Investigation of flow patterns and energy efficiency in electric submersible pumps under varying oil-water ratios

Electric submersible pumps (ESPs) are widely used in oil production to lift multiphase fluids, yet the presence of oil-water mixtures can substantially complicate performance prediction and compromise operational stability, especially in multistage systems. This study investigates the internal flow dynamics and energy characteristics of a three-stage ESP under different oil-water ratios using Euler-Euler two-phase simulations validated against experimental data. Quantitative results show that both total head and hydraulic power decrease gradually as the oil content increases, with reductions of 1.29% and 1.75%, respectively, when the oil volume fraction rises from 0.1 to 0.3. A critical oil volume fraction of 0.3-0.4 is identified, at which phase inversion occurs from an oil-in-water to a water-in-oil regime, leading to an abrupt drop in total head to 18.47 m. The first-stage impeller is particularly sensitive to changes in oil-water ratio: unstable vortices near the pressure side are progressively suppressed with increasing oil content, reducing energy loss and improving efficiency, whereas downstream stages exhibit greater robustness. At the 0.5-span location, oil-dominated regions occupy up to 60% of the first-stage impeller blade chord, with marked accumulation near the suction-side trailing edge. In contrast, subsequent stages display more fragmented and disordered phase distributions due to shear-induced breakup. Overall, these findings provide new insights into the phase-inversion mechanism, inter-stage flow evolution, and energy-dissipation characteristics, offering practical guidance for optimizing ESP design and operation under oil-water multiphase conditions.