由于缺乏对钻柱在斜井或水平井中运动规律清楚的认识,故无法采取有效措施避免钻柱的非正常磨损以及由于钻柱偏磨导致的钻杆磨穿问题.基于Lagrange动力学普遍方程,综合考虑了钻柱的黏滑运动、横向及扭转变形以及钻井液阻尼的影响,建立了斜直井中钻柱非规则运动的4自由度非线性动态模型.针对不同井斜角条件下钻柱运动的数值研究表明:当井斜角为90°时,钻柱将会沿着自身旋转方向约30°扇形域的井壁蠕动,并且由于摩阻扭矩的集聚-释放,伴随随机的黏滑和翻滚.随着井斜角的减小,局部的摩擦翻滚幅度增加并逐渐扩展成为整个井眼内的带有随机碰撞的回旋运动.该模型有助于更好地认识定向井作业中钻柱的井下工况,为有效实施减弱钻柱磨损和预防钻杆磨穿的举措提供理论指导.%Effective measures can't be taken to avoid drill-strings' abnormal wear and drill-pipe worn through caused by drill rod's eccentric wear due to the lack of knowing clearly motion laws of drill-string in a deviated well.A 4-DOF nonlinear dynamic model for irregular motion of a drill-string in a deviated well was established here based on Lagrange equations considering drill-pipe's stick-slip motion,its lateral and torsional deformations and well fluid damping effects.Under different inclinations (α),numerical studies showed that when α =90°,the drill-string creeps along the well wall within a 30° sector region about the drill-pipe's spinning direction;with decrease in the inclination,due to friction damping torque's concentration and release,accompanying with random stick-slip and tumbling,the drill-pipe's local friction and tumbling motion grows and gradually extends to a whirl motion with random impacts in the whole wellbore;the built 4-DOF nonlinear dynamic model can be used to better understand the downhole working conditions of directional drilling,and provide a theoretical guide for decreasing drill-strings' abnormal wear and preventing drill-pipe worn through.
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