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 ∼7 cm in ∼10(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).