定向井套管应力随地应力条件的变化规律研究

Study on varying rules of casing stress in directional hole with in-situ stress conditions

基于坐标变换方法建立了适用于任意井眼轨迹的定向井套管应力三维有限元计算模型。以室内岩心试验结果和现场常用套管尺寸为基础,研究了三种不同地应力条件下软、硬地层内套管最大有效应力随井斜角、方位角的变化规律。地应力条件包括:上覆岩层压力为最大主应力且水平地应力均匀,上覆岩层压力为最大主应力且水平地应力非均匀,上覆岩层压力为中间主应力。计算结果表明,复杂的原地应力场、井眼轨迹及地层性质对定向井套管的受力状态有重要影响,各种组合条件下均存在井眼轨迹优选值。在油井设计时,应充分考虑这些特点,合理确定井眼轨迹。

A 3D finite element model for calculating the casing stress in the directional wells was developed based on the theory of coordinate conversion. The rock Lab. tests and conventional casing sizes in the field were used to calculate the maximum effective stress varying with deviation angle and azimuth angle under different combinations of in-situ stresses and formation property. Three different situations were considered for the in-situ stress. (1) The overburden stress is the maximum principal one, and the horizontal stresses are uniform. (2) Similar to situation (1), but the horizontal stresses are non-uniform. (3) The overburden stress is the middle principal one. It is found that the casing stress in the directional well is significantly affected by the complex in-situ stress field, well track and the formation property. An optimal well track exists for any combination of these factors. All these factors should be carefully considered in the casing design process.