Comparative analysis of an electrical submersible pump's performance handling viscous Newtonian and non-Newtonian fluids through experimental and CFD approaches

Abstract

Electrical Submersible Pumps (ESPs) are among the most common artificial lifting methods employed nowadays in the O&G industry. This work aims to carry out an exhaustive analysis of the performance and flow features of a multistage ESP when handling Shear-Thinning non-Newtonian fluids, which are commonly found in mature, heavy oil wells. Currently, no studies have been conducted for multistage centrifugal pumps operating under such conditions. In this study, water, two Newtonian oils of different viscosities, and two non-Newtonian fluids, consisting of two CMC solutions in water (0.5% and 1% w/w), were tested. The testing facility consisted of a four-stage ESP located in a closed-loop arrangement in which the flowrate could be freely manipulated. Experimental measurements were taken to determine the pressure rise and power consumption by the ESP's motor. The CFD model was validated against experimental data collected in this study. The CFD head rise was in excellent agreement against the experimental data for water, with MSE of 4.91%. Good agreement was also observed, with a slight overprediction, for the pump's efficiency, with an MSE of 10.6%. The non-Newtonian fluids best fitted the Cross viscosity model. CMC 0.5% obtained a 12% higher average head rise than that of CMC 1%, despite the latter exhibiting a more pronounced Shear-Thinning trend (higher Cross time constant). It was found that the non-Newtonian fluids tested out-performed, in terms of head rise, the Newtonian oils by an average of 23.5%, and 11.4% against the heavier and the lighter oil, respectively. This improved performance was observed despite the non-Newtonian range of effective viscosities being over one or more orders of magnitude higher than the oils' dynamic viscosities. Furthermore, it was noted that the pump's performance with both non-Newtonian fluids did not deteriorate as rapidly as it did for the viscous oils. This lead to a shift in the BEP towards higher flowrates for the non-Newtonian fluids. This observation was supported by the CFD effective viscosity profiles, which showed a decline in the viscosity as the flowrate increased. CFD proved to be a valuable tool to analyze and understand in depth the viscosity variations and flow features throughout the pump's domain and their connection with the global performance observed for the ESP.