Mass and Momentum Transfer Considerations for Oil Displacement in Source Rocks Using Microemulsion Solutions

Existing strategies for hydrocarbon extraction have been designed primarily based on macroscopic properties of fluids and rocks. However, recent work on tight formations and source rocks (such as shale) revealed that the fluid properties and phase change of the hydrocarbons stored in the lower end of the pore size distribution inside the organic nanopores deviate significantly from their bulk phases in the large pores. The cause for such deviations is primarily the presence of strong fluid-wall molecular interactions in the nanopore. Organic nanopores, in source rock, store more hydrocarbons than those pores in a conventional reservoir for the same pore volume because nanopore confined hydrocarbons are more compacted and denser than the bulk phase. However, the recovery factor from these pores were reported to be considerately lower. Surfactants, introduced in the form of micelle or microemulsion, have the potential to increase the recovery. Whereas the transport behavior of micelles and their adsorption on solid walls are well-established, the role of microemulsion on the recovery of hydrocarbons under confinement remains poorly understood. In this work, molecular dynamics (MD) simulations were employed to investigate the two-phase flow in kerogen nanopores containing oil, water, and a microemulsion droplet. A slit-shaped pore was modeled representing the organic nanopore, and a mixture of hydrocarbon was chosen to represent the oil phase. Initially, the microemulsion droplets containing nonionic surfactant dodecylhepta(oxyethylene)ether (C12E7), swollen with solvent (d-limonene), were introduced to the water phase. We showed that the droplets were dispersed under the strong molecular interactions existing in the nanopore space. Subsequently, both the solvent and the surfactant components played essential roles in displacing the oil phase. The surfactant molecules were deposited at the interface between the aqueous phase and the oil, thereby reducing the interfacial tension. The solvent molecules, originally solubilized in a microemulsion droplet, penetrated the oil film near the pore walls. Those solvent molecules were exchanged with the adsorbed oil molecules and transformed that portion of oil into free oil for enhanced recovery. In addition, we considered the Couette flow of water near the organic wall with a film of oil, and found that the oil phase, which consisted of free and adsorbed molecules, could be mobilized by the viscous force caused by the flowing water. Hence, the chemicals introduced by the water mobilized both the free oil and a portion of adsorbed oil inside the oil-wet pores. However, there existed a slip at the oil/water interface which inhibited the momentum transfer from the water phase to the oil phase. When the surfactants were present at the interface, they acted as a linker that diminished the slip at the interface, hence, allowing the momentum transfer from the water phase to the oil phase more effectively. As a result, the fractional flow of oil increased due to the presence of both the surfactant and the solvent. At the final part, we extended our study from a single channel to three-dimensional (3D) kerogen pore network, where the pore sizes were less than or equal to 7 nm. The MD results showed that the dispersed microemulsion droplets also mobilized and displaced the oil present within the kerogen pore network. The results of this work are important for our understanding of flow and displacement under confinement and its application to oil recovery from source rocks.

Structural control of polyelectrolyte/microemulsion droplet complexes (PEMECs) with different polyacrylates

Polyelectrolyte/microemulsion complexes (PEMECs) are very versatile hybrid systems, combining high loading capacities of microemulsions with larger-scale structuring induced by polyelectrolytes.

Anti-Inflammatory Activity of Babassu Oil and Development of a Microemulsion System for Topical Delivery

Babassu oil extraction is the main income source in nut breakers communities in northeast of Brazil. Among these communities, babassu oil is used for cooking but also medically to treat skin wounds and inflammation, and vulvovaginitis. This study aimed to evaluate the anti-inflammatory activity of babassu oil and develop a microemulsion system with babassu oil for topical delivery. Topical anti-inflammatory activity was evaluated in mice ear edema using PMA, arachidonic acid, ethyl phenylpropiolate, phenol, and capsaicin as phlogistic agents. A microemulsion system was successfully developed using a Span® 80/Kolliphor® EL ratio of 6 : 4 as the surfactant system (S), propylene glycol and water (3 : 1) as the aqueous phase (A), and babassu oil as the oil phase (O), and analyzed through conductivity, SAXS, DSC, TEM, and rheological assays. Babassu oil and lauric acid showed anti-inflammatory activity in mice ear edema, through inhibition of eicosanoid pathway and bioactive amines. The developed formulation (39% A, 12.2% O, and 48.8% S) was classified as a bicontinuous to o/w transition microemulsion that showed a Newtonian profile. The topical anti-inflammatory activity of microemulsified babassu oil was markedly increased. A new delivery system of babassu microemulsion droplet clusters was designed to enhance the therapeutic efficacy of vegetable oil.

