Buoyant currents arrested by convective dissolution

CW MacMinn & R Juanes, Geophysical Research Letters, 40(10):2017-2022, 2013. doi:10.1002/grl.50473

When CO2 is injected into a saline aquifer for carbon sequestration, it will rise and migrate due to buoyancy. It will also dissolve into the water via a hydrodynamic instability known as "convective dissolution". Here, we use a theoretical model and laboratory experiments to study the impact of convective dissolution on upslope migration.

Videos 0, 1, and 2 show an experiment in a Hele-Shaw cell where the upslope migration of a buoyant current of water (dark) is arrested by convective dissolution into the ambient propylene glycol (light). The Hele-Shaw cell is 5.2cm tall with a 1.4mm gap between the plates, and the cell is tilted about 2.5 degrees counterclockwise relative to horizontal.

Video 0. The raw experimental snapshots in greyscale. This video shows about 30 minutes of real time in about 23 seconds.

Video 1. Surface-growth model for the fingered front (cyan line; Eq. 2) overlayed onto snapshots of the experiment. This simple growth model provides an excellent approximation to the evolution of the fingered front. This video shows about 30 minutes of real time in about 23 seconds.

Video 2. The actual fingered front (red dots) and the paths of the fingertips (blue curves) overlayed onto snapshots of the same experiment. We measure the depth of the fingered front at each horizontal position (red points) as the depth where the intensity of the image becomes smaller than a threshold value. We identify the fingertips as local minima of the fingered front. The paths of the fingertips illustrate the coarsening of the fingering pattern as the fingers grow and merge. This video shows about 30 minutes of real time in about 23 seconds.

Videos 3 and 4 show two experiments in a quasi-two-dimensional flow cell packed with glass beads (1.25mm diameter). The cell is about 5.2cm tall and is tilted about 2.5 degrees counterclockwise relative to horizontal.

Video 3. A buoyant gravity current (water, dark) migrates over the denser, more viscous ambient fluid (a mixture of glycerol and water, light). There is no convective dissolution in this system, so the buoyant current migrates indefinitely. The red curve is from a gravity-current model. This video shows about 1 hour of real time in about 18 seconds.

Video 4. A buoyant gravity current (water, dark) migrates over the denser, more viscous ambient fluid (propylene glycol, light). With this pair of fluids, convective dissolution slows and ultimately arrests the migration of the buoyant current. The red curve is again from a gravity-current model. This video shows about 10 hours of real time in about 19 seconds.