Drill bits manufactured from synthetic diamonds were originally developed to tap geothermal energy deep below the surface. Despite drilling wells that supply two-thirds of our oil, they never gained traction for geothermal among energy companies. Pools of crude have proved far more attractive.
More than 30 years later, polycrystalline diamond compact (PDC) bit technology is returning to its original purpose. Benefiting from decades of improvements by the oil and gas industry, and new support by the U.S. Navy and Sandia National Labs, PDC is drillling new geothermal wells cheaper and deeper than ever before. If successful, the new research may open far more geothermal resources across the U.S. An MIT review (PDF) puts the cumulative geothermal capacity that can be achieved at more than 100 GW in the next 30 years with a modest federal investment in research and development.
Today, it remains too expensive to prospect for geothermal energy under the hard, basement rock formations of North America. While the fossil fuel industry has sprinted ahead in technology, geothermal drillers never had the government subsidies or scale to attract much investment from the drilling industry.
Stimulus money from the American Recovery and Reinvestment Act has put PDC back in the lab, led by California’s Sandia National Laboratories and the Navy. Researchers are picking up where they left off in the 1970s, creating a diamond cutting rig capable of cutting longer and deeper than conventional equipment. To create PDC, a one millimeter-thick layer of diamond is deposited on the bits’ cutting faces by heating and compressing a graphite powder.
Geothermal drillers need every millimeter of diamond to reach the subterranean depths where it’s hot enough to create power. “You have to go through the hardest rock, sometimes at high temperatures and pressures,” said the project’s Principal investigator David Raymond in a release by Sandia National Laboratories. “The [Department of Energy’s] vision for advanced geothermal development is to drill to great depths, up to 30,000 feet (5.7 miles), to access heat for geothermal.”
Test wells have already drilled in the basement rock in California’s Chocolate Mountains to see if geothermal resources in the region can be found that are undetectable at the surface. In the first tryout, the two test bits drilled half a mile down in about four days, tripling the conventional speed of 30 feet per hour. Researchers will now see how far they can push the technology.
It’s all feeding a small but promising boom in geothermal energy, a sector that has lagged far behind the explosion in wind and solar energy, reports Pike Research. Although global geothermal capacity was only 10.7 GW in 2010, that’s expected to hit 14.4 gigawatts by 2020 from hundreds of projects now underway. By making exploration cheaper, the next generation of oil gushers may actually be plumes of clean hot steam from geothermal energy.