Characterization of CO2 and mixed methane/CO2 hydrates intercalated in smectites by means of atomistic calculations

• CO2 and CH4CO2 hydrates in smectites interlayer are studied by Molecular Dynamics.
• Water molecules form a gas hydrate-like hydrogen bonding network in the interlayer.
• The smectite 2:1 layer surface promotes the formation of gas hydrate complexes.
• Smectite-CH4 hydrate complexes are more stable than smectite-CO2 hydrate complexes.

The recent increase in anthropogenic CO2 gas released to the atmosphere and its contribution to global warming make necessary to investigate new ways of CO2 storage. Injecting CO2 into subsurface CH4 hydrate reservoirs would displace some of the CH4 in the hydrate crystal lattice, converting simple CH4 hydrates into either simple CO2 hydrates or mixed CH4CO2 hydrates. Molecular simulations were performed to determine the structure and behavior of CO2 and mixed hydrate complexes in the interlayer of Na-rich montmorillonite and beidellite smectite. Molecular Dynamics (MD) simulations used NPT ensembles in a 4 × 4 × 1 supercell comprised of montmorillonite or beidellite with CO2 or mixed CH4/CO2 hydrate complexes in the interlayer. The smectite 2:1 layer surface helps provide a stabilizing influence on the formation of gas hydrate complexes. The type of smectite affects the stability of the smectite-hydrate complexes, where high charge located on the tetrahedral layer of the smectites disfavor the formation of hydrate complexes.

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