Droplets evolution during ex situ dissolution technique for geological CO2 sequestration: Experimental and mathematical modelling

CO2 can flow upward and leak through thief zones due to buoyancy effect during geological sequestration. To tackle this issue, the ex situ dissolution (ESD) concept was introduced aiming at full dissolution of CO2 at the surface, before it is injected into the ground, to increase the storage capacity and lower the risk of leakage. A mathematical model for CO2 droplets evolution in the ESD process is presented, followed by an experimental investigation to verify the proposed model. The developed model accounts for the droplet break-up process and transient mass transfer involved in the ESD. A number of mathematical correlations were developed to compute the average droplet size, break-up frequency, and droplet population in a turbulent dispersion regime. Experimental and mathematical results revealed that a minimum stable CO2 droplet is achievable within a pipeline length of less than 50 m if the CO2 volume fraction is in the range of 5–15% and the brine flow rate varies between 0.25 and 2.0 Mt/yr. An acceptable agreement between the predicted and experimental droplet size distributions is observed. This study confirms that the ESD can reduce the leakage risk because of the formation of fine CO2 droplets.

► Evolution of CO2 droplets in ESD is studied mathematically.
► Equations are obtained to calculate break-up frequency and droplet population.
► Brine flow rate, CO2 hold up and PVT behaviour affect droplet size distribution.
► ESD can reduce leakage risks because of formation of fine CO2 droplets.
► Good agreement is observed between predicted and experimental droplet size distributions.