While emulsions stabilized by colloidal solid particles have been widely used for industrial and consumer applications, their use for enhanced oil recovery purposes has been very limited. This is because the colloidal solids generally cannot be transported long distances within oil reservoirs, e.g. from injection well to production well. Nanoparticles are two orders of magnitude smaller than colloids and thus can migrate through the pore throats in sedimentary rocks. Emulsions stabilized with nanoparticles can withstand the high-temperature reservoir conditions for extended periods. This can substantially expand the range of reservoirs to which EOR can be applied. Finally, nanoparticles can carry additional functionalities such as super-paramagnetism and reaction catalysis. The former could enable transport to be controlled by application of magnetic field. The latter could enable in situ reduction of oil viscosity.

We have employed aqueous suspensions of surface-modified silica nanoparticles (5- & 20-nm diam.) in a set of laboratory experiments. We report the phase behavior of nanoparticle-stabilized oil/water emulsions and the transport of these emulsions in porous media. Very stable oil/water emulsions were generated, with average droplet size between 2 and 4 microns, at ambient and at elevated temperature. The emulsion stability was not strongly dependent on nanoparticle concentration or on salinity. The transport in glass-bead packs (ca. 20 Darcy) of the silica-stabilized oil/water emulsions showed a sharp emulsion-bank front, with no visible loss of their integrity, and high apparent viscosity (30 cp). Permeability to the aqueous phase post-flush was significantly reduced. It was not possible to determine whether emulsion droplets were retained in pores during emulsion injection, or whether the post-flush fingered through the emulsion and failed to displace all of it. An on-going modeling effort to characterize the equilibrium and stability of the emulsions suggests formation of relatively compact interfacial layer of nanoparticles at the droplet surface.

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