The term is mainly used for underground gas storage for natural gas , but also for hydrogen and oil storage and increasingly for carbon dioxide storage . These storage facilities serve to compensate imbalances between supply / production and demand / consumption and to increase security of supply. As a rule, natural gas storage facilities are filled in the warm summer months with low gas requirements and emptied in the winter months to cover the additional demand.
The volume available in the accumulator is divided into working gas and cushion gas volumes. The working gas volume is the volume of gas that can be used over the course of the year (volume handled). The cushion gas maintains the minimum pressure in the storage facility and remains in the caverns or in the formation (pore storage facility) to ensure geomechanical stability.
Since the gas in the underground storage facility usually has a higher pressure than the gas pipeline, the gas has to be compressed with a compressor for feeding . Some of the energy used for this can be recovered in an expander gas turbine when it is extracted again. In such a case, the underground storage also acts as a mechanical energy storage , such as a compressed air storage power plant . Since the pressure in the storage facility drops sharply during withdrawal in the winter half-year, compression is sometimes necessary during withdrawal in order to bring the gas to gas pipeline pressure. After it has been stored in the underground storage facility, the gas usually has to be dried in order to comply with the standardized properties (e.g. DVGW 260).
Pore storage (including exhausted natural gas deposits)
Porous rock can absorb gases and liquids like a sponge (see → storage rock ). In this case, often on already-developed or explored geological formations resorted: In the pores and crevices of limestone and sandstone layers deep below ground gained over the course of millions of years of natural gas . Many such natural gas deposits in Central Europe were already extracted in the 20th century, which means that they no longer produce natural gas today. The pore space of the reservoir rock, which is still accessible or re-accessible via boreholes, can, however, be "refilled" from above ground with natural gas extracted elsewhere. Pore storage facilities are therefore often " recycled " natural deposits. Such a deposit is sealed at the top by a very low-porous rock layer (e.g. claystone) (so-called seal). The former deposit has proven its tightness and thus its suitability as a storage facility, as the gas was able to hold there for millions of years. Examples of "recycled" natural gas reservoirs are the Haidach, Tallesbrunn and Schönkirchen fields in the Austrian part of the Molasse basin and the Vienna basin , which are supplied with imported natural gas from Russia via the compressor station in Baumgarten an der March . One example in Germany is the Kirchheilingen underground gas storage facility in the central part of the Thuringian Basin ("storage formation": Zechstein ).
Pore storage in rock layers, from which groundwater was displaced by natural gas forced in from above, is known as aquifer storage .
Due to the large storage quantities, the natural gas in pore storage is mainly used to cover seasonal fluctuations in demand.
These artificially created cavities in salt domes are created by drilling and extracting brine . They are cylindrical, can have a diameter of up to 100 m and heights between 50 and 500 m and lie hundreds of meters below the surface of the earth, in Germany sometimes at depths (mining depths ) of up to 2,500 m.
The caverns can be filled with natural gas, oil, petroleum products, compressed air or other gases such as hydrogen.
The amount of gas stored varies between 40 and 100 million standard cubic meters per individual cavern.
Cavern storage facilities are used for peak coverage and as commercial storage facilities as well as to compensate for seasonal fluctuations in consumption. They are also available to compensate for short-term import disruptions or fluctuations.
The gas content of each storage tank is basically divided into cushion gas and working gas. The cushion gas consists of the gas volume that is required in a storage facility to enable the minimum storage pressure required for optimal injection and withdrawal. In caverns, the cushion gas is also required to ensure stability. The cushion gas portion is about 1/3 to 1/2 of the maximum storage volume and remains permanently in the storage. The working gas is defined as the volume of gas that can be stored or removed at any time in addition to the cushion gas.
One of the largest cavern storage facilities in Europe is located in Epe in the Münsterland. Up to 4 billion m³ of working gas can be stored in a total of 80 caverns.
When used as a crude oil reservoir, brine serves as a balancing fluid. When crude oil is pumped into the storage facility, the brine is displaced from the cavern. Crude oil is outsourced by pumping in brine. There is also a cavern storage facility for crude oil in Epe.
Storage in former mines
Under certain conditions, crude oil or natural gas can also be stored in former mines. For this purpose, the former production shaft is provided with a pipe tour and sealed. One example is the Burggraf-Bernsdorf natural gas storage facility operated by Ontras Gastransport GmbH.
