A gas hydrate is an ice mass with a hydrocarbon gas contained in it, most often methane, or it is a mixture of water and methane in certain concentrations, capable of forming ice under certain thermobaric conditions. The gas hydrate, for example, is formed at 0 Celsius and at a pressure of 25 atmospheres. If the temperature is higher, then an increase in water pressure is necessary for the formation of gas hydrate. That is why gas hydrates are found mainly in oceans and seas at depths from 300 to 1200 meters.

The main element of a gas hydrate is a crystalline cell of water molecules, inside which a combustible gas molecule is placed. The cells form a dense crystal lattice, similar to ice.

Gas hydrates were first discovered in the mid-1970s by Canadian fishermen. Often, when trawls with fish were lifted from the depths, large pieces of a snow-like substance stained with bottom silt turned out to be in them. It occurred to someone to set fire to this deep-sea "snow". And he caught fire!

There is a theory according to which, at a certain time, due to various fluctuation phenomena, conditions arise when the gas is released from the crystalline cell of water, forms vacuum pits with high potential energy, where ships, planes and everything that moves above and across the sea disappear, falling through . If we take into account that in the area of ​​the Bermuda Triangle at the bottom of the ocean there is a large (1500-2010 m) gas hydrate deposit with methane gas, then the riddle of the Bermuda Triangle can be considered solved

Methane hydrate - the gas fuel of the future

Despite the development of alternative energy sources, fossil fuels still retain and, in the foreseeable future, will retain a major role in the planet's fuel balance. According to ExxonMobil experts, energy consumption in the next 30 years on the planet will increase by half. As the productivity of known hydrocarbon deposits declines, new large deposits are discovered less and less, and the use of coal is detrimental to the environment. However, depleting reserves of conventional hydrocarbons can be offset.

The same ExxonMobil experts are not inclined to dramatize the situation.

First, oil and gas production technologies are evolving. Today in the Gulf of Mexico, for example, oil is extracted from a depth of 2.5-3 km below the surface of the water, such depths were unthinkable 15 years ago.

Secondly, technologies for processing complex types of hydrocarbons (heavy and sour oils) and oil surrogates (bitumen, oil sands) are being developed. This makes it possible to return to traditional mining areas and resume work there, as well as start mining in new areas. For example, in Tatarstan, with the support of Shell, the production of the so-called "heavy oil" begins. In Kuzbass, projects for the extraction of methane from coal seams are being developed.

The third direction of maintaining the level of hydrocarbon production is associated with the search for ways to use their non-traditional types. Among the promising new types of hydrocarbon raw materials, scientists single out methane hydrate, the reserves of which on the planet, according to tentative estimates, are at least 250 trillion cubic meters (in terms of energy value, this is 2 times more than the value of all oil, coal and gas reserves on the planet combined) .

Methane hydrate is a supramolecular compound of methane with water. Below is a model of methane hydrate at the molecular level. A lattice of water (ice) molecules is formed around the methane molecule. The compound is stable at low temperature and high pressure. For example, methane hydrate is stable at 0 °C and pressures of the order of 25 bar or more. Such pressure occurs at a depth of about 250 m in the ocean. At atmospheric pressure, methane hydrate remains stable at a temperature of −80 °C.

If the methane hydrate is heated or the pressure is increased, the compound decomposes into water and natural gas (methane). From one cubic meter of methane hydrate at normal atmospheric pressure, 164 cubic meters of natural gas can be obtained.

According to the US Department of Energy, the reserves of methane hydrate on the planet are enormous. However, until now this compound is practically not used as an energy resource. The department has developed and is implementing an entire program (R&D program) to search for, evaluate and commercialize the extraction of methane hydrate.

It is no coincidence that the United States is ready to allocate significant funds for the development of technologies for the production of methane hydrate. Natural gas accounts for almost 23% of the country's fuel balance. Most of the U.S. natural gas is sourced through pipelines from Canada. In 2007, natural gas consumption in the country amounted to 623 billion cubic meters. m. By 2030, it can grow by 18-20%. Using conventional natural gas fields in the US, Canada and offshore, it is impossible to provide such a level of production.

