Abstract: The application of graphene oxide nanomaterials in tertiary oil recovery has garnered considerable interest, yet improving their stability in saline formation water remains a critical technical challenge. This study characterized the morphology and dimensions of graphene oxide (GO) nanosheets using atomic force microscopy and dynamic light scattering, while systematically investigating the stabilization effects of tannic acid, small-molecule organic acid salts, and macromolecular polyelectrolytes on GO nanosheets in saline environments. Results showed that sodium polyacrylate (PAA), a macromolecular polyelectrolyte with optimized charge density and amphiphilicity, exhibited superior stabilization performance through efficient adsorption onto GO surfaces via non-covalent interaction and thus effectively enhanced the electrostatic repulsion between GO nano-sheets. At a concentration of 150 mg/L, PAA enabled GO to maintain stability for 24 h in 10 000 mg/L sodium chloride solution. The PAA-modified graphene oxide demonstrated synergistic interaction with anionic surfactant viscosity reducers, enhancing their adaptability to heavy oil and amplifying emulsification-based viscosity reduction. Meanwhile, the extremely high specific surface area enables PAA-modified graphene oxide to efficiently adsorb at the oil/water interface and generate structural seperation pressure, promoting the seperation of oil and solid phases. Under the dual enhancement mechanism above, PAA-modified graphene oxide can increase the oil removal efficiency of anionic surfactants by 2.1 times at a low concentration of 10 mg/L. However, excessive adsorption capacity of nonionic surfactants on nanomaterial surfaces was found to compromise emulsification at oil-water interfaces, resulting in lower oil-washing efficiency for the mixed systems compared to single surfactant systems.

Key words: graphene oxide, polyelectrolyte, salt-tolerant capacity, oil-washing performance