Stable dispersion of graphene oxide–copolymer nanocomposite for enhanced oil recovery application in high-temperature offshore reservoirs

Abstract

Thermostable and highly water-soluble polymers are essential for polymer flooding—one of the most effective methods used in the enhanced oil recovery (EOR) in high-temperature (HT) offshore reservoirs. In this research, the copolymerization reaction of the acrylamide (AM) and N-vinylpyrrolidone (NVP) monomers was performed via a free-radical mechanism induced by gamma-rays (γ-rays) irradiation. The impact of input data (the ratio and the concentration of the monomer to the viscosity of resultant solution) was scanned in detail and used to optimize the copolymerization conditions. The optimal viscosity values of the polymer concentration were 0.5 wt%. The optimal conditions for copolymerization were obtained at 1.7 for the AM/NVP monomer ratio and 23.2 wt% for the monomer concentration. The copolymerization induced by γ-rays irradiation under the optimized conditions was then carried out, and the obtained viscosity of 0.5 wt% of produced copolymers' solutions was 5.02 cP. These results were in good agreement with the calculated values. The obtained copolymers were then covalently coupled with graphene oxide (GO) synthesized from natural graphite using the modified Hummer’s method. The product nanocomposites (GO–P(AM-NVP) were characterized by Fourier transform infrared spectroscopy, Raman spectroscopy, scanning electron microscopy, and gel permeation chromatography. The thermal and chemical stabilities of the brine-dispersed P(AM-NVP) copolymers annealed at 123 °C (the WT Miocene reservoir temperature) and the GO–P(AM-NVP) nanocomposite dispersion annealed at 135 °C (the WT Oligocene reservoir temperature) for 31 days were observed through the visual inspection and viscosity testing. Results indicated that the dispersions of the P(AM-NVP) copolymers and P(AM-NVP) copolymers conjugated on the GO nanosheets exhibited excellent thermal and chemical stabilities; therefore, they can serve asa promising agent for EOR in HT offshore reservoirs.