Expansion and growth of liquid bridge in saline water-in-oil emulsion under synchronized magnetic field coupled low-intensity electric field

Abstract

Unconventional crude oil and offshore oilfield extraction often lead to the formation of stable oil–water emulsions with high mineralization, posing significant threats to environmental protection and pipeline transportation safety. Electric–magnetic coupling separation technology represents a novel approach to emulsion breaking, offering superior separation performance compared to the conventional electric coalescence methods. However, its underlying mechanism remains elusive. To address this gap, this study comparatively investigates the liquid bridge dynamic during droplet coalescence under a single electric field and electric–magnetic coupling field conditions. High-speed camera experiments reveal that synchronized coupled magnetic fields suppress the extension of liquid bridges, with this suppression effect being augmented by increasing ion concentration and electric field strength. Nevertheless, the enhancement of the inhibition effect is not pronounced at electric field strengths up to 224 kV m−1 and within the frequency range of 50–500 Hz. Molecular dynamics simulations demonstrate that the mutual repulsion effect between water molecules and the hydration effect between water molecules and ions are intensified under the coupling field. Finally, by integrating flow field and velocity analyses, a mechanism is proposed to elucidate the hysteresis in the evolution of liquid bridges, attributed to the mutual repulsion of water molecules hydrated by deflecting ions and convecting water molecules in the coupled field. This study offers valuable insights for the development of electric–magnetic coupling separation techniques, with implications for mitigating oil contamination and facilitating dewatering treatments.