Impact of Graphene Quantum Dots on Gas Foam Stability

Abstract

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.

Graphene Quantum Dot-Stabilized Foam for Enhanced Oil Recovery

“…Furthermore, the lamellae film formed in nanofluid-stabilized foam is thicker (98.9 μm) compared to its counterpart which has a much thinner film (13.8 μm). This may justify the enhanced stability and apparent viscosity provided by GQD-stabilized foam, which agrees with our previous study …”

“…Foam quality varied from 60 to 90% at a fixed flow rate, and the corresponding pressure drop and oil recovery were recorded. The maximum pressure drop in the core samples was achieved at a foam quality of 60%, which was lower than that reported in sandpacks Figure shows that the pressure drop decreased as the foam quality increased for all of the core samples.…”

“…In this study, graphene quantum dot (GQD) nanoparticles were utilized in synergy with an amphoteric surfactant to investigate their impact on oil recovery from porous media. This represents a continuation of our previous work where the addition of GQDs was found to increase both the foam half-life and steady-state apparent viscosity compared to pure surfactant . GQDs were utilized in this study due to several factors.…”

“…Bakken oil contains approximately 0.003 wt % of asphaltene, sulfur content is less than 0.5 wt %, and TAN is less than 0.1 mg KOH. Based on our previous dynamic and static bulk foam experiments, the optimum concentrations for foam generation in oil-wet sandpacks were at 4000 ppm ACS surfactant and 500 ppm GQD nanoparticles . Thus, this composition was used for the nanofluid in this study.…”

“…At that point, foam flooding was started at the same flow rate through the continuous injection of both methane and nanofluid at a certain foam quality and flow rate until reaching a steady-state pressure. A foam quality of 60% (i.e., gas fraction with respect to the total flow rate) was primarily selected to cover a wider range of foam qualities than our previous study in sandpacks . Continuous foam flooding was implemented by co-injecting methane and nanofluid simultaneously until reaching steady-state pressure drop across the sample.…”