| The Baiyun sag is a giant hydrocarbon-generation sag in the Pearl River Mouth Basin where a number of gas reservoirs have been discovered.The breakthrough has been made in oil exploration in northeastern Baiyun sag,showing great hydrocarbon exploration potential.As an important structural element in petroliferous basins,faults are closely related to the formation and distribution of hydrocarbon reservoirs.Diversified faults,because of multi-stage extension,in northeastern Baiyun sag played an important role in hydrocarbon generation,migration and accumulation.In this paper,based on 3D seismic data,drilling data and well logging data,petroliferous basin analysis is employed to investigate the fault deformation style and its effects on hydrocarbon migration and accumulation,and establish the hydrocarbon accumulation mode in northeastern Baiyun Sag.Results show that single fault can be divided into plate and listric style and multiple faults formed domino,conjugate,“Y”-pattern and shovel fan combination in profile.On the plane,single fault is shown as rectilinear figure,arc and “S”-shaped,multiple faults are formed into paralleled combination,en echelon combination,brush combination,forked combination.According to the distribution of extensional structure and the combination of fault blocks,many typical structural styles can be identified,such as the horst,graben,half-graben,tilted fault block and fault terrace.In this paper,faults have been divided into three types according to its influence on hydrocarbon accumulation.The first kind is oil source fault,connecting source rocks and traps and faulting in the hydrocarbon generation and expulsion period(10.5Ma)heavily,which is beneficial to the vertical transport of hydrocarbon.The second kind is reservoir-controlling fault,constructing structural traps and sealing the hydrocarbon;The third kind is other fault,which have lower correlation with hydrocarbon accumulation.In addition,the section morphology of the faults in the study area includes three types: planar,concave and convex and the convex section has best capability carrying hydrocarbon to migrate.Faulting zone is a complex three-dimensional geological body with heterogeneous structures,the interior of which can be divided into different structural units with different properties,such as low-permeability slip damage zone,high-permeability induced fracture zone.The fracture zone of hanging wall of fault is obviously stronger which causes faults to have dual nature differences in transporting and sealing.Besides,quantitative calculation of shale gouge ratio and normal stress on fault plane indicates faults have good sealing capacity.The oil source fault and structure ridge of sand body control the dominant pathway for hydrocarbon migration in northeastern Baiyun Sag.Fault block trap of footwall constructed by backward faults related to formation direction of dip is benefited for the hydrocarbon accumulation and preservation.The hydrocarbon migration is an inherited process that the most of the early oil pathways subsequently acted as migration pathways for lately-formed gas,forming the distribution pattern of “oil in the inner and gas in the outer” in northeastern Baiyun Sag. |
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