| The Bohai Sea area is part of the Bohai Bay basin and is an important oil and gas enrichment area.In recent years,there have been significant breakthroughs in oil and gas exploration in the Bohai Sea area,which is closely related to the rich fault system in the Bohai Sea area.The NW trending fault system in the Bohai Sea area mainly includes the Bohai section of the NW trending Zhangjiakou Penglai fault zone,the NW trending concealed Qinhuangdao Lushun fault zone,and the NW trending shallow faults in the basin.Based on a thorough investigation of previous studies on the NW trending fault system in the Bohai Sea area,combined with relevant seismic and geological data,this paper conducts research on the structural characteristics of NW trending faults,determines the differences in activity,and clarifies the control effect of NW trending faults on oil and gas.The research results show that: 1)The main branch faults in the Bohai section of the NW Zhangjiakou Penglai fault zone are mainly distributed in reverse S-shaped,arc shaped,and linear shapes in the plane;The planar combination styles are oblique,comb,and feather combination styles.In the section,the single fracture is mainly in the form of plate and shovel;Multiple fault combinations form Y-shaped,negative flower shaped,and flower like structures.As boundary faults,NW trending faults mainly control three types of hydrocarbon rich sag structures:tensile single fault type,tensile oblique intersection type,and strike-slip tensile classification type.2)The branch fault in the Bohai section of the NW Zhangjiakou Penglai fault zone has the strongest activity during the sedimentary period of the third member of the Shahejie Formation,followed by the activity of the Dongying Formation.The overall activity rate of the Paleogene fault is greater than the activity rate of the Neogene.Using the scatter plot and broken line diagram,it can be found that the fault activity is positively correlated with the thickness of the source rock.3)Based on previous research results and plate dynamics,the mechanism of sinistral strike-slip along the NW Zhangjiakou Penglai fault zone is discussed.The Zhangjiakou Penglai fault zone and the Qinhuangdao Lvshun fault zone form the boundary between the north south division of the Bohai Sea area and superimpose the strike-slip action of the NE trending Tanlu fault,resulting in differences in the tectonic pattern of each region.Through comparison of current equilibrium profiles,it is believed that the strike-slip action of the Zhangjiakou Penglai fault zone gradually increases from west to east.4)The Bohai Sea area has developed a large discrete structural transition zone and a local structural transition zone.As a primary transition zone,the Zhangjiakou Penglai fault zone played a controlling role in the distribution of early sedimentary systems,hydrocarbon source rocks,and magmatic rocks in the Bohai Sea area.As a secondary local structural transition zone,NW trending faults have played a role in sealing and migrating oil and gas in the JZ25-1 oil and gas field and the Chengbei Kendong structural transition zone research area.In the QHD22-3 structural research area,NW trending faults control the development of fault block traps,while the exploration potential of No.1 fault block controlled by NW trending faults in T8 reflector is the largest.5)NW trending faults have a poor matching degree between early Paleogene activity and oil and gas accumulation periods,and have a good matching degree with the development of hydrocarbon source rocks,which is conducive to oil and gas migration;The relatively weak activity of the fault in the Neogene is conducive to the dominant accumulation of oil and gas in the shallow layer and late reservoir formation. |
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