Controlling factors and models for hydrocarbon enrichment/depletion in Paleogene and Neogene,Bohai sea

Petroleum exploration has been carried out for more than 40 years in the Bohai sea,however,weak understanding for the hydrocarbon vertical-occurrence mechanism and controlling factors in this area has seriously restricted exploration programs.The present paper intensively investigated different hydrocarbon accumulations and controlling factors based on studies on faulting activities,evolutions of source rocks and regional caprocks in all the discovered oil fields across the area.The result showed that faulting activities during Neotectonism played the most important role in hydrocarbon accumulations and vertical occurrence.The potential conducting hydrocarbon migration along faults was probably dependant upon fault activity rate(FAR).Once FAR10m/Ma,little or none of hydrocarbons migrated along faults,in contrast,mass flux of hydrocarbons moved along faults when FAR25m/Ma.The faulting activity rate at the late stage,combined with active source rock distributions and caprock occurrence and together with their spatiotemporal match during Neotectonism had controlled hydrocarbon enrichment/depletion in the Paleogene or/and Neogene.Thus,four models were established on the basis of FAR,i.e.a Paleogene oil-enrichment model,a Paleogene and Neogene oil-enrichment model,a Neogene oil-enrichment but Paleogene oil-depletion model and a Neogene oil-depletion model.All the models are valuable in selecting payable zones or targets within both the Paleogene and Neogene of this area.