Study On Basin Architecture And Tectonic Evolution Of Paleogene Shahejie Period In Cangdong Sag

Bohai Basin is an important continental extensional faulted basin in the east of China,there are abundant petroleum and gas resources in this Basin,and this place is also the important economic and politic area of China.Cangdong Sag for this study is located in the middle of Bohai Basin and in the south area of Huanghua depression,the basin type of Cangdong Sag in Shahejie Formation Sedimentation Period is fault downthrown basin,and the basin architecture and tectonic evolution in Cangdong Sag is importantly influenced by the tectonic activity of Cangdong Fault and Xuxi Fault.This Study of Cangdong Sag in Shahejie Formation Sedimentation Period is mianly based on 3D seismic interpretation,related seismic data and logging data of important well in researching area,and also based on previous division of the second-order tectonic sequence of the Shahejie Formation in Cangdong Sag.Therefore,for this study,Shahejie Formation had been divided into five third-order tectonic sequences,which are Es₃^x,Es₃^z,Es₃^s,Es₂ and Es₁.For the basin architecture analysis and basin tectonic evolution in Cangdong Sag,tectonic units dividing is the previous basic task.In this study,tectonic units dividing is mainly based on the layout of uplift and downthrown and strata thickness distribution of inner basin.Cangdong Sag Area had been divided into three positive tectonic units,which are Kongdian raised tectonic belt,Cangshi skirt and nose like tectonic belt and Xiaoji Duanliubo faulted tectonic belt,and three negative tectonic units,which are Cangdong Subsag,Nanpi Subsag and Changzhuang Subsag.Based on the results of this study and former related study,some ponits can be concluded:?1?Based on the interpretation of the 3D seismic body in the researching area,get the interpretated across seismic sections of the study area,and analysis the basin architecture.By observing the geometry of stratigraphic distribution shown in the seismic profiles of various sections within the basin and the relationship between the strata and faults,analyze the basin architecture,and the conclusion is as follows:The basin architecture in Cangdong Sag is characterized by different in east-west areas and different in north-south belts,from the view of perpendicular to the strike of the basin,the overall basin architecture of cangdong sag is a faulted downthrown basin architecture.?2?Based on the interpretation of the 3D seismic body in the researching area,get the interpretated across seismic sections of the fault in researching area,and analysis geometry of fault.By observing and comparing the geometry of fault distribution in the seismic sections within the basin,the association relationship between all levels of faults,and the relationship between faults and strata,analyze the fault geometry in the basin,and the conclusion is as follows:The main faults in Cangdong Sag are Cangdong Fault,Xuxi Fault,Kongdong Fault and Kongxi Fault,and the main structural forms are planar,listric and zigzag,etc.,and the structure of the two boundary faults are obviously characterized by segment differences.?3?According to the statistical method of fault fall,analysis fault activity,the magnitude of fault fall value directly reflects the variation of fault tectonic activity.By observing and comparing the changes and differences of the fault fall of the major and subordinate faults in the basin in each section and period,the activity of major faults and subordinate faults in Cangdong Sag is analyzed,and the conclusion is as follows:In the Cangdong Sag,the strongest period of fault activity is the sedimentary period of the Third member of Shahejie Formation,and the sedimentary period of the First member of Shahejie Formation is gradually weakened.The most active fault areas are the northern part of Cangdong Fault and the northern and southern parts of Xuxi fault.?4?Using the plane mapping module of seismic software,made the isopachic map of the three-order tectonic sequence of Shahejie Period in Cangdong Sag,and using the logging data and other data in the researching area for correction,then by observing the thickness distribution of the basin strata in the Shahejie Period analysis the paleotectonic framework of the basin.By observing and comparing the thickness variation and distribution of strata in Cangdong Sag in each period,the migration of the sedimentary center of strata,and the relationship between the sedimentary center of strata and the major faults in the basin,the basin tectonic evolution process of Shahejie Period in Cangdong Sag is analyzed from the perspective of plane observation,and the conclusion is as follows:The sedimentary center of the basin in the Cangdong Sag Area of Shahejie Period and the Kongdian Uplift in the north of the basin are obviously controlled by the fault activity,which reflects that the tectonic evolution of the basin is a process in which the positive extension gradually weakens and the strike-slip extension gradually increases.?5?Through the balance section technology,the balance section is drawn in the direction of the vertical of basin strike of Cangdong Sag,then by observing the equilibrium profile analysis the tectonic evolution of Shahejie Period of the basin.Through the observation and comparison of the equilibrium section of each section of Cangdong Sag Basin in Shahejie Formation Sedimentation Period,the basin tectonic evolution process of Shahejie Formation Sedimentation Period in Cangdong Sag is analyzed from the view of perpendicular observation,and the conclusion is as follows:In Shahejie Formation Sedimentation Period,the central part of the basin in cangdong sag has the strongest extensional effect,and the extensional effect gradually weakens to the north and south sides,and the strongest extensional effect is in the sedimentary period of the third member of Shahejie Formation,while the extensional effect gradually weakens in the sedimentary period of the first member of Shahejie Formation.Based on other research results of this study,it can be concluded that the basin tectonic evolution of Cangdong Sag during Shahejie Formation Sedimentation Period changed from positive extension to strike-sliping gradually.