A collaboration between Sandia National Laboratories and industrial manufacturer Atlas Copco has resulted in just such a technology: a new type of downhole hammer that can endure the heat required for geothermal drilling.
Downhole hammers employ a rapid hammering action, much like a jackhammer, in order to cut through rock. They have been used in the oil, gas, and mining industries since the 1950s, but because of their use of oil-based lubricants and plastic parts, the conventional design is unsuitable for the high temperatures of geothermal drilling.
HOT Engineering
Like the piston in a car engine, a downhole hammer has moving parts that need to be lubricated. And just as the oil in your car loses its effectiveness over time, conventional hammer lubricants become much less effective as temperature increases. Therefore, one of the critical aspects of the project was developing a lubricant suitable for geothermal drilling.
“The technology behind the new hammer is fundamentally the same, but … [with] material selection and dry lubricant technology that will work in the high-temperature environment,” said Sandia’s Jiann Su, a mechanical engineer.
In order to test the hammer, Sandia engineers constructed the high operating temperature (HOT) test facility, a three-sided open concrete structure that houses a 20-foot-tall drill rig, heating chamber and process gas heater. An engineering challenge in itself, construction of the HOT test facility required integrating electrical, mechanical, pneumatic and control subsystems. But the effort was worthwhile, as the test facility offers realistic operating conditions with temperatures up to 300˚C, almost twice that seen in conventional drilling.
Atlas Copco focused on designing a hammer without plastic parts and ultimately the combined efforts of the two companies proved successful. “We were able to reach our drilling rates, the materials held up, the coatings worked well,” said Su.
“We developed a tool that can be used in high-temperature environments that can help increase the drilling rates and the rate of penetration to maybe 5 to 10 times that of conventional drilling operations, so that’s a big plus for drillers,” Su commented. “It adds to the available options drillers have. This is not necessarily the final option for every drilling situation but it does provide a good option for the right situation.”
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