Insights into Mobilization of Shale Oil using Microemulsion

Abstract

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.

Molecular simulations of NAPL removal from mineral surfaces using microemulsions and surfactants

“…Once released from the micelle, the limonene swelled the oil phase drastically, breaking up any nanoaggregate structures formed by asphaltenes and allowing the oil to become more mobile. This finding is consistent with Bui et al 33 In order to quantify this effect, the total accessible volume of the oil droplet was calculated using the double cubic lattice method (DCLM) with a probe radius of 0.14 nm. 46 The surfactant induced a 13% increase in droplet volume while the microemulsion caused a 34% increase in the total droplet volume due to the infiltration of the limonene solvent (see Figure 5, Supporting Information).…”

“…This method of simulating induced flow is similar to that used by previous studies. 33,44 3. RESULTS AND DISCUSSION…”

“…They showed that the organic solvent from the microemulsion is able to penetrate the organic layer after dissociating onto the hydrocarbon layer. 33 Microemulsions were found to effectively reduce the interfacial tension between the water and hydrocarbon and improve the shear profile at the interface during an induced flow. Despite showing that microemulsions do indeed form under specific conditions and that the solvent is critical in penetrating the oil layer, this study did not reveal the mechanism by which a microemulsion interacts with, desorbs, and partitions a contaminant droplet.…”

Evaluation of Methods to Improve Matrix Stimulation of Horizontal Carbonate Wellbores

“…The composition of the microemulsion can be altered to minimize IFT and optimize wettability, resulting in a reduced capillary pressure and enhanced oil displacement within the formation. The optimized wettability comes at the expense of surfactant adsorption on the formation surface, but even this can be tailored by modifying the solvent to water ratio of the microemulsion formulation (Bui et al 2015).…”