Structural Features Of Baxian Sag And Its Control To Hydrocarbon Accumulation

Baxian sag is an oil-rich sag in the eastern Jizhong depression of Bohai Bay basin.Based on continuous 3d seismic data,this paper use the existing oil and gas exploration data to analyze the structural characteristics and its control to oil and gas.There are four results.(1)Baxian sag,controlled by the Niudong fault,is a Cenozoic half-graben with faulting in west and overlap in east.The internal structure changes along with the geometric shape of Niudong fault.Niudong fault shows a series of striking NE-NNE,dipping SE fault terrace zone dipping east in north.These faults control the Paleogene half-graben migrating eastward,the wedge-shaped Paleogene layers thickness thin westward.In central,Niudong fault presents as listric fault,controling two deposition centers in north central and south central part.And in south,Niudong fault is characterized as brush structure,Paleogene sag shows depression structure in early stage and rifting structure in later stage.(2)Niudong fault shows a sectional activity in Paleogene,and activity strength migrates from south to north with time.There are mainly three periods: in Ek-Es~4 period,north-central segment present a stronger activity;in Es3-Es2 period,south-central and north-central segments became stronger;in Es~1-Ed period,the whole fault has strong activity while the north has stronger activity.The fault activities since Cenozoic may be divided into three phases: Eocene extensional activities,Oligocene extensional activities,and Neogene strike-slip activity,the fault systems can be divided into three types accordingly.There are differences in the ways and characteristics of fault activity in different periods.(3)Baxian sag underwent rifting stage in Paleogene and depression stage in Neogene-Quaternary.And the rifting stage is subdivided into three sub-rift screens: Ek – Es~4 period?Es3 – Es2 period and Es~1-Ed period.(4)Niudong fault controls two deposition-sedimentary centers in North and south of Baxian sag,and it control the evolution of depositional system in different evolution stages,further controls the distribution of source reservoir cap.The internal faults in Baxian sag control trap styles and distribution.