悬空套管段承温能力分析

Study on Temperature Bearing Capacity of Un-cemented Casing Section

针对高温高压井因井筒温度升高导致的悬空套管段附加载荷,建立计算模型,对套管的承温能力、环空降压效果进行了分析。计算表明:套管在密闭外环空附加压力和轴向温度应力共同作用下,会很快到达屈服极限,最危险位置在水泥环端面附近;外环空附加压力导致套管径向收缩,能够引起固井段的水泥环与套管剥离;环空降压可以大幅度提高套管承温能力,同时由于环空压力低时套管径向膨胀,能够阻止水泥环与套管的剥离。研究成果对高温高压井套管设计、防护措施选择、生产参数确定等实际问题具有重要参考价值。

Wellbore temperature rising brings in additional loads on suspended casing string section. This paper builds up a calculation model to discuss the capacity of suspended casing on high temperature and the effect of annular pressure discharging measures. Calculation indicates that if both the closed annular pressure and axial temperature stress are exerted on such easing section, it will reach the yielding limit quickly, and the most dangerous position is near above the cement top. Outer annular pressure makes the casing shrink in radial direction, and then induces casing separation from cement sheath. By discharging annular pressure, the temperature bearing capacity of casing can be improved greatly, and at the same time, the separation of cement sheath from casing is prevented because casing expands in the radial direction under lower annular pressure. These results are valuable to casing program design, casing protection measure selection and optimization of operation parameters in high pressure high temperature wells.