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NEW YORK – Newly confirmed data reveals that superhot, superdeep rock miles beneath the surface can form permeable fractures, enhancing geothermal energy prospects.
This rock, under supercritical conditions, increases permeability tenfold compared to surface-level rock, suggesting a potentially economical and sustainable energy solution.
Potential for Superhot Geothermal Energy
New laboratory data confirm the potential for geothermal energy’s “holy grail”: tapping into superhot, superdeep rock miles beneath the Earth’s surface, which could generate a clean, renewable energy source capable of replacing a substantial portion of the fossil fuels driving global warming. The findings, published in Nature Communications, are among the first to demonstrate that such rock can form fractures that connect and increase permeability. Until now, geologists were unsure whether this was even possible.
These fractures are crucial because water passing through them can become supercritical, a steam-like phase that most people are unfamiliar with. (Common phases include liquid water, ice, and vapor, like the kind that forms clouds.) Supercritical water, in turn, “can penetrate fractures faster and more easily and can carry far more energy per well to the surface—roughly five to ten times the energy produced by today’s commercial geothermal wells,” according to the 2021 report “Superhot Rock Geothermal, A Vision for Zero-Carbon Energy ‘Everywhere,’” by the Clean Air Task Force.
The data also show that rock that fractures at superhot conditions can be ten times more permeable than rock that fractures at conditions closer to the Earth’s surface, and can also deform more readily. Those factors could make this geothermal resource “much more economic,” says Geoffrey Garrison, Vice President of Operations for Quaise Energy, one of the funders for the work. Quaise is working on a novel drilling technique for accessing superdeep, superhot rock.
A Geological Debate
Until now, geologists had been divided as to whether this superdeep, superhot resource can be tapped. Rock under such high pressures and temperatures—more than 375oC, or 707 oF—is ductile, or gooey, as opposed to a smashable stone from your backyard. As a result, some have argued that fractures can’t be created. And if they can, will they stay open?
The current work, led by a team at the Ecole Polytechnique Fédéral de Lausanne (EPFL), confirms that fractures can indeed form in superhot, superdeep rock located near the brittle-to-ductile transition in the crust. The latter is where hard, brittle rock begins to transition into a material that’s ductile, or more pliable.
“There are also lots of other data coming out of this work that will inform our approach to tapping the resource,” Garrison says. For example, “how strong is the rock? How far do the fractures go? How many fractures can we create?”
“All of this will help us derisk the drilling involved, which is very expensive. You don’t get a lot of chances. You don’t get to drill a hole then, like hanging a picture, move it over if you’ve missed the best location.”
“Exciting Finding”
Peter Massie is director of the Geothermal Energy Office at the Cascade Institute, which recently released a report with the Clean Air Task Force about drilling for superhot geothermal energy. Massie, who was not involved in the Nature Communications work, made the following comment about it on X:
“Exciting finding: extreme heat & pressure can help create better enhanced geothermal systems [EGS]. At very high temps, rocks become ductile (plasticky), which was expected to impede EGS. This supports [the] prospect of ultradeep, ‘supercritical’ geothermal with major boost in output.”
The research was led by Associate Professor Marie Violay, head of the Laboratory of Experimental Rock Mechanics at EPFL. Says Violay:
“This work is exciting because it presents the first permeability measurements conducted during deformation at pressure and temperature conditions characteristic of deep supercritical geothermal reservoirs near the brittle-to-ductile transition in the crust.
“We have shown that the brittle-to-ductile transition is not a cutoff for fluid circulation in the crust, which is promising for the exploitation of deep geothermal reservoirs. There are very few in situ data available, and these are among the first experimental results that shed light on such extreme conditions.”
Violay’s coauthors of the Nature Communications paper are first author Gabriel G. Meyer and Ghassan Shahin, both of EPFL, and Benoit Cordonnier of the European Synchrotron Radiation Facility.
Read more at SciTechDaily
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