| Abstract |
The research frontier of drilling and well construction for superhot rock (SHR) geothermal energy systems — the production of renewable, baseload electricity by circulating water in deep (greater than 5 km), hot (greater than 374˚C) rock — is steadily advancing. Recent achievements in polycrystalline diamond compact (PDC) drill bit design, improved rates of penetration (ROP) into hard rock, and the development of insulated drill pipe show that deep drilling for SHR geothermal projects is within reach. However, several key technology gaps stand in the way of drilling in hostile subsurface domains. Specialized drilling rigs, bit technology, high-temperature downhole tools, and temperature management equipment must achieve further engineering feats to successfully access and develop SHR resources. This study reviews state-of-the-art geothermal drilling and well-construction technologies, identifies existing technology gaps for SHR drilling, and suggests strategies to overcome these gaps. Specific technologies covered in this report include conventional (rotary) drilling, hybrid-conventional (percussive, waterjet, and particle) drilling, and direct energy (plasma and millimeter wave) drilling methods, as well as high-temperature downhole tools (measurement-while-drilling tools, magnetic ranging instruments, and downhole motors), temperature management equipment (insulated drill pipe, drilling fluids, and mud coolers), and corrosion inhibition technologies. Overall, we find that SHR geothermal wells can be drilled by deploying a combination of existing technologies and that the technological challenges to SHR drilling are surmountable. A first-order gap these technologies share is the lack of access to SHR conditions, both in-field and in controlled laboratory settings. Without open-access experimental facilities and pilot sites, these technologies cannot undergo iterative improvements necessary to de-risk SHR drilling and propel the industry forward. |