Quantification of CO2-cement-rock interactions at the well-caprock-reservoir interface and implications for geological CO2 storage

Simulation results suggest that cement tortuosity and diffusion coefficient are the two most important parameters that dictate cement carbonation penetration distance. Portlandite (Ca(OH)2) reacts with CO2 and forms calcite, reducing porosity, in turn directly impacting CO2 leakage rates by infilling pathways. Simulated calcium-silicate-hydrate (CSH) degradation is limited, suggesting that a wellbore will maintain its integrity and structure under the considered conditions. Simulations also suggest that sulfate concentration <2500 mg/L in the leaking brine would not cause monosulfate degradation. Without an existing fracture, CO2 will likely not enter the caprock, and the cement would not degrade accordingly. For the FWU specifically, the wellbore cement would likely keep its structure and integrity after 100 years. However, if a fracture exists at the cement-caprock interface, calcite dissolution in the limestone caprock fracture could occur and increase the fracture volume, a concern for caprock integrity.