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."
The economic risk for oil and gas wells also is different. Because many more oil and gas wells are drilled per year, that industry has the resources and can invest significantly in research and testing to improve the ability to drill under increasingly difficult conditions.
The geothermal industry has advanced far more slowly. 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, since 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, formations typically encountered during geothermal drilling.
A key part of the demonstration project was to test and evaluate PDC bits and related technologies in a real-wo
|Contact: Stephanie Holinka|
DOE/Sandia National Laboratories