Effect of dissolved H2SO4 on the interaction between CO2-rich brine solutions and limestone, sandstone and marl

The added H2SO4 lowered the pH of the injected brine by ~ 1.5 pH units with respect to the pH of ~ 3.6 of the H2SO4-free brine. In both H2SO4-free and H2SO4-rich brine, calcite dissolution fostered gypsum precipitation. A comparison between the reactivity of the rocks reacted in H2SO4-free and H2SO4-rich brine showed that calcite dissolution and gypsum precipitation rates were increased by 27-48% and 25-75%, respectively, in H2SO4-rich brine. Overall rock porosity increments in H2SO4-rich brine were 2.9-3.6%, 3.7-4.8%, and 2.1-2.7% for sandstone, limestone and marl, respectively. Porosities in H2SO4-rich brine were 6%, 23% and 250%, higher, respectively, than under pure CO2. Modeled porosity increments in the acid inlet zone in H2SO4-rich brine for sandstone, limestone and marl were 28-29%, 44-45% and 24-28%, respectively, corresponding to an increase of 1%, 250% and 25%, respectively, relative to H2SO4-free brine. Gypsum precipitation was consistently higher in marl than in limestone and sandstone, indicating kinetically favorable conditions for gypsum precipitation within the cap rock. Our results provide relevant data for long-term storage simulations of impure CO2 injection.