Experimental determination of CO₂ diffusion coefficient in aqueous solutions under pressure at room temperature via Raman spectroscopy: impact of salinity (NaCl)

Abstract

The accurate determination of the diffusion coefficient of dissolved CO 2 in aqueous solutions is a key parameter to predict the transport of the dissolved gas in the aqueous solution of porous aquifers and caprocks in the context of the mitigation of greenhouse gases emissions. A better understanding of the diffusion kinetics of dissolved CO 2 as a function of subsurface conditions is essential to ensure the integrity of CO 2 storage in saline aquifers. Experimental data are available to predict the CO 2 diffusion kinetics as a function of temperature and pressure. However, the impact of salinity on CO 2 diffusivity is still poorly documented. In this work, the diffusion coefficients of dissolved CO 2 were determined using in situ Raman microspectrometry in Fused Silica Capillaries in a range of salinity from 0.0 to 6.0 mol NaCl kg −1 H2O . The diffusion coefficient of CO 2 dissolved in pure water at 21 ± 1 °C and 40 bar is 1.71 × 10 −9 ± 0.06 m 2 s −1 . In the same conditions of pressure and temperature, the diffusion coefficient of dissolved CO 2 decreases with salinity increase: from 0.0 to 6.0 mol NaCl kg −1 H2O (the diffusion kinetics of dissolved CO 2 is divided by two). Consequently, the impact of salinity on the diffusion coefficient of dissolved CO 2 must be taken into account to evaluate the transport of dissolved gases in the brine of the reservoir and caprock. Copyright © 2015 John Wiley & Sons, Ltd.