Impact of Graphene Quantum Dots on Gas Foam Stability

This study presents a new application of coal-derived graphene quantum dots (GQD) in stabilizing surfactant-based foams. The methane foam generated by the surfactant itself is susceptible to rapid collapse due to various factors. When the GQDs are added to the surfactant in a mass ratio between 1:8 to 1:16, they self-assemble at the lamella and prevent liquid drainage and coalescence. The nanofluid composed of GQD and amphoteric surfactant reduced both the oil-brine and brine-gas interfacial tension to a greater extent compared to the surfactant alone. In addition, GQD helped alter the rock wettability to strongly water-wet conditions, as compared to weakly water-wet conditions with pure surfactant. The foam formed by the nanofluid was made up of smaller uniformly shaped bubbles with a thick lamella, whereas the foam formed by the surfactant had large polyhedral shaped bubbles with a thin lamella. The transmission electron microscope micrographs of the nanofluid emulsion with crude oil showed that the GQDs are highly interfacially active and tend to assemble on the surface of the oil droplets. Next, the foam stability and strength were investigated with pure surfactant and nanofluid in high salinity brine using water-and oil-wet sandpacks at reservoir conditions relevant to the Bakken formation. The dependence of foam half-life and steady-state apparent viscosity was studied as a function of surfactant and GQD concentration, gas fraction, flow rate, and brine salinity. It was observed that the addition of GQD increases both the foam half-life and steady-state apparent viscosity compared to pure surfactant. This work paved the way for the application of novel carbonaceous nanoparticles under challenging conditions where traditional nanoparticles cannot be used.