The term “geothermal energy” comes from Greek word earth (geo) and thermal (thermal). Essentially geothermal energy comes from the earth itself. Heat from the earth's core, which averages 3,600 degrees Celsius, radiates toward the planet's surface.
Heating of springs and geysers underground at a depth of several kilometers can be carried out using special wells through which hot water (or steam from it) flows to the surface, where it can be used directly as heat or indirectly to generate electricity by turning on rotating turbines.
Since the water beneath the earth's surface is constantly replenished, and the Earth's core will continue to generate heat relative to human life indefinitely, geothermal energy, in ultimately, clean and renewable.
Methods for collecting the Earth's energy resources
Today there are three main methods for collecting geothermal energy: dry steam, hot water and the binary cycle. The dry steam process directly drives the turbine drives of electricity generators. Hot water flows from the bottom up, then is sprayed into the tank to create steam to drive the turbines. These two methods are the most common, generating hundreds of megawatts of electricity in the US, Iceland, Europe, Russia and other countries. But location is limited since these plants operate only in tectonic regions where access to heated water is easier.
With binary cycle technology, warm (not necessarily hot) water is extracted to the surface and combined with butane or pentane, which has low temperature boiling. This liquid is pumped through a heat exchanger where it is evaporated and sent through a turbine before being recirculated back into the system. Binary cycle technologies provide tens of megawatts of electricity in the United States: California, Nevada and Hawaii.
The principle of energy production
Disadvantages of Geothermal Energy
At the utility level, geothermal power plants are expensive to build and operate. Finding a suitable location requires expensive well surveys with no guarantee of hitting a productive underground hot spot. However, analysts expect this capacity to nearly double over the next six years.
In addition, areas with high temperature underground sources are located in areas with active geological and chemical volcanoes. These "hot spots" form at the boundaries of tectonic plates in places where the crust is quite thin. The Pacific region, often referred to as the ring of fire for many volcanoes, has many hot spots, including in Alaska, California and Oregon. Nevada has hundreds of hot spots covering much of the northern United States.
There are other seismic active areas. Earthquakes and the movement of magma allow the water to circulate. In some places, water rises to the surface and natural hot springs and geysers occur, such as in Kamchatka. The water in the geysers of Kamchatka reaches 95° C. 
One of the problems with an open geyser system is the release of certain air pollutants. Hydrogen sulfide is a toxic gas with a very recognizable odor " rotten egg" - Not large number arsenic and minerals released with steam. Salt can also pose an environmental problem.
In offshore geothermal power plants, significant amounts of interfering salt accumulate in the pipes. In closed systems there are no emissions and all liquid brought to the surface is returned.
Economic potential of the energy resource
Seismically active points are not the only places where geothermal energy can be found. There is a constant supply useful heat for direct heating purposes at depths anywhere from 4 meters to several kilometers below the surface almost anywhere on earth. Even the soil in your own backyard or local school has economic potential in the form of heat to be released into the house or other buildings.
In addition, there is a huge amount of thermal energy in dry rock formations very deep below the surface (4 – 10 km).
Using the new technology could expand geothermal systems, where people could use that heat to produce electricity on a much larger scale than conventional technologies. The first demonstration projects of this principle of generating electricity were shown in the United States and Australia back in 2013.
If the full economic potential of geothermal resources can be realized, it will represent a huge source of electricity for production capacity. Scientists estimate that conventional geothermal sources have a potential of 38,000 MW, which can produce 380 million MW of electricity per year.
Hot dry rocks occur at depths of 5 to 8 km everywhere underground and at shallower depths in certain places. Access to these resources involves the introduction of cold water, circulation through hot rocks and the removal of heated water. There are currently no commercial applications for this technology. Existing technologies do not yet allow the recovery of thermal energy directly from magma, very deeply, but this is the most powerful resource geothermal energy.
With the combination of energy resources and its consistency, geothermal energy can play an indispensable role as a cleaner, more sustainable energy system.
Geothermal power plant structures
Geothermal energy is pure and stable heat from the Earth. Great resources are found in a range of several kilometers below the earth's surface, and even deeper, to high temperature molten rock called magma. But as described above, people have not yet reached the magma.
Three designs of geothermal power plants
The technology of application is determined by the resource. If the water comes from the well as steam, it can be used directly. If the hot water is at a high enough temperature it must pass through a heat exchanger.
The first well for energy production was drilled before 1924. Deeper wells were drilled in the 1950s, but real development occurred in the 1970s and 1980s.
Direct use of geothermal heat
Geothermal sources can also be used directly for heating purposes. Hot water is used to heat buildings, grow plants in greenhouses, dry fish and crops, improve oil recovery, aid in industrial processes such as milk pasteurizers, and heat water in fish farms. In the United States, Klamath Falls, Oregon and Boise, Idaho, have used geothermal water to heat homes and buildings for over a century. On the East Coast, Warm Springs, Virginia gets its heat directly from spring water using heat sources at one of the local resorts.
In Iceland, almost every building in the country is heated by hot spring water. In fact, Iceland gets more than 50 percent of its primary energy from geothermal sources. In Reykjavik, for example (population 118 thousand), hot water is conveyed by conveyor over 25 kilometers, and residents use it for heating and natural needs.
