Abstract This work aims at assessing the cement integrity during CO2 injection by illustrating the relevance of injection operations to the failure modes of cement. A single-phase flow model for pure CO2 is developed to provide the temperature and pressure profiles in the well and solved by a finite difference method. With the downhole temperature predicted by the flow model as a boundary condition, we present a mechanical model to estimate the stress state in the well section under plane-strain conditions as well as the stress intensity factor at a radial crack tip. This study introduces four failure factors corresponding to shear compressive failure, radial cracking, interfacial debonding, and fracture propagation. Further parametric studies are implemented to reveal the effects of injection operations, including injection temperature, rate, and time, on the above failure factors. They indicate that the injection rate is the most influential factor for cement integrity. High injection rates could cause radial cracking and its propagation as well as interfacial debonding but reduce the risk of shear compressive failure. Low injection temperatures or a long injection time would undermine the tensile and interfacial strength and extend the radial crack in cement while they benefit on shear compressive strength. The results provide guidelines to optimize injection operations for long-term well integrity during CO2 injection.

中文翻译：

---

通过井眼流动模型和应力分析评估 CO2 注入井的水泥完整性

摘要 这项工作旨在通过说明注入操作与水泥破坏模式的相关性来评估 CO2 注入过程中的水泥完整性。开发了纯 CO2 的单相流动模型，以提供井中的温度和压力分布，并通过有限差分方法求解。以流动模型预测的井下温度作为边界条件，我们提出了一个力学模型来估计平面应变条件下井段的应力状态以及径向裂纹尖端的应力强度因子。本研究介绍了与剪切压缩破坏、径向开裂、界面脱粘和断裂扩展相对应的四种破坏因素。实施进一步的参数研究以揭示注射操作的影响，包括注射温度、速率、和时间，关于上述失效因素。他们表明注入速率是水泥完整性的最影响因素。高注射率可能会导致径向开裂及其扩展以及界面脱粘，但会降低剪切压缩破坏的风险。较低的注入温度或较长的注入时间会破坏抗拉强度和界面强度并扩大水泥中的径向裂缝，而它们有利于剪切抗压强度。结果为在 CO2 注入期间优化注入操作以实现长期井完整性提供指导。高注射率可能会导致径向开裂及其扩展以及界面脱粘，但会降低剪切压缩破坏的风险。较低的注入温度或较长的注入时间会破坏抗拉强度和界面强度并扩大水泥中的径向裂缝，而它们有利于剪切抗压强度。结果为在 CO2 注入期间优化注入操作以实现长期井完整性提供指导。高注射率可能会导致径向开裂及其扩展以及界面脱粘，但会降低剪切压缩破坏的风险。较低的注入温度或较长的注入时间会破坏抗拉强度和界面强度并扩大水泥中的径向裂缝，而它们有利于剪切抗压强度。结果为在 CO2 注入期间优化注入操作以实现长期井完整性提供指导。