Effect of Viscous and Buoyancy Forces on Nonwetting Phase Trapping in Porous Media

Abstract

The trapping of residual nonwetting phase in packings of equal spheres has been investigated for a wide range of capillary numbers, vμ/σ (ratio of viscous to capillary forces) and Bond numbers, ΔpgR2/σ (ratio of gravity to capillary forces). For vertical displacement, residual saturations varied from normal values of about 14.3% when the Bond number was less than 0.00667 and the capillary number was less than 3 × 10−6, down to near zero when either the Bond number exceeded 0.35 or the capillary number exceeded about 7 × 10−4. Precise correlation of residual saturation with a linear combination of Bond and capillary numbers showed that the effects of gravity and viscous forces on trapping are superposed. The equivalence of gravity and viscosity forces is used to determine relative permeability of the displacing fluid at the flood front. Relative permeabilities to the wetting phase behind the flood front at less than normal residual saturations are reported. For displacement at various dip angles, the effect of gravity is greater than that predicted by using results for vertical displacement with the Bond number resolved according to angle of dip.