Sandia LabNews

Initial geothermal investment comes full circle in new project

Elton Wright
Elton Wright (6916) shows a torsional spring that’s used to simulate the rotational vibration of the drill string in a Sandia experiment. (Photo by Randy Montoya) 

Nearly two-thirds of the oil we use comes from wells drilled using polycrystalline diamond compact (PDC) bits, originally developed nearly 30 years ago to lower the cost of geothermal drilling. A recent demonstration project by Sandia and the US Navy brings the technology full-circle, potentially helping geothermal drillers reap the benefit of the original technology, as well as decades of subsequent oil and gas industry R&D.

Sandia and the Navy’s Geothermal Program Office (USN GPO) conducted the Phase One demonstration tests as part of a geothermal resources evaluation at the Chocolate Mountains Aerial Gunnery Range (CMAGR) in Imperial Valley, Calif.

Sandia has a long history of involvement with both geothermal and drill bit technology development. Three decades ago Sandia geothermal researchers played a large role in the development of PCDs for drilling applications. That work focused on resolving material issues, laboratory testing, and development of data and design codes that now form the basis of the bit industry. Since then, Sandia has received geothermal funding to improve PCD bits. The work was intended to increase access to geothermal resources in the continental US by enabling the drilling of deep, hot resources in hard, basement rock formations.

Geothermal drilling more demanding

Because oil and gas drilling is easier than geothermal drilling, PCDs were appropriated for oil and gas resources.

“Because of the greater challenges associated with geothermal drilling, drilling for oil and gas has been traditionally easier than drilling for geothermal resources,” says principal investigator David Raymond (6916).

“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. 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 rock types, and in hotter environments,” says David.

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

“Drilling for geothermal energy is still the most difficult drilling on a cost-per-foot basis,” says David. “You have to go through the hardest rock, sometimes at high temperatures and pressures. The DOE vision for advanced geothermal development is to drill to great depths, up to 30,000 feet, to access heat for geothermal.”

Oil/ gas industry has a bigger appetite for risk

In addition to technical problems, the economic risk profile for oil and gas wells is different. Because many more oil and gas wells are drilled per year, the oil and gas industry has the resources and risk appetite for significant research and testing to improve the ability to drill under increasingly difficult conditions.

The geothermal industry advances far more slowly than the oil and gas industry. Because geothermal drillers create only a small number of new wells each year, the drilling service industry finds it difficult and expensive to support innovation, when each well represents a substantial risk.

The Sandia/Navy demonstration project called for a test hole to evaluate geothermal resources in the Camp Billy Machen/Hot Mineral Spa region that would have been otherwise undetectable at the surface. The basement rock at the Chocolate Mountains includes granite and andesite, typical formations encountered during geothermal drilling.

A key part of the demonstration project was to test and evaluate PDC bits and related technologies in a real-world drilling environment. Sandia worked with PDC bit manufacturer NOV Reed Hycalog to specify PDC bit solutions. NOV provided both commercially available drill bits and knowledgeable on-site personnel to counsel the drilling contractor during drilling runs.

Sandia worked with the USN GPO drilling contractor Barbour Well in evaluating the subject drilling technologies during the production drilling process.

Sandia, Prime Core, and the Barbour Well mud logging company Prospect Geotech fielded instrumentation on the Barbour rig to allow monitoring of drill rig during the drilling process.

In the tests, two test bits drilled 1,291 feet of the overall well depth of 3,000 feet. The two bits were in the well just over four days, penetrating approximately 30 feet per hour throughout their drilling interval, an improvement of nearly a factor of 3 over the standard roller bit that was being used. The downhole data was successfully retrieved from both bits and downloaded for subsequent analysis.

Phase two will evaluate drill performance

The collected data will be compiled and analyzed to provide insight into bit performance at the site.

In a planned second phase of the project, Sandia will continue work with Reed Hycalog to evaluate drill performance and improve the bit design and materials for subsequent demonstration.

Sandia personnel include David Raymond, Steve Knudsen (6916), Jiann Su (6916), Dennis King (6916) and Keith Barrett (6916). Elton Wright (06916), a technologist in the geothermal research department, has supported laboratory testing of PCD technology for nearly two decades.

Cooperative work between the USN GPO and Sandia was covered by a Memorandum of Understanding between the Department of Defense and the Department of Energy addressing collaborative development of renewable energy resources.

Phase one and two of this work are funded an ARRA project, “Technology Development and Field Trials of EGS Drilling Systems,” under the supervision of DOE.