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Dissolution of CO 2 into brine causes the density of the mixture to increase. The density gradient induces natural convection in the liquid phase, which is a favorable process of practical interest for CO 2 storage. Correct estimation of the dissolution rate is important because the time scale for dissolution corresponds to the time scale over which free phase CO 2 has a chance to leak out. However, for this estimation, the challenging simulation on the basis of convection-diffusion equation must be done. In this study, pseudo-diffusion coefficient is introduced which accounts for the rate of mass transferring by both convection and diffusion mechanisms. Experimental tests in fluid continuum and porous media were performed to measure the real rate of dissolution of CO 2 into water during the time. The pseudo diffusion coefficient of CO 2 into water was evaluated by the theory of pressure decay and this coefficient is used as a key parameter to quantify the natural convection and its effect on mass transfer of CO 2 . For each experiment, fraction of ultimate dissolution is calculated from measured pressure data and the results are compared with predicted values from analytical solution. Measured CO 2 mass transfer rate from experiments are in reasonable agreement with values calculated from diffusion equation performed on the basis of pseudo-diffusion coefficient. It is suggested that solving diffusion equation with pseudo diffusion coefficient herein could be used as a simple and rapid tool to calculate the rate of mass transfer of CO 2 in CCS projects.

A number of forced gravity drainage experiments have been conducted using a wide range of the physical and operational parameters, wherein the type, length, and permeability of the porous medium as well as oil viscosity and injection rate were varied. Results indicate that an increase in the Bond number has a positive effect on oil recovery whereas the capillary number has an opposite effect. These trends were observed over a two-order of magnitude change in the value of the dimensionless groups. Furthermore, it was found that use of each number alone is insufficient to obtain a satisfactory correlation with recovery. A combined dimensionless group is proposed, which combines the effect of all the three forces. Recoveries from all the experiments conducted in this study show a very good correlation with the proposed group. The exponent of the Bond number in the proposed group is larger than the capillary number suggesting a larger importance for the former. We then show that the same group provides a good correlation for recovery from additional experiments conducted in this study (in the presence of connate water) with that of another set of experiments in the literature.

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A detailed investigation into the effect of dissolved amphiphilic compounds of crude oil in salt water on its surface tension/interfacial tension (ST/IFT) behavior has been conducted in this paper. To simulate water–oil contact during water injection into oil reservoirs, 16 single-salt aqueous solutions of NaCl, CaCl2, and Na2SO4 having ionic strengths of up to 2.0 M were mixed with a natural acidic–basic crude oil. The mixing was performed by a rocking mechanism in a visual pressure–volume–temperature cell at an elevated temperature. After the mixing process, two phases were completely separated from each other using a high-temperature centrifuge. Finally, in addition to pH measurements, the air–water ST and decane–water IFT of salt water were measured using the pendant-drop method. The results reveal that the dissolution of crude oil amphiphilic compounds, especially the acidic or basic compounds, in salt water can considerably decrease its ST/IFT. It seems that there is the same optimal ionic strength for the aqueous solutions of the three studied salts, in which both the air–water ST and the decane–water IFT of salt water are minimized after its contact with crude oil. It was observed that, among the three studied salts, the aqueous solutions of Na2SO4 had the lowest ST/IFT values for all ionic strengths after their contact with crude oil. This result can be because the crude oil used was more basic than acidic.