Geothermal energy and methods of its production. Geothermal energy forwards

For Russia, the Earth's heat energy can become a constant, reliable source of cheap and affordable electricity and heat using new high, environmentally friendly technologies for its extraction and supply to the consumer. This is especially true nowadays

Limited resources of fossil energy raw materials

The demand for organic energy raw materials is great in industrialized and developing countries(USA, Japan, countries of united Europe, China, India, etc.). At the same time, these countries’ own hydrocarbon resources are either insufficient or reserved, and a country, for example the United States, buys energy raw materials abroad or develops deposits in other countries.

In Russia, one of the richest countries in terms of energy resources, economic needs for energy are so far satisfied by the possibilities of using natural resources. However, the extraction of fossil hydrocarbon raw materials from the subsoil is very at a fast pace. If in the 1940–1960s. the main oil-producing areas were “Second Baku” in the Volga region and the Urals, then, from the 1970s to the present time, such an area has been Western Siberia. But here, too, there is a significant decrease in the production of fossil hydrocarbons. The era of “dry” Cenomanian gas is becoming a thing of the past. Previous stage of extensive mining development natural gas has come to an end. Its recovery from such giant deposits as Medvezhye, Urengoyskoye and Yamburgskoye amounted to 84, 65 and 50%, respectively. The share of oil reserves favorable for development is also decreasing over time.

Due to the active consumption of hydrocarbon fuels, onshore oil and natural gas reserves have decreased significantly. Now their main reserves are concentrated on continental shelf. And although raw material base oil and gas industry is still sufficient for oil and gas production in Russia in required volumes, in the near future it will be provided all in to a greater extent through the development of deposits with complex mining and geological conditions. The cost of hydrocarbon production will increase.

Most of the non-renewable resources extracted from the subsoil are used as fuel for power plants. First of all, this is , the share of which in the fuel structure is 64%.

In Russia, 70% of electricity is generated at thermal power plants. Energy companies countries annually burn about 500 million tons of e.g. t. in order to generate electricity and heat, while the production of heat consumes 3–4 times more hydrocarbon fuel than the generation of electricity.

The amount of heat obtained from the combustion of these volumes of hydrocarbon raw materials is equivalent to the use of hundreds of tons of nuclear fuel - the difference is huge. However nuclear energy requires security environmental safety(to prevent a recurrence of Chernobyl) and protect it from possible terrorist acts, as well as carry out the safe and expensive decommissioning of obsolete and expired nuclear power plant units. Proven recoverable uranium reserves in the world are about 3 million 400 thousand tons. Over the entire previous period (until 2007), about 2 million tons were mined.

RES as the future of global energy

Raised in last decades In the world, interest in alternative renewable energy sources (RES) is caused not only by the depletion of hydrocarbon fuel reserves, but also by the need to solve environmental problems. Objective factors (fossil fuel and uranium reserves, as well as environmental changes associated with the use of traditional fire and nuclear energy) and energy development trends suggest that the transition to new methods and forms of energy production is inevitable. Already in the first half of the 21st century. There will be a complete or almost complete transition to non-traditional energy sources.

The sooner a breakthrough is made in this direction, the less painful it will be for the entire society and the more beneficial for the country where decisive steps will be taken in this direction.

The world economy has now already set a course for the transition to a rational combination of traditional and new energy sources. Energy consumption in the world by 2000 amounted to more than 18 billion tce. t., and energy consumption by 2025 may increase to 30–38 billion tce. t., according to forecasts, by 2050 consumption may reach 60 billion tce. t. Characteristic trends in the development of the world economy in the period under review are a systematic decrease in the consumption of fossil fuels and a corresponding increase in the use of non-traditional energy resources. The thermal energy of the Earth occupies one of the first places among them.

Currently, the Ministry of Energy of the Russian Federation has adopted a program for the development of non-traditional energy, including 30 major projects the use of heat pump units (HPU), the operating principle of which is based on the consumption of low-grade thermal energy of the Earth.

Low-grade heat energy of the Earth and heat pumps

Sources of low-potential heat energy of the Earth are solar radiation And thermal radiation heated interior of our planet. Currently, the use of such energy is one of the most dynamically developing areas of energy based on renewable energy sources.

