Abstract

The occurrence of electric submersible pump (ESP) failures due to spinning diffusers is of a tolerable frequency in moderate operating cost circumstances. However, extremely high well servicing expenses are associated with many ESP applications. Examples include deep wells, arctic locations, offshore wells that must be killed with high-density fluids and sea floor completions. In these or other high cost circumstances, early pump failures of any mode cannot be tolerated.

Longitudinal compressive force is imposed on the diffuser stack of ESP's during assembly to prevent diffuser rotation. If this is done improperly the diffusers can spin due to torque transferred from the impellers, resulting in early pump failure. This paper analyzes the mechanics of the spinning diffuser failure mode and demonstrates why some pumps having inadequate compressive force can pass common pump tests, but subsequently fail in this mode. Equations are developed to calculate the restraining force as it changes under varying conditions and the minimum value required to prevent diffuser spinning. Testing procedures are proposed that would emulate the effects of well conditions conducive to diffuser spinning, thereby detecting the defective pumps currently being missed. Practical examples are included which illustrate the utility of the concepts herein presented.

P. 519

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