It is no secret that at present the traditional sources of hydrocarbons are being depleted more and more actively, and this fact makes mankind think about the energy of the future. Therefore, the vectors of development of many players in the international oil and gas market are aimed at developing deposits of unconventional hydrocarbons.

Following the “shale revolution”, there has been a sharp increase in interest in other types of unconventional natural gas, such as gas hydrates (GG).

What are gas hydrates?

Gas hydrates look very similar to snow or loose ice, which contains the energy of natural gas inside. From a scientific point of view, gas hydrate (they are also called clathrates) are several water molecules holding a methane or other hydrocarbon gas molecule inside their compound. Gas hydrates are formed at certain temperatures and pressures, which makes it possible for such "ice" to exist at positive temperatures.

The formation of gas hydrate deposits (plugs) inside various oil and gas facilities is the cause of major and frequent accidents. For example, according to one version, the cause of the largest accident in the Gulf of Mexico on the Deepwater Horizon platform was a hydrate plug formed in one of the pipes.

Due to their unique properties, namely, the high specific concentration of methane in compounds, the high prevalence along the coasts, natural gas hydrates have been considered the main source of hydrocarbons on Earth since the middle of the 19th century, amounting to approximately 60% of the total stock. Strange, isn't it? After all, we are used to hearing from the media only about natural gas and oil, but perhaps in the next 20-25 years the struggle will go for another resource.

To understand the full scale of gas hydrate deposits, let's say that, for example, the total volume of air in the Earth's atmosphere is 1.8 times less than the estimated volume of gas hydrates. The main accumulations of gas hydrates are located in close proximity to the Sakhalin Peninsula, the shelf zones of the northern seas of Russia, the northern slope of Alaska, near the islands of Japan and the southern coast of North America.

Russia contains about 30,000 trillion. cube m of hydrated gas, which is three orders of magnitude higher than the volume of traditional natural gas today (32.6 trillion cubic meters).

An important problem is the economic component in the development and commercialization of gas hydrates. It's too expensive to get them today.

If today our stoves and boilers were supplied with household gas extracted from gas hydrates, then 1 cubic meter would cost about 18 times more.

How are they mined?

Clathrates can be mined today in various ways. There are two main groups of methods - mining in the gaseous state and in the solid state.

The most promising is the production in the gaseous state, namely the depressurization method. The deposit is opened, where gas hydrates are located, the pressure begins to fall, which brings the "gas snow" out of balance, and it begins to decompose into gas and water. This technology has already been used by the Japanese in their pilot project.

Russian projects for the research and development of gas hydrates began in the days of the USSR and are considered fundamental in this area. Due to the discovery of a large number of traditional natural gas fields, which are economically attractive and accessible, all projects were suspended, and the accumulated experience was transferred to foreign researchers, leaving many promising developments out of work.

Where are gas hydrates used?

A little-known, but very promising energy resource can be used not only for furnaces and cooking. The result of innovative activity can be considered the technology of transportation of natural gas in the hydrated state (HNG). It sounds very complicated and scary, but in practice everything is more than clear. A man came up with the idea of ​​“packing” the produced natural gas not into a pipe and not into the tanks of an LNG tanker (liquefaction of natural gas), but into an ice shell, in other words, to make artificial gas hydrates for transporting gas to a consumer.

With comparable volumes of commercial gas supplies, these technologies consume 14% less energy than gas liquefaction technologies (when transported over short distances) and 6% less when transported over distances of several thousand kilometers, require the least reduction in storage temperature (-20 degrees C versus -162). Summarizing all the factors, we can conclude that gas hydrate transport more economical liquefied transport by 12−30%.

With hydrate gas transport, the consumer receives two products: methane and fresh (distilled) water, which makes such gas transport especially attractive for consumers located in arid or polar regions (for every 170 cubic meters of gas, there is 0.78 cubic meters of gas). water).

Summing up, we can say that gas hydrates are the main energy resource of the future on a global scale, and also have tremendous prospects for the oil and gas complex of our country. But these are very far-sighted prospects, the effect of which we can see in 20 or even 30 years, not earlier.

