Effects of electrolytes on the stability and dynamic rheological properties of an oil-in-water pickering emulsion stabilized by a nanoparticle-surfactant-polymer system

Information on the effect of electrolytes on the stability and rheological properties of Pickering emulsion is required for their application in enhanced oil recovery for deep offshore and onshore crude oil reservoirs. In this study, the dynamic rheological properties (viscosity, yield stress, and dynamic moduli) of nanoparticle-surfactant-polymer-salt (NSPS) stabilized Pickering emulsions are investigated at varying pressure (0.1 and 30 MPa) and temperature (298 to 371 K) and compared with those of an NSP stabilized emulsion system. We used nanoparticles (SiO<inf>2</inf> and clay of size ∼15 nm and <80 nm in diameter, respectively), surfactant (sodium dodecyl sulfate, SDS), polymer (polyacrylamide, PAM), and sodium chloride (NaCl) for the formulation of the emulsion. The presence of salt of an appropriate concentration of 1.0 wt % in a NSP emulsion system is observed to improve droplet packing with uniform distribution as observed from microscopic characterization. The interfacial tension of the NSPS emulsion system is observed to reduce significantly in the presence of salt as compared to that of the NSP emulsion system. Dynamic rheological properties of the NSPS emulsion system showed that the presence of salt marginally affected the viscosity and yield stress as compared to those of the NSP emulsion system. The presence of salt affected the elastic modulus, G′, and viscous modulus, G' providing a stable viscous behavior at elevated pressure (30 MPa) and temperature (371 K) conditions. G' is observed to be higher than G′ for measured frequency ranges indicating a viscous-like behavior of NSPS emulsion system. With reference to the phase angle (δ), the values of δ for the NSPS emulsion system remains around 90° because of negligible G′ indicating viscous behavior that concurs with literature observations. The results indicated the suitability of a NSPS emulsion system for high pressure high temperature (HPHT) applications such as enhanced oil recovery or drilling fluid design for a saline environment.