Understanding Imbibition Mechanisms of Catanionic Surfactant–Stabilized Nanoemulsion for Enhanced Oil Recovery in Tight Sandstone Reservoirs: Experimental and Numerical Assessment

Surfactant-induced imbibition is considered a promising method for increasing oil recovery from tight oil reservoirs beyond primary production. Nanoemulsion (nE) offers a great potential for this application owing to its unique physicochemical properties, such as kinetic stability, large surface area, and low oil-aqueous interfacial tension (IFT). Herein, we designed and prepared a series of surfactant-stabilized oil-in-water (O/W) nE using efficient catanionic surfactants by a low-energy method. The physicochemical properties of the nE samples were comprehensively characterized to better perform experimental and numerical simulations and constrain the modeling. We conducted imbibition tests on Chang 7 tight cores using nE and brine and also assessed the imbibition dynamics. Results indicated that nE was successfully synthesized at a surfactant concentration ranging from 0.4 to 1.0 wt%. The oil droplets in nE had a mean size of 10 nm. All the nE samples were able to lower the oil-aqueous IFT to an ultralow level of 10^–3 mN/m. In addition, nE demonstrated superior capacities in wettability alteration, and oil solubilization and emulsification, which were all integrated into numerical modeling. The imbibition oil recovery was increased by 18.8% of the initial oil in place when nE1 (0.4 wt%) was used compared to that of brine. Because of the interactions among oil, nE, and rock surface, nE required a longer time to reach imbibition equilibrium than brine. The simulation results, for the first time, suggested that the dominant imbibition mechanisms of nE varied with time, during which IFT reduction and wettability alteration played the leading roles in the first 50 hours. The reactions of oil solubilization and emulsification became significant after 50 hours and then contributed equally to the oil recovery with IFT reduction and wettability alteration. The diffusion of nanosized oil droplets increased the equilibrium time of imbibition, thereby promoting the ultimate oil recovery.