136-8 The formation mechanism of high-quality reservoirs in overmature marine deep shales

Session: Micro-Nano Scale Pore-Fracture Architecture and Fluid Dynamics in Shale and Coal Reservoirs

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The exploration and development of deep shale gas started later, and the related geological theories and understanding were relatively poor. To clarify the characteristics and formation mechanism of deep organic-rich marine shale reservoirs, this study analyzes shale core samples from the Wufeng and Longmaxi Formations in the southeastern Sichuan Basin. Based on X-ray diffraction mineral component analysis, low-temperature gas physisorption, high-pressure mercury intrusion, field emission-scanning electron microscopy, energy spectrum analysis and cathodoluminescence, qualitative descriptions and quantitative characterizations of the pore structure features are conducted, and the diagenetic types are identified. The results show that the pore development in deep shale is influenced by lithofacies and TOC contents, with the micropores of argillaceous siliceous shale and siliceous shale are more developed. Overall, the deep shale develops a large number of nanoscale pores, and the pores are mainly composed of micropores and mesopores. The organic-rich shale mainly has five diagenetic types, such as compaction, recrystallization, dissolution, cementation, and thermal evolution of organic matter. The diagenetic difference of different lithofacies has a significant influence on the pore structure, in which the siliceous shale has more authigenic quartz from the transformation of siliceous organisms in the early diagenesis. This early cementation enhances the compaction resistance of the reservoir, and the retained pores can provide space for the migration and enrichment of organic matter. Finally, the development mechanism of high-quality shale reservoirs is summarized, which can serve as a reference for studying the pore formation mechanism and reservoir distribution prediction in marine deep shale.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-6395

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