Kirill Degtyarev, Researcher, Moscow State University them. M. V. Lomonosov.
In our country, rich in hydrocarbons, geothermal energy is a kind of exotic resource that, in the current state of affairs, is unlikely to compete with oil and gas. Nevertheless, this alternative form of energy can be used almost everywhere and quite efficiently.
Photo by Igor Konstantinov.
Change in soil temperature with depth.
Temperature increase of thermal waters and dry rocks containing them with depth.
Change in temperature with depth in different regions.
The eruption of the Icelandic volcano Eyjafjallajökull is an illustration of violent volcanic processes occurring in active tectonic and volcanic zones with a powerful heat flow from the earth's interior.
Installed capacities of geothermal power plants by countries of the world, MW.
Distribution of geothermal resources on the territory of Russia. The reserves of geothermal energy, according to experts, are several times higher than the energy reserves of organic fossil fuels. According to the Geothermal Energy Society Association.
Geothermal energy is the heat of the earth's interior. It is produced in the depths and comes to the surface of the Earth in different forms and with different intensities.
The temperature of the upper layers of the soil depends mainly on external (exogenous) factors - sunlight and air temperature. In summer and during the day, the soil warms up to certain depths, and in winter and at night it cools down following the change in air temperature and with some delay, increasing with depth. The influence of daily fluctuations in air temperature ends at depths from a few to several tens of centimeters. Seasonal fluctuations capture deeper layers of soil - up to tens of meters.
At a certain depth - from tens to hundreds of meters - the temperature of the soil is kept constant, equal to the average annual air temperature near the Earth's surface. This is easy to verify by going down into a fairly deep cave.
When the average annual air temperature in a given area is below zero, this manifests itself as permafrost (more precisely, permafrost). In Eastern Siberia, the thickness, that is, the thickness, of year-round frozen soils reaches 200-300 m in places.
From a certain depth (its own for each point on the map), the action of the Sun and the atmosphere weakens so much that endogenous (internal) factors come first and the earth's interior is heated from the inside, so that the temperature begins to rise with depth.
The heating of the deep layers of the Earth is associated mainly with the decay of the radioactive elements located there, although other sources of heat are also called, for example, physicochemical, tectonic processes in the deep layers earth's crust and robes. But whatever the reason, the temperature rocks and related liquid and gaseous substances increases with depth. Miners face this phenomenon - it is always hot in deep mines. At a depth of 1 km, thirty-degree heat is normal, and deeper the temperature is even higher.
The heat flow of the earth's interior, reaching the surface of the Earth, is small - on average, its power is 0.03-0.05 W / m 2,
or about 350 Wh/m 2 per year. Against the background of the heat flow from the Sun and the air heated by it, this is an imperceptible value: the Sun gives each square meter of the earth's surface about 4,000 kWh annually, that is, 10,000 times more (of course, this is on average, with a huge spread between polar and equatorial latitudes and depending on other climatic and weather factors).
The insignificance of the heat flow from the depths to the surface in most of the planet is associated with the low thermal conductivity of rocks and features geological structure. But there are exceptions - places where the heat flow is high. These are, first of all, areas tectonic faults, increased seismic activity and volcanism, where the energy of the earth's interior finds a way out. Such zones are characterized by thermal anomalies of the lithosphere, here the heat flow reaching the Earth's surface can be many times and even orders of magnitude more powerful than the "usual" one. Great amount heat is brought to the surface in these zones by volcanic eruptions and hot water springs.
It is these areas that are most favorable for the development of geothermal energy. On the territory of Russia, this is, first of all, Kamchatka, Kurile Islands and the Caucasus.
At the same time, the development of geothermal energy is possible almost everywhere, since the increase in temperature with depth is a ubiquitous phenomenon, and the task is to “extract” heat from the bowels, just as mineral raw materials are extracted from there.
On average, the temperature increases with depth by 2.5-3 o C for every 100 m. The ratio of the temperature difference between two points lying at different depths to the difference in depth between them is called the geothermal gradient.
