Macro- and micro-scale observations of a surface-functionalized nanocellulose based aqueous nanofluids in chemical enhanced oil recovery (C-EOR)

Nanocellulose was surface-functionalized for applications in chemical enhanced oil recovery (C-EOR) processes as a green alternative to synthetic polymers in order to reduce environmental impact. This paper focuses on the adsorption isotherms and oil displacement behaviors of an amphiphilic nanocellulose (S-NFC) based nanofluid in sandstone porous media. Particular attention was given to the oil displacement mechanisms of this nanofluid at pore level. The isotherms indicated that the equilibrium adsorption of S-NFC on a sandstone surface was approximately 5.08 mg/mm2 under our experimental conditions. The micrographs of Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM) clearly showed the micro morphological change of the surface induced by S-NFC adsorption and aggregates, which, in turn, rendered oil-wet surfaces water-wet as confirmed previously. The injection of S-NFC nanofluid after waterflooding could further increase the oil recovery even for highly heterogeneous models. The oil displacement dynamics observed in a visual micromodel revealed that the nanofluid flooding improved the sweep efficiency and also reduced the residual oil saturation (Sor) after waterflooding process largely due to its bulk viscosity and surface-activation. Emulsification, dragging and wettability alteration were found to be three dominant pore level EOR mechanisms for this nanofluid. These results promise nanocellulose a candidate material for C-EOR applications, but more efforts are needed to further improve its dispersity in electrolytes.