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The viscosity of water-oil emulsions plays an important role in oil production and transportation. The objective of this study was to improve the basic understanding of the influence of nanoparticles on the viscosity of water-in-oil emulsions. Using crude oil and different industrial nanomaterials, the droplet size distribution, droplet mean size, and rheological models of emulsions were investigated. Experimental results show that the addition of nanoparticles increases the crude oil viscosity; however, the Newtonian flow behaviour of oil is not affected by nanoparticles. It is observed that the viscosity of crude oil increased from 36.5 to 49 cP when the nanoparticle concentration was elevated from 0 to 0.1 wt%. From the results of rheological experiments, it can be concluded that the influence of nanoparticles on the emulsion viscosity is mainly affected by the type and amount of nanoparticles, water/oil-ratio and aging time. Mean droplet diameter decreased from 5.68 to 4.11 micrometre when 0.1 wt% nanoparticles were added to emulsion. The results also suggest that the properties of stabilized water-in-oil emulsions are significantly time-dependent, and the droplet size and viscosity of emulsions is reduced by time. Most of previously published correlations have huge errors and could not precisely predict the apparent viscosities of non-solid stabilized and solid-stabilized emulsions. None of the previously utilized equations did ever consider the effect of added solids to the emulsion.

Emulsion flooding is a promising technique for enhanced recovery of the residual oil that cannot be recovered through waterflooding processes. Visual micromodels are powerful tools for examining the mechanisms of oil recovery from porous media at the pore level. A glass micromodel was used to investigate the effects of polymer and different industrial nanomaterials on emulsion viscosity, stability and recovery factor of crude oil. The used micromodel has uniform pore throats and grains. Experiments showed that injection of nanoparticle-stabilized water-in-oil emulsions is an effective enhanced oil recovery method. Ultimate oil recovery was greater using nanoparticle-stabilized emulsion/water than water/nanoparticle-stabilized emulsion/water, and the efficiency of nanoparticle-stabilized emulsion/polymer/water also achieved greater recovery. Image analysis showed that the ultimate recovery factor was increased from 33.99 % using water flooding to 63.28 % using nanoparticle-stabilized emulsion/polymer/water flooding. The results of this study are helpful for the mechanistic understanding of enhanced oil recovery projects.