Oil & Gas Geology ›› 2020, Vol. 41 ›› Issue (2): 284-294.doi: 10.11743/ogg20200205

• Petroleum Geology • Previous Articles     Next Articles

Reservoir characteristics and exploration of the Lower Cambrian shale gas in the Middle-Upper Yangtze area

Bo Gao1,2,3(), Zhongbao Liu1,2,3, Zhiguo Shu4, Haotian Liu4, Ruyue Wang3, Zhiguang Jin5, Guanping Wang6   

  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. Petroleum Exploration and Production Research Institute, SINOPEC, Beijing 100083, China
    4. Research Institute of Exploration and Development of Jianghan Oilfield Branch Company Ltd., SINOPEC, Wuhan, Hubei 430223, China
    5. College of Geosciences, China University of Petroleum(Beijing), Beijing 102249, China
    6. School of Energy Resources, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2019-04-08 Online:2020-04-28 Published:2020-04-03

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Abstract:

The study aims to clarify the reservoir pore characteristics and the factors influencing the ancient shale sequences in Southern China with the samples taken from the Lower Cambrian shale in the Middle-Upper Yangtze area.An integration of multiple technical methods, including the thin section observation, joint tests of high pressure mercury injection and nitrogen adsorption, argon ion milling-scanning electron microscopy, focused ion beam scanning electron microscopy (FIB-SEM), whole-rock X-ray diffraction analysis is applied to systematically study the structure, types and influential factors of shale pores.Meanwhile, the potential targets for exploration of the Lower Cambrian shale gas are also pointed out based on the characteristics of the shale reservoir and the geological conditions for shale gas generation.It is concluded that the Lower Cambrian in the study area mainly develops three types of organic-rich shale in terms of depositional genesis, namely the extensional-trough, shelf-margin slope, and platform-front slope.The organic-rich shale of the intra-shelf extensional-trough type is dominated by intergranular pores and interlayer pores of clay mineral, followed by organic pores; that of the platform-front slope type mainly develops organic pores and calcite intragranular dissolution pores; while that of the shelf-margin slope type mainly develops organic pores with almost no inorganic mineral pores.As a whole, the pore development in the Lower Cambrian shale is controlled by a variety of factors including the mineral composition of shale, the abundance of organic matter, thermal evolution degree, and preservation conditions.Given the analysis of shale gas preservation conditions and drilling results of exploration wells, it is suggested that we should pay more attention to the distribution of intra-shelf extensional-trough shale in the Lower Cambrian shale gas exploration within the Sichuan Basin, and this is especially true for the organic-rich shale intervals in the upper part of the Qiongzhusi Formation.While as for the outer area of the Sichuan Basin, the organic-rich shale of both the platform-front and the shelf-margin slope types, featuring moderate thermal evolution and relatively good preservation conditions, should be the research focus.

Key words: organic pore, pore type, preservation condition, shale reservoir, Lower Cambrian, Middle-Upper Yangtze area

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