Graphene Quantum Dots for the Mobilization and Solubilization of Nonaqueous Phase Liquids in Natural Porous Media

Abstract

This study proposes an approach to synthesize graphene quantum dots (QDs) with remarkable physicochemical properties that allow them to effectively mobilize and solubilize nonaqueous phase liquids (NAPLs) such as crude oils in porous media. QDs are first extracted by mild oxidation of coal and then partially functionalized by alkylamines using a starch template to generate engineered QDs (EQDs). When mixed in equal amounts, the nanofluid can synergistically interact at oil/water interfaces and lower the interfacial tension (IFT) from 19.6 to 0.9 mN/m. The two quantum dots exhibit different behavior on minerals. EQDs do not adsorb because of steric hindrance caused by their aliphatic tails, whereas QDs adsorb moderately on sandstones through hydrogen bonding, leading to wettability alteration from oil-wet to weakly water-wet state. The nanofluid provides mixed-wet conditions that, together with IFT reduction, result in 21 vol % of incremental NAPL recovery compared to waterflooding. The performance of this mixture is curbed in carbonates with only 9.6 vol % of additional recovery because of strong QD adsorption and pore plugging. The ability of this nanofluid to alter wettability was further confirmed in a miniature silicate-rich rock using X-ray microtomography. The in situ contact angle distributions on quartz and carbonate shifted to a more water-wet state and covered a wide range of values, denoting a nonuniform wettability reversal. Thus, the application of QD-based nanofluids is more suitable in silicate-rich formations where chemical retention by the rock is minimum. This study paves the way for the development of more EQDs by tuning their structure via chemical functionalization of their oxygen-rich active sites.

Impact of Graphene Quantum Dots on Gas Foam Stability

“…The amphoteric surfactant consisted of Amphosol CS-50 (Cocamidopropyl hydroxysultaine, ACS) from Stepan Company. The graphene quantum dots were extracted from Wyoming’s Powder River Basin coal according to a procedure described elsewhere. ,, The molecular structure of the surfactant and the quantum dot is shown in Table . The high number of oxygen-containing groups in GQD is responsible for their stability in high-salinity water.…”

“…The high number of oxygen-containing groups in GQD is responsible for their stability in high-salinity water. Although not shown in the table, GQD also contain trace amounts (0–2 wt %) of nitrogen and sulfur that are inherited from the parent coal . Foam stability was tested in sandpacks containing 89% 20/40-mesh sand and 11% 40/70-mesh sand, both supplied from Magnolia Frac Sand.…”

“…Previous studies with graphene quantum dots (GQD) have been mainly focused on applications as tracers . Some used engineered GQDs as enhanced oil recovery (EOR) additives and displayed their ability to reduce the interfacial tension (IFT) and alter wettability. , This study has extended the applications of GQDs to improve the half-life and apparent viscosity of the surfactant-methane-generated foam. To this effect, we have tested these parameters using water- and oil-wet sandpacks.…”

New Insights into Asphaltene Structure and Aggregation by High-Resolution Microscopy

“…Characterization of asphaltene fractions by other spectroscopic and microscopic methods was also performed to better interpret the trends observed by HRTEM. The new insights provided by this work have many implications not only for flow assurance and surface processing but also for the synthesis of high-value-added graphitic materials from asphaltenes. , …”

“…The new insights provided by this work have many implications not only for flow assurance and surface processing but also for the synthesis of high-value-added graphitic materials from asphaltenes. 36,37 2. EXPERIMENTAL SECTION 2.1.…”