套管水泥环刚度与强度对抗挤性能影响分析

油气井固井水泥环的作用就是减小和改善套管的受力状况，延长套管的使用寿命。套管水泥环组合体在一定的外挤压力作用下，均有可能进入屈服状态或发生强度破坏，而水泥环弹性模量、泊松比及其几何参数均表现为组合体刚度对抗挤性能的影响，所以在套管抗挤性能分析中，应该同时考虑组合体刚度以及套管、水泥环的强度对组合体抗挤性能的影响。文章根据厚壁筒弹塑性力学理论，建立了组合体刚度以及套管、水泥环强度对抗挤性能影响的控制方程，揭示了套管、水泥环强度及组合体刚度对抗挤性能的影响规律，得到套管水泥环组合体抗挤性能控制图。在均匀外挤压力作用下，套管、水泥环的强度将确定组合体抗挤性能的刚度控制区，在组合体刚度控制区内，水泥环对套管抗挤强度的提高程度取决于组合体刚度控制线斜率，在套管钢级和壁厚一定条件下，提高水泥环材料弹性模量，增大组合体刚度控制线斜率，可以提高套管水泥环组合体的抗挤性能。

Effects of Stiffness and Strength of Casing/Cement-Sheath on Collapsing Strength

The major function of cement sheath is to reduce and improve the load distribution on the casing so as to elongate the working life of the casing. The casing/cement-sheath combination tends to be destroyed under certain collapse stress. The elastic modulus, Poisson ratio and the geometric parameters of the cement sheath all demonstrate the effects of the stiffness of the combination on the collapsing strength. So, the stiffness of the combination and the strength of casing-cement should be considered when evaluating its collapsing strength. So based on the elastic-plastic theory of thick-wall cylinder, the corresponding control equation is put forward, the law of the influence of the stiffness of the combination and the strength of casing-cement on collapsing strength is disclosed, and a control chart is drawn. When under uniform collapse load, the stiffness control region for the collapsing strength of the combination will be determined by the strength of casing and cement. Inside the control region, the extent of improvement of the casing collapsing strength by cement sheath depends on the gradient of the combination stiffness control line. For a casing with certain steel grade and thickness, the collapsing strength of the casing/cement-sheath combination can be improved by increasing the elastic modulus of the cement sheath and increase the gradient of the stiffness control line of the combination.