SPE-194387-MS Advancing High-Temperature ESP Technology for SAGD Applications Jose Caridad and Song Shang, Schlumberger Copyright 2019, Society of Petroleum Engineers This paper was prepared for presentation at the SPE Gulf Coast Section Electric Submersible Pumps Symposium held in The Woodlands, Texas, USA, 13—17 May 2019. This paper was selected for presentation by an SPE program committee following review of information contained in an abstract submitted by the author(s). Contents of the paper have not been reviewed by the Society of Petroleum Engineers and are subject to correction by the author(s). The material does not necessarily reflect any position of the Society of Petroleum Engineers, its officers, or members. Electronic reproduction, distribution, or storage of any part of this paper without the written consent of the Society of Petroleum Engineers is prohibited. Permission to reproduce in print is restricted to an abstract of not more than 300 words; illustrations may not be copied. The abstract must contain conspicuous acknowledgment of SPE copyright. Abstract A new high-temperature electric submersible pump (ESP) system was introduced in 2017 that is designed to address documented failure mechanisms and improve system reliability for steam-assisted gravity drainage (SAGD) operations at 250°C. A closed-loop product improvement workflow based on equipment dismantle, inspection and failure analysis (DIFA) has significantly driven high-temperature ESP technology development and reliability. In this paper, the authors discuss the unique closed-loop design workflow, present the new engineering features to address the identified failure modes, review field results and demonstrate the positive effects of the design modifications by comparing reliability trends based on nearly 150 field installations of the new generation equipment. Introduction Since the early 2000s, operators have demonstrated that ESPs are a viable method to economically produce SAGD wells. Gaviria and Santos (2007) and Solanki et al. (2005) concluded that ESPs allow greater operational flexibility and lead to improved economics when compared to gas lift and natural lift. ESP technology has evolved through continuous improvement efforts and new products with increased capabilities, as shown by Scrupa et al. (2013). Noonan et al. (2010) documented the results of a thorough qualification protocol for a high temperature ESP rated to 250°C completed at C-FER facilities in a joint effort between Conoco-Phillips and Schlumberger. Similar efforts later between additional operators and ESP manufacturers, were summarized by Waldner (2012). As these new products were successfully brought to market, operators started to take advantage of the higher temperature ratings to increase production. Moreover, as operators become more familiar with a technology and comfortable with the equipment capabilities, technology is often used more aggressively and operated at the rated limit to achieve production goals, enable new operational schemes, or both. ESPs are currently the most popular method of artificial lift used in SAGD applications, and run life remains a parameter of primary importance to reduce the frequency of costly workovers. As a result, it is in the best interests of ESP manufacturers to improve the technology based on ESP performance in the field to continually increase runlife. 2 SPE-194387-MS SAGD conditions are severe for an ESP, particularly temperature. Each new generation of equipment pushes the technology boundary in search of improvement. This paper describes the development of a new generation of ESPs, which benefitted from a successful feedback loop with operations, and technological improvements that led to superior reliability via unique design methodology, collaboration, and innovations. Failure analysis After an ESP fails and it is pulled from the well, it is typically sent to the ESP manufacturer’s local facility for further action. Depending on equipment condition, it could be retested for re-use, dismantled for failure analysis, or scrapped. The decision whether to dismantle a failed ESP string or not rests with the operator but is typically made based on factors such as accumulated runlife, well criticality, or use of new equipment or different operational schemes. Equipment dismantle, inspection and failure analysis (DIFA) provides a wealth of information to ESP manufacturers, not only for identifying root causes but also for assessing the condition of components that may become the next failure mode. In the spirit of continuous improvement for high-temperature ESPs used in SAGD applications, intensive collaboration amongst operators, field personnel and engineering resulted in a database of failure modes and recurrence frequency. A Pareto chart of failures, such as that shown in Fig. 