Composition and properties of gas hydrates. Gas hydrates - iv_g

National Mineral Resource University Mining

Scientific adviser: Gulkov Yury Vladimirovich, Candidate of Technical Sciences, National Mineral and Raw Materials University of Mining

Annotation:

This article discusses the chemical and physical properties gas hydrates, the history of their study and research. In addition, the main problems that impede the organization of commercial production of gas hydrates are considered.

In this article we describe the chemical and physical characteristics of gas hydrates, the history of their study and research. In addition, the basic problems hindering the organization of commercial production of gas hydrates are considered.

Keywords:

gas hydrates; energy; commercial mining; Problems.

gas hydrates; power engineering; commercial extraction; Problems.

UDC 622.324

Introduction

Initially, man used his own powers as a source of energy. After some time, the energy of wood and organics came to the rescue. About a century ago, coal became the main energy resource; 30 years later, oil shared its primacy. Today, the energy of the world is based on the gas-oil-coal triad. However, in 2013 this balance was shifted towards gas by Japanese energy companies. Japan- world leader in gas imports. The State Corporation of Oil, Gas and Metals (JOGMEC) (Japan Oil, Gas & Metals National Corp.) managed to be the first in the world to get gas from methane hydrate at the bottom of the Pacific Ocean from a depth of 1.3 kilometers. Trial production lasted only 6 weeks, despite the fact that the plan considered a two-week production, 120 thousand cubic meters of natural gas were produced. This discovery will allow the country to become independent of imports, radically change its economy. What is a gas hydrate and how can it affect the global energy industry?

The purpose of this article is to consider problems in the development of gas hydrates.

For this, the following tasks were set:

• Explore the history of gas hydrate research
• Study chemical and physical properties
• Consider the main problems of development

Relevance

Traditional resources are not evenly distributed over the Earth, moreover, they are limited. According to modern estimates, oil reserves by today's consumption standards will last for 40 years, natural gas energy resources - for 60-100. The world reserves of shale gas are estimated at about 2,500-20,000 trillion. cube m. This is the energy reserve of mankind for more than a thousand years. Commercial extraction of hydrates would raise the world energy to a qualitatively new level. In other words, the study of gas hydrates has opened up an alternative source of energy for mankind. But there are also a number of serious obstacles to their study and commercial production.

History reference

The possibility of the existence of gas hydrates was predicted by IN Strizhov, but he spoke about the inexpediency of their extraction. Methane hydrate was first obtained in the laboratory by Villars in 1888, along with hydrates of other light hydrocarbons. Initial collisions with gas hydrates were seen as problems and hindrances to energy production. In the first half of the 20th century, it was found that gas hydrates are the cause of plugging in gas pipelines located in the Arctic regions (at temperatures above 0 °C). In 1961 the discovery of Vasiliev V.G., Makagon Yu.F., Trebin F.A., Trofimuk A.A., Chersky N.V. was registered. "The property of natural gases to be in the solid state of the earth's crust", which heralded a new natural source hydrocarbons - gas hydrate. After that, they started talking louder about the exhaustibility of traditional resources, and already 10 years later, the first gas hydrate deposit was discovered in January 1970 in the Arctic, on the border of Western Siberia, it is called Messoyakha. Further, large expeditions of scientists from both the USSR and many other countries were carried out.

Chemistry and physics word

Gas hydrates are gas molecules surrounded by water molecules, like a "gas in a cage". This is called the water clathrate framework. Imagine that in the summer you caught a butterfly in your palms, a butterfly is a gas, your palms are water molecules. Because you protect the butterfly from external influences, but it will retain its beauty and individuality. This is how a gas behaves in a clathrate framework.

Depending on the conditions of formation and the state of the hydrate former, hydrates externally look like clearly defined transparent crystals of various shapes or represent an amorphous mass of densely compressed "snow".

Hydrates occur under certain thermobaric conditions - phase equilibrium. At atmospheric pressure gas hydrates of natural gases exist up to 20-25 °C. Due to its structure, a single volume of gas hydrate can contain up to 160–180 volumes of pure gas. The density of methane hydrate is about 900 kg/m³, which is lower than the density of water and ice. When the phase equilibrium is violated: an increase in temperature and / or a decrease in pressure, the hydrate decomposes into gas and water with the absorption of a large amount of heat. Crystalline hydrates have high electrical resistance, conduct sound well, and are practically impermeable to free water and gas molecules, and have low thermal conductivity.

Development

Gas hydrates are difficult to access, because To date, it has been established that about 98% of gas hydrate deposits are concentrated on the shelf and continental slope of the ocean, at water depths of more than 200-700 m, and only 2% - in the subpolar parts of the continents. Therefore, problems in the development of commercial production of gas hydrates are encountered already at the stage of development of their deposits.

To date, there are several methods for detecting gas hydrate deposits: seismic sounding, gravimetric method, measurement of heat and diffuse flows over the deposit, study of the dynamics of the electromagnetic field in the region under study, etc.

In seismic sounding, two-dimensional (2-D) seismic data are used in the presence of free gas under a hydrate-saturated reservoir, the lower position of hydrate-saturated rocks is determined. But during seismic exploration, it is impossible to detect the quality of the deposit, the degree of hydrate saturation of the rocks. In addition, seismic exploration is not applicable to complex terrain. But it is more profitable from the economic side, however, it is better to use it in addition to other methods.

For example, gaps can be filled by applying electromagnetic exploration in addition to seismic exploration. It will allow to more accurately characterize the rock, due to individual resistances at the occurrence points of gas hydrates. The US Department of Energy plans to conduct it from 2015. The seismoelectromagnetic method was used to develop the Black Sea deposits.

It is also cost-effective to develop a field of saturated deposits using a combined development method, when the process of hydrate decomposition is accompanied by a decrease in pressure with simultaneous thermal exposure. Lowering the pressure will save the thermal energy spent on the dissociation of hydrates, and the heating of the pore medium will prevent the re-formation of gas hydrates in the bottomhole formation zone.

Mining

The next stumbling block is directly the extraction of hydrates. Hydrates lie in solid form, which causes difficulties. Since the gas hydrate lies under certain thermobaric conditions, if one of them is violated, it will decompose into gas and water, in accordance with this, the following hydrate extraction technologies have been developed.

