内压作用下含裂纹射孔套管临界开裂应力分析

An Analysis of the Critical Cracking Stress of Perforated Casing with Cracks under the Effect of Internal Pressure

为了了解内压作用下含裂纹射孔套管临界开裂应力,为现场确定泵压等施工参数提供参考依据,用ANSYS有限元分析软件建立了射孔套管有限元模型,给出了含孔边裂纹射孔套管应力强度因子计算公式,对内压作用下含裂纹射孔套管临界开裂应力进行分析计算,得到了临界开裂应力与纵向裂纹长度的关系曲线。研究结果表明,套管最大应力集中在孔边裂纹处,在内压产生的应力作用下裂纹有可能沿轴向产生脆性扩展,因此,孔边裂纹大大削弱了射孔套管的强度;射孔套管临界开裂应力随裂纹长度的增加而减小;在短裂纹区(10 mm<a<20 mm),临界开裂应力随a的变化较大;在长裂纹区(a<20 mm),临界开裂应力变化趋于平缓,即当裂纹长度达到某一定值时,孔边裂纹对套管承载能力影响不再明显。

To understand the critical cracking stress of perforated casing with cracks under the effect of internal pressure, the finite element ANSYS software was adopted to establish the finite element model of perforated casing so as to provide the reference for determining operating parameters such as pump pressure. The calculation formula for stress intensity factor of perforated casing with hole-edge cracks was given. The critical cracking stress of perforated casing with cracks under the effect of internal pressure was analyzed. The relation curve between critical cracking stress and longitudinal crack length was obtained. The findings show that the maximum stress of casing concentrates on hole-edge cracks. Under the effect produced by internal pressure, it is possible for cracks to make an axial brittle expansion. Therefore, hole-edge cracks remarkably weaken the strength of perforated casing. The critical cracking pressure of the casing decreases with the increase of crack length. In the zone of short cracks （ 10 mm 〈 a 〈 20 ram） , the stress changes remarkably with a. In the zone of long cracks （a 〈 20 mm） , the stress changes less and less remarkably. In other words, when the crack length reaches a certain value, the hole-edge crack does not have remarkable effect on the loading capacity of casing.