New Zealand receives an additional 10% of its electricity. is underdeveloped, despite the presence of thermal waters.
As society developed and became established, humanity began to look for more and more modern and at the same time economical ways obtaining energy. For this purpose, various stations are being built today, but at the same time, the energy contained in the bowels of the earth is widely used. What is it like? Let's try to figure it out.
Geothermal energy
Already from the name it is clear that it represents the heat of the earth’s interior. Under the earth's crust there is a layer of magma, which is a fiery liquid silicate melt. According to research data, the energy potential of this heat is much higher than the energy of world reserves natural gas, as well as oil. Magma - lava - comes to the surface. Moreover, the greatest activity is observed in those layers of the earth on which the boundaries of tectonic plates are located, as well as where the earth’s crust is characterized by thinness. Geothermal energy from the earth is obtained as follows: Lava and the planet's water resources come into contact, causing the water to begin to heat up sharply. This leads to the eruption of the geyser, the formation of so-called hot lakes and underwater currents. That is, precisely those natural phenomena whose properties are actively used as energy.
Artificial geothermal springs
The energy contained in the bowels of the earth must be used wisely. For example, there is an idea to create underground boilers. To do this, you need to drill two wells of sufficient depth, which will be connected at the bottom. That is, it turns out that in almost any corner of the land it is possible to obtain geothermal energy using an industrial method: cold water will be pumped into the formation through one well, and hot water or steam will be extracted through the second. Artificial heat sources will be profitable and rational if the resulting heat produces more energy. The steam can be sent to turbine generators, which will generate electricity.
Of course, the heat removed is only a fraction of what is available in the total reserves. But it should be remembered that the deep heat will be constantly replenished due to the processes of compression of rocks and stratification of the subsoil. As experts say, the earth's crust accumulates heat, total quantity which is 5000 times greater than the calorific value of all the fossil fuels of the earth as a whole. It turns out that the operating time of such artificially created geothermal stations can be unlimited.
Features of sources
The sources that make it possible to obtain geothermal energy are almost impossible to fully utilize. They exist in more than 60 countries around the world, with the largest number of land-based volcanoes on the territory of the Pacific volcanic ring of fire. But in practice it turns out that geothermal sources in different regions of the world are completely different in their properties, namely average temperature, salinity, gas composition, acidity and so on.
Geysers are sources of energy on Earth, the peculiarity of which is that they spew boiling water at certain intervals. After the eruption has occurred, the pool becomes free of water; at its bottom you can see a channel that goes deep into the ground. Geysers are used as energy sources in regions such as Kamchatka, Iceland, New Zealand and North America, and single geysers are found in some other areas.
Where does the energy come from?
Uncooled magma is located very close to the earth's surface. Gases and vapors are released from it, which rise and pass through the cracks. Mixing with groundwater, they cause them to heat up and themselves turn into hot water in which many substances are dissolved. Such water is released to the surface of the earth in the form of various geothermal sources: hot springs, mineral springs, geysers, and so on. According to scientists, the hot bowels of the earth are caves or chambers connected by passages, cracks and channels. They are just being filled with underground waters, and very close to them there are pockets of magma. So naturally and the thermal energy of the earth is generated.
Earth's electric field
There is another alternative source of energy in nature, which is renewable, environmentally friendly, and easy to use. True, this source is still only being studied and not used in practice. So, the potential energy of the Earth lies in its electric field. Energy can be obtained in this way by studying the basic laws of electrostatics and the characteristics of the Earth's electric field. Essentially, our planet, from an electrical point of view, is a spherical capacitor charged up to 300,000 volts. Its inner sphere has a negative charge, and its outer sphere - the ionosphere - has a positive charge. is an insulator. Through it there is a constant flow of ionic and convective currents, which reach a force of many thousands of amperes. However, the potential difference between the plates does not decrease.
This suggests that in nature there is a generator, the role of which is to constantly replenish the leakage of charges from the capacitor plates. The role of such a generator is the Earth’s magnetic field, rotating together with our planet in the flow of solar wind. The energy of the Earth's magnetic field can be obtained precisely by connecting an energy consumer to this generator. To do this, you need to install reliable grounding.
Renewable sources
As our planet's population grows steadily, we need more and more energy to power our population. The energy contained in the bowels of the earth can be very different. For example, there are renewable sources: wind, solar and water energy. They are environmentally friendly, and therefore can be used without fear of harming the environment.
Water energy
This method has been used for many centuries. Today, a huge number of dams and reservoirs have been built in which water is used to generate electrical energy. The essence of the operation of this mechanism is simple: under the influence of the river flow, the wheels of the turbines rotate, and accordingly, the water energy is converted into electricity.
Today there are a large number of hydroelectric power plants that convert the energy of water flow into electricity. The peculiarity of this method is that they are renewed, and, accordingly, such structures have a low cost. That is why, despite the fact that the construction of hydroelectric power stations takes quite a long time, and the process itself is very expensive, these structures still have a significant advantage over electricity-intensive industries.
