Integrated Lithofacies, Well-Log, and Seismic Identification and Sedimentary Evolution of Local Intraplatform Reef–Shoal Bodies in the Changxing Formation, Pengxi–Wusheng Area, Sichuan Basin

Abstract

Studies of Upper Permian Changxing Formation reef–shoal bodies in the Sichuan Basin have mainly focused on platform-margin belts along the Kaijiang–Liangping trough. The sequence position, diagnostic criteria, and spatial configuration of local intraplatform high-energy bodies remain insufficiently constrained. Using Well Pengshen 10 as the key well, this study integrates core, thin-section, log, wavelet, INPEFA, 3D seismic, RMS, and well-tie evidence. Three sequence boundaries, SB1, SB2, and SB3, divide the Changxing Formation into Sq1 and Sq2. High-energy reef–shoal deposition is concentrated in the highstand systems tract of Sq2. In Well Pengshen 10, the high-energy interval consists mainly of sponge framestone and bioclastic grainstone modified by dolomitization, dissolution, and fracturing. Some intervals show continuous low gamma-ray responses. Seismic profiles show a localized body with mound-shaped to lenticular geometry and weak internal reflection continuity. RMS anomalies are patchy in map view. Well-tie sections indicate that this body overlies platform-interior deposits and is separated from the continuous platform-margin belt to the east. These observations define it as a local intraplatform reef–shoal complex. The published results of gas tests demonstrate industrial gas deliverability at Well Pengshen 10. Integrated lithofacies, gamma-ray, and seismic-geometry constraints can therefore help identify comparable intraplatform targets beyond continuous platform-margin belts.