Abstract This study addresses gaps in research on the pore structures of deep, organic-rich marine shales, focusing on the lower Silurian Longmaxi Formation in Sichuan's Luzhou Block, using wells L1 and L2. Employing techniques like organic geochemistry, mineral composition analysis, CO₂ and N₂ adsorption-desorption, high-pressure mercury intrusion, FIB-SEM, and NMR, the study identifies pyrobitumen as the main pore contributor, accounting for approximately 59.95%-62.00% of pores. It documents a reduction in pore storage and connectivity from the over-mature to semi-graphitised stages, with mesopores showing a smaller decline (8.37%-9.14%) compared to micropores and macropores (25.02%-52.86%). Additionally, connectivity of 100–1000 nm pores decreased significantly (33.46%-62.09%). Changes in the stages of maturity affected the pore characteristics: retained oil in mature stages transformed into pyrobitumen, reducing surface porosity. In the over-mature stage, diagenesis and thermal evolution led to gas-filled pyrobitumen pores which balanced with formation pressures to preserve pore structure. The semi-graphitised stage saw a significant reduction in pore volume and surface porosity due to compaction and carbonization.
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Wang et al. (2024) studied this question.