Solar energy: modern and promising
Solar energy is obtained using solar panels, but modern technologies allow the use of new methods for this. The largest system in the world is built in the California desert. It fully supplies energy to 2,000 homes. The design works as follows: mirrors reflect sun rays, which are sent to the central water boiler. It boils and turns into steam, which rotates the turbine. It, in turn, is connected to an electric generator. Wind can also be used as the energy that the Earth gives us. The wind inflates the sails and turns the mills. And now, with its help, you can create devices that will generate electrical energy. By rotating the windmill blades, it drives the turbine shaft, which in turn is connected to an electric generator.
Internal energy of the Earth
It appeared as a result of several processes, the main ones being accretion and radioactivity. According to scientists, the formation of the Earth and its mass occurred over several million years, and this happened due to the formation of planetesimals. They stuck together, and accordingly, the mass of the Earth became more and more. After our planet began to have its modern mass, but was still devoid of an atmosphere, meteoroid and asteroid bodies fell unhindered on it. This process is precisely called accretion, and it led to the release of significant gravitational energy. And the larger the bodies that hit the planet, the greater the volume of energy contained in the bowels of the Earth.
This gravitational differentiation led to the fact that substances began to stratify: heavy substances simply sank, while light and volatile ones floated up. Differentiation also affected the additional release of gravitational energy.
Atomic energy
Using the earth's energy can happen in different ways. For example, through the construction of nuclear power plants, when thermal energy is released due to the decay of the smallest particles of atomic matter. The main fuel is uranium, which is contained in earth's crust. Many believe that this particular method of generating energy is the most promising, but its use is associated with a number of problems. First, uranium emits radiation that kills all living organisms. In addition, if this substance gets into the soil or atmosphere, then a real man-made disaster. The sad consequences of the accident Chernobyl nuclear power plant we experience it to this day. The danger lies in the fact that radioactive waste can threaten all living things for a very, very long time, for millennia.
New time - new ideas
Of course, people do not stop there, and every year more and more attempts are made to find new ways to obtain energy. If the earth's heat energy is obtained quite simply, then some methods are not so simple. For example, it is quite possible to use biological gas, which is obtained by rotting waste, as an energy source. It can be used for heating houses and heating water.
Increasingly, they are being built when dams and turbines are installed across the mouths of reservoirs, which are driven by the ebb and flow of tides, respectively, generating electricity.
By burning garbage we get energy
Another method, which is already used in Japan, is the creation of waste incineration plants. Today they are built in England, Italy, Denmark, Germany, France, the Netherlands and the USA, but only in Japan did these enterprises begin to be used not only for their intended purpose, but also to generate electricity. Local factories burn 2/3 of all waste, and the factories are equipped with steam turbines. Accordingly, they supply heat and electricity to nearby areas. Moreover, in terms of costs, building such an enterprise is much more profitable than building a thermal power plant.
The prospect of using the Earth's heat where volcanoes are concentrated looks more tempting. In this case, there will be no need to drill the Earth too deeply, since already at a depth of 300-500 meters the temperature will be at least twice as high as the boiling point of water.
There is also such a way to generate electricity as Hydrogen - the simplest and easiest chemical element- can be considered an ideal fuel, because it exists where there is water. If you burn hydrogen, you can get water, which decomposes into oxygen and hydrogen. The hydrogen flame itself is harmless, that is, it will not cause harm to the environment. The peculiarity of this element is that it has a high calorific value.
What's next?
Of course, the energy of the Earth’s magnetic field or that obtained at nuclear power plants cannot fully satisfy all the needs of humanity, which are growing every year. However, experts say that there is no reason to worry, since the planet still has enough fuel resources. Moreover, more and more new sources, environmentally friendly and renewable, are being used.
The problem of pollution remains environment, and it is growing catastrophically quickly. Quantity harmful emissions goes off scale, accordingly, the air we breathe is harmful, the water has dangerous impurities, and the soil is gradually depleted. That is why it is so important to promptly study such a phenomenon as energy in the bowels of the Earth in order to look for ways to reduce the need for fossil fuels and more actively use non-traditional energy sources.
Doctor of Technical Sciences N.A. I hate it, professor,
academician Russian Academy technological sciences, Moscow
In recent decades, the world has been considering the direction of more effective use energy of the Earth's deep heat in order to partially replace natural gas, oil, and coal. This will become possible not only in areas with high geothermal parameters, but also in any areas globe when drilling injection and production wells and creating circulation systems between them.
In recent decades, the world's interest in alternative sources energy is caused by the depletion of hydrocarbon fuel reserves and the need to solve a number of environmental problems. Objective factors (fossil fuel and uranium reserves, as well as changes in the environment caused by traditional fire and nuclear energy) suggest that the transition to new methods and forms of energy production is inevitable.
The world economy is currently heading towards a transition to a rational combination of traditional and new energy sources. The warmth of the Earth occupies one of the first places among them.
Geothermal energy resources are divided into hydrogeological and petrogeothermal. The first of them are represented by coolants (accounting for only 1% of the total geothermal energy resources) - groundwater, steam and steam-water mixtures. The latter represent geothermal energy contained in hot rocks.
