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The mass transfer of CO 2 into water and aqueous solutions of sodium dodecyl sulphate (SDS) is experimentally studied using a pressure, volume, temperature (PVT) cell at different initial pressures and a constant temperature (T D 25 ı C). It is observed that the transfer rate is initially much larger than expected from a diffusion process alone. The model equations describing the experiments are based on Fick's Law and Henry's Law. The experiments are interpreted in terms of two effective diffusion coefficients-one for the early-stages of the experiments and the other one for the later stages. The results show that at the early stages, the effective diffusion coefficients are one order of magnitude larger than the molecular diffusivity of CO 2 in water. Nevertheless, in the later stages the extracted diffusion coefficients are close to literature values. It is asserted that at the early stages, density-driven natural convection enhances the mass transfer. A similar mass transfer enhancement was observed for the mass transfer between a gaseous CO 2 rich phase with an oil (n-decane) phase. It is also found that at the experimental conditions studied addition of pure SDS does not have a significant effect on the mass transfer rate of CO 2 in water.

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Concern over global warming has increased interest in quantification of the dissolution of CO2 in (sub-)surface water. The mechanisms of the mass transfer of CO2 in aquifers and of transfer to surface water have many common features. The advantage of experiments using bulk water is that the underlying assumptions to the quantify mass-transfer rate can be validated. Dissolution of CO2 into water (or oil) increases the density of the liquid phase. This density change destabilizes the interface and enhances the transfer rate across the interface by natural convection. This paper describes a series of experiments performed in a cylindrical PVT-cell at a pressure range of p i = 10−50 bar, where a fixed volume of CO2 gas was brought into contact with a column of distilled water. The transfer rate is inferred by following the gas pressure history. The results show that the mass-transfer rate across the interface is much faster than that predicted by Fickian diffusion and increases with increasing initial gas pressure. The theoretical interpretation of the observed effects is based on diffusion and natural convection phenomena. The CO2 concentration at the interface is estimated from the gas pressure using Henry’s solubility law, in which the coefficient varies with both pressure and temperature. Good agreement between the experiments and the theoretical results has been obtained.

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Wettability plays a crucial role on the performance of enhancing oil recovery techniques because of its effect on fluid saturations and flow behavior in porous medium. This study is directed toward determining contact angles (i.e., wettability) in systems with carbon dioxide, brine, and an oil-saturated rock system. Two situations are considered: Rock system I is partially water-wet, whereas rock system II is effectively oil-wet. Contact angles have been determined experimentally as a function of brine salinity and pressure using the pendant-drop shape analysis. The experiments were carried out at a constant temperature of 318 K and pressures varying between 0.1 up to 16.0 MPa in a pendant-drop cell. For rock system I, the partially water-wet substrate, brine, and CO 2 system, the dependence on the pressure at constant salinity is very small. For this system, at a constant pressure, the contact angle decreases for increasing brine salinity. The results show that the carbon dioxide is the nonwetting phase in the pressure and salinity range studied. This behavior can be quantitatively understood in terms of the expected dependencies of the three interfacial tensions (IFTs) in Young's equation on pressure and brine salinity. For rock system II, the effectively oil-wet substrate, brine, and CO 2 system, the dependency of contact angle on pressure is considerable. This study proves that carbon dioxide becomes the wetting phase at pressures higher than 10.0 MPa. Beyond 10.0 MPa (i.e., in the supercritical region), the contact angle remains practically constant. The effect of salinity on the contact angle of the oil-wet rock system II is small. The behavior can again be quantitatively understood based on expected trends of the three IFTs that determine the contact angle. It is also shown that use of the equation of state method makes it possible to approach the experimental data quantitatively. We conclude that contact angle measurements form an essential ingredient to determine the efficiency of carbon dioxide flooding and storage.