Underground storage of CO2 will lead to chemical fluid-rock interactions which may potentially alter the porosity and the flow patterns in faults. In this study, we present a coupled numerical model combining chemical fluid-rock interactions, aqueous diffusion, fluid flow, and mechanical processes, aiming at a better understanding of mineral reactions leading to changes of the rock properties, the associated flow patterns and the mechanical stability of faulted caprock on the long-term (500 yrs). In the examples that we studied the mechanical stability of the caprock system was not affected, but significant porosity changes were predicted for low-consolidated fault gouges. Coupled chemical-flow modelling is preferred over chemical modelling as this showed significantly higher porosity increases.
Global emissions of carbon dioxide (CO2 ) into the atmosphere, mainly as a result of fossil fuel burning and cement production, is believed to significantly influence global warming . Carbon capture and storage (CCS) is potentially able to reduce these emissions on a short to medium time scale by storing CO2 in geological structures of the deep subsurface. The CO2 is trapped below a sealing caprock in porous media like sandstones or carbonate rocks. One of the main risks associated with storage activities is the leakage of CO2 into shallower regions of continental groundwater systems . The release of CO2 results preferentially in water acidification and potential mobilization of trace elements, which may have a toxic effect on the environment . Uncertainties are mainly related to potential leakage mechanisms, through faults and fractures, along wellbores and sealing caprock material, by convection and diffusion.