LAUSR

Abstract In carbon capture and storage (CCS) wells, the well cement is attacked by CO 2 -rich fluids, coupled with tensile stress. In this study, well cement samples were designed to be exposed to humid CO 2 gas and CO 2 saturated brine and simultaneously subjected to external tensile stresses with load levels of 25%, 50%, and 75% of the initial tensile strength. The experimental results showed that a higher external tensile stress (50% and 75%) facilitated the generation and propagation of micro-cracks in the tension zone of loaded samples. Hence, the aggressive CO 2 -rich medium found direct paths to penetrate further into the core, significantly accelerating the rate of carbonation and failure of the well cement. As a result of the faster ion exchange and transfer, the carbonation rate was faster and the onset of failure in samples immersed in CO 2 -saturated brine occurred earlier than in the supercritical CO 2 scenario. Findings from this study provide new, important information for understanding the integrity of well cement sheath under actual CCS well conditions, thereby promoting superior cement system design and safer operation.