Research on dehydration mechanisms and characteristics of shale oil under high-frequency electric field treatment

High-frequency pulsed electrical dewatering is widely used in crude oil emulsification, but the mechanisms for shale oil dehydration remain unclear due to its complex composition. This study evaluated the dewatering performance of six shale oil samples under gravity alone, followed by physical property testing, droplet size analysis, and compositional evaluation of two selected samples. We investigated the effects of electric field frequency, strength, pulse width ratio, and dewatering time on the dewatering efficiency of pretreated shale oils subjected to a high-frequency pulsed electric field. The results showed that the average droplet diameter in shale oil ranged from 2 to 3 μm, which was a smaller and more concentrated distribution than in conventional crude oil. Optimal parameters for emulsion breaking were identified for two shale oil types: SH-A, with a 4 kHz frequency, 150 kV/m strength, 50 % pulse width ratio, and 60 °C, achieved a water content reduction from 40 % to 0.69 % in 60 min; SH-B, with a 5 kHz frequency, 150 kV/m strength, 50 % pulse width ratio, and 60 °C, reduced water content from 40 % to 0.68 % in 50 min. In contrast, unpretreated shale oil is extremely poorly dewatered. The theoretical mechanisms of shale oil pretreatment in enhancing electrical dewatering are based on increasing dipole aggregation force in the electric field. This is achieved by increasing the water content, which enlarges the droplet radius, raises the permittivity of the emulsion, and reduces the spacing between droplets. These findings provided essential insights into optimizing the electrical dewatering process for shale oil.