油气井套管CO2点状腐蚀剩余强度分析

在高温高压含CO₂油气井中，套管腐蚀是相当严重的，CO₂腐蚀以点状（坑状）腐蚀为主，腐蚀的形状大多呈球窝形。为此，文章建立CO₂点蚀模型，以点蚀后套管的剩余强度为出发点，应用弹塑性有限元方法分析了点蚀套管的抗挤强度、抗内压强度、抗拉强度的变化。同时运用无因次分析和曲线拟合方法，建立了点蚀套管无因次剩余强度与套管点蚀无因次形状参数之间的关系曲线以及拟合曲线。有限元程序的计算结果与试验结果具有良好的一致性。结果表明，点蚀套管强度剩余的百分数并不正比于套管剩余壁厚百分数，剩余强度曲线呈降-稳-降三段式变化。由多腐蚀点干扰分析发现，多腐蚀点同时存在时，应力分布及其大小与单腐蚀点情况相差不大。

ANALYSIS ON RESIDUAL STRENGTH OF CO2 TUBERCULAR CORROSION FOR CASINGS OF OIL/GAS WELLS

The casing corrosion is quite severe in CO_2 oil/gas wells with high temperature and pressure. CO_2 corrosion mainly is tubercular corrosion. The corrosion shape mostly appears spherical. According to the residual strength of casings after tubercular corrosion, with elastic-plastic finite element method, the changes of collapse resistance, burst strength, and tensile resistance of casings are analyzed. With dimensionless analysis and curve fit method, the relation curves and the fit curves between the dimensionless residual strength of casings after tubercular corrosion and the dimensionless shape parameters of casing tubercular corrosion are set up. The calculating results from the finite element program are matching with the test results very well. The results show the percentage of casing residual strength after tubercular corrosion is not proportional with the percentage of casing residual thickness after tubercular corrosion. The residual strength curves appear in the 3 sections of down-stable-down. By the interference analysis of multiple corrosion points, it is found the stress distribution and amount when many corrosion points exist is almost the same with that when a single corrosion point exists.