Superhot rock energy

Clean Air Task Force (CATF) is a global nonprofit organisation comprised of scientists, engineers, business managers, lawyers, policy, and communication experts. They aim to safeguard against the worst impacts of climate change by driving forward the technological and policy changes required to achieve net zero by 2050. Philip Ball is their Chief of Geothermal Innovation, and he explains that his visionary Superhot Rock Energy team is dedicated to “decarbonising the energy sector through superhot rock energy, with the goal of demonstrating and commercialising it anywhere in the world, thereby providing affordable access to the largest untapped energy source on the planet.”

Enhanced geothermal

Superhot rock energy is an enhanced geothermal system that requires deep drilling technologies to access dry rocks at temperatures of around 400°C or greater. Water is then pumped into the system to produce superheated steam or water at the surface to drive a turbine and generate electricity. Superheated steam or water carries vast energy so has the potential to make power plants significantly more efficient.

“Superhot rock energy is anticipated to produce renewable energy 24 hours a day with firm seasonal availability. Its land footprint is projected to be smaller than that of any other energy source, and because it will be available almost anywhere, it can produce domestic energy and potentially reduce global resource conflicts. At CATF we believe it could be a key component of the energy transition.”

Philip and his team are currently cataloguing wells drilled into rocks at temperatures greater than 350°C globally to get a clearer idea of where in the world superhot temperatures are approached or reached. So far, they have a database of 48 wells (www.catf.us/shrmap), although not all of these have sufficient pressure (22.1 MPa) required to reach the supercritical conditions that are targeted for supercritical geothermal exploitation. The team is also working to map and characterise heat globally using a reference model for Earth’s key isotherms (the 450°C isotherm for the research described on page 22), with the aim of exploring where superhot rock energy may be accessible today, using existing technology, or in the near future with emerging technologies that may allow us to unlock deeper geothermal resources.

“While the current model is low resolution, it provides a consistent approach that allows us to globally assess the potential of superhot rock geothermal. The maps are not at the prospecting scale, but we aim to use them to inform on the possible size of the superhot resource, using workflows more typical to the oil and gas industry, and to strategically identify areas and governments with whom we should talk to ensure the right investments in research and development of technology are made, and where policy and regulation are needed.”

CATF believes that superhot rock energy could reach demonstration scale within five years, early commercialisation in ten years and full global scale in twenty years

Philip explains that while the depth of the ~400°C isotherm varies considerably around the world, there are many regions where it might be accessible at less than 10 km (and dramatically more regions where it might be accessible at 10 to 15 km depth).

“With our current maps, we see significant opportunities globally at depths between 7.5 and 12.5 km deep. If, via deep drilling innovation, we can harness the heat and use it to produce power, we could potentially develop tera watts of power in numerous countries globally, which would lead to significant decarbonisation of energy.”

Ongoing development

There is currently vast underinvestment in superhot rock energy compared to other clean energy technologies, and Philip emphasises that to successfully drill through hard rock will require funding, research, and testing. It is essential to better understand which rocks are best suited to mine heat, as well as the components of reservoir creation and maintenance. However, he and the team at CATF believe there are significant opportunities.

“The good news is that none of these areas require major scientific breakthroughs. Rather, numerous small incremental advancements in drilling and engineering will hopefully bring superhot rock energy to its first commercial projects, then enabling scalability.

“Different methods of advanced drilling through hard, hot rock are being tested by a range of companies around the world, while work on cements, casing, equipment, and reservoir creation is underway in numerous labs and in the field. To demonstrate viability of this approach, we will need to bring the resource to the surface, over a sustained time, in multiple successful demonstrations – this will take a global effort.”

With appropriate investment, CATF believes that superhot rock energy could reach demonstration scale within five years, early commercialisation in ten years and full global scale in twenty years.

“To make this happen, what is needed right now is significant and resilient funding sources that are patient enough to allow the industry to quickly learn from observations and failures along the way. We need to invest in superhot rock at a level that adequately reflects its potential to disrupt the status quo of energy production.”

