Observational evidence confirms modelling of the long-Term integrity of CO 2-reservoir caprocks

Storage of anthropogenic CO 2 in geological formations relies on a caprock as the primary seal preventing buoyant super-critical CO 2 escaping. Although natural CO 2 reservoirs demonstrate that CO 2 may be stored safely for millions of years, uncertainty remains in predicting how caprocks will react with CO 2-bearing brines. This uncertainty poses a significant challenge to the risk assessment of geological carbon storage. Here we describe mineral reaction fronts in a CO 2 reservoir-caprock system exposed to CO 2 over a timescale comparable with that needed for geological carbon storage. The propagation of the reaction front is retarded by redox-sensitive mineral dissolution reactions and carbonate precipitation, which reduces its penetration into the caprock to â 1/47 cm in â 1/410 5 years. This distance is an order-of-magnitude smaller than previous predictions. The results attest to the significance of transport-limited reactions to the long-Term integrity of sealing behaviour in caprocks exposed to CO 2.