The reciprocal is the geothermal step, or the depth interval at which the temperature rises by 1 o C.
The higher the gradient and, accordingly, the lower the step, the closer the heat of the Earth's depths approaches the surface and the more promising this area is for the development of geothermal energy.
In different areas, depending on the geological structure and other regional and local conditions, the rate of temperature increase with depth can vary dramatically. On the scale of the Earth, fluctuations in the values of geothermal gradients and steps reach 25 times. For example, in the state of Oregon (USA), the gradient is 150 ° C per 1 km, and in South Africa- 6 o C per 1 km.
The question is what is the temperature great depths- 5, 10 km and more? If the trend continues, the temperature at a depth of 10 km should average about 250-300 o C. This is more or less confirmed by direct observations in ultra-deep wells, although the picture is much more complicated than a linear increase in temperature.
For example, in Kola ultra-deep well, drilled in the Baltic crystalline shield, the temperature to a depth of 3 km changes at a rate of 10 ° C / 1 km, and then the geothermal gradient becomes 2-2.5 times greater. At a depth of 7 km, a temperature of 120 o C was already recorded, at 10 km - 180 o C, and at 12 km - 220 o C.
Another example is a well laid in the Northern Caspian, where at a depth of 500 m a temperature of 42 o C was recorded, at 1.5 km - 70 o C, at 2 km - 80 o C, at 3 km - 108 o C.
It is assumed that the geothermal gradient decreases starting from a depth of 20-30 km: at a depth of 100 km, the estimated temperatures are about 1300-1500 o C, at a depth of 400 km - 1600 o C, in the Earth's core (depths of more than 6000 km) - 4000-5000 o WITH.
At depths up to 10-12 km, the temperature is measured through drilled wells; where they do not exist, it is determined by indirect signs in the same way as at greater depths. Such indirect signs may be the nature of the passage of seismic waves or the temperature of the erupting lava.
However, for the purposes of geothermal energy, data on temperatures at depths of more than 10 km are not yet of practical interest.
There is a lot of heat at depths of several kilometers, but how to raise it? Sometimes nature itself solves this problem for us with the help of a natural coolant - heated thermal waters that come to the surface or lie at a depth accessible to us. In some cases, the water in the depths is heated to the state of steam.
A strict definition of the concept " thermal waters" No. As a rule, they mean hot groundwater in liquid state or in the form of steam, including those emerging on the Earth's surface with a temperature above 20 ° C, that is, as a rule, higher than the air temperature.
Warmly groundwater, steam, steam-water mixtures - this is hydrothermal energy. Accordingly, energy based on its use is called hydrothermal.
The situation is more complicated with the production of heat directly from dry rocks - petrothermal energy, especially since sufficiently high temperatures, as a rule, begin from depths of several kilometers.
On the territory of Russia, the potential of petrothermal energy is a hundred times higher than that of hydrothermal energy - 3,500 and 35 trillion tons, respectively. reference fuel. This is quite natural - the warmth of the Earth's depths is everywhere, and thermal waters are found locally. However, due to obvious technical difficulties, heat and electricity are currently used for the most part thermal waters.
Waters with temperatures from 20-30 to 100 o C are suitable for heating, temperatures from 150 o C and above - and for generating electricity at geothermal power plants.
In general, geothermal resources on the territory of Russia, in terms of tons of standard fuel or any other unit of energy measurement, are about 10 times higher than fossil fuel reserves.
Theoretically, only due to geothermal energy, it would be possible to fully satisfy energy needs countries. Practically on this moment in most of its territory, this is not feasible for technical and economic reasons.
In the world, the use of geothermal energy is most often associated with Iceland - a country located at the northern end of the Mid-Atlantic Ridge, in an exceptionally active tectonic and volcanic zone. Probably everyone remembers the powerful eruption of the Eyjafjallajökull volcano in 2010.
It is thanks to this geological specificity that Iceland has huge reserves of geothermal energy, including hot springs that come to the surface of the Earth and even gushing in the form of geysers.
