Numerical Simulation Of In-situ Stress Fields And Optimization Of Borehole Trajectory In Shunbei No.5 Fault Zone

In-situ stress plays an important role in the formation of oil and gas reservoirs,especially in the present stress field,which has an extremely important guiding significance for the exploration and development of oil and gas fields.Shunbei area of Tarim Basin has made great oil and gas breakthrough in recent years,and the continuous discovery of large strike slip fault zone also proves that this area has good exploration and development prospects.However,the lack of systematic understanding of in-situ stress system leads to frequent borehole instability,which seriously affects the efficiency of exploration and development.The in-situ stress orientation of key wells is determined by using the analysis of elliptical hole,wellbore collapse and drilling induced fracture orientation.In addition,acoustic emission experiment and triaxial total stress-strain experiment are used to determine the magnitude of insitu stress and rock mechanics parameters,respectively.On this basis,the geological model is established based on the finite element analysis method,and the rock mechanics parameters are assigned and the boundary conditions are loaded.Then the current in-situ stress field of Shunbei No.5 fault zone in Tarim Basin is numerically simulated by ANSYS software to obtain the maximum principal stress,intermediate principal stress and minimum principal stress in the study area,and to clarify the distribution law of the current in-situ stress field in the study area.Then the stress field simulation results are compared with the actual geological data to further verify the rationality and accuracy of the finite element model and simulation results.On the basis of in-situ stress simulation results,the stress state of wellbore is analyzed by using linear elastic theory,and the stress distribution model of wellbore is established.Based on the shear failure criterion and tension failure criterion,the calculation model of wellbore stability safety window is derived,and the wellbore safety window to prevent wellbore instability is given,so as to realize the purpose of wellbore trajectory optimization.The results show that the plane distribution of Ordovician triaxial principal stress in Shunbei No.5 fault zone has certain similarity,and the distribution characteristics are as follows: the strata near the fault zone are higher,the strata far away from the fault zone are lower,and the strata in the middle are higher,and the strata around the fault zone are lower.The vertical principal stress is 123 ? 231 MPa,and the direction is vertical downward;The maximum horizontal principal stress ranges from 72 to 180 MPa,and the main direction is NE-SW;The horizontal minimum principal stress is 58 ? 166 MPa,and the direction is mainly NW-SE.Comparing the numerical simulation results with the measured results,the error is less than 8%,which shows that the numerical simulation results are basically in line with the actual geological law within a reasonable error range.Combined with the two common failure criteria,under the normal fault in-situs stress state in the study area,the direction of horizontal minimum principal stress is the best drilling direction,in which the borehole inclination angle more than 50° is the best well trajectory.The research results of numerical simulation method of tectonic stress field and wellbore trajectory optimization can play a guiding role in further exploration and development of Shunbei oil and gas field in Tarim Basin.