1. Depressurization:

When the hydrate is out of phase equilibrium, it decomposes into gas and water. This technology is famous for its triviality and economic feasibility, in addition, the success of the first Japanese mining in 2013 falls on its shoulders. But not everything is so rosy: the resulting water during low temperatures may clog the equipment. In addition, the technology is really effective, because. 13,000 cu. m of gas, which is many times higher than the production rates at the same field using heating technology - 470 cubic meters. m of gas in 5 days. (see table)

2. Heating:

Again, you need to decompose the hydrate into gas and water, but by means of heat supply. Heat can be supplied in different ways: coolant injection, hot water circulation, steam heating, electric heating. I would like to dwell on an interesting technology invented by researchers from the University of Dortmund. The project involves laying a pipeline to gas hydrate deposits on seabed. Its peculiarity is that the pipe has double walls. Sea water heated to 30-40˚С, the phase transition temperature, is supplied to the field through the inner pipe, and bubbles of gaseous methane, together with water, rise up through the outer pipe. There, methane is separated from the water, sent to tanks or to the main pipeline, and warm water returns down to the gas hydrate deposits. However, this extraction method requires high costs, a constant increase in the amount of heat supplied. In this case, the gas hydrate decomposes more slowly.

3. Introduction of the inhibitor:

Also, for the decomposition of the hydrate, I use the introduction of an inhibitor. At the Institute of Physics and Technology of the University of Bergen, carbon dioxide was considered as an inhibitor. Using this technology, it is possible to obtain methane without the direct extraction of the hydrates themselves. This method is already being tested by the Japan National Oil, Gas and Metals Corporation (JOGMEC) with the support of the US Department of Energy. But this technology is fraught with environmental hazards and requires high costs. The reactions proceed more slowly.

Project name	the date	Participating countries	Companies	Technology
Mallik, Canada		Japan, USA Channel, Germany, India	JOGMEC, BP, Chevron Texaco	Heater (coolant-water)
North Slope of Alaska, USA		USA, Japan	Conoco Phillips, JOGMEC	Carbon dioxide injection, inhibitor injection
Alaska, USA			BP, Schlumberger	Drilling to study the properties of gas hydrate
Mallik, Canada		Japan, Canada	JOGMEC as part of a private public consortium	Depressurization
fire in iceIgnikSikumi), Alaska, USA		USA, Japan, Norway	Conoco Phillips, JOGMEC, University of Bergen (Norway)	carbon dioxide injection
A joint project (jointIndustryproject) Gulf of Mexico, USA			Chevron as consortium leader	Drilling to study the geology of gas hydrates
Near the Atsumi Peninsula, Japan			JOGMEC, JAPEX, Japan Drilling	Depressurization

Source - analytical center based on open source materials

Technology

Another reason for the lack of development of commercial production of hydrates is the lack of technology for their profitable production, which provokes large investments. Depending on the technology, different barriers are encountered: operation of special equipment for the introduction of chemical elements and / or local heating to avoid the re-formation of gas hydrates and clogging of wells; the use of technologies that prevent the extraction of sand.

For example, in 2008, according to preliminary estimates for the Mallik field in the Canadian Arctic, it was indicated that development costs ranged from 195-230 dollars per thousand tons. cube m for gas hydrates located above the free gas, and in the range of 250-365 dollars / thousand. cube m for gas hydrates located above free water.

To solve this problem, it is necessary to popularize the commercial extraction of hydrates among scientific personnel. Organize more scientific conferences, competitions to improve old or create new equipment, which could provide lower costs.

environmental hazard

Moreover, the development of gas hydrate deposits will inevitably lead to an increase in the volume of natural gas emissions into the atmosphere and, as a result, to an increase in the greenhouse effect. Methane is a powerful greenhouse gas and, despite having a shorter atmospheric lifetime than CO₂, the warming caused by emissions large quantities methane will be ten times faster than the warming caused by carbon dioxide. In addition, if global warming, the greenhouse effect or for other reasons causes the collapse of at least one gas hydrate deposit, this will cause a colossal release of methane into the atmosphere. And, like an avalanche, from one occurrence to another, it will lead to global change climate on Earth, and the consequences of these changes cannot even be approximately predicted.

To avoid this, it is necessary to integrate data from complex exploration analyzes and predict the possible behavior of deposits.

Detonation

Another unsolved problem for miners is the rather unpleasant property of gas hydrates to “detonate” at the slightest shaking. In this case, the crystals quickly go through the phase of transformation into a gaseous state, and acquire a volume several tens of times greater than the original one. Therefore, the reports of Japanese geologists very carefully talk about the prospects for the development of methane hydrates - after all, the disaster of the Deepwater Horizon drilling platform, according to a number of scientists, including Professor Robert Bee of the University of California at Berkeley, was the result of the explosion of a giant methane bubble, which was formed from bottom hydrate deposits disturbed by drillers.

Oil and gas

Gas hydrates are considered not only from the side of an energy resource, they are more often encountered during oil production. And again, we turn to the sinking of the Deepwater Horizon platform in the Gulf of Mexico. Then, to control the escaping oil, a special box was built, which was planned to be placed above the emergency wellhead. But the oil turned out to be very carbonated, and methane began to form entire ice floes of gas hydrates on the walls of the box. They are about 10% lighter than water, and when the amount of gas hydrates became large enough, they simply began to raise the box, which, in general, was predicted by experts in advance.

The same problem was encountered in the production of conventional gas. 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. To prevent this from happening, not added to natural gas a large number of inhibitor or just use heating.

These problems are solved in the same way as in production: by lowering the pressure, by heating, by introducing an inhibitor.

Conclusion

In this article, the barriers that stand in the way of commercial production of gas hydrates were considered. They are encountered already at the stage of development of gas fields, directly during the production itself. In addition, gas hydrates are currently a problem in oil and gas production. Today, impressive reserves of gas hydrates, economic profitability require the accumulation of information and clarifications. Experts are still on the lookout optimal solutions development of gas hydrate deposits. But with the development of technology, the cost of developing deposits should decrease.

Bibliographic list:

1. Vasiliev A., Dimitrov L. Evaluation of the spatial distribution and reserves of gas hydrates in the Black Sea // Geology and Geophysics. 2002. No. 7. v. 43.
2. Dyadin Yu.A., Gushchin A.L. gas hydrates. // Soros Educational Journal, No. 3, 1998, p. 55–64
3. Makogon Yu.F. Natural gas hydrates: distribution, formation models, resources. – 70 s.
4. Trofimuk A. A., Makogon Yu. F., Tolkachev M. V., Chersky N. V. Features of detection of exploration and development of gas hydrate deposits - 2013 [Electronic resource] http://vimpelneft.com/fotogalereya/ 6-komanda-vymlnefti/detail/32-komanda-vympelnefti
5. Chemistry and Life, 2006, No. 6, p. 8.
6. The Day The Earth Nearly Died - 5. 12. 2002 [ electronic resource] http://www.bbc.co.uk/science/horizon/2002/dayearthdied.shtml

Reviews:

12/1/2015, 12:12 Mordashev Vladimir Mikhailovich
Review: The article is devoted to a wide range of problems related to the urgent task of developing gas hydrates - a promising energy resource. The solution of these problems will require, among other things, the analysis and generalization of heterogeneous data from scientific and technological research, which are often disordered and chaotic. Therefore, the reviewer recommends the authors in their further work pay attention to the article "Empiricism for Chaos", site, No. 24, 2015, p. 124-128. The article "Problems of development of gas hydrates" is of undoubted interest for a wide range of specialists, it should be published.