1, was prepared using the database, which enabled the prioritization of improvements according to their impact on equipment reliability. Figure 1—Pareto chart of failures The analysis of failure data showed that some failure modes that had been identified during the development phase were exacerbated under field conditions. Moreover, new failure modes were identified because of equipment operating at or even outside the published rating or exposed to specific conditions required by field operations. Regardless of the cause, solutions were engineered to address the failure modes, improve long-term reliability and increase tolerance under field conditions. SPE-194387-MS 3 High-temperature ESPs are subjected to very challenging conditions. Extreme temperatures and steam push the technological limits of all non-metallic materials; if time is added, material aging is the result. Not surprisingly, components in areas where heat is generated were amongst those identified in the failure database, as shown in Fig 2: • • • • The motor insulating system is particularly challenged because of high well temperature in addition to the heat created by the Joule effect Bearings are subject to high friction resulting from the mechanical load and low oil viscosity Shaft seals are perhaps the components exposed to the most challenging conditions because they need to handle well fluid, abrasives and high temperature, including heat generated by the running faces Elastomers are attacked by steam and temperature and will get a compression set over time. Figure 2—Typical failure modes in SAGD operation. -Brittle insulating materials -Damaged thrust bearing runner -Worn shaft seal faces -Aged Elastomers Design improvements Design changes were proposed and subsequently qualified using rigorous verification protocols, including controlled laboratory tests and holistic computational fluids dynamics (CFD) simulations. Some examples of the design changes are shown in Fig. 3. Manufacturing trials were also conducted to confirm that the product could be assembled consistently and with quality every single time. The main improvements of the new system are detailed below. Insulating system: One of the key opportunities identified to increase long-term reliability was improvement of the insulation system, including motor wire insulation and other components providing electrical insulation. Because of the inherent high temperatures that these components must withstand, thermal aging was a common occurrence. A new insulating system was proposed with improved materials less susceptible to water and with increased dimensional stability and dielectric strength to extend the life of the motor. Internal testing proved higher breakdown voltages and improved aging behavior with no identified drawbacks in the manufacturing process. Bearing system: Mechanical stability is of paramount importance in rotating systems. Ceramics are typically used for radial and thrust bearings in SAGD conditions because of their higher stiffness and ability to conduct heat away. The drawback of ceramics is lower toughness. Design improvements were incorporated to remove or modify features that could act as stress enhancers and lead to cracks. In certain components, larger bearings areas, different materials, or both were used to improve load capability and toughness, as proven by qualification protocols. 4 SPE-194387-MS Shaft Seals: Mechanical shaft seals are critical for ESP reliability. These are sacrificial components that delay the ingress of well fluid into the motor. As a result, improving shaft seal reliability will directly improve system reliability. An upgraded shaft seal was introduced with the new high-temperature ESP system that featured a more stable design able to maintain flatness across a wider temperature range. Moreover, increased axial travel capabilities to absorb thermal expansion and a more stable bellows design were also implemented as part of the improvements. Component prototype testing showed a noticeable improvement in leak rate as well as in the condition of the running track in the seal faces after testing. Elastomers: Joint O-rings are the barriers first exposed to operational instabilities such as steam flashing in case of very low sub cools or operational schemes such as steaming past the ESP. Steam is very detrimental to elastomers. It penetrates the elastomer and decomposes the crosslinks, causing loss of seal force and leading to eventual seal failure. This is a gradual process that is aggravated by higher temperatures, greater steam percentage in the mixture, and longer exposure. As operators become more confident with ESPs in SAGD applications, it is increasingly common to see more challenging field conditions (e.g. more aggressive sub cools), and elastomers often pay the price, resulting in reduced