In Iceland, more than 60% of all energy consumed is currently taken from the Earth. Including due to geothermal sources provides 90% of heating and 30% of electricity generation. We add that the rest of the electricity in the country is produced by hydroelectric power plants, that is, also using a renewable energy source, thanks to which Iceland looks like a kind of global environmental standard.
The "taming" of geothermal energy in the 20th century helped Iceland significantly economically. Until the middle of the last century, it was a very poor country, now it ranks first in the world in terms of installed capacity and production of geothermal energy per capita and is in the top ten in terms of absolute value installed capacity of geothermal power plants. However, its population is only 300 thousand people, which simplifies the task of switching to environmentally friendly clean sources energy: the need for it is generally small.
In addition to Iceland, a high share of geothermal energy in the total balance of electricity production is provided by New Zealand and island states South-East Asia(Philippines and Indonesia), the countries of Central America and East Africa, whose territory is also characterized by high seismic and volcanic activity. For these countries, at their current level of development and needs geothermal energy makes a significant contribution to socio-economic development.
(Ending follows.)
Here is published the dynamics of changes in winter (2012-13) ground temperatures at a depth of 130 centimeters under the house (under the inner edge of the foundation), as well as at ground level and the temperature of the water coming from the well. All this - on the riser coming from the well.The chart is at the bottom of the article.
Dacha (on the border of New Moscow and the Kaluga region) winter, periodic visits (2-4 times a month for a couple of days).
The blind area and the basement of the house are not insulated, since autumn they have been closed with heat-insulating plugs (10 cm of foam). The heat loss of the veranda where the riser goes in January has changed. See Note 10.
Measurements at a depth of 130 cm are made by the Xital GSM system (), discrete - 0.5 * C, add. the error is about 0.3 * C.
The sensor is installed in a 20mm HDPE pipe welded from below near the riser, (on the outside of the riser thermal insulation, but inside the 110mm pipe).
The abscissa shows dates, the ordinate shows temperatures.
Note 1:
I will also monitor the temperature of the water in the well, as well as at the ground level under the house, right on the riser without water, but only upon arrival. The error is about + -0.6 * C.
Note 2:
Temperature at ground level under the house, at the water supply riser, in the absence of people and water, it already dropped to minus 5 * C. This suggests that I did not make the system in vain - By the way, the thermostat that showed -5 * C is just from this system (RT-12-16).
Note 3:
The temperature of the water "in the well" is measured by the same sensor (it is also in Note 2) as "at ground level" - it stands right on the riser under the thermal insulation, close to the riser at ground level. These two measurements are made at different times. "At ground level" - before pumping water into the riser and "in the well" - after pumping about 50 liters for half an hour with interruptions.
Note 4:
The temperature of the water in the well can be somewhat underestimated, because. I can't look for this fucking asymptote, endlessly pumping water (mine)... I play as best I can.
Note 5: Not relevant, removed.
Note 6:
The error of fixing the street temperature is approximately + - (3-7) * С.
Note 7:
The rate of cooling of water at ground level (without turning on the pump) is very approximately 1-2 * C per hour (this is at minus 5 * C at ground level).
Note 8:
I forgot to describe how my underground riser is arranged and insulated. Two stockings of insulation are put on PND-32 in total - 2 cm. thickness (apparently, foamed polyethylene), all this is inserted into a 110mm sewer pipe and foamed there to a depth of 130cm. True, since PND-32 did not go in the center of the 110th pipe, and also the fact that in its middle the mass of ordinary foam may not harden for a long time, which means it does not turn into a heater, I strongly doubt the quality of such additional insulation .. It would probably be better to use a two-component foam, the existence of which I only found out later...
Note 9:
I want to draw the attention of readers to the temperature measurement "At ground level" dated 01/12/2013. and dated January 18, 2013. Here, in my opinion, the value of +0.3 * C is much higher than expected. I think that this is a consequence of the operation "Filling the basement at the riser with snow", carried out on 12/31/2012.
Note 10:
From January 12 to February 3, he made additional insulation of the veranda, where the underground riser goes.
