Bridging the Gaps: A Survey of Methods, Challenges, and Pathways Forward for Superhot Rock Siting and Characterization

The report provides a comprehensive survey of subsurface characterization technologies for superhot rock (SHR) geothermal systems, defined by temperatures above 374°C. It categorizes methods by spatial scale: exploration (100s-10s km), reservoir (10s-1 km), and monitoring (1 km-1 m). Key findings highlight that while many geophysical tools are mature, they lack validation in SHR-specific environments. The authors emphasize the need for integrated data analysis, such as joint inversion and machine learning, to reduce exploration risk and improve the accuracy of temperature and stress models. The report concludes that advancing SHR energy requires standardized data sharing, increased investment in high-temperature sensors, and the development of SHR-specific play fairway analyses.

• Superhot Rock (SHR) geothermal systems are defined by temperatures where water becomes supercritical (>374°C) and are typically accessible at depths of 15 km or less, though they can be found within 5 km in areas of active magmatism.
• Magnetotellurics (MT) is considered the most effective electromagnetic method for geothermal exploration due to its depth sensitivity and ability to resolve magmatic/hydrothermal systems, though it may fail to detect smaller resistive features like magma sills.
• The Brittle-Ductile Transition (BDT) zone serves as a critical depth marker for temperature and impacts permeability; however, the bottom of the seismogenic zone is often used to constrain BDT depth.
• Seismic methods, specifically the identification of the 'K-horizon' reflector, have been used to indicate the presence of supercritical fluids, as seen in Larderello, Italy, though further drilling validation is required.
• Play Fairway Analysis (PFA), adapted from the oil and gas industry, is used to identify 'fairways' with high likelihood of hosting resources, but current models often rely on expert-opinion weighting which may introduce bias.
• Machine learning (ML) shows potential for removing expert bias in geothermal assessments, but its application to SHR is constrained by a severe lack of positive-labelled training sites.
• The Stanford Thermal Model (STM) predicts temperatures at depth for the contiguous USA with a mean average error of 4.8°C, though it is limited to the top 7 km of the crust and assumes steady-state conductive heat transfer.
• Supercritical water hydrofracturing experiments in granite have demonstrated the creation of a 'cloud-fracture network' (CFN) of distributed damage, rather than the localized fractures seen at lower temperatures.
• Induced seismicity in SHR projects can be mitigated using Adaptive Traffic Light Systems (ATLS), which control water injection rates and pressure based on real-time monitoring.
• Geochemical exploration tools for conventional geothermal systems are limited in SHR environments due to a lack of understanding of equilibrium reactions and mineral conditions at supercritical temperatures.

APA

Chhun, C., Pearce, R., Salinas, P. C., Saltiel, S., & Saez, C. M. (n.d.). Bridging the Gaps: A Survey of Methods, Challenges, and Pathways Forward for Superhot Rock Siting and Characterization. Clean Air Task Force. https://cdn.catf.us/wp-content/uploads/2025/01/11102623/shr-bridging-gaps-siting.pdf

Chicago

Chhun, Chanmaly, Rebecca Pearce, Pascal Caraccioli Salinas, Seth Saltiel, and Carolina Munoz Saez. Bridging the Gaps: A Survey of Methods, Challenges, and Pathways Forward for Superhot Rock Siting and Characterization. Clean Air Task Force, n.d. https://cdn.catf.us/wp-content/uploads/2025/01/11102623/shr-bridging-gaps-siting.pdf.

Wikipedia

{{cite report |last1=Chhun |first1=Chanmaly |last2=Pearce |first2=Rebecca |last3=Salinas |first3=Pascal Caraccioli |last4=Saltiel |first4=Seth |last5=Saez |first5=Carolina Munoz |title=Bridging the Gaps: A Survey of Methods, Challenges, and Pathways Forward for Superhot Rock Siting and Characterization |publisher=Clean Air Task Force |url=https://cdn.catf.us/wp-content/uploads/2025/01/11102623/shr-bridging-gaps-siting.pdf |access-date=23 October 2026 |via=Climate Insights Directory}}

BibTeX

@techreport{chhunndbridging, author = {Chhun, Chanmaly and Pearce, Rebecca and Salinas, Pascal Caraccioli and Saltiel, Seth and Saez, Carolina Munoz}, title = {{Bridging the Gaps: A Survey of Methods, Challenges, and Pathways Forward for Superhot Rock Siting and Characterization}}, institution = {Clean Air Task Force}, url = {https://cdn.catf.us/wp-content/uploads/2025/01/11102623/shr-bridging-gaps-siting.pdf}, urldate = {2026-10-23}, note = {Indexed by Climate Insights Directory} }