The electrical submersible pump (ESP) is widely used in the petroleum industry to maintain high crude-oil production rate. Its performance deteriorates with the increase of gas entrainment. Previous studies showed that bubble size is an important factor affecting ESP boosting pressure under multiphase flow. In this paper, a novel indirect approach is proposed to obtain the representative bubble sizes inside a rotating ESP impeller by matching numerical-simulation results with experimental performance curves. A 3D computational-fluid-dynamics (CFD) model is implemented on a three-stage ESP geometry to simulate the pump-pressure increment under various flow conditions. By use of structured hexahedral grids and the frozen-rotor technique, the mesh independence and numerical accuracy are verified. ESP boosting pressure in single-phase simulations is found to match well with experimental data. For two-phase simulations, the Eulerian-Eulerian model is used. At low inlet gas volumetric fractions (GVFs), the numerically simulated pump-pressure increment using constant bubble sizes agrees well with experimental measurements. At higher GVFs, the simulation results deviate from experimental pump-performance curves considerably. By increasing bubble sizes, the simulated ESP performance can be tuned to match experimental results. Through this process, a bubble-size change trend with varying GVFs is obtained. A mechanistic model that is based on the maximum stable bubble in a rotating turbulent flow field is developed to correlate the CFD simulated bubble sizes. Further, numerical-simulation results incorporating the proposed bubble-size prediction model agree well with experimental data.