As a result, according to approximate estimates, the heat loss of the veranda was reduced from 100 W / sq.m. floor to about 50 (this is at minus 20 * C on the street).
This is also reflected in the charts. See the temperature at ground level on February 9: +1.4*C and on February 16: +1.1 - there have not been such high temperatures since the beginning of real winter.
And one more thing: from February 4 to February 16, for the first time in two winters, from Sunday to Friday, the boiler did not turn on to maintain the set minimum temperature because it did not reach this minimum ...
Note 11:
As promised (for "order" and to complete the annual cycle), I will periodically publish temperatures in the summer. But - not in the schedule, so as not to "obscure" the winter, but here, in Note-11.
May 11, 2013
After 3 weeks of ventilation, the vents were closed until autumn to avoid condensation.
May 13, 2013(on the street for a week + 25-30 * C):
- under the house at ground level + 10.5 * C,
- under the house at a depth of 130 cm. +6*С,
June 12, 2013:
- under the house at ground level + 14.5 * C,
- under the house at a depth of 130 cm. +10*С.
- water in the well from a depth of 25 m not higher than + 8 * C.
June 26, 2013:
- under the house at ground level + 16 * C,
- under the house at a depth of 130 cm. +11*С.
- water in the well from a depth of 25m is not higher than +9.3*C.
August 19, 2013:
- under the house at ground level + 15.5 * C,
- under the house at a depth of 130 cm. +13.5*С.
- water in the well from a depth of 25m not higher than +9.0*C.
September 28, 2013:
- under the house at ground level + 10.3 * C,
- under the house at a depth of 130 cm. +12*С.
- water in the well from a depth of 25m = + 8.0 * C.
October 26, 2013:
- under the house at ground level + 8.5 * C,
- under the house at a depth of 130 cm. +9.5*С.
- water in the well from a depth of 25 m not higher than + 7.5 * C.
November 16, 2013:
- under the house at ground level + 7.5 * C,
- under the house at a depth of 130 cm. +9.0*С.
- water in the well from a depth of 25m + 7.5 * C.
February 20, 2014:
Probably this last record in this article.
All winter we live in the house all the time, the point in repeating last year's measurements is small, so only two significant figures:
- the minimum temperature under the house at ground level in the very frosts (-20 - -30 * C) a week after they began, repeatedly fell below + 0.5 * C. At these moments, I worked
Well, who doesn’t want to heat their home for free, especially during a crisis, when every penny counts.
We have already touched on the topic of how, it was the turn of the controversial technologies for heating a house with the energy of the earth (Geothermal heating).
At a depth of about 15 meters, the temperature of the earth is about 10 degrees Celsius. Every 33 meters, the temperature rises by one degree. As a result, in order to heat a house of about 100 m2 for free, it is enough to drill a well about 600 meters and get 22 degrees of heat throughout your life!
Theoretically, the system of free heating from the energy of the earth is quite simple. Injected into the well cold water, which heats up to 22 degrees and, according to the laws of physics, with a little help from a pump (400-600 watts), rises through insulated pipes into the house.
Disadvantages of using land energy for heating a private house:
- Let's take a closer look at the financial costs of creating such a heating system. average cost 1 m of drilling a well is about 3000 rubles. A total depth of 600 meters will cost 1,800,000 rubles. And that's just drilling! Without installation of equipment for pumping and lifting the coolant.
- Different regions of Russia have their own soil characteristics. In some places, drilling a well of 50 meters is not an easy task. Reinforced casing pipes, shaft reinforcement, etc. are required.
— Insulation of the mine shaft to such a depth is almost impossible. It follows that the water will not rise with a temperature of 22 degrees.
– In order to drill a well of 600 meters, a permit is required;
- Let's say water heated to 22 degrees enters the house. The question is how to “remove” all the energy of the earth from the carrier completely? Maximum, when passing through pipes in a warm house, drop to 15 degrees. Thus, a powerful pump is needed, which will drive water from a depth of 600 meters ten times more to get at least some effect. Here we lay the energy consumption incomparable with the savings.