The heat of the Earth can be used in various types of buildings and structures for heating, hot water supply, air conditioning (cooling), as well as for heating paths in the winter, preventing icing, heating fields in open stadiums, etc. In English technical literature, systems , utilizing the Earth's heat in heating and air conditioning systems, are designated as GHP - “geothermal heat pumps” (geothermal heat pumps). Climatic characteristics the countries of Central and Northern Europe, which, together with the USA and Canada, are the main areas for the use of low-grade heat from the Earth, determine this mainly for heating purposes; air cooling even in summer period Required relatively rarely. Therefore, unlike the USA, heat pumps in European countries operate mainly in heating mode. In the USA, they are more often used in air heating systems combined with ventilation, which allows both heating and cooling of outside air. In European countries, heat pumps are usually used in water heating systems. Since their efficiency increases as the temperature difference between the evaporator and condenser decreases, underfloor heating systems are often used to heat buildings, in which a coolant circulates at a relatively low temperature (35–40 o C).

Types of systems for using low-potential heat energy from the Earth

IN general case Two types of systems for using low-potential heat energy from the Earth can be distinguished:

– open systems: groundwater supplied directly to heat pumps is used as a source of low-grade thermal energy;

– closed systems: heat exchangers are located in the soil mass; when a coolant with a lower temperature relative to the ground circulates through them, thermal energy is “selected” from the ground and transferred to the evaporator of the heat pump (or when using a coolant with a higher temperature relative to the ground, it is cooled).

The disadvantages of open systems are that wells require maintenance. In addition, the use of such systems is not possible in all areas. The main requirements for soil and groundwater are as follows:

– sufficient permeability of the soil, allowing water reserves to be replenished;

- good chemical composition groundwater (e.g. low iron content), avoiding problems associated with the formation of deposits on the walls of pipes and corrosion.

Closed systems for using low-potential heat energy from the Earth

Closed systems can be horizontal or vertical (Figure 1).

Rice. 1. Scheme of a geothermal heat pump installation with: a – horizontal

and b – vertical ground heat exchangers.

Horizontal ground heat exchanger

In Western and Central Europe horizontal ground heat exchangers usually they are separate pipes laid relatively tightly and connected to each other in series or parallel (Fig. 2).

Rice. 2. Horizontal ground heat exchangers with: a – serial and

b – parallel connection.

To save the area where heat is removed, improved types of heat exchangers have been developed, for example, heat exchangers in the shape of a spiral (Fig. 3), located horizontally or vertically. This form of heat exchangers is common in the USA.

Geothermal energy- this is the energy of heat that is released from the internal zones of the Earth over hundreds of millions of years. According to geological and geophysical studies, the temperature in the Earth's core reaches 3,000-6,000 °C, gradually decreasing in the direction from the center of the planet to its surface. Thousands of volcanoes erupt, blocks move earth's crust, earthquakes indicate the action of the powerful internal energy of the Earth. Scientists believe that the thermal field of our planet is due to radioactive decay in its depths, as well as gravitational separation of core matter.
The main sources of heating the planet's interior are uranium, thorium and radioactive potassium. Processes radioactive decay on continents they occur mainly in the granite layer of the earth's crust at a depth of 20-30 km or more, in the oceans - in the upper mantle. It is assumed that at the base of the earth's crust at a depth of 10-15 km, the probable temperature value on the continents is 600-800 ° C, and in the oceans - 150-200 ° C.
Man can use geothermal energy only where it manifests itself close to the Earth's surface, i.e. in areas of volcanic and seismic activity. Now geothermal energy is effectively used by such countries as the USA, Italy, Iceland, Mexico, Japan, New Zealand, Russia, the Philippines, Hungary, and El Salvador. Here, the internal heat of the earth rises to the very surface in the form of hot water and steam with temperatures up to 300 ° C and often breaks out as the heat of gushing sources (geysers), for example, the famous geysers of Yellowstone Park in the USA, geysers of Kamchatka and Iceland.
Geothermal energy sources divided into dry hot steam, wet hot steam and hot water. A well, which is an important source of energy for electrical railway in Italy (near the city of Larderello), since 1904 it has been feeding dry hot steam. Two other famous hot dry steam sites in the world are the Matsukawa Field in Japan and the Geyser Field near San Francisco, which also have a long and effective use of geothermal energy. The most wet hot steam in the world is found in New Zealand (Wairakei), geothermal fields of slightly less power are in Mexico, Japan, El Salvador, Nicaragua, and Russia.
Thus, four main types of resources can be distinguished geothermal energy:
ground surface heat used by heat pumps;
energy resources of steam, hot and warm water at the surface of the earth, which are now used in the production of electrical energy;
heat concentrated deep below the surface of the earth (possibly in the absence of water);
magma energy and heat that accumulates under volcanoes.

