New Method to Reduce Residual Oil Saturation by Polymer Flooding

Abstract

Abstract Six coreflood experiments were conducted to investigate the effect of hydrolyzed polyacrylamide (HPAM) polymer solutions on the residual oil saturation in Bentheimer sandstone cores. All six cores were first saturated with brine and then flooded in the following sequence: oil to zero water cut, brine to zero oil cut, glycerin solution to zero oil cut, polymer in low-salinity brine to zero oil cut and finally polymer in high-salinity brine to zero oil cut. The first polymer solution had about the same viscosity as the glycerin solution. The first polymer flood was designed to maximize the effect of viscoelasticity on the residual oil saturation by flooding the cores at a high Deborah number, and as expected resulted in a lower residual oil saturation. The second polymer flood in high-salinity brine had about the same viscosity, but a much lower relaxation time and the flood had a much lower Deborah number. Unexpectedly, there was a further substantial reduction in residual oil saturation during the second polymer flood. The lowest residual oil saturation after the second polymer flood was only 0.07. This is a truly remarkable result considering there was no reduction in interfacial tension, the capillary numbers were maintained below the critical capillary number for Bentheimer sandstone, and the viscosities of both polymer solutions were equal to or less than the glycerin solution.