This article covers the challenges, advantages and deployment process for ultrahigh-speed ESPs in a field in Ecuador. This project obtained some advantages, including reduction in field assembly time, improved capability to deploy in more aggressive deviated wells, adaptable logistics, and successful flow handling.
JORGE L. VILLALOBOS LEÓN and KEVIN I. ANDAGOYA, SLB
Introduction
Because the power supply frequency typically runs on 50 Hz or 60 Hz in different countries, and the first electrical submersible pumps (ESPs) relied on switchboards that would run at the same input frequency, historically this is why ESPs designs would be sized at these frequencies. However, after the implementation of variable speed drives (VSDs), the advantages of centrifugal pumps could be exploited to the fullest, to accommodate reservoir flow by using the frequency to control the motor speed.
The traditional ESP speed range between 35 Hz and 70 Hz (assuming two-pole motors) or 2,100 rev/min. to 4,200 rev/min. can vary, not only from a technical perspective but also per operator/stakeholder preference or perspective of what is too high or too low. The industry classifies, as high-speed technology, running at 4,200 rev/min. to 6,000 rev/min. (70 Hz to100 Hz, assuming two-pole motors) and ultrahigh speed (UHS) as running above 6,000 rev/min. (Ye, et al. 2020).
In this sense, a true concern on spinning the components faster than before is answering the question, “how long will they last?” Because the moving parts have to deal with erosion, friction and load (Shakirov, Koropetsky, et al. 2018), the material used must have a robust design to handle the requirements and avoid any fatigue damage. But there are more expected benefits from increasing the operational frequency: As the frequency is increased, the string stages can be reduced in length, and this length reduction becomes handy when setting the ESP in highly deviated sections of the well, usually those that were unreachable before. Another benefit is the lower total cost of ownership for these short ESP designs, particularly during installation, as fewer components are assembled, making the whole assembly process faster and reducing rig time, and also during repair operations, which can proceed faster with fewer components.
Several records suggest the effectiveness of massifying UHS ESPs in certain oil fields (Alexeev, Shakirov, and Gorlov 2019) by showing the benefits of deepening the string were translated to gained production. That’s because the flowing pressure can be dropped, and the capabilities for managing high gas volume fractions improved (Ejim, et al. 2023).
Nevertheless, although the work carried out in previous studies provided knowledge on the performance of UHS ESPs that use permanent magnet motors, there is not much literature on the performance of UHS ESP deployments that use induction motors.
The objective of the work herein is to evaluate the deployment of a UHS ESP running on an induction motor and with the challenge to be deployed at a depth of 11,420 ft, measured depth (MD) (9,760 ft, true vertical depth [TVD]) and reservoir temperature of 226°F. This will also provide perspective on upcoming deployments.
CHALLENGES AND SOLUTIONS
Each of the concerns that were reviewed during the UHS ESP design process are described in this section.
Solids and deposits. The wear caused by solids and deposits is a valid concern because the pump will be running at higher than traditional revolutions per minute. To overcome the fatigue issue, the material stage was upgraded from a Ni-Resist alloy to a 5530 premium alloy that provides higher erosion- and corrosion-resistant properties to the stage.
Regarding the axial bearings of the pump (Fig. 1), tungsten carbide material is used in a configuration that increases the string robustness, because each bearing improves the shaft stabilization during operations and provides a hard material that can deal better with abrasives. The protector (Fig. 2) for the UHS ESP also incorporates sand filters that mitigate abrasives from entering the protector chambers. The protector is built with four series of elastomer bags, working as redundant chambers to avoid contamination inside the motor.
Due to the waterflooding project that this field is facing, additional sand and deposit control mechanisms such as desanders or chemical tail pipes (Andagoya, et al. 2022) may be required. However, the UHS ESP is compatible with any of these additional tools, with no additional adapter or rebuilding needed.
High-speed reliability. It is beneficial for a compression pump to handle the thrust of the stages in a securely lubricated environment, avoiding erosion and friction in each stage. The thrust bearing has been upgraded for high load bearing with active cooling. Tungsten carbide axial bearings are not only part of the pump but also are part in each component of the string.
To test the reliability, an accelerated sand loop test was carried out for over 65 hrs at 10,000 rpm and about 5,000 ppm of sand concentration. The successful results of the test proved the robustness of the new high-speed ESP in comparison to existing standard-speed ESP. Shown in Fig. 3 is an image from the dismantled sand loop pump.
Gas handling. To handle gas content, two options were considered for the UHS ESP design. The first is a gas separator (Fig. 4) to move the gas to the annulus, and the second is a gas handler (Fig. 5), designed with axial stages that successfully compresses the gas and put it back into solution.