At a depth of about 15 meters, the temperature of the earth is approximately 10 degrees Celsius
A logical conclusion follows that heating a house with the energy of the earth is far from free, only a person who is far from poor, who does not particularly need savings on heating, can afford. Of course, one can say that such technology will serve both children and grandchildren for hundreds of years, but all this is fantasy.
An idealist will say that he builds a house for centuries, and a realist will always rely on the investment component - I build it for myself, but I will sell it at any moment. It is not a fact that the children will be attached to this house and will not want to sell it.
Earth energy for home heating is effective in the following regions:
In the Caucasus, there are operating examples of working wells with mineral water self-spouting outside, with a temperature of 45 degrees, taking into account the deep temperature of about 90 degrees.
In Kamchatka, the use of geothermal sources with an outlet temperature of about 100 degrees is the most best option using the energy of the earth to heat the house.
Technology is developing at a frantic pace. The efficiency of classical heating systems is growing before our eyes. Undoubtedly, the heating of the house with the energy of the earth will become less expensive.
Video: Geothermal heating. Earth energy.
This might seem like fantasy if it weren't true. It turns out that in harsh Siberian conditions, you can get heat directly from the ground. The first objects with geothermal heating systems appeared in the Tomsk region last year, and although they can reduce the cost of heat by about four times compared to traditional sources, there is still no mass circulation "under the ground". But the trend is noticeable and, most importantly, it is gaining momentum. In fact, it is the most accessible alternative source energy for Siberia, where they cannot always show their effectiveness, for example, solar panels or wind generators. Geothermal energy, in fact, just lies under our feet.
“The depth of soil freezing is 2–2.5 meters. The ground temperature below this mark remains the same both in winter and in summer, ranging from plus one to plus five degrees Celsius. The work of the heat pump is built on this property, says the power engineer of the education department of the administration of the Tomsk region Roman Alekseenko. - Connecting pipes are buried in the earth contour to a depth of 2.5 meters, at a distance of about one and a half meters from each other. A coolant - ethylene glycol - circulates in the pipe system. The external horizontal earth circuit communicates with the refrigeration unit, in which the refrigerant - freon, a gas with a low boiling point, circulates. At plus three degrees Celsius, this gas begins to boil, and when the compressor sharply compresses the boiling gas, the temperature of the latter rises to plus 50 degrees Celsius. The heated gas is sent to a heat exchanger in which ordinary distilled water circulates. The liquid heats up and spreads heat throughout the heating system laid in the floor.
Pure physics and no miracles
A kindergarten equipped with a modern Danish geothermal heating system was opened in the village of Turuntaevo near Tomsk last summer. According to the director of the Tomsk company Ecoclimat George Granin, the energy-efficient system allowed several times to reduce the payment for heat supply. For eight years, this Tomsk enterprise has already equipped about two hundred objects in different regions of Russia with geothermal heating systems and continues to do so in the Tomsk region. So there is no doubt in the words of Granin. A year before the opening of a kindergarten in Turuntaevo, Ecoclimat equipped a geothermal heating system, which cost 13 million rubles, another Kindergarten « sun bunny" in the microdistrict of Tomsk "Green Hills". In fact, it was the first experience of its kind. And he was quite successful.
Back in 2012, during a visit to Denmark, organized under the program of the Euro Info Correspondence Center (EICC-Tomsk region), the company managed to agree on cooperation with the Danish company Danfoss. And today, Danish equipment helps to extract heat from the Tomsk bowels, and, as experts say without too much modesty, it turns out quite efficiently. The main indicator of efficiency is economy. "The heating system of the kindergarten building with an area of 250 square meters in Turuntaevo cost 1.9 million rubles, - says Granin. “And the heating fee is 20-25 thousand rubles a year.” This amount is incomparable with the one that the kindergarten would pay for heat using traditional sources.
The system worked without problems in the conditions of the Siberian winter. A calculation was made of the compliance of thermal equipment with SanPiN standards, according to which it must maintain a temperature of at least + 19 ° C in the kindergarten building at an outdoor air temperature of -40 ° C. In total, about four million rubles were spent on redevelopment, repair and re-equipment of the building. Together with the heat pump, the amount was just under six million. Thanks to heat pumps today, kindergarten heating is completely insulated and independent system. There are no traditional batteries in the building now, and the space is heated using the “warm floor” system.
