NREL and its partners are reinventing the future of geothermal drilling and advanced wells.
Drilling, constructing, and operating wells in harsh geothermal environments requires advanced techniques and technologies relative to drilling for water or oil and gas. As developers target deeper and hotter resources, technologies also need to improve.
High-Temperature, High-Pressure Tools
Downhole drilling tools significantly improve the accuracy of data. Surface measurements are impaired by boundary effects because of torque and drag alongside the drill string, torsional drill-string wrapping, and drilling dysfunctions. These effects make it challenging to discern true downhole bit conditions. Downhole data collection in the oil and gas industry has decreased drilling time and cost and increased penetration rates by 35%–55%. NREL scientists are using new materials and designs to increase the temperature and pressure capability of these tools for use in high-temperature (>250°C) geothermal wells.
Innovative Drilling Systems
NREL researchers are working to advance high-temperature/hard-rock geothermal drilling. Rotary drilling has been used to drill wells of all types for more than a century. Over this time, advances have led to faster drilling rates, which have increasingly allowed for economic access to oil and gas plays throughout the world. However, geothermal heat is often found in harder, hotter, and potentially deeper rock. Currently, geothermal drilling averages 125 ft/day through hard rock and crystalline formations, making it time-consuming and expensive compared with petroleum industry drilling.
Well Construction Materials
NREL is using its expertise in ceramics, metallurgy, and polymer development to advance well construction materials and designs.
Unlike short-lived oil and gas wells, geothermal wells must last decades under constant use and harsh conditions. The higher the well temperature, the more economically attractive the geothermal well is. It is therefore important that the geothermal industry develop well materials (both casing and cement backing) that can survive for years in temperatures over 300°C and in potentially highly saline (>1M) fluid.
NREL is developing a new generation of electronics for harsh environments and specifically focusing on sensors, interface electronics, and packaging for downhole applications. Gallium oxide-based electronics have the potential for very high-temperature operation, so initial work has focused on developing sensors for downhole applications. To accomplish this also requires the development and qualification of new high-temperature contact metallurgies and robust packaging. We are investigating new inorganic and polymer composite encapsulants for both the sensor packages and downhole casing applications.
The objectives of NREL's materials for harsh geothermal environments effort are to:
- Develop next-generation sensors and power electronics based on gallium oxides and other functional oxides.
- Develop thermodynamically and mechanically stable contacts for harsh environments
- Develop packaging for downhole environments based on novel tunable composites
- Validate the performance of new packaged electronics in downhole conditions
- Develop new approaches to stabilizing well casings for significantly longer downhole lifetimes.
Increased downhole sensor temperature limits facilitate geothermal drilling efficiency by incorporating NREL's aluminum gallium nitride materials in high-temperature sensing electronics.
National Oilwell Varco
In the RePED 250 project, NREL researchers are working to adapt Tetra Innovation Institute's patented pulsed power drilling technology to the hotter, harder, crystalline rock found in geothermal wells using high-temperature power electronics, including alternators, capacitors, and high-voltage, pulsed-power switches. If successful, the technology is expected to disrupt the global drilling industry and replace traditional drilling technologies within 10 years of commercialization.
Competitive market modeling shows the potential for an additional 50 GW of geothermal deployed in the U.S. because of cost and time improvements from this technology. High-temperature power electronics developed through this research will also have immediate applicability to industries including petroleum, aviation, fuel cells, vehicles, smart grid, and the military.
This technology would increase drilling rates tenfold, reduce geothermal well drilling costs by 75%, and cut development timelines, significantly increasing the market competitiveness of geothermal power.
Tetra Innovation Institute, TPL Inc., and the University of New Mexico
NREL is developing methods to increase the lifetime and durability of metal casings for geothermal applications. The focus is on sprayable polymer/oxide composite materials that are more chemically inert than metals. These materials derive strength and abrasion resistance from oxide fillers such as aluminum oxide and boron nitride, and they derive flexibility and tensile strength from very high-temperature, novel polymers.
In addition, we are investigating methods to harden mild steel with a process called boronization, which can make it more robust in the corrosive and abrasive environment of the subsurface.
Combining borided steel with composite coatings may increase the lifetime of geothermal well casings by years, which will make geothermal projects more economic.
NREL works with industry partners to design cost-effective drilling technologies that will enable the deployment of deeper and hotter geothermal across the United States. NREL's geothermal capabilities run the gamut from analysis to downhole tools and sensors and from reservoir modeling to full-scale field research validation. Learn more about these advanced wells capabilities:
These capabilities also support NREL's advanced wells activities: