基于最小功耗率原理和钻井液动力润滑作用的钻柱涡动理论与实验研究

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, this project will establish the mathematical model of Newton fluid laminar flow induced by spin and revolution as well as radial motion of drill string, the mathematical model of drill string buckling under axial compress force and sliding friction as well as drilling fluid power, combine them together, using mechanical equilibrium and the minimum potential energy principle as well as the principle of minimum power consumption rate as criterions, research the buckling and whirling of rotary drill string under compression immersed in drilling fluid and draw whirl trajectories theoretically and experimentally, compare with site drill string wear and fracture data, 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，本项目拟建立钻柱自转、公转和径向运动诱发牛顿液体层流流动的数学模型、轴向压力和滑动摩擦力与钻井液动力作用下的钻柱屈曲参数的数学模型，并将其结合为一体，以力学平衡、最小势能原理和最小功耗率原理为判据，从理论和实验两方面研究钻井液的动力润滑作用和受压钻柱的屈曲和涡动状态并绘制涡动轨迹，与现场钻柱磨损和断裂资料进行对比，为钻柱防断设计提供理论基础。

以浸泡在钻井液内的旋转的受压钻柱为研究对象，调研了油气井杆管柱力学研究进展与争论，展望了油气井杆管柱力学重点研究方向。提出了钻柱力学三原理：所研究物体的运动和变形状态必须依次满足力学平衡原理、最小势能原理和最小耗散功率原理。建立了基于钻柱力学三原理的钻柱涡动模拟实验装置，研究了动力润滑作用对钻柱涡动的影响：钻井液的动力润滑作用可以减小钻柱正向涡动幅值，并能阻碍反向涡动的形成；提高钻井液的动力润滑性、减小井径、增加井斜角，出现反向涡动的轴向压力增大；钻柱随轴向压力增加可能出现两次反向涡动；钻柱运动状态转换符合最小耗散功率原理。依据叠加原理研制了内杆与外筒分别自转诱发流体平面流场的测量装置，并进行了实验研究：存在出现二次流的偏心率临界值；二次流分布区域随内杆与外筒转速差增大、偏心率增大而扩大。尝试建立了非惯性坐标系下的钻柱自转、公转和径向运动诱发牛顿液体层流流动的数学模型，通过MATLAB软件对偏心自转流场进行求解，并与FLUENT软件仿真进行了对比，计算结果相似。建立了滑动摩擦力和钻井液动力作用下的钻柱屈曲参数的数学模型，分析了钻柱材料内阻和最小耗散率原理在钻柱运动状态转换中的作用。通过对现场钻柱失效资料的调研和统计分析，建立了钻柱失效故障树，确定了钻柱磨损和断裂与润滑作用的相关性。研究结论可以为钻柱动力学研究和现场工作提供借鉴。.主要成果：（1）河北省自然科学三等奖1项，中国产学研合作促进奖1项。（2）国际学术会议分组报告3次，国内学术会议分组报告7次。（3）国际英文刊物发表论文21篇，国内中文刊物发表论文10篇；其中SCI收录8篇，Ei收录16篇。（4）申请发明专利12项，批准发明专利7项。（5）培养在读博士研究生2名，培养毕业硕士研究生8名。