The prospects for virtually unlimited clean geothermal power generation are now much brighter. EPFL’s Laboratory of Experimental Rock Mechanics (LEMR) has shown that semi-plastic, sticky rocks at supercritical depth can still fracture and allow water to pass through.
Geothermal power, along with nuclear power in the form of nuclear fission or fusion, and one or two other cutting-edge energy sources, has made the concept of general energy scarcity as outdated as worrying about saber-toothed cats. has a true promise to. By harnessing the vast heat inside the Earth, it is theoretically possible to extract enough clean power to meet all of humanity’s energy needs for millions of years to come, and climate change The biggest problem can be solved more or less overnight.
The problem is that all that amazing energy is locked up miles below the Earth’s crust, and the cost of getting there is astronomical. As a result, geothermal power today is a niche power source available only in a few scattered volcanic regions where the heat is much closer to the earth’s surface, typically far from where the energy is needed.
But almost everywhere on Earth, far more powerful supercritical geothermal resources await exploitation. If we can drill far enough to reach the extremely hot rock found beneath the surface. Although we’re still only talking a small distance within the Earth’s crust, its subsurface is hot enough to heat water to temperatures of over 400 °C (752 °F).
At these temperatures, water becomes “supercritical” and begins to behave like something halfway between a liquid and a gas, flowing as easily as a gas, but retaining the density of a liquid. This phase can be used to extract large amounts of energy. In practical terms, if water can be obtained up to supercritical temperatures, it is possible to run geothermal power plants ten times more powerful than conventional ones using water at lower temperatures.
The bad news is that drilling to such depths (sometimes exceeding the world record 12 kilometers (7.5 miles) depth of the Kola borehole) is currently beyond the state of the art in engineering. However, there are some very promising projects that can solve this problem. Relatively short order.
The good news is that if we can master drilling to such depths, we will be able to install geothermal power plants almost anywhere on the planet. For example, a geothermal power plant could be installed on the site of an abandoned coal-fired power plant that has been shut down. They already have the power grid and lots of steam turbine equipment, so why not turn the sword of climate action into a plowshares?
There are still many unresolved issues. One is that geothermal requires maximum contact between the rock surface and the fluid it heats. One of the best ways to significantly increase that contact area is to fracture the rock using a very similar process. to those used in oil and gas hydraulic fracturing. Fervo Energy has successfully demonstrated how much of a difference this approach can make to geothermal power plants.
But because no one had ever drilled that far, science couldn’t determine whether the rock there would crack open and allow water to pass through. Observations taken near the 10 km (6.2 miles) point showed that the rocks were beginning to behave very differently than they did near the surface.
Instead of being hard and brittle, it becomes soft, plastic, and sticky. This suggests that at supercritical temperatures it may be impossible to fracture rocks and allow water to flow through them.
At least that was the case until the EPFL team led by Gabriel Meyer conducted laboratory tests using a new gas-based triaxial instrument, high-resolution synchrotron 3D imagery, and finite element modeling.
“As we approach the 10km mark, the rock stops breaking and instead deforms uniformly, like a soft caramel, and its behavior becomes complex,” Meyer said. “Deformation occurs at the level of the crystal structure within the grains. We wanted to know whether water could circulate within the rock that had changed into this unusual, ductile shape.”
What Meyer and his team did was to recreate the pressures and conditions found within the Earth’s crust and observe how the crust changes during the so-called brittle-to-ductile transition (BDT). It was. These clinical tests are especially important because such observations are nearly impossible to make in the real world. Instead, the test equipment recreated the temperature and pressure conditions inside the rock sample, which was scanned by a synchrotron to create 3D images that were fed into a computer simulation.
They discovered that this stone behaved less like putty than Silly Putty, a popular toy that behaves like both a liquid and a solid. With Silly Putty, you can easily mold it into any shape you want, and when you put it on, it slowly oozes out like a liquid. But the clever thing is that when you hit this soft, flowing putty with a hammer, it shatters like glass.
New EPFL research shows that the rocks that cover the supercritical zone behave similarly. Although it is ductile, it can fracture to allow water to flow through it. This means that with advanced deep fracturing technology, it is possible to build very serious geothermal power plants.
EPFL
“Geologists have long believed that the brittle-to-ductile transition point is the lower limit of water circulation in the Earth’s crust,” Meyer says. “However, we have shown that water can circulate even in ductile rocks. This is a very promising finding that opens further avenues of research in our field.”
This research works to demonstrate that record-breaking, ultra-deep geothermal boreholes can be drilled using particle accelerator technology developed for the fusion energy field, instead of drill bits that simply cannot be drilled. It’s especially relevant for companies like East Coast startup Quaise Energy. As the temperature rises, it will drop to that point.
Companies like Fervo and Sage Geosystems have proven that the hydraulic fracturing approach to geothermal energy can extract far more power than traditional methods. This study proves that this concept can do the same for ultra-deep, supercritical geothermal projects.
As mentioned before, if these companies are successful and can bring these types of power plants to market on a large scale, humanity’s continued energy needs will simply not be a problem. Clean, grid-enabled, 24/7, virtually unlimited… There is theoretically plenty of reason to be optimistic, and while many unprecedented problems remain to be solved, further progress is likely to be reported soon. I hope that.
The study was published in the journal Nature Communications.
Source: EPFL
