Comparison between a polyacrylamide and a hydrophobically modified polyacrylamide flood in a sandstone core

Polymer flooding in oil reservoirs to enhance oil recovery (EOR) has been used worldwide. However, the polymers applied, such as partially hydrolyzed polyacrylamides and xanthan gum, show a number of limitations related to their low salt tolerance and biological degradation, respectively. Therefore, the polymeric properties must be improved to maximize their application. With this goal in mind, a new class of polymers, named “hydrophobically modified water-soluble polymers”, has been developed. These polymers are very similar to conventional polymers used in EOR, except that they have a small number of hydrophobic groups incorporated into the polymer backbone. At incorporation levels of less than 1 mol% these hydrophobic groups can change polymer performance. In this work, a water-soluble polymer made of acrylamide and N,N-dihexylacrylamide was obtained. After characterization of the copolymer, its performance in a porous medium was evaluated through core flood experiments in Botucatu sandstone. In the presence of sodium chloride, the amphiphilic copolymer exhibited a significant increase in viscosity at low polymer concentrations, in addition to resistance factor and residual resistance factor values higher than those of a commercial polyacrylamide. This behavior can increase oil recovery, mainly in high salinity and high-permeability reservoirs, by improving waterflood sweep efficiency.