Trapping and mobilization of residual fluid during capillary desaturation in porous media

We discuss the problem of trapping and mobilization of nonwetting fluids du ring immiscible two-phase displacement processes in porous media. Capillary desaturation curves give residual saturations as a function of capillary n umber. Interpreting capillary numbers as the ratio of viscous to capillary forces the breakpoint in experimental curves contradicts the theoretically predicted force balance. We show that replotting the data against a novel m acroscopic capillary number resolves the problem for discontinuous mode dis placement.