Summary The cement sheath acts as a primary barrier, providing both zonal isolation and mechanical support in the annular space between the casing and the surrounding formation. During carbon dioxide (CO2) sequestration, cement failure can occur due to mechanical, chemical, or operational factors. Numerous studies have shown that a microannulus—formed at the cement/formation or cement/casing interface—can become a major leakage pathway. While many researchers have focused on the development of microannuli during cement placement and setting, relatively few have investigated their evolution during CO2 injection. The lower temperature of the injected CO2, compared with the surrounding formation, can lead to thermal contraction of the casing and cement, resulting in interfacial debonding and cracking due to induced thermal stresses. Both laboratory and field studies have shown that such failures can significantly compromise long-term well integrity. In this paper, we present a mathematical model that integrates both mechanical and thermal effects to accurately predict the evolution of microannuli. The model has been implemented in the Eushaw Dynamics Simulator (EDS), a compositional simulation tool developed by Ashaw Energy. The focus of this study is specifically on wellbore integrity; a detailed discussion of CO2 compositional modeling will be provided in a separate publication. The results of this model can be used to help prevent zonal isolation failure and the potential release of CO2 to the surface. It is therefore critical to consider the mechanical and thermal properties of cement when designing the cement sheath for wells exposed to changing conditions—particularly in shallow reservoirs. While existing research has primarily focused on developing cement systems with high mechanical strength and flexibility, these studies often overlook the influence of formation properties and the impact of temperature gradients.
Khan et al. (2026) studied this question.