An Extended Buckley-Leverett Model for Non-Newtonian Foam Injection

Abstract

Scope: Surfactant-alternating-gas (SAG) is the preferred method of foam injection to improve sweep efficiency in enhanced-oil-recovery (EOR). Here, for the first time, fractional-flow theory is extended to include the shock for gas injection in the high-quality regime for radial flow in a non-Newtonian SAG process for shear-thinning and shear-thickening foams.
Methodology: To represent non-Newtonian behavior in the high-quality regime, the limiting water saturation for foam stability varies as superficial velocity decreases with radial distance from the well. We look at the interactions between the shock and the characteristics. The mobility control at the shock front and injectivity are examined. The system is compared to a Newtonian foam.
Results and conclusions: For shear-thinning foam, the foam front’s dimensionless velocity decreases with time, while the characteristics accelerate and collide with the shock. As the foam front propagates, the mobility ratio and mobility control becomes more favorable. The injectivity decreases until breakthrough, then improves slightly.
For shear-thickening foam, dimensionless velocity of the foam front increases with time, while the shocks slow down. Mobility control worsens and injectivity improves as the foam propagates, even before breakthrough. For extremely shear-thickening foam, the near-wellbore region exhibited shear-thinning behavior. This has three causes: a shift from the high- to the low- quality regime, the extrapolation of f mdry over a too large range, and the Namdar Zanganeh correction.
Recommendations: Future models should replace the shock with the colliding characteristic, instead of eliminating the characteristic. For shear-thickening foams, new characteristics should split off from the shock. Include the shear-thinning factor for the low-quality regime to check if the foam is still in the high-quality regime.