Gypsum solubility under pressure conditions relevant to CO₂ geological storage

Deep saline aquifers are among the preferred potential repositories for carbon dioxide Geological Storage (CGS). Modeling the interaction of the injected CO₂ with the brine is essential for proper planning of CGS, including avoidance of local precipitation of minerals such as sulfates which may clog the injection borehole and decrease the injectivity of the surrounding rock mass. In the present study gypsum solubility at various molal concentrations of dissolved CO₂ at pressures of up to 100 bar was investigated. A series of semi-batch experiments was performed in a novel flow-through reactor system, designed to withstand high pressures, temperatures and corrosion. Solubilities attained in the experiments match (within a 3% uncertainty) the new PHREEQC v.3′s predictions (Appelo et al., 2014) in which pressure and dissolved CO₂ concentrations are two of the new variables. Accordingly, gypsum solubility was found to increase as pressure rises and to decrease as CO₂ concentration ascends.