Drag reduction behavior of hydrolyzed polyacrylamide/polysaccharide mixed polymer solutions-effect of solution salinity and polymer concentration

Anionic polyacrylamide is a hydrolyzed form of polyacrylamide (HPAM), which suffers from mechanical degradation at turbulent flow rates. In order to investigate the possibility of improving the shear resistance of HPAM, various polyacrylamide/polysaccharide mixtures as well as single xanthan gum (XG) and guar gum (GG) polymer solutions were prepared and drag reduction (DR) measurements were performed in a closed flow loop. It was found that the DR efficiencies of both XG and GG solutions were directly proportional to polymer concentration and both solutions exhibited excellent mechanical resistance at turbulent conditions. The presence of XG in concentrated HPAM/XG solutions (C > 450 wppm) significantly improved both DR efficiency and shear resistance of the solutions (6-8% decline after shearing for 2 h). GG solutions exhibited smaller DR efficiencies than XG solutions. Due to small molar mass and low flexibility, GG was not as good a friction reducer as XG and HPAM; therefore, the presence of GG did not improve the DR behavior of the binary solutions. Another issue associated with HPAM is sensitivity to the presence of salt ions in the solution. The effect of salt on the DR behavior was verified by addition of 2% KCl to single and binary solutions. Drag reduction efficiencies of HPAM/XG/KCl solutions were 28 and 20% compared to 10% DR of 1000 wppm HPAM/KCl solution. It was found that the presence of XG in binary solutions significantly reduced the negative effect of salt ions on HPAM molecules.