How underground gas storage facilities are arranged: an overview of gas storage options

It would seem that knowledge of how underground gas storage facilities are arranged has no practical value for an ordinary user. But humanity is too dependent on "blue" fuel and so one wants to be sure that there will never be any interruptions in its supply. Isn't that right?

And every compatriot can be reassured by the information about underground gas storage facilities (UGS) - as long as they are full of problems with gas supply. Read more about the storage device and storage features in our article.

Construction of underground gas storage facilities

If for storing gas for household needs, the owners of private houses use

gasholders, then on a national scale we are talking about completely different storage options. So, officially, underground gas storage is a complex of engineering and technical structures that serve for the injection, storage and withdrawal of "blue" fuel. They consist of ground and underground components.

TO terrestrial relate:

• gas distribution point, which serves to distribute the gas flow to several technological ones;
• compressor shopwhere the fuel is prepared (by increasing the pressure) for injection into the wells;
• gas treatment plants.

Underground UGS components are: wells, workings, tanks. And the last point (containers) is the most interesting - the way the gas storage is arranged depends on where the "blue" fuel is stored.

Overview of gas storage tanks

With the same weight, gas occupies much larger areas than any solids. And since it is used in huge quantities, the same capacity is needed to store it.

Moreover, specialists refused to store gas in man-made ground tanks a century ago.

The reason is that this would require:

• to occupy vast areas of the planet with complexes for storing low-pressure "blue" fuel;
• use expensive and explosive high pressure gas tanks.

As a result, in order to neutralize the above negative points, the choice was made in favor of underground storage facilities, and such are considered to be tanks located at a considerable depth. Which, in most cases, ranges from 300 to 1000 meters. And you can store fuel there in reservoirs created by nature.

In total, engineers have learned to successfully use 7 types of natural gas storage tanks:

• formed in water-saturated porous formations;
• preserved after the production of carbohydrates, namely the same gas, oil;
• formed in rock salt deposits;
• created in the mine workings of mines;
• created in durable permafrost;
• with a low-temperature ice-type shell;
• formed after underground atomic explosions.

Although there are many options, only the first 4 methods of gas storage differ in practicality. The rest of the tank options are suitable only theoretically.

The reason for the impracticality of the remaining three options is as follows:

• It is possible to store gas in frozen rocks, as evidenced by several existing storage facilities in the northern regions of the planet. But their volumes are extremely insignificant, therefore they do not have any industrial significance today.
• Tanks formed by underground nuclear explosions are quite suitable for storing significant gas reserves, which has already been proven experimentally. But the bottom line is that powerful weapons were tested away from people's places of residence. Therefore, there are usually no consumers, engineering communications.

As a result, these types of containers are simply unsuitable for use.

Although UGS facilities are called storage facilities, in fact, saving gas is not their primary task. Since what is in them for the most part is used to smooth out unevenness and consumption. Which is daily, weekly, seasonal. Only in the last instance are UGS facilities created to mitigate the consequences of force majeure circumstances.

Next, we will consider in more detail each of the options for storing gas underground.

Option # 1 - storage in water-saturated reservoirs

Storage facilities in water-saturated formations are designed to level the effects of seasonal irregularities in the use of gas. And also to create strategic reserves.

An important feature of the arrangement of such storage facilities is the minimum human participation - most often at the stage of creating wells required for gas injection.

These containers are sought in artesian strata. Gas storage facilities are created where the rock structure is permeable, porous. The remaining liquid is removed by gas, which compresses it and then squeezes it out.

The so-called fuel storage tanks themselves are not really such. More precisely, they do not exist at all - they use voids in porous formations. And the whole procedure for creating a gas storage consists in displacing part of the water to the periphery. They do this in order to create space for "blue" fuel.

The procedure described above will only work if a number of factors contribute to this:

• The porous permeable formation is covered with a dome (seal) of gas-impermeable rocks, which are usually pressed clays.
• The aquifer extends from the boundaries of the storage for tens of kilometers. Better yet, if it has an exit to the surface. All of the above makes it possible for the gas to successfully squeeze out the water in the reservoir.
• The length of the dome is sufficient to provide the ability to store significant volumes of gas.
• The porosity and permeability of the rock provides an acceptable gas capacity and the ability to release it during development.

