Ablation of water drops suspended in asphaltene/heptol solutions due to spontaneous emulsification

Self-Propulsion by Directed Explosive Emulsification

An active droplet system, programmed to repeatedly move autonomously at a specific velocity in a well-defined direction, is demonstrated. Coulombic energy is stored in oversaturated interfacial assemblies of charged nanoparticle-surfactants by an applied DC electric field and can be released on demand. Spontaneous emulsification is suppressed by an increase in the stiffness of the oversaturated assemblies. Rapidly removing the field releases the stored energy in an explosive event that propels the droplet, where thousands of charged microdroplets are ballistically ejected from the surface of the parent droplet. The ejection is made directional by a symmetry breaking of the interfacial assembly, and the combined interaction force of the microdroplet plume on one side of the droplet propels the droplet distances tens of times its size, making the droplet active. The propulsion is autonomous, repeatable, and agnostic to the chemical composition of the nanoparticles. The symmetry-breaking in the nanoparticle assembly controls the microdroplet velocity and direction of propulsion. This mechanism of droplet propulsion will advance soft micro-robotics, establishes a new type of active matter, and introduces new vehicles for compartmentalized delivery.

Forecasting the Problem of Excessive Oil Entrainment in a Desalter Using Spinning Drop Method

Frequent desalter upsets in the refineries processing opportunity crude oils are often triggered by a rapid and uncontrollable buildup of the rag layer, a thick water-in-oil emulsion, at the oil-brine interface. This is caused by spontaneous emulsification of brine in oil. This study investigates a unique observation from a spinning drop (SD) tensiometer, revealing the low apparent interfacial tension and rigidity of SD caused by spontaneous emulsification. Fine droplets of brine generated through spontaneous emulsification decorate the SD surface and form a stable, low-energy bilayer. Simulated rag layers using the brines from upset incidences exhibit similar behavior, indicating that spontaneous emulsification is driven by chemical species in brine, which promote osmotic water transport. The rate of rag layer buildup correlates with the rate of spontaneous emulsification, with the temperature coefficient of interfacial tension reduction serving as a sensitive indicator. An imminent upset in the operation can be forecasted by measuring this temperature coefficient, enabling preventive measures.

Microfluidic Platform for Characterization of Crude Oil Emulsion Stability

Microfluidic technology has gained significant scientific interest in the characterization of crude oil emulsions that are often formed in the process of oil production. Microfluidic platforms can be used to mimic the pores of natural rock and study multiphase displacement, as well as emulsion formation at a microscale level. This mini-Review focuses on the applications of microfluidics to probe the stability of emulsified droplets against coalescence (e.g., in the presence of additives, electric field, etc.) for both water-in-oil (W/O) and oil-in-water (O/W) emulsion systems. Additionally, this study summarizes the recent efforts made to identify the effects of various experimental factors, including crude oil composition, aging, salinity, and pH on the interfacial properties of water/oil interface and their ultimate roles in the formation/stability of emulsions. Finally, main findings and some recommendations for future work related to the potential of microfluidics in different aspects of crude oil emulsion studies are discussed.

Physicochemical Characterization of Asphaltenes Using Microfluidic Analysis

Crude oils are complex mixtures of organic molecules, of which asphaltenes are the heaviest component. Asphaltene precipitation and deposition have been recognized to be a significant problem in oil production, transmission, and processing facilities. These macromolecular aromatics are challenging to characterize due to their heterogeneity and complex molecular structure. Microfluidic devices are able to capture key characteristics of reservoir rocks and provide new insights into the transport, reactions, and chemical interactions governing fluids used in the oil and gas industry. Understanding the microscale phenomena has led to better design of macroscale processes used by the industry. One area that has seen significant growth is in the area of chemical analysis under flowing conditions. Microfluidics and microscale analysis have advanced the understanding of complex mixtures by providing in situ imaging that can be combined with other chemical characterization methods to give details of how oil, water, and added chemicals interface with pore-scale detail. This review article aims to showcase how microfluidic devices offer new physical, chemical, and dynamic information on the behavior of asphaltenes. Specifically, asphaltene deposition and related flow assurance problems, interfacial properties and rheology, and evaluation of remediation strategies studied in microchannels and microfluidic porous media are presented. Examples of successful applications that address key asphaltene-related problems highlight the advances of microscale systems as a tool for advancing the physicochemical characterization of complex fluids for the oil and gas industry.

