Investigation of Main Control Factors Governing Gas-Bearing Capacity in Deep Marine Shales: Insights from Quantitative Characterization of Quartz of Multiple Origins

Deep shale gas in western Chongqing is a critical successor to conventional resources, but its distinct enrichment mechanisms make sweet-spot identification—particularly of productive layers—significantly challenging. To address this, we developed an integrated approach combining high-fidelity gas-content testing under simulated high-temperature, high-pressure (HTHP) conditions with advanced mineralogical characterization using automated mineralogy (TIMA). Four exploration wells in comparable sedimentary-structural settings were analyzed to establish correlations between reservoir properties and gas content. Results show that the lower Longmaxi Formation in central-western Chongqing exhibits optimal reservoir quality, with high porosity, total organic carbon (TOC), brittleness, and gas content. A substantial free-gas fraction enhances recoverability. The reservoir's quartz-organic matter microfacies provides strong mechanical brittleness, adsorption capacity, and gas supply. High TOC and abundant authigenic microcrystalline quartz are key controls on gas accumulation. These findings clarify the geological drivers of deep shale gas enrichment and provide a direct basis for geology-engineering integration in sweet-spot optimization and development planning.