井眼中钻柱稳定性分析的有限元法

通过引入单元荷载刚度矩阵，提出了一种用于分析钻柱结构稳定性问题的有限单元法。该方法可以用于分析变截面钻柱在变轴力和变横向力共同作用下的钻柱稳定性问题，也可用于分析弯曲井眼中钻柱的稳定性问题。在所建立的力学模型中，考虑了钻柱自重和井眼曲率的影响。分析结果表明，在斜直井眼中，除了钻柱自身密度及截面面积外，影响钻柱荷载的因素还有井眼状况及钻柱两端部的约束条件，但当钻柱长度超过８０ｍ时可以不考虑端部约束的影响。对于弯曲井眼，钻柱临界压力不仅与钻柱的长度、截面尺寸有关，还与井眼曲率有关，即随着曲率的增大而增大。

ANALYSIS OF DRILLSTRING STABILITY IN WELLBORE BY USING FINITE ELEMENT METHOD

Rigidity matrix of load on an element is introduced, and a finite element mehtod for analyzing the stability of drill stem is presented. The method can be applied to analyze the stability of drill stem with variable sections under the variable axial and lateral forces in inclined hole and curved hole. The dead weight of stem and cavity of hole are taken into account in modeling the mechanical system. The affecting factors on load of drill stem include gravity and section area of drill stem, wellbore parameters and limited conditons for two ends of drill stem in an inclined wellbore. For the curved hole, critical load of drill stem is related to length and section area of drill stem, and ridius of curvature of wellbore.