Fault System And Its Control On Oil-gas Reservoir In Bozhong Sag

Bozhong sag is in the middle of Bohai Bay basin which has wide area of distribution and is rich in petroleum,but its oil-gas exploration is in a low level.From this research,we are going to determine fault system characteristics and hydrocarbon transport system,summarize controlling effect on hydrocarbon accumulation of fault systems in Bozhong sag,and lay a foundation of further oil-gas exploration in Bozhong sag.In this paper,the basic characteristics of faults in Bozhong sag are discussed in details.And the hydrocarbon transport systems are also studied.Through accurate dissection of discovered oil-gas reservoirs,favorable factors for hydrocarbon accumulation are determined,as well as controlling effect on hydrocarbon accumulation of fault systems are summarized.This paper studies the Bozhong fault system in different times by using seismic measures,such as detecting coherent data volume and seismic profiles.Bozhong sag has experienced agent of extension and formed normal faults in Paleogene,in which strike-slip fault was formed by dextral strike-slip movement of Tan-Lu fault in Neogene.Over time faults evolve from one to assemblage,like branches.Fault size and fault grade decreases;fault continuity becomes worse;fault patterns evolves from the en-echelon,brush into parallel and oblique.Fault activity rate is calculated by thickness difference in two fault sides of synsedimentary fault and is used to study fault activity.The tendency of fault activity in Bozhong sag is in the form of “M+up tail”.The fault activity period of Bozhong area are E2s3,E3d3,E3d2,N1 g and N2 m,according to the comprehensive study on regional tectonic activity,formation cut by fault,fault activity and hydrocarbon reservoir formation period.This paper studies deeply on accurate dissection of discovered oil-gas reservoirs,and summarizes hydrocarbon migration modes.In Bozhong sag,hydrocarbon migration is divided into three kinds: fault passage system,step faults-sandstone passage system and surface of unconformity-fault-sandstone passage system.By counting oil-gas reservoirs influencing factors of 237 reservoirs in Bozhong area,we confirm that the fault has effect on hydrocarbon accumulation: major faults connect source rock and are vertical hydrocarbon transport systems;a large number of secondary faults in Neogene distribute oil and gas again,expand oil and gas distribution and form a lot of structural trap,major faults and secondary faults constitute hydrocarbon transport system like branches.If formation dip is same as fault,secondary faults will transport hydrocarbon,or shelter oil and gas.Those faults,whose fault activity rate is 0-30m/Ma,SGR>0.3,Rm>0.35,fault patterns are oblique,parallel,en-echelon,Y-shaped,flower shaped,flower liking and stepladder are favorable for hydrocarbon accumulation.At intersection of faults,concave place,fault has good shelter and benefits for hydrocarbon accumulation.Fault sealing is the major factor for hydrocarbon accumulation,hydrocarbon migration is second,then is fault activity rate,fault type and fault sheltered type.