Turuntayevsky kindergarten is insulated, as they say, “from” and “to” - additional thermal insulation is equipped in the building: a 10-cm layer of insulation equivalent to two or three bricks is installed on top of the existing wall (three bricks thick). Behind the insulation is an air gap, followed by metal siding. The roof is insulated in the same way. The main attention of the builders was focused on the "warm floor" - the heating system of the building. It turned out several layers: a concrete floor, a layer of foam plastic 50 mm thick, a system of pipes in which hot water circulates and linoleum. Although the temperature of the water in the heat exchanger can reach +50°C, the maximum heating of the actual floor covering does not exceed +30°C. The actual temperature of each room can be adjusted manually - automatic sensors allow you to set the floor temperature in such a way that the kindergarten room warms up to the degrees required by sanitary standards.
The power of the pump in the Turuntayevsky garden is 40 kW of generated thermal energy, for the production of which the heat pump requires 10 kW of electrical power. Thus, out of 1 kW consumed electrical energy The heat pump produces 4 kW of heat. “We were a little afraid of winter - we did not know how heat pumps would behave. But even in very coldy it was consistently warm in the kindergarten - from plus 18 to 23 degrees Celsius, - says the director of the Turuntaevskaya high school Evgeny Belonogov. - Of course, here it is worth considering that the building itself was well insulated. The equipment is unpretentious in maintenance, and despite the fact that this is a Western development, it proved to be quite effective in our harsh Siberian conditions.”
A comprehensive project for the exchange of experience in the field of resource conservation was implemented by the EICC-Tomsk region of the Tomsk Chamber of Commerce and Industry. Its participants were small and medium-sized enterprises that develop and implement resource-saving technologies. In May last year, Danish experts visited Tomsk as part of a Russian-Danish project, and the result was, as they say, obvious.
Innovation comes to school
A new school in the village of Vershinino, Tomsk region, built by a farmer Mikhail Kolpakov, is the third facility in the region that uses the heat of the earth as a source of heat for heating and hot water supply. The school is also unique because it has the highest energy efficiency category - "A". The heating system was designed and launched by the same Ecoclimat company.
“When we were deciding what kind of heating to install in the school, we had several options - a coal-fired boiler house and heat pumps,” says Mikhail Kolpakov. - We studied the experience of an energy-efficient kindergarten in Zeleny Gorki and calculated that heating in the old fashioned way, on coal, will cost us more than 1.2 million rubles over the winter, and we also need hot water. And with heat pumps, the cost will be about 170 thousand for the whole year, along with hot water.”
The system needs only electricity to produce heat. Consuming 1 kW of electricity, heat pumps in a school produce about 7 kW of thermal energy. In addition, unlike coal and gas, the heat of the earth is a self-renewable source of energy. Installation of a modern heating system The school cost about 10 million rubles. For this, 28 wells were drilled on the school grounds.
“The arithmetic here is simple. We calculated that the maintenance of the coal boiler, taking into account the salary of the stoker and the cost of fuel, would cost more than a million rubles a year, - notes the head of the education department Sergey Efimov. - When using heat pumps, you will have to pay for all resources about fifteen thousand rubles a month. The undoubted advantages of using heat pumps are their efficiency and environmental friendliness. The heat supply system allows you to regulate the heat supply depending on the weather outside, which eliminates the so-called "underheating" or "overheating" of the room.
By preliminary calculations, expensive Danish equipment will pay for itself in four to five years. The service life of Danfoss heat pumps, with which Ecoclimat LLC works, is 50 years. Receiving information about the air temperature outside, the computer determines when to heat the school, and when it is possible not to do so. Therefore, the question of the date of switching on and off the heating disappears altogether. Regardless of the weather, climate control will always work outside the windows inside the school for children.
