Sedimentation–diagenesis–tectonics coupling and its control on gas reservoir development in Sinian carbonates, western Deyang-Anyue Rift Trough, Sichuan Basin

Abstract

The Sinian Dengying Formation in the western Deyang-Anyue Rift Trough is a key target for deep carbonate gas exploration, yet its reservoir controls remain debated. Integrating core, thin-section, and geochemical data, this study clarifies the coupled mechanisms governing reservoir development. Results reveal that reservoirs predominantly occur in platform-margin and high-energy shoal facies, with pore systems comprising intercrystalline, dissolution, and fracture pores. Primary porosity is largely obliterated by deep-burial compaction and cementation, yielding an overall low-porosity, low-permeability matrix. However, structurally influenced platform-margin exposure zones and fracture-affected mound–shoal bodies outside strongly cemented fault cores locally contain higher-quality reservoirs because of dissolution and fracture-enhanced connectivity. Vertically, reservoirs are zoned: tight lower intervals transition upward into dissolution-enhanced, comparatively porous middle-upper sections. Critically, reservoir evolution is dictated by a “sedimentation–diagenesis–tectonics” coupling: sedimentary architecture and thickness define macroscopic reservoir distribution; compaction and cementation induce densification, while dissolution and fracturing create secondary pore-fracture networks. Hydrothermal activity superimposes a “dissolution-filling alternation,” drastically intensifying heterogeneity. This multi-scale, multi-stage coupling ultimately controls the pronounced spatial variability of the Dengying Formation reservoirs and provides a geological framework for screening favorable targets in deeply buried carbonate successions.