Development and exploration potential of large-scale carbonate platform-margin belts along the western margin of the Yangtze block

The western margin of the Yangtze block serves as a crucial hydrocarbon exploration zone, characterized by multiple large-scale platform margin belts developed from the Sinian to Permian systems, exhibiting superior geological conditions for forming high-abundance medium to large gas fields. To systematically investigate the sedimentary framework and developmental mechanisms of these multi-phase platform margins, this study comprehensively integrates seismic data from the 3D seismic survey, outcrop profiles, and newly drilled wells in western Sichuan area. The research focuses on analyzing the ocean-continent transition process and platform margin evolution patterns from the Sinian to Permian periods, with particular emphasis on gas enrichment laws and controlling factors. Key findings include: 1) identification of four superimposed platform margin belts in the Sinian Dengying formation (Dengying Group), Devonian, and Permian Qixia and Maokou formations. The Sinian Dengying platform margins were controlled by intracontinental rifting related to back-arc extension, with two-phase development closely linked to prolonged extension and intermittent exposure. Devonian platform margins were influenced by Paleo-Tethys Ocean expansion, characterized by high-energy facies deposition controlled by syn-depositional fault shoulders in passive continental margins, while Permian Qixia-Maokou high-energy facies show clear inheritance from Devonian counterparts. 2) The Dengying platform margins exhibit dual-source hydrocarbon supply from the Qiongzhusi and Doushantuo formations, with Devonian-Permian systems demonstrating a lower-generation-upper-storage reservoir formation model. Indosinian thrust faults and strike-slip faults serve as primary hydrocarbon migration channels, establishing a three-dimensional reservoir formation model featuring "proximity to hydrocarbon source centers, multi-layer enrichment, dynamic adjustment, and vertical accumulation". 3) Comprehensive evaluation reveals optimal source-reservoir-cap configurations in these large-scale platform margins, with predicted geological resources approaching 2 trillion cubic meters and significant exploration potential. This study systematically elucidates the developmental processes and formation mechanisms of multi-phase platform margins, providing crucial insights for exploring new frontiers in deep hydrocarbon exploration in the western Yangtze block.