On the choice of analogue fluids in CO2 convective dissolution experiments

Mixtures of ethylene glycol and methanol (EG-MeOH) have been used as an analogue system (i.e., EG-MeOH/water) in recent experiments in the context of convective dissolution of CO2 in deep saline aquifers. We have conducted a linear stability analysis of a gravitationally unstable diffusive boundary layer as well as direct numerical simulation of convective mixing involved in dissolution of EG-MeOH species in water. We provide new evidences that EG-MeOH does not resemble the dynamics of convective instabilities and subsequent mixing associated with dissolution of CO2 in water. It is found that there are fundamental differences in the evolution of the buoyancy-driven instability and dynamics of convective mixing between CO2/water and a typical EG-MeOH/water analogue system. Our results show that for a constant Rayleigh number, the onset of convective instabilities for EG-MeOH/water can be different by an order of magnitude as compared with CO2/water. In addition, EG-MeOH/water system reveals different dynamics associated with the convective mixing as compared to CO2/water system. This study improves our understanding of the instability behavior of analogue systems, their proper selection, and motivates further experiments.