12/18/2015 2:02 AM Reply to the author's review Polina Robertovna Kurikova:
I got acquainted with the article, with the further development of the topic, the solution of the problems covered, I will use these recommendations. Thanks to.

A few years ago, among economists, that is, people far from technology, the theory of "depletion of hydrocarbons" was popular. In many publications that make up the color of the global financial elite, it was discussed: what will the world be like if the planet soon runs out of, for example, oil? And what will be the prices for it when the process of "exhaustion" enters, so to speak, into an active phase?

However, the “shale revolution”, which is now taking place literally before our eyes, has removed this topic at least into the background. It became clear to everyone what only a few experts had said before: there are still enough hydrocarbons on the planet. It is obviously too early to talk about their physical exhaustion.

The real issue is the development of new production technologies that allow hydrocarbons to be extracted from sources previously considered inaccessible, as well as the cost of the resources obtained with their help. You can get almost anything, it will just be more expensive.

All this makes humanity look for new "non-traditional sources of traditional fuel." One of them is the shale gas mentioned above. GAZ Technology has already written about various aspects related to its production more than once.

However, there are other such sources. Among them are the "heroes" of our today's material - gas hydrates.

What it is? In the very general sense gas hydrates are crystalline compounds formed from gas and water at certain temperature (rather low) and pressure (rather high).

Note: a variety of chemicals can take part in their formation. It doesn't have to be about hydrocarbons. The first gas hydrates scientists ever observed consisted of chlorine and sulfur dioxide. By the way, this happened at the end of the 18th century.

However, since we are interested in the practical aspects associated with the production of natural gas, we will talk here primarily about hydrocarbons. Moreover, under real conditions, it is methane hydrates that predominate among all hydrates.

According to theoretical estimates, the reserves of such crystals are literally amazing. According to the most conservative estimates, we are talking about 180 trillion cubic meters. More optimistic estimates give a figure that is 40,000 times higher. With such indicators, you will agree, it is even somehow inconvenient to talk about the exhaustibility of hydrocarbons on Earth.

It must be said that the hypothesis of the presence of huge deposits of gas hydrates in the conditions of the Siberian permafrost was put forward by Soviet scientists back in the formidable 40s of the last century. After a couple of decades, she found her confirmation. And in the late 60s, the development of one of the deposits even began.

Subsequently, scientists calculated that the zone in which methane hydrates are able to be in a stable state covers 90 percent of the entire sea and ocean floor of the Earth and plus 20 percent of the land. It turns out that we are talking about a potentially common mineral.

The idea of ​​extracting "solid gas" really looks attractive. Moreover, a unit volume of hydrate contains about 170 volumes of the gas itself. That is, it would seem that it is enough to get quite a few crystals in order to obtain a large yield of hydrocarbons. From a physical point of view, they are in a solid state and represent something like loose snow or ice.

The problem, however, is that gas hydrates are located, as a rule, in very hard-to-reach places. “Intrapermafrost deposits contain only a small part of the gas resources that are associated with natural gas hydrates. The main part of the resources is confined to the zone of stability of gas hydrates - that interval of depths (usually a few hundred meters), where thermodynamic conditions for hydrate formation take place. In the north of Western Siberia, this is a depth interval of 250-800 m, in the seas - from the bottom surface to 300-400 m, in especially deep areas of the shelf and continental slope up to 500-600 m below the bottom. It was in these intervals that the bulk of natural gas hydrates was discovered, ”Wikipedia reports. Thus, we are talking, as a rule, about working in extreme deep-sea conditions, at high pressure.

The extraction of gas hydrates may be associated with other difficulties. Such compounds are capable, for example, of detonating even with slight shocks. They very quickly pass into a gaseous state, which in a limited volume can cause sudden pressure surges. According to specialized sources, it is precisely these properties of gas hydrates that have become a source of serious problems for production platforms in the Caspian Sea.

In addition, methane is one of the gases that can create a greenhouse effect. If industrial production causes its massive emissions into the atmosphere, this is fraught with an aggravation of the problem. global warming. But even if this does not happen in practice, the close and unfriendly attention of the "green" to such projects is practically guaranteed. And their positions in the political spectrum of many states today are very, very strong.

All this extremely "weights" projects for the development of technologies for the extraction of methane hydrates. In fact, there are no truly industrial ways to develop such resources on the planet yet. However, relevant developments are underway. There are even patents issued to the inventors of such methods. Their description is sometimes so futuristic that it seems written off from a book by some science fiction writer.

For example, "Method of extraction of gas hydrate hydrocarbons from the bottom water basins and a device for its implementation (RF patent No. 2431042)”, stated on the website http://www.freepatent.ru/: “The invention relates to the field of mining on the seabed. The technical result is to increase the production of gas hydrated hydrocarbons. The method consists in destroying the bottom layer with sharp edges of buckets fixed on a vertical conveyor belt moving along the bottom of the pool with the help of a caterpillar mover, relative to which the conveyor belt moves vertically, with the possibility of deepening into the bottom. At the same time, the gas hydrate is lifted to the zone isolated from water by the surface of the overturned funnel, where it is heated, and the released gas is transported to the surface using a hose fixed at the top of the funnel, subjecting it to additional heating. A device for implementing the method is also proposed. Note: all this should take place in sea water, at a depth of several hundred meters. It is even difficult to imagine how difficult this engineering task is, and how much methane produced in this way can cost.

There are, however, other ways. Here is a description of another method: “There is a known method for extracting gases (methane, its homologues, etc.) from solid gas hydrates in the bottom sediments of the seas and oceans, in which two strings of pipes are immersed into a well drilled to its bottom of the identified gas hydrate formation - pumping and pumping. Natural water at natural temperature or heated enters through the injection pipe and decomposes gas hydrates into a gas-water system that accumulates in a spherical trap formed at the bottom of the gas hydrate formation. Emitted gases are pumped out of this trap through another pipe string ... The disadvantage of the known method is the need for underwater drilling, which is technically burdensome, costly and sometimes irreparably disrupting the existing underwater environment of the reservoir ”(http://www.findpatent.ru).

Other descriptions of this kind could be given. But it is clear from what has already been listed: the industrial production of methane from gas hydrates is still a matter of the future. It will require the most complex technological solutions. And the economics of such projects is not yet obvious.