Geothermal heat reserves (~ 8 * 1030J) are 35 billion times greater than annual global energy consumption. Just 1% of the geothermal energy in the earth's crust (10 km depth) can provide an amount of energy that is 500 times greater than all the world's oil and gas reserves. However, today only a small part of these resources can be used, and this is due primarily to economic reasons. The industrial development of geothermal resources (the energy of hot deep waters and steam) began in 1916, when the first geothermal power plant with a capacity of 7.5 MW was commissioned in Italy. Over the past time, considerable experience has been accumulated in the field of practical development of geothermal energy resources. The total installed capacity of existing geothermal power plants (GeoTES) was: 1975 - 1,278 MW, in 1990 - 7,300 MW. The greatest progress in this matter has been achieved by the USA, Philippines, Mexico, Italy, and Japan.
The technical and economic parameters of geothermal power plants vary over a fairly wide range and depend on the geological characteristics of the area (depth of occurrence, parameters of the working fluid, its composition, etc.). For the majority of geothermal power plants put into operation, the cost of electricity is similar to the cost of electricity produced at coal-fired power plants and amounts to 1200 ... 2000 US dollars / MW.
In Iceland, 80% of homes are heated using hot water extracted from geothermal wells near the city of Reykjavik. In the western United States, about 180 homes and farms are heated using geothermal hot water. According to experts, between 1993 and 2000, global electricity generation from geothermal energy more than doubled. There are so many reserves of geothermal heat in the United States that it could, theoretically, provide 30 times more energy than the state currently consumes.
In the future, it is possible to use the heat of magma in those areas where it is located close to the Earth's surface, as well as the dry heat of heated crystalline rocks. In the latter case, wells are drilled over several kilometers, cold water is pumped down, and hot water is received back.

The term “geothermal energy” comes from the Greek words for earth (geo) and heat (thermal). In fact, 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) to the surface, where it can be used directly as heat or indirectly to generate electricity by turning on rotating turbines.

Since the water below the earth's surface is constantly replenished, and the earth's core will continue to produce heat relatively human life endlessly, 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, as 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" formed at the borders tectonic plates in places where the bark is quite thin. Pacific region, often referred to as a ring of fire for many volcanoes, where there are many hot spots, including in Alaska, California and Oregon. Nevada has hundreds of hot spots spanning most northern part of the USA.

There are other seismically 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 open system geysers is the release of certain air pollutants. Hydrogen sulfide - toxic gas with a very recognizable "rotten egg" odor - small amounts of arsenic and minerals released with the 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 of 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 great amount 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 requires the introduction cold water, circulating through hot rocks and discharging heated water. There are currently no commercial applications for this technology. Existing technologies do not yet allow restoration thermal energy directly from the magma, very deep, but it is the most powerful geothermal energy resource.

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 clean, sustainable 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 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 production, help in industrial processes like milk pasteurizers and water heating 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.

Doctor of Technical Sciences ON THE. I hate it, professor,
academician Russian Academy Technological Sciences, Moscow

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 areas globe when drilling injection and production wells and creating circulation systems between them.

The growing interest in alternative energy sources in the world in recent decades 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 (they make up only 1% of shared resources geothermal energy) - groundwater, steam and steam-water mixtures. The latter represent geothermal energy contained in hot rocks Oh.