“When last year an emergency and plenipotentiary ambassador of the Kingdom of Denmark and visited our kindergarten in Zelenye Gorki, he was pleasantly surprised that those technologies that are considered innovative even in Copenhagen are applied and work in the Tomsk region, - says Commercial Director company "Ecoclimate" Alexander Granin.
In general, the use of local renewable energy sources in various industries economy, in this case in social sphere, which includes schools and kindergartens, is one of the main areas implemented in the region as part of the program for energy saving and energy efficiency. The development of renewable energy is actively supported by the governor of the region Sergey Zhvachkin. And three budget institutions with a geothermal heating system - only the first steps towards the implementation of a large and promising project.
The kindergarten in Zelenye Gorki was recognized as the best energy-efficient facility in Russia at a competition in Skolkovo. Then the Vershininskaya school appeared with geothermal heating as well. the highest category energy efficiency. The next object, no less significant for the Tomsk region, is a kindergarten in Turuntaevo. This year, the Gazhimstroyinvest and Stroygarant companies have already begun construction of kindergartens for 80 and 60 children in the villages of the Tomsk region, Kopylovo and Kandinka, respectively. Both new facilities will be heated by geothermal heating systems - from heat pumps. In total, this year for the construction of new kindergartens and the repair of existing district administration intends to spend almost 205 million rubles. It is planned to reconstruct and re-equip the building for a kindergarten in the village of Takhtamyshevo. In this building, heating will also be implemented by means of heat pumps, since the system has proved itself well.
temperature inside the earth. The determination of the temperature in the Earth's shells is based on various, often indirect, data. The most reliable temperature data refer to the uppermost part of the earth's crust, which is exposed by mines and boreholes to a maximum depth of 12 km (Kola well).
The increase in temperature in degrees Celsius per unit of depth is called geothermal gradient, and the depth in meters, during which the temperature increases by 1 0 C - geothermal step. The geothermal gradient and, accordingly, the geothermal step vary from place to place depending on geological conditions, endogenous activity in different areas, as well as inhomogeneous thermal conductivity of rocks. At the same time, according to B. Gutenberg, the limits of fluctuations differ by more than 25 times. An example of this are two sharply different gradients: 1) 150 o per 1 km in Oregon (USA), 2) 6 o per 1 km registered in South Africa. According to these geothermal gradients, the geothermal step also changes from 6.67 m in the first case to 167 m in the second. The most common fluctuations in the gradient are within 20-50 o , and the geothermal step is 15-45 m. The average geothermal gradient has long been taken at 30 o C per 1 km.
According to VN Zharkov, the geothermal gradient near the Earth's surface is estimated at 20 o C per 1 km. Based on these two values of the geothermal gradient and its invariance deep into the Earth, then at a depth of 100 km there should have been a temperature of 3000 or 2000 o C. However, this is at odds with the actual data. It is at these depths that magma chambers periodically originate, from which lava is poured onto the surface, having maximum temperature 1200-1250 o. Considering this kind of "thermometer", a number of authors (V. A. Lyubimov, V. A. Magnitsky) believe that at a depth of 100 km the temperature cannot exceed 1300-1500 o C.
With more high temperatures the mantle rocks would be completely melted, which contradicts the free passage of transverse seismic waves. Thus, the average geothermal gradient can be traced only to some relatively small depth from the surface (20-30 km), and then it should decrease. But even in this case, in the same place, the change in temperature with depth is not uniform. This can be seen in the example of temperature change with depth Kola well located within the stable crystal shield of the platform. When laying this well, a geothermal gradient of 10 o per 1 km was expected and, therefore, at the design depth (15 km) a temperature of the order of 150 o C was expected. However, such a gradient was only up to a depth of 3 km, and then it began to increase by 1.5 -2.0 times. At a depth of 7 km the temperature was 120 o C, at 10 km -180 o C, at 12 km -220 o C. It is assumed that at the design depth the temperature will be close to 280 o C. Caspian region, in the area of more active endogenous regime. In it, at a depth of 500 m, the temperature turned out to be 42.2 o C, at 1500 m - 69.9 o C, at 2000 m - 80.4 o C, at 3000 m - 108.3 o C.
