Effect of dispersion on the onset of convection during CO2 sequestration

Dissolution of carbon dioxide (CO2) injected into saline aquifers causes an unstable high-density diffusive front. Understanding how instability fingers develop has received Much attention because they accelerate dissolution trapping, which favours long-term sequestration. The time for the onset of convection as the dominant transport mechanism has been traditionally Studied by neglecting dispersion and treating the CO2-brine interface as a prescribed concentration boundary by analogy to a thermal convection problem. This work explores the effect of these simplifications. Results show that accounting for the CO2 mass flux across the prescribed concentration boundary has little effect on the onset of convection. However, accounting for dispersion causes a reduction of Lip to two orders of magnitude on the onset time. This implies that CO2 dissolution can be accelerated by activating dispersion as a transport mechanism, which can be achieved adopting a fluctuating injection regime.