Multi-stage fault systems and their control on hydrocarbon accumulation in the Nanpu Sag, Bohai Bay Basin, China: insights from OVT seismic data

The evolution of fault systems exerts a critical control on hydrocarbon migration and accumulation in rift basins. This study utilizes high-resolution OVT (Offset Vector Tile) seismic data to decipher the multi-phase tectonic evolution of the Nanpu Sag, Bohai Bay Basin, and to assess its impact on hydrocarbon enrichment. The main research outcomes are as follows: First, a six-fold genetic classification scheme for fault systems (Types A–F) is established, based strictly on their activity timing and mechanical properties across three distinct tectonic stages: early NW–SE extension, middle SN-oriented extension, and late NW–SE transtension. Second, the critical coupling between fault activity and hydrocarbon charging timing is clarified. The long-lived Type E (middle-to-late phase) and Type F (all-phase) systems are identified as the dominant vertical conduits during key accumulation periods, effectively channeling hydrocarbons from deep sources to shallow reservoirs. Conversely, Types A, B, and D faults, inactive during these periods, act as effective lateral seals in deep strata, defining significant yet underexplored plays. Finally, these findings provide a predictive framework for exploration, highlighting shallow targets near Type E/F fault intersections and deep structural traps sealed by Type A/B/D faults. This study establishes a clear genetic link between fault evolution and hydrocarbon migration pathways, offering a transferable model for fault-controlled hydrocarbon exploration in similar rift basins.