Understanding the flow behaviour of copolymer and associative polymers in porous media using extensional viscosity characterization: Effect of hydrophobic association

Associative polymer (AP) and hydrolyzed polyacrylamide (HPAM), the two commonly used polymers for heavy oil recovery, are reported to exhibit very different flow behaviour in porous media despite having similar shear viscosity. The kind of hydrophobic association (intramolecular or intermolecular) that AP exhibit is concentration dependent and will influence both shear and elongational flow in the porous media. To understand flow behaviour of these two polymers in porous media, the role of hydrophobic association on shear and extensional rheology and its effect on the resistance factor (RF) and residual resistance factor in porous media are investigated over a non-associating HPAM polymer. The results suggest that shear rheology and the Deborah number cannot explain the porous media flow behaviour. However, direct measurements of extensional properties using a capillary breakup extensional rheometer have shown the marginal difference between two polymers at a lower concentration (1000ppm) and the considerable difference at a higher concentration (2000ppm), indicating an intramolecular and intermolecular association, respectively. These results are in accordance with porous media observations where both polymers have shown a similar RF at 1000ppm. Whereas, at 2000ppm AP showed a much higher RF at low/intermediate fluxes, and a similar RF at high flux, suggesting the transformation from intermolecular association to intramolecular association. The significant drop in the extensional viscosity at high strain rates after exhibiting the maxima explains this behaviour.