Effect of electric field intensity on electrophoretic migration and deformation of oil droplets in O/W emulsion under DC electric field: A molecular dynamics study

New insight into the role of the self-assembly of heteroatom compounds in heavy oil viscosity enhancement

Unveiling the role of heteroatom compounds in heavy oil viscosity is pivotal for finding targeted viscosity reduction methods to improve oil recovery. This research investigates the impact of heteroatoms in asphaltene molecules by utilizing quantum chemical calculations and molecular dynamics simulations to analyze their electrostatic potential characteristics, pairwise interactions, and dynamic behavior within realistic reservoirs. Heteroatom compounds can influence the molecular-level properties of asphaltenes and thus impact the macroscopic behavior of heavy oils. Research results suggest that the presence of ketone and aromatic rings in asphaltene molecules leads to the unrestricted movement of pi electrons due to their collective electronegativity. Two distinct configurations of asphaltene dimers, face-to-face, and edge-to-face, were observed. Intermolecular interactions were predominantly governed by van der Waals forces, highlighting their significant role in stabilizing asphaltene aggregates. The distribution of asphaltene molecules in the oil phase can be summarized as the "rebar-cement" theory. In the heteroatom-free system, the face-to-face peaks in the radial distribution function exhibit significantly reduced magnitudes compared to those in the heteroatom-containing system. This emphasizes the pivotal function of heteroatoms in connecting molecular components to form a more compact asphaltene structure, which may result in a higher viscosity of heavy oil. These findings give insight into the significance of heteroatoms in bridging molecular components and shaping the intricate structure of asphaltene and advance our understanding of heavy oil viscosity properties.

Study on microstructure evolution of waxy crude oil emulsions under dynamic cooling conditions

A rheo-microscopy in situ synchronous measurement system was utilized to investigate the dynamic behavior of water droplets in W/O waxy crude oil emulsions subjected to dynamic cooling conditions, the microstructural evolution of water droplets aggregates can be categorized into three stages based on the various forms of wax crystals. The results show that under the joint action of wax crystals and water droplets, the water droplets aggregation trend and complexity in the system are negatively correlated with the changes of temperature and shear rate, and the water droplets movement behavior is positively correlated with the changes of temperature and shear rate. As the temperature decreases, the minimum edge distance of water droplets decreases by a maximum of 32.1%, the specific surface area (SA) decreases by a maximum of 12.0%, and the fractal dimension increases by a maximum of 11.7%. As the shear rate increases, the minimum edge distance of water droplets increases by up to 27.9%, the specific surface area (SA) increases by up to 10.1%, and the fractal dimension decreases by up to 8.5%. Additionally, an analysis is conducted on the collision aggregation behavior of water droplets in shear flow field based on population balance theory.

Surface charging and electrophoretic behavior of conductive polymer micro-droplets in conductive polymer liquid solutions

This study investigates the surface charging and electrophoretic motion of polyethylene glycol-rich (PEG-rich) micro-droplets in dextran-rich solutions or dextran-rich micro-droplets in PEG-rich solutions. The electrophoretic velocities of the droplets were measured in a centimeter-sized chamber under an optical microscope. It was found that the direction of electrophoretic motion of both the PEG-rich droplets and dextran-rich droplets is opposite to the applied electric field, meaning that both the PEG-rich droplets and dextran-rich droplets are negatively charged. The electrophoretic velocity is independent of droplet size but proportional to the electric field strength. Increasing the NaCl concentration reduces the electrophoretic velocity of PEG-rich droplets and increases it for dextran-rich droplets, suggesting different surface charge changes due to ion affinity. The charge densities and velocities are affected by the PEG and dextran mass fractions. Physical models for droplet surface charging under different conditions were proposed to explain the experimental results.

Electrophoresis of a dielectric droplet with constant surface charge density

Electrophoresis of a dielectric fluid droplet with constant surface charge density is investigated theoretically in this study. A pseudo-spectral method based on Chebyshev polynomials is adopted to solve the governing electrokinetic equations. It is found, among other things, that the larger the electrolyte strength in the ambient solution is, the slower the droplet moves in general. This is due to the strong screening effect of the large amount of indifferent counterions in the neighborhood of the droplet, with no reinforcement of potential-determining ions adsorbing to the droplet surface. The droplet comes to a complete halt eventually. Critical points are discovered for highly charged droplets, at which the droplet surface becomes immobile and the interior fluid stops recirculating. The droplet moves like a rigid particle with constant mobility regardless of its viscosity, a situation referred to as the "solidification phenomenon." The deadlock between the spinning motions on the charged droplet surface induced by the electric driving force and the hydrodynamic driving force respectively is responsible for this peculiar phenomenon. This is also observed for a dielectric droplet with constant surface electric potential. We demonstrate here that it occurs in the constant surface charge density situation as well.