High dogleg severity. A standard pump will face higher bending at the same dogleg severity (DLS) condition than a shorter ESP. Preliminary studies suggest that the string deployed in this well is capable of withstanding a DLS as high as 3.5°/100 ft; however, this has to be contrasted with a micro-DLS survey to detect any tortuosity and micro-DLS values that a traditional survey may not capture. As the string is shorter, at a same well DLS, the components will be less exposed for bending.
High temperatures and power requirements. To effectively deal with high temperatures, the induction motor employs an optimized electromagnetic design achieved through advanced multiphysics analysis software, encompassing electromagnetics, structural mechanics, and heat transfer. This approach enabled fine-tuning the motor's magnetic circuit geometry, enhancing its performance by optimizing the stator and rotor lamination profiles, rotor bars, and copper end-ring geometries. The refined stator and rotor profiles improve the distribution of magnetic flux within the circuit, reducing magnetic saturation in the steel and minimizing the current needed to generate the same magnetic field in the air gap. Consequently, less power is required to produce the same torque from the rotor (Fig. 6) (Escobar, Radov and Vasilache 2021).
The motor’s construction can handle higher temperature rates, compared with a traditional motor, not only in terms of the winding isolation, but also in terms of the type of elastomers.
Vibration. Another concern was the possibility to have any vibration or dynamic loads that may cause fasteners to become loose. To mitigate this effect, wedge-locking washers were used in this application. This type of washers utilizes tension, instead of friction, to secure bolted joints.
PREPARATION PRIOR TO DEPLOYMENT
As a first deployment, every component of the UHS ESP system was tested locally to assure the deployment success. In addition, the ESP string was fully assembled in the workshop to make sure every spare part that could be needed was ready. As seen in Fig. 7, the short length of the UHS ESP was fully stacked up by only using five dollies. The total length of this ESP design is 44.69 ft.
The ESP motor was run and tested, using the configuration displayed in Fig. 8. Notice that a switchboard was used, only because all instrumentation needed to record the power consumption had been installed. The functional test was run up to 167 Hz with no issues.
Design. Previous ESP failures from this pilot were recorded to understand root cause and set preventive recurrence. The aim of this exercise is to evaluate the technology and develop metrics on its performance. Table 1 compiles the workover record and ESP failure reasons.
To analyze the design and performance of the UHS ESP system, we compare it with a traditional ESP. Table 2 presents a comparison with a standard ESP configuration that would have been used.
In terms of length, the reduction in total ESP length was 99 ft, meaning that it is 68% shorter than the standard traditional ESP that would have been used in this well. Fig. 9 shows that length comparison. The UHS ESP system is made up of six elements, whereas a traditional system is made up of 10 elements. In comparing the motor, the UHS motor has nine rotors, whereas a traditional ESP with similar horsepower carries 14 rotors.
INSTALLATION PROCESS
As with any ESP installation, after the components of the ESP string arrive to the location, each one was measured and checked. Starting from the motor and gauge, all components were raised one by one to the rig floor. The advantage on the short UHS ESP string was that after making up all the connections for a whole string of only 44 ft in length, it was possible to finish all assembly of the pump and raise the whole string. This enabled the start of installation of the capillary tubing used for chemical injection treatment located from the bottom of the gauge and installation of all extra accessories to protect the ESP and motor lead extension (MLE) for the run in hole, such as cable and MLE protectors, Fig. 10. This simple makeup is one of the reasons the installation process was straightforward.
After the accessories were installed, the discharge pressure was installed above the pump, and, finally, the threaded discharge was connected to the tubing.
Based on the experience in this field, a pre-established run-in-hole (RIH) speed has been standardized to avoid any cable hit. This is a concern for the field, due to the long life of the wells, casing conditions, and well trajectories. Table 3 shows the standard criteria for all installations. Table 4 shows the effective speed for this installation, for which effective speed does not consider the time spent for making up connections, only the time the tubing is displaced.
STARTUP PROCEDURE
The supply voltage for this well location was 480 V. The surface equipment consists of a shift transformer, 12-pulse VSD, and step-up transformer. All of them were rated to 400 kVA.
Prior to start up, the voltage drop was estimated for 11,400 ft, which for a cable size 4 represents 291 V. The operating frequency for this design required 3,600 V. Based on the supply network and experience, a tap in the step-up transformer of 3,811 V was selected to assure the voltage. Note that this consideration is performed, regardless of the type of ESP technology, and it is a common practice in this field.
