Control of source–migration–trap coupling on hydrocarbon accumulation in the Shahejie Formation, Qikou Sag, Bohai Bay Basin

Understanding the spatial heterogeneity of hydrocarbon accumulation in continental rift basins remains a major challenge in petroleum geoscience because the relative roles of hydrocarbon supply, migration pathways, and trap effectiveness are often poorly constrained. Focusing on the lower section of the first member of the Shahejie Formation (Es 1 L ), this study formulates a hierarchical control framework that synthesizes source supply, migration pathways, and trap effectiveness to elucidate the mechanisms of hydrocarbon accumulation. Integrating three-dimensional (3D) seismic, well logging, and geochemical data, this study delineates the distribution of effective source rocks, systematically characterizes vertical and lateral hydrocarbon migration pathways, and identifies the development locations of effective traps in the target interval combined with the evaluation of fault lateral sealing capacity to carry out coupled hydrocarbon accumulation analysis of source-migration-trap. A total of 18 migration pathways and 24 effective trap locations were identified. The hierarchical framework identifies source-rock expulsion intensity as the first-order control, defining the upper limit of hydrocarbon supply; migration-pathway architecture as the second-order control, regulating hydrocarbon focusing, dispersion, and charging efficiency; and trap effectiveness, particularly fault sealing capacity, as the third-order control, governing hydrocarbon preservation and final filling degree. The results indicate that hydrocarbons mainly accumulate in zones with optimal matching of source-migration-trap elements, characterized by sufficient hydrocarbon supply from source rocks, unobstructed migration pathways and effective trap conditions. Production-testing results from Well BS-4, located within one of the predicted favorable hydrocarbon accumulation zones, provide field-based support for the proposed coupling framework. The proposed hierarchical source-migration-trap framework provides a process-based approach for evaluating favorable hydrocarbon accumulation zones in lower-source upper-reservoir petroleum systems of mature faulted basins.