Wetting Properties of the CO2–Water–Calcite System via Molecular Simulations: Shape and Size Effects

Abstract

Assessment of the risks and environmental impacts of carbon geosequestration requires knowledge about the wetting behavior of mineral surfaces in the presence of CO 2 and the pore fluids. In this context, the interfacial tension (IFT) between CO 2 and the aqueous fluid and the contact angle, θ, with the pore mineral surfaces are the two key parameters that control the capillary pressure in the pores of the candidate host rock. Knowledge of these two parameters and their dependence on the local conditions of pressure, temperature and salinity is essential for the correct prediction of structural and residual trapping. We have performed classical molecular dynamics simulations to predict the CO 2 -water IFT and the CO 2 -water-calcite contact angle. The IFT results are consistent with previous simulations, where simple point charge water models have been shown to underestimate the water surface tension, thus affecting the simulated IFT values. When combined with the EPM2 CO 2 model, the SPC/Fw water model indeed underestimates the IFT in the low pressure region at all temperatures studied. On the other hand, at high pressure and low temperature, the IFT is overestimated by ∼5 mN/m. Literature data regarding the water contact angle on calcite are contradictory. Using our new set of force field parameters, we performed NVT simulations at 323 K and 20 MPa to calculate the contact angle of a water droplet on the calcite {10.4} surface in a CO 2 atmosphere. We performed simulations for both spherical and cylindrical droplet configurations for different initial radii, to study the size dependence of the water contact angle on calcite in the presence of CO 2 . Our results suggest that the contact angle of a cylindrical water droplet on calcite {10.4}, in the presence of CO 2 , is independent of droplet size, for droplets with a radius of 50 Å or more. On the contrary, spherical droplets make a contact angle that is strongly influenced by their size. At the largest size explored in this study, both spherical and cylindrical droplets converge to the same contact angle, 38 • , indicating that calcite is strongly wetted by water.

Molecular Origin of Wettability Alteration of Subsurface Porous Media upon Gas Pressure Variations

“…Long-range electrostatic interactions were computed using the PPPM (particle-particle-particle-mesh) solver. For calcite, we used the force field provided by Silvestri et al 5 (a file containing all force field parameters was provided in the Supporting Information of Silvestri et al 5 Note that because the TRaPPE force field was used for CO 2 , we adjusted the interaction of a CO 2 molecule with an SPC water molecule using the Lorentz−Berthelot mixing rules).…”

CO2-Fluid-Rock Interactions and the Coupled Geomechanical Response during CCUS Processes in Unconventional Reservoirs

“…Classical molecular dynamics (MD) has been used to predict the interfacial tension between CO 2 and water (brine) [84], as well as the CO 2 -water-mineral surface contact angle [85]. The latter has been proved to be a function of temperature, pressure, and salinity.…”

“…The influence of the contact line's curvature on the contact angle can be ignored in the macroscopic size of the droplet. However, at the nanoscale, the liquid and solid surface forces will change the droplet's shape, resulting in the influence of the contact line's curvature that cannot be ignored [85,86]. The influence of contact lines is usually described by introducing contact line tension [87].…”

“…As a representative of the silicate strata' composition, quartz and mica have been used as the mineral base for contact angle measurement in many experiments. Some studies have also reported gas-liquid contact angles on the calcite surface (carbonate formation) [85,[88][89][90]. Since calcite is a suitable material to adsorb organic matters even in dilute solutions and organic materials and adsorbed ions can significantly change the wettability of mineral surfaces, the contact angle can be observed from the initial strong water wet (0°< θ < 75°), scattering to between 2°and 60° [91].…”

Molecular Dynamics Simulation of Wetting Behavior: Contact Angle Dependency on Water Potential Models

“…Molecular dynamics (MD) simulation is a powerful tool to obtain the microscopic details of atomistic system, and it has been widely used to investigate the physiochemistry of surface and the wetting behaviors [17][18][19][20][21][22][23][24][25][26][27][28][29][30][31][32][33] . One of the key issue in MD simulation is the potential models adopted to describe the interaction between molecules.…”