However, work in this direction is underway, and quite actively. They are especially interested in countries located in the fastest growing region of the world, which means that there is ever-new demand for gas fuel. We are talking, of course, about Southeast Asia. One of the states working in this direction is China. Thus, according to the newspaper "People's Daily", in 2014, marine geologists conducted a large-scale study of one of the sites located near its coast. Drilling has shown that it contains gas hydrates of high purity. A total of 23 wells were drilled. This made it possible to establish that the area of ​​distribution of gas hydrates in the area is 55 square kilometers. And its reserves, according to Chinese experts, amount to 100-150 trillion cubic meters. The given figure, frankly speaking, is so high that it makes one wonder if it is not too optimistic, and whether such resources can really be extracted (Chinese statistics in general often raise questions among specialists). Nevertheless, it is obvious that Chinese scientists are actively working in this direction, looking for ways to provide their rapidly growing economy with much-needed hydrocarbons.

The situation in Japan, of course, is very different from what is observed in China. However, the country's fuel supply rising sun and in calmer times was by no means a trivial task. After all, Japan is deprived of traditional resources. And after the tragedy at the Fukushima nuclear power plant in March 2011, which forced the country's authorities under pressure public opinion reduce nuclear energy programs, this problem has escalated almost to the limit.

That is why in 2012 one of the Japanese corporations began test drilling under the ocean floor at a distance of only a few tens of kilometers from the islands. The depth of the wells themselves is several hundred meters. Plus the depth of the ocean, which in that place is about a kilometer.

It must be admitted that a year later, Japanese specialists managed to get the first gas in this place. However, talking about complete success until you have to. Industrial production in this area, according to the forecasts of the Japanese themselves, may begin no earlier than 2018. And most importantly, it is difficult to estimate what the final cost of fuel will be.

Nevertheless, it can be stated that humanity is still slowly “approaching” the deposits of gas hydrates. And it is possible that the day will come when it will extract methane from them on a truly industrial scale.

For years, they also discover the first deposits of gas hydrates in the north of the USSR. At the same time, the possibility of the formation and existence of hydrates in natural conditions finds laboratory confirmation (Makogon).

Since then, gas hydrates have been considered as a potential source of fuel. According to various estimates, hydrocarbon reserves in hydrates range from 1.8·10 14 to 7.6·10 18 m³. It turns out their wide distribution in the oceans and permafrost of the continents, instability with increasing temperature and decreasing pressure.

Properties of hydrates

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

Gas hydrates in nature

Most natural gases (CH 4 , C 2 H 6 , C 3 H 8 , CO 2 , N 2 , H 2 S , 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 are introduced into wells and pipelines (methyl alcohol, glycols, 30% CaCl 2 solution), and the temperature of the gas flow is maintained above the temperature of hydrate formation using heaters, thermal insulation of pipelines and selection of the operating mode, providing the 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.

Scientific research

In recent years, interest in the problem of gas hydrates has increased significantly throughout the world. The growth in research activity is explained by the following main factors:

• intensifying the search for alternative sources of hydrocarbon raw materials in countries that do not have energy resources, since gas hydrates are an unconventional source of hydrocarbon raw materials, pilot development of which may begin in the coming years;
• the need to assess the role of gas hydrates in the near-surface layers of the geosphere, especially in connection with their possible impact on global climate change;
• studying the patterns of formation and decomposition of gas hydrates in the earth's crust in general theoretical terms in order to substantiate the search and exploration of traditional hydrocarbon deposits (natural hydrate occurrences can serve as markers for deeper conventional oil and gas deposits);
• active development of hydrocarbon deposits located in difficult natural conditions (deep-water shelf, polar regions), where the problem of technogenic gas hydrates is exacerbated;
• the feasibility of reducing operating costs to prevent hydrate formation in field gas production systems through the transition to energy-resource-saving and environmentally friendly technologies;
• the possibility of using gas hydrate technologies in the development, storage and transportation of natural gas.

In recent years (after the 2003 meeting at OAO Gazprom), research on hydrates in Russia continued in various organizations both through state budget funding (two integration projects of the Siberian Branch of the Russian Academy of Sciences, small grants from the Russian Foundation for Basic Research, a grant from the Governor of Tyumen, a grant from the Ministry of Higher Education of the Russian Federation), and through grants from international funds - INTAS, SRDF, UNESCO (according to the "floating university" program - sea expeditions under the auspices of UNESCO under the slogan Training Through Research - training through research), KOMEKS (Kurele-Okhosk-Marine Experiment), CHAO (Carbon-Hydrate Accumulations in the Okhotsk Sea), etc.

In 2002-2004 research on unconventional sources of hydrocarbons, including gas hydrates (taking into account the commercial interests of OAO Gazprom), continued at OOO Gazprom VNIIGAZ and OAO Promgaz with a small scale of funding. At present, studies on gas hydrates are being carried out at OAO Gazprom (mainly at OOO Gazprom VNIIGAZ), at institutes of the Russian Academy of Sciences, and at universities.

Studies of the geological and technological problems of gas hydrates were started in the mid-60s by VNIIGAZ specialists. At first, technological issues of preventing hydrate formation were raised and solved, then the topics gradually expanded: the kinetic aspects of hydrate formation were included in the sphere of interest, then considerable attention was paid to geological aspects, in particular, the possibilities of the existence of gas hydrate deposits, and theoretical problems of their development.

Geological studies of gas hydrates

The next stage of research into the thermodynamics of hydrate formation is associated with the development of giant northern deposits - Urengoy and Yamburg. To improve the methods for preventing hydrate formation in relation to systems for the collection and field processing of condensate-containing gases, experimental data were needed on the conditions of hydrate formation in highly concentrated methanol solutions in a wide range of temperatures and pressures. In the course of experimental studies (V. A. Istomin, D. Yu. Stupin, and others), serious methodological difficulties were revealed in obtaining representative data at temperatures below minus 20 °C. For this reason, it has been developed new technique studies of phase equilibria of gas hydrates from multicomponent gas mixtures with the registration of heat fluxes in the hydrate chamber and, at the same time, the possibility of the existence of metastable forms of gas hydrates (at the stage of their formation) was found, which was confirmed by subsequent studies of foreign authors. Analysis and generalization of new experimental and field data (both domestic and foreign) made it possible to develop (V. A. Istomin, V. G. Kvon, A. G. Burmistrov, V. P. Lakeev) instructions for the optimal consumption of hydrate formation inhibitors (1987).

