Diffusion coefficients of water in CO2 under the condition of CO2 sequestration in saline aquifers

For CO2 sequestration in saline aquifers, brine evaporation might lead to salt precipitation, impacting the CO2 injection efficiency and storage security. It is essential to study the diffusion of water in CO2, which indirectly controls the evaporation rate of brine. However, the research on high temperature and pressure under CO2 sequestration conditions is very limited. In this work, the diffusion process of water in CO2 under the condition of saline aquifers is observed and the quantitative Raman spectroscopy is used to acquire the concentration profiles to determine the diffusion coefficient. The results show the diffusion coefficient of water in CO2 increases linearly with the increase of temperature and reciprocal of CO2 density, and decreases with the increase of pressure. An equation to predict the diffusion coefficient based on CO2 density is proposed. When applied to porous reservoirs, it is predicted that the effective diffusion coefficient of water in CO2 is much higher in saline aquifer with a depth of less than 1 km.