PNNL

Abstract

Geologic storage of carbon dioxide is a promising strategy for reducing CO2 concentrations in the atmosphere. In this process, silicate minerals in the host rock can react to permanently trap CO2 as precipitated carbonates. In addition, expandable clays in caprocks can swell or shrink and impact the integrity of the caprock seal. While the reactivity of minerals in CO2-rich aqueous fluids has been well studied, much less is known about mineral transformations in supercritical CO2 (scCO2) containing dissolved water. This chapter focuses on experimental investigations of mineral reactivity and transformations in variably hydrated scCO2. We summarize research regarding reservoir rocks, including carbonates, sandstone, granite, basalt, and peridotite. We also cover studies on several mineral systems, including phyllosilicate (montmorillonite), olivine (forsterite), serpentine (antigorite), pyroxene (enstatite), and feldspars (albite, anorthite, and microcline). For expandable phyllosilicate clay minerals, it is shown that volume changes are induced by both H2O and CO2 intercalation. For metal silicate minerals, a common observation is the adsorption of ångstroms- to nanometers-thick H2O films, which facilitate mineral dissolution, ion transport, and nucleation of metal carbonate precipitates. Many silicates exhibit a threshold concentration of adsorbed H2O, before which carbonation is limited to possibly amorphous phase precipitation or surface complexation, but beyond which carbonation is continuous and crystalline carbonates can form.