Fault Characteristics And Its Effects On Hydrocarbon Migration In The Shinan Middle Zone,Bohai Basin

Located in the middle of the Bohai Sea,the Shinan middle zone is surrounded by the Shijiutuo uplift,427 structural belt,Bozhong sag and 428 structural belt.It is a transition area where the oil and gas migrate from the Bozhong sag to the Shijiutuo uplift.The abundant hydrocarbon shows and great exploration potential is closely related to the abundant fault system developed since Cenozoic,Based on drilling data,logging data and 3D seismic data,this paper clarifies the development characteristics,conduction and sealing capabilities of the faults in the Shinan middle zone.Besides,the influence of faults on the migration paths of the oil and gas is defined.The research results show that the boundary faults in the study area are mainly shovel and slope styles on profiles,while small and medium faults are mainly plate and shovel style.Multiple faults are combined to form structural patterns such as "X","Y",and stepped types.On the plane,it is found that the faults are distributed differently in number,strikes and scales.The shapes of a single fault changed from straight,arc,and "S" style to straight style.The combination of multiple faults changed from broom style to parallel style.Through calculating fault activity rate and compiling balanced cross section,the activity characteristics of faults in the Shinan middle zone present as "strongweakness-strong",The main periods of activity were Shahejie,Dong-3 member,and from Ming-1 member to Quaternary sedimentary periods.The oil source fault is determined according to the relationship between the fault and hydrocarbon accumulation.It connects source rocks and traps,and activity occurs during oil and gas charging and its rate reach 25m/Ma,which can effectively transport oil and gas.The vertical conductivity of oil source faults is not only related to the activity rate in the accumulation period,but also to the fracture combination style and section morphology.The lateral migration of oil and gas depends on the displacement pressure of sand body.When the displacement pressure of fault zone is greater than the displacement pressure of sand body,oil and gas can migrate laterally.Due to the development of the "Y" type combination pattern in the study area,the main fault communicates with the oil source and transports oil and gas vertically,and the shallow and secondary faults distribute oil and gas again.Oil and gas mainly transported in "Z" shape or �flower� shape along faults and fault sand body transport system,forming the oil and gas migration mode of vertical transportation and accumulation from the near-source.