水泥环对套管强度影响的理论和试验研究

The theory and test research about cement sheath influence to the casing strength

针对有关水泥封固质量是否对套管柱强度有帮助作用的讨论 ,采用弹性力学分析方法推导了平面应力和平面应变状态下水泥环与套管接触处的接触压力表达式 ,对水泥环分担内、外压的能力进行了计算。采用全尺寸实物试验方法对套管有无水泥环情况下的抗挤毁能力做了对比试验。分析和试验指出 ,水泥环对提高套管柱整体抗挤毁能力较之提高抗破裂能力作用更大一些 ,但封固良好的水泥环对提高套管抗挤毁能力的作用有限。如果水泥封固质量不高 ,高压介质经过短时间渗透直接作用在套管外表面 ,水泥环的卸载作用被短路 ,对提高套管抗挤强度无任何帮助 ,所以在管柱设计时不应考虑水泥环对套管强度的增强作用。

The expression of the contact pressure of cement sheath and casing under the plane stress and plane strain is derived by using elastic mechanics method. The bearing capability of the cement sheath on the internal and external pressures is calculated. A comparison is made on the anti-collapse capability of the casing with and without cement sheath by means of full-scale test. The results of analysis and test show that, the cement sheath is more useful for improving theanti-collapse capability of the casing string than that of its anti-crack capability, accept for the well-cememted sheath. The cement sheath may not have any help to improving the capability of the casing if not well cemented. Therefore theeffect of the cement sheath on improving the casing strength should not be considered in the design of the casing string.