复合磨损套管爆裂失效机理及剩余强度预测OA北大核心CSTPCDEI

Complex oil and gas wells such as ultra-deep wells,horizontal wells and extended reach wells are operated under exceptionally severe conditions,with serious casing composite wear,which poses a great threat to wellbore integrity.Moreover,the residual strength of composite wear casing is difficult to predict accurately.In this paper,based on the Casing Wear Data of Well 501 in the Shunnan block,the north slope of central Tarim Basin and the stress-strain constitutive relationship of P110 tubing,an infinite element mechanical model of composite wear casing is built,which fully considers the wear pattern,clamping angle,wear overlap depth and wear depth caused by the combination of drill pipe body and joint.With this model,the casing elasto-plastic deformation,yielding,crack sprouting,expansion and bursting behavior under various composite wear patterns are simulated,and the stress distribution,residual internal pressure yield strength and bursting strength of casing with different composite wears are obtained.The results indicate that the stress interference weakens the stress concentration when the crescent angle is 0°-90° and enhances the stress concentration when the crescent angle is 90°-180°.This interaction mechanism allows the residual strength of composite wear casing to increase and then decrease as the crescent angle increases.Crack sprouts from the position with the maximum equivalent stress,i.e.the center of the wear crescent,and expands radially from the inner wall to the outer wall of the casing and perpendicular to the maximum circumferential stress.Once a crack initiates,it will expand quickly and induce a burst failure of the casing.The grey correlation analysis is conducted to investigate how the residual strength of casing with composite wear is sensitive to the wear depth,crescent angle,composite wear pattern,and overlap crescent depth.It is clarified that the wear depth is the main controlling factor for the residual strength of casing.The research results can provide technical reference for the design and optimization of casing strength,and be significant for accurately predicting the residual strength of composite wear casing and securing the wellbore safety and integrity.