Predicting CO2–water interfacial tension under pressure and temperature conditions of geologic CO2 storage

Abstract

Storage in subsurface geologic formations, principally saline aquifers, is currently under development as a major approach to counter anthropogenic CO 2 emissions. To ensure the stability and long-term viability of geologic carbon storage, injected CO 2 must be kept in place by an overlying cap rock of very low permeability. Capillary forces in the cap rock act to prevent upward migration and escape of the stored supercritical fluid, with interfacial tension (IFT) between the aqueous brine phase and the CO 2 phase being the primary control. However, published experimental CO 2 -water IFT data vary widely, mainly because of inadequate experimental protocols or inappropriate use of bulk-fluid properties in computing IFT from experimental observations. Only two published data sets were found to meet all criteria of merit for an accurate measurement of IFT over the entire range of pressure (5-45 MPa) and temperature (298-383 K) pertinent to geologic carbon storage. In such circumstances, molecular simulations can enhance the utility of limited data when used to validate assumptions made in their interpretation, resolve discrepancies among data, and fill gaps where data are lacking. Simulations may also be used to provide insight into the relationship between IFT and fundamental properties, such as the strength of the CO 2 -H 2 O interaction. Through molecular dynamics simulations, we compared the quality of three CO 2 models and two H 2 O models (SPC/E and TIP4P2005) in predicting IFT under the pressure and temperature conditions relevant to geologic CO 2 sequestration. Interfacial tension at fixed temperature simulated via molecular dynamics decreased strongly with increasing pressure below the critical CO 2 pressure of 7 MPa, then leveled off, in agreement with experiment, whereas increasing temperature from 300 to 383 K at fixed pressure had little effect on IFT, which is also

Interfacial tensions of systems comprising water, carbon dioxide and diluent gases at high pressures: Experimental measurements and modelling with SAFT-VR Mie and square-gradient theory

“…An overview of the published modelling studies for the systems of interest in this paper is presented in Table 1. Previous modelling studies of (H 2 O + CO 2 ) cover a wide range of pressures up to 60 MPa, within a more limited temperature range from 287 K to 398.15 K [14,25,26,[28][29][30][31][32][33][34][35][36], exempting the study of [28] in which the system was considered, but no results presented. These ranges of temperature and pressure cover both vapour-liquid equilibrium (VLE) and liquid-liquid equilibrium (LLE) between H 2 O and a compressed CO 2 -rich phase.…”

Analysis of Ginzburg-Landau-type models of surfactant-assisted liquid phase separation

“…Thus, the interfacial tension is in the order of 50 mJ/m 2 [24], and the width of the interface loaded by macromolecules is in the order of δ 0 ≈ 0.1 µm [25]. The molecular weight of macromolecular surfactants is typically in the order of 1000g/mol, while the density is considered to be approximately 1 g/cm 3 [26,27], yielding the average density of the system ρ ≈ 1000 kg/m 3 .…”

High-pressure densities and interfacial tensions of binary systems containing carbon dioxide+n-alkanes: (n-Dodecane, n-tridecane, n-tetradecane)

“…On the other hand, theoretical descriptions of these mixtures have been made by employing Density Functional Theory (DFT) [13,14,22], Density Gradient Theory (DGT) or Square Gradient Theory (SGT) [23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38]. Furthermore, molecular simulations based either on Molecular Dynamics or Monte Carlo schemes have also been employed [19,30,31,39,40,41] to garner information on the interfacial properties of these systems. An analysis of the above mentioned references reveals that there are key points that must be taken into account: First, an unequivocal full description of interfacial properties requires -at least-two independent approaches, as some previous works have demonstrated (see for instance and references therein).…”