Investigation of cation-assisted, chemically and thermally enhanced nitrogen-doped graphene nanofluid application as an efficient micro-emulsifier from EOR perspective

Innovatively designed additives have been introduced in last decade to make EOR processes more efficient under challenging conditions. However, nitrogen-doped graphene (NDG) is not known as such a stable efficient method to be injected into reservoir under harsh thermodynamic condition. Some treatment has been applied to molecular structure of commonly used nitrogen-doped graphene aqueous solution for improvement of stability and quality of aqueous solution. These treatments involve both nano-structure and the aqueous carrier fluid properties. Nano-structure modification has been conducted in three successive steps: oxidation with acid vapor and modified Hummers method, citric acid polymerization and heat treatment that succeed in NDG functionalization with carboxyl and hydroxyl groups and structure enhancement in molecular scale. Existing free mono- and divalent cations in aqueous carrier phase improve the emulsification dominant mechanism from Pickering unstable emulsion toward more stable micro-emulsion mechanism which appeared to be superior to conventional emulsifiers used in EOR process because of improved solubility and more facile transport through porous media. Zeta potential of solution has increased from −30 to −12.2 mV highlighting more emulsion stability. The interfacial tension between aqueous fluid containing 500 ppm APH-NDG1 and free mono- and divalent cations and crude oil would be 50 % less in comparison to distilled water/crude oil IFT. Furthermore, APH-NDG, regardless of carrier aqueous type, causes a great decrease in contact angle and as a result, makes the rock surface become more water-wet.