The crazy project of drilling 20 km deep for unlimited access to the Earth’s internal heat!

In the race for energies renewables, there is one particularly promising one: geothermal energy. Our planet is indeed a formidable powerhouse, totally inexhaustible, at least on a human scale. The heat resulting from the cooling of the inner core diffuses outwards, feeding the passage movements of convection from coat that support major earth processes, such as volcanism and plate tectonics. If on the surface this flow of energy is little felt from day to day, it is enough to dig a little to realize its existence. The further down you go, the higher the temperature. This state of affairs is illustrated by the gradient geothermal, which is on average 3°C every 100 meters, or 30°C per kilometre. This increase in temperature with depth is however extremely variable geographically, with areas where it will be lower (such as at the level of cratons continental), or stronger (as in the rift zones).

The promise of clean and unlimited energy

It quickly became apparent that humanity could take advantage of this state of affairs. Geothermal energy is indeed an inexhaustible source of energy, available there, directly under our feet. In theory, it is sufficient to drill and circulate a liquid which heats up on contact with the rocks at depth and rises to supply either turbines or a heating network. Of course, the deeper you drill, the greater the energy recovered. Over the last few decades, the objective has thus been to drill deeper and deeper, up to four or even five kilometers. This is called deep geothermal energy. At this depth, the water is indeed over 150°C. By drilling in areas with a strong geothermal gradient, it is even possible to recover fluids at 200°C. Enough to supply small towns with electricity 24 hours a day, 7 days a week, because unlike wind power or solar, geothermal energy is not dependent on environmental factors. An idyllic vision, which however comes up against many technical constraints. Because drilling in the continental crust over several kilometers proves to be a real challenge: it requires a detailed knowledge of the subsoil in order to avoid unfortunate accidents (presence of active faults or unstable, of a aquifersalt layers, etc.), equipment and sensors able to withstand heat and pressuremaintenance of equipment subjected to the circulation of highly mineralized geothermal fluid, maintenance of a network of porosity and open faults which allow the circulation of the fluid… not to mention the realization of the well itself, a long and very expensive operation.

The crazy gamble of drilling 20 kilometers deep

It is in this context that the company Quaise Energy, founded by MIT engineers (Massachusetts Institute of Technology), proposes a crazy project: to considerably facilitate and accelerate the drilling operation thanks to a new technology resulting from work on the nuclear fusion and sink a geothermal well 20 kilometers deep, the deepest well ever.

An extremely ambitious project knowing that currently, the record for the deepest drilling is 12 kilometers. It was made on the Kola Peninsula, Russia. Started in 1970, it will end 24 years later in the face of insurmountable technical problems: difficulty in extracting excavated materials, twist and fracture of the drilling axis due to its length and a temperature of 180°C melting the sensors. If this was a scientific challenge, it appears that conventional drilling techniques are not at all suitable for an industrial purpose.

Melt rock instead of crushing it

Quaise Energy is thus betting on a completely different technique. Instead of crushing the rock using traditional drill heads, the company simply offers to vaporize it using microwave light beams. A kind of non-contact drilling, called gyrotrons, which vitrifies the rock as it descends and could thus make it possible to drill much more easily and quickly at great depths, even up to 20 kilometers.

A very attractive objective: at this depth, the temperatures reached would be over 500°C! The geothermal fluid, which is then in a so-called supercritical state, would then be sucked into the hole and transformed into vapor on the surface, and from there into electrical energy. For the founders of Quaise Energy, this would provide access to a near-infinite source of clean energy for the first time.

The supercritical state is defined as a 4^e state of matterafter the state solid, liquid and gaseous. It can be compared to a fluid as dense as a liquid which behaves like a gas. However, when it is in the supercritical state, a fluid contains up to 10 times more energy per unit of mass than a subcritical fluid. Energy efficiency is therefore very important.

Currently, gyrotrons are already used, but to heat material during nuclear fusion tests. The goal now is to adapt and apply this technology to the drilling of a deep well. The old power stations coal and gas would be reused to house and operate these new boreholes. Such drilling could also be carried out almost anywhere on the globe, thus giving everyone access to clean, carbon-free, renewable and unlimited energy.

Reality… or fiction?

An extremely ambitious and attractive concept, which remains no less than a concept at the present time. Because if the company advances the date of 2026 for its first tests, for the moment nothing proves that this objective is achievable. Quaise Energy itself admits that there are still many technical considerations to be resolved. Among them, the management of the enormous pressures and temperatures prevailing at these depths and the resistance materials used. Another question, and not the least: the stability of the well and the maintenance of its opening under the phenomenal lithostatic pressure which reigns at a depth of 20 kilometers and which will tend to immediately close the slightest fracture.

How will a well whose walls are vitrified (and therefore impermeable) also be able to drain the fluid and how will it be brought to the surface? For the moment, the company does not present any solution to this type of question, however crucial.

So, fact or fiction? We will certainly have to wait for the start of the first tests at medium depth to consider the feasibility of the project. Be that as it may, the new drilling technology developed by Quaise Energy could certainly be applied to less ambitious drilling, thus allowing a drastic reduction in costs and therefore in the energy produced. The use of gyrotrons to drill five kilometers deep could already represent a real revolution in the field of deep geothermal energy.