Late-stage hydrocarbon accumulation and enrichment in the Huanghekou Sag,southern Bohai Sea

The Huanghekou Sag is one of the major oil-bearing areas in the offshore Bohai Bay Basin and is characterized by late-stage accumulation.The Easy Ro% model is used to simulate the hydrocarbon generation time of source rocks,showing that the major source rock has matured since 5.1 Ma.The analysis of the migration system reveals that hydrocarbons in the Huanghekou Sag migrate through faults and fractures which are the main pathways.The analysis of reservoir inclusions shows that the main charge time is 5.1 Ma or later.The late-stage accumulation in the Huanghekou Sag is characterized by late quick hydrocarbon generation,late vertical migration through faults,near-source accumulation and late charge.The main factors controlling the hydrocarbon enrichment are the regional reservoir-cap assemblage of the Shahejie Formation and lower member of the Minghuazhen Formation,dominant migration pathways,and traps formed by Neotectonic movement.Paleogene overpressured reservoirs with near source rocks and Neogene shallow water deltaic reservoirs are the most important hydrocarbon accumulation models in the Huanghekou Sag.