Coal-derived nanomaterials for enhanced NAPL flow in porous media

This study investigates the synthesis and characterization of high value-added carbonaceous nanomaterials from coal and explores their application as flow enhancers in subsurface formations containing non-aqueous phase liquids (NAPLs) such as crude oils. A modified Hummer's method is used to exfoliate coal and extract graphene oxide nanosheets. Dodecylamine is then grafted to one side of the nanosheets using starch as a template. The reaction products are engineered carbon nanosheets (E-CNS) with an amphiphilic character that endues them with both surfactant-like and nanoparticle-like properties, including high interfacial activity and stability inwater. As a result, the engineered nanosheets are able to reduce the NAPL/water interfacial tension by more than 60%, enhancing NAPL emulsification and its mobilization through small pores. They also promote NAPL solubilization by reversing wettability of both aged quartz and calcite from NAPL-wet towards neutral-wet to weakly water-wet conditions. The E-CNS exhibit a unique self-assembly behavior at the NAPL/water interface, flattening the curvature of both concave and convex menisci in glass tubes. Compared to waterflooding, nanofluid flooding can enhance NAPL recovery by 13% and 6% in Edwards limestone and Berea sandstone, respectively, with minimum rock retention, which demonstrates their potential application in aquifer remediation or enhanced oil recovery processes. (C) 2020 Elsevier Ltd. All rights reserved.