What is the temperature in the deeper zones of the mantle and core of the Earth? More or less reliable data have been obtained on the temperature of the base of the B layer in the upper mantle (see Fig. 1.6). According to V. N. Zharkov, "detailed studies of the phase diagram of Mg 2 SiO 4 - Fe 2 Si0 4 made it possible to determine the reference temperature at a depth corresponding to the first zone phase transitions(400 km) "(i.e., the transition of olivine to spinel). The temperature here, as a result of these studies, is about 1600 50 o C.
The question of the distribution of temperatures in the mantle below layer B and in the Earth's core has not yet been resolved, and therefore various views are expressed. It can only be assumed that the temperature increases with depth with a significant decrease in the geothermal gradient and an increase in the geothermal step. It is assumed that the temperature in the Earth's core is in the range of 4000-5000 o C.
Average chemical composition Earth. To judge the chemical composition of the Earth, data on meteorites are involved, which are the most likely samples of protoplanetary material from which the planets were formed. terrestrial group and asteroids. To date, many have fallen to Earth in different times and in different places meteorites. According to the composition, three types of meteorites are distinguished: 1) iron, consisting mainly of nickel iron (90-91% Fe), with a small admixture of phosphorus and cobalt; 2) iron-stone(siderolites), consisting of iron and silicate minerals; 3) stone, or aerolites, consisting mainly of ferruginous-magnesian silicates and inclusions of nickel iron.
The most common are stone meteorites - about 92.7% of all finds, stony iron 1.3% and iron 5.6%. Stone meteorites are divided into two groups: a) chondrites with small rounded grains - chondrules (90%); b) achondrites that do not contain chondrules. The composition of stony meteorites is close to that of ultramafic igneous rocks. According to M. Bott, they contain about 12% iron-nickel phase.
Based on the analysis of the composition of various meteorites, as well as the obtained experimental geochemical and geophysical data, a number of researchers give modern estimate gross elemental composition of the Earth, presented in Table. 1.3.
As can be seen from the data in the table, the increased distribution refers to the four most important elements - O, Fe, Si, Mg, constituting over 91%. The group of less common elements includes Ni, S, Ca, A1. Other elements periodic system Mendeleev on a global scale in terms of general distribution are of secondary importance. If we compare the given data with the composition of the earth's crust, we can clearly see a significant difference consisting in a sharp decrease in O, Al, Si and a significant increase in Fe, Mg and the appearance of S and Ni in noticeable amounts.
The shape of the earth is called the geoid. The deep structure of the Earth is judged by longitudinal and transverse seismic waves, which, propagating inside the Earth, experience refraction, reflection and attenuation, which indicates the stratification of the Earth. There are three main areas:
Earth's crust;
mantle: upper to a depth of 900 km, lower to a depth of 2900 km;
the core of the Earth is outer to a depth of 5120 km, inner to a depth of 6371 km.
The internal heat of the Earth is associated with the decay of radioactive elements - uranium, thorium, potassium, rubidium, etc. The average value of the heat flux is 1.4-1.5 μkal / cm 2. s.
1. What is the shape and size of the Earth?
2. What are the methods for studying the internal structure of the Earth?
3. What is the internal structure of the Earth?
4. What seismic sections of the first order are clearly distinguished when analyzing the structure of the Earth?
5. What are the boundaries of the sections of Mohorovic and Gutenberg?
6. What average density Earth and how does it change at the boundary between the mantle and the core?
7. How does the heat flow change in different zones? How is the change in geothermal gradient and geothermal step understood?
8. What data is used to determine the average chemical composition of the Earth?
Literature
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Voytkevich G.V. Fundamentals of the theory of the origin of the Earth. M., 1988.
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Zharkov V.N. Internal structure Earth and planets. M., 1978.
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Magnitsky V.A. Internal structure and physics of the Earth. M., 1965.
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Essays comparative planetology. M., 1981.
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Ringwood A.E. Composition and origin of the Earth. M., 1981.
