Research On The Distribution And Influence Factors Of In-situ Stress In Complex Fault Tectonic Region

In-situ stress are important parameters for well location deployment,drilling sc heme design,wellbore stability analysis,casing damage analysis,fracturing construction design,engineering dessert prediction,etc.The Carboniferous igneous reservoir in the three-dimensional area of Well Su 13 in Chepaizi area,western Junggar Basin,has many faults with changeable strike,high complexity,short exploration and development time,low well density.It is in the early stage of exploration and development.It is urgent to provide data support for improving oil and gas productivity and furt her exploration and development through in-situ stress research.Therefore,taking the Carboniferous igneous reservoir in the three-dimensional area of Well Su 13 as an example,fractal dimension D is used to characterize the structural complexity of the s tudy area and the similarity between the numerical simulation model and the actual reservoir.The P-S wave velocity conversion formula and the dynamic and static elastic modulus,Poisson's ratio rotation determined by rock acoustic wave measurement experiment and rock triaxial compression experiment are used in this paper.The rock mechanics parameters of each well in the block are calculated by changing the formula.The boundary load values of the study area are obtained by using the method of ANSYS optimization module,COMSOL Multiphyics solid mechanics module and BP neural network.Finally,the seepage-stress coupling effect of the study area is simulated by COMSOL Multiphyics software.The results show that:(1)Three-grade,four-grade,five-grade and below-five-grade reverse faults are developed in the study area.Faults cut each other,showing the law of East-West zoning and North-South block in the plane.Model 1 is a simplified model with only three-grade faults retained,and the fractal dimension value is 1.1964.The fractal dimension value is the smallest and simple.The fractal dimension of model 3 is 1.8111,and the fractal dimension is the largest,and the overall structure is more complex.Model 2 retains the third-order and fourth-order faults,with the fractal dimension value of 1.6464,which is between model 1 and model 3.The simplification is moderate and the structure is relatively complex.The larger the fractal dimension,the more complex the structure in the study area is.(2)The extension direction of the in-situ stress numerical simulation model is NEE-SWW,and the azimuth angle is 62 degrees.The size of the enlarged boundary area is 5km.The four boundary loads of the numerical simulation model of in-situ stress in the study area are 23.67 MPa,27.81 MPa,20.31 MPa and 15.30 MPa.(3)With the increase of the number of faults,the in-situ stress value tends to decrease.The influence of faults of grade 5 and below on the overall distribution law of maximum horizontal principal stress is not obvious.The stress field distribution between faults is crisscrossed and shows the law of North-South block.The maximum and minimum horizontal principal stresses in faults with the same strike and load directions are smaller than those in other strike faults,and have less influence on the stress field nearby.Faults perpendicular to the strike and load directions have the greatest influence on the stress field nearby.Considering the influence of oil and gas exploitation,the maximum horizontal principal stresses in the study area increase.The numerical simulation model of in-situ stress is model 3 considering all faults in the study area.The maximum horizontal principal stress of effective stress field is 21.4-30.8 MPa and the minimum horizontal principal stress is14.5-20.1 MPa.The maximum horizontal principal stress tends to be higher in Southeast and lower in northwest,while the minimum horizontal principal stress tends to be higher in northeast and lower in southwest.(4)Under the interaction of seepage and stress,the formation pressure decreases gradually with the development of production time,and the fluid outside the 6.5 km distance from the wellhead is not affected by the production wells.The radius of the recoverable area of a single well is 6.5 km.The maximum and minimum horizontal principal stresses in the study area are larger when the seepage-stress interaction is taken into account,and the maximum and minimum principal stresses near the wellhead are larger when the seepage-stress interaction is considered.The maximum horizontal principal stress is 22.7-32.3MPa and the minimum horizontal principal stress is 15.3-21.8 MPa in the study area after considering seepage-stress interaction.The maximum horizontal principal stress is 24 MPa and the minimum horizontal principal stress is 16.6 MPa in the fault area.The direction of maximum and minimum horizontal principal stress is basically the same before and after coupling.The direction of maximum horizontal principal stress is NEE-SWW in the northeastern region.After the F1 fault,the direction of stress deflects to NE-SW.Within and near the fault,the direction of maximum and minimum horizontal principal stress deflects.In the interior and vicinity of faults parallel to the direct ion of load action,the stress direction deflects rapidly and has no definite regularity.