Foam trapping in a 3D porous medium: in situ obser- vations by ultra-fast X-ray microtomography

Abstract : One of the challenges in the study of foam transport in 3D porous media is having an adequate spatial and temporal resolution, to get a better understanding of the local phenomenon at the pore scale in a non-destructive way. We present an experimental study in which ultra fast X-Ray microtomography is used to characterize the foam trapping while the foam is flowing in a 3D porous medium. A preformed aqueous foam is injected into a rotating cell containing a 3D granular medium made of silica grains. The use of rotating seals allows the cell to rotate continuously at the rate of one revolution per second, compatible with the fast X-ray tomography at SOLEIL synchrotron. We visualize the foam flow and track the trapping of bubbles with an acquisition time of about one second and a spatial resolution of a few microns (pixel size of one micron). This allows us to extract characteristics and reliable statistics about trapped bubbles inside the granular medium and to observe their local behavior. With this setup and technique we access to the dynamics of foam trapping during the flow and the texture variations of the foam in the trapped zones. These local trapping events are well correlated with the macroscopical measurement of the pressure gradient over the cell.