Insights Into Mobilization of Shale Oil by Use of Microemulsion
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Copyright 2015, Unconventional Resources Technology Conference. Molecular dynamics simulation is employed to investigate the nature of two-phase (oil-water) flow in organic capillaries. The capillary wall is modeled using graphite to represent kerogen pores in liquid-rich resource shale. We consider that the water carries a nonionic surfactant and a solubilized terpene solvent in the form of a microemulsion, and that it has previously been introduced to the capillary during hydraulic fracturing operation. The water has already displaced a portion of the oil in-place mechanically and now occupies the central part of the capillary. The residual oil, on the other hand, stays by the capillary walls as a stagnant film. Equilibrium simulations show that, under the influence of organic walls, the solvent inside the microemulsion droplets enables not only the surfactant but also the complete droplet to adsorb to the interfaces. Hence, delivering the surfactant molecules to the oil-water interface is achieved faster and more effectively in the organic capillaries. Once the droplet arrives at the interface, the droplet breaks down, the solvent dissolves into the oil film and diffuses. This process is similar to drug delivery at nano-scale. Using non-equilibrium simulations based on the external force field approach we numerically performed steady-state flow measurements to establish that the solvent and the surfactant molecules play separate roles that are both essential in mobilizing the oil film. The surfactant deposited at the oil-water interface reduces the surface tension and acts as a linker that diminishes the slip at the interface. Hence, it effectively enables momentum transfer from the mobile water phase to the stagnant oil film. The solvent penetrating the oil film, on the other hand, modifies flow properties of the oil. In addition, due to selective adsorption, the solvent displaces the adsorbed oil molecules and transforms that portion of the oil into the free oil phase. Consequently, the fractional flow of oil is additionally increased in the presence of solvent. The results of this work are important for understanding the effect of the microemulsion on flow in organic capillaries and its effect on shale oil recovery.
author list (cited authors)
Bui, K., Akkutlu, I. Y., Zelenev, A., Saboowala, H., Gillis, J. R., & Silas, J. A.