Gypsum crystal growth kinetics under conditions relevant to CO2 geological storage

Abstract

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 crystal growth kinetics at the pressure range of 1–100 bar and with the addition of different molal concentrations of dissolved CO2 was investigated. A series of flow-through experiments were performed in a novel reactor system, designed to withstand high pressures, temperatures and corrosion. Gypsum growth rate was found to decrease with ascending pressure and increase with rising dissolved CO2 concentrations. Yet, separating the overall effect of these variables to their impact on the thermodynamics of the solution (i.e. super saturation) and on the reaction kinetics, reveal a very complex effect on the rate coefficient (khet). While due to the kinetic effect, the rate coefficient mostly decreases with rising dissolved CO2 concentrations, it has a second order polynomial behavior while pressure ascends. This implies that under the studied pressures and dissolved CO2 concentrations the thermodynamic is the main dominant parameter which governs the overall growth rate. It is suggested that both the thermodynamic and the kinetic effects arise from the respective dependence of the supersaturation of the solution and the rate coefficient (khet) on the solubility.