FAST, IMMISCIBLE FLUID-FLUID DISPLACEMENT IN 3-DIMENSIONAL POROUS-MEDIA AT FINITE VISCOSITY CONTRAST

The crossover from capillary to viscous how during immiscible fluid-fluid displacement has been studied in transparent, three-dimensional porous media. The defending and the invading fluids have equal densities, so that gravity effects are eliminated. The viscosity ratio of defending fluid to injected fluid m is moderate m similar or equal to 14. Dense, ball-like displacement structures are generated at high injection rates. Surprisingly, the how appears to be nearly completely stabilized even though the viscosity of the invading fluid is significantly lower than that of the defending fluid. For the physical system studied here, fully developed ball-like patterns arise for capillary numbers Ca greater than or equal to 5 x 10(-3) A similar behavior is found in experiments using the same grains and fluids in a two-dimensional system.