Vibration-induced mobilization of trapped non-aqueous phase liquids in porous media
Acoustic wave stimulation, such as vibration-induced mobilization, is a promising enhancement approach to remove trapped NAPLs (Non-Aqueous Phase Liquids) usually encountered in multiphase flows through porous media, especially the remediation of underground water contamination and incomplete petroleum recovery from oil reservoirs, with advantages of high efficiency, low cost and environmental safety relative to traditional mobilization methods;According to a simple hypothesized capillary-physics mechanism, specific predictions can be deduced that vibration will be the most effective in mobilizing trapped non-aqueous phase liquids with a comparative higher acceleration amplitude and lower vibration frequency;Quasi-two-dimensional glass micro-model experiments were carried out and it was shown that for fixed acceleration amplitude TCE (trichloroethylene), the trapped organic phase, was more quickly displaced as the vibration frequency decreased from 60 Hz to 10 Hz. And for fixed vibration frequency, TCE displacement became more and more efficient as the acceleration amplitude increased from 0.5 m/s2 to 5.0 m/s2;Moreover, numerical simulations were performed using FLUENT to investigate single droplet flow and the related stimulation effects of vibration. Implementing vibration was demonstrated to be more helpful and efficient to mobilize a trapped droplet in capillary tubes. For fixed acceleration amplitude, the efficiency increases as the vibration frequency decreases from 50 Hz to 10 Hz. For fixed vibration frequency, the average bulk flow rate increase and the time necessary to mobilize the trapped droplet decrease as the acceleration amplitude increase;In addition, analysis of droplet breakup in constricted capillary tubes driven by interfacial tension was performed. A criterion was derived to determine whether droplet breakup could be initiated in sinusoidally constricted tubes, and was further validated by simulations and published data. Droplet breakup was shown to be strongly dependent on the shape of the constriction, viscosity ratio, and interfacial tension, but not on density ratio;In all, the work together with the capillary physics mechanism can make it possible to understand the physics of the mobilization effect of low frequency vibration, which can then be applied to the predictions of the stimulation effect in the field after further full parameter space investigations are performed.