Numerical investigation of the effect of viscosity in a multistage electric submersible pump

Abstract

Electric submersible pump (ESP) systems are commonly used as an artificial lift technique by the petroleum industry. Operations of ESPs in oil wells are subjected to performance degradation due to the effect of oil viscosity. To understand this effect a numerical study to simulate the flow in three stages of a multistage mixed-flow type ESP operating with a wide range of fluid viscosities, flow rates, and rotational speeds was conducted. The problem was solved by using a commercial computational fluid dynamics (CFD) software. The numerical model was validated with experimental head curves from the literature at different viscosities and rotational speeds available for the same ESP model used in this study, and good agreement was found. Performance degradation was evaluated by analyzing the effect of viscosity on head and flow rate. In addition, a flow field analysis to compare the flow behavior when the pump operates at different viscosities was carried out. The interaction between stages was also analyzed, and the influence of a previous stage on the upstream flow was evidenced. The flow field was analyzed at a curved surface that follows the complex mixed-flow geometry of the stages. CFD proved to be useful for exploring this kind of feature, a task whose accomplishment by means of experimental methods is not trivial. Such analysis helps to understand the flow pattern behind head and flow rate degradation when the Reynolds number is decreased. The results from this work are helpful as they provide a basis to estimate performance degradation for general scenarios.