Design and application of a ring-shaped acoustic focusing piezoelectric transducer for emulsion separation

As oil production enters its middle and later stages, high water content and severe emulsification in oil wells are becoming increasingly prominent, leading to excessive energy consumption and environmental pollution. Existing downhole oil-water (O/W) separation technologies, such as gravity-based separation and hydrocyclone separation, prove inadequate for separating micro-sized oil droplets in heavily emulsified production fluids. Acoustic O/W separation has shown promising capabilities for micron-sized droplet removal, yet current studies predominantly address emulsions with high oil content. Acoustic separation techniques targeting high-water-cut emulsions have only been validated in stationary, millimeter-scale channels and lack research in large-scale, high throughput, and rapid flow rates under realistic downhole conditions. To overcome this limitation, this study introduces a novel ring-shaped acoustic focusing piezoelectric transducer. The transducer employs the inverse piezoelectric effect to excite the radial contraction-expansion vibrations of the annular structure, generating a diametrically focused full-wave acoustic field within the emulsion, with the center of the pipe serving as the focal point. Under the combined effects of acoustic radiation and acoustic streaming drag forces, dispersed oil droplets migrate toward the pressure antinode, enabling O/W phase separation. Experimental results from both static and dynamic conditions indicate that the proposed transducer effectively enriches micron-sized oil droplets in high-water-cut oil-in-water emulsion and achieves separation. Nevertheless, under dynamic conditions, separation efficiency is sensitive to the flow velocity and declines as flow rate increases. In summary, the proposed acoustic transducer provides an efficient solution for downhole high-water-cut produced fluids, supporting further developments in acoustic-based downhole separation technologies.