Investigation of microcrack propagation behavior in the cement sheath of CCUS wells under corrosion effects

Abstract

To clarify how corrosion-driven degradation of cement stone properties affects crack propagation in CCUS well cement sheaths, this study investigated the microstructural evolution and mechanical response of cement stone adjacent to cracks after varying periods of corrosion exposure. An XFEM-based composite model consisting of casing, a microcracked cement sheath, and formation was developed to evaluate crack propagation under different corrosion degrees and to reveal the associated mechanisms. The main findings are as follows: (1) the corroded zone of cement stone exposed to supercritical CO2 exhibits a multilayered structure, and its thickness, composition, and mechanical properties vary with increasing corrosion duration; (2) supercritical CO2 corrosion promotes crack propagation in the cement sheath, with crack growth becoming increasingly pronounced as the corrosion duration increases. After 10 days of corrosion, the crack length on the inner side of the cement sheath reaches 153 mm, while the crack area increases by only 0.02% relative to the initial area. After 60 days of corrosion, the crack length reaches 158 mm, and the crack area increases by 1.3% compared with the initial area. These findings can provide support for evaluating cement sheath sealing performance and developing technologies to ensure the long-term effectiveness of zonal isolation.