Structural Modeling Of The Middle Segment Of The Western Margin Of Ordos Basin

The middle segment of the western margin of Ordos Basin is located at the south and north of the conversion zone of the western margin of the basin.In recent years,many high-yielding industrial oil wells have been found in the Yanchang Formation and Yan'an Formation in the middle segment of the Western margin of Ordos Basin,showing a large potential for exploration.The geologic conditions are complex and the structural styles are changing.It has been found that the reservoirs are closely related to fault and structure,but the nature,distribution characteristics and structural models of the structure and fault are not clear.In this paper,the middle segment of the Western margin of Ordos Basin is selected as the research object,based on the theory of fault-related folds,geophysics,sedimentary petrology and structural geology,a large number of high-density two-dimensional seismic data and three-dimensional seismic data,drilling data,field outcrop profile and logging data are used.The structural characteristics of the study area,the structural characteristics of different fault zones and the tectonic evolution of different tectonic zones and their controlling factors are studied in detail,so as to establish different structural models of the middle segment of the Western margin of Ordos Basin.The main achievements are as follows:(1)According to the characteristics of unconformity development,the whole study area is divided into five structural layers:the Neoproterozoic tectonic strata,the Lower Paleozoic tectonic strata,the Upper Paleozoic tectonic strata Layer,Mesozoic tectonic layer and Cenozoic tectonic layer.Therefore,we can see that the study area is formed by multi-stage tectonic motion control.(2)Based on the tectonic-sequence stratigraphy,the interpretation of seismic data and the combination of different strata faults in the study area,the study area is divided into three large tectonic zones: Shi Gouyi Oblique,Leading edge transition zone and Tianhuan depression.Among them,the leading edge of the transition zone can be divided into South and North two districts.The northern area is divided into three sub-tectonic units: Jijiajing thrust,Haizijing thrust and Majiatan thrust,theMajiatan thrusting section has obvious characteristics of segmentation,which can be divided into three tectonic belts in the north,central and southern.The front transition zone in the northern area is dominated by the Jijiajing fault and the Majiatan fault,and the strata structure,secondary thrust and receding rupture are developed along the Carboniferous-Permian or Triassic Liujiagou Formation.In addition,the deformation front Majiatan area is complex,and there are differences in the slip-off layers of different fault zones.The southern area is divided into Shen Jiazhuang thrusting seat,Ma Erzhuang thrust seat and Yu Jialiang thrust three sub-tectonic belt.The front transition zone is mainly located in the Shenjiazhuang fault and the Ma'erzhuang fault,and the strata structure is formed along the Carboniferous-Permian or Triassic Liujiagou Formation.The secondary fault is developed and the slip-off layer is obviously different.The development of the eruption zone between the front transition zone and the Tianhuan depression.It can be seen that each thrust seat is controlled by thrust fault,and there are obvious differences in geological structure characteristics.The structural features are complex and varied,and there are multiple conversion bands.(3)Huianbao-Shajingzi fault zone development of Shi Gouyi Oblique,The rest of the five fault zones(Jijiajing fault zone,Haizijing fault zone,Majiatan fault zone,Shenjiazhuang fault zone,Ma'erzhuang fault zone and Yujialiang fault zone)developed broken anticline,and the fault zone is mainly deposited in the Permian,Triassic,Meso-Lower Jurassic,Lower Cretaceous and Quaternary.On the plane,the faults are NW,NNW and SN show,all have the characteristics of "steep and slow down".Huianbao-Shajingzi fault breaking distance,the level of the maximum distance up to 12 km,and the maximum breaking distance of the rest rupture zone is between 1500-5000 m.The early stage of the Huianbao-Shajingzi fault is the normal fault formed in the tensile environment,and the later stage is stopped.In the Yanshan period,the fault structure is reversed and the thrusting is developed,and the medium of Yanshan is the most intense,and Himalayan period,thrust push forward inheritance development.It can be seen that the early stage of the study area is in the tensile environment and the local area develops the normal fault.Yanshanian,early faultstructure reversal,thrust thrusting strong,large distance from the front transition zone to form a large number of thrust faults,strong tectonic movement,geological structure characteristics of complex,broken distance is relatively small(4)Three kinds of structural deformation in the study area and its adjacent areas are: the Extension-Agglomeration Cyclic Restricted Inversion structural Fault System,the Extended Landform Deformation System Restricted by Deformation System in Inner Orogenic Belt,and the Post-orogenic extensional deformation system.It is known that the reverse structural fault system is a superposition deformation system formed by the early formation of the positive fault structural inversion.The extended foreland deformation system is a reverse structural deformation system formed by extrusion deformation in Yanshan period.The post-orogenic extensional deformation system is the rift basin formed by the relative decline of the crust since the Cenozoic.