考虑钻井液动力润滑作用的旋转钻柱涡动状态研究

Buckling and whirling of the rotary drill string under compression immersed in drilling fluid, result fatigue failure and well deviation. This topic has been carried out more in-depth study, but many problems yet to be resolved: (1) Why with the deviation angle increases, the whirling phenomenon decreases until it disappears? (2) Is the buckled drill string must touch the well wall? (3) Is there sliding between the drill string surface and the wellbore wall? If there is sliding, and what factors are related? How to calculate? (4) Gyroscopic stability increases with the rotary speed, how is the stability of the drill string with the rotary speed? (5) The higher the rotary speed of the radial bearing, the smaller the eccentricity; how is the eccentricity of the drill string with the rotary speed? To answer these questions, on the basis of fundamental equations for dynamic analysis of rod and pipe string in oil-gas wells, mathematical model of Newton fluid laminar flow induced by spin and revolution of drill string, existing drill string buckling theory and the radial bearing lubrication theory, using mechanical equilibrium, the minimum potential energy principle and the principle of minimum dissipation as criterions, researches the buckling and whirling of rotary drill string under compression immersed in drilling fluid, compares with experimental results, provides a theoretical basis of crack-proof design of the drill string.

浸泡在钻井液内的旋转的受压钻柱，在屈曲和涡动的作用下，容易发生疲劳断裂和产生井斜。对此课题，已经进行了比较深入的研究，但很多问题还没有解决：（1）为什么随着井斜角的增加，涡动现象减小，直至消失？（2）屈曲后的钻柱一定与井壁接触吗？（3）钻柱表面与井壁间无滑动吗？如果有滑动，与哪些因素有关？如何计算？（4）陀螺的稳定性随转速增加而增加，钻柱的稳定性随转速如何变化？（5）径向滑动轴承的转速越高偏心率越小，钻柱的偏心率随转速如何变化？为了回答上述问题，本项目拟在油气井杆管柱动力学基本方程、钻柱自转和公转诱发牛顿液体层流流动的数学模型、现有的钻柱屈曲理论和径向滑动轴承润滑理论的基础上，以力学平衡、最小势能原理和最小耗散能原理为判据，研究旋转的受压钻柱的屈曲和涡动状态，并与实验结果进行对比，为钻柱防断裂设计提供理论基础。

浸泡在钻井液内的旋转受压钻柱，在屈曲和涡动的作用下，容易发生疲劳断裂和使井眼倾斜。对此现象业界已进行了较深入的研究，但还有一些问题没有解决，如随着井斜角的增加涡动现象减小直至消失的原因、屈曲后的钻柱是否一定与井壁接触、钻柱表面与井壁间是否存在滑动及滑动的影响因素、钻柱的稳定性和偏心率随转速的变化规律等。为了寻求上述问题的研究方法，在介绍钻柱的正弦屈曲和螺旋屈曲、旋转钻柱的最大涡动角速度、旋转钻柱与钻井液的相互作用、旋转钻柱与井壁的碰撞和涡动4方面的研究进展基础上，分析了这些研究方法中存在的问题，提出钻井液动力润滑学与钻柱动力学相结合是钻柱涡动理论研究的必然。钻柱力学遵循力学平衡、最小势能和最小耗散能三个原理。研究发现润滑理论本身并不完善、甚至出现谬论。实验发现随着转速的增加钻柱涡动幅度在某一区间会迅速减小。