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 degrees 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 angstrom, occurred in a sample with an initial d(0 0 1) of 11.3 angstrom at P(CO2) = 57 bars. Thus, montmorillonite can expand by 9% in contact with CO2 when small amounts of H2O are present in the interlayer. Little to no expansion occurs for samples with an initial d(0 0 1) <= 10.0 angstrom or d(0 0 1)=12.3-12.5 angstrom. The reaction with CO2 is complete by similar to 50 bars; increasing P(CO2) from 50 to 640 bars did not result in any significant further increase of d(0 01). This work shows that a smectite-rich cap rock above a carbon sequestration reservoir may be significantly altered by reacting with CO2. (C) 2012 Elsevier Ltd. All rights reserved.