The fountain technology (self-flowing) used in our country and abroad for the extraction of natural steam and geothermal waters is simple, but ineffective. With a low flow rate of self-flowing wells, their heat production can recoup the cost of drilling only at a shallow depth of geothermal reservoirs with high temperatures in areas of thermal anomalies. The service life of such wells in many countries does not even reach 10 years.
At the same time, experience confirms that in the presence of shallow natural steam reservoirs, the construction of a geothermal power plant is the most profitable option for using geothermal energy. The operation of such geothermal power plants has shown their competitiveness compared to other types of power plants. Therefore, the use of reserves of geothermal waters and hydrothermal steam in our country on the Kamchatka Peninsula and on the islands of the Kuril ridge, in the regions of the North Caucasus, and also possibly in other areas is advisable and timely. But steam deposits are rare; its known and predicted reserves are small. Much more common deposits of thermal energy water are not always located close enough to the consumer - the heat supply object. This excludes the possibility of their effective use on a large scale.
Often in complex problem issues of combating salt deposits are growing. The use of geothermal, usually mineralized, sources as a coolant leads to overgrowing of well zones with iron oxide, calcium carbonate and silicate formations. In addition, problems of erosion-corrosion and scale deposits negatively affect the operation of equipment. The problem also becomes the discharge of mineralized waste water containing toxic impurities. Therefore, the simplest fountain technology cannot serve as the basis for the widespread development of geothermal resources.
According to preliminary estimates on the territory of the Russian Federation, the forecast reserves of thermal waters with a temperature of 40-250 °C, a salinity of 35-200 g/l and a depth of up to 3000 m are 21-22 million m3/day, which is equivalent to burning 30-40 million tons of hydrocarbons. .T. per year.
The forecast reserves of steam-air mixture with a temperature of 150-250 °C on the Kamchatka Peninsula and the Kuril Islands is 500 thousand m3/day. and reserves of thermal waters with a temperature of 40-100 °C - 150 thousand m3/day.
The priority for development is considered to be thermal water reserves with a flow rate of about 8 million m3/day, with a salinity of up to 10 g/l and a temperature above 50 °C.
Of much greater importance for the energy sector of the future is the extraction of thermal energy, practically inexhaustible petrogeothermal resources. This geothermal energy, contained in solid hot rocks, accounts for 99% of the total underground thermal energy resources. At a depth of 4-6 km, massifs with a temperature of 300-400 °C can be found only near the intermediate centers of some volcanoes, but hot rocks with a temperature of 100-150 °C are distributed almost everywhere at these depths, and with a temperature of 180-200 °C in a fairly large part territory of Russia.
For billions of years, nuclear, gravitational and other processes inside the Earth have generated and are generating thermal energy. Some of it is emitted into outer space, and the heat is accumulated in the depths, i.e. The heat content of the solid, liquid and gaseous phases of earthly matter is called geothermal energy.
The continuous generation of intraterrestrial heat compensates for its external losses, serves as a source of accumulation of geothermal energy and determines the renewable part of its resources. The total transfer of heat from the subsoil to the earth's surface is three times higher than the current capacity of power plants in the world and is estimated at 30 TW.
However, it is clear that renewability matters only for limited natural resources, and the total potential of geothermal energy is practically inexhaustible, since it should be defined as the total amount of heat available to the Earth.
It is no coincidence that in recent decades, the world has been considering the direction of more efficient use of the energy of the Earth's deep heat with the aim of partially replacing natural gas, oil, and coal. This will become possible not only in areas with high geothermal parameters, but also in any area of the globe when drilling injection and production wells and creating circulation systems between them.
Of course, with low thermal conductivity of rocks for efficient work circulation systems must have or create a sufficiently developed heat exchange surface in the heat extraction zone. Such a surface is possessed by porous strata and zones of natural fracture resistance that are often found at the above depths, the permeability of which makes it possible to organize forced filtration of the coolant with the effective extraction of energy from rocks, as well as the artificial creation of an extensive heat exchange surface in low-permeability porous massifs by hydraulic fracturing (see figure).
Currently, hydraulic fracturing is used in the oil and gas industry as a way to increase the permeability of formations to enhance oil recovery during the development of oil fields. Modern technology allows you to create a narrow but long crack, or a short but wide one. There are known examples of hydraulic fracturing with cracks up to 2-3 km long.
The domestic idea of extracting the main geothermal resources contained in solid rocks was expressed back in 1914 by K.E. Tsiolkovsky, and in 1920 the geothermal circulation system (GCS) in a hot granite massif was described by V.A. Obruchev.
In 1963, the first GCS was created in Paris to extract heat from porous rocks for heating and air conditioning in the premises of the Broadcasting Chaos complex. In 1985, there were already 64 GCS operating in France with a total thermal capacity of 450 MW, with annual savings of approximately 150 thousand tons of oil. In the same year, the first similar GVC was created in the USSR in the Khankala Valley near the city of Grozny.
