Experimental Study on Charged Nanogels for Interfacial Tension Reduction and Emulsion Stabilization at Various Salinities and Oil Types

Nanoparticles have been widely investigated for their mechanisms in enhanced oil recovery, such as rock wettability alternation, oil displacement by disjoining pressure, and the stabilization of emulsion and foam. Nanogels are nanosized cross-linked polymeric particles that have the properties of both nanoparticles and hydrogels. The goal of this study is to investigate the oil-water interfacial behavior in the presence of nanogels, especially the dynamic interfacial tension and the stability of oil-in-water (o/w) emulsions. The nanogels synthesized in this study are able to reduce the oil-water interfacial tension and stabilize the o/w emulsions. The diameter and zeta potential of the charged nanogels are dramatically influenced by brine salinity, whereas the neutral charged nanogels are barely affected by salt. The synthesized nanogels have been stable in distilled water and brines at room temperature for more than 60 days. The dynamic interfacial tension results show that the nanogels are able to reduce the oil-water interfacial tension to as much as 1/30 of the original value. In addition, the interfacial tension reduction is more significant at a higher salinity (ranging from 10 000 to 50 000 ppm NaCl concentration). The emulsion stability results demonstrated that the stability of emulsified oil drops was controlled by both the strength of the adsorbed nanogel layers and the interactions among oil drops. The core flooding experiments have indicated the residual oil can be fragmented and produced in the o/w emulsion state. In addition, the diameter of emulsified oil drops in effluent is inversely proportional to the shear rate. The salt-dependent interfacial tension and emulsion stability indicated that the appropriate charged nanogel can be a promising candidate for enhanced oil recovery.