垂直井筒内悬挂管柱屈曲演变有限元分析

Finite element analysis of buckling evolution of suspended tubings in vertical wellbores

关键词:  悬挂管柱  正弦屈曲  螺旋屈曲  有限元  正向加载  逆向加载

Key words:  suspended tubing  sinusoidal buckling  helical buckling  finite element  forward loading  backward loading

摘要:

摒弃常规方法中管柱屈曲挠曲线的假设,建立垂直井筒内悬挂管柱的几何和接触双重非线性力学模型,虚拟较大的阻尼比,进行有限元计算。采用正向加载法得到管柱稳定的连续接触的螺旋屈曲构型;采用逆向加载法,根据螺旋屈曲构型,逐渐增加悬挂拉力,进行屈曲演变分析;并分析摩擦力和管柱长度对临界载荷的影响。结果表明:螺旋屈曲向正弦屈曲转变是突变的过程,屈曲模态构型包括螺旋屈曲构型、刚螺旋屈曲和正弦屈曲。摩擦力对临界载荷的影响甚微。随着管柱长度增加,各阶屈曲模态的临界载荷均逐渐减小并趋于常值。此方法适用于斜井、曲率井和水平井管柱的屈曲过程分析。

Abstract:

The assumption of buckling deflection curve in conventional methods was abandoned. A geometric and contact double nonlinear mechanical model of suspended tubings in vertical wellbores was established, and the finite element calculation was carried out with the large damping ratio. By using the forward loading method, the helical buckling with continuous contact was obtained. According to the helical buckling configuration, the suspension tension was gradually increased by the backward loading method, and the buckling evolution was analyzed. The effects of the frictional force and tubing length on the critical load were also analyzed. The results show that the transition from the helical buckling to sinusoidal buckling is a process of sudden change. The buckling modes include the helical buckling configurations, the just helical buckling and the sinusoidal buckling. It is also found that the frictional force has little effect on the critical load. With the increase of the tubing length, the critical load of each buckling mode gradually decreases and tends to a constant. This method can also be extended to tubing buckling analysis of inclined, curvature and horizontal wellbores.