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Due to the influence of gravity, the liquid film formed after the vortex tool in the inclined pipeline has the characteristics of being thin on top and thick at the bottom. Besides, the liquid film is affected by the tangential force. • Liquid unloading mechanism of vortex tools is explained. • Structural optimization progress of vortex tools is reviewed. • Technology application of surface vortex tools is summarized. • Liquid unloading model of swirl annular flow is proposed. The paper presents an in-depth review of the liquid unloading by vortex tools in the low production gas wells or hilly pipelines from the perspective of liquid unloading mechanism analysis, experiments and numerical simulation, and technology application. Moreover, future research directions are suggested that can promote future applications. The review points out that optimizing the vortex tools should take into account the liquid unloading capacity and pressure drop. The challenges are also discussed. Specifically, it is necessary to: 1. establish a liquid unloading model of vortex flow by considering the gravity in the inclined pipe; and 2. predict the effective operating distance between the vortex tools. [ABSTRACT FROM AUTHOR]

The separation characteristics of W/O emulsion were investigated under ultrasonic standing wave field in this paper. The effects of the irradiation time, acoustic intensity, frequency, oil viscosity, and oil-water interfacial tension on the separation characteristics of emulsion were studied in details. It was proved that there existed an optimal irradiation time, acoustic intensity and oil-water interfacial tension to achieve the maximum separation efficiency in ultrasonic treatment process. Excessive long irradiation time had little effect on improving the dehydration rate of emulsion but rather increased unnecessary processing time. Excessive high acoustic intensity caused the occurrence of acoustic cavitation phenomenon. The acoustic cavitation would cause the aggregated droplets to be dispersed by oscillating bubbles or even emulsified again by high speed micro jets. The acoustic cavitation threshold is effectively and accurately obtained by a spectral analysis method. The micro acoustic streaming which resulted from the attenuation of acoustic energy occurred with the increase of frequency. It sheared the aggregated droplets, destroyed the stable droplets banding and reduced the separation efficiency of emulsion. The excess surfactant adsorbed on the oil-water interface resulted in the increase of the interfacial film strength, which hindered the coalescence process of droplets and reduced the separation efficiency. [ABSTRACT FROM AUTHOR]