By not taking part in the large-scale development of gas hydrates, the Russian oil and gas complex may face some significant risks. Alas, today's low prices for hydrocarbons and the economic crisis are increasingly calling into question research projects and the start of industrial development of gas hydrates, especially in our country.

Gas hydrates are solid solutions, the solvent of which is a crystal lattice consisting of water molecules. Molecules of "dissolved gas" are placed inside the water, the sizes of which determine the possibility of the formation of hydrates only from methane, ethane, propane and isobutane. The formation of gas hydrates requires low temperatures and pressures, combinations of which are possible under reservoir conditions only in areas where a thick layer of permafrost develops.

According to various estimates, the reserves of terrestrial hydrocarbons in hydrates range from 1.8·10 5 to 7.6·10 9 km³. Now natural gas hydrates are attracting special attention as a possible source of fossil fuels, as well as a participant in climate change.

Formation of gas hydrates

Gas hydrates are divided into technogenic (artificial) and natural (natural). All known gases at certain pressures and temperatures form crystalline hydrates, the structure of which depends on the composition of the gas, pressure and temperature. Hydrates can stably exist in a wide range of pressures and temperatures. For example, methane hydrate exists at pressures from 2*10 -8 to 2*10 3 MPa and temperatures from 70 to 350 K.

Some properties of hydrates are unique. For example, one volume of water during the transition to the hydrate state binds 207 volumes of methane. At the same time, its specific volume increases by 26% (when water freezes, its specific volume increases by 9%). 1 m 3 methane hydrate at P=26 atm and T=0°C contains 164 volumes of gas. In this case, the share of gas accounts for 0.2 m 3, for water 0.8 m 3. The specific volume of methane in the hydrate corresponds to a pressure of about 1400 atm. The decomposition of the hydrate in a closed volume is accompanied by a significant increase in pressure. Figure 3.1.1 shows a diagram of the conditions for the existence of hydrate of some components of natural gas in the pressure-temperature coordinates.

Figure 3.1.1 - Curves of gas-hydrate formation for some components of natural gas.

The following three conditions are necessary for the formation of a gas hydrate:

1. Favorable thermobaric conditions. The formation of gas hydrates is favored by a combination of low temperature and high pressure.

2. The presence of a hydrate-forming substance. Hydrate-forming substances include methane, ethane, propane, carbon dioxide, etc.

3. Enough water. Water should not be too little or too much.

To prevent gas hydrate formation, it is sufficient to exclude one of the three conditions.

Natural gas hydrates are a metastable mineral, the formation and decomposition of which depends on temperature, pressure, the chemical composition of gas and water, the properties of the porous medium, etc.

The morphology of gas hydrates is very diverse. Currently, there are three main types of crystals:

massive crystals. They are formed due to the sorption of gas and water on the entire surface of a continuously growing crystal;

whisker crystals. Arise during tunnel sorption of molecules to the base of a growing crystal;

gel crystals. They are formed in the volume of water from the gas dissolved in it when the conditions of hydrate formation are reached.

In rock layers, hydrates can be either distributed in the form of microscopic inclusions or form large particles, up to extended layers of many meters in thickness.

Due to its clathrate structure, a single volume of gas hydrate can contain up to 160-180 volumes of pure gas. The density of the hydrate is lower than the density of water and ice (for methane hydrate about 900 kg/m³).

The following phenomena contribute to the accelerated formation of gas hydrates:

· Turbulence. The formation of gas hydrates actively proceeds in areas with high flow rates of the medium. When mixing gas in a pipeline, process tank, heat exchanger, etc. the intensity of gas hydrate formation increases.

centers of crystallization. The center of crystallization is a point at which there are favorable conditions for a phase transformation, in this case, the formation of a solid phase from a liquid one.

· Free water. The presence of free water is not a prerequisite for hydrate formation, but the intensity of this process in the presence of free water increases significantly. In addition, the water-gas interface is a convenient center of crystallization for the formation of gas hydrates.

