(590b) Utilizing Solubilized Solvent for Surfactant Based Enhanced Oil Recovery

In enhanced oil recovery, the production is influenced by the ability of injected surfactants to adsorb and to modify interfacial tension at different interfaces. It has previously been demonstrated that surfactant and microemulsion additives enhance the production to a different extent but the mechanisms behind the differences in their action are not fully understood.

Here, we report salient new results on the adsorption from microemulsion at solid-liquid, and liquid-liquid interfaces. The simulation involves an aqueous solution in the presence of an oil (heptane) phase. The solution consists of nonionic surfactant dodecylhepta(oxy-ethylene)ether or C₁₂E₇, and a solubilized terpene solvent. We found that the presence of solvent inside the micelles causes the mechanism of adsorption behavior to deviate from those expected for adsorption from micellar surfactant solutions. In the case of solubilized terpene, the swollen micelles adsorb on the surface as one entity. The delivery of a surfactant to the interface and the associated reduction of the interfacial tension is influenced by the change in interaction potential between the surface and surfactant aggregate, and it is controlled by the solvent concentration.

Another significant finding is that both surfactant and terpene solvent can contribute to the two-phase flow in a nanopore containing oil and water. There exists a slip at the oil-water interface which inhibits the momentum transfer from the water phase to the oil phase. The surfactant acts like a linker that diminishes the slip at the oil-water interface, hence, allowing the momentum transfer from the water phase to the oil phase more effectively. The solvent, originally solubilized in a microemulsion droplet, penetrates the thin film of oil. Furthermore, those solvent molecules displace up to 14% the oil molecules in the adsorbed phase and transform that portion of oil into free oil. The resulting mixture of oil and solvent has different properties from the oil alone, indicating a primary difference between the mechanism of action between surfactant and a combination of surfactant and solvent.

The results are important for our understanding of microemulsion behavior under confinement and its application to organic rich shale oil recovery.