The fountain technology (self-flow) 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, issues of combating salt deposits develop into a complex problem. 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 in the territory 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 fuel equivalent. in year.

The forecast reserves of the 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.

Much higher value For the energy sector of the future, there 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 the earth's 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 heat transfer from the subsurface to earth's surface three times 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 total 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 operation of circulation systems it is necessary to have or create a sufficiently developed heat exchange surface in the heat extraction zone. Such a surface is possessed by porous layers 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 using the hydraulic fracturing method (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 United States, testing of an experimental GVC with hydraulic fracturing of an almost impermeable massif began at the Fenton Hill site in New Mexico. Injected through a well (injection) cold fresh water was heated due to heat exchange with a 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), which also intersected this crack, superheated water came to the surface in the form of a jet of steam. When circulating in closed loop under pressure, the temperature of superheated water on the surface reached 160-180 °C, and the thermal power of the system was 4-5 MW. Coolant leaks into the surrounding massif accounted for about 1% of the total flow rate. 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 hydrostatic fluid pressure. 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, English 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. The development of the Earth's thermal energy experiences great difficulties during the construction of 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 a progressive technology for developing the main part 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 technology 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. Hard rock drilling speed ( average density 2500-3300 kg/m3) up to 30 m/h, well 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 a large economic efficiency and enormous potential value. The introduction of BS into production will open up new stage in the construction of wells and provide access to obtaining inexhaustible sources thermal energy of the Earth.

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 equivalent fuel. 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 energy balance 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.

THEM. Kapitonov

Earth's nuclear heat

Earthly warmth

The earth is a fairly hot body and is a source of heat. It heats up primarily due to the solar radiation it absorbs. But the Earth also has its own thermal resource comparable to the heat it receives from the Sun. This self-energy of the Earth is believed to have the following origin. The Earth arose about 4.5 billion years ago following the formation of the Sun from a protoplanetary disk of gas and dust rotating around it and compacting it. At the early stage of its formation, the earth's substance was heated due to relatively slow gravitational compression. The energy released when small cosmic bodies fell on it also played a major role in the Earth’s thermal balance. Therefore, the young Earth was molten. Cooling down, it gradually came to its present state with a solid surface, a significant part of which is covered with oceanic and sea ​​waters. This hard outer layer is called earth's crust and on average, on land, its thickness is about 40 km, and under ocean waters - 5-10 km. The deeper layer of the Earth, called mantle, also consists of solid. It extends to a depth of almost 3000 km and contains the bulk of the Earth's substance. Finally, the innermost part of the Earth is its core. It consists of two layers - external and internal. Outer core this is a layer of molten iron and nickel at a temperature of 4500-6500 K, 2000-2500 km thick. Inner core with a radius of 1000-1500 km, it is a solid iron-nickel alloy heated to a temperature of 4000-5000 K with a density of about 14 g/cm 3, which arose under enormous (almost 4 million bar) pressure.
In addition to the internal heat of the Earth, which it inherited from the earliest hot stage of its formation, and the amount of which should decrease with time, there is another - long-term, associated with the radioactive decay of nuclei with a long half-life - primarily 232 Th, 235 U , 238 U and 40 K. The energy released in these decays - they account for almost 99% of the Earth's radioactive energy - constantly replenishes the Earth's thermal reserves. The above nuclei are contained in the crust and mantle. Their decay leads to heating of both the outer and inner layers of the Earth.
Part of the enormous heat contained within the Earth is constantly released to its surface, often in very large-scale volcanic processes. The heat flow flowing from the depths of the Earth through its surface is known. It is (47±2)·10 12 Watt, which is equivalent to the heat that can be generated by 50 thousand nuclear power plants (the average power of one nuclear power plant is about 10 9 Watt). The question arises whether any significant role radioactive energy in the total thermal budget of the Earth and if it plays, what kind? The answer to these questions remained unknown for a long time. There are now opportunities to answer these questions. The key role here belongs to neutrinos (antineutrinos), which are born in the processes of radioactive decay of nuclei that make up the Earth's matter and which are called geo-neutrino.