ESP runlife. To succeed in the face of these operational challenges, a new elastomer was developed with a different recipe to improve initial sealing force and ultimately be more tolerant to steam. The new elastomer showed a 50% improvement in sealing force compared with the previous bestin-class elastomer across all the conditions tested. Motor Oil: Oil is the lifeblood of an ESP system. In SAGD conditions, viscosity and lubricity are very low because of the high temperatures. This directly affects the performance of radial and thrust bearings because it is increasingly more difficult for the fluid to sustain the load. Consequently, a new motor oil was introduced with increased viscosity at operating temperatures, thereby improving the bearing system as a whole. Figure 3—Examples of design improvements Left: Close up of part of the insulating system Center: Detail of thrust runner Right: Computational Fluids Dynamics (CFD) image of Gas Purging System As part of the root cause analysis of failed SAGD equipment, new failure modes were identified that had not been considered during development of the previous generation of equipment. A new design feature added to the hardware to account for these failure modes was a gas purging system (GPS) to handle potential gas coming out of solution from motor oil and causing damage to the bearing system (Fig. 3). An additional benefit of the gas purging system is an increase in oil circulation, which enhances heat transfer and keeps the bearings cool. SPE-194387-MS 5 Field performance The latest high-temperature ESP generation incorporating the improvements described above was introduced to address the documented failure modes, with the goal of improving reliability. Survivability trends were prepared with a database of approximately 150 strings deployed in 15 SAGD oil fields in Canada and an evaluation window of 2 years. Fig. 4 shows the survivability plot based on the Kaplan-Meier method for the new system as well as plots for the two previous generations of high-temperature ESPs. Figure 4—Survivability plot comparison between different generations of equipment The reliability predictions show a survivability improvement of approximately 10% at 1 year, which is very significant and in line with design expectations. The plot in Fig. 4 also shows a clear change in the shape of the survivability curve, indicating a healthy progression toward wear-out mode. Conclusions The latest generation of high-temperature ESPs includes improvements to nearly all non-metallic component of the system. Design or material changes were made to shaft seals, insulating materials, elastomers, the bearing system, and more. A gas purging system (GPS) was added to increase oil recirculation and to address potential gas coming out of solution from motor oil and affecting bearing performance. Survivability plots were prepared to evaluate the effect of the design changes on reliability compared with the previous generation of equipment. Very encouraging run-life trends have been suggested by the field data captured from the main SAGD operating fields, showing an improvement of approximately 10% in 1-year survivability. A closed loop among engineering, field personnel and operators that enabled capture of failure data and feeding back to development teams to address identified failure modes has proven successful for hightemperature ESPs, resulting in clear improvements in reliability metrics. Acknowledgements The authors would like to thank the management of Schlumberger for permission to publish this paper 6 SPE-194387-MS References 1. 2. 3. 4. 5. Gaviria, F., and Santos, R. 2007. Pushing the Boundaries of Artificial Lift Applications: SAGD ESP Installations at Suncor Energy, Canada. Presented at the SPE Annual Technical Conference and Exhibition, Anaheim, California, USA, 11-14 November. SPE-110103-MS. https://doi.org/10.2118/110103-MS Noonan, S.G., Dowling, M., D’Ambrosio, L., and Klaczek, W. 2010. Getting Smarter and Hotter with ESPs for SAGD. Presented at the SPE Annual Technical Conference and Exhibition, Florence, Italy, 19-22 September. SPE-134528-MS. https://doi.org/10.2118/134528-MS Scrupa, C., Shang, S., Caridad, J., Hong, C; and Velev, L. 2013. Expanding Horizons for HT ESPs. Presented at the SPE Artificial Lift Applied Technology Workshop Phuket, Thailand, 24-27 November Solanki, S., Karpuk, B., Bowman, R., and Rowatt, D. 2005. Steam Assisted Gravity Drainage with Electric Submersible Pumping Systems. Presented at the SPE-Gulf Coast ESP Workshop, The Woodlands, Texas, USA, 27-29 April Waldner, L, Wonitoy, K., Klaczek, W., and Noonan, S. 2013. Thermal Performance of a High Temperature ESP Motor for SAGD Applications. Presented at the SPE-Gulf Coast ESP Workshop, The Woodlands, Texas, USA, 24-26 April. SPE-160317-MS. https:// doi.org/10.2118/160317-MS
