Gravity Effects in the Displacement of Oil by Surfactant Solutions

Summary The displacement of isooctane by aqueous surfactant solutions was investigated in model porous media consisting of a thin layer of lightly sintered glass beads. Pre-equilibrated oil/surfactant pairs were prepared that exhibited interfacial tensions (IFT's) in the range 0.06 to 2.08 mN/m [0.06 to 2.08 dynes/cm]. Because aqueous solution viscosity was always higher than that of the isooctane, a stable displacement would normally be expected. While systems with IFT's greater than about 1 mN/m [1 dyne/cm] showed sharp interfaces and generally stable displacements, experiments conducted at lower IFT exhibited a considerable degree of instability. In particular, at lower tensions, the interfaces became fuzzy, and there was distinct evidence of gravity underride by the aqueous phase. The onset of gravity segregation with decreasing IFT was successfully related to capillary and viscpus forces operating within the systems. The degree of instability was found to increase with decreasing IFT, but oil recoveries did not necessarily decrease because of recovery mechanisms that involved mobilization and coalescence of zones of bypassed oil.