Integrating mechanical and chemical perspectives: Assessing and enhancing cement sheath integrity in CO2 geological storage wells

Long-term sealing integrity of cement sheaths remains a critical concern for CO 2 geological storage, particularly under coupled chemical-mechanical degradation. This study presents an integrated multi-scale framework to assess cement sheath integrity under supercritical CO 2 conditions. Macroscopic experiments were conducted to evaluate strength loss and degradation depth over time, complemented by nanoindentation tests to calibrate micromechanical properties of degraded cement. A time-dependent finite element model was developed to simulate the coupled chemical-mechanical degradation process of the cement sheath. Sensitivity analysis further quantified the roles of cement shrinkage and bonding strength in driving the development of micro-annuli. Results show that after 28 d of CO 2 exposure, the degradation depth reached approximately 1.28 mm, and compressive strength declined by 28.5%. Numerical simulations indicate a 30.4% increase in radial tensile stress and 9.1% enlargement of the interfacial micro-annulus. Latex-modified cement demonstrated superior sealing performance, attributed to its enhanced resistance to CO 2 -induced degradation. Practical recommendations include maintaining cement shrinkage below 0.2% and interfacial bonding strength above 0.5 MPa to ensure sealing effectiveness. This work provides a mechanistic understanding and quantitative guidance for improving well integrity in CCS operations.