One of the sources of energy that can replace the exhaustible resources of oil and natural gas is right under our feet - the warmth of deep rocks.
People learned how to mine it back in the early 1960s, but things are not moving beyond experimental petrothermal stations. Progress is hampered not only by the high cost of projects and technological difficulties, but also by negative public opinion.
Disturbed subsoil response
In 2005, drilling began in the vicinity of Basel in Switzerland to extract energy from hot granites. The technology required crushing rocks at a depth of five kilometers.
To do this, a liquid was pumped into the well under high pressure, which literally broke the granites and made them permeable to water. This method is called hydraulic fracturing and is used in oil fields to “invigorate” an impoverished well.
For the next six days, while the fluid was being pumped, the area experienced earthquakes of magnitude three and higher. The shocks were felt by local residents. Protests began, and the multimillion-dollar project was eventually scrapped.
A similar situation has developed in Germany - in Landau and Unterhaching, where geothermal power plants operate. In 2009, micro-earthquakes were felt there. But, despite the protests of activists, the projects were not closed, they are still functioning.
Promotional video:
Induced earthquakes in the area of petrothermal power plants.
Enthusiasm pumped into the ground
Petrothermal energy is one of the most promising areas that scientists expect will replace fossil fuel energy.
Unlike oil and coal, which must not only be mined, but also transported, and even processed, the Earth's heat can be used directly.
Due to radioactive decay in the core of the planet, the bowels are heated to a high temperature. This phenomenon is faced by miners.
At a depth of three kilometers, the temperature can go up to 150, and at ten kilometers - up to three hundred degrees Celsius. The heat of the bowels is constant, it does not depend on the weather and other external conditions. Unlike hot springs, geysers or dry steam, which are rare and are usually located in zones of active volcanism, far from consumers, hot rocks are everywhere on the planet.
Getting to them is not a problem, since deep drilling technologies are well established in the world.
To extract heat from underground, you need to drill two wells. Water (coolant) is pumped into one, which penetrates into cracks or pores of rocks at a depth and heats up. The hot liquid rises up the second well (production). This idea was proposed by Konstantin Tsiolkovsky at the end of the 19th century, and the Soviet geologist Vladimir Obruchev described it in detail in the story "Heat Mine".
Petrothermal power station.
Petroenergy works even if the subsoil is not hot enough, for example, their temperature is about 80 degrees. In this case, a binary cycle is used: through a heat exchanger, heat from the well is transferred to freon or liquid hydrocarbons - a low-boiling liquid.
The generated steam is fed to a turbine that generates electricity.
This technology is enough to provide mankind with energy forever, says Academician Sergei Alekseenko from the Institute of Thermophysics. S. S. Kutateladze SB RAS.
Public opinion commands progress
The first petrothermal station was built in France in 1963. In 1977, in the USA, near the Los Alamos laboratory, hydraulic fracturing was first used during the construction of a similar plant.
Now there are 22 petrothermal stations in the world, most of them in Europe. Of these, 14 generate electricity, the rest work for heating. Only one project, Soultz-sus-Forets in France, supplies electricity to the grid.
The technology faces many challenges. First, deep drilling is expensive. It eats up most of the project budget. Secondly, hydraulic fracturing has environmental consequences: from soil disturbance and groundwater pollution to artificial earthquakes.
The constant circulation of hot saline water through the well contributes to its rapid overgrowth and wear of equipment.
In addition, crystalline rocks contain many impurities, often toxic, readily soluble salts, all of which ends up in the coolant. There is a problem of its disposal, as well as the risk of environmental pollution.
So far, petrothermal energy is not developing very actively. Experts note that it has not yet passed the scientific stage. Each deep-seated heat plant is unique and requires constant research.
The public is against this technology, as well as against nuclear and wind power, storage of carbon dioxide on the shelf. Nevertheless, scientists do not lose hope and predict an increase in its share in global energy production by the end of the 21st century.
Tatiana Pichugina
