Pore Structure Characteristics of the Jurassic Dongyuemiao Shale Reservoir in the Fuxing Area, Sichuan Basin

XRD analysis reveals that the shale mineral composition in the study area is dominated by clay minerals (15.21%–79.68%, avg. 59.88%), primarily illite, with subordinate chlorite and kaolinite, followed by quartz (10.24%–45.84%, avg. 21.59%). Total organic carbon (TOC) ranges from 0.391% to 2.19%, with kerogen types predominantly sapropelic-humic (Type II₂) and humic (Type III). Vitrinite reflectance (R₀ = 1.52%–1.54%) indicates high thermal maturity. Pore systems are dominated by parallel-plate interlayer clay pores, supplemented by calcite intraparticle pores, interparticle pores, and organic-hosted pores. Based on pore size classification, mesopores (2–50 nm) contribute the largest proportion to total pore volume, followed by macropores (>50 nm) and micropores (<2 nm). The influence of mineralogy and TOC on pore structure varies by lithofacies: in clay-rich shales, clay minerals and TOC synergistically enhance pore development, while in silty shales, quartz content exhibits a positive correlation with pore volume, likely due to grain-supported frameworks preserving primary porosity.