The Benefits of Electric Drives in Downhole Equipment
by Branko Beric, Business Development Engineer, maxon international ag
From surveying and preparing extraction fields to maximizing and optimizing the production of mature oil and gas wells, collecting big data and controlling the downhole processes has become an essential aspect of every oil and gas extraction project.
The goals of the oil and gas extraction industry have remained the same over the years: maximize production to meet the market’s energy demands while doing so efficiently, cost effectively, and sustainably. As the industry sets its goals toward zero net-carbon emission, efficiency and sustainability are taking center stage. Downhole drilling is the segment with the largest potential for technological innovation even while facing many environmental and technological challenges. Meeting these goals means that industry mindsets need to accept a more data driven approach, which is leading downhole drilling toward electrification.
Electric drive benefits
Although the idea of electrifying downhole operations is not new, progress has been slow over the years due to a combination of overcoming the extremely demanding environmental conditions, a lack of advanced technology, and fear of change. Yet, as conventional solutions such as hydraulics are no longer cost effective in meeting the new goals set by the industry, technical innovations in motors, electronics, and battery technologies are providing the tools needed to move into the electrification of the oil and gas industry. There are key advantages of an all-electric system as well.
There are efficiencies that are gained through digitalization. With a real-time reservoir of data and precise control positioning, operators can make better and continuous strategic production control decisions. Digitalization is increasingly important for future production operations management, both offshore and onshore. With electric production systems, large amounts of data can be collected in real time, including data related to the reservoir behavior, production processes, well integrity and safety, and the health and performance of the equipment. This digitized approach increases overall efficiency and safety and reduces the carbon footprint of an entire project.
Building an electric infrastructure is much more cost efficient and easier to maintain. An electric cable has further reach compared to hydraulic and a single line can be used to operate multiple systems as well as transfer feedback from multiple sensors. This makes infrastructure with multiple branches and extensions simpler to build and maintain. An electric line also completely takes away the leakage risk associated with hydraulic lines. Innovations in battery technologies have also made their usage possible in harsh environments.
Using electric motors for valve control and various actuation operations enables precise and fast control. Inputs and commands to the electric drive happen in real-time and are executed instantaneously, enabling operators to adjust parameters quickly and optimize their operation without delays. Electric motors can be controlled using various parameters, such as speed and position (using motor halls or resolver), torque (through motor current measurement), and potentially other parameters depending on the sensors included. This enables full motor control as well as the possibility to collect information that can be used for predicting the motor health condition.
Technical challenges and solutions
Extreme ambient conditions have been a major challenge preventing the wider use of electric drives in downhole operations. Conventional electric motor components are not able to withstand downhole temperatures that often reach upwards of +200°C, as well as high pressures and potentially high shocks and vibrations. To reach targeted cost efficiency goals and avoid costly downtime, motors must operate reliably while prolonging the lifetime of a downhole tool and reducing maintenance requirements. As the industry is aiming for better productivity and efficiency, it is crucial to maximize the production of existing wells but also reach more challenging, unconventional wells, pushing the technological limits of electric motors even further.
As conventional motors are not suitable for these industry demands, custom solutions tailored to downhole specifications needed to be developed. To do this, successful motor manufacturers must have the expertise and resources to perform all the development steps, plus ensure reliable production and testing processes. Designing such drive system requires specialized knowledge in material behavior at extreme temperatures as well as extensive testing to make sure all components can survive the HPHT (high pressure, high temperature) environment found in downhole operations.
Conventional permanent magnet DC motors typically use neodymium magnets which start to demagnetize once temperatures of +150°C are exceeded. Similarly, conventional winding insulations are not able to withstand the extreme conditions. It is important to keep in mind that temperature ratings include ambient, and the added temperature caused by the load. That means a certain safety margin needs to be considered as the motor must be able to operate under load without overheating. Other motor parts must be made of high-grade stainless steel and the use of adhesives or plastics should be avoided.
Choosing the right components is only one part of the developmental process. It is also necessary to define and conduct suitable environmental tests which will confirm that the right design has been implemented and that the motor can provide the required lifetime under these extreme conditions. Finally, production processes must be defined to ensure robust manufacturing, including suitable tests during the production and at the final inspection.
