Western Sichuan is located in a complex foreland thrust system, where intense multi-stage tectonic deformation makes hydrocarbon preservation a critical control on accumulation and exploration success. Focusing on the Middle Permian strata, this study aims to systematically evaluate hydrocarbon preservation conditions and clarify their spatial variability. Based on integrated seismic interpretation, formation water geochemistry, pressure data and regional geological and exploration information, a multi-indicator evaluation framework was established, incorporating tectonic deformation intensity (fault distance and fault development), exposed strata, caprock integrity and formation water characteristics. The results reveal a clear zonation of preservation conditions across western Sichuan. Near the Longmenshan fault front, dense faulting, severe caprock destruction and low-salinity NaHCO₃–Na₂SO₄-type formation water indicate an open system with poor preservation. In the basin–mountain transition zone, fault activity weakens and partial caprock preservation remains, accompanied by moderate-salinity mixed NaHCO₃–CaCl₂ water, reflecting intermediate preservation. Towards the basin interior, structures become stable and closed, regional gypsum–mudstone caprocks are well developed, and high-salinity CaCl₂-type brines dominate, indicating long-term sealed systems and favourable preservation. These conditions are confirmed by multiple high-yield gas discoveries, including the Pingluoba-1 well with a tested gas flow of 66.76 × 10⁴ m³/d. The proposed multi-indicator evaluation method and preservation zonation provide a robust geological basis for optimising exploration strategies in complex foreland basins such as western Sichuan.

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Multi-Indicator comprehensive evaluation of middle Permian hydrocarbon preservation conditions in Western Sichuan and its exploration significance