The Hydrophobicity of Micro Water Pool and the Interfacial Fluidity of PC-Based W/O Microemulsion Droplet Involved with Reactivity of Phospholipase A2

The impact of physicochemical character of the W/O microemulsion droplet on the reactivity of phospholipase A2 (PLA2) was investigated for optimal design of the micro-reactor. Hydrophobicity of micro water pool and fluidity of micro-scaled interface of W/O microemulsion droplet were dominant factors to determine the appearance of maximum reactivity. Phosphatidylcholine (PC) in this system performed not only as a substrate for PLA2 but also as an amphiphilic molecule to form W/O microemulsion droplet. The organic phase was composed by isooctane (C8*) as a main solvent and 1-butanol (C4) as a co-solvent. The molar ratio was fixed as isooctane:1-butanol =11:1. The water content in the W/O microemulsion was indicated by the molar ratio of H2O moles to PC moles presented by Wsoln [-](≡[mol-H2Osoln]/[mol-PC]). By the increasing of the water content from 1 to 5, the reactivity of PLA2 was remarkably increased from 0.01 to 0.03 [mM･s-1･mg-PLA2-1]. Over 5 of Wsoln range, the reactivity was decreased. The optimal water content was indicated as Wsoln=5 [-]. The hydrophilicity of micro water pool and the interfacial fluidity of the water pool were detected by the signal of the fluorescence probes, Coumarin 343 and TMA-DPH, respectively. The hydrophobicity was decayed with the increasing of the water content. More than 10 of Wsoln, the hydrophobicity was fully decayed and achieved to bulk aqueous one. The interfacial fluidity was decreased with the increasing of the water content. In more than Wsoln of 5, the reactivity was decreased by the decline of the collision frequency between PLA2 and PC molecule due to lower fluidity of micro-scaled interface.

Droplet Based Microfluidics for Synthesis of Mesoporous Silica Microspheres

Herein we present methods for synthesizing monodisperse mesoporous silica particles and silica particles with bimodal porosity by templating with surfactant micelle and microemulsion phases. The fabrication of monodisperse mesoporous silica particles is based on the formation of well-defined equally sized emulsion droplets using a microfluidic approach. The droplets contain the silica precursor/surfactant solution and are suspended in hexadecane as the continuous oil phase. The solvent is then expelled from the droplets, leading to concentration and micellization of the surfactant. At the same time, the silica solidifies around the surfactant structures, forming equally sized mesoporous particles. We show that hierarchically bimodal porous structures can be obtained by templating silica microparticles with a specially designed surfactant micelle/microemulsion mixture. Oil, water, and surfactant liquid mixtures exhibit very complex phase behavior. Depending on the conditions, such mixtures give rise to highly organized structures. A proper selection of the type and concentration of surfactants determines the structuring at the nanoscale level. Tuning the phase state by adjusting the surfactant composition and concentration allows for the controlled design of a system where microemulsion droplets coexist with smaller surfactant micellar structures. The microemulsion droplet and micellar dimensions determine the two types of pore sizes.

Controlled Synthesis of BaF2 Nanorods via Hydrothermal Microemulsion Method

BaF2 nanorods were synthesized by hydrothermal microemulsion method using sodium fluoride (NaF) and barium chloride (BaCl2) as the raw materials. The as-prepared products were characterized by powder X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and transmission electron microscopy (TEM). The results showed that the products were composed of BaF2 nanorods with diameters of 18-62 nm and lengths up to 1μm. A directed aggregation growth process mediated by the microemulsion droplet building blocks is proposed for the formation of BaF2 nanorods. Further work is in progress to evaluate the possibility of synthesizing other fluoride 1D nanostructures using a similar method.