Correlation between capillary number and residual water saturation

Displacement of a wetting phase by a nonwetting phase is controlled by the viscous as well as the capillary forces. The ratio of viscous forces to that of the capillary is called the capillary number. It is found that the residual water saturation was affected by increasing the viscosity of the displacing phase and by reducing the interfacial tension between oil and water. However, the effect of these two parameters will be observed after certain values of the viscosity and the interfacial tension. These values will be functions of absolute permeability of the core sample. It is expected that, for a higher permeability core sample, the residual water saturation will be lower than that of a lower permeability for the same displacing phase. Correlation between the residual water saturation and the capillary number resulted in two different curves when including viscosity and the interfacial tension effects. A new dimensionless number resulted in a unique correlation with the residual water saturation.