If at least one of the conditions is not met, then it will be impossible to create an underground storage facility.

The principle of operation of modern underground storage facilities is simple. The features can be considered using the example of large UGS facilities used to smooth out seasonal irregularities.

So, usually in the warm season, the required amount of gas is pumped into them. Which they begin to select only with the onset of the heating season. Moreover, not some huge amount of gas is sent to the main pipe, but the average amount, known from the operating experience in past winters.

And if suddenly the temperature drops sharply and daily consumption becomes an order of magnitude higher, then a large UGS facility will still not increase the volume of withdrawal. And the shortage will be covered by small storage facilities designed to smooth out daily, weekly consumption. The reason is that it is easier and faster to select from them.

The advantage of UGS facilities in water-saturated formations is their significant capacity. And the disadvantage is that geologists, when studying the features of the aquifer, may not identify and take into account some important factor. As a result, the storage will be unusable.

And the worst thing is that this is often revealed after huge investments in the construction of above-ground and underground infrastructure. Quite often, there are also less significant troubles, from which the operation of UGS facilities in water-saturated rocks is accompanied by significant unplanned costs.

Option # 2 - tanks after hydrocarbon production

Engineering complexes that belong to this type serve to smooth out seasonal fluctuations in the consumption of "blue" fuel. And also to create strategic reserves.

The storage arrangement of this type is the same as in the case of analogs created in water-saturated formations. That is, the fuel is stored in the voids of porous rocks.

UGS facilities created in rocks, where hydrocarbons were once located, are the most in the world. So, their number reaches a significant 70%, the reason for this is a number of advantages.

These include: significant capacity and savings on investment in exploration, creation infrastructure or at least part of it, drilling - oil production has already been carried out at the site of such UGS facilities, gas.

But the tanks that have survived after the production of hydrocarbons cannot be called ideal.

They have many disadvantages:

• problems with the tightness of old wells - especially for former oil fields;
• insufficient porosity, rock permeability;
• mixing gas with residual oil - which sometimes leads to significant losses, since the resulting mixture can no longer be used.

And also quite often in oil fields a dangerous impurity in the form of hydrogen sulphide appears in the gas. Which is harmful to human health, and also destroys all kinds of steel structures, even those related to stainless.

The operation of UGS facilities based on places of depleted hydrocarbon deposits is possible in view of the fact that gas, when injected, displaces residual oil from the required formation. In addition, it, like water, has the effect of compressibility and mobility, which facilitates the task of arranging the container. Sometimes oil under gas pressure is not squeezed out into the rock, but rises to the top, which becomes an additional source of profit.

Option # 3 - Reservoirs in rock salt deposits

Such containers with gas serve to smooth out the daily, weekly unevenness of its use, and also take part in leveling the seasonal. In addition, storage facilities in salt formations successfully cope with the role of a backup source for important consumers.

These UGS facilities are being created by washing out part of the salt deposits in order to create a cavity of the required size. For this, several wells are initially drilled through which water is supplied for a long period of time.

Although the described procedure is long and costly, it pays for itself, since the injected natural gas is stored without losses. The reason is that the salt caves are airtight. In addition, they have the effect of self-healing - tectonic and other cracks are quickly overgrown with salt deposits.

The advantage of such underground gas storage facilities is that the required volume of fuel is withdrawn with virtually no speed limits. Which is several times higher than when performing the same operations in containers of other types. And also an important advantage of UGS facilities built in salt caves is a high percentage of gas extraction - one of the highest among all its types.

But the number of caverns in salt formations does not exceed 2% of the total number of storages.

This indicator is influenced by a number of negative points:

• The presence of a huge amount of salt water after washing out caves to conserve gas. As a result, if there is no sea or even salt processing plants nearby, there is nowhere to put the liquid. This is the main reason for the small number of such UGS facilities.
• Decrease in usable volume during operation. This phenomenon is caused by the evaporation of salt in places with higher pressure and accumulation where it is lower.
• The appearance of impurities in the gas, which are often the remnants of the liquid previously used to wash out the cave.
• Small volumes, which does not allow to create stocks in sufficient quantities.

