Carbon dioxide (CO2) sorption to Na-rich montmorillonite at Carbon Capture, Utilization and Storage (CCUS) P-T conditions in saline formations

Abstract

Carbon capture, utilization and storage (CCUS) in confined saline aquifers in sedimentary formations has the potential to reduce the impact of fossil fuel combustion on climate change by storing CO2 in geologic formations in perpetuity. At PT conditions relevant to CCUS, CO2 is less dense than the pre-existing brine in the formation, and the more buoyant CO2 will migrate to the top of the formation where it will be in contact with cap rock. A typical cap rock is clay-rich shale, and interactions between shales and CO2 are poorly understood at PT conditions appropriate for CCUS in saline formations. In this study, the interaction of CO2 with clay minerals in the cap rock overlying a saline formation has been examined, using Na-rich montmorillonite as an analog for clay-rich shale. Attenuated Total Reflectance -- Fourier Transform Infrared Spectroscopy (ATR -FTIR) was used to identify potential crystallographic sites (AlAlOH, AlMgOH and interlayer space) where CO2 could interact with montmorillonite at 35"C and 50"C and from 0-1200 psi. Analysis of the data indicates that CO2 that is preferentially incorporated into the interlayer space, with dehydrated montmorillonite capable of incorporating more CO2 than hydrated montmorillonite. No evidence of chemical interactions between CO2 and montmorillonite were identified, and no spectroscopic evidence for carbonate mineral formation was observed. Further work is needed to determine if reservoir seal quality is more likely to be degraded or enhanced by CO2 - montmorillonite interactions.