Pore Development Characteristics of Shales in the Dalong Formation, Western Hubei, Under the Coupled Control of Authigenic Quartz–Clay Minerals–Organic Matter

The upper Permian Dalong Formation in western Hubei Province is a crucial strategic successor for shale gas development in South China. However, the geological controls on reservoir pore development, particularly the influence of organic–inorganic interactions on the pore system, remain poorly understood. This restricts the precise optimization of shale gas exploration targets in this formation. To investigate the pore development characteristics and main controlling factors of the Dalong Formation shale reservoirs, this study takes the DFS from the Shuanghe section in western Hubei as the research object. X-ray diffraction (XRD), argon-ion polishing-scanning electron microscopy (SEM), and N2/CO2 gas adsorption–desorption technologies were integrated to achieve qualitative characterization and quantitative assessment of the pore network, with analyses of pore size distribution. The results show that the pores of the DFSs are dominated by interparticle pores and organic matter pores, and the pore structures of organic-rich and organic-lean shales exhibit significant differentiation characteristics. The quartz in the DFSs are mainly of diagenetic origin, and authigenic quartz cementation blocks primary intergranular pores, exerting a significant negative effect on pore development. In contrast, the smectite-to-illite transformation promotes the development of interlayer micropores, leading to a good positive correlation between clay mineral content and micropore volume, as well as specific surface area. Organic matter abundance is the core controlling factor for the construction of micro–nano pore networks. This study clarifies the dominant mechanisms of pore development driven by organic–inorganic interactions in the DFS. Authigenic diagenetic quartz impedes pore development, while smectite-to-illite transformation promotes micropore formation. Organic matter abundance is the dominant control on the micro-nanopore system. This study lays a critical geological theoretical foundation for the exploration evaluation and target selection of shale gas in the Dalong Formation.