射孔套管剩余抗挤能力分析

Remaining collapse resistance analysis of perforated gasing

套管射孔后其抗挤能力将有所降低。建立了射孔段套管弹性抗挤性能分析控制的一般方程 ,并利用摄动理论给出了射孔套管弹性抗挤能力系数的一般计算公式。利用弹塑性有限元方法确定了孔口附近塑性区随射孔套管的外压增加的变化规律 ,并给出了确定射孔套管抗挤能力的计算方法。研究结果表明 ,孔眼附近的应力集中所引起的塑性区的存在 ,明显影响了射孔套管的抗挤强度。与弹性分析结果比较 ,弹塑性分析结果更接近实验值。孔眼的形状对射孔套管抗挤能力有直接影响。长轴在环向的椭圆形孔眼的套管抗挤能力降低得最少 ,方形孔眼的降低得最多。在孔眼形状相同的情况下 ,孔眼面积增大 ,射孔套管的抗挤能力降低。当射孔密度小于 2 0孔 /m时 ,无论采用何种布孔方式 ,除方形孔眼外 ,套管抗挤能力的降低均不会超过 4 % ;大于 2 0孔 /m时 。

The perforated casing is more vulnerable than common casing under external pressure. The governing differential equations for expressing the elastic resistance to collapse of perforated casing and general formulas for calculating the coefficient of elastic collapsing pressure with perturbation method were given. The relationship between the plastic zone and external pressure of perforated casing was determined by the use of elastic-plastic finite element method. A method for analyzing the critical collapsing pressure of perforated casing was presented. The existence of plastic zone resulted from the stress concentration near the performed hole on the casing has an obvious effect on the resistance to collapse. The result of elastic-plastic analysis is more closed to that of experiment than that of elastic analysis. The shape of hole on the perforated casing directly affects on the resistance to collapse. The reduction of critical collapsing pressure is below four percent when the perforation density is less than 20 holes per meter under the same shape of perforated hole. When the perforating density is more than 20 holes per meter,the effect of perforating parameters on collapsing pressure is evident,which must be taken into account when designing perforating interval on casing.