Interaction of Carbon Dioxide with Na-exchanged Montmorillonite at Pressures to 640 Bars: Implications for CO2 Sequestration

Na-exchanged montmorillonite swells upon interacting with CO2 under the conditions P(CO2) ≤ 50 bars, T = 22-47°C, as shown by experiments in high-pressure environmental chambers using powder X-ray diffraction techniques. The amount of swelling depends on the initial H2O content of the montmorillonite. Maximum expansion, to 12.3 Å, occurred in a sample with an initial d(001) of 11.3 Å at P(CO2) = 57 bars. Thus, montmorillonite can expand by 9% in contact with CO2 where small amounts of H2O are present in the interlayer. Little to no expansion occurs for samples with an initial d(001) ≤ 10.0 Å or d(001) = 12.3 to 12.5 Å. The reaction with CO2 is complete by ~50 bars; increasing P(CO2) from 50 to 640 bars did not result in any significant further increase of d(001). This work shows that a smectite-rich cap rock above a carbon sequestration reservoir may be significantly altered by reacting with CO2.