Formation of viscous fingers at interphase boundaries during the joint displacement of three viscous liquids from porous media

This study examines the peculiarities of the unstable displacement of viscous fluids from porous media. The joint displacement of three viscous fluids is studied. When the viscosity of the displacing fluid is lower than the viscosity of the displaced fluid, the well-known Saffman-Taylor instability occurs at the displacement front. It is proposed to consider the result of displacement of three fluids with different viscosity differences at the interfaces between the fluids. The leakage of “viscous fingers” of one interphase boundary through the “viscous fingers” formed at the other boundary is observed. The numerical modeling results also showed the temporary “trapping” of the displaced fluid at a certain viscosity difference at the interface. The formation of "viscous fingers" during frontal displacement, similar to “fingers” during radial displacement, was revealed. The factors influencing the formation of “fingers” at an angle to the direction of flow are determined. A comparison is made with the results obtained when displacing oil with a polymer solution: an additional solution – a liquid with the addition of high-molecular polymer compounds, the presence of which leads to an increase in the viscosity of the liquid – is pre-injected into the reservoir. As a result, the viscosity difference at the solution-oil interface is reduced, which leads to a significant increase in oil recovery.