High intervention costs to replace electric submersible pump (ESP) completions and high deferral production caused by ESP failures in offshore and remote locations are driving the efforts to increase ESP reliability around the world. ESP designs vary considerably depending on the application, for example, unconventional resource, heavy oil, high temperature, and high abrasives. Because of the wide range of ESP applications, the equipment specification requires a tailored solution for each application to increase reliability. This paper presents typical failures and the evolution of ESP technology deployed in the North Sea as well as the enhancements proposed to increase system reliability. The equipment improvements are based on failure analysis performed in the strings pulled from the North Sea. A large ESP population is analyzed, including 219 installations and 162 failures. Survival analysis enabled splitting the population into subsystems and analyzing the ESP performance individually after each major change in equipment specification. This approach made it possible to confirm the effectiveness of the changes and quantify the increase in reliability after each investment in equipment enhancement. It was also possible to identify the "less reliable" subsystem to focus on further improvements.

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.

Peregrino is a Brazilian offshore field which has been operated by Equinor since 2011. The fields crude oil viscosity ranges from 129 to 364 cp and the API gravity varies between 13° and 15° API. Electrical Submersible Pumps (ESP's) were selected as the Artificial Lift method to produce the heavy oil from Peregrino. The ESP equipment design has been modified throughout the years to address various failure modes, therefore improve system reliability by adapting customized solutions. This paper describes in detail the ESP application and solutions implemented in the field to overcome those challenges. Every ESP string pulled from Peregrino is dismantled and inspected and this paper will discuss the routines used to conduct failure analysis and continuous improvement. The main challenge with the ESP operations in Peregrino has been asphaltene precipitation in the seal sections and emulsion formation. Emulsion instabilities cause pressure, temperature and electrical current fluctuations, which increase stress in downhole equipment. This paper will discuss how the ESP equipment in Peregrino has been improved to meet the various challenges, an overview of the following equipment changes will be discussed:Packer penetratorPump diffusersESP MotorNew Seal construction An overview of the ESP equipment reliability spanning the lifetime of Peregrino's operations will also be described in this paper.

Although being widely used as an artificial lift method for heavy oil field developments, Electrical Submersible Pump (ESP) system performance in high viscous applications is not fully understood. A miscomprehension of challenges and equipment performance in such conditions might lead to operation inefficiencies and equipment failures. This paper presents results of single-phase and multiphase tests performed by University of Campinas (UNICAMP). It also presents operation data, lessons learnt, and failure examples gathered over 10 years of ESP operation in Peregrino field which is a heavy oil, high viscous oilfield offshore Brazil operated by Equinor. Affinity laws commonly used for ESP simulations don't hold true for high viscosity applications. Hydraulic performance of centrifugal pumps is affected by fluid parameters like viscosity and density; operation parameters such as flow rate and rotational speed; and specific stage design characteristics. To determine degradation in head and efficiency as well as power requirement increase in viscous applications, Equinor performs one-phase high viscosity flow loop test to qualify each stage type prior to deployment in Peregrino field. For the qualification of ESPs, single phase qualification tests are performed using mineral oil with viscosities specifically chosen to cover the viscosity range of the specific field. Each stage type is qualified using a prototype with reduced number of stages due to flow loop limitations. Qualification tests for the Peregrino field confirmed that affinity laws are not accurate for high viscous applications and provided important insights regarding pump performance that are used in equipment specification and system surveillance. The UNICAMP research team has designed and performed multiphase flow tests to evaluate emulsion formation inside centrifugal pump stages and effective viscosity behavior. Phase inversion phenomenon investigation was also included in studies. Studies performed using a prototype stage allowed visualization and evaluation of oil drops dynamics inside the impeller in different rotational speeds. Two phase flow loop tests investigated the shear forces influence in effective viscosity inside pump stages and downstream pump discharge. Phase inversion phenomenon was also a point of great interest during the studies. Data gathered during lab tests was used to evaluate accuracy of mathematical models existing in the literature when a centrifugal pump is added to the system. Hysteresis effect associated to catastrophic phase inversion (CPI) was confirmed and replicated during flow loop tests. Such behavior can be related with operation parameters instabilities and equipment failures noticed in actual application in Peregrino field which are also presented in this paper.

The oil industry is going through a transformation in which reducing costs and increasing rig efficiency became paramount. In spite of this changing period, safety is, and must remain, the main concern for every offshore installation. In order to achieve a step change in safety during offshore ESP deployment in the North Sea, procedures and standard working instructions were reviewed and opportunities for improvements were identified. Innovative tools including a new cable spooling system and special subs were developed to increase safety and address operator concerns during ESP assembly. Special attention was also paid to the service quality and efficiency of the ESP offshore installation. The toolstore used during ESP completion was redesigned using lean and 5S techniques to optimize installation time, and a high efficiency tool was introduced to install cable protectors, considerably reducing ESP installation time. In order to monitor the changes and continue improving, a recording system was introduced and every offshore installation is recorded and used for assessment and training. The objective of this paper is to describe novel ideas developed in the North Sea that created a new level of safety and quality during ESP deployment. The improvements described in the paper might inspire other initiatives to increase quality and safety standards in the oil industry.