水平井钻柱接触问题的间隙元法

Gap-element Method of Three-dimension Contact Problem for Drillstring in Horizontal Well

长中半径水平井钻柱与井壁的接触问题是大面积接触的几何非线性问题。本文通过构造“多向接触间隙元”把钻柱与井壁结合起来研究,能方便正确地反映这种接触状态的变化规律,也能解决一般有限元法会遇到的总刚奇异性问题。运用本文方法,可以对整体钻柱或下部钻柱进行接触有限元分析。采用欧拉-修正的牛顿迭代法进行运算,给出钻头受力变形值,为井眼轨道控制提供了重要依据。 现场实验证明,在井眼轨道跟踪预测和钻具组合性能评价方面,本文计算结果与实测结果符合很好,对提高钻进速度,保证钻井质量有较大的实用意义。

The contact between drillstring and bore hole wall in the process of horizontal drilling is of large area and geometrically nonlinear. Considering both wall and drillstring, the Multidirectional Contact Gap Element (MCGE) is presented in this paper in order to make it easy to correctly describe the contact state, which also contributes to avoiding the global stiffness matrix singularity that often appears when using normal finite element method. Using the method recommended by this paper, we can make a thorough analysis of BHA (bottom hole assembly) or the whole drillstring. Through Euler-Modified Newton iteration, we can get the mechanical deformation of a drillstring at bit, which is very important for the control of the hole trajectory.The result of numerical calculation provided by this paper is satisfactorily agreed with that of field test in terms of prediction of hole trajectory and evaluation of BHA. Therefore it is practically important for the increase of drillstring efficiency and the guarantee of drilling quality.