title: Molecular dynamics computations of brine-CO2 interfacial tensions and brine-CO2-quartz contact angles and their effects on structural and residual trapping mechanisms in carbon geo-sequestration.
abstract: In the context of carbon geo-sequestration projects, brine-CO(2) interfacial tension γ and brine-CO(2)-rock surface water contact angles θ directly impact structural and residual trapping capacities. While γ is fairly well understood there is still large uncertainty associated with θ. We present here an investigation of γ and θ using a molecular approach based on molecular dynamics computer simulations. We consider a system consisting of CO(2)/water/NaCl and an α-quartz surface, covering a brine salinity range between 0 and 4 molal. The simulation models accurately reproduce the dependence of γ on pressure below the CO(2) saturation pressure at 300 K, and over predict γ by ~20% at higher pressures. In addition, in agreement with experimental observations, the simulations predict that γ increases slightly with temperature or salinity. We also demonstrate that for non-hydroxylated quartz surfaces, θ strongly increases with pressure at subcritical and supercritical conditions. An increase in temperature significantly reduces the contact angle, especially at low-intermediate pressures (1-10 MPa), this effect is mitigated at higher pressures, 20 MPa. We also found that θ only weakly depends on salinity for the systems investigated in this work.
authors.affiliation: Curtin University, Department of Petroleum Engineering, Kensington, Australia. stefan.iglauer@curtin.edu.au
authors.forename: S
authors.initials: S
authors.lastname: Iglauer
authors.forename: M S
authors.initials: MS
authors.lastname: Mathew
authors.forename: F
authors.initials: F
authors.lastname: Bresme
mesh_terms: D002245:Carbon Dioxide / Q000737:chemistry*; D057965:Carbon Sequestration; D056004:Molecular Dynamics Simulation; D011791:Quartz / Q000737:chemistry*; D012492:Salts / Q000737:chemistry*
chemical_list: D012492:Salts; C017082:brine; D002245:Carbon Dioxide; D011791:Quartz