Phase space study of viscous fingering and saturation pre- and post-breakthrough using lattice Boltzmann simulations of two-phase flow

Abstract

Viscous fingering is the occurrence of narrow fingers of an invading less viscous fluid such as water in a porous medium filled with a more viscous fluid such as oil, and its occurrence dramatically affects enhanced oil recovery by water flooding. We conduct 2D simulations using the lattice Boltzmann method for two-phase flow through a porous medium initially saturated with a fluid of a given viscosity in which a fluid of another viscosity is injected from the left side of the model. We conduct suites of simulations over viscosity ratios (∼1 / (mobility ratio)) from M = 0.01 through M = 100 and for wetting angles from non-wetting to fully wetting. We plot the phase space of saturation (= Recovery Factor) versus wetting angle and viscosity ratio. We remove the dominant viscosity ratio effect to study the effect of wetting angle and find that while there is some tendency for the saturation to be higher with increasing wettability, the saturation landscape is complex with hills and valleys in which optimal wetting angles exist that maximize saturation. Furthermore, the phase space landscape is found to depend on the porous matrix geometry. We also plot saturation post-breakthrough and find that the saturation continues to increase albeit at an ever decreasing rate. This research demonstrates the potential of the lattice Boltzmann method for two-phase flow to reveal unexpected behavior and phenomena with both scientific and practical significance such as optimization of recovery factors in enhanced oil recovery (EOR).