Investigation of physical properties and displacement mechanisms of surface-grafted nano-cellulose fluids for enhanced oil recovery

In our previous reports, nano-cellulose (NC) has been proposed for enhanced oil recovery (EOR) application as a “green” displacing agent. To further improve its physical properties towards EOR, surface-grafting by AMPS (2-acrylamido-2-methylpropane sulfonic acid) and hydrophobic groups (HG) was conducted on NC, and producing NC-KY and NC-KYSS, respectively. The primary objective of this work was to comprehensively investigate the static and dynamic properties of these two well-defined nano-fluids compared to the control (NC). The results showed that the proposed nano-fluids can reverse the strongly oil-wet carbonate and sandstone surfaces to intermediate or water-wet states relying on surface adsorption. Due to the incorporation of the hydrophobic groups, NC-KYSS exhibited superior salt-tolerant and pronounced salt-thickening behaviors, as revealed by dispersity and rheology studies. The IFT (interfacial tension) between oleic and aqueous phases was reduced to 0.4 mN/m. Moreover, the prepared O/W emulsions were fairly stable upon storage due to the interface stabilizing effect of the nano-fluids. The displacement dynamics observed in a visualization micromodel indicated that 6% of incremental oil recovery was produced by 0.4 PV of NC-KYSS nano-fluid (0.3 wt%). Flow diversion and residual oil reduction were observed visually with the nano-fluid migrating in the porous media. The oil recovery mechanisms of the nano-fluid flooding were finally elucidated based on the observations.