Viscoelastic displacement and anomalously enhanced oil recovery of a novel star-like amphiphilic polyacrylamide

[Display omitted] •The core-shell structure imparted higher viscoelasticity to SHPAM.•The elasticity of SHPAM solutions was determined by quantifying the relaxation time.•The anomalous EOR efficiency of SHPAM was elucidated. Star-like amphiphilic polyacrylamide (SHPAM), consisting of nano-SiO2 as the core and a layer of amphiphilic chains as the shell, having two gradient molecular weights, was prepared via a facile method. To elucidate its enhanced oil recovery (EOR) potential, the viscoelastic flow and displacement efficiency of SHPAM were studied using geological rock-core samples. The results showed that the core-shell microstructure and intermolecular interactions imparted viscoelasticity to SHPAM in a lower-concentration region. The elasticity mechanism of SHPAM solutions in porous media was determined by quantifying the relaxation time. Low-field nuclear magnetic resonance experiments suggested that SHPAM flowed through the dominant porous media followed by intermediate porous media having radii of 0.08–10.0μm. The thickness of the adsorbed layer was independent of the shear rate, demonstrating that SHPAM was compatible with porous media owing to the reversibly viscoelastic flow. The core flooding tests demonstrated that even after hydrolyzed polyacrylamide flooding, 3.0% oil saturation was further recovered by SHPAM flooding even in a region with low capillary number (