Pumps that thrive under pressure
The evolution of hydraulic transmission technology in the pressure pumping market.
Fracking technology is driving transformation of North American energy production capabilities. Since 2005, most of the increase in domestic natural gas production resulted from ongoing development of horizontal drilling and hydraulic fracturing technology.
Producers developed more efficient ways to extract gas and crude oil from deposits of shale, sandstone, carbonate, and other geologic formations. The hydraulic transmission technology that fracking applications rely on has evolved to meet demanding and increasing performance and reliability requirements.
The 30K-foot view
All hydraulic transmissions operate on the same basic principles. Clutch operation is activated via hydraulic pressure. To shift, there is a sequence of activity in which a control system tells a solenoid to turn on or off, directing pressurized hydraulic fluid to various clutches within the transmission.
In most cases, power is transmitted from the engine to the transmission through a torque converter, which is a hydrodynamic device that multiplies torque. These components help engines operate in the most efficient speed range, producing rated horsepower regardless of load demand.
For example, in a car, as soon as the accelerator is pressed, the torque converter is engaged in order to provide adequate power until the input shaft of the transmission reaches a certain speed. Once that happens, a clutch inside the torque converter is engaged, bypassing the hydraulic circuit and directly connecting the engine to the transmission.
Hydraulic transmissions for fracking applications must be able to transmit tremendously high horsepower to the pumps. They must also be efficient, preventing the loss of power output as waste heat.
Fracking applications must operate at top capacity in dirty, dusty and often hot environments. The transmissions must be designed to protect them from foreign materials. To reduce downtime, the transmissions must be designed to minimize the frequency of oil changes required.
Hydraulic fracturing rigs are vulnerable to excessive vibration. Torsional vibrations and shock loads can cause harmful torque spikes, reducing the service life of the equipment. Fracking transmissions must be capable of withstanding these vibrations.
Transmissions must also have long life and durability. Fracking sites now run longer stages for longer hours. In past years, frack pumps on a wellsite might only run for six hours at time. Now, they need to run 24 to 36 hours at a time.
Case study: Universal Well
When companies began extracting natural gas from the vast reserves found in the Marcellus Shale in the Appalachian Basin, it required equipment with higher-power pumps and engines than required for shallow vertical wells. This put greater performance demands on the transmissions involved.
While upgrading its fracking fleet, Universal Well Services Inc., a provider of hydraulic fracturing services, needed a replacement transmission for its pressure pumping applications that would provide greater reliability and improved service life. This required a drop-in replacement transmission that would be compact enough to fit in its fleet of existing fracking rigs while providing enough horsepower to meet the increased demands.
Great Lakes Power Service Co., a power transmission distributor serving the Southeast, worked with Universal Well to find the best solution. The Great Lakes team recommended use of a purpose-built Twin Disc TA90-7500 fracking transmission, which consists of a 9-speed coaxial power-shift transmission that provides up to 2,600 HP and incorporates an advanced electronic control system.
Designed to be smaller and requiring less complicated plumbing than other transmissions, the TA90-7500 could be more easily fit the fracking rigs. The transmissions proved durable. Over a five-year period, many of the transmissions saw up to 14,000 engine operating hours without failure.
Twin Disc engineers used the lessons learned from working with the Universal Well applications and folded them into the next generation of the technology — the TA90-7600. This included the addition of a planetary reduction gear on the output of the 7500 to create a new transmission.
Although traditional transmissions in oil & gas applications are required to use hydraulic torque converters, the TA90-7600 has a master clutch that eliminates need for the convertor. The master clutch, guided by the integrated control system, allows full power shifts to all the ranges without losing torque. Elimination of the torque converter reduces the required footprint for the transmissions.
As fracking technology evolves, hydraulic transmission technology will have to keep advancing. The market sector demands ever-smaller transmission units, challenging designers running up against the constraints of the laws of physics.
Key to reducing the size of hydraulic transmissions is increased efficiency. The more completely a transmission transmits all energy coming out of the engine to the pump, the better. This means less generation of waste heat, allowing designers to reduce the size of the cooling components. Developing clutch technology that allows transmission of torque more effectively will boost system performance overall.
Even something as mundane as the oil composition used within the transmissions is important. Advances in synthetic oil chemistry reduce the number of oil changes needed, allowing units to operate for longer periods of time without interruption.
Importance of control systems
During the past 10 years, many innovations in hydraulic transmission technology focused on the creation of increasingly sophisticated electronic control systems to direct the activation of clutches with the transmissions. The control systems can allow smarter operation of the transmissions and greater control of oil pressure.
With smarter electronic controls, transmission performance can be fine-tuned, improving performance and reducing problems that can cut down on the unit’s lifespan. This can include managing potentially harmful torque spikes resulting from vibration and high loads.
Although fracking applications share common characteristics in general, each has specific needs for how control systems are integrated within a rig’s rate controller. Electronic controls must prevent overspeed, shift shocks and reduce the effects of operator errors, limiting wear and tear on machine components.
The best electronic control systems ensure safe shifting, avoiding potential harm to clutches, transmission or other equipment. This requires good communication between the unit’s rate controller and the transmission controller.
Summing it up
Hydraulics transmissions have been around for a very long time, but the demanding performance requirements of oil & gas production applications continue to drive technology innovations. Market pressures require development of smaller and more durable transmissions that provide ever-greater amounts of horsepower to keep up with the advancement of fracking applications.
Original content can be found at Oil and Gas Engineering.