卡点计算的有限元分析

FEM ANALYSIS OF THE FREE POINT OF DRILL STRING

在修井作业中钻杆被卡不是偶然的事,常常需要判断钻杆卡点位置。为了寻找判断卡点位置的理论依据,需要弄清楚钻杆在套管中的力学行为特征。在深达千米甚至数千米的油水井中,利用常规手段是难以描述出钻杆工作时的应力应变状态以及钻杆的变形形态。而利用有限元法有望模拟直井中钻杆在套管中的变形形态,并给出提升力与钻杆变形量的计算结果。现场施工工程师可以根据提升力与钻杆变形量之间的关系,判断出钻杆在井下的卡钻的位置,从而利用合理的手段和工具解决卡钻问题。研究目的就是要实现直井管柱的有限元模拟过程,并通过对有限元计算结果的分析,认识套管中修井钻杆的力学行为特征,为判断卡点位置提供分析依据。

In repairing the casing damaged wells, it occurs frequently that drill strings are stuck. Therefore, it is necessary to judge the positions of free points of the drill strings. In order to find the theory basis of estimating the sticking positions, the mechanical behaviors of drill strings in casing pipes have to be learnt. It is very difficult by normal methods to depict the states of stress and strain when they work in a few kilometers in oil wells or water wells. However, for vertical wells, finite element methods （FEM） can solves the difficulties above. Based on the relation between the lifting force and the displacement of the drill string calculated by FEM, the field engineers and technicians can judge accurately the position of the free point of a drill string and get rid of the problem. The target of the paper is to simulate a pipe string of a vertical well with FEM. By the analysis of results of FEM, the mechanical behavior of drill strings in casing pipes can be learnt well. It is the basis of judging the positions of free points of drill strings.