Advances in the Understanding of H2S Paths into the ESP Electrical System

Abstract

Abstract One of the challenges electric submersible pumps (ESPs) face in harsh environments is the corrosion of copper electric components caused by H2S. Copper is aggressively and quickly corroded by H2S, compromising the electrical integrity of the system. ESP improvements, such as the metal-to-metal motor lead extension (MLE), has had a positive impact in the ESP's run life in sour environments, and it sparked the creativity for further similar enhancements throughout the ESP system. Understanding the path of the H2S into the motor is of paramount importance to effectively aim the resources for these additional enhancements. This paper offers an outlook of the components that play a key role in allowing the H2S to enter the electrical system. It is supported by evidence from the dismantle, inspection and failure analysis (DIFA) of motors, MLEs, and seal sections with and without H2S scavenger, and having different times of exposure based on their run life. For the objective of this paper, all observations are to revolve around the electrical integrity of the ESP. When examining the copper end rings of motor rotors, it has been observed that the H2S attack is concentrated at the top of the motor. Similarly, from tandem seals with bags in series and H2S scavengers, where the scavenger (copper tube) in the top chamber was corroded more severely than in the bottom chamber. Furthermore, in ESP systems where the H2S had been successfully scavenged at the top of the motor or the seals no further corrosion was observed in the lower parts of those components. These observations indicate that the source of the contamination is at the top of the seal section, with no concerning H2S entrance happening below (i.e., flanges and threaded parts relying on o-rings). For all practical purposes, these conclusions are of great benefit in determining the components that require enhanced H2S protection. They also suggest that developing and implementing metal-to-metal connections all along the ESP components is either not necessary or of least priority. The findings of this paper are intended to help direct the efforts of future ESP improvements in terms of H2S resistance toward key components. The analysis of the novel information presented here confirms that the main entry point for H2S in the ESP electric system is the top of the seal section. The shaft mechanical seals are a particular suspect. If so, vibration could be a major contributor, but further study is required to understand the effect of vibration on the rate of contamination through the shaft mechanical seals.