水泥环缺失对水平井套管强度安全性影响分析

在水平井固井过程中,常常发生水泥环缺失,影响套管的强度安全性。为此,综合考虑水泥环缺失位置、缺失厚度与环向缺失角度,利用有限元分析方法,建立了水平井套管-水泥环-地层力学分析模型,考虑套管内压与非均匀地应力的作用,模拟水平井中水泥环缺失段套管的应力分布情况,着重分析了第一胶结面和第二胶结面水泥环缺失厚度对套管强度安全性的影响。分析结果表明:水泥环第一胶结面缺失对套管的应力分布影响较大,缺失比存在一个临界值,若缺失厚度大于该临界值,套管的应力将发生突变;水泥环第二胶结面缺失时,套管应力随缺失厚度增大而逐渐增大,没有应力突变;套管应力极值点位置随着水泥环环向缺失角度的变化而变化,环向缺失角度为60°时,套管的应力极值最大。所得结论可为水平井固井过程中套管的强度判断提供依据。

Analysis of the Influence of Cement Sheath Absence on Casing Strength Safety in Horizontal Well

The cement sheath absence in the horizontal well affects the strength and safety of the casing. To address the problem,considering the cement sheath absence position,thickness and angle,the finite element analysis method was used to establish the horizontal well casing-cement sheath-formation mechanical analysis model.The effect of casing internal pressure and non-uniform geostatic stress,the stress distribution of the casing at the cement sheath absence section in horizontal well was simulated. The influence of the thickness of the cement sheath at the first and the second cementing surface on the safety of the casing strength was analyzed. The analysis results showed that the absence of the first cementing surface of the cement sheath has a great influence on the stress distribution of the casing. There is a critical value in the absence ratio,at which abrupt casing stress occurs when the cement sheath absence increases. Under the second cementing surface absence,the casing stress gradually increases with the thickness of cement sheath absence,but without sudden stress change. The position of the casing stress extreme value was observed at the absence angle of 60°. The study results can provide a basis for evaluating the casing strength during horizontal well cementing.