Successful superhot rock geothermal projects, such as the Krafla geothermal power plant in Iceland (shown here), provide proof-of-concept for superhot rock geothermal projects by demonstrating feasibility of deep drilling, well construction and the handling of superhot fluids. Image: Ásgeir Eggertsson, CC BY-SA 3.0, via Wikimedia Commons

Pivot opportunities

Superhot rock energy and the wider geothermal industry offer the potential to transition a significant portion of the oil and gas industry.

“Many of the innovations needed for superhot rock energy to commercialise could be generated by the oil and gas industry – they have the subsurface know-how, drilling expertise, and the investment resources to demonstrate and scale this resource. While superhot rock energy works at a higher temperature than most oil and gas efforts, there is significant overlap in the engineering and scientific knowledge. The oil and gas industry owns large volumes of data from mapping oil and gas plays, much of which is also relevant for geothermal, so there are opportunities for collaboration. We want to engage the oil and gas industry in drilling for the high-enthalpy resources that could replace fossil fuels.”

The greatest potential for the UK lies with deep geothermal heat, particularly given the matched skill sets and technologies with the oil and gas sector, and the opportunity to support the North Sea Transition

Globally there is a realisation of the synergies between geothermal and the core competency areas of oil and gas companies, and Philip lists several examples, although not all are directly linked to superhot geothermal resource exploitation:

“In the US, the Department of Energy’s GEODE project is providing $165 million to the consortium formed by Project InnerSpace, the Society of Petroleum Engineering International, and Geothermal Rising to develop a roadmap to accelerate the growth and development of geothermal, leveraging expertise, technologies, and methods from the oil and gas industry. Additionally, Chevron Technology Ventures will explore the application of an Enhanced Geothermal System project in Sonoma, California, and closed loop projects in Japan in partnership with MEOCO, while Devon Energy also recently announced a strategic investment in the geothermal energy company FERVO. The Austrian oil and gas company OMV recently invested €34 million into the Canadian geothermal company EAVOR (following investments from BP and Chevron in 2021). There is so much going on globally; I hope that it really leads to something material for the energy transition.”

Geothermal spectrum

Philip is keen to stress that superhot rock energy is only one part of the “geothermal spectrum of technology opportunities at varying depth, temperature and pressure”, noting that there are many exciting projects worldwide across a wide playing field.

In the UK, Philip is particularly excited about the United Downs Deep Geothermal Power project in Cornwall, which will be the first commercial hot rock geothermal electricity project in the UK, as well as the potential for using old coal mines as local district energy heating and cooling networks. He notes that the 2023 government report, Dig Deep: Opportunities To Level Up Through Deep Geothermal Heat & Energy On The Way To Net Zero, concludes that the greatest potential for the UK lies with deep geothermal heat, particularly given the matched skill sets and technologies with the oil and gas sector, and the opportunity to support the North Sea Transition.

A drilling rig at the United Downs Deep Geothermal Power project in the UK, which aims to generate electricity from hot geothermal resources on a commercial scale

In Canada, construction of the first geothermal power plants (in Saskatchewan and Alberta) will begin in 2023, in Geretsried, Germany, construction is under way for the world’s first Eavor-Loop™ (a closed-loop geothermal system where a benign working fluid circulates underground without the need for a pump) for heat and power, with the aim of being operational within four years, while Eavor, in their quest to drill the hottest and deepest geothermal well in history, have reached depths of 5.5 km and 250°C with their first deep well.

Philip is also enthused by various intersections: “I am interested in the use of geothermal energy to decarbonise mining, green hydrogen, direct air capture of CO₂ and also the potential of capturing minerals and natural hydrogen from the brines of geothermal wells. All these technologies, concepts and innovations are emerging, and it is fascinating.”

DR Philip Ball

Chief of Geothermal Innovation in the Superhot Rock Energy team at Clean Air Task Force (CATF)

Interview by Amy Whitchurch

Further reading

• CATF (2022) Superhot Rock Energy: A Vision for Firm, Global Zero-Carbon Energy. CATF; www.catf.us/resource

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