In 1977, under the project of the Los Alamos National Laboratory in the USA, tests of an experimental GVC with hydraulic fracturing of an almost impermeable massif began at the Fenton Hill site in New Mexico. Cold fresh water injected through the well (injection) was heated due to heat exchange with the rock mass (185 OS) in a vertical crack with an area of 8000 m2, formed by hydraulic fracturing at a depth of 2.7 km. Through another well (production), also crossing this crack, superheated water came to the surface in the form of a jet of steam. When circulating in a closed loop under pressure, the temperature of superheated water on the surface reached 160-180 °C, and the thermal power of the system reached 4-5 MW. Coolant leaks into the surrounding area were about 1% total flow. The concentration of mechanical and chemical impurities (up to 0.2 g/l) corresponded to the conditions of fresh water drinking water. The hydraulic fracture did not require support and was maintained open by the hydrostatic pressure of the fluid. The free convection developing in it ensured the effective participation in heat exchange of almost the entire surface of the hot rock mass outcrop.
Extraction of underground thermal energy from hot impermeable rocks, based on the methods of inclined drilling and hydraulic fracturing developed and long practiced in the oil and gas industry, did not cause seismic activity or any other harmful effects on the environment.
In 1983, British scientists repeated the American experience by creating an experimental GCS with hydraulic fracturing of granites in Carnwell. Similar work was carried out in Germany and Sweden. There are more than 224 geothermal heating projects in the United States. It is assumed that geothermal resources can provide the bulk of the US's future needs for thermal energy for non-electrical needs. In Japan, the capacity of geothermal power plants in 2000 reached approximately 50 GW.
Currently, research and exploration of geothermal resources is carried out in 65 countries. In the world, stations with a total capacity of about 10 GW have been created based on geothermal energy. The UN provides active support for the development of geothermal energy.
The experience gained in many countries around the world in the use of geothermal coolants shows that under favorable conditions they are 2-5 times more profitable than thermal and nuclear power plants. Calculations show that one geothermal well can replace 158 thousand tons of coal per year.
Thus, the heat of the Earth is perhaps the only large, renewable energy resource, the rational development of which promises to reduce the cost of energy compared to modern fuel energy. With equally inexhaustible energy potential Solar and thermonuclear installations, unfortunately, will be more expensive than existing fuel ones.
Despite the very long history of harnessing the Earth’s heat, today geothermal technology has not yet reached its high development. Developing the Earth's thermal energy experiences great difficulties during construction deep wells, which are a channel for bringing the coolant to the surface. Due to the high temperature at the bottom (200-250 °C), traditional rock cutting tools are unsuitable for working in such conditions; special requirements are imposed on the selection of drilling and casing pipes, cement slurries, drilling technology, casing and completion of wells. Domestic measuring equipment, serial operational fittings and equipment are produced in versions that allow temperatures not higher than 150-200 °C. Traditional deep mechanical drilling of wells sometimes takes years and requires significant financial costs. In fixed production assets, the cost of wells ranges from 70 to 90%. This problem can and should be solved only by creating advanced technology development of the bulk of geothermal resources, i.e. extracting energy from hot rocks.
Our group of Russian scientists and specialists has been dealing with the problem of extracting and using the inexhaustible, renewable deep thermal energy of hot rocks of the Earth on the territory of the Russian Federation for many years. The goal of the work is to create, based on domestic, high technologies technical means for deep penetration into the depths of the earth's crust. Currently, several variants of drilling assemblies (DS) have been developed, which have no analogues in world practice.
The operation of the first version of the BS is linked to the current traditional well drilling technology. Drilling speed for hard rocks (average density 2500-3300 kg/m3) up to 30 m/h, hole diameter 200-500 mm. The second version of the BS drills wells in an autonomous and automatic mode. The launch is carried out from a special launching and acceptance platform, from which its movement is controlled. One thousand meters of BS in hard rock can be covered within a few hours. Well diameter is from 500 to 1000 mm. Reusable BS options have great cost-effectiveness and enormous potential value. The introduction of BS into production will open up new stage in the construction of wells and provide access to the Earth's inexhaustible sources of thermal energy.
For heat supply needs, the required depth of wells throughout the country ranges from up to 3-4.5 thousand m and does not exceed 5-6 thousand m. The coolant temperature for housing and communal heat supply does not go beyond 150 °C. For industrial facilities, the temperature, as a rule, does not exceed 180-200 °C.
The purpose of creating a GCS is to provide constant, accessible, cheap heat to remote, hard-to-reach and undeveloped areas of the Russian Federation. The duration of operation of the GCS is 25-30 years or more. Payback period of stations (including latest technologies drilling) - 3-4 years.
The creation in the Russian Federation in the coming years of appropriate capacities for the use of geothermal energy for non-electrical needs will make it possible to replace about 600 million tons of fuel equivalent. Savings could amount to up to 2 trillion rubles.
By 2030, it becomes possible to create energy capacity to replace fire energy by up to 30%, and by 2040, almost completely eliminate organic raw materials as fuel from the energy balance of the Russian Federation.
