New Method To Reduce Residual Oil Saturation by Polymer Flooding

Abstract

SummarySix coreflood experiments were conducted to investigate the effect of hydrolyzed-polyacrylamide (HPAM) polymer solutions on the residual oil saturation (ROS) 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 approximately the same viscosity as the glycerin solution. The first polymer flood was designed to maximize the effect of viscoelasticity on the ROS by flooding the cores at a high Deborah number (NDe), and, as expected, resulted in a lower ROS. The second polymer flood in high-salinity brine had approximately the same viscosity, but a much lower relaxation time, and the flood had a much lower NDe. Unexpectedly, there was a further substantial reduction in ROS during the second polymer flood. The lowest ROS after the second polymer flood was only 0.07. This is a truly remarkable result, considering that there was no reduction in interfacial tension (IFT), 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 that of the glycerin solution.