Analysis Of Casing Wear And Residual Strength In Three-dimensional Curved Wellbore

Generally,the wellbore of oil and gas wells is three-dimensionally curved,and the drill string is inevitably in contact with the casing,so the rotating drill string is bound to wear the casing inserted in the previous period.However,the previous casing wear analysis did not consider that the wellbore is three-dimensionally curved,which may cause a large error.Therefore,the analysis of casing wear degree and residual strength in the three-dimensionally curved wellbore is of great significance for casing wear prediction.Considering wellbore trajectory is usually three-dimensionally curved state,according to the actual oil field drilling of well depth,Angle and azimuth Angle parameter information,using quintic splines interpolation method of wellbore trajectory interpolation,the use of each two neighboring wellbore space point fitting a section of borehole trajectory equation,so the two wellbore space point through the adjacent two points set up the three-dimensional curved wellbore trajectory equation.On this basis,through the analysis of the three-dimensional curved of the casing wear form,deduced the "olive shape" casing wear volume and wear depth formula in the three-dimensional curved wellbore.In addition,based on the three-dimensional curved wellbore,through the tool joint and casing contact force calculation is derived,and established a three-dimensional curved wellbore on contact force of casing wear degree of volume calculation formula.In order to analyze the influence of three-dimensional curved wellbore on the residual strength of the Wear casing,the finite element calculation model of threedimensional curved wellbore wear casing was established in this paper.Through ANSYS finite element analysis of three different specifications of casing with different dogleg severity and different wear rate,the residual collapse strength and residual burst strength of the threedimensional curved wellbore wear casing were obtained.The results show that the average error of quintic spline interpolation method is smaller and the fitting effect is better than that of cubic spline interpolation method.Through the calculation formula of wear degree of "half olive" casing,it is believed that the greater the dogleg degree,the greater the contact force between drill pipe and casing,and the more serious the casing wear.Through finite element analysis,the greater the dogleg degree is,the greater the wear rate is,and the smaller the residual strength of the wear casing is.