Experimental determination of CO sub(2) diffusion coefficient in aqueous solutions under pressure at room temperature via Raman spectroscopy: impact of salinity (NaCl)

• Published in: Journal of Raman spectroscopy Vol. 46; no. 10; pp. 1025 - 1032
• Main Authors: Belgodere, Clement, Dubessy, Jean, Vautrin, Denis, Caumon, Marie-Camille, Sterpenich, Jerome, Pironon, Jacques, Robert, Pascal, Randi, Aurelien, Birat, Jean-Pierre
• Format: Journal Article
• Language: English
• Published: 01.01.2015
• Subjects: Aqueous solutions; Aquifers; Carbon dioxide; Diffusion; Diffusion coefficient; Dissolution; Microspectrometry; Salinity
• ISSN: 0377-0486; 1097-4555
• DOI: 10.1002/jrs.4742

The accurate determination of the diffusion coefficient of dissolved CO sub(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 sub(2) as a function of subsurface conditions is essential to ensure the integrity of CO sub(2) storage in saline aquifers. Experimental data are available to predict the CO sub(2) diffusion kinetics as a function of temperature and pressure. However, the impact of salinity on CO sub(2) diffusivity is still poorly documented. In this work, the diffusion coefficients of dissolved CO sub(2) were determined using in situ Raman microspectrometry in Fused Silica Capillaries in a range of salinity from 0.0 to 6.0mol sub(NaCl)kg super(-1) sub(H2O). The diffusion coefficient of CO sub(2) dissolved in pure water at 21 plus or minus 1 degree C and 40bar is 1.7110 super(-9) plus or minus 0.06m super(2)s super(-1). In the same conditions of pressure and temperature, the diffusion coefficient of dissolved CO sub(2) decreases with salinity increase: from 0.0 to 6.0mol sub(NaCl)kg super(-1) sub(H2O) (the diffusion kinetics of dissolved CO sub(2) is divided by two). Consequently, the impact of salinity on the diffusion coefficient of dissolved CO sub(2) must be taken into account to evaluate the transport of dissolved gases in the brine of the reservoir and caprock. In this work, the diffusion coefficients of dissolved CO sub(2) were determined using in situ Raman microspectrometry in Fused Silica Capillaries in a range of salinity from 0.0 to 6.0mol sub(NaCl).kg super(-1) sub(H2O). The diffusion coefficient of CO sub(2) dissolved in pure water at 21 plus or minus 1 degree C and 40bar is 1.7110 super(-9) plus or minus 0.06m super(2).s super(-1). In the same conditions of pressure and temperature, the diffusion coefficient of dissolved CO sub(2) decreases (divided by two) with salinity increase from 0.0 to 6.0mol sub(NaCl).kg super(-1) sub(H2O).