On the Influence of Viscosity on ESP Performance

This paper presents experimental data and a preliminary analysis of the influence of fluid viscosity on centrifugal-pump performance. Two centrifugal pumps, a conventional radial (specific speed N-q=8 rev/min) and a semi axial electrical submersible pump (ESP) (N-q=28 rev/min) were tested with 1-cp water and clear glycerin. Adjusting and controlling the fluid temperature in a closed test loop, it was possible to vary the glycerin viscosity from 67 to 1,020 cp within the range of light and heavy crude oils. The main purpose of these tests, in addition to appraising the influence of viscosity on the pump's overall performance through the measurement of the derating factors for head, flow, and power, was to supply detailed information on the energy-transfer processes taking place in the pump's internal components. To accomplish this, the pressure distribution along the flow path from the pump inlet eye to the discharge section, including detailed pressure difference across impellers and diffusers, was measured. Thus in addition to measuring the flow rate, the overall pressure difference, the speed, the power and the mean operation temperature for fluids with various viscosities within a full range of operational conditions, detailed data on the energy-transfer processes performed by impellers and diffusers were also taken. Later analyses indicated that, in addition to the physical dimensions, operational conditions, and fluid properties, the pump performance is set by the strong flow interactions that exist between impellers and diffusers. In other words, these succeeding internal blade rows influence each other in terms of the head gain and the viscous dissipation effects. Thus, any generalizing approach dealing with the influence of viscosity on the pump performance must account for those interactions to give a proper measure of the derating factors over an extended range of operational conditions. Unfortunately, this is not true for the procedures available in the open literature. They lack representation and do not deliver proper correction factors for pumps that are not similar to those that generate the correlation database or for pumps working under operational conditions other than at the best-efficiency point (BEP). The data presented herein can be a launching point for a deeper analysis aimed to tackle these limitations.