旋转钻柱动力屈曲临界条件与后屈曲蛇形摆动和螺旋涡动行为研究

With the development of drilling technology, vertical and lateral extensions of wellbores are increasing, and the mechanical behaviors of drill strings become more complicated. When drill strings enter dynamic buckling states under rotary drilling mode, the problems including fatigue failure, wear, high torque and so on become prominent, which brings serious threats to safe drilling operations. Current studies on tubular buckling problems at home and abroad are mainly confined to statics, and there are only few studies involved dynamic buckling. The complex dynamical buckling and post-buckling behaviors of drill strings have not been revealed. This project takes rotating drill strings constrained in wellbores as the research object and studies the mechanical behaviors with theoretical and experimental methods. On the basis of fundamental kinetic equations of tubular strings, the differential equations of snake-swing and helical-whirling motions of drill strings are derived by introducing sinusoidal and helical configurations. The critical conditions for sinusoidal buckling and helical buckling are deduced with buckling criterion and diagrams of dynamic buckling phases are drawn. The stabilities of different modes for snake-swing and helical-whirling motions and mechanical behaviors under different modes are analyzed by solving differential equations. An experimental platform is built and some experiments are carried out to validate and amend theoretical models. The above studies can provide important theoretical bases for drilling optimal design and safe control.

随着钻井技术的发展，井眼垂深和横向位移不断增大，钻柱力学行为变得更加复杂。在旋转钻进过程中，当钻柱发生动力屈曲后，疲劳失效、磨损、高摩扭等问题突出，严重威胁着钻井作业安全。目前，国内外关于钻柱屈曲问题的研究主要局限于静力范畴，只有少数研究涉及动力屈曲问题，未能充分揭示钻柱动力屈曲及后屈曲复杂力学行为。本项目以受井眼约束的旋转钻柱为研究对象，利用理论与实验相结合的方法研究其动力屈曲行为。基于管柱动力学基本方程，考虑正弦和螺旋变形模态，推导钻柱蛇形摆动和螺旋涡动的微分方程；利用屈曲判别条件，推导正弦屈曲和螺旋屈曲的临界条件，绘制其屈曲状态相图；求解屈曲微分方程，揭示屈曲状态下钻柱不同蛇形摆动和螺旋涡动模式的稳定性以及不同模式下的力学行为；搭建实验平台并开展实验研究，以验证和修正理论模型。上述研究可为钻进优化设计和安全控制提供重要的理论基础。

随着定向钻井垂深和横向位移的不断增大，钻柱力学行为与失效特征更加复杂多变。然而，现有的钻柱屈曲研究主要局限于静力范畴，未能充分揭示钻柱动力屈曲临界条件以及屈曲状态下的复杂力学行为。本项目围绕旋转钻柱动力屈曲问题开展研究，取得了几项主要成果：①基于受井眼约束管柱力学理论，推导了旋转钻柱的动力屈曲控制方程，建立了旋转钻柱蛇形运动与螺旋涡动的微分方程，为旋转钻柱动力屈曲研究奠定了理论基础；②建立了旋转钻柱正弦屈曲临界条件的计算方法，揭示了动态屈曲临界载荷低于静态屈曲临界载荷的原因，阐明了周期性激励力下钻柱局部与整体蛇形摆动行为特征及两种行为的过渡界限；③建立了旋转钻柱螺旋屈曲临界条件的计算方法，揭示了螺旋屈曲状态下钻柱无涡动、正向涡动与反向涡动行为特征及三种行为的过渡界限；④搭建了一套井下管柱动力屈曲的实验平台，通过实验研究验证了理论模型的准确性。研究成果可为定向钻井钻柱优化设计与安全作业控制提供重要的科学依据。在《SPE Journal》、《Journal of Petroleum Science and Engineering》、《Petroleum Science》、《石油学报》等行业主流期刊上发表论文17篇，申请发明专利5件，学术会议交流8次，获国家科技进步二等奖1项。

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