Suggesting a numerical pressure-decay method for determining CO2 diffusion coefficient in water

Carbon Capture and Storage is developed as state-of-the-art method to bring CO2 emissions under control. Among different options, saline aquifers are viable choices to sequestrate CO2 in which this gas can be dissolved in the pertinent brine through a gradual progressive diffusive layer and subsequent possible density-induced convection. Quantification of CO2 dissolution rate in saline aquifers is dependent on the true estimation of CO2 diffusivity in brine. In this work, equilibrium dissolution and diffusion coefficient of CO2 in water-saturated porous medium is modeled. The simple and well-known pressure-decay method is applied numerically in different porous systems. Also, interference of density-driven convection using different permeability values is addressed and the idea of using a porous medium such as glass bead model is proposed to block convective swirls or postpone onset of convection. Convective currents are suppressed at Rayleigh numbers (Ra) fewer than 40. For controlled convective dissolution, the onset of convection should be late enough for that early diffusive dissolution to dominate. Also, convective dissolution should deviate from diffusive dissolution to find the onset of convection and time at the end of early convection. The former and latter require Ra < 1100 and Ra > 150, respectively. Under these circumstances, pressure decay results can be analyzed to estimate the gas-liquid diffusion coefficient using early pressure-time data, onset of convection, the maximum Sherwood and time at the end of early convection. (C) 2015 Elsevier B.V. All rights reserved.