Because the well was expected to be filled with killing fluid after the workover job, the ESP was run during the evacuation process with lower frequency. The startup frequency was set to 7 Hz, to assure the minimum supply voltage for the downhole gauge, and the ESP was set to a starting target frequency of 20 Hz. Electric parameters were reviewed, and the frequency was raised to 30 Hz, using a ramp of 3 Hz/sec. This step was repeated from 30 Hz to 40 Hz, and from 40 Hz to 50 Hz. After 50 Hz, the differential pressure between the intake and discharge was reviewed to assure that the ESP was running at the correct rotation.
After assuring that the ESP was running at the correct rotation, the frequency was set to the operating target frequency of 144 Hz and keeping the ramp of 3 Hz/sec. During the evacuation process, prior steady flow from the reservoir developed to cool the motor, a maximum temperature of 362°F was recorded, and the stable operating motor temperature dropped and maintained stability at 332°F.
As soon as the flow from the reservoir was stable, all downhole parameters became stable, as shown in Fig. 11.
RESULTS AND RUNNING CONDITIONS
The UHS ESP with a final length of 44.69 ft required only 50% of rig time, compared with a standard operation, which also reduced HSE exposure during the operation. Currently, the pump is running at a depth of 11,420 ft at 144 Hz and a total flow of 1,482 bfpd (Fig. 12), showing steady parameters, Fig. 13.
To compare power consumption (kW/bbl) against traditional ESPs in real conditions, the UHS ESP was taken as a datum and compared with other traditional systems operating at similar conditions, Fig. 14. The positive percentages represent standard systems running with a higher consumption, while the negative percentages represent standard systems running with less consumption. The spread on this analysis is not quite conclusive, because consumption not only depends on the technology but also depend on several factors, such as head, fluid properties, pump curve efficiency at the production rate, and even run life. Still, this study brings promising expectations, with the highest consumption posing a relatively large 25% gap.
FUTURE WORK
Based on the results of this first pilot of the UHS ESP, new candidate wells have been tracked. Figure 15 summarizes the wells where the requirement of setting the ESP deeper or within a high-tortuosity profile would benefit from this solution to maximize production. The light green dots represent wells that can run on the same design as the studied well in this article, while the dark green dots represent wells for which a design adjustment would be made to deploy the UHS solution.
As the installed population increases, new electrical studies will play an important role for a deep dive on the performance of UHS systems, and the new data accrued will result in technology improvement. This technology shows a bright future as an artificial lift method. This is not only due to the results previously mentioned, but also as a concept that helps along the supply chain by considerably reducing the bill of materials.
Regarding the installation optimization, it was observed that the whole string can be preassembled from the warehouse to significantly reduce the rig time required for ESP assembly while reducing HSE exposure of all the personnel on the rig. To perform this preassembly, new shipping boxes will be built to accommodate the whole string, and an expandable cargo bed will be required to move the extended box. WO
ACKNOWLEDGEMENTS
The authors gratefully acknowledge the different teams that took place on this project, including Technology Life Management (TLM), Research and Development (R&D), Sales, Product Service Delivery (PSD), Planning and Supply Chain (P&SC), Engineering, Reservoir, Workover, and Execution. This article is derived from SPE paper 221567-MS, presented at the SPE Middle East Artificial Lift Conference and Exhibition, Oct. 29-30, 2024.
REFERENCES
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Andagoya, Kevin, Jorge Luis Villalobos, Osiris Sierra, Alvaro Correal, María Quinzo, Andrés Orozco, Luis Enriquez, Carlos Reyes, Fernando Leon, and Diego Marquez. 2022. "ESP Run Life Increased by 230% Using a Small, Customized Device: The Next Step in Flow Assurance and Chemical Injection for ESP-Lifted Wells." Paper presented at the ADIPEC, October 31–November 3, 2022. SPE-211213-MS. doi:https://doi.org/10.2118/211213-MS.
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JORGE LUIS VILLALOBOS LEÓN is a global artificial lift systems product champion at SLB, based in Houston, Texas. He supports new product development, commercialization and sustaining of the electric submersible pump (ESP) portfolio. He also contributes to geothermal projects, leveraging his expertise in artificial lift systems to drive innovation, improve performance and support energy transition initiatives across global oilfield operations.
KEVIN ANDAGOYA is a petroleum engineer with more than 12 years of experience in drilling and artificial lift services. He is an artificial lift customer engagement coordinator for Shaya at the Auca Project, one of Ecuador’s largest producers. Mr. Andagoya has authored technical papers and led innovations in tool development, research and technology deployment, contributing significantly to the advancement of artificial lift solutions in the region.