Geo-neutrino

Geo-neutrino is the combined name for neutrinos or antineutrinos, which are emitted as a result of the beta decay of nuclei located under the earth's surface. Obviously, thanks to their unprecedented penetrating ability, recording them (and only them) with ground-based neutrino detectors can provide objective information about the radioactive decay processes occurring deep inside the Earth. An example of such a decay is the β − decay of the 228 Ra nucleus, which is a product of the α decay of the long-lived 232 Th nucleus (see table):

The half-life (T 1/2) of the 228 Ra nucleus is 5.75 years, the released energy is about 46 keV. The energy spectrum of antineutrinos is continuous with an upper limit close to the released energy.
The decays of nuclei 232 Th, 235 U, 238 U are chains of successive decays, forming the so-called radioactive series. In such chains, α-decays are interspersed with β−-decays, since during α-decays the final nuclei are shifted from the β-stability line to the region of nuclei overloaded with neutrons. After a chain of successive decays, at the end of each series, stable nuclei are formed with a number of protons and neutrons close to or equal to the magic numbers (Z = 82,N= 126). Such final nuclei are stable isotopes of lead or bismuth. Thus, the decay of T 1/2 ends with the formation of a double magic nucleus 208 Pb, and on the path 232 Th → 208 Pb six α-decays occur, interspersed with four β − decays (in the 238 U → 206 Pb chain there are eight α- and six β − - decays; in the 235 U → 207 Pb chain there are seven α- and four β − decays). Thus, the energy spectrum of antineutrinos from each radioactive series is a superposition of partial spectra from individual β − decays included in this series. The spectra of antineutrinos produced in the decays of 232 Th, 235 U, 238 U, 40 K are shown in Fig. 1. The 40 K decay is a single β − decay (see table). Antineutrinos reach their highest energy (up to 3.26 MeV) in decay
214 Bi → 214 Po, which is a link in the radioactive series 238 U. The total energy released during the passage of all decay links of the series 232 Th → 208 Pb is equal to 42.65 MeV. For the radioactive series 235 U and 238 U, these energies are 46.39 and 51.69 MeV, respectively. Energy released in decay
40 K → 40 Ca, is 1.31 MeV.

Characteristics of cores 232 Th, 235 U, 238 U, 40 K

Core	Share in % in the mixture isotopes	Number of cores relates Si nuclei	T 1/2 billion years	First links disintegration
232 Th	100	0.0335	14.0
235U	0.7204	6.48·10 -5	0.704
238U	99.2742	0.00893	4.47
40 K	0.0117	0.440	1.25

An estimate of the geoneutrino flux, made on the basis of the decay of the 232 Th, 235 U, 238 U, 40 K nuclei contained in the Earth's matter, leads to a value of the order of 10 6 cm -2 sec -1. By registering these geo-neutrinos, it is possible to obtain information about the role of radioactive heat in the overall thermal balance of the Earth and test our ideas about the content of long-lived radioisotopes in the composition of the earth's matter.

Rice. 1. Energy spectra of antineutrinos from nuclear decay

232 Th, 235 U, 238 U, 40 K, normalized to one decay of the parent nucleus

The reaction is used to detect electron antineutrinos

P → e + + n, (1)

in which this particle was actually discovered. The threshold for this reaction is 1.8 MeV. Therefore, only geo-neutrinos produced in decay chains starting from the 232 Th and 238 U nuclei can be registered in the above reaction. The effective cross section for the reaction under discussion is extremely small: σ ≈ 10 -43 cm 2. It follows that a neutrino detector with a sensitive volume of 1 m 3 will register no more than a few events per year. Obviously, to reliably detect geo-neutrino fluxes, large-volume neutrino detectors are required, located in underground laboratories for maximum protection from the background. The idea of ​​using detectors designed to study solar and reactor neutrinos to register geoneutrinos arose in 1998. Currently, there are two large-volume neutrino detectors that use a liquid scintillator and are suitable for solving this problem. These are neutrino detectors from the KamLAND (Japan,) and Borexino (Italy,) experiments. Below we consider the design of the Borexino detector and the results obtained on this detector for registering geo-neutrinos.

