Pore Network Modeling of Capillary Pressure -- Saturation Relations Through Retention Cells and Equilibrium Fluid Distributions in Long Columns

Standard methods for experimentally determining capillary pressure -- saturation relations of a porous medium use retention cells: a small cell filled with the porous medium is connected to two pressure reservoirs for the two given fluids. Then, the saturation is recorded as the pressure difference is changed. Conversely, one can infer capillary pressure -- saturation relations by analyzing equilibrium fluid distributions in long vertical columns. Capillary pressure -- saturation relations measured in retention cells differ from those inferred from equilibrium fluid distributions in long columns: at the point where the nonwetting phase starts invading the porous medium, retention cell curves are much smoother than long-column curves, which possess a close to angular shoulder. The objectives of our contribution are to (1) use a pore-network model to simulate long-column experiments and thus capillary pressure-saturation relations, (2) compare simulation results to actual measurements in a glass bead and a sand column, and (3) shed additional light onto the adequacy of both retention cell and long-column experiments for the determination of capillary pressure -- saturation relations.