The structure of hydrates

In the structure of gas hydrates, water molecules form an openwork frame (i.e., the host lattice), in which there are cavities. It has been established that the framework cavities are usually 12-sided (“small” cavities), 14-, 16- and 20-sided (“large” cavities), slightly deformed relative to the ideal shape. These cavities can be occupied by gas molecules (“guest molecules”). Gas molecules are connected to the water frame by van der Waals bonds. In general, the composition of gas hydrates is described by the formula M n H 2 O, where M is a hydrate-forming gas molecule, n is the number of water molecules per one included gas molecule, and n is a variable number depending on the type of hydrate generator, pressure and temperature.

Cavities, combined with each other, form a continuous structure of various types. According to the accepted classification, they are called CS, TS, GS - respectively, cubic, tetragonal and hexagonal structure. In nature, hydrates of types KS-I (eng. sI), KS-II (eng. sII) are most common, while the rest are metastable.

Table 3.2.1 - Some structures of clathrate frameworks of gas hydrates.

Figure 3.2.1 - Crystalline modifications of gas hydrates.

With an increase in temperature and a decrease in pressure, the hydrate decomposes into gas and water with the absorption of a large amount of heat. Decomposition of hydrate in a closed volume or in a porous medium (natural conditions) leads to a significant increase in pressure.

Crystalline hydrates have high electrical resistance, conduct sound well, and are practically impermeable to free water and gas molecules. They are characterized by anomalously low thermal conductivity (for methane hydrate at 273 K it is five times lower than that of ice).

To describe the thermodynamic properties of hydrates, the van der Waals-Platteu theory is currently widely used. The main provisions of this theory:

· the host lattice is not deformed depending on the degree of filling with guest molecules or on their type;

Each molecular cavity can contain no more than one guest molecule;

interaction of guest molecules is negligible;

Statistical physics applies to the description.

Despite the successful description of the thermodynamic characteristics, the van der Waals-Platteu theory contradicts the data of some experiments. In particular, it has been shown that guest molecules are able to determine both the symmetry of the hydrate crystal lattice and the sequence of phase transitions of the hydrate. In addition, a strong influence of the guests on the host molecules was found, causing an increase in the most probable frequencies of natural oscillations.

Most natural gases (CH4, C2H6, C3H8, CO2, N2, H2S, isobutane, etc.) form hydrates that exist under certain thermobaric conditions. The area of ​​their existence is confined to sea bottom sediments and areas of permafrost. The predominant natural gas hydrates are methane and carbon dioxide hydrates.

During gas production, hydrates can form in wellbores, industrial communications and main gas pipelines. Being deposited on the walls of pipes, hydrates sharply reduce their throughput. To combat the formation of hydrates in gas fields, various inhibitors (methyl alcohol, glycols, 30% CaCl2 solution) are introduced into wells and pipelines, and the temperature of the gas flow is maintained above the temperature of hydrate formation using heaters, thermal insulation of pipelines and selection of an operating mode that ensures maximum temperature of the gas stream. To prevent hydrate formation in main gas pipelines, gas drying is the most effective - gas purification from water vapor.

Composition and properties of water

About 71% of the Earth's surface is covered with water (oceans, seas, lakes, rivers, ice) - 361.13 million km2. On Earth, approximately 96.5% of water is in the oceans, 1.7% of the world's reserves are groundwater, another 1.7% are glaciers and ice caps of Antarctica and Greenland, a small part is in rivers, lakes and swamps, and 0.001% in clouds (formed from particles of ice and liquid water suspended in the air). Most of the earth's water is salty, unsuitable for agriculture and drinking. The share of fresh water is about 2.5%, and 98.8% of this water is in glaciers and groundwater. Less than 0.3% of all fresh water is found in rivers, lakes and the atmosphere, and an even smaller amount (0.003%) is found in living organisms.

The role of water in the origin and maintenance of life on Earth, in the chemical structure of living organisms, in the formation of climate and weather is extremely important. Water is the most important substance for all living beings on planet Earth.

