The Influence of Fluid Viscosity, Interfacial Tension, and Flow Velocity on Residual Oil Saturation Left by Waterflood

Results of short-core flow tests are presented for six different sandstones and one limestone to show the influence of interfacial tension, fluid viscosity, and flow velocity on waterflood Sor. To make certain that oil trapping occurred in the presence of the test flood water, the floods were initiated at-saturations at which the oil phase was continuous and in contact with the test flood water as the connate water. It was found for strongly water-wet cores (cos θ ≅ 1) that Sor could be described in terms of the Moore and Slobod dimensionless group expanded to include viscosity effects: (νμw/σ o-w)(μw/μo)0.4 Normal waterfloods are described by values of the group &le 10-6. To reduce Sor, flood-water properties or test conditions had to be modified to increase the value of the group by 100 to 1,000 times. These increases in the dimensionless group were obtained primarily with increases in flow velocity and water viscosity, although interfacial tensions as low as 1.5 dynes/cm were used in some floods. Assuming that this dimensionless group will hold for other combinations of the variables, we can estimate reductions in residual oil saturation that can be achieved for selected values of these variables.