Carbonate formation in Wyoming montmorillonite under high pressure carbon dioxide

► We report a high-pressure CO2 induced carbonation in Wyoming montmorillonite. ► We observed clay structural deformations associated with the carbonation. ► CO2 fluid is more favorable for carbonate formation at 70°C than it is at 22°C. ► Carbonation occurs predominantly within the first two days of exposure to CO2. Carbonation reaction with silicate minerals that are common components of the host rock and cap rock within geological storage reservoirs and the associated structural deformation were investigated for better understanding of the geochemical reactions associated with geologic CO2 storage. Exposure of a model expanding clay, Wyoming montmorillonite, SWy-2, to high-pressure CO2 resulted in the formation of a mineral carbonate phase via dry CO2–clay mineral interactions at two different temperatures. The experimental evidence suggests that the properties of CO2 fluid at 70°C provide more favorable conditions for carbonate formation at the clay surface less accessible to CO2 at 22°C. The carbonation reaction occurred predominantly within the first couple of days of exposure to the fluid and then proceeded slower with continuing exposure. As compared to the as-received clay under the same ambient conditions, the (001) basal spacing of the clay bearing carbonates (after the CO2 exposure) was slightly expanded at a relative humidity (RH) level of 12% but it was slightly collapsed at the RH level of 40%. Experimental observations suggest that the carbonation reaction occurs at the external surface as well as internal surface (interlayer) of the clay particles.