Literature
1. Goncharov S.A. Thermodynamics. M.: MGTUim. N.E. Bauman, 2002. 440 p.
2. Dyadkin Yu.D. and others. Geothermal thermophysics. St. Petersburg: Nauka, 1993. 255 p.
3. Mineral resource base of the fuel and energy complex of Russia. Condition and prognosis / V.K. Branchugov, E.A. Gavrilov, V.S. Litvinenko and others. Ed. V.Z. Garipova, E.A. Kozlovsky. M. 2004. 548 p.
4. Novikov G.P. et al. Drilling wells for thermal waters. M.: Nedra, 1986. 229 p.
The main sources of thermal energy of the Earth are [, ]:
To date, only the first four sources have been quantified. In our country, the main credit for this goes to O.G. Sorokhtin And S.A. Ushakov. The data below is mainly based on the calculations of these scientists.
Heat of Earth's gravitational differentiation
One of the most important patterns in the development of the Earth is differentiation its substance, which continues to this day. Due to this differentiation, the formation occurred core and crust, change in the composition of the primary mantle, while the division of an initially homogeneous substance into fractions of different densities is accompanied by the release thermal energy, and the maximum heat release occurs when the earth's matter is divided into dense and heavy core and residual lighter silicate shell - earth's mantle. Currently, the bulk of this heat is released at the boundary mantle - core.
Energy of gravitational differentiation of the Earth over the entire period of its existence, it stood out - 1.46*10 38 erg (1.46*10 31 J). This energy for the most part first goes into kinetic energy convective currents of mantle matter, and then in warm; the other part of it is spent on additional compression of the earth's interior, arising due to the concentration of dense phases in the central part of the Earth. From 1.46*10 38 erg the energy of the Earth's gravitational differentiation went into its additional compression 0.23*10 38 erg (0.23*10 31 J), and was released in the form of heat 1.23*10 38 erg (1.23*10 31 J). The magnitude of this thermal component significantly exceeds the total release of all other types of energy in the Earth. The time distribution of the total value and rate of release of the thermal component of gravitational energy is shown in Fig. 3.6 .
Rice. 3.6.
The current level of heat generation during gravitational differentiation of the Earth is 3*10 20 erg/s (3*10 13 W), which is from the size of the modern heat flow, passing through the surface of the planet at ( 4.2-4.3)*10 20 erg/s ((4.2-4.3)*10 13 W), is ~ 70%
.
Radiogenic heat
Caused by the radioactive decay of unstable isotopes. The most energy-intensive and long-lived ( with half-life, commensurate with the age of the Earth) are isotopes 238 U, 235 U, 232 Th And 40 K. Their main volume is concentrated in continental crust. Current level of generation radiogenic heat:
- by American geophysicist V. Vaquier - 1.14*10 20 erg/s (1.14*10 13 W) ,
- by Russian geophysicists O.G. Sorokhtin And S.A. Ushakov - 1.26*10 20 erg/s(1.26*10 13 W) .
This is ~ 27-30% of the current heat flow.
From the total amount of radioactive decay heat in 1.26*10 20 erg/s (1.26*10 13 W) in the earth's crust stands out - 0.91*10 20 erg/s, and in the mantle - 0.35*10 20 erg/s. It follows that the share of mantle radiogenic heat does not exceed 10% of the total modern heat losses of the Earth, and it cannot be the main source of energy for active tectono-magmatic processes, the depth of their origin can reach 2900 km; and the radiogenic heat released in the crust is relatively quickly lost through the earth's surface and practically does not participate in heating the deep interior of the planet.
In past geological epochs, the amount of radiogenic heat released in the mantle must have been higher. Its estimates at the time of the formation of the Earth ( 4.6 billion years ago) give - 6.95*10 20 erg/s. Since this time, there has been a steady decrease in the rate of release of radiogenic energy (Fig. 3.7 ).
For all the time in the Earth, it has been released ~4.27*10 37 erg(4.27*10 30 J) thermal energy of radioactive decay, which is almost three times lower than the total heat of gravitational differentiation.
Tidal Friction Heat
It stands out during the gravitational interaction of the Earth primarily with the Moon, as the nearest large cosmic body. Due to mutual gravitational attraction, tidal deformations arise in their bodies - swelling or humps. The tidal humps of the planets, with their additional attraction, influence their movement. Thus, the attraction of both tidal humps of the Earth creates a pair of forces acting both on the Earth itself and on the Moon. However, the influence of the near swelling, facing the Moon, is somewhat stronger than that of the distant one. Due to the fact that the angular speed of rotation modern Earth (7.27*10 -5 s -1) exceeds the orbital speed of the Moon ( 2.66*10 -6 s -1), and the substance of the planets is not ideally elastic, then the tidal humps of the Earth seem to be carried away by its forward rotation and noticeably advance the movement of the Moon. This leads to the fact that the maximum tides of the Earth always occur on its surface somewhat later than the moment climax of the Moon, and an additional moment of force acts on the Earth and the Moon (Fig. 3.8 ) .