The maxon solution
maxon’s heavy-duty platform portfolio provides the robust design that is critical for extreme operating conditions. For example, their EC 22 HD brushless DC motor with GP 22 HD planetary gearhead provides:
• An Ultra compact (Ø22 mm), highly efficient (>75 %) and powerful (240 W) drive solution
• A fully welded stainless-steel assembly along with encapsulated samarium-cobalt magnet
• A high temperature ironless core winding, proven to withstand temperatures up to 240° C
• A gearhead designed for high torque (12 Nm overload torque capability)
Along with these technical capabilities, these motors incorporate new materials and process technologies. An ironless core winding and high-performance rotor is the “heart” of maxon heavy duty motors. Together with the powerful gearhead, maxon provides high torque drive solutions. Most parts of heavy-duty drives are made of stainless steel. The assembly minimizes the use of adhesives, concentrating instead on the connection of individual components through mechanical fits and secured with laser welding. This results in a reliable and mechanically robust drive system.
Some key advantages of maxon HD motors include:
• Wide temperature range (-50 to 200°C) components tested up to 240°C
• Robust design laser welded connections
• High performance to volume ratio, compact, high-power density
• Low energy consumption, high efficiency
• Excellent control properties, linear motor characteristics
• Operation in air or in hydraulic oil • Low magnetic interference
• High quality/reliability production process controls
Qualification and production testing
To ensure that motors can withstand harsh downhole conditions, it is important to define and conduct proper tests during the design qualification phase as well as during serial production. Manufacturers must have enough resources and expertise to develop and conduct these tests and implement all the necessary steps on the production line to ensure that each unit produced meets the requirements. There are three specific tests that are required to assure the long life and proper operation of these motors.
Internal full load test
Motors are tested in air or in hydraulic oil at extreme temperatures and under full load during continuous operation. During this load test the winding heats up to its maximum rated temperature. Continuous monitoring provides information on the drive’s performance characteristics.
Vibration and thermal stress test
Drives are placed in a climate-controlled enclosure and subjected to high vibration. Testing is carried out with the motors in operation at high temperature. The motors are required to continue functioning within their performance specification while vibrations are applied in all directions.
The laboratory system performs a variety of shock loads of more than 1,000 G. After the shock test, the drives must be fully functional.
Standard test procedures are also performed prior to delivery to the customer. All of maxon’s HD drives—the motor plus accessories—must pass these procedures, which include:
• Environmental Stress Screening (ESS)
o high temperature test
o load test
• General Electrical Test
o insulation test o maxon standard test
• Visual and Dimensional Check
o visual inspection
o dimension checks
A typical use for electric motors in downhole operations is Measurement While Drilling (MWD) systems, which use electric actuators in their mud pulser units. This equipment is responsible for using the complex technology that provides a second-by-second feed on the progress of the bore. Because the data transferred to the drilling technicians is critical to the operation—allowing them to respond quickly to make drilling corrections—the motor used in the actuator must provide power efficiency, reliability, and robustness.
Battery technology developments have increased the use of electric motors in downhole operations where they can also be used generators to power the batteries. For this to happen, the motors must be very efficient. Brushless HD motors from maxon are not only suitable for the extreme environments attributed to downhole operations they can be used as DC or AC voltage generators using the drilling fluids pumped downhole. A voltage rectifier is required for DC voltage production, while AC voltage can be acquired using two of the three motor phases. The basic calculations are very simple due to the linear behavior of motors with slotless windings.
Another emerging use for electric actuators is intelligent flow control valves. Instead of switching between fully open or closed positions, electric motors allow for highly precise control of flow valves to achieve optimal flow rate at any time. Software development has provided easy monitoring and control via user friendly interfaces at the surface. For example, it has been shown that smart gas lift systems have the potential to reduce lifting costs significantly, plus increase the well production capabilities with less intervention.
Well inspection is another segment with large potential for using electric actuators to achieve more efficient operation. Whether actuating a wheel assembly to drive a conveyor or controlling fingers of a multi-finger imaging tool to inspect the casing, electric drives are a great choice for increasing operational speed and precision. High precision positioning linear movements can be made by incorporating linear actuators with ball screws integrated into the gearhead and a heavy-duty resolver at the back of the motor. Overall, electric motors can solve challenges in various downhole tools, from drilling operations to completion and well inspection.
In the following years and decades, the oil and gas industry will see numerous changes and innovations to meet strategic priorities such as delivering low-cost and zero carbon energy. The emergence of all-electric systems can help drive these innovations and make the changes feasible. It is expected that all areas of an oil and gas extraction project will see shifts toward electrification, including the downhole segment. Even today there are many applications that are already switching towards electric actuation instead of more traditional technologies such as hydraulics. With challenging goals in sight for the industry, it is exciting to see where the road leads and what kind of innovations emerge in the future.
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