Dissecting the Chain Length Effect on Separation of Alkane-in-Water Emulsions with Superwetting Microchannels

Oil/water separation is an essential process in the petrochemical industry, environmental remediation, and water treatment. Alkanes are the major components of crude oil and are difficult to separate once they form emulsions in water. Much less attention has been focused on the feature of liquid alkanes that could, in turn, influence the separation process. The role of chain length is systematically studied herein by separating the alkane-in-water emulsions with superwetting titanium microchannels of 14-55 μm. The chain length covers the entire liquid alkane spectrum with carbon numbers ranging from 6 to 16. The separation efficiency decreases while the TOC content increases with the chain length of liquid alkanes for a given channel. This is attributed to the small Ostwald ripening rate with the long chains, which stabilize the oil droplets of small sizes that could pass through the zigzag channels. Accordingly, a high separation efficiency of >99.97% and a low TOC content of <5 ppm are achieved with superhydrophilic channels of 14 μm for alkanes with less than 12 carbons. The metallic microchannels surpass the conventional organic membranes and inorganic frameworks over the entire liquid n-alkane spectrum, paving the way for the future development of oil/water separation using porous metals.

Phase-Dependent Surfactant Transport on the Microscale: Interfacial Tension and Droplet Coalescence

Liquid-liquid emulsion systems are usually stabilized by additives, known as surfactants, which can be observed in various environments and applications such as oily bilgewater, water-entrained diesel fuel, oil production, food processing, cosmetics, and pharmaceuticals. One important factor that stabilizes emulsions is the lowered interfacial tension (IFT) between the fluid phases due to surfactants, inhibiting the coalescence. Many studies have investigated the surfactant transport behavior that leads to corresponding time-dependent lowering of the IFT. For example, the rate of IFT decay depends on the phase in which the surfactant is added (dispersed vs continuous) due in part to differences in the near-surface depletion depth. Other key factors, such as the viscosity ratio between the dispersed and continuous phases and Marangoni stress, will also have an impact on surfactant transport and therefore the coalescence and emulsion stability. In this feature article, the measurement techniques for dynamic IFT are first reviewed due to their importance in characterizing surfactant transport, with a specific focus on macroscale versus microscale techniques. Next, equilibrium isotherm models as well as dynamic diffusion and kinetic equations are discussed to characterize the surfactant and the time scale of the surfactant transport. Furthermore, recent studies are highlighted showing the different IFT decay rates and its long-time equilibrium value depending on the phase into which the surfactant is added, particularly on the microscale. Finally, recent experiments using a hydrodynamic Stokes trap to investigate the impact of interfacial surfactant transport, or "mobility", and the phase containing the surfactant on film drainage and droplet coalescence will be presented.

Redox-Driven Spontaneous Double Emulsion

The formation of spontaneous double emulsions is a peculiar phenomenon in emulsion systems. When compared to the traditional one-step and two-step methods for preparing double emulsions, spontaneous emulsification can not only steadily load uniform water droplets into an oil phase, but can also facilitate the preparation of emulsions with higher stability. However, the limited solubility of salts, which are typically used to modify osmotic pressure, in organic oils has inhibited the viability of this method for the preparation of W/O/W double emulsions. In this paper, a redox-driven spontaneous emulsification method is developed and investigated. Instead of employing oil-soluble salts, an oxidation reaction is implemented in the oil phase, which produces cation radicals and iodide counterions to generate osmotic pressure. Additionally, amphiphilic polymer chains are harnessed as stabilizers for the newly formed W/O interfaces. Various characterization methods have been used to elucidate the mechanism of both the oxidation reaction and the spontaneous formation of double emulsions.

Advances of spontaneous emulsification and its important applications in enhanced oil recovery process

Emulsions, including oil-in-water (O/W) and water-in-oil (W/O) emulsions, can play important roles in both controlling reservoir conformance and displacing residual oil for enhanced oil recovery (EOR) projects. However, current methods, like high-shear mixing, high-pressure homogenizing, sonicators and others, often use lots of extra energy to prepare the emulsions with high costs but very low energy efficiency. In recent decades, spontaneous emulsification methods, which allow one to create micro- and nano-droplets with very low or even no mechanical energy input, have been launched as an overall less expensive and more efficient alternatives to current high extra energy methods. Herein, we primarily review the basic concepts on spontaneous emulsification, including mechanisms, methods and influenced parameters, which are relevant for fundamental applications for industrials. The spontaneity of the emulsification process is influenced by the following variables: surfactant structure, concentration and initial location, oil phase composition, addition of co-surfactant and non-aqueous solvent, as well as salinity and temperature. Then, we focus on the description of importance for emulsions in EOR processes from advances and categories to improving oil recovery mechanisms, including both sweep efficiency and displacement efficiency aspects. Finally, we systematically address the applications and outlooks based on the use of spontaneous emulsification in the practical oil reservoirs for EOR processes, in which conventional, heavy, high-temperature, high-salinity and low-permeability oil reservoirs, as well as wastewater treatments after EOR processes are involved.