The absolute values of the tidal interaction forces in the Earth-Moon system are now relatively small and the tidal deformations of the lithosphere caused by them can reach only a few tens of centimeters, but they lead to a gradual slowdown of the Earth’s rotation and, conversely, to an acceleration of the orbital movement of the Moon and to its distance from the Earth. The kinetic energy of the movement of the earth's tidal humps turns into thermal energy due to internal friction of the substance in the tidal humps.
Currently, the rate of tidal energy release is G. Macdonald amounts to ~0.25*10 20 erg/s (0.25*10 13 W), while its main part (about 2/3) is presumably dissipates(dissipates) in the hydrosphere. Consequently, the fraction of tidal energy caused by the interaction of the Earth with the Moon and dissipated in the solid Earth (primarily in the asthenosphere) does not exceed 2 %
total thermal energy generated in its depths; and the share of solar tides does not exceed 20 %
from the effects of lunar tides. Therefore, solid tides now play virtually no role in feeding tectonic processes with energy, but in some cases they can act as “triggers”, for example earthquakes.
The amount of tidal energy is directly related to the distance between space objects. And if the distance between the Earth and the Sun does not assume any significant changes on a geological time scale, then in the Earth-Moon system this parameter is a variable value. Regardless of ideas about almost all researchers admit that early stages development of the Earth, the distance to the Moon was significantly less than modern, but in the process of planetary development, according to most scientists, it gradually increases, and according to Yu.N. Avsyuku this distance experiences long-term changes in the form of cycles "coming and going" of the Moon. It follows from this that in past geological epochs the role of tidal heat in the overall heat balance of the Earth was more significant. In general, over the entire period of the Earth’s development, it has evolved ~3.3*10 37 erg (3.3*10 30 J) tidal heat energy (this is subject to the successive removal of the Moon from the Earth). The change in the rate of release of this heat over time is shown in Fig. 3.10 .
More than half of the total tidal energy was released in catarchaea (shit)) - 4.6-4.0 billion years ago, and at that time only due to this energy the Earth could additionally warm up by ~500 0 C. Starting from the late Archean, lunar tides made only a negligible impact on the development energy-intensive endogenous processes .
Accretion heat
This is the heat retained by the Earth since its formation. In progress accretion, which lasted for several tens of millions of years, thanks to the collision planetesimals The Earth experienced significant heating. However, there is no consensus on the magnitude of this heating. Currently, researchers are inclined to believe that during the process of accretion the Earth experienced, if not complete, then significant partial melting, which led to the initial differentiation of the Proto-Earth into a heavy iron core and a light silicate mantle, and to the formation "magma ocean" on its surface or at shallow depths. Although even before the 1990s, the model of a relatively cold primary Earth, which gradually warmed up due to the above processes, accompanied by the release of a significant amount of thermal energy, was considered almost universally accepted.
An accurate assessment of the primary accretion heat and its fraction preserved to the present day is associated with significant difficulties. By O.G. Sorokhtin And S.A. Ushakov, who are supporters of the relatively cold primary Earth, the amount of accretion energy converted into heat is - 20.13*10 38 erg (20.13*10 31 J). This energy, in the absence of heat loss, would be enough for complete evaporation earthly matter, because the temperature could rise to 30 000 0 С. But the accretion process was relatively long, and the energy of planetesimal impacts was released only in the near-surface layers of the growing Earth and was quickly lost with thermal radiation, so the initial heating of the planet was not great. The magnitude of this thermal radiation, going in parallel with the formation (accretion) of the Earth, these authors estimate at 19.4*10 38 erg (19.4*10 31 J)
.
In the modern energy balance of the Earth, accretion heat most likely plays a minor role.
People have long known about the spontaneous manifestations of gigantic energy hidden in the depths of the globe. The memory of mankind contains legends about catastrophic volcanic eruptions that claimed millions of human lives and changed the appearance of many places on Earth beyond recognition. The power of the eruption of even a relatively small volcano is colossal; it is many times greater than the power of the largest power plants created by human hands. True, there is no need to talk about the direct use of the energy of volcanic eruptions: people do not yet have the ability to curb this unruly element, and, fortunately, these eruptions are quite rare events. But these are manifestations of energy hidden in the bowels of the earth, when only a tiny fraction of this inexhaustible energy finds release through the fire-breathing vents of volcanoes.
The small European country of Iceland (“the land of ice” in literal translation) is completely self-sufficient in tomatoes, apples and even bananas! Numerous Icelandic greenhouses receive energy from the heat of the earth; there are practically no other local energy sources in Iceland. But this country is very rich hot springs and famous geysers - fountains hot water, with the precision of a chronometer bursting out of the ground. And although Icelanders do not have priority in using the heat of underground sources (even the ancient Romans brought water from underground to the famous baths - the Baths of Caracalla), the inhabitants of this small northern country the underground boiler room is operated very intensively. The capital city of Reykjavik, where half the country's population lives, is heated only by underground sources. Reykjavik is the ideal starting point for exploring Iceland: from here you can go on the most interesting and varied excursions to any corner of this unique country: geysers, volcanoes, waterfalls, rhyolite mountains, fjords... Everywhere in Reykjavik you will feel PURE ENERGY - the thermal energy of geysers gushing from underground, the energy of purity and space of a perfectly green city, the energy of cheerful and incendiary nightlife Reykjavik all year round.
