Effect of Leakage Flow Path Wear on Axial Thrust in Downhole Electrical Submersible Pump Unit

Abstract

Subsea production fluid is quite often characterized by the presence of frac sand, which causes wear within the pump, and alters the performance envelop. One of the design parameters critically affecting reliability is the thrust load generated by an impeller. The change in thrust load due to the erosion of the pump stages is not completely understood, and no relationship exists to foresee these reactive forces due to the complexity involved in predicting the flow characteristics. The purpose of this study is to understand the change in axial thrust due to commonly encountered wear mechanisms across the pump section especially wear across stage clearance seals. Based on in-house erosion testing of a mixed flow pump, three mesh models were built with each representing the pump condition at three different time intervals, namely, 0 h, 52 h, and 117 h of the total test time. The pump numerical models were validated using performance data collected from experimental testing. Axial thrust was found to increase with an increase in wear rate across stage seals. Since the increased clearance causes head degradation as well as an increase in thrust, the relationship of this head degradation is correlated with a change in thrust to further expand the affinity laws.