Viscous fingering and interface splitting instabilities in air-water-oil systems

Viscous fingering instabilities of air displacing water displacing mineral oil is controlled by the air injection rate. Given the lower viscosity of the water, air would tend to finger through the water and then after it reaches the oil, proceed to finger through the oil.

In a radial Hele-Shaw cell, experiments were conducted on air injection into mineral oil and air injection into a volume of water at the center of the cell which in turn is surrounded by mineral oil. The images of the fingers are analyzed to quantify the fingering patterns to compare the behaviours between the two and three phase systems.

Significantly different fingering patterns occur between the two and three phase systems. When air fingers penetrate the water layer and reach the oil, the air propagates along the interface between water and oil in an interface splitting instability mode resulting in development of more intricate fingering patterns. It was also observed that air fingers penetrate within water fingers that penetrate the oil. In addition, the fingertip moves faster with the presence of water exhibiting a discontinuity of the fingertip velocities across the water and mineral oil regions.