Measurement of CO2 diffusivity in synthetic and saline aquifer solutions at reservoir conditions: the role of ion interactions

• Published in: Heat and mass transfer 2015-11, Vol.51 (11), p.1587-1595
• Main Authors: Jafari Raad, Seyed Mostafa, Azin, Reza, Osfouri, Shahriar
• Format: Article
• Language: English
• Subjects: Engineering; Engineering Thermodynamics; Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Original; Thermodynamics
• ISSN: 0947-7411; 1432-1181
• DOI: 10.1007/s00231-015-1508-4

Storage and disposal of CO 2 as the main component of greenhouse gases in saline aquifers require careful measurement of diffusivity for predicting rate of transfer and cumulative amount of trapped gas. Little information is available on diffusion of CO 2 in highly concentrated saline aquifers at reservoir conditions. In this study, diffusivity of CO 2 was measured into different solutions, including saline aquifer taken from oil field, distilled water and synthetic solutions prepared from four most common ions, Mg 2+ , Ca 2+ , K + , Na + . The roles of salvation effect and hydration phenomenon were studied on diffusivity of dissolved CO 2 . Synthetic solutions were prepared at concentration ranges of 83–200 g/l. Experimental measurements were reported at temperature and pressure ranges of 30–40 °C and 5,880–6,265 kPa, respectively. Results show that both type and concentration of ion affect CO 2 diffusivity. Diffusion coefficient was found dependent on effective radius of hydrated ions. Also, CO 2 diffusivity increase by increasing strength of bonds between ion and neighbor water molecules. Also, presence of ions in water solution creates hydration competition between solution metal ions and aqua ions from diffusive gas. The Mg 2+ cation, which has strongest hydration competition among other ions, has an increasing effect on gas diffusivity into saline aquifer. However, increasing ion concentration in solution decreases diffusivity of CO 2 due to growth in fraction of contact ion pairs. Results of this study provide unique measures of CO 2 diffusion coefficient in saline aquifer at high pressure and temperature conditions and conceptual information about effect of each common saline formation ion on gas diffusivity.