This causes a local density increase, which induces natural convection currents accelerating the rate of CO 2 dissolution [1] . The occurrence of natural convection enhances the total storage rate in the aquifer since convection currents bring the carbon dioxide lean brine to the top and the contaminated brine to the bottom. Natural convection will eventually become less important as the brine becomes fully saturated with CO 2 (see Chapters 2 and 3). Chapter 2 Visualization and Numerical

more »

... gation of Natural Convection Flow of CO 2 in Aqueous and Oleic Systems ABSTRACT Optimal storage of carbon dioxide (CO 2 ) in aquifers requires dissolution in the aqueous phase. Nevertheless, transfer of CO2 from the gas phase to the aqueous phase would be slow if it were only driven by diffusion. Dissolution of CO2 in water forms a mixture that is denser than the original water or brine. This causes a local density increase, which induces natural convection currents accelerating the rate of CO 2 dissolution. The same mechanism also applies to carbon dioxide enhanced oil recovery. This study compares numerical models with a set of high pressure visual experiments, based on the Schlieren technique, in which we observe the effect of gravity-induced fingers when sub-and super-critical CO2 at in situ pressures and temperatures is brought above the liquid, i.e., water, brine or oil. A short but comprehensive description of the Schlieren set-up and the transparent pressure cell is presented. The Schlieren set-up is capable of visualizing instabilities in natural convection flows; a drawback is that it can only be practically applied in bulk flow, i.e., in the absence of a porous medium. All the same many features that occur in a porous medium also occur in bulk, e.g., unstable gravity fingering. The experiments show that natural convection currents are weakest in highly concentrated brine and strongest in oil, due to the higher and lower density contrasts respectively. Therefore, the set-up can screen aqueous salt solutions or oil for the relative importance of natural