Prospects for the application of gas hydrate technologies in industry

Technological proposals for the storage and transport of natural gas in the hydrated state appeared in the 40s of the 20th century. The property of gas hydrates at relatively low pressures to concentrate significant volumes of gas has attracted the attention of specialists for a long time. Preliminary economic calculations have shown that the most efficient is the sea transport of gas in the hydrated state, and an additional economic effect can be achieved with the simultaneous sale to consumers of the transported gas and pure water remaining after the decomposition of the hydrate (during the formation of gas hydrates, water is purified from impurities). At present, the concepts of maritime transport of natural gas in the hydrated state under equilibrium conditions are being considered, especially when planning the development of deep-water gas (including hydrate) fields remote from the consumer.

However, in recent years, more and more attention has been paid to the transport of hydrates under nonequilibrium conditions (at atmospheric pressure). Another aspect of the application of gas hydrate technologies is the possibility of organizing gas hydrate gas storages in equilibrium conditions (under pressure) near large gas consumers. This is due to the ability of hydrates to concentrate gas at a relatively low pressure. So, for example, at a temperature of +4°C and a pressure of 40 atm., The concentration of methane in the hydrate corresponds to a pressure of 15-16 MPa (150-160 atm.).

Aleksey Shchebetov, Russian State University of Oil and Gas. I.M. Gubkin Alexey Shchebetov, Russian State University of Oil and Gas named after I.M. IM Gubkina Gas hydrate fields have the greatest potential compared to other unconventional gas sources. Today, the cost of gas produced from hydrates is incomparable with that of gas produced from traditional gas fields.

Aleksey Shchebetov, Russian State University of Oil and Gas. I.M. Gubkina

Aleksey Shchebetov, Russian State University of Oil and Gas. I.M. Gubkina

Gas hydrate fields have the greatest potential compared to other unconventional gas sources. Today, the cost of gas produced from hydrates is incomparable with that of gas produced from traditional gas fields. However, it is quite reasonable to believe that in the near future the progress in gas production technologies will be able to ensure the economic feasibility of developing gas hydrate deposits. Based on the analysis of the geological conditions of occurrence of typical gas hydrate deposits and the results of numerical modeling, the author assessed the prospects for gas production from hydrates.

Gas hydrates are solid compounds of gas and water molecules that exist at certain pressures and temperatures. One cubic meter of natural hydrate contains up to 180 m3 of gas and 0.78 m3 of water. If earlier hydrates were studied from the standpoint of technological complications in the production and transportation of natural gas, then since the discovery of deposits of natural gas hydrates, they have been considered as the most promising source of energy. Currently, more than two hundred gas hydrate deposits are known, most of which are located on the seabed. According to the latest estimates, 10-1000 trillion m3 of methane is concentrated in the deposits of natural gas hydrates, which is commensurate with the reserves of traditional gas. Therefore, the desire of many countries (especially gas-importing countries: the USA, Japan, China, Taiwan) to develop this resource is quite understandable. But, despite the recent progress in exploration drilling and experimental studies of hydrates in porous media, the question of an economically viable method of extracting gas from hydrates remains open and requires further study.

Gas hydrate deposits

The very first mention of large accumulations of gas hydrates is associated with the Messoyakha field, discovered in 1972 in Western Siberia. Many researchers have been involved in the analysis of the development of this field, more than a hundred scientific articles have been published. According to the work, the existence of natural hydrates is assumed in the upper part of the productive section of the Messoyakha field. However, it should be noted that direct studies of the hydrate content of the deposit (core sampling) have not been carried out, and the signs by which hydrates have been identified are indirect and allow for different interpretations.

Therefore, to date, there is no consensus on the hydrate content of the Messoyakha deposit.

In this regard, the most indicative example is another supposed hydrate-bearing region - the northern slope of Alaska (USA). For a long time it was believed that this area has significant gas reserves in the hydrated state. Thus, it was argued that in the area of ​​the Prudhoe Bay and Kiparuk River oil fields there are six hydrate-saturated reservoirs with reserves of 1.0-1.2 trillion m3. The assumption of hydrate content was based on the results of testing wells in the probable interval of hydrate occurrence (these intervals were characterized by extremely low gas flow rates) and interpretation of geophysical data.

At the end of 2002, Anadarko, together with the US Department of Energy, organized the drilling of the exploration well Hot Ice No. 1 (HOT ICE #1) in order to study the conditions of occurrence of hydrates in Alaska and evaluate their resources. In early 2004, the well was completed at a target depth of 792 m. However, despite a number of indirect signs of the presence of hydrates (data from geophysical surveys and seismic surveys), as well as favorable thermobaric conditions, no hydrates were found in the extracted cores. This once again confirms the thesis that the only reliable way to detect hydrate deposits is exploratory drilling with core sampling.

At the moment, only two deposits of natural hydrates, which are of the greatest interest from the point of view of industrial development: Mallik - in the Mackenzie Delta in northwestern Canada, and Nankai - offshore Japan.

Mallik deposit

The existence of natural hydrates was confirmed by drilling a research well in 1998 and three wells in 2002. Field experiments on gas production from hydrate-saturated intervals were successfully carried out at this field. There is every reason to believe that it is characteristic type continental hydrate deposits to be discovered in the future.

On the basis of geophysical studies and the study of core material, three hydrate-bearing formations (A, B, C) with a total thickness of 130 m in the interval 890-1108 m were identified. permafrost has a thickness of about 610 m, and the hydrate stability zone (HZZ) (i.e., the interval where the thermobaric conditions correspond to the hydrate stability conditions) extends from 225 to 1100 m. changes in the cut temperature (see Fig. 1). The upper point of intersection is the upper boundary of the SGI, and the lower point is, respectively, the lower boundary of the SGI. The equilibrium temperature corresponding to the lower boundary of the hydrate stability zone is 12.2°C.

Reservoir A is located in the range from 892 to 930 m, where a hydrate-saturated sandstone interlayer (907-930 m) is separately distinguished. According to geophysics, hydrate saturation varies from 50 to 85%, the rest of the pore space is occupied by water. Porosity is 32-38%. The upper part of formation A consists of sandy silt and thin sandstone interlayers with hydrate saturation of 40-75%. Visual inspection of the cores raised to the surface revealed that the hydrate mainly occupies the intergranular pore space. This interval is the coldest: the difference between the equilibrium temperature of hydrate formation and reservoir temperature exceeds 4°C.

Hydrate layer B (942-992 m) consists of several sand interlayers 5-10 m thick, separated by thin interlayers (0.5-1 m) of hydrate-free clays. Saturation with hydrates varies widely from 40 to 80%. Porosity varies from 30 to 40%. The wide range of changes in porosity and hydrate saturation is explained by the layered structure of the formation. Hydrate layer B is underlain by an aquifer with a thickness of 10 m.

