Effect of salinity on solution properties of a partially hydrolyzed polyacrylamide

The growing energy demand requires maximization of oil recovery from known reserves, while enhanced oil recovery (EOR) techniques are focused on sweeping residuals available in reservoirs previously flooded with water. Polymer additives are widely applied in EOR processes, as they can increase the viscosity and reduce the water permeability leading to mobility decrease of the injected solution. In this study, structural and rheological characterizations of a partially hydrolyzed polyacrylamide (FLOPAAM 3630S) were performed in a wide range of salinity relevant to conditions in existing oil reservoirs. Macromolecular solutions were identified at low polymer concentrations and/or at elevated salt levels, while gelation, i.e., formation of coherent structure, was observed at high FLOPAAM 3630S doses at low salinity. The transition points between these stages were determined and a comparison of scattering and rheology measurements revealed that the driving force of such a transformation is of non-electrostatic origin, but rather relies on the hydrophobic intermolecular interactions. The results bring new insights into the design of efficient EOR processes applied in oil reservoirs of different salt levels.