Science & Technology: Geothermal Drilling in Search of Supercritical Fluids - Looking for the Eureka Moment

Want Unlimited Clean Energy? Just Drill the World's Hottest Well (Wired)

Geothermal Sunset, by Fabio Sartori. GRC Photo Contest 2019.
Nuova Monterotondo geothermal power plant, Italy.

An engineering team bored 2 miles into hot rock without causing major earthquakes—a good sign for harnessing the Earth's heat as a power source.

There’s treasure buried deep beneath the viridescent foothills of Tuscany’s Apennine Mountains, where the stark metal trusses of the Venelle-2 drilling tower mark its location like an X on a map. This geothermal well reaches nearly two miles beneath the surface to a region where temperatures and pressures are so high that rock begins to bend.

Here, conditions are ripe for supercritical geothermal fluids, mineral-rich water that exhibits characteristics of both a liquid and a gas. It’s not exactly gold, but if Venelle-2 could tap into a reservoir of supercritical fluids and use them to spin a turbine on the surface, it would be one of the most energy-dense forms of renewable power in the world.

Drilling at Venelle-2 stopped just shy of the K horizon when temperatures at the bottom of the well overwhelmed the equipment. Sensors at the bottom of the well indicated temperatures had breached 1,000 degrees Fahrenheit and pressures 300 times greater than at the surface. Nevertheless, Venelle-2 is the hottest borehole ever created, and it demonstrated that it's possible to drill at the extreme end of supercritical conditions.

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Riccardo Minetto, Domenico Montanari, Thomas Planès, Marco Bonini, Chiara Del Ventisette, Verónica Antunes, Matteo Lupi. Tectonic and Anthropogenic Microseismic Activity While Drilling Toward Supercritical Conditions in the Larderello‐Travale Geothermal Field, Italy. Journal of Geophysical Research: Solid Earth, 2020; 125 (2) DOI: 10.1029/2019JB018618