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.