Study On Structural Framework Of Qinnan Sag And Its Adjacent Areas In Bohai Basin Based On Satellite Gravity Anomaly

Bohai Basin is the area with the most offshore oil and gas fields found in China.Qinnan Sag,as a potential oil and gas-rich sag in Bohai Basin,has high exploration potential.The faults in Qinnan Sag and its adjacent areas are developed and the tectonic units are complex.The study of its tectonic framework is of great significance and application value.In this paper,the Bouguer gravity anomaly is obtained by correcting the gravity anomaly of topography and seawater from the satellite gravity anomaly.The plane position and apparent depth of faults,Cenozoic thickness and tectonic unit distribution in Qinnan sag and adjacent areas are obtained by using normalized total horizontal derivative vertical derivative(NVDR-THDR),Werner deconvolution,minimum curvature potential field separation and rapid inversion of gravity field of double interface model.Combined with geological and geophysical data,the distribution characteristics of main faults and tectonic units in the study area were analyzed.The results show that the faults in Qinnan sag and its adjacent areas are mainly NNENEE trending Tancheng-Luzhou fault its eastern branch extends about 135 km,and the apparent depth is 5-20 km,and the western branch extends about 200 km,and the apparent depth is 5-20 km.The NW-trending Zhangjiakou-Penglai fault zone extends about 107 km,and the apparent depth is 5-10 km.The NW-trending Qinhuangdao-Lushun fault extends about 180 km and the apparent depth is about 5-20 km.The Qinnan No.1 fault is nearly EWNEE trending,with an extension length of about 120 km and apparent depth of 5-20 km.The NEE-trending Qinnan No.2 fault extends about 131 km,with an apparent depth of 10-20 km.The structural units in the adjacent area include Liaoxi sag,Bozhong sag,Laoting sag,Shijiutuo uplift and Qinnan uplift,which are alternately distributed in NE and NEE directions.The thickness of Cenozoic is between 1 and 11 km.According to the processing results,the sag on the west side of Qinnan sag is classified into Laoting sag,and other structural units are modified.The Cenozoic sediments in the eastern subsag of Qinnan sag are the thickest,followed by the southeastern subsag and the thinnest in the western subsag.The distribution of tectonic units in Liaodong Bay Depression is NE-trending three sags and three uplifts,Bozhong Depression is NEE-NE-trending two sags and two uplifts,and the western Bohai Sea is NWW-trending two sags and one uplift.The northern part of the Bohai Sea is distributed in three sags and three uplifts.The results of this study on the fault distribution,structural unit distribution characteristics of Qinnan sag and its adjacent areas can provide geophysical support for oil and gas exploration in Qinnan sag and its adjacent areas.