Abstract: Currently, breakthroughs have been made in two exploration targets of the Qiongzhusi Formation in the Sichuan Basin (organic-rich shale and organic-lean shale), demonstrating good exploration potential. To clarify the sequence development pattern and its control on reservoir quality, this study utilized outcrop-drilling-seismic data, geochemistry, paleobiology, and other information to identify five third-order sequence boundaries and four third-order sequences within the Qiongzhusi Formation shale strata in the southern Sichuan Region. SQ1 corresponds to the bottom of the first member of the Qiongzhusi Formation, distributed only in the core of the intracratonic sag; SQ2 and SQ3 correspond to the upper part of the first member and the second member of the Qiongzhusi Formation, distributed on the western side and within the intracratonic sag; SQ4 corresponds to the third member of the Qiongzhusi Formation, widely distributed across the entire intracratonic sag. The sequence filling succession reflects the process of gradual filling and leveling the intracratonic sag. The transgressive systems tract (TST) is characterized by the development of black shale with high total organic carbon, high brittleness, and relatively high porosity. The deposition thickness is large within the intracratonic sag and gradually thins towards both sides. The regressive systems tract (RST) is dominated by organic-lean shale with strong heterogeneity. Only the RST of SQ3 on the western side of the intracratonic sag exhibits high porosity and brittleness, with good gas test results. This research holds significant guidance for predicting favorable exploration targets within the sequence framework.

Key words: Southern Sichuan Basin, Qiongzhusi Formation, shale, sequence stratigraphy, reservoir characteristics