| Liupanshan basin is located in the northeastern margin of the Tibetan Plateau,with Alashan block in the north,with Ordos block in the east,with Qilian block in the southwest,with Qinling orogenic belt in the southeast.It is formed in two tectonic units of the North China platform and Qinling geosyncline binding site of the Cenozoic superimposed basins.The basin is an important oil and gas exploration area in Northwest China,the unexplored favorable structural traps and stratigraphic traps in the region are important exploration targets.In order to study the geological structure and hydrocarbon accumulation in Liupanshan basin and the adjacent areas,through systematic collection,processing and interpretation of gravity and magnetic data in Liupanshan basin and its adjacent areas,the gravity magnetic anomaly in the area of different size of the moving average anomaly map,analytical continuation anomalies,derivative anomaly map and other conversion parameters anomaly maps were obtained,and combined with geological,drilling and seismic data,the gravity and magnetic fields of the basin were studied comprehensively.Inferred fault structure system in liupanshan basin,determined the distribution characteristics of the magnetic body,and inverted,the main density interface depth by the Park-Oldenburg method,At last,combined with petroleum geological features,basin oil and gas prospect area were predicted.The main achievements and conclusions are as follows:1)The Bouguer gravity in the study area is distributed abnormally.From west t o east its distribution pattern is low-high-low-high.The high and low gravity in the area reflects the tectonic pattern of basement uplift and depression.According to th e residual gravity anomaly reflected by different sizes of filter.It is concluded that the high and low gravity anomalies in the basin mainly reflects the local structure of the depression and the uplift area.Low gravity is mostly caused by the MesozoicCenozoic strata,high gravity is caused by the pre-Cenozoic stratum or pre-Cambrian ba sement uplift.2)It is suggested that fracture system mainly includes north-north-west,north-south and north-north-east in liupanshan basin,and North-North-West is the most developed,which isalso the main fracture of the basin,and it controls the distribution of stratigraphic and structural framework.3)Mesozoic and Cenozoic developed widely in Liupanshan basin,the lower boundary of the depth is different.In view of the overall distribution pattern,the high areas are embedded with lower ones.There are multiple subsidence centers in the basin,among which the Cenozoic and Mesozoic sediments of the Haiyuan depression,the Xingrenbao depression and the Hejiakouzi depression are stable,they're also thicker and larger.Mesozoic buried depth is larger in the Xingren and Haiyuan depression,which is about6000 m.Sedimentary strata are not evenly distributed in local uplift and depression.4)The magnetic body mainly developed in local area around the basin,it is not developed inside Liupanshan basin.It is inferred that the magnetic body around the basin is caused by the magmatic activity in the fault structure.5)Liupanshan basin can be divided into three first-order tectonic units,including the west uplift,central depression and the eastern slope,among which the central depression can be further divided into 7 secondary tectonic units,including Shagou step fault,Guyuan depression,Haiyuan depression,Tongxin depression,Xingrenbao depression,Lihuaping uplift and Hejiakouzi depression.The eastern slope can be further divided into two secondary tectonic units: Yaoshan-Tanshan uplift and Hongsibao shallow depression.Research shows that sedimentary formations is thick in Haiyuan depression,Guyuan depression,Xingrenbao depression and Hejiakouzi depression,which has a good source-reservoir-seal assemblage.The west and north of Haiyuan depression,east of Tongxin depression and Xingrenbao depression is the favorable exploration area of oil and gas. |
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