Douglas is an oil field in the Irish Sea where electric submersible pumps (ESPs) are used as artificial lift method. This paper presents the ESP failures and root causes in early stages of production, and the improvements implemented that contributed to the outstanding improvement in ESP run life. These improvements increased field production, minimized deferred production, and minimized workover costs.
Every ESP system pulled from the Douglas field was dismantled, and a failure analysis was performed to identify the failure root cause. When the root cause is confirmed, applicable equipment upgrades were recommended to address the failure modes and increase ESP run life. In order to monitor system performance, reliability was tracked and compared over the years. The ESP reliability was analyzed using data gathered from ESP run life and failure analysis covering more than 20 years of ESP operation in the Douglas field.
Failure analysis performed in the pulled strings indicated failures related to poor electrical power quality. A power study was performed on the Douglas platform, and it was observed that the wells exhibited natural system resonance frequency amplifying drive harmonics. Resonant peak frequencies were observed between five and seven kilohertz, and voltage impulses were observed up to nine kilovolts. Such impulses were weakening insulation in some downhole components, such as penetrators, cables, and motors. Following the recommendations from the study, load filters were installed in every well to eliminate voltage overshoots. The filters provided cleaner voltage and current waveforms to the system, power cable, and at the motor terminals.
In addition to the power supply issues, it was noted that there was H2S contamination in the protectors and motors pulled from the field. In order to increase ESP reliability, an advanced H2S scavenger protector design was introduced. The advanced protector has features that delay the ingression of H2S into the motor and copper liners that serve as sacrificial parts to be consumed by H2S.
The solutions proposed for ESP operation in combination with ESP design improvements helped to improve ESP reliability considerably allowing ESP systems to achieve outstanding run lives in the Douglas field.