The chemical composition of water

Water (hydrogen oxide) is a binary inorganic compound with the chemical formula H 2 O. The water molecule consists of two hydrogen atoms and one oxygen, which are interconnected by a covalent bond. Under normal conditions, it is a transparent liquid, colorless (in a small volume), odor and taste. In the solid state it is called ice (ice crystals can form snow or frost), and in the gaseous state it is called water vapor. Water can also exist as liquid crystals (on hydrophilic surfaces). It is approximately 0.05 the mass of the Earth.

The composition of water can be determined using the decomposition reaction by electric current. Two volumes of hydrogen are formed per one volume of oxygen (the volume of gas is proportional to the amount of substance):

2H 2 O \u003d 2H 2 + O 2

Water is made up of molecules. Each molecule contains two hydrogen atoms linked by covalent bonds to one oxygen atom. The angle between bonds is about 105º.

The world reserves of shale gas are estimated at approximately 200 trillion cubic meters, conventional gas (including oil associated) - at 300 trillion cubic meters ... But this is only a negligible part of the total amount of natural gas on Earth: its main part found in the form of gas hydrates at the bottom of the oceans. Such hydrates are clathrates of natural gas molecules (primarily methane hydrate). In addition to the ocean floor, gas hydrates exist in permafrost.

It is still difficult to accurately determine the reserves of gas hydrates at the bottom of the oceans, however, according to an average estimate, there is about 100 quadrillion cubic meters of methane (when reduced to atmospheric pressure). Thus, gas reserves in the form of hydrates at the bottom of the world's oceans are a hundred times greater than shale and conventional gas combined.

Gas hydrates have a different composition, these are clathrate-type chemical compounds(the so-called lattice clathrate), when foreign atoms or molecules (“guests”) can penetrate into the cavity of the “host” (water) crystal lattice. In everyday life, the most famous clathrate is copper sulfate (copper sulfate), which has a bright blue color (this color is only in crystalline hydrate, anhydrous copper sulfate is white).

Gas hydrates are also crystalline hydrates. At the bottom of the oceans, where for some reason natural gas was released, natural gas does not rise to the surface, but chemically binds with water, forming crystalline hydrates. This process is possible at great depths, where is the pressure, or in permafrost conditions, where always negative temperature.

Gas hydrates (in particular, methane hydrate) is a solid, crystalline substance. 1 volume of gas hydrate contains 160-180 volumes of pure natural gas. The density of the gas hydrate is approximately 0.9 g/cm3, which is less than the density of water and ice. They are lighter than water and should have floated up, and then the gas hydrate would have decomposed into methane and water with a decrease in pressure, and the whole would have evaporated. However, this does not happen.

This is prevented by the sedimentary rocks of the ocean floor - it is on them that hydrate formation occurs. Interacting with the sedimentary rocks of the bottom, the hydrate cannot emerge. Since the bottom is not flat, but indented, then gradually samples of gas hydrates, together with sedimentary rocks, sink down and form joint deposits. The zone of hydrate formation is at the bottom, where natural gas comes from a source. The process of formation of deposits of this type lasts a long time, and gas hydrates in a "pure" form do not exist, they are necessarily accompanied by rocks. The result is a gas hydrate field - an accumulation of gas hydrate rocks on the ocean floor.

The formation of gas hydrates requires either low temperatures or high pressures. The formation of methane hydrate at atmospheric pressure becomes possible only at a temperature of -80 °C. Such frosts are possible (and even then very rarely) only in Antarctica, but in a metastable state, gas hydrates can exist at atmospheric pressure and at higher temperatures. But these temperatures must still be negative - ice crust formed by the disintegration of the upper layer, further protects hydrates from decay, which is what takes place in permafrost regions.

For the first time, gas hydrates were encountered during the development of the seemingly ordinary Messoyakhskoye field (Yamal-Nenets Autonomous Okrug) in 1969, from which, by a combination of factors, it was possible to extract natural gas directly from gas hydrates - about 36% of the volume of gas extracted from it had hydrate origin.

Besides, gas hydrate decomposition reaction is endothermic, that is, energy during decomposition is absorbed from the external environment. Moreover, a lot of energy must be expended: if the hydrate begins to decompose, it cools itself and its decomposition stops.

