高内压下固井水泥环损坏机理研究

为了研究压裂酸化、高压注水等高内压作业对水泥环的损坏机理,进行了水泥环套管地层组合体的高内压物理模拟实验,研究了高内压条件下复合体的应力应变特征,测定了水泥环在双向应力的作用下的应变值和破坏载荷,确定了水泥环破裂的应力条件;在实验基础上建立套管水泥环地层复合体高内压应力应变模型,模型考虑了套管的偏心、双向不等的地应力、套管水泥环地层轴向应力不一致等因素,分析表明水泥环在高内压下的张性破坏、套管偏心是高内压水泥环套管损坏的关键因素,提出了高内压条件下保护套管水泥环的建议。

RESEARCH ON MECHANISM OF CEMENT SHEATH DAMAGE UNDER HIGH INNER PRESSURE

In order to study the mechanism of failure on cement sheath when performing fracturing & acidizing,or high-pressure water injection operations,the high inner pressure physical simulation was done based on the combination of cement,casing,and the formation to study the complex stress-strain characteristics.And the value of strain and failure load of cement sheath was measured under the action of biaxial stress and strain,and the rupture stress condition of the cement sheath was successfully determined.Based on the experiments,a complex stress-strain model of the combination of cement,casing,and the formation was established under high inner pressure,and in this model,the factors such as casing eccentric,two-way ranging in-situ stress and the inconsistent axial stress among cement,casing,and the formation have been considered.The analysis results showed that tensile damage was the main damage form of cement sheath,and casing eccentricity was the key factor in the damage of casing & cement sheath under high inner pressure.Based on all analysis,some suggestions on the protection of casing & cement sheath were put forward under conditions of high inner pressure.