Characterization of Hydrophobically Modified Polyacrylamide in Mixed Polymer-Gemini Surfactant Systems for Enhanced...

The study deals with the synthesis and characterization of the hydrophobically modified polyacrylamide (HMPA) copolymer and its functional property evaluation in mixed polymer-gemini surfactant systems for application in enhanced oil recovery (EOR). The copolymer was initially prepared in the laboratory using acrylamide and N-phenylacrylamide monomer units via an addition polymerization route. The synthesized copolymer was characterized by Fourier transform infrared and proton nuclear magnetic resonance to identify suitable functional groups in the compound. Gel permeation chromatography tests showed that the polymer has a molecular weight of 2.098 × 10⁵ Da. Copolymer solution showed favorable tolerance to variations in temperature and salinity. Salt precipitation studies identified tolerance limit up to 25% NaCl at a temperature of 343 K. Viscosity of HMPA fluids showed an increase with increasing concentration. Interestingly, salt addition until 1.0% NaCl showed an increase in solution viscosity owing to the electrostatic shielding of the HMPA polymer and strengthened intermolecular association of the hydrophobic groups. This behavior is against physicochemical properties observed in the case of conventional polymers but exhibits promising functionality in EOR processes wherein better oil mobility control is desired under subsurface conditions. Gemini surfactants accommodate onto "vacant adsorption" sites onto the liquid surface, improving the interfacial adsorption property and reducing surface tension. In the presence of gemini surfactant polymers forming mixed nanoemulsion fluid systems with favorable pseudoplastic character, their viscosities initially increase with surfactant concentration due to binding of surfactant molecules to hydrophobic junctions of polymer chains to form mixed micelles. Eventually, polymer hydrophobes get saturated with surfactant micelles, and viscosity decreases due to electrostatic repulsion among surfactant micelles. Dynamic light scattering analyses confirmed the formation of nanoemulsion droplets with sizes of <310 nm in the case of {surfactant + copolymer} encapsulation. Zeta potential measurements showed that an increase in 14-6-14 gemini surfactant concentration enhanced the stability of nanoemulsion fluid due to increasing zeta potential values. However, the nonionic SF-6-SF surfactant does not affect the zeta potential of nanoemulsions. Surfactant addition reduced the oil-aqueous interfacial tension of polymer solutions to several magnitudes of an order of 10^-1 to 10^-2 mN/m. Contact angle studies identified the ability of the polymer as well as polymer-surfactant nanoemulsions to alter the wettability of the reservoir rock from the intermediate-wet (90°-120°) to strongly water-wet state (<20°) at different temperatures. Analyzed formulations showed favorable miscibility with crude oil at 343 K. In summary, HMPA/gemini surfactant-based emulsions possess promising physicochemical and stabilization attributes for application in EOR.