The formation mechanism of high-quality clastic rock reservoir controlled by coupling of “structure-lithofacies-fluid” in the foreland thrust belt in northern Kuqa, Tarim Basin, Northwestern China

The formation mechanisms of deep high-quality reservoirs in the Dibei area of Kuqa Depression foreland thrust belt were investigated through an integrated multidisciplinary approach combining petrographic analysis (thin section and cathodoluminescence microscopy), geochemical characterization (fluid inclusion microthermometry, stable isotope analysis) and structural modeling (2D finite element simulation). Systematic analysis reveals that the Ahe Formation reservoirs exhibit superior storage capacity characterized by: (1) high fracture density (0–8 m −1 , based on imaging log interpretation and core analysis), (2) intensive feldspar dissolution (resulting in up to 5% porosity enhancement, derived from thin section point counting-derived), and (3) limited authigenic clay mineral content (<3 vol%, thin section point counting-derived). Reservoir heterogeneity is mechanistically controlled by structural-lithofacies-fluid interactions, with optimal reservoir development occurring in sandstone-mudstone interbeds of back thrust structures. These units display composite pore networks composed of dissolution pores (50–500 μm) interconnected by shear-induced microfractures (aperture: 5–15 μm). Two-dimensional finite element simulations demonstrate that differential deformation between ductile lithofacies (mudstones and coals) and brittle sandstones promotes fracture proliferation in interbedded sequences, with increasing fracture density by 40%–60% compared to massive sandstone units. Organic acid migration induces LREE-MREE enrichment in calcite and kaolinite, coupled with depleted δ 13 C (−15.2‰ to −9‰) and δ D (−96.8‰ to −84.1‰) values, indicative of redox-driven diagenetic alteration. Open fracture networks in shear-tension zones (mid-upper sections of back thrust structures) provide effective migration pathways for organic acids, establishing localized open geochemical systems that drive feldspar dissolution while inhibiting authigenic clay precipitation (kaolinite <0.5 vol%, illite <1 vol%). Conversely, weakly deformed opposing thrust structures in compression-dominated regimes exhibit reduced fracture connectivity (aperture <5 μm), limited dissolution (dissolution porosity <3%), and pervasive pore-filling cements (authigenic quartz >1 vol%, kaolinite >1 vol%), collectively degrading reservoir quality.