Injecting oil-in-water (O/W) emulsions stabilized with nanoparticles or surfactants is a promising option for enhanced oil recovery (EOR) in harsh-condition reservoirs. Stability and rheology of flowing emulsion in porous media are key factors for the effectiveness of the EOR method. The objective of this study is to use microfluidics to (1) quantitatively evaluate the synergistic effect of surfactants and nanoparticles on emulsion's dynamic stability and how nanoparticles affects the emulsion properties, and (2) investigate how emulsion properties affect the sweep performance in emulsion flooding.

A microfluidic device with well-defined channel geometry of a high-permeability pathway and multiple parallel low-permeability pathways was created to represent a fracture – matrix dual-permeability system. Measurement of droplets’ coalescence frequency during flow is used to quantify the dynamic stability of emulsions. A nanoparticle aqueous suspension (2 wt%) shows excellent ability to stabilize macro-emulsion when mixed with trace amount of surfactant (0.05 wt%), revealing a synergic effect between nanoparticles and surfactant.

For a stable emulsion, it was observed that flowing emulsion droplets compress each other and then block the high-permeability pathway at a throat structure, which forces the wetting phase into low-permeability pathways. Droplet size shows little correlation with this blocking effect. Water content was observed much higher in the low-permeability pathways than in the high-permeability pathway, indicating different emulsion texture and viscosity in channels of different sizes. Consequently, the assumption of bulk emulsion viscosity in the porous medium is not applicable in the description and modeling of emulsion flooding process.

Flow of emulsions stabilized by the nanoparticle-surfactant synergy shows droplet packing mode different from those stabilized by surfactant only at high local oil saturation region, which is attributed to the interaction among nanoparticles in the thin liquid film between neighboring oil-water interfaces. This effect is believed to be an important contributing mechanism for sweep efficiency attainable from nanoparticle-stabilized emulsion EOR process.

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