Effect of Vibration on Electric-Submersible Pump Failures

Abstract

Summary Electric submersible pumps (ESP's) historically have had short run lives. Their failures usually were unexplained and accepted as the norm. Because the equipment has generally been downhole, finding all the influences that shorten equipment life expectancy has been difficult. Horizontal surface installations for water injection have been made where machine operating conditions could be monitored and equipment performance analyzed. Unbalanced pump vibration has been identified as the cause of many seal problems and ultimately motor and pump failures. In fact, excessive vibration appears to be an inherent mechanical characteristic of ESP's. To illustrate the severity of this problem, this paper presents data gathered from field installations with monitoring equipment, from equipment tear-down analysis, and from statistics on ESP failure modes. Introduction ESP's have been used for more than 50 years, typically for moving large volumes of fluid where other means of artificial lift have not been feasible. Recently, the application of these pumps has expanded. It is not uncommon to use these pumps to move 500 bbl [80 m3] of fluid from less than 2,000 ft [600 m]. The industry has made great strides in improving ESP performance. Run times have improved significantly over those existing only 10 years ago. These pumps are now economically competitive with other pumping systems in many environments. A unique application of ESP technology has been in water-injection systems. Water-injection pumps often must move large volumes at high pressures. Not surprisingly, ESP's fit this criterion. Although ESP's are not a panacea for all pumping applications, these examples demonstrate the applicability of ESP technology to an increasing number of applications. Nevertheless, the significant problems that still exist with the technology must be addressed before the equipment can achieve adequately long run times for it to be widely applied. Current estimates are that ESP's are used in only about 5% of the lift applications in the petroleum industry. This leaves considerable room for further application. History and Design Before the problems with ESP's are addressed, the construction of the pumping system should be analyzed. This analysis will demonstrate the problems to be solved. The design of today's ESP's remains basically unchanged from the first pumps. The pump assembly is a slender centrifugal pump of up to hundreds of stages. The stages consist of an impeller that "floats" on a shaft. The impeller is mated with a diffuser for directing the flow between stages. The impeller/diffuser assembly is stacked inside a small-diameter tubular.