Molecular dynamics investigation on the adsorption behaviors of H2O, CO2, CH4 and N2 gases on calcite (1 (1)over-bar 0) surface

Molecular dynamics simulations (MD) were carried out to investigate the adsorption behaviors of H2O, CO2, CH4 and N-2 gases, which are the main and important components in gas wells, on the calcite surface at reservoir conditions. By analyzing the binding energy and Helmholtz free energy, we found that the preferential adsorption order of these four gases is: H2O > CO2 > CH4 > N-2. Moreover, we have also calculated the radial distribution function profiles of the system. It shows that the H2O molecules will form two compact adsorbed layers on the surface, which denotes the calcite (1 (1) over bar 0) surface is hydrophilic. The CO2 molecules can also form a adsorbed layer on the surface, while there are no significant features indicating that the CH4 and N-2 molecules were apparently adsorbed on calcite (1 (1) over bar 0) surface. Our calculations results can not only give a microscopic insight into the wettability of gas reservoirs but also provide theoretical instructions for hydrate risk evaluation of enhanced gas recovery. (C) 2016 Elsevier B.V. All rights reserved.