油井热采水泥环内套管承载应力预测研究

Prediction of Bearing Stress of Casing in Thermal Recovery of Oil Well

热采井在蒸汽吞吐生产的过程中,水泥环缺陷的出现会引起套管应力集中以及承载能力下降等一系列不良影响。由于井下工况的复杂性,有能仿真套管在井眼中受力的真实状况,从而无法对套管承载应力分布进行优化来减少套管损坏。针对以上问题建立了不同水泥环缺失程度下的套管-水泥环-地层耦合的平面弹性应变模型,并借助有限元软件ANSYS进行求解,分析发现套管的最大变形或主要变形都出现在水泥环缺失的位置,说明水泥环的缺失会直接导致套管应力的集中。热应力导致的套损主要发生在注汽阶段,在整个注汽和焖井过程中,套管的变形起伏较大,为交变变化过程,套管可能发生低应力水平下的热应力疲劳破坏,也是热采井套管损坏的主要原因,通过以上分析能为热采井套管损坏的研究提供有益借鉴。

In the paper, a mathematical model for thermal stress of thermal recovery wells was established. Besides, an elastic plane strain model was established to analyze the coupled effect of casing - cement - formation with different degree of cement sheath defect. The model was solved with the help of ANSYS finite element software. Simulation results show that due to thermal stress, casing damage mainly occurs at the stage of steam injection. Casing suffers from alternating deformation during injection and soaking stage, which may cause casing fatigue damage under low stress level. The analysis reveals the main causes of casing damage in thermal recovery wells, and provides a scientific basis for casing damage prevention in thermal recovery wells.