Mesozoic-Cenozoic Numerical Simulation Of Tectonic Stress Field And Fracture Forecasting In Baima Area,Eastern Chongqing

The Baima area in eastern Chongqing is tectonically located in the western Hunan-Hubei-eastern Sichuan ‘trough-block’ transition zone,the southern Wanxian synclinorium,the large-scale fault-Qiyueshan fault that controls the basin boundary on the east side,the Shimen fault that divides the regional boundary on the west side,and the Jinfoshan uplift on the outside of the southern end region.The tectonic structure is complex due to the combined influence of multiple tectonic movements.At the same time,tectonic stress field is one of the important factors affecting oil and gas migration,accumulation and even preservation.Therefore,it is practical significance to clarify the structural characteristics of the complex tectonic structure and the development law of the fault system in the Baima area,and to study the distribution law of the stress field in the middle Yanshan period,which has a major impact on the region,not only to improve the theoretical understanding of the structural characteristics of the Jiaoshiba area,but also to clarify the fracture development law and the migration and preservation of shale gas.In this paper,seismic interpretation data are used as the basis for fine structural analysis.Combined with the geological background of Sichuan Basin,the structural characteristics,fault characteristics,structural characteristics of different structural units and the tectonic evolution sequence in Baima area are obtained by using regional buried depth,fault distribution,curvature and other geological data.Based on the understanding of regional characteristics such as geological conditions,tectonic boundary and fault system,the geological model of the key two stages of Mesozoic and Cenozoic in Baima area is constructed.Based on the finite element analysis method,the rock mechanics parameters of the model and the boundary constraints.Two models are simulated by ANSYS software.After repeated trial and error,the horizontal maximum principal stress and horizontal minimum principal stress of the middle Yanshan period are obtained,and the distribution law of paleo tectonic stress field is clarified.According to the two-stage differential stress value,the rock fracture criterion is calculated and superimposed to obtain the distribution of the fracture coefficient in the middle Yanshan period,and the numerical simulation of the stress field and the distribution of the fracture coefficient are analyzed from the perspective of structure.The research results can be divided into three parts: structural characteristics,boundary conditions and simulation results.As follows :The Baima area in eastern Chongqing is a structural form of narrow north and wide south,with east-west zoning characteristics.On the whole,the east side is a syncline belt and the west side is a structural high.The Qiyueshan fault and the Shimen fault are oppositely developed,forming a structural conversion zone,and the structural structure is complex and diverse.The first,third,fourth and fifth faults are developed in the region;it is divided into 6 levels and 15 tectonic units,which are mainly affected by thrust and compression torsion.The middle Yanshan period corresponds to the tectonic activity of Jiangnan uplift,resulting in the direction of SE-NW principal stress.During this period,all visible faults were developed in the area.In the late period,it corresponds to the north-south compression of Jinfoshan uplift,with joint development and almost no fault formation.The direction of the maximum principal stress in the middle Yanshanian is SE100-SE135,and the value is 112MPa-180 MPa.The direction of the minimum principal stress is NE10-NE35,which is similar to the strike of most faults,and the value is 3MPa-105 MPa.The direction of the maximum and minimum principal stress in the late stage of middle Yanshan is opposite to that in the middle stage.The maximum principal stress is 95MPa-162 MPa,which is smaller than that in the late stage,and the minimum principal stress is 14MPa-103 MPa,which is slightly larger than that in the middle stage.The major range of two-stage superimposed shear fracture coefficient is0.6-1.3.The numerical simulation results are affected by factors such as fault zone distribution,burial depth and stratigraphic dip angle,and there will be disturbances.