Oil & Gas Geology ›› 2022, Vol. 43 ›› Issue (2): 325-340.doi: 10.11743/ogg20220207

• Petroleum Geology • Previous Articles     Next Articles

Evolution and genesis of organic pores in Triassic Xujiahe Formation shale, Western Sichuan Depression, Sichuan Basin

Liang Xu1,2,3(), Wei Yang1,2(), Zhenxue Jiang1,2, Dongxia Chen1,4, Yaohua Wang1,2, Jiankang Lu1,2, Mingzhu Zhao1,2, Lan Li1,2   

  1. 1.State Key Laboratory of Petroleum Resources and Prospecting,China University of Petroleum (Beijing),Beijing 102249,China
    2.Unconventional Oil and Gas Science and Technology Research Institute,China University of Petroleum(Beijing),Beijing 102249,China
    3.Shale Gas Research Institute,Southwest Oil & Gasfield Company,PetroChina,Chendu,Sichuan 610051,China
    4.College of Geoscience,China University of Petroleum (Beijing),Beijing 102249,China
  • Received:2020-10-28 Revised:2022-01-20 Online:2022-04-01 Published:2022-03-11
  • Contact: Wei Yang E-mail:2062198594@qq.com;yangw@cup.edu.cn

Abstract:

Samples from non-marine organic rich shale in the Xujiahe Formation, Western Sichuan Depression, Sichuan Basin, were analyzed with field emission scanning electron microscope and EDS energy spectrum. Three maceral components, including solid bitumen, vitrinite and intertinite, as well as microscopic subcomponents such as oil bitumen, tar bitumen, structured vitrinite, unstructured vitrinite, detrital-vitrinite, fusinite, semi-fusinite, detrital-intertinite, and sclerotinite were identified in these organic-rich shale samples. The organic pores of different types vary greatly under scanning electron microscopy: the organic pores develop the best in solid bitumen in organoclay complex, well in individual solid bitumen flakes, and the worst in vitrinite and intertinite mainly with residual primary pores. Controlled by difference in hydrocarbon generation potential, the three macerals have their weight percentages of carbon increasing and hydrocarbon generation and pore-forming potential deteriorating successively from solid bitumen, vitrinite to intertinite. Higher content of illite means higher specific catalytic activity, which promotes the development of pores in solid bitumen near the illite. Thermal simulation experiments show that the pore evolution of different macerals varies greatly. With maturity increasing, solid bitumen responds differently from other two maceral groups, it develops a large number of honeycomb pores with increasing cross-sectional porosity, which later gradually decreases due to the exhaustion of hydrocarbon generation. Meanwhile vitrinite and intertinite develop less pores and have their primary pores decreasing rapidly. However, the widely developed microcracks in the latter two groups connect bituminous pores and other inorganic pores, forming a microscopic pore-fracture network and improving the storage and seepage capacity of shale reservoirs.

Key words: pore-forming capacity, maceral, pore heterogeneity, pore evolution, shale, Xujiahe Formation, Western Si-chuan Depression, Sichuan Basin

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