Shaft Failure Analysis in Soft-Starter Fed Electrical Submersible Pump Systems

Sheikh F Rabbi,Jianming Yang,Xiaodong Liang,Jalal Taheri Kahnamouei

doi:10.1109/ojia.2019.2956987

Abstract

Electric submersible pumps (ESPs) are widely used for high volumetric oil and gas recovery from downhole wells. ESPs in oil fields can be equipped with multiple ac motors in tandem. To assist a motor start-up, a solid-state soft-starter can be deployed in such ESP wells. ESP shafts have a long axial length, and thus experience significant dynamic torsion when started from reduced voltage soft-starters. Premature shaft breakdowns had occurred in the field during the motor start-up for soft-starter fed ESPs. This paper investigates the shaft breakdown phenomenon in a 750-HP ESP system using a real-world case scenario. A lumped parameter electro-mechanical model for the ESP system is developed to observe its dynamics. The effects of static as well as fluctuating torsional stress on the interconnected pump shafts are analyzed to determine the root cause of the shaft breakdown. Criteria for successful start-up for soft-starter driven ESP systems are also presented to increase the equipment's operational life.

Highlights

A N ELECTRIC submersible pump (ESP) is an artificial lift technique commonly used for oil and gas recovery from downhole reservoirs
This paper presents a systematic root cause analysis for shaft breakdown phenomena in a soft-starter driven 750-HP ESP system during its practical oil field application in a shallow well
Selection of the maximum starting current for a soft-starter plays an important role on successful start-up of an ESP system

Summary

INTRODUCTION

A N ELECTRIC submersible pump (ESP) is an artificial lift technique commonly used for oil and gas recovery from downhole reservoirs. RABBI ET AL.: SHAFT FAILURE ANALYSIS IN SOFT-STARTER FED ELECTRICAL SUBMERSIBLE PUMP SYSTEMS are still widely used for operating induction motors in ESP systems. The starting motor torque requirement can be significantly high during soft-starting an ESP system to maintai a sufficient rotor acceleration to pass the critical speed swiftly for avoiding severe torsional oscillations. SOFT-START Fig. 9 illustrates a direct-on-line scenario where the ESP system is started directly from the switchboard In this case, a reduced pedestal voltage (Vstart = 0.5 ∗ Vrated) is applied to the motor terminals during starting at t = 0 s, the voltage is ramped up to the full rated voltage after t = 2 s.

SOFT-START

ANALYSIS OF FATIGUE IN ESP SHAFTS

Findings

CONCLUSIONS