Reservoir C (1070-1107 m) consists of two interlayers with hydrate saturation in the range of 80-90% and is in conditions close to equilibrium. The base of reservoir C coincides with the lower boundary of the hydrate stability zone. The porosity of the interval is 30-40%.

Below the hydrate stability zone, there is a gas-water transition zone with a thickness of 1.4 m. transition zone an aquifer with a thickness of 15 m follows.

According to the results laboratory research it was found that the hydrate consists of methane (98% or more). The study of the core material showed that the porous medium in the absence of hydrates has a high permeability (from 100 to 1000 mD), and when saturated with hydrates by 80%, the permeability of the rock drops to 0.01-0.1 mD.

The density of gas reserves in hydrates near the drilled exploratory wells amounted to 4.15 billion m3 per 1 km2, and the reserves in the whole field - 110 billion m3.

Nankai field

Active exploration work has been carried out on the shelf of Japan for several years now. The first six wells drilled between 1999-2000 proved the presence of three hydrate interlayers with a total thickness of 16 m in the interval 1135-1213 m from the sea surface (290 m below the seabed). The rocks are mainly sandstones with a porosity of 36% and saturation with hydrates of about 80%.

In 2004, 32 wells were already drilled at sea depths from 720 to 2033 m. Separately, it should be noted the successful completion of vertical and horizontal (with a horizontal wellbore of 100 m) wells in weakly stable hydrate formations at a sea depth of 991 m. The next stage in the development of the Nankai field will be experimental gas production from these wells in 2007. K industrial development the Nankai field is scheduled to start in 2017.

The total volume of hydrates is equivalent to 756 million m3 of gas per 1 km2 of area in the area of ​​drilled exploration wells. In general, gas reserves in hydrates on the shelf of the Sea of ​​Japan can range from 4 trillion to 20 trillion m3.

Hydrate deposits in Russia

The main directions for the search for gas hydrates in Russia are now concentrated in the Sea of ​​Okhotsk and Lake Baikal. However, the greatest prospects for discovering hydrate deposits with commercial reserves are associated with the Vostochno-Messoyakhskoye field in Western Siberia. Based on the analysis of geological and geophysical information, it was suggested that the Gazsalinsky unit is in favorable conditions for hydrate formation. In particular, the lower boundary of the gas hydrate stability zone is at a depth of approximately 715 m, i.e. the upper part of the Gazsalinsky member (and in some regions the entire member) is under thermobaric conditions favorable for the existence of gas hydrates. Well testing did not give any results, although this interval is characterized by logging as productive, which can be explained by a decrease in rock permeability due to the presence of gas hydrates. In favor of the possible existence of hydrates is the fact that the Gazsalinsky unit is productive in other nearby fields. Therefore, as noted above, it is necessary to drill an exploratory well with coring. In case of positive results, a gas hydrate deposit with reserves of ~500 bcm will be discovered.

Analysis possible technologies development of gas hydrate deposits

The choice of technology for the development of gas hydrate deposits depends on the specific geological and physical conditions of occurrence. At present, only three main methods for inducing gas inflow from a hydrate reservoir are considered: lowering the pressure below the equilibrium pressure, heating hydrate-bearing rocks above the equilibrium temperature, and a combination of both (see Fig. 2). The known method for the decomposition of hydrates using inhibitors is unlikely to be acceptable due to the high cost of inhibitors. Other proposed stimulation methods, in particular, electromagnetic, acoustic and injection of carbon dioxide into the reservoir, are still little studied experimentally.

Let us consider the prospects of gas production from hydrates using the example of the problem of gas inflow to a vertical well that has completely penetrated a hydrate-saturated reservoir. Then the system of equations describing the decomposition of hydrate in a porous medium will have the form:

a) the law of conservation of mass for gas and water:

where P - pressure, T - temperature, S - water saturation, v - hydrate saturation, z - coefficient of supercompressibility; r - radial coordinate; t - time; m - porosity, g, w, h - density of gas, water and hydrate, respectively; k(v) is the permeability of the porous medium in the presence of hydrates; fg(S), fw(S) - functions of relative phase permeabilities for gas and water; g, w are the viscosities of gas and water; - mass content of gas in the hydrate;

b) energy conservation equation:

where Ce is the heat capacity of the rock and host fluids; cg, cw are the heat capacity of gas and water, respectively; H is the heat of phase transition of the hydrate; - differential adiabatic coefficient; - throttling factor (Joule-Thomson coefficient); e is the thermal conductivity of the rock and host fluids.

At each point of the formation, the condition of thermodynamic equilibrium must be satisfied:

T = Aln P + B, (3)

where A and B are empirical coefficients.

The dependence of the permeability of the rock on the saturation of hydrates is usually represented as a power dependence:

k (v) = k0 (1 - v)N, (4)

where k0 is the absolute permeability of the porous medium in the absence of hydrates; N is a constant characterizing the degree of permeability deterioration with increasing hydrate saturation.

At the initial moment of time, a homogeneous and unit thickness reservoir has pressure Р0, temperature Т0 and saturation with hydrates v0. The pressure reduction method was modeled by setting a constant flow rate on the well, and the thermal method was modeled by a constant power heat source. Accordingly, in the combined method, a constant gas flow rate and the power of the heat source required for the stable decomposition of hydrates were set.

When modeling gas production from hydrates by the considered methods, the following limitations were taken into account. At an initial reservoir temperature of 10°C and a pressure of 5.74 MPa, the Joule-Thomson coefficient is 3-4 degrees per 1 MPa of drawdown. Thus, at a drawdown of 3-4 MPa, the bottomhole temperature can reach the freezing point of water. As is known, the freezing of water in the rock not only reduces the permeability of the bottomhole zone, but also leads to more catastrophic consequences - the collapse of casing strings, the destruction of the reservoir, etc. Therefore, for the pressure reduction method, it was assumed that for 100 days of well operation, the bottomhole temperature should not drop below 0°C. For the thermal method, the limitation is the temperature increase on the well wall and the heater itself. Therefore, in the calculations it was assumed that for 100 days of well operation, the bottomhole temperature should not exceed 110°C. When modeling the combined method, both limitations were taken into account.

The effectiveness of the methods was compared by the maximum flow rate of a vertical well that completely penetrated a gas hydrate reservoir of a single thickness, taking into account the limitations mentioned above. For thermal and combined methods, energy costs were taken into account by subtracting from the flow rate the amount of gas required to obtain the required heat (assuming that heat is generated from burning part of the produced methane):

Q* = Q - E/q, (5)

where Q - gas flow rate at the bottomhole, m3/day; E - brought to the bottom thermal energy, J/day; q is the heat of combustion of methane (33.28.106), J/m3.

