深部盐膏岩地层套管磨损后等效应力分析

Analysis of equivalent stress on casings after casing wear in deep salt-gypsum formation

针对盐膏层蠕变和套管磨损联合作用下套管变形破坏的关键技术难题,结合室内盐岩蠕变试验,确定盐膏岩的蠕变参数,考虑盐膏层蠕变的影响,研究深部盐膏层非均匀地应力条件下蠕变、磨损程度、磨损位置对套管等效应力的影响。结果表明:蠕变在一定程度上降低了磨损套管抵抗外部载荷的能力,套管等效应力的非均匀性增强;随着蠕变时间的增加,套管等效应力逐渐增加,在1 a左右达到平衡;套管磨损越深,套管的等效应力越大且非均匀性越强;磨损位置明显改变了套管等效应力的分布规律,沿最小地应力方位磨损时,套管等效应力最大,最容易屈服;磨损位置不同时,只有当磨损程度较小时套管最大等效应力才出现在水平最小地应力方位;沿0°方向磨损时,只有当磨损程度较小时才会有'套管最大等效应力随磨损程度变化不大'的结论。

Aimed to the problems of casing collapse induced by the combined effect of salt-gypsum creep and casing wear, the creep parameters of the salt-gypsum formation were determined by salt creep experiments. The effects of salt creep, wear rate and wear position on the equivalent stress on casings were analyzed by considering rock salt creep in non-uniform in-situ stress field. The results show that the ability resisting external loads of worn casing is reduced by formation creep, and the nonuniformity of e- quivalent stress on casings increases. The equivalent stress on casings increases gradually with creep time increasing and reaches balance in one year or so. The equivalent stress on casings and its nonuniformity increase with the wear depth increasing. The dis- tribution of equivalent stress on easing varies with the easing wear position, and when the wear position locates along the direction of the minimum in-situ stress, equivalent stress on casing could be the largest which leads to the casing being failed more easily. The maximum equivalent stress on casings is in the direction of the minimum horizontal stress when the casing has a little wear. When the wear position locates along the direction of the maximum in-situ stress, the variation of the equivalent stress on casing with the wear rate is small only when the easing has a little wear.