Late Cenozoic Faults and Shallow Oil Accumulation in the Nanpu Sag

The Nanpu Sag, located in the north part of Huanghua Depression of Bohai Bay Basin, is a Cenozoic petroliferous extensional sag, the shallow oil reservoirs have great exploration potential. Former exploration suggested that there is complex relationship between Late cenozoic faults and hydrocarbon accumulation, but there is no detailed discussion. Based on the structural interpretation of 3D seismic data, the Late Cenozoic fault characters including typical fault configuration in profile and fault arrays in plane are analyzed, furthermore, the formation mechanism of the faults is discussed. It is concluded that late Cenozoic faults were formed by extension other than strike-slip movement, which was controlled by the mechanism of pure shear in the lower crust during the period. In addition, the relationship between Late Cenozoic faults and shallow hydrocarbon accumulation is discussed, it indicates that the faults controlled the formation of shallow closures and constituted the effective hydrocarbon pathways connecting deep source rock and shallow traps.