下部钻具组合上切点的位置确定方法

下部钻具组合的上切点始终处于井眼底边这一假设条件，并不适用于下部钻具组合静力学分析的所有情况。基于建立的适用于下部钻具组合静力学分析的三维坐标系及其变换关系，提出了描述井壁上上切点位置的方法；根据最小势能原理，提出了一种确定上切点位置的迭代计算方法；以光钻铤钻具组合为例，讨论了井眼几何参数与钻井参数对上切点位置及钻头侧向力的影响规律。结果表明:在二维问题的力学分析中，当钻头处井斜角很小、井眼的井斜变化率很大时，下部钻具组合的上切点将有可能处于井眼的高边；与对上切段长度的影响相比，井斜方位变化率对上切点井壁方位角的影响更大；与对钻头井斜力的影响相比，井斜方位变化率对钻头方位力的影响更大；钻压和钻头扭矩对上切点位置及钻头侧向力的影响都很小。 

A Method for Determining Upper Tangential Point at Bottomhole Assembly

The assumption that upper tangential point is always lies on the low side of wellbore,is not suitable for all cases in static analysis of bottomhole assembly(BHA).Therefore,this topic has been studied.The method describing the location of the upper tangential point in wellbore was proposed based on 3D coordinate system and its conversion relationship suitable for static analysis of BHA;according to the principle of minimum potential energy,an iterative method to calculate the location of upper tangential point was established.Finally,taking a slick bottom-hole assembly as an example,the effect of wellbore geometry and drilling parameters on the location of the upper tangential point and bit side force were determind.The results show that in two-dimensional static analysis,if inclination at the bit is small and inclination rate large,the tangential point of BHA may lie on the high side of wellbore.Moreover,the influence of azimuth rate on the azimuth angle at upper tangential point is greater than on the length of tangential section.The effect of azimuth rate on the bit azimuth side force is greater than on the bit inclination side force.In addition,the impact of weight on bit and torque at the bit on the location of the upper tangential point and bit side force is very limited.