(88d) Carbon Dioxide and Methane Mixture Adsorption on Clay Mineral Surfaces in the Presence of Residual Water Content: A Molecular Simulation Study

Gas storage and release in shale is of interest for carbon sequestration as well as natural gas extraction applications. To properly predict carbon storage efficiency, enhanced natural gas production, or flow in natural and induced fractures, knowledge about the competitive sorption of carbon dioxide and methane is essential. In shales, sorption primarily occurs on clay minerals and in kerogen of the rock matrix. Although water content in shale plays is generally low, it is believed that even residual amount of water can profoundly affect sorption behavior of carbon dioxide and methane.

In this work, we employ a combination of Monte Carlo and molecular dynamics simulations to estimate mixed CO2/CH4 adsorption isotherms on illitic clay surfaces in the presence of water. Three bulk phase mixture compositions are explored to study the effect of concentrations on competitive sorption. The illitic systems bear two limiting charge localizations of the isomorphic substitutions to cover a range of possible charge distributions in nature. The computed isotherms are compared with those predicted for dry illitic clay to deduce effect of water on CO2 and CH4 interactions with clay surfaces. The role on the counter-balancing ions forming inner- and outer-sphere complexes in pore space is also discussed. Sensitivity parameters reflecting preferential sorption one species over another, density profiles, transport properties, and thermodynamic quantities are reported and analyzed.