Abstract
Carbon capture, utilization and storage (CCUS) in saline reservoirs in sedimentary formations has the potential to
reduce the impact of fossil fuel combustion on climate change by reducing CO2 emissions to the atmosphere and
storing the CO2 in geologic formations in perpetuity. At pressure and temperature (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. Interactions between clay-rich shale cap
rocks 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+ exchanged montmorillonite (Mt) (Na+-STx-1) (Na+ Mt) as an analog for clay-rich shale. Attenuated Total
Reflectance-Fourier Transform Infrared Spectroscopy (ATR-FTIR) was used to discern mechanistic information
for CO2 interaction with hydrated (both one- and two-water layers) and relatively dehydrated (both dehydrated
layers and one-water layers) Na+-STx-1 at 35 °C and 50 °C and CO2 pressure from 0–5.9 MPa. CO2-induced perturbations associated with the water layer and Na+-STx-1 vibrational modes such as AlAlOH and AlMgOH were
examined. Data indicate that CO2 is preferentially incorporated into the interlayer space, with relatively
dehydrated Na+-STx-1 capable of incorporating more CO2 compared to hydrated Na+-STx-1. Spectroscopic
data provide no evidence of formation of carbonate minerals or the interaction of CO2 with sodium cations in
the Na+-STx-1 structure.
