Liutex-based flow structure characterization in vibrating downhole hydrocyclone for oil-water-sand multiphase systems

Abstract

The hydrocyclone, a key component in single-well injection-production (SWIP) systems for downhole oil-water separation (DOWS), faces complex vibrational challenges in wellbore operations. Produced fluids inevitably carry solid sand particles. Yet, existing studies largely ignore the combined effects of vibration and sand - laden conditions, creating a critical research gap. This study employs innovative CFD modelling integrating Mixture model, Discrete Phase Model (DPM), and dynamic mesh techniques to investigate oil-water-sand flow under vibration. Uniquely, we combine the Ω criterion with the advanced Liutex vortex identification method to reveal transformative flow phenomena: vibration shifts vortex structures from conventional Rankine patterns to axially elongated cylindrical forms, accompanied by a transitional zone between the forced and free vortex regions. Vortex cores migrate toward the geometric centre of hydrocyclones, contrasting with off-centre behaviour in static conditions. Crucially, vibration induces a low-pressure zone in the small conical segment that obstructs oil discharge while increasing solid particle residence time by 113 % (0.342 s to 0.728 s)—a previously unreported synergy that impairs separation efficiency.