Research On The Fault Activity Of Central Huanghekou Sag And Their Controlling On Hydrocarbon Migration And Accumulation

The Central Huanghekou Sag is a petroliferous sub-sag in Bohai sea area,and many large and medium-sized oil and gas fields and hydrocarbon structural traps have been discovered.However,the faults in the study area are well developed,and the studies on their controlling on hydrocarbon accumulation are controversial.Meanwhile the relevant studies on oil and gas migration and transportation are still weak.Fault description,fault static elements and fault activity are important research contents to judge the hydrocarbon transportation and accumulation,and to guide oil and gas exploration.Based on drilling wells and 3D seismic data,the detailed description,fault assemblage,fault activity,transporting and sealing were systematically analyzed with oil and gas reservoirs discovered to summary the faults' controlling on hydrocarbon accumulation.The research statistics show that most faults in Central Huanghekou Sag are normal ones.The faults are oblique and parallel on the plane,and consist of "Y" and cabbage types vertically,which are beneficial for hydrocarbon accumulation.Boundary strikeslip faults have a controlling effect on the internal faults development in the sub-sag and high-intensity point movement of each faults in different periods,resulting in different fault activity in different areas.The steep slope of the sub-sag is controlled by the eastern strike-slip fault,and the other areas are controlled by the central branch strike-slip fault.The faults' activity plays a controlling role in the vertical migration of crude oil.The oil has strong vertical migration ability with the fault activity rate more than 10m/Ma,weak between 5.6 m/Ma and 10m/Ma,and is sealed by the fault with the activity rate less than 5.6m/Ma.The SGR and ratio of caprock thickness via fault throw are good parameters to evaluate lateral sealing ability of fault.When the ratio greater than 0.6 and SGR greater than 0.5,the crude oil is sealed by the fault for its vertical migration,and mainly migrates in horizontal.On the contrary,vertical migration is dominant with the ratio less than 0.6 and SGR less than 0.5.With the fault activity,hydrocarbon transport system and the existing oil reservoirs,the hydrocarbon accumulation pattern of the steep slope in the north is dominated by vertical penetrating type while the southern gentle slope has two patterns,which are stepped and gentle types.