Oil & Gas Geology ›› 2023, Vol. 44 ›› Issue (2): 379-392.doi: 10.11743/ogg20230210

• Petroleum Geology • Previous Articles    

Control of organic matter enrichment on organic pore development in the Permian marine organic-rich shale, eastern Sichuan Basin

Pengwei WANG1(), Zhongbao LIU1, Dianwei ZHANG1, Xiong LI2, Wei DU1, Haotian LIU2, Peng LI1, Ruyue WANG1   

  1. 1.Petroleum Exploration and Production Research Institute,SINOPEC,Beijing 102206,China
    2.Exploration and Production Research Institute,Jianghan Oilfield Company,SINOPEC,Wuhan,Hubei 430070,China
  • Received:2022-10-21 Revised:2023-01-09 Online:2023-04-01 Published:2023-03-17

Abstract:

Organic matter abundance, macerals and occurrence that have been suggested to significantly control upon pore development in marine shales have not been well studied. Guided by organic geochemistry, organic petrology and other theoretical methods, this study is focused on a systematic analysis and comparison of the abundance, macerals and occurrence of organic matter in the overmature marine shales in the Permian Maokou and Wujiaping Formations at the eastern Sichuan Basin through scanning electron microscope observation and energy spectrum testing among others, to discuss the control of organic matter enrichment on organic pore development in shales and establish an evolution model for the pores. The following results are obtained. Both the Maokou and Wujiaping marine shales are characterized by “high organic matter abundance (TOC) and predominance of algae in their primitive components”. However, they also have some differences in respect of organic matter occurrence. The Maokou Formation shale has relatively higher TOC, with organic matter enriching along bedding or at local position. The Wujiaping Formation shale has relatively lower TOC, with organic matter containing structural vitrinite and structureless vitrinite enriching dispersively or locally. The existence of favorable primitive organic components are a prerequisite for the pore development. Pores are mostly developed in sapropel compositions such as algae but are rarely found in vitrinite. TOC is the key to the pore development. Within a certain range, TOC is positively correlated with organic porosity. The organic matter occurrence influences the pore preservation. Pores are well preserved in dispersed organic matter within brittle mineral framework. The organic matter enriched locally or along bedding usually has less pores preserved under compaction due to a lack of effective framework support.

Key words: organic matter abundance, organic macerals, organic matter pore, marine shale, the Permian, Sichuan Basin

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