ABSTRACT The shale gas resources in the Sichuan Basin have great potential, large distribution area and good preservation conditions, which is of great significance for the production of shale gas in China. The exploitation practice of shale gas in China shows that pressure condition has a significant influence on the nanopore occurrence and structure. In this study, X‐ray diffraction (XRD), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP) and low‐temperature N 2 adsorption (LTNA) are integrated to reveal the evolution of physical property and nanoscale pore of shale reservoir in the Sichuan Basin. Three shale lithofacies are determined in Longmaxi Formation 1st Member: siliceous shale (S), argillaceous shale (CM) and mixed shale (M) lithofacies. Nanopores in S lithofacies are composed of organic nanopores in solid bitumen and interparticle nanopores between rigid grains. Nanopores in M lithofacies are composed of organic nanopores and intraparticle nanopores within carbonate grains. Organic nanopores are the primary type of pore identified in the CM lithofacies. Under overpressure conditions, the organic nanopores in all three types retain their morphological characteristics, with the S lithofacies exhibiting the most well‐preserved pore system. With decreasing pressure coefficient, the rigid quartz‐supported grain framework in the S lithofacies effectively mitigates compaction, allowing nanopore structures and porosity to be largely preserved under deep burial. In contrast, in the M lithofacies, the replacement of carbonate minerals by illite weakens the grain framework, reducing its resistance to compaction and resulting in significant pore and porosity loss. The CM lithofacies lacks rigid framework‐forming minerals; thus, clay minerals and organic matter are directly subjected to compaction during pressure reduction, leading to a sharp decrease in both nanopore abundance and pore size. The evolution of nanopore structure and quantity is directly reflected in porosity variations and indirectly controls shale gas adsorption and storage capacity. These results demonstrate that lithofacies‐dependent pressure responses fundamentally govern nanopore preservation and reservoir quality in deeply buried shales, providing new insights into shale gas evaluation under variable pressure conditions.
Zhang et al. (Thu,) studied this question.