In-Situ X-ray Tomography Study of Cement Exposed to CO₂ Saturated Brine

For successful CO₂ storage in underground reservoirs, the potential problem of CO₂ leakage needs to be addressed. A profoundly improved understanding of the behavior of fractured cement under realistic subsurface conditions including elevated temperature, high pressure and the presence of CO₂ saturated brine is required. Here, we report in situ X-ray micro computed tomography (μ-CT) studies visualizing the microstructural changes upon exposure of cured Portland cement with an artificially engineered leakage path (cavity) to CO₂ saturated brine at high pressure. Carbonation of the bulk cement, self-healing of the leakage path in the cement specimen, and leaching of CaCO₃ were thus directly observed. The precipitation of CaCO₃, which is of key importance as a possible healing mechanism of fractured cement, was found to be enhanced in confined regions having limited access to CO₂. For the first time, the growth kinetics of CaCO₃ under more realistic well conditions have thus been estimated quantitatively. Combining the μ-CT observations with scanning electron microscopy resulted in a detailed understanding of the processes involved in the carbonation of cement.