Effect of liquid viscosity on energy performance and gas–liquid flow characteristics in an electric submersible pump

During deep-sea oil and gas extraction, increased crude oil viscosity critically impairs electrical submersible pump (ESP) performance, causing overload and efficiency decline. To address this industry challenge, this study integrates numerical simulations and experimental measurements to systematically analyze the evolution of energy characteristics and internal flow mechanisms of ESPs under different liquid viscosity conditions. The results shown that as liquid viscosity increases, the energy performance of the pump deteriorates significantly, and the pressurization capacity of each stage is markedly reduced. The entropy production loss primarily shifts from turbulent dissipation entropy production to direct dissipation entropy production, while wall entropy production increases substantially. Regions of high turbulent kinetic energy closely correspond to those with high eddy viscosity. Viscosity-flow coupling drives transitions between turbulent, transitional, and laminar flow regimes. Increased viscosity reduces the isosurface area of the gas, restricts gas distribution, and lowers gas velocity, leading to a more stabilized vortex structure. This work enables optimized ESP deployment in high-viscosity deep-sea extraction, reducing failure risks and enhancing production efficiency.