The calculations were carried out with the following parameters: P0 = 5.74 MPa; T0 = ​​283 K; S=0.20; m = 0.35; h = 910 kg/m3, w = 1000 kg/m3; k0 = 0.1 µm2; N = 1 (coefficient in formula (4)); g = 0.014 mPa.s; w = 1 mPa.s; = 0.134; A = 7.28 K; B = 169.7 K; Ce = 1.48.106 J/(m3.K); cg = 2600 J/(kg.K), cw = 4200 J/(kg.K); H = 0.5 MJ/kg; e = 1.71 W/(m.K). The calculation results are summarized in Table. one.

The analysis of these calculation results shows that the pressure reduction method is suitable for hydrate formations where the saturation with hydrates is low, and gas or water has not lost its mobility. Naturally, with an increase in hydrate saturation (and hence a decrease in permeability according to equation (4)) the efficiency of this method drops sharply. Thus, when the saturation of pores with hydrates is more than 80%, it is almost impossible to obtain an inflow from hydrates by reducing the bottomhole pressure.

Another drawback of the pressure reduction method is associated with the technogenic formation of hydrates in the bottomhole zone due to the Joule-Thomson effect. On fig. Figure 3 shows the distribution of water and hydrate saturation obtained as a result of solving the problem of gas inflow to a vertical well that has penetrated a gas hydrate reservoir. This figure clearly shows a zone of insignificant decomposition of the hydrate (I), a zone of secondary hydrate formation (II), and a zone of gas filtration only (III), since in this zone all free water has turned into a hydrate.

Thus, the development of hydrate deposits by lowering the pressure is possible only with the injection of inhibitors into the bottomhole zone, which will significantly increase the cost of produced gas.

The thermal method for the development of gas hydrate deposits is suitable for formations with a high content of hydrates in the pores. However, as the calculation results show, the thermal effect through the bottom hole is ineffective. This is due to the fact that the process of decomposition of hydrates is accompanied by the absorption of heat with a high specific enthalpy of 0.5 MJ/kg (for example: the heat of melting ice is 0.34 MJ/kg). As the decomposition front moves away from the bottom of the well, more and more energy is spent on heating the host rocks and the roof of the formation, so the zone of thermal impact on hydrates through the bottom of the well is calculated in the first meters. On fig. Figure 4 shows the dynamics of thawing of a reservoir completely saturated with hydrates. From this figure it can be seen that for 100 days of continuous heating, the decomposition of hydrates will occur within a radius of only 3.5 meters from the well wall.

The combined method has the greatest prospects, consisting in the simultaneous pressure reduction and heat supply to the well. Moreover, the main decomposition of the hydrate occurs due to a decrease in pressure, and the heat supplied to the bottomhole makes it possible to reduce the zone of secondary hydrate formation, which has a positive effect on the flow rate. The disadvantage of the combined method (as well as the thermal one) is a large amount of produced water (see Table 1).

Conclusion

Thus, at modern level oil and gas technologies, it is difficult to expect that the cost of gas produced from hydrates will be comparable to that of traditional gas fields. This is due to the great problems and difficulties facing developers and researchers. However, even now gas hydrates can be compared with another unconventional source of gas - coal-bed methane. Twenty years ago, it was believed that extracting methane from coal fields is technically difficult and unprofitable. Now only in the USA about 45 billion m3 is produced annually from more than 10 thousand wells, which was achieved through the development of oil and gas science and the creation of the latest gas production technologies. By analogy with coal methane, we can conclude (see Table 2) that gas production from hydrates can be quite profitable and will begin in the near future.

Literature

1. Lerche Ian. Estimates of Worldwide Gas Hydrate Resources. Paper OTC 13036, presented at the 2001 Offshore Technology Conference in Houston, Texas, 30 April - 3May 2001.

2. Makogon, Y.F., Holditch, S.A., Makogon T.Y. Russian field illustrates gas hydrate production. Oil&Gas Journal, Feb. 7, 2005, vol. 103.5, pp. 43-47.

3. Ginsburg G.D., Novozhilov A.A. On hydrates in the bowels of the Messoyakha field.// Gas Industry, 1997, No. 2.

4. Collett, T.S. Natural gas hydrates of the Prudhoe Bay and Kuparuk River area, North Slope, Alaska: AAPG Bull., Vol. 77, no. 5, 1993, pp. 793-812.

5. Ali G. Kadaster, Keith K. Millheim, Tommy W. Thompson. The planning and drilling of Hot Ice #1 - Gas Hydrate Exploration Well in the Alaskan Arctic. Paper SPE/IADC 92764 presented at the SPE/IADC Drilling Conference held in Amsterdam, The Netherlands, 23-25 ​​February 2005.

6. Dallimore, S., Collett, T., Uchida, T. Scientific Results from JAPEX/JNOC/GSC Mallik 2L-38 Gas Hydrate research Well, Mackenzie Delta, Northwest Territories, Canada. Geological Survey of Canada, Bulletin 544, 1999, p. 403.

7. Takahashi, H., Yonezawa, T., Takedomi, Y. Exploration for Natural Hydrate in Nankai-Trough Wells Offshore Japan. Paper presented at the 2001 Offshore Technology Conference in Houston, Texas, 30 April - 3 May 2001. OTC 13040.

8. Takahashi, H., Tsuji, Y. Japan explores for hydrates in the Nankai Trough. Oil&Gas Journal, Sept.5, 2005, vol. 103.33, pp. 48-53.

9. Takahashi, H., Tsuji, Y. Japan drills, logs gas hydrate wells in the Nankai Trough. Oil&Gas Journal, Sept. 12, 2005, vol. 103.34, pp. 37-42,

10. Soloviev V.A. Gas hydrate content of the bowels of the World Ocean// "Gas Industry", 2001, No. 12.

11. Agalakov S.E. Gas hydrates in the Turonian deposits in the north of Western Siberia// "Geology of oil and gas", 1997, No. 3.

Gas hydrates (also natural gas hydrates or clathrates) are crystalline compounds formed under certain thermobaric conditions from water and gas. The name "clathrates" (from Latin clathratus - "to put in a cage") was given by Powell in 1948. Gas hydrates are non-stoichiometric compounds, that is, compounds of variable composition.

For the first time, gas hydrates (sulfur dioxide and chlorine) were observed at the end of the 18th century by J. Priestley, B. Peletier and W. Karsten. The first descriptions of gas hydrates were given by G. Davy in 1810 (chlorine hydrate). In 1823, Faraday approximately determined the composition of chlorine hydrate, in 1829 Levitt discovered bromine hydrate, and in 1840 Wöhler obtained H2S hydrate. By 1888, P. Villard was receiving CH4, C2H6, C2H4, C2H2 and N2O hydrates.

