Experimental and molecular dynamic studies of amphiphilic graphene oxide for promising nanofluid flooding

Owing to its extremely high aspect ratio, water dispersibility, and dramatic lightness, graphene oxide (GO) has been considered a promising alternative to chemical enhanced oil recovery (CEOR). However, the long-term stability of GO under reservoir conditions and the mechanisms underpinning the cost-effectiveness of this nanofluid flooding remain underexplored. Herein, a two-dimensional (2D) GO derivative in the form of amphiphilic graphene oxide (GOA) composed of a hydrophobic graphene center and a hydrophilic polyethylene glycol periphery for CEOR was investigated by combining experimental characterizations and molecular dynamics simulations. The thickness of the GOA is only 2.33 nm, but the lateral dimension extends up to a few micrometers, which endows GOA with good dispersibility and stability in brine. GOA functions as a 2D amphiphile, which adheres to the interface and decreases the interfacial energy after reaching a threshold concentration as low as 45 mg/L. These nanosheets spontaneously accumulate at the oil–brine interface to produce colloidal lamellae with higher local viscosity at the water–oil interface. GOA tuned the oil-wet and water-wet surfaces to almost neutrally wet surfaces, but the amount of physical adsorption of GOA was rather low. GOA-based nanofluid has desirable compatibility with rock pores. The oil recovery factor of GOA-based nanofluid after extensive brine flooding was characterized at the pore scale, being 18.2 % of the original oil in place at a GOA concentration of 100 mg/L. The dimensionless capillary number of GOA-based nanofluid flooding is ∼ 1000-fold that of brine flooding. The results confirm that this atomically thin, amphiphilic, highly water dispersible 2D sheet should enable highly cost-effective application in CEOR.