Sequence-Stratigraphic Architecture and Intraplatform Reef–Shoal Evolution of the Upper-Permian Changxing Formation: Implications for Reservoir-Quality Prediction and Efficient Hydrocarbon Exploration

Marine intraplatform reef–shoal systems are important carbonate reservoirs. Understanding their evolution and reservoir response is critical for reducing exploration uncertainty and supporting more efficient hydrocarbon exploration. This study integrates field outcrops, cores, thin sections, well logs, integrated prediction-error filter analysis (INPEFA), petrophysical data, and 3D seismic data to establish a sequence-stratigraphic framework for the Upper Permian Changxing Formation in the central Sichuan Basin. The formation is divided into two third-order sequences and five fourth-order sequences (ssq1–ssq5). Reef–shoal bodies occur mainly in highstand system tracts and progressively expand from ssq2 to ssq5, showing multi-stage stacking and strong lateral heterogeneity. Palaeogeomorphic highs favor the development of bioclastic shoals and local reefs. Reservoirs occur mainly in bioclastic shoals and reefs, with pore systems dominated by dissolution pores, vugs, intercrystalline pores, and fractures. Sequence architecture primarily influences reef–shoal development stages, whereas palaeogeomorphology contributes to their spatial differentiation. Multi-stage stacking influences reservoir scale, while diagenesis plays a major role in determining reservoir quality. These results provide a geological basis for favorable reservoir prediction, reduced geological uncertainty, and more efficient hydrocarbon exploration.