Energy conversion mechanisms and flow boundaries of gas–liquid multiphase flow in a mixed-flow electrical submersible pump for offshore oilfields

Abstract

Gas entrainment threatens the hydraulic stability and energy conversion efficiency of electrical submersible pumps (ESPs). To elucidate multiphase performance variations and underlying energy dissipation mechanisms, a mixed-flow ESP widely applied in offshore oilfields was investigated. A robust Euler–Euler inhomogeneous multiphase numerical method was experimentally validated to quantitatively evaluate the spatial distributions of input power, effective power, and power losses within the impeller. Furthermore, critical flow pattern transition boundaries were systematically extracted across varying liquid flow rates and inlet pressures. Results show that gas accumulation and flow blockage near the suction side severely obstruct flow passages and induce intense wake vortices; specifically, at a 15% inlet gas volume fraction (GVF), global power loss surges by 280%, causing a 44.5% plunge in effective power. Macroscopically, pressurization exhibits a three-stage degradation. Elevating inlet pressure effectively shrinks the deteriorated gas pocket region, substantially broadening the stable operational envelope. Additionally, critical gas tolerance boundaries demonstrate a distinct nonlinear “hump” morphology, achieving optimal gas handling capacity near the design flow rate due to minimized incidence-induced separation and maximized interphase sweeping momentum. Ultimately, by incorporating a flow-deviation-based Gaussian decay term alongside phase density and pressure ratios, a critical GVF prediction model is proposed. This model dynamically evaluates the pump's gas handling capability, providing a reliable theoretical guideline for the operation of offshore oilfield ESP systems.