When it comes to engineering challenges for extreme environments, oil drilling could easily be tops on anyone's list. Downhole drilling in the oil and gas industry is now using innovative electric motion controls. Sophisticated electric actuators can be combined with remote navigational control for drills located miles deep in the borehole to obtain real-time downhole sensory data.
This rugged instrumentation and actuation must survive high temperatures and pressures, gases, fluids, and steam that all fall outside the normal range of industrial equipment. As anyone in the oil and gas industry knows, reliability is critical to the economics of drilling. According to industry sources, the average cost of drilling is $1 million per day offshore and about $250,000 per day onshore. So engineers design systems to maximize production and performance.
Many drilling operators still employ hydraulic steering systems, but some have begun exploiting intelligent electric actuators for directional drilling. The most advanced downhole directional steering systems are integrated electromechanical assemblies that employ custom-engineered brushless servomotors and electronic subassemblies housed in sealed enclosures.
Communications between the downhole drill bit and the control systems at the rig's surface involve pulses in the mud inside the drill string pipe, which includes the drill pipe, drill collars, and drill bit. Mud-driven alternators and turbines supply power for the electrically actuated rotary steerable drill heads.
Some drill operators use miles of wire for power and communication for actuation tools. Electrical current passed over miles of wire with a relatively large electrical resistance results in voltage drops that the electronics can't tolerate. Downhole exploration and production requires electronics that operate reliably from -40C to 240C and are packaged to keep contaminants away from sensitive electronics and mechanics.
Electronic devices, magnetic materials, and mechanical systems exhibit behaviors such as nonlinearities and unmodeled dynamics at high temperatures. Magnet and semiconductor makers don't often publish the device or material specs in these temperature ranges, requiring engineers to develop empirical knowledge on site and in labs. Experimental testing gives designers a better understanding of how these materials behave at extreme temperatures.
For example, the permanent magnet brushless motor design is a significant challenge, since the magnetic properties of the stator windings and rotor magnets can't be modeled using textbook analysis. Brushless servomotors, using insulation materials on the stator windings, are specifically designed for these applications. Motor design, proper material selection, and manufacturing processes combine to create a highly robust motor with the appropriate form factor and reliability for demanding upstream oil and gas applications.
The ability to put electric systems downhole, whether in Arctic temperatures or the sweltering heat of the Middle East, has changed the economics of drilling and production. Producers have become dependent on instrumentation and downhole intelligence. As the search for resources ventures into ever more hostile environments in which electronics and mechanical devices often don't perform well or survive for very long, intelligent actuator systems will be at the forefront.
Manufacturers must fund research into high-temperature, high-pressure electronics with wide thermal characteristics, advanced sensorless algorithms, and alternator active conditioning electronics. The goal is to minimize the size of the packaged solution. Engineers are working hard with oil and gas customers to develop:
- Semiconductor power devices for PWM circuits that can switch a 600V dc bus at 200C temperatures reliably
- Advanced sensorless algorithms to simplify designs by eliminating RDC circuitry and resolvers
- Alternator active conditioning to provide clean power in downhole drilling
Real-time data on depth and heading, formation resistivity, pressure, temperature, drill bit strain, and vibration are changing the economics of upstream exploration and production, and engineered motion-control solutions must keep pace. The costs of nonproductive time and unexpected device failure have never been higher. But that's what makes extreme engineering design so exciting.
R. Scott Scheffler is market manager for oil and gas solutions at Moog.