复合磨损对弯曲套管抗挤强度的影响

Influence of Compound Wear on the Collapse Strength of Bending Casing

在大位移井、水平井和三维定向井的弯曲造斜段,由于井眼轨迹复杂,造成套管弯曲变形、扁化、严重磨损或磨穿,井下摩阻扭矩过高导致卡钻和断钻具等井下事故频发,出现了许多新的套管损坏问题。鉴于此,建立了弯曲套管力学模型,发现随着套管弯曲曲率增加,截面扁化程度加剧,套管抗挤强度降低。同时分析了复合磨损对套管抗挤强度的影响;在单尺寸月牙磨损理论假设的基础上,根据参与磨损的钻杆接头尺寸不同,建立了复合锐进型月牙磨损和复合钝进型月牙磨损两种几何模型;采用解析法计算了复合磨损情况下套管的抗挤强度;通过有限元模拟验证,发现在相同磨损深度下,复合月牙磨损与最小磨损半径单月牙磨损的套管抗挤强度十分接近,最大误差控制在5%以内,且误差随磨损深度的增加而减小。研究结果可为复杂井井眼轨迹设计提供参考。

The hole trajectory in the bending section of extended reach well,horizontal well and three-dimensional directional well is complicated,so some complex situations are induced,e.g.casing bending deformation,flattening,serious wear and even wear through,and some new casing damage problems occur.In this paper,the mechanical model of bending casing was established.It is shown that with the increase of bending curvature,the section flattening degree increases and the casing collapse strength decreases.In addition,the influence of compound wear on casing collapse strength was analyzed.Based on the assumption of single-size crescent wear theory,two geometric models(i.e.,compound sharp crescent wear and compound blunt crescent wear)were established according to the different sizes of drill pipe joints involved in the wear.The casing collapse strength under the condition of compound wear was calculated by using analytical method and verified by means of finite element simulation.It is indicated that at the same wear depth,the collapse strength is quite close between the composite crescent wear casing and the single crescent wear casing with minimum wear radius.The maximum error is basically controlled within 5%and it decreases with the increase of wear depth.The research results provide the reference for the trajectory design of complex holes.