An introduction to the next clean energy frontier: Superhot rock and a review of past ventures and ongoing research activities

This blog is part of a series exploring and explaining the science behind next-generation geothermal, with a special focus on superhot rock geothermal, through a curated tour of influential technical and academic papers. This edition highlights key features of the Geothermal Energy article by Reinsch et al. (2017) Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities. The full blog series, in addition to their reference reports, can be found at the Superhot Rock Resource Library. 

With growing demand for clean, firm energy, geothermal technologies are increasingly being recognized for their unrealized potential. Among these, superhot rock geothermal (SHR) systems stand out for their potential to unlock deeper, hotter, and more energy-dense geothermal resources. Early high temperature projects in Iceland, for example, have found that SHR can generate up to 10x the energy output for a single well when compared to conventional geothermal systems. 

To date, most projects have been developed from lower temperature systems (<250 °C), but these lower temperature projects are essential to reducing the overall costs of future geothermal projects – including those at higher temperatures. Unfortunately, few wells have so far encountered the supercritical conditions required for SHR due to the technical challenges associated with drilling deeper at higher temperatures. Lessons learned from lower temperature projects have proven invaluable to reducing the overall cost of geothermal projects, but given the higher energy density of SHR systems and the potential for competitive costs at scale, the dedicated research and development (R&D) needed to achieve the necessary advancements to commercialize SHR appear to be worth the effort. 

In their 2017 article, Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities, Reinsch et al. detail both the history of SHR development as well as the technology advancement needed to further SHR development. With next-generation geothermal having its moment in the spotlight, it is worth looking at the technology advancements needed to reach commercialization of SHR to achieve geothermal anywhere at competitive costs. 

Early projects have encountered large and frequent hurdles that still need to be overcome 

Reinsch et al. detail the challenges that early projects have encountered related to drilling, well completion, fluid handling, logging tools, site characterization, and monitoring. Although these challenges have so far prevented full commercialization, projects in several countries – including Italy, Iceland, Japan, and the U.S. – had already achieved supercritical conditions by the time Reinsch et al. was published in 2017. More information can be found on each of these projects at Clean Air Task Force’s Superhot Rock Heat Endowment and Project Map. Some of the challenges experienced on these high temperature projects have been summarized below: 

Italy 

Early projects experienced elevated temperatures and corrosive conditions that led to drilling problems including tool deviation, drill pipe corrosion, breakage, fishing, and side tracking – sometimes causing wells to blow out. Additionally, repeated issues with the cement caused the casing to be heavily damaged, ultimately causing the well to be abandoned. 

Iceland 

Overall, difficulties with projects have included issues with lost circulation, drill strings getting stuck, and well obstructions. An initial attempt to deepen an exploratory well on the Reykjanes peninsula was unsuccessful after it suffered a wellbore collapse during flow testing. A later attempt at the Krafla geothermal field unexpectedly drilled into magma (IDDP-1). The well was completed at a slightly shallower depth, allowing for successful flow testing—until corrosion of the surface equipment and wellhead failure ultimately forced it to be shut in. Subsequent research has shown that scrubbing techniques can be deployed to mitigate the impacts from these corrosive fluids.  

Japan 

Exploration by projects beyond the brittle-ductile boundary (i.e., the boundary between the shallower, more brittle crust, and the deeper, more ductile crust) was unable to identify existing fractures (i.e., permeability) for reservoir creation. This exploration, however, was able to demonstrate the feasibility of drilling at elevated temperatures using borehole cooling techniques in regions where the bottom-hole temperature was up to 500 °C. 

United States 

In the U.S., high-temperature wells have been drilled at The Geysers, Salton Sea, and Puna geothermal fields. Exploration at The Geysers has encountered casing collapse, drilling difficulties caused by elevated temperatures, and extreme bit wear. At Salton Sea, an exploration well had to be plugged and abandoned due to elevated pressures encountered at depth. At Puna, difficulties included lost circulation, difficulty cementing the casing, well obstructions, encountering magma, and drill strings becoming stuck.  

Despite setbacks, we have learned a lot from early projects

Although hurdles in SHR development have been common and caused project failures, they’ve also yielded critical lessons. Since the publication of Reinsch et al. in 2017, research to advance SHR has already begun across several key areas, including: 

• Exploration methods for better resource assessment: Some of the early drilling campaigns have unexpectedly reached supercritical conditions, which caused the well designs to not be appropriate to handle the corrosive and extreme environments around supercritical fluids.  

• Field- and bench-scale laboratory experiments at SHR conditions: Reservoir models are not sufficiently informed at SHR conditions. As part of this effort, researchers at GNS Science are working to improve laboratory simulations in order to advance their research into developing New Zealand’s SHR resources. Additionally, to better understand the gaps in laboratory capabilities at SHR conditions, CATF is initiating a project to gather laboratory capabilities. This information will be used to develop a database of SHR laboratory capabilities. You can access the survey for this effort here. 

• Improvements in drilling, completion, and cementing practices: Many of the difficulties encountered in early projects were due to circulation loss, high bit wear, very low rates of penetration, and blocking of the drill string. This is in addition to issues with cement-job failures. Advancements have already been made since Reinsch et al. was published, with the development and testing of drilling technologies like millimeter wave drilling and plasma drilling. Additionally, researchers in the Geothermal Materials Group at Brookhaven National Laboratory are actively researching the behavior of cements in harsh geothermal environments. 

Many of the hurdles detailed in Reinsch et al. are also included in CATF’s Bridging the Gaps Reports, which covers the remaining technological gaps in heat extraction, power production, drilling, well design and construction, and siting and characterization. Altogether, this series identifies where future research, development, and testing efforts should be concentrated for SHR projects to be successful at a commercial scale. 

What’s next? 

The advancement of SHR projects has encountered numerous hurdles, which have resulted in closed wells and failed projects. However, with these materials failures have come numerous learnings and further advancements in developing the technology needed to commercialize SHR. With the potential to generate 10x the energy output for a single well when compared to a typical commercial geothermal well, SHR has the potential to reshape our energy system – illustrating that the challenge is worth the effort. Early project hurdles have identified the research needed to advance this essential technology. Understanding these hurdles allows for a greater focus on key research and funding needs. Efforts by early industry leaders to aim for higher temperatures and research identified gaps are the key to advancing SHR. 

Stay tuned for more from CATF as we continue to push forward bold ideas on how to scale superhot rock geothermal as an essential source of reliable and clean electricity. 

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This blog is part of a series exploring and explaining the science behind next-generation geothermal energy, with a special focus on superhot rock geothermal:

• Superhot rock geothermal and a vision for firm, global clean energy
• Superhot rock geothermal and pathways to commercial liftoff
• Superhot rock and the future of geothermal
• Superhot rock and the challenges in developing enhanced geothermal systems
• Superhot rock and the opportunities for responsible development
• Superhot rock and closed-loop geothermal systems

Through a curated tour of influential technical and academic papers, the series aims to provide a fresh perspective from a geoscientist entering the geothermal industry. The goal is to share my learning journey and encourage collaboration around these groundbreaking solutions, which are critical to achieving a clean energy future. Whether you’re new to geothermal or looking to deepen your knowledge, I hope this series offers valuable insights into this fast-evolving field.