Influence of Weak Hydrophobic Interactions on in Situ Viscosity of a Hydrophobically Modified Water-Soluble Polymer

Polymers are attractive enhanced oil recovery (EOR) chemicals that improve sweep and accelerate production. There is an ongoing search for polymers that are more temperature-, salinity-, and shear-stable as fields in increasingly challenging environments open to EOR methods. This paper investigates one type of hydrophobically modified polyacrylamides (HMPAM), which has promising properties. This weakly hydrophobic PAM-based polymer has been characterized with regard to in situ viscosity and rheological properties. The polymer shows similar viscosity as HPAM with regard to shear and concentration dependency but exhibits significantly higher in situ viscosity. The enhanced in situ viscosity can be ascribed to flow-induced hydrophobic interactions and not permeability reduction, as is often reported. In situ rheology is concentration dependent and between 1000-3000 ppm, the polymer changes flow behavior from near-Newtonian to rheo-thinning. This gel like behavior cannot be explained from bulk measurements as these shows a viscous dominated flow up to much-higher concentrations. It is therefore likely that the spatial restrictions in pore flow enforce hydrophobic interactions to be significant at lower concentrations than those in bulk. This is also observed during core saturation, in which the 3000 ppm solution requires a larger through-put to reach equilibrium. This is most likely not related to multilayer adsorption. The experiments reported here suggest that PAMs that have weak hydrophobic interactions can benefit from both polyacrylamide-like behavior in the form of low residual resistance factor and enhanced in situ viscosity and shear stability related to the associative properties.