Diffusion of carbon dioxide in formation water as a result of CO₂ enhanced oil recovery and CO₂ sequestration

Flooding carbon dioxide into oil reservoirs is a promising technique for improving the pressure of a reservoir when it is depleted through primary and secondary production. In the context of global warming, it is a viable method for geological storage of CO₂ emissions. Once CO₂ is injected into a reservoir, it is forced to come into partial contact with formation water. To estimate the rate of CO₂ transfer and the total amount of CO₂ dissolved in the formation water, correct estimation of CO₂ diffusivity is required. In this study, the rate of CO₂ diffusion in water was experimentally determined in a PVT cell using the pressure depletion method at reservoir conditions (temperature: 50–75 °C and pressure: 17,450 kPa). As expected, the rate of CO₂ diffusion in water increases with increasing temperatures. In addition, the impact of salinity of the water on the rate of CO₂ diffusion was investigated. A significant decrease in the rate of CO₂ diffusion was found with increasing salinity. Subsequently, a diffusion model describing the experiments was developed to predict the behavior of CO₂ diffusivity under simulated conditions. Unique correlations between CO₂ diffusion coefficients and water at different temperatures and salinities were obtained using the results of modeling.