定向井全井段钻柱下放过程应力及接触力分析

Stress and Contact Force Analysis of Whole Hole Drill String Running in Directional Well

钻柱在下放过程中,由于井眼轨迹的影响和井壁的约束,钻柱会产生弯曲应力、接触压力和摩擦力等初始应力。忽略钻柱轴线与井眼轴线重合这一前提假设,模拟了整个钻柱的下放全过程,得到了真实的钻柱初始状态,对钻柱下放过程中的应力及接触力进行了分析。在有限元处理中把整体模型假设为细长梁在管内沿管轴线的下放过程,将井壁考虑为刚体。模拟结果表明,从全井段应力变化来看,直径段由于重力作用呈线性减小趋势,而进入造斜段时则迅速增加,在接触处和截面突变处变化剧烈,进入稳斜段后,在靠近钻头附近趋于平稳,维持在较低水平。

In the practical running process the drill string will produce initial stresses such as bending stress, contact stress and friction force due to the effect of hole path and constraint of well wall. Neglecting the presupposition that the axes of drill string and those of hole coincide, the whole landing process of drill string was simulated, the real initial state of drill string was obtained and the stress and contact force in the setting process of drill string were analyzed. In the finite element treatment the whole model was assumed as the slender beam which ran along the pipe axis within the pipe and the well wall was considered to be a rigid body. The simulation shows that in view of whole hole stress change, the stress of diameter section tends to decrease linearly due to the effect of gravity and it increases fast in the building up section. It changes drastically in the steady inclined section and tends to be stable near the drill bit at a relatively low level.