Carbonated water injection for EOR and CO₂ storage: a simulation study

CO₂ Enhanced Oil Recovery (EOR) techniques have gained massive attention by oil companies as they target the oil industry's two main concerns of CO₂ contribution to the climate change and the decline in oil production. Carbonated Water Injection (CWI) is a promising EOR technique that promotes safe and economic CO₂ storage, moreover, it mitigates the pitfalls of CO₂ injection which include low sweep efficiency, early CO₂ breakthrough, and the risk of CO₂ leakage in subsurface formations. Upon the contact of Carbonated Water (CW) with oil inside the reservoir, CO₂ molecules cross the interface between the two fluids moving towards the oil phase due to the concentration gradient and its higher solubility in hydrocarbons. Subsequently CO₂ molecules diffuse inside the oil until thermodynamic equilibrium is reached. CO₂ dissolution in oil causes it to swell and consequently leads to changes in its physical properties (viscosity and density). Such changes in oil properties lead to improved sweep and displacement efficiency and thus higher recovery factor. Several experimental studies have been reported in the literature, but little work has been done on the simulation of CWI due to the complex multi-physics nature of this process. In this paper, Schlumberger equilibrium-based compositional simulator (ECLIPSE300) has been used to investigate the oil recovery and CO₂ storage during CWI. The carbonated water has been simulated using two injector wells placed at the same location where they inject free CO₂ and water at a certain volumetric ratio to account for the mass fraction of dissolved CO₂ inside the carbonated water. CO₂SOL option has been used to account for CO₂ solubility inside the water phase and a 2D cartesian model (x, y) has been considered to avoid the effects of gravity which might reduce the amount of CO₂ dissolved inside the oil phase. A sensitivity analysis on CW injection rate, and the effect of CO₂ diffusion have been investigated. It was found that low injection rate promotes longer contact time thus more CO₂ molecules will get transferred to the oil leading to high oil recovery and CO₂ storage. In addition, it was found that CO₂ diffusion between grid cells has minimal impact on oil recovery and CO₂ storage in this case study.