In the 1940s, Soviet scientists put forward a hypothesis about the presence of gas hydrate deposits in the permafrost zone (Strizhov, Mokhnatkin, Chersky). In the 1960s, they also discovered the first deposits of gas hydrates in the north of the USSR, at the same time, the possibility of the formation and existence of hydrates in natural conditions finds laboratory confirmation (Makogon).

Since then, gas hydrates have been considered as a potential source of fuel.
According to various estimates, hydrocarbon reserves in hydrates range from 1.8×10^14 to 7.6×10^18 m³.
It turns out their wide distribution in the oceans and permafrost of the continents, instability with increasing temperature and decreasing pressure.

In 1969, the development of the Messoyakha field in Siberia began, where it is believed that for the first time it was possible (by pure chance) to extract natural gas directly from hydrates (up to 36% of the total production as of 1990)

Gas hydrates in nature
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.

Problems and prospects associated with natural gas hydrates
The development of fields in the north of Western Siberia from the very beginning faced the problem of gas emissions from shallow intervals of the permafrost. These releases occurred suddenly and led to the shutdown of wells and even fires. Since the blowouts occurred from a depth interval above the gas hydrate stability zone, for a long time they were explained by gas flows from deeper productive horizons through permeable zones and adjacent wells with poor-quality casing. In the late 1980s, on the basis of experimental modeling and laboratory studies of frozen core from the permafrost zone of the Yamburgsky GCF, it was possible to reveal the distribution of scattered relic (mothballed) hydrates in Quaternary deposits. These hydrates, together with local accumulations of microbial gas, can form gas-bearing interlayers, from which blowouts occur during drilling. The presence of relict hydrates in the shallow layers of the permafrost zone was further confirmed by similar studies in northern Canada and in the area of ​​the Bovanenkovo ​​gas condensate field. Thus, ideas have been formed about a new type of gas deposits - intrapermafrost metastable gas-gas hydrate deposits, which, as tests of permafrost wells at the Bovanenkovskoye gas condensate field have shown, are not only a complicating factor, but also a certain resource base for local gas supply.

Intrapermafrost deposits contain only an insignificant part of gas resources, which are associated with natural gas hydrates. The main part of the resources is confined to the zone of stability of gas hydrates - that interval of depths (usually a few hundred meters), where thermodynamic conditions for hydrate formation take place. In the north of Western Siberia, this is a depth interval of 250-800 m, in the seas - from the bottom surface to 300-400 m, in especially deep areas of the shelf and continental slope up to 500-600 m below the bottom. It is in these intervals that the bulk of natural gas hydrates was discovered.

During the study of natural gas hydrates, it turned out that it is not possible to distinguish hydrate-containing deposits from frozen ones using modern means of field and borehole geophysics. The properties of frozen rocks are almost completely similar to those of hydrate-containing rocks. Certain information about the presence of gas hydrates can be given by a nuclear magnetic resonance logging device, but it is very expensive and is used extremely rarely in the practice of geological exploration. The main indicator of the presence of hydrates in sediments are core studies, where hydrates are either visible during visual inspection or determined by measuring the specific gas content during thawing.

Prospects for the application of gas hydrate technologies in industry
Technological proposals for the storage and transport of natural gas in the hydrated state appeared in the 40s of the 20th century. The property of gas hydrates at relatively low pressures to concentrate significant volumes of gas has attracted the attention of specialists for a long time. Preliminary economic calculations have shown that the most efficient is the sea transport of gas in the hydrated state, and an additional economic effect can be achieved with the simultaneous sale to consumers of the transported gas and pure water remaining after the decomposition of the hydrate (during the formation of gas hydrates, water is purified from impurities). Currently, the concepts of maritime transport of natural gas in the hydrated state under equilibrium conditions are being considered, especially when planning the development of deep-sea gas (including hydrate) fields remote from the consumer.

However, in recent years, more and more attention has been paid to the transport of hydrates under nonequilibrium conditions (at atmospheric pressure). Another aspect of the application of gas hydrate technologies is the possibility of organizing gas hydrate gas storages in equilibrium conditions (under pressure) near large gas consumers. This is due to the ability of hydrates to concentrate gas at a relatively low pressure. So, for example, at a temperature of +4°C and a pressure of 40 atm., the concentration of methane in the hydrate corresponds to a pressure of 15-16 MPa.

The construction of such a storage facility is not complicated: the storage facility is a battery of gas tanks placed in a pit or hangar and connected to a gas pipe. In the spring-summer period, the storage is filled with gas that forms hydrates, in the autumn-winter period it releases gas during the decomposition of hydrates using a low-potential heat source. The construction of such storage facilities near heat and power plants can significantly smooth out seasonal fluctuations in gas production and represent a real alternative to the construction of UGS facilities in a number of cases.

Currently, gas hydrate technologies are being actively developed, in particular, for the production of hydrates using modern methods of intensifying technological processes (surfactant additives that accelerate heat and mass transfer; the use of hydrophobic nanopowders; acoustic effects of various ranges, up to the production of hydrates in shock waves, etc.).

http://ru.wikipedia.org/wiki/Gas_hydrates
http://en.wikipedia.org/wiki/Clathrate_hydrate

Russian Chemical Journal. V. 48, No. 3 2003. "Gas hydrates"
http://www.chem.msu.su/rus/journals/jvho/2003-3/welcome.html
http://www.chem.msu.su/rus/journals/jvho/2003-3/5.pdf

http://www1.eere.energy.gov/vehiclesandfuels/facts/favorites/fcvt_fotw102.html

http://marine.usgs.gov/fact-sheets/gas-hydrates/title.html

Gas Hydrate Studies - a part of the geophysics group

Gas Hydrate Stability Curve

Gas Hydrate Stability in Ocean Sediments

http://woodshole.er.usgs.gov/project-pages/hydrates/what.html

Since the 1970's, naturally occurring gas hydrate, mainly methane hydrate, has been recognized worldwide, where pressure and temperature conditions stabilize the hydrate structure. It is present in oceanic sediments along continental margins and in polar continental settings. It has been identified from borehole samples and by its characteristic responses in seismic-reflection profiles and oil-well electric logs. much as ~1000 meters thick directly beneath the sea floor; the base of the layer is limited by increasing temperature. At high latitudes, it exists in association with permafrost.

Off the southeastern United States, a small area (only 3000 km2) beneath a ridge formed by rapidly-deposited sediments appears to contain a volume of methane in hydrate that is equivalent to ~30 times the U.S. annual consumption of gas. This area is known as the Blake Ridge. Significant quantities of hydrates in in , including quantities