Surface-functionalized cellulose nanocrystals (CNC) and synergisms with surfactant for enhanced oil recovery in low-permeability reservoirs

Nanocellulose, a natural polymeric nanomaterial, has attracted significant attention in enhanced oil recovery (EOR) applications due to its abundance, nanoscale, high oil–water interfacial adsorption efficiency. In this study, surface-functionalized cellulose nanocrystals (SF-CNCs) were prepared via hydrochloric acid hydrolysis and chemical modification, with adaptable nanosize and considerable dispersion stability in low-permeability reservoirs. The SF-CNCs were structurally characterized by FT-IR, Cryo-TEM, which have a diameter of 5–10 nm and a length of 100–200 nm. The SF-CNC dispersions possessed higher stability and stronger salt-tolerance than those of corresponding CNC dispersions, due to the strong hydrophilicity of the sulfonic acid group. It was synergistically used with a non-ionic surfactant (APG1214) to formulate a combined flooding system (0.1 wt% SF-CNC + 0.2 wt% APG1214). The combined flooding system exhibits strong emulsification stability, low oil–water interfacial tension of 0.03 mN/m, and the ability to alter the wettability for oil-wetting rocks. Furthermore, the combined system was able to provide an optimum EOR efficiency of 20.2% in low-permeability cores with 30.13 × 10−3 μm2. Notably, it can enlarge the sweep volume and increase the displacement efficiency simultaneously. Overall, the newly formulated nanocellulose/surfactant combined system exhibits a remarkable EOR performance in low-permeability reservoirs.