As a result, salt storages are usually used only where it is not possible to use the types of containers listed above.

Option # 4 - underground gas storage in mine workings

Their volumes are insignificant. Nevertheless, the Swedes and the Norwegians store part of their strategic gas reserves in containers of this type.

PVC in mine workings is the only gas storage facility fully equipped by humans. So, in one of the mines, a container is created by explosions, which is then sheathed with steel sheets.

Although it is profitable to operate UGS facilities in abandoned mines, due to the high percentage and rate of extraction, their number will not increase significantly in the near future. The reason is that the storage facilities described are difficult to build. Since it is not always possible to achieve complete tightness, which leads to significant losses.

This happens due to the fact that during the operation of the mine, they try to bring the maximum amount of air there. Why is a ventilation system created with a mass of exits to the surface, which, when arranging a storage facility, cannot always be sealed.

As a result, today, there are only a few successful examples of the implementation of the idea of ​​gas storage in abandoned mines (on the territory of Sweden, Norway, Germany).

Are the storage facilities sealed?

Fuel leaks are frequent and cannot be avoided. There are too many reasons.

For convenience, they are divided into 3 categories:

• geological;
• technological;
• technical.

To the group geologicalreasons include the heterogeneity of the UGS seals, the presence of tectonic faults, as well as the features of hydrodynamics and geochemistry. For example, gas can simply migrate through the reservoir, and experts will not influence this in any way.

Technologicalcauses are among the most frequent, as errors regularly occur when assessing any facts. For example, the effectiveness of hydrotraps, gas reserves, and ongoing physical and chemical processes.

Technical reasons most often associated with the condition of the wells used, with the help of which gas injection is carried out.

Peculiarities of UGS construction

In 95% of cases, UGS facilities are created gas squeezing water, oil residues from porous formations. Thus, “containers” are created for storing “blue” fuel.

And the most important feature is that the volume of gas used to squeeze out liquids can no longer be used for supply to consumers. Its task is to prevent the return of water and hydrocarbon residues to their old place. Otherwise, the repository will simply cease to exist.

That is, the specified gas is buffer. As a rule, it is not less than half of the total volume pumped into the UGS facility. And in some cases, the buffer gas is 3 times more than what can be used to supply consumers, which is called active.

It is interesting that the amount of the buffer gas cannot be calculated in advance. That is, everything is checked exclusively in an experimental way. Which in many cases takes years. However, when the result obtained is unsatisfactory, the buffer gas can be pumped out in full.

The order of filling the storage

After geologists have carried out studies of any reservoir and have decided that a gas storage can be created in the right place, gas producers build an engineering complex.

And then the pumping of "blue" fuel into the future UGS facility begins, which is supplied from the nearest main pipeline. And it goes to the cleaning site, where all kinds of mechanical impurities are removed.

Clean fuel is supplied to the metering and metering point. And after that, to the compressor shop, where the compression is performed - this is the name of the preparation of gas for pumping into the storage. It represents the increase in gas pressure to the desired value.

Then it is transported to gas distribution points. Where the total flow is divided into several and enters different technological lines. From where it is sent through plumes to the wells for injection.

Throughout the entire process, specialists control a number of parameters, including gas pressure and temperature, and the productivity of each well.

Conclusions and useful video on the topic

The video material attached below is devoted to the creation of an UGS facility to smooth out uneven fuel consumption, which will be supplied by the Power of Siberia gas pipeline.

Underground gas storages are the most reliable and profitable way of leveling uneven gas consumption and its stable supply in case of force majeure. And the most interesting thing is that for this you need to thank not a human genius, but nature, which has prudently created layers of rocks suitable for this..

Have you personally participated in the creation of underground gas storage facilities and would like to supplement the above material with useful information? Or have you noticed a discrepancy in the facts? Leave your comments and comments - the feedback block is located below the article.