In our effort to improve CO2 mitigation strategies, we require a more comprehensive understanding of the mechanisms controlling the interaction of supercritical CO2 (scCO2) with components of the subsurface system, including brines and clay minerals. Here we describe the use of classical molecular dynamics (MD) simulations to investigate the partitioning of cations between aqueous solution and scCO2, to reproduce measured contact angles for water droplets on both the hydrophobic and hydrophilic surfaces of kaolinite, and to predict the behavior of three-phase systems that include scCO2, brine, and a clay mineral.Molecular simulations suggest that the solvation energies for metal cations are smaller in CO2 than in water; therefore these cations will partition preferentially into water. However, the energies also suggest that large cations will partition into CO2 more than small ones. Simulations of the interface between scCO2 and an aqueous solution support this suggestion; large cations like Cs+ partition into the scCO2 phase, often with a partial solvation shell of water molecules. Therefore, scCO2 and subsurface brine may mix more easily than anticipated using the equations of state currently invoked in field-scale models.Molecular simulations have proved useful to examine the relative wettability of mineral surfaces with different fluid phases. MD simulations were conducted to establish a dynamic equilibrium between a liquid water droplet, water vapor, and the kaolinite surfaces. The calculated contact angles for the siloxane (hydrophobic) and gibbsite (hydrophilic) surfaces of kaolinite compare favorably to those reported in the literature. In three-phase simulations, scCO2 forms a droplet above the gibbsite surface, separated from the mineral by distinct layers of water. In contrast, on the siloxane surface, an adsorbed layer composed of CO2 and H2O molecules separates the mineral from aqueous droplets. The MD simulations provide a fundamental understanding of interfacial processes that should be considered in risk-assessment models.

Molecular insights into CO<sub>2</sub>-brine, clay-water, and clay-CO<sub>2</sub>-brine interfaces for carbon capture and sequestration

248th National Meeting (2014)

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Molecular insights into CO2-brine, clay-water, and clay-CO2-brine interfaces for carbon capture and sequestration

Molecular insights into CO₂-brine, clay-water, and clay-CO₂-brine interfaces for carbon capture and sequestration