水泥环性质对套管强度影响的有限元分析

Finite Element Analysis on Effect of Cement Sheath Property on Casing Strength

在油层和泥岩部位易出现套管损害严重的问题,主要原因在于注入水窜入泥岩层后,引起泥岩力学性质改变,地应力重新分布造成套管损坏。石油行业常采用提高水泥环的质量以保证套管的安全。以"地层-水泥环-套管"为研究对象,采用有限元分析方法,将"地层-水泥环-套管"简化为平面系统,分别在均匀地应力和非均匀地应力情况下研究了水泥环弹性模量对套管应力载荷的影响;考虑到两个水平地应力不等的实际情况,选择在非均匀地应力情况分析各因素对套管应力的影响,主要包括水泥环不居中和水泥环发生缺陷时其缺陷角度与套管内压等因素,得出套管应力在不同水泥环性质时的变化规律,为解决套管损坏问题提供了参考依据。优选水泥环性质参数是提高套管抗挤强度的保证。

Casings in sandstone and mudstone are often damaged seriously and the main reason is that injected water seeps into mudstone and results in the change of mechanical properties of mudstone and ground stress redistribution which result in casing wear.In oil industry,safety of casings is assured often through improvement of cement sheath quality.Taken is 'formation-cement sheath-casing' as the study object and adopted is finite element analysis method to simplify 'formation-cement sheath-casing' to a plane system and study the effect of cement sheath elastic modulus on casing stress loading in homogeneous and inhomogeneous ground stress conditions respectively.Considering the two ground stresses are not equal,selected is inhomogeneous ground stress condition for analyzing effect of cement sheath not being centered,its defect angle and casing internal pressure on casing stress if any defect occurs in the sheath and obtained are change rules of casing stress in different types of cement sheaths,which can provide valuable references for decreasing cement sheath damage.