砂泥岩夹层套管损坏的有限元分析及防控措施

据大港油田不完全统计，在沙泥岩夹层的套管损坏占63%。针对在砂泥岩夹层套管损坏严重的问题，基于弹塑性力学和断裂力学理论，建立了沙岩—泥岩—沙岩三岩层剖面的轴对称有限元模型，并借助有限元软件进行求解，分析不同钢材和壁厚条件下三岩层剖面上套管内应力分布情况。结果显示，套管内的Von Mises 应力在砂泥岩界面和泥岩段应力最大，且在砂泥岩界面应力发生突变出现尖角，因此在砂泥岩界面和泥岩段套管容易损坏。针对砂泥岩夹层研究了泥岩段套管损坏的防控措施，研究发现，相同钢级下，增加套管壁厚不能有效防控泥岩段套管损坏，提高套管的钢级才是有效方法。通过以上分析研究对砂泥岩界面防控套管损坏的研究提供技术借鉴。

Finite element analysis and control measures on casing failure in sand shale interbeds

According to the incomplete statistics of Dagang Oilfield, the casing failure in sand shale interbeds accounts for 63%. To solve this problem, an axisymmetric finite element model was established for sandstone-shale-sandstone three-layer section according to the theories of plasto elasticity and fracturing mechanics. Then, it was solved by means of the finite element software to analyze the stress distribution inside the casing on the three-layer section by varying steel grade and wall thickness. It is indicated that the Von Mises stress inside the casing is the highest at sandstone-shale interface and shale interval, and the stress changes abruptly at sandstone-shale interface, resulting in sharp edges, so the casing at sandstone-shale interface and shale interval gets failed easily. Based on the characteristics of sand shale interbeds, the control measures on casing failure in shale interval were analyzed. And it is shown that the casing failure in shale interval can’t be controlled effectively by thickening the casing wall if the steel grade is kept the same. And the effective way is to increase the steel grade. This paper provides the beneficial reference for the study on casing failure control at sandstone-shale interface.