Polycrystalline diamond drill bits (PDC) open up options for...

Polycrystalline diamond drill bits (PDC) open up options for geothermal energy news
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22 March 2012

Sandia has a long history in geothermal research and drill bit technology development. Three decades ago, Sandia played a large role in developing PDCs for geothermal drilling. That work focused on resolving issues with materials, devising laboratory tests and developing data and design codes that now form the basis of the bit industry. Recently, Sandia received American Recovery and Reinvestment Act (ARRA) funding to improve PDC bits, potentially increasing access to geothermal resources in the continental U.S. by enabling the drilling of deeper, hotter geothermal resources in hard, basement rock formations.

Because oil and gas drilling is generally less complicated than geothermal drilling, PDCs were first used to drill for oil and gas, said principal investigator David Raymond. 'Oil and gas drilling is normally done in softer and less-fractured rock, resulting in fewer problems with fluid circulation to remove debris and cool the bit,'' he said. ''Oil and gas drilling also doesn't usually involve the higher temperatures that geothermal wells exhibit.''

But as the oil and gas industry looks for new sustained resources in deeper reservoirs, it encounters more difficult drilling conditions similar to those found in geothermal drilling. 'Oil and gas drilling must now go deeper into the ground, into harder and sometimes fractured rocks, and in hotter environments,'' said Raymond.

Raymond said geothermal resources are typically associated with igneous and metamorphic rocks, which are harder than the sedimentary rocks through which most oil and gas wells are drilled. Igneous and metamorphic rocks also can contain large amounts of abrasives such as quartz, which can cause vibration and accelerated wear that damages drill bits. These types of rocks are often fractured, which can change the impact loading on drills and cause more damage.

''Drilling for geothermal energy is still the most difficult drilling on a cost-per-foot basis,'' said Raymond. ''You have to go through the hardest rock, sometimes at high temperatures and pressures. The DOE (Department of Energy) vision for advanced geothermal development is to drill to great depths, up to 30,000 feet, to access heat for geothermal.''