Mass Transfer of CO₂ in a Carbonated Water–Oil System at High Pressures

Abstract

In this paper, CO2 diffusion coefficients in a carbonate water–oil system are determined by measuring the pressure buildup in the closed water–oil system experimentally and modeling the pressure change mathematically. The mathematical method of investigating one-dimensional, time-dependent heat conduction in a composite medium is adopted to solve the mass transfer problem between two liquid phases. The model is combined with well-designed trial-and-error method to determine diffusion coefficients of CO2 in both water and oil phases at the same time. The model considers a moving interface between carbonated water and oil as well as variations of interface concentrations of CO2 in these two phases, which more effectively conforms to reality. Results show that the pressure buildup during the diffusion process resulted from the increased density and swelling of the oil phase. The diffusion coefficient of CO2 in the water phase plays a major role in the interphase mass transfer process.

Analytical solution of Buckley-Leverett equation for gas flooding including the effect of miscibility with constant-pressure boundary

“…The diffusivity of the gas was found to increase with temperature and pressure (Jamialahmadi et al, 2006). Shu et al (2017) concluded that the pressure is the most important factor affecting the mass transfer during the gas injection. They pointed that the interface concentration of CO 2 in the oil phase increased with the pressure.…”

Experimental evaluation of carbonated waterflooding: A practical process for enhanced oil recovery and geological CO2 storage

“…Due to the gradual and steady nature of the CO 2 transfer, the swelling and expansion of oil are expected to happen steadily. Hence in porous media flooded by CW, oil ganglia are believed to expand continuously leading to high overall swelling . Moreover, as water loses the dissolved CO 2 , slight decreases ensue in both the density and the viscosity of the aqueous phase …”

“…Hence in porous media flooded by CW, oil ganglia are believed to expand continuously leading to high overall swelling. 10,11 Moreover, as water loses the dissolved CO 2 , slight decreases ensue in both the density and the viscosity of the aqueous phase. [12][13][14] The theory is that the incremental oil recovery is obtained due to the mass transfer of CO 2 from the water phase into the oil phase, causing oil mobilization because of oil swelling and coalescence of the isolated oil ganglia, viscosity reduction, 6,15-18 and a reduced oil-water IFT.…”

Molecular Dynamics Simulation of CO2 Diffusion in a Carbonated Water–Decane System

“…When the system reaches equilibrium, even if the solubility of CO 2 in the oleic phase is not saturated (CO 2 concentration is far from saturated solubility), the CO 2 in the aqueous phase will not continue to move to the oleic phase. The CO 2 distribution between the aqueous and oleic phases according to a certain partition coefficient (k pc ) [11], which reflects the diffusion degree of CO 2 to the oleic phase, is presented in Table 1. The calculation results are in good agreement with the previous experiments [11,38,39].…”

“…Unlike other methods, CWI technology uses saturated CO 2 water to displace formed crude oil, which has the advantages of gas injection and water injection (WI). CWI is less affected by reservoir heterogeneity, which leads to a higher sweep efficiency [10,11], and it significantly reduces the residual oil saturation and improves the oil recovery [12]. In addition, the traditional CO 2 injection and WAG require continuous injection for a large amount of CO 2 , which leads to the economic decline of many reservoir projects.…”