At a temperature of 0 °C, methane hydrate will be stable at a pressure of 2.5 MPa. The water temperature near the bottom of the seas and oceans is strictly +4 ° C - under such conditions, water has the highest density. At this temperature, the pressure necessary for the stable existence of methane hydrate will already be twice as high as at 0 °C and will be 5 MPa. Accordingly, methane hydrate can only occur at a water depth of more than 500 meters , since approximately 100 meters of water correspond to a pressure of 1 MPa.

In addition to "natural" gas hydrates, the formation of gas hydrates is a big problem in main gas pipelines located in temperate and cold climates, since gas hydrates can clog the gas pipeline and reduce its throughput. In order to prevent this from happening, a small amount of a hydrate formation inhibitor is added to natural gas, mainly methyl alcohol, diethylene glycol, triethylene glycol, and sometimes chloride solutions (mainly table salt or cheap calcium chloride) are used. Or they simply use heating, preventing the gas from cooling to the temperature of the beginning of hydrate formation.

Given the huge reserves of gas hydrates, interest in them is currently very high - after all, apart from the 200-mile economic zone, the ocean is a neutral territory and any country can start extracting natural gas from natural resources of this type . Therefore, it is likely that natural gas from gas hydrates is the fuel of the near future, if it can be developed cost-effective way to extract it.

However, the extraction of natural gas from hydrates is an even more difficult task than the extraction of shale gas, which is based on hydraulic fracturing of oil shale. It is impossible to extract its gas hydrates in the traditional sense: the layer of hydrates is located on the ocean floor, and just drilling a well is not enough. Need to break down hydrates.

This can be done either by lowering the pressure in some way (the first method), or by heating the rock with something (the second method). The third method involves a combination of both actions. After that, it is necessary to collect the released gas. It is also unacceptable for methane to enter the atmosphere, because methane is a strong greenhouse gas, acting about 20 times stronger than carbon dioxide. Theoretically, it is possible to use inhibitors (the same ones used in gas pipelines), but in reality the cost of inhibitors is too high for their practical application.

The attractiveness of hydrate gas production for Japan is that, according to ultrasonic studies, gas hydrate reserves in the ocean near Japan are estimated in the range from 4 to 20 trillion cubic meters. There are many hydrate deposits in other areas of the ocean. In particular, there are huge reserves of hydrates at the bottom of the Black Sea (according to approximate estimates, 30 trillion cubic meters) and even at the bottom of Lake Baikal.

A pioneer in extracting natural gas from hydrates the Japanese company Japan Oil, Gas and Metal National Corporarion spoke. Japan is a highly developed country, but extremely poor in natural resources, and is the largest importer of natural gas in the world, the demand for which has only increased since the accident at the Fukushima nuclear power plant.

For the experimental production of methane hydrates using a drilling ship, Japanese specialists choose the pressure reduction option (decompression) . Test production of natural gas from hydrates has been successfully carried out about 80 km south of the Atsumi Peninsula, where the sea is about a kilometer deep. The Japanese research vessel Chikyu has been drilling three test wells to a depth of 260 meters (excluding ocean depth) for approximately a year (since February 2012). With the help of a special depressurization technology, gas hydrates decomposed.

Although the trial production lasted only 6 days (from March 12 to 18, 2013), despite the fact that a two-week production was planned (bad weather interfered), 120 thousand cubic meters of natural gas were produced (an average of 20 thousand cubic meters per day). The Ministry of Economy, Trade and Industry of Japan described the production results as "impressive", the output far exceeded the expectations of Japanese specialists.

Full-scale industrial development of the field is planned to begin in 2018-2019 after the "development of appropriate technologies." Whether these technologies will be profitable and whether they will appear - time will tell. Too many technological problems will need to be solved. In addition to gas production, also it will need to be compressed or liquefied, which will require a powerful compressor on the ship or a cryogenic plant. Therefore, the production of gas hydrates is likely to cost more than shale gas, the production cost of which is $120-150 per thousand cubic meters. For comparison: the cost of traditional gas from traditional fields does not exceed $50 per thousand cubic meters.

Nikolai Blinkov