In essence, “super-hot rock” geothermal, is the type of geothermal energy production that seeks to tap into extremely deep, extremely hot rock. It can be said also that it is a form of EGS (Enhanced/Engineered-Geothermal-Systems).
1. How does super-hot-rock geothermal work?
In a super-hot-rock system, water is injected deep into hot fractured rock, heated, and returned to the Earth’s surface as steam that can be used to produce power in electric turbines or to generate hydrogen using a high temperature process.
At extremely high heat, the performance of geothermal doesn’t just rise, it takes a leap. When water exceeds 373°C and 220 bars of pressure, it becomes “supercritical,” a new phase that is neither liquid nor gas.
Super-hot-rock geothermal could have a few distinct advantages over other energy sources. It is projected to be affordable, requiring little area to produce large amounts of energy (high energy density) due to the very large amount of energy that can be produced per well. Super-hot-rock is expected to produce five to ten times as much energy as the power produced from one of today’s commercial geothermal wells.
Source: Superhot Rock Geothermal – A vision for Zero-Carbon Energy “Everywhere”. CATF, Oct. 2021
1. Super-hot-rock geothermal “mines” deep at very high temperature and heat in the Earth’s crust. This contrasts with today’s small (~15 GW globally) commercial geothermal industry that typically depends on upwelling of hot groundwater at locations with high near surface heat.
Conceptual model of the Reykjanes geothermal field showing the existing conventional geothermal wells (brown) and the IDDP-2 well (blue) (Friðleifsson et al. 2016)
2. Super-hot-rock geothermal injects water into super-hot dry crystalline rock by opening existing fractures at a depth where water is so hot it possesses properties of both liquids and gasses, allowing injected water to travel rapidly through existing rock fractures and gather very large volumes of heat energy.
3. Production wells bring this steam energy to the surface to produce power in electric turbines and/or to generate hydrogen.
Conceptual model of the JBBP project for supercritical geothermal systems in northern Honshu, Japan (Asanuma et al. 2015). These systems lie above shallow magma chambers that are associated with Miocene and younger caldera complexes in the Tohoku region
2. The value of superhot rock geothermal
- Energy dense, high energy with a small surface footprint
- Generate carbon-free hydrogen without carbon as a transportation fuel
- Accessible worldwide with super deep drilling innovation
- Significant engineering advancements required but does not depend on scientific breakthroughs
There are two important things about super-hot “supercritical” water. First, its enthalpy is much higher than water or steam, meaning it holds anywhere from 4 to 10 times more energy per unit mass. And second, it is so hot that it almost doubles its conversion efficiency to electricity.
Power Output comparison of three wells on a 400°C project versus 42 EGS wells at 200°C: Similar output using less fluid and a fraction of the physical footprint. Source: ARPA-E
A test well drilled by the Iceland Deep Drilling Project (IDDP) demonstrated that an estimated 36 megawatts (MW) of energy could be produced at the surface—approximately 5 times that of a typical 5-7 MW commercial geothermal well today. If this substantial amount of energy can be produced at reasonable development costs, SHR could be competitive at potentially $20-35 per megawatt-hour (MWh).
The darker red areas are generally regions where super-hot-rock is shallower, in the realm of current drilling technologies, and could be initially demonstrated and commercialized. The remainder of the world should be able to tap into superhot rock as super-deep drilling innovation allows.
Experience to date shows that the hotter geothermal gets, the more competitive its power price, to the point that super-hot-rock geothermal could be the cheapest baseload energy available.
No well is currently producing electricity from supercritical water, but several past wells (in Hawaii and California’s Salton Sea, e.g.) have encountered supercritical water and there are exploratory projects in Japan, Italy, Mexico, and several other countries to learn more.
Global superhot drilling and research sites. Brown areas are where SHR heat is less than 10 km and therefore the most viable regions for earlier SHR development. (Heat map: Pacific Northwest National Laboratory and HERO)
3. Challenges for the implementation of super-hot-rock geothermal:
The main challenges for the implementation of super-hot-rock Geothermal are mainly engineering since the current oil and gas technologies were not designed for very high temperatures. These challenges includes: Technology for drilling in very hot dry rocks; development of casings and cements that can resist very high heat and corrosion; water chemistry at high heat needs to be better understood; and downhole tools and materials in general need to be perfected for handling very high heat.
4. Deep hot drilling methods innovations:
Deep hot drilling poses a significant challenge for the development of super-hot-rock geothermal, to tackle this, innovative “non-contact – non-mechanical” drilling methods, also called “energy drilling” are being developed. Once these technologies become robust and applicable, they should significantly improve drilling speed and economics, thus further enabling economic access to greater depths.
These methods basically soften or melt rock through energy directed downhole. Two principal energy drilling methods are currently being tested: Plasma Drilling and Millimeter-Wave Drilling. GA Drilling (Slovakia) is preparing to test its Plasmabit drill in the field in the coming year, while Quaise (USA) is developing the Millimeter-Wave drill.
AltaRock Newberry SHR Geothermal Energy (NEWGEN) Project:
Newberry Volcano, located near Bend, Oregon, sits atop one of the largest geothermal heat reservoirs in the western United States. After extensive research, AltaRock Energy and its partners have concluded that Newberry could support a commercially viable enhanced geothermal system (EGS) power plant. Using super-hot-rock extraction technology developed by AltaRock Energy, the Newberry SHR Project could one day generate up to 10 gigawatts of electricity (GWe) – enough to power 3 million homes.
5. The path forward for super-hot-rock geothermal
Super-hot-rock technology development can begin today by drilling near existing geothermal fields where the Earth’s temperature is very hot near the surface. With success, intensive drilling campaigns can begin to develop super-hot-rock beyond commercial fields. From there, energy drilling technology can target deeper rock and ancient granites that are hot from radiogenic decay. As energy drilling matures, very deep systems can be tapped into, expanding superhot rock geothermal globally.
Directional drilling may be a key tool, as it would allow an SHR project to: (a) drill from a small surface pad, minimizing impacts and maximizing efficiency; (b) access fractures at angles that allow for better water circulation; and (c) mine heat from progressively deeper heat resources. Source: Superhot Rock Geothermal – A vision for Zero-Carbon Energy “Everywhere”. CATF, Oct. 2021
6. Final comments on super-hot-rock-geothermal
Commercial super-hot-rock geothermal energy could make a transformational contribution to global energy system decarbonization. Super-hot-rock is a high-energy-density, zero-carbon, always available energy source that could potentially be accessed worldwide for baseload power, heat, hydrogen production and industrial process energy. Super-hot-rock could be economically competitive with most zero-carbon technologies and capable of being deployed rapidly in much of the world. Super-hot-rock promises a small environmental footprint and could potentially repower or replace many existing fossils fuel energy facilities.
The reward: cheap baseload power, available almost anywhere.
Resources:
· “Geothermal energy is poised for a big breakout” https://www.vox.com/energy-and-environment/2020/10/21/21515461/renewable-energy-geothermal-egs-ags-supercritical
· Article: Super-hot Geothermal https://www.catf.us/work/superhot-rock/
· Article: Utilizing supercritical geothermal systems: a review of past ventures and ongoing research activities https://geothermal-energy-journal.springeropen.com/articles/10.1186/s40517-017-0075-y