But people draw energy from the depths of the earth not only for heating. Power plants using hot underground springs have been operating for a long time. The first such power plant, still very low-power, was built in 1904 in the small Italian town of Larderello, named after the French engineer Larderelli, who back in 1827 drew up a project for using the numerous hot springs in the area. Gradually, the power of the power plant grew, more and more new units were put into operation, new sources of hot water were used, and today the power of the station has already reached an impressive value - 360 thousand kilowatts. In New Zealand, there is such a power plant in the Wairakei area, its capacity is 160 thousand kilowatts. 120 km from San Francisco in the USA, a geothermal station with a capacity of 500 thousand kilowatts produces electricity.
Geothermal energy
People have long known about the spontaneous manifestations of gigantic energy hidden in the depths of the globe. The memory of mankind contains legends about catastrophic volcanic eruptions that claimed millions of human lives and changed the appearance of many places on Earth beyond recognition. The power of the eruption of even a relatively small volcano is colossal; it is many times greater than the power of the largest power plants created by human hands. True, there is no need to talk about the direct use of the energy of volcanic eruptions - people do not yet have the ability to curb this rebellious element, and, fortunately, these eruptions are quite rare events. But these are manifestations of energy hidden in the bowels of the earth, when only a tiny fraction of this inexhaustible energy finds release through the fire-breathing vents of volcanoes.
A geyser is a hot spring that spews its water at a regular or irregular height, like a fountain. The name comes from the Icelandic word for "to pour". The appearance of geysers requires a certain favorable environment, which is created only in a few places on earth, which makes them quite rare. Almost 50% of geysers are located in national park Yellowstone (USA). The activity of a geyser may cease due to changes in the subsoil, earthquakes and other factors. The action of a geyser is caused by the contact of water with magma, after which the water quickly heats up and, under the influence of geothermal energy, is thrown upward with force. After the eruption, the water in the geyser gradually cools, seeps back into the magma, and gushes out again. The frequency of eruptions of different geysers varies from several minutes to several hours. The need for high energy for geysers to operate is the main reason for their rarity. Volcanic areas may have hot springs, mud volcanoes, fumaroles, but there are very few places where geysers are found. The fact is that even if a geyser was formed in a place of volcanic activity, subsequent eruptions will destroy the surface of the earth and change its condition, which will lead to the disappearance of the geyser.
Earth energy (geothermal energy) is based on the use natural warmth Earth. The bowels of the Earth contain a colossal, almost inexhaustible source of energy. The annual radiation of internal heat on our planet is 2.8 * 1014 billion kW * hour. It is constantly compensated by the radioactive decay of certain isotopes in the earth's crust.
Geothermal energy sources can be of two types. The first type is underground pools of natural heat carriers - hot water (hydrothermal springs), or steam (steam thermal springs), or a steam-water mixture. Essentially, these are ready-to-use "underground boilers" from which water or steam can be extracted using conventional boreholes. The second type is the heat of hot rocks. By pumping water into such horizons, it is also possible to obtain steam or superheated water for further use for energy purposes.
But in both use cases main drawback lies, perhaps, in a very weak concentration of geothermal energy. However, in places where peculiar geothermal anomalies form, where hot springs or rocks come relatively close to the surface and where, when immersed deeper for every 100 m, the temperature increases by 30-40 ° C, concentrations of geothermal energy can create conditions for its economic use. Depending on the temperature of water, steam or steam-water mixture, geothermal sources are divided into low and medium temperature (with temperatures up to 130 - 150° C) and high temperature (over 150°). The nature of their use largely depends on the temperature.
It can be argued that geothermal energy has four beneficial distinguishing features.
Firstly, its reserves are practically inexhaustible. According to estimates from the late 70s, to a depth of 10 km, they amount to a value that is 3.5 thousand times higher than reserves traditional types mineral fuel.
Secondly, geothermal energy is quite widespread. Its concentration is mainly associated with belts of active seismic and volcanic activity, which occupy 1/10 of the Earth's area. Within these belts, we can identify some of the most promising “geothermal areas”, examples of which are California in the USA, New Zealand, Japan, Iceland, Kamchatka, North Caucasus in Russia. Only in former USSR By the beginning of the 90s, about 50 underground hot water and steam pools had been opened.
Thirdly, the use of geothermal energy does not require large costs, because in this case we're talking about about “ready-to-use” energy sources created by nature itself.
Finally, fourthly, geothermal energy is completely harmless from an environmental point of view and does not pollute the environment.
Man has long been using the energy of the internal heat of the Earth (remember, for example, the famous Roman baths), but its commercial use began only in the 20s of our century with the construction of the first geoelectric power stations in Italy, and then in other countries. By the beginning of the 80s, there were about 20 such stations in the world with a total capacity of 1.5 million kW. The largest of them is the Geysers station in the USA (500 thousand kW).
Geothermal energy is used to generate electricity, heat homes, greenhouses, etc. Dry steam, superheated water or any coolant with a low boiling point (ammonia, freon, etc.) are used as a coolant.
