Strength And Safety Analysis Of Fracturing Casing In Three-dimensional Curved Wellbore And Design Of Experiment Table

Most of the oil and gas wells in our country can't drill in accordance with the designed trajectory,and in the process of fracturing,the casing will be in a complex mechanical environment,and the residual strength of the casing will change accordingly,resulting in casing deformation and damage.Therefore,it is of practical significance to carry out the strength safety analysis and the design of the experimental platform for the casing structure design of threedimensional curved wellbore and subsequent construction parameter control.Considering the space geometry characteristics of three-dimensional curved wellbore trajectory,considering the influence of depth sounding,well inclination and azimuth angle,based on the characteristics of the spatial quintic PH curve,such as continuous unit tangent and directed curvature,no iterative calculation,using the Bézier polynomial interpolation optimization calculation model and algorithm,the space parameters among them can be accurately inverted and calculated according to the determined space four points Based on this,the analytic function of well trajectory is established to generate well trajectory curve.On this basis,the fracture casing axial load analysis is carried out considering well trajectory,casing structure,fracturing construction requirements,casing self weight,buoyancy,internal and external pressure,temperature load and fluid friction resistance.The mechanical model of micro segment casing axial load is established,the axial force of micro segment casing is calculated,and the tensile strength of fracture casing is analyzed.According to the Thick-walled cylinder theories,the paper analyzes the circumferential stress and radial stress caused by internal and external pressure,the axial stress caused by axial force,and the shear stress caused by bending load.The fourth strength theory of material mechanics is used to calculate the strength safety factor of three-dimensional curved casing in different well depths under complex threedimensional stress.In order to test the bending strength of the casing,according to the basic theory of the four-point bending test,a four-point bending test-bed is designed special for the casing,and the static performance of the key parts of the fixture is checked and calculated by the finite element method.The results show that: by using the spatial quintic PH curve interpolation method,the error of the well trajectory obtained is smaller than that of the cubic spline;the maximum axial load of the fracturing casing is at the wellhead position,and the most dangerous position of the threedimensional stress is at the dog leg position;a four points bending method is designed and developed to measure the bending strength of the casing experimental platform.The research results provide the basis for the description of three-dimensional curved wellbore trajectory,the analysis of fracturing casing strength safety and the control of fracturing construction parameters.