Anomalous persistent fluid flow through thin films in porous media (Data)

We visualize two phase flow in indexed match porous media using a laser scanning confocal microscope (Leica SP-2), with a 10x objective lens with NA=0.4, and we use a 488-nm laser for excitation of all fluorophores. We visualize the non-wetting phase using an emission wavelength of 615 nm, and the fluorescent beads within the non-wetting phase using the emission wavelength of 514 nm. We image each frame having a 0.5 × 0.5 mm cross section, a 3 µm depth of field, at a spacing of 2 µm for the PIV imaging and no overlapping space for the 3D reconstructed images. Each frame takes about 100 milliseconds to collect; and the full stack of 300 frames takes roughly a minute to collect. The overlapping of the frames enables us to determine the velocity field of the wetting phase using particle image velocimetry (PIV) through correlation of the particle positions in consecutive frames. We also image a 6×1×0.3 mm volume of the porous medium by stitching stacks together; the full volume can be imaged in approximately an hour. From these images, we reconstruct the 3D structure of the porous media, the residual ganglia, and the displacing phase. The images before snap-off were taken after 24 hours corresponding to ~80 additional PV of steady state flow of the displacing fluid, and the image after snap-off was taken approximately one hour later.