Generation, stability, and transport of nanoparticle-stabilized oil-in-water emulsions in porous media
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The ability of nanoparticles to stabilize oil/water emulsions provides many interesting opportunities for the petroleum industry. Emulsions can be used as a displacing fluid for enhanced oil recovery to improve sweep efficiencies. Emulsions can be used to improve conformance control by effectively blocking thief zones in reservoirs with a high degree of heterogeneity. As shown in this thesis emulsions can be used to deliver fluids that contact and mobilize residual oil. It is imperative to understand emulsion behavior in porous media for design purposes in enhanced or improved oil recovery processes involving emulsions. Nanoparticle-stabilized oil-in-water emulsions were continuously generated by co-injecting aqueous nanoparticle dispersion and oil through a beadpack. There exists a critical shear rate below which a stable emulsion will not be generated. The critical shear rate increased with decreasing bead size. Above the critical shear rate, the droplet size of the generated emulsion was a function of shear rate and decreased with increasing shear rate. The stable emulsions were characterized by their droplet size and rheology. The emulsion viscosity was highly dependent upon droplet size and not the bulk oil viscosity in the emulsion. The emulsions were highly shear thinning and emulsions with smaller droplets were more viscous than emulsions with larger droplets. Highly stable emulsions that were generated by co-injection were collected, separated from excess phase(s) and injected into beadpacks. In most experiments the injected emulsion coalesced into the bulk fluids. Whether the bulk fluids generated a new emulsion in the bead pack depended on the shear rate, bead size, and initial saturation of the beadpack. Different beadpack experiments showed the transition from one flow regime to a second flow regime as the slow movement of a coalescence/regeneration front propagated through the beadpack. Coreflood experiments confirmed the mechanisms hypothesized for the beadpack emulsion injection experiments. When a stable emulsion was injected the effluent emulsion rheology and droplet size were altered solely as a result of being forced through sandstone cores, not because of fluids contacted within the core. The shear rate controlled whether the emulsion coalesced and produced no effluent emulsion, regenerated into an emulsion with larger droplets, or regenerated into an emulsion with smaller droplets. Oil recovery experiments showed that nanoparticle-stabilized oil-in-water emulsion increased the recovery of oil compared to a waterflood for cores with immobile and mobile oil. The mechanism is the coalesced oil droplets form a flowing phase that is miscible with oil present in the core and thus achieves a much more efficient displacement. The possible continuous generation and coalescence of droplets may have increased the apparent viscosity, improving the sweep efficiency of the emulsion injection. A novel oil recovery mechanism was shown in imbibition experiments where nanoparticle dispersion was used to displace oil. Large shear rates coupled with the affinity for nanoparticles at the oil water interface enabled residual oil to be mobilized, or for residual oil blobs to spawn smaller droplets that are stabilized by the nanoparticles and thus can be transported with the dispersion through the core.