Chemo-mechanical effects of carbonates dissolution on a Carbonate Clay

The effectiveness of CO2 underground storage is strictly connected to the sealing capacity of the caprock, which must necessarily prevent CO2 leakage. However, its hydro-mechanical behaviour might be affected by the dissolution of CO2in the brine, which acidifies the pore fluid and triggers chemical reactions with the solid phase, a highly critical aspect for carbonate-bearing rocks. The results of an experimental campaign aimed at studying the chemo-mechanical effects due to the dissolution of carbonates in a Carbonate Clay (CC) exposed to acidic solutions are presented. Titration tests allowed determining the sequence by which carbonate minerals dissolve upon addition of H+ in a clay-water suspension, thus exerting a buffering effect on the pH. Calcite dissolved first, followed by ankerite, and finally dolomite. The results of long-exposure tests of reconstituted CC specimens to diffusive or advective transport of an acidic solution also highlight the fundamental role of the transport mechanism, exposure times and concentrations on the extent of geomechanical effects on caprock.