Sequence Stratigraphic, Resource Potential, and Global Cretaceous Event Linkage of the Shahezi Formation in the Xujiaweizi Fault Depression: New Insights from Well SK2

The Xujiaweizi Fault Depression in the Songliao Basin is a significant area for deep natural gas exploration, and the Shahezi Formation has been recognized as the primary hydrocarbon-source rock. This research integrates core, logging, and seismic data from Well SK2, the world’s first scientific drilling well to reach a depth of 7018 m and obtain 2624 m of continuous cores from the Shahezi Formation. The study aims to redefine the stratigraphic framework, resource characteristics, and sedimentary evolution of the formation in the Cretaceous period. The Shahezi Formation, dating from 118 to 112 Ma (mid-Aptian to early Albian), is divided into five third-order sequences (SQ1–SQ5). The upper section of SQ5 and SQ2 shows the highest potential for deep gas, featuring high-maturity Type III kerogen, 35 gas anomaly layers with a total thickness of 79 m, and a 59% proportion of dark mudstone. A three-stage sedimentary evolution model, including initial faulting, intense faulting, and contraction, is proposed, establishing a link between terrestrial sedimentation and global Early Cretaceous events (e.g., OAE1b). This research provides crucial insights for deep gas exploration and global marine–terrestrial sedimentary comparisons.