大位移井摩阻/扭矩预测计算新模型

井下摩阻/扭矩预测是大位移井钻井成功的关键技术之一。常用的预测模型大都忽略了井眼的间隙,因此无法判断钻杆接头和本体与井壁的接触情况。通过假设井壁对钻柱的支承点按一定的间隔分布,将钻柱在支承点处断开,相邻两断点间的钻柱作为一跨,根据加权余量法在每一跨内计算出钻柱的转角与弯矩的关系;根据相邻两跨在断开点处的转角相同,求出弯矩的迭代方程;再由已知的边界条件计算出各点的弯矩;进而计算出各支承点处支反力的大小和方向,根据这一方向逐渐调整钻柱在井眼中的位置;推导出一套新的没有忽略井眼间隙的摩阻与扭矩计算公式。新模型能够计算出钻柱与井壁的接触情况,为合理的确定减扭接头或钻杆保护器等工具在钻柱上的安放位置提供更准确的依据。

New model for forecasting drag and torque in Extended Reach Well

Drag/torque prediction is a key technique of drilling an Extended Reach Well successfully.The contact situation between drill pipe and wall of well was not clear because the clearance was ignored in most models.It was assumed that there is an support point every 3 meter between wall of borehole and drillstring,disconnected the drillstring at the support point,according to the residual method,the relationship of corner and moment in one segment was found;based on the condition that the corners of drillstring are same when two segments are adjacent to each other,the moment iterative formulas were found;and base on the bounder condition,the moments could be calculated,which could be used to calculating the support force.The position of drillstring could be repositioned by the direction of support force.So we got a new set of friction and torque calculation formulas and the clearance was not ignored and the contact situation between drill pipe and wall of well is clear,which could be used for determining the proper position of torque reduction sub and drill pipe protection sub.