The control of fault-caprock configurations on hydrocarbon accumulation in the Pinghu Slope Belt of the Xihu Depression, East China Sea Shelf Basin (ECSSB)

Significant progress has been achieved in Paleogene hydrocarbon exploration in the Pinghu Slope Belt of the Xihu Depression, but the mechanisms by which fault-caprock configurations control differential accumulation remain unclear. Using 3D seismic interpretation, geochemical data, fault activity analysis, and fluid-inclusion geochronology, this study investigates the multistage evolution of the Pinghu Fault (F1) and its coupling with caprock development in governing hydrocarbon migration. The results indicate that the Pinghu Slope Belt has excellent source rock conditions, and the geochemical characteristics of oil and gas suggest that hydrocarbon accumulation is characterized by near-source hydrocarbon charging. F1 evolved from multiple isolated segments into a unified fault plane through lateral and dip linkage, followed by late-stage segmented reactivation. Source rocks reached peak hydrocarbon generation by the end of the Miocene, with two key charging events at ∼15 Ma (local) and ∼5 Ma (regional). Pre-Late Miocene dip linkage and subsequent reactivation provided critical vertical migration pathways during peak generation. Although thick mudstone caprocks occur in the Pinghu Formation, faulting has disrupted their continuity. Analysis of fault-caprock configurations shows that seal integrity is lost when residual thickness falls below 63.6 m, while fault throws under 100 m reduce accumulation potential near faults. Under a multiphase tectonic background, the coupled fault-caprock sealing capacity plays a critical role in hydrocarbon migration and vertical distribution. This provides important insights for predicting exploration targets in faulted basins.