Borexino detector and geo-neutrino registration

The Borexino neutrino detector is located in central Italy in an underground laboratory under the Gran Sasso mountain range, whose mountain peaks reach 2.9 km in height (Fig. 2).

Rice. 2. Layout of the neutrino laboratory under the Gran Sasso mountain range (central Italy)

Borexino is a non-segmented massive detector whose active medium is
280 tons of organic liquid scintillator. A nylon spherical vessel with a diameter of 8.5 m is filled with it (Fig. 3). The scintillator is pseudocumene (C 9 H 12) with the spectrum-shifting additive PPO (1.5 g/l). Light from the scintillator is collected by 2212 eight-inch photomultiplier tubes (PMTs) placed on a stainless steel sphere (SSS).

Rice. 3. Diagram of the Borexino detector

A nylon vessel with pseudocumene is an internal detector whose task is to register neutrinos (antineutrinos). The internal detector is surrounded by two concentric buffer zones that protect it from external gamma rays and neutrons. The internal zone is filled with a non-scintillating medium consisting of 900 tons of pseudocumene with dimethyl phthalate additives that quench scintillation. The outer zone is located on top of the SNS and is a water Cherenkov detector containing 2000 tons of ultrapure water and cuts off signals from muons entering the installation from the outside. For each interaction that occurs in the internal detector, the energy and time are determined. Calibration of the detector using various radioactive sources made it possible to very accurately determine its energy scale and the degree of reproducibility of the light signal.
Borexino is a detector of very high radiation purity. All materials have undergone strict selection, and the scintillator has been purified to minimize internal background. Due to its high radiation purity, Borexino is an excellent detector for detecting antineutrinos.
In reaction (1), a positron gives an instantaneous signal, which after some time is followed by the capture of a neutron by a hydrogen nucleus, which leads to the appearance of a γ-quantum with an energy of 2.22 MeV, creating a signal delayed relative to the first. In Boreksino, the neutron capture time is about 260 μs. The instantaneous and delayed signals are correlated in space and time, allowing precise recognition of the event caused by e.
The threshold for reaction (1) is 1.806 MeV and, as can be seen from Fig. 1, all geoneutrinos from the decays of 40 K and 235 U are below this threshold, and only a part of the geoneutrinos produced in the decays of 232 Th and 238 U can be registered.
The Borexino detector first detected signals from geoneutrinos in 2010, and new results have recently been published based on observations over 2056 days between December 2007 and March 2015. Below we present the data obtained and the results of their discussion, based on article.
As a result of the analysis of experimental data, 77 candidates for electron antineutrinos were identified that passed all selection criteria. The background from events simulating e was estimated as . Thus, the signal-to-background ratio was ≈100.
The main source of background were reactor antineutrinos. For Borexino, the situation was quite favorable, since there are no nuclear reactors near the Gran Sasso laboratory. In addition, reactor antineutrinos are more energetic compared to geo-neutrinos, which made it possible to separate these antineutrinos from the positron by the magnitude of the signal. The results of the analysis of the contributions of geoneutrinos and reactor antineutrinos to the total number of registered events from e are shown in Fig. 4. The number of registered geo-neutrinos given by this analysis (in Fig. 4 they correspond to the darkened area) is equal to . In the geo-neutrino spectrum extracted as a result of the analysis, two groups are visible - less energetic, more intense and more energetic, less intense. The authors of the described study associate these groups with the decays of thorium and uranium, respectively.
The analysis discussed used the ratio of the masses of thorium and uranium in the Earth's matter
m(Th)/m(U) = 3.9 (in the table this value is ≈3.8). This figure reflects the relative content of these chemical elements in chondrites, the most common group of meteorites (more than 90% of meteorites that fell to Earth belong to this group). It is believed that the composition of chondrites, with the exception of light gases (hydrogen and helium), repeats the composition of the Solar system and the protoplanetary disk from which the Earth was formed.

Rice. 4. Spectrum of light output from positrons in units of the number of photoelectrons for antineutrino candidate events (experimental points). The shaded area is the contribution of geo-neutrinos. The solid line is the contribution of reactor antineutrinos.