Deep-saline aquifers are potential repositories for excess CO₂, currently being emitted to the atmosphere from anthropogenic activities, but the reactivity of supercritical CO₂ with host aquifer fluids and formation minerals needs to be understood. Experiments reacting supercritical CO₂ with natural and synthetic brines in the presence and absence of limestone and plagioclase-rich arkosic sandstone showed that the reaction of CO₂-saturated brine with limestone results in compositional, mineralogical, and porosity changes in the aquifer fluid and rock that are dependent on initial brine composition, especially dissolved calcium and sulfate. Experiments reacting CO₂-saturated, low-sulfate brine with limestone dissolved 10% of the original calcite and increased rock porosity by 2.6%. Experiments reacting high-sulfate brine with limestone, both in the presence and absence of supercritical CO₂, were characterized by the precipitation of anhydrite, dolomitization of the limestone, and a final decrease in porosity of 4.5%. However, based on favorable initial porosity changes of about 15% due to the dissolution of calcite, the combination of CO₂ co-injection with other mitigation strategies might help alleviate some of the well-bore scale and formation-plugging problems near the injection zone of a brine disposal well in Paradox Valley, Colorado, as well as provide a repository for CO₂.

Experiments showed that the solubility of CO₂ is enhanced in brine in the presence of limestone by 9% at 25 °C and 6% at 120 °C and 200 bar relative to the brine itself. The solubility of CO₂ is enhanced also in brine in the presence of arkosic sandstone by 5% at 120 °C and 300 bar. The storage of CO₂ in limestone aquifers is limited to only ionic and hydraulic trapping. However, brine reacted with supercritical CO₂ and arkose yielded fixation and sequestration of CO₂ in carbonate mineral phases. Brine desiccation was observed in all experiments containing a discrete CO₂ phase, promoting porosity-reducing precipitation reactions in aquifers near saturation with mineral phases.