THE EFFECTS OF GRAVITY AND VISCOUS FORCES ON RESIDUAL NONWETTING-PHASE SATURATION

In this paper, we investigate theoretically and experimentally the com bined effects of gravity and viscous forces on residual nonwetting-pha se saturation in immiscible displacements. We develop simplified model s of oil entrapments to account for the combined effects of gravity an d viscous forces on snap-off and bypass processes. Both models demonst rate theoretically that the combined effects of gravity and viscous fo rces can be represented by the Brownell-Katz number (N-BK), the sum of a capillary number (ratio of viscous force to capillary force, del Pk /sigma) and a Bond number (ratio of gravity force to capillary force, Delta rho k/sigma). The magnitude of the Bond number in comparison to capillary number depends on the permeability of the medium and the wet ting-phase relative permeability. Immiscible displacements were conduc ted in a vertical sandpack (119 cm long and 1.95 cm in diameter) to te st the proposed theory. We obtained a wide range of Bond numbers and c apillary numbers by varying interfacial tension (IFT), phase density d ifference, and injection rates for mixtures of brine, isopropanol, and iso-octane. Results from displacements with gravity forces assisting and with gravity forces impeding recovery support the linear combinati on of capillary and Bond numbers (N-BK). The experimental results pres ented along with previously available experimental data verify that th e scaling results hold for variation of any of the parameters that app ear in the Bond and capillary numbers.