底部钻具规则涡动轨迹的内摆线描述方法

Hypocycloid method for describing regular whirling of bottom hole assembly

为了认识和控制钻井过程中的钻柱涡动,基于几何学原理提出内摆线描述方法。该方法将涡动视为规则运动,从分析钻柱外缘固定点的运动特性入手,求解底部钻具(BHA)与井壁的摩擦接触的运动轨迹方程,确定轨迹上各点的速度,分析钻柱自转和公转速度对底部钻具运动轨迹的影响。结果表明:底部钻具的涡动可能造成钻柱以远高于其自转速度的角速度沿着井壁快速公转,导致井下工具过早失效;钻柱规则涡动引起BHA外缘某点沿井壁的运动轨迹可用几何方法进行描述,轨迹方程证实线速度是影响井下工具磨损的重要参数;根据现场测试与室内试验所获得的钻柱规则运动轨迹可以反推涡动方程,从而掌握BHA的运动状态;利用内摆线描述法所得结果与文献试验数据吻合较好。

On the basis of geometry,a hypocycloid method was proposed to identify and control drillstring whirling.Treating the whirling as a regular pattern,this method was used to describe motion characteristics of a fixed point on drillstring circumference,to solve equations representing bottom hole assembly（BHA） motion trajectories,to define velocities of each point on the trajectory,and to analyze the impacts of rotation and revolution speeds on BHA whirling.The results show that whirling might cause drillstring rolling around borehole wall with a revolution speed much higher than rotating,inducing downhole tools premature failures.The regular motion patterns of a fixed point on BHA circumference can be expressed by geometry measures,and the trajectory equation indicates that the linear velocity plays an important role in tool wear.The whirling equations representing BHA motion can be worked out from inversions of field and laboratory tests and the results properly match documented tests.