Solvation structure of supercritical CO2 and brine mixture for CO2 plume geothermal applications: A molecular dynamics study

Abstract

This paper reports an investigation for solvation structure of supercritical CO2 (scCO2) and brine mixture for CO2 plume geothermal (CPG) applications. Molecular dynamics simulations are performed to calculate radial distribution function, coordination number and hydrogen-bond number for mixtures of different compositions. This study can help reveal the solvation structures of scCO2/brine mixture under different temperatures (373.15 K–473.15 K) and ion concentrations (1 wt% to 10 wt%). Results show that H2O molecules bind more tightly to Na+ ion than Cl− ion while scCO2 molecules seem have a uniform distribution in the scCO2/brine mixture. Both the interaction of Na+-H2O pairs and that of Cl--H2O pairs become stronger under higher temperature conditions. Besides, the increase of ion concentration not only reduces the number of H2O molecules in the solvation shell of Na+ ion, but also weakens the interaction of hydrogen bonds. Moreover, it seems that the scCO2/brine mixture is heterogeneous in the CPG application.