Objective  The cement sheath of CCUS well is exposed to CO₂ corrosion environment for a long time, and the cement sheath will be corroded, leading to CO₂ leakage. Therefore, it is necessary to predict the corrosion rate. However, the current corrosion prediction models mainly rely on wellbore and semi empirical formulas, which leads to inaccurate prediction of cement sheath corrosion and restricts the research on the prevention and control of cement sheath corrosion in CCUS wells.

Methods  In response to this issue, a CO₂ corrosion depth prediction model was established based on the conservation laws of CO₂ and calcium mass. This model analysed the impact of corrosion time, temperature, CO₂ partial pressure, water-cement ratio, and corrosion-resistant material dosage on corrosion depth. An evaluation model was also established to rank the degree of influence of these factors.

Results  The research results indicated that the CO₂ corrosion depth increased with the corrosion time, temperature, chloride ion content, CO₂ partial pressure, water-cement ratio, and water saturation, and decreased with the cement sheath density and corrosion-resistant material dosage. Additionally, the CO₂ concentration within the cement sheath showed a non-linear decrease with the increase in corrosion depth. The strength of the influencing factors was: water saturation > corrosion resistant material > water-cement ratio > cement ring density > CO₂ partial pressure > corrosion time > chloride content > temperature.

Conclusion  The research results have guiding significance for controlling CO₂ carbonization corrosion of cement sheath in CCUS well to ensure well integrity.