan Formation in northeastern Sichuan Basin that was deep in stagnant water with good sealing and reducing properties during the Permian provided an ideal place for organic matter enrichment.In terms of preservation, the formation was not only confined by the regional Lower Triassic gypsolyte cap rocks, but also perfectly clamped between the Changxing Formation limestone (on top) and the Maokou Formation limestone (at the bottom).(4) The high organic carbon content (TOC>2%), thermal evolution maturity (Ro>2%), porosity (Φ>5%), quartz content (>40%), gas content (desorption gas content>3 m3/t), and high pressure coefficient (about 1.5) of the formation indicate favorable conditions for shale gas generation.(5) The Longtan Formation, similar to such typical marine shales as the Wufeng-Longmaxi Formations in the same basin, or as the Barnett, Ohio, Antrim and New Albany shales in the U.S., is geographically favorable to the generation of large-scale shale gas deposits.It is expected to take the lead in making strategic shale gas exploration breakthroughs, especially in the northeastern and eastern parts of the basin where the burial depth is relatively shallow and the siliceous shale is relatively thick.

Key words: occurrence condition, transitional facies, marine facies, plate tectonics, shale gas, Longtan Formation, Permian, Sichuan Basin

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