Capillary pinning

B Zhao, CW MacMinn, HE Huppert, and R Juanes, Water Resources Research, 50(9):7067-7081, 2014 (pdf).

When CO2 is injected into a saline aquifer for carbon sequestration, it will rise and migrate due to buoyancy. Since the CO2 is immscible with the ambient groundwater, capillarity can play an important role in this process. Here, we use laboratory experiments and a theoretical model to study the impact of capillarity on the buoyant spreading of CO2 in horizontal and sloping aquifers.

Video 1. Gravity-driven flow of a buoyant, nonwetting fluid (air) over a dense, wetting fluid (propylene glycol) in a packing of glass beads.  Red line represent predictions from the macroscopic sharp-interface model that we developed to incorporate the effects of capillary pinning and blunting.

Video 2. Simulations of evolution of immiscible gravity currents under varying amount of capillarity. Capillary pinning and blunting limits the migration distance of immiscible gravity currents. 

Video 3. An experiment in a quasi-2D porous medium consisting of a Hele-Shaw cell etched with cylindrical posts. The post centers are arranged on a regular grid, but their diameters are randomly distributed between 0.25 and 0.75 mm. The buoyant fluid is air (white) and the dense, ambient fluid is silicone oil (dyed blue). The cell is oriented such that gravity is pointing downward, toward the bottom of the page.

 

Video 4. A quasi-static simulation of this process in the same geometry using a simple drainage model.