Underground storage facilities in different countries
International storage capacity
The countries with the world's largest storage capacity in 2014 were:
|country||Number of memories||Storage volume in billions of cubic meters|
|Russia||23||70.4 (excluding strategic reserves)|
Underground storage in Germany
There are a total of 52 underground storage facilities in Germany (as of 2016). Around 24.18 billion cubic meters of natural gas are stored here to cover peaks, to compensate for short-term import disruptions and seasonal fluctuations in demand. The largest underground storage facility in Western Europe is the Wingas facility in Rehden with 4.4 billion cubic meters. Further examples of such storage facilities are the Inzenham West storage facilities of RWE Dea AG, Bierwang (in Unterreit ) and Epe of E.ON Ruhrgas AG, Dötlingen of BEB Speicher / EMGSG , Etzel of STORAG Etzel and the Frankenthal natural gas storage facility of Enovos Deutschland . The Spandau natural gas storage facility in Berlin (closed in 2016), for example, had a maximum volume of 1 billion cubic meters of natural gas. According to the Federal Association of German Gas and Water Management (BGW), Bonn, another 5 underground storage facilities are under construction, expansion or in the planning stage.
Underground storage in Austria
As of April 2014 there are 11 underground storage facilities for natural gas in Austria, sorted in descending order by capacity:
- Haidach bei Straßwalchen ( Salzburg ), (RAG with participation of WINGAS and Gazprom Export ), since 2007 with 1.2 billion cubic meters, since 2011 with 2.64 billion cubic meters, at a depth of 1600 m, extension 3.5 × 5 km
- Schönkirchen-Reyersdorf near Gänserndorf (Lower Austria), (OMV), since 1977 with 1.57 billion cubic meters in 5 horizons (510 m 120 million cubic meters, 550 m 160 million cubic meters, 750 m 210 million cubic meters, 1050 m 550 Million cubic meters, 1150 m 530 million cubic meters)
- Puchkirchen bei Timelkam (Upper Austria), ( RAG ), since 1982 with 860 million cubic meters at a depth of 1100 m, extension 6 × 2 km; since 2010 with 1.08 billion cubic meters by including the Haag am Hausruck gas field at a depth of 1000 m, extension 5 × 2 km
- Seven Fields in the border area of Upper Austria and Salzburg, (RAG with participation of E.ON Gas Storage ), in the final expansion around 2 billion cubic meters in 7 fields at a depth of 1300 to 2300 m, on April 1, 2011 commissioning of the first expansion stage with 1.165 billion . Cubic meters in the two storage facilities in Zagling (between Straßwalchen and Frankenmarkt ; 450 million cubic meters, extension 2 × 2 km) and Nussdorf (approx. 700 million cubic meters, extension 7 × 1.5 km), commissioning of the second expansion stage with the Oberkling and Pfaffstätt reservoirs southwest of Mattighofen (approx. 685 million cubic meters)
- Tallesbrunn near Gänserndorf ( Lower Austria ), ( OMV ), with 300 million cubic meters since 1974
- Thann bei Steyr ( Upper Austria ), (OMV), since 1977 with 250 million cubic meters at a depth of 650 m
- Aigelsbrunn near Straßwalchen (Salzburg), (RAG), since 2011 with 100 million cubic meters at a depth of 1350 m, extension 1.5 × 1 km
- Haidach 5 near Straßwalchen (Salzburg), (RAG), since 2006 with 16 million cubic meters at a depth of 1450 m, extension 0.5 × 1 km
With a total storage capacity of around 7 billion cubic meters, Austria could currently store almost its annual demand for natural gas, which is a top value in Europe.
In addition to ongoing expansions to some of the storage facilities mentioned above, the following new storage projects are under construction:
- Schönkirchen-Tief bei Gänserndorf (Lower Austria), (OMV), 1.6 billion cubic meters at a depth of 2800 to 2900 m, commissioning in two expansion stages in 2014 (900 million cubic meters) and 2018 (additional 700 million cubic meters)
Underground storage for other purposes
In the case of hydropower plants, storage basins can also be designed as underground storage, which have less impact on the environment and can also be designed to be more topography-independent. In Austria, the first was built at the Naßfeld storage power plant.
In 1980, a total of 15 million cubic meters of natural gas flowed uncontrolled from an underground storage facility in Frankenthal in the Palatinate for 15 days until the defect could be remedied by a blowout preventer . Previous attempts to seal the leak with 1000 tons of concrete failed.
In Gronau in the Münsterland, oil came to the surface from a storage facility in the Gronau-Epe cavern field and contaminated the ground. The operator, the Salt Extraction Company Westphalia (SGW), has started to repair the damage (status 2014). In April 2019 the WDR reported that even five years after the leak was sealed, remnants of the leaked 75 m³ of crude oil would still contaminate the water, but that these would be removed in a controlled manner.
In Porter Ranch in the US state of California, there was a gas leak in an underground gas storage facility operated by Southern California Gas (SoCalGas) in mid-October 2015 , which could only be sealed on February 11, 2016. By then, around 100,000 tons of natural gas had escaped. The area had been evacuated for this period and 2,200 families had to move temporarily. The greenhouse effect of the methane released is said to correspond to that of the CO 2 emissions of more than half a million cars in the USA within one year.
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