Interaction of carbon dioxide with Na-exchanged montmorillonite at pressures to 640bars: Implications for CO 2 sequestration

Na-exchanged montmorillonite swells upon interacting with CO ₂ under the conditions P(CO ₂)≤50bars, 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 H ₂O content of the montmorillonite. Maximum expansion, to 12.3Å, occurred in a sample with an initial d(001) of 11.3Å at P(CO ₂)=57bars. Thus, montmorillonite can expand by 9% in contact with CO ₂ when small amounts of H ₂O are present in the interlayer. Little to no expansion occurs for samples with an initial d(001)≤10.0Å or d(001)=12.3-12.5Å. The reaction with CO ₂ is complete by ∼50bars; increasing P(CO ₂) from 50 to 640bars 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 CO ₂.