Goryach-kamen: millimeter waves will help extract heat from the depths of the Earth

Russian scientists have proposed a project to extract heat from super-hot rocks at a depth of 10-25 km. These levels are expected to be achieved using millimeter-wave drilling technology. It was tested by vaporizing granite using a 10 kW source. Calculations have shown that with a capacity of 1 MW, the drilling speed of solid rocks will reach several meters per hour. The technology will also be in demand in geological exploration, construction and other fields, experts believe.

An environmentally friendly energy source

Russian developments will help provide people with an inexhaustible supply of environmentally friendly energy anywhere in the world. This project was presented by scientists at the S.S. Kutateladze Institute of Thermophysics of the Siberian Branch of the Russian Academy of Sciences and the A.V. Gaponov-Grekhov Institute of Applied Physics of the Russian Academy of Sciences.

They proposed a technology for extracting heat from super-hot rocks that are located in the bowels of the Earth at a depth of 10-25 km. At this level, the temperature reaches 400-450 °C.

Photo: IPF RAS press service

— Geothermal energy uses the heat of the Earth's interior. This direction has two branches. The first is the use of underground hot water and steam, but their reserves are limited. The second uses the heat of deep dry rocks. The concept of their development was proposed by Tsiolkovsky. He also carried out the initial calculations," Academician Sergey Alekseenko, scientific director of the ITF SB RAS, told Izvestia.

Experiments on extracting such energy in the world were carried out in the 1970s, the scientist added. The stations for these purposes are arranged in the form of a complex of wells. Some have water pumped into them. It passes through the cracks of hot rocks, heats up and exits through others in the form of hot steam. Its energy is converted into electricity or heat.

However, classical deep drilling methods are expensive. For example, it costs $5,000 per meter to create a 5-kilometer well. Therefore, projects to extract heat from hot rocks are limited only to experimental stations, the academician said.

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How radiation will help to reach the bowels of the Earth

Nevertheless, the direction may get a second wind thanks to the innovative technology of ultra-deep drilling using millimeter waves, the scientists said. Generators of such radiation are called gyrotrons. In particular, they are used in thermonuclear reactors to heat plasma.

— The world is looking for low-cost drilling methods. Microwave radiation in the millimeter wave range may be promising because it propagates well through waveguides and does not lose power over long distances," said Alexander Vodopyanov, Doctor of Physico—Mathematical Sciences, Head of the Department of Plasma Physics at the IPF RAS.

Photo: IPF RAS press service

A startup has already been launched in the United States, which conducts field experiments in this direction, he added. The company promises to supply electricity to the grid in a few years.

In Russia, work on this technology began last year. The advantage of Russian scientists is in the competence to create metawatt gyrotrons. In addition, the country has already accumulated significant experience in researching the interaction of microwave radiation with various materials and developing high-power signal transmission systems.

— In March of this year, we started testing the evaporation of granites and basalts. They form the basis of the earth's crust and have the highest evaporation temperature. We are also studying heat loss channels and working on different ways to remove the evaporated substance. There is already reason to believe that microwave drilling will be faster and cheaper than traditional methods," said Alexander Vodopyanov.

According to him, in the experiment, the rocks were evaporated by a 10 kW source. However, estimates have shown that with a capacity of 1 MW, the drilling speed will be several meters per hour.

As Sergey Alekseenko explained, in the proposed technology, the first section of the well is drilled with a conventional drill. Then a waveguide is lowered into it, through which microwave radiation is supplied, evaporating granite or basalt at the bottom. The resulting vapors are removed up the annular channel by purging with an inert gas, such as argon. In this case, part of the evaporated material settles on the walls and forms a glassy film that prevents leakage of the coolant through possible cracks. According to calculations, such a scheme is at least five times cheaper than traditional drilling of ultra-deep wells.

Photo: IZVESTIA/Pavel Volkov

The academician noted that, according to European experts, in Russia, superheated rocks are most available in Kamchatka, the Magadan region, in the Baikal and Tuva regions. Here they are located at a depth of about 10 km. According to scientists, the development of only 1% of such reserves can provide the country with energy for half a century.

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Will the new technology revolutionize the energy industry

"The development of such technology can be a real breakthrough in the field of drilling, comparable to the transition from traditional tools to carbide and then diamond tools," Denis Simisinov, Vice—rector for Research at Ural State Mining University, told Izvestia. — This will allow you to work at much greater depths and effectively drill in difficult geological conditions, where tool wear becomes the main limitation.

The project requires a wide range of experts, from geologists and thermophysicists to economists, who will conduct surveys and verify profitability, he explained.

— The idea is interesting, but how to deliver the radiation source to the mining site and how to transfer energy to it? In addition, during the drilling process, the stability of the barrel and the technology for removing fracture products are of primary importance. This is associated with the highest costs and accidents," said Konstantin Porozhsky, Professor of the Department of Mining Machinery and Complexes at UGSU.

At the same time, it is necessary to study whether it is safe for a person to work near a source or whether it is worth switching to robotics, the scientist added.

Photo: IZVESTIA/Konstantin Kokoshkin

— The prospects of such technologies directly depend on their payback. Therefore, economic calculations must be carried out at several typical sites with different tectonics, geological structure and distance to potential energy consumers," Tamara Zhuravleva, a leading engineer at the Laboratory of Rock Mechanics at MIPT, explained to Izvestia.

According to her, one of the Russian companies studied the topic of microwave drilling for the development of oil fields in the Bazhenov formation (a group of oil-bearing rocks) in Western Siberia. However, the economy was not in favor of the project.

— There are really a lot of questions. Firstly, depths of 10-25 km are extreme values, and it is not yet clear whether it will be possible to develop technologies and materials capable of working in such conditions. Secondly, even drilling at 2-3 km is already considered an expensive operation, and here we are talking about wells many times deeper. Nevertheless, if these tasks can be solved, humanity will have access to an almost inexhaustible source of energy," says Stanislav Yankovsky, associate professor at the I.N. Butakov TPU Scientific and Educational Center.

According to the expert, although the concept itself looks almost fantastic, the results of the first tests inspire some optimism.