大庆油田嫩二底标志层套管剪切失效的有限元分析

Finite element analyses of casing shear failure in Member Ⅱof Nenjiang Formation in Daqing Oilfield

大庆油田嫩二底标志层套损以剪切错断和剪切变形为主,标志层是否封固对套管剪切过程的受力和变形影响较大。考虑套管、水泥环和地层弹塑性力学特征,分别建立了封固与不封固三维有限元计算模型,计算并对比了2种模型在地层滑移过程中套管和地层的Mises应力、套管对地层的反作用力、塑性变形范围和套管内壁位移量。计算结果表明,嫩二底标志层封固与不封固2种模型的应力都集中于剪切面附近,套管的受力和变形程度都大于井壁岩石;不封固套管的受力和变形相对分散,更有利于标志层剪切套损的预防和修复。

Casing impairment of N2 bottom marker bed is mainly shearing failure and shearing deformation in Daqing Oilfield. It has a great influence on stress and deformation in the progress of casing shear if the marker bed is cemented. Considering the elastoplastic mechanics characteristics of casing, cement and rock, the cemented and uncemented three-dimensional finite element calculation models were established respectively. Mises stress of casing and rock, reaction force of casing to rock, elastic deformation region and displacement of casing inside wall from two cementing methods were calculated and compared. Result shows that stress concentrates on shear slip surface, stress and deformation of casing is greater than that of side wall rock in the two models. Casing stress and deformation of uncemented condition is more diffuse than that of cemented condition. Uncemented condition is conducive to prevent and repair casing shear failure in marker bed.