The Nüttermoor underground natural gas storage

Natural gas is an easily transported and extremely environmentally friendly fuel. Approx. three quarters of the gas consumed in Germany is imported - often over long distances. However, optimum efficiency for the producer, supply company and consumers is only achieved when a steady constant gas flow is maintained in the pipeline. For this reason, the increased demand in winter can only be met by storing gas in summer. The economical and safe storage of such large volumes of gas- approx. 14 % of the total annual consumption of approx. 75 Mrd. m³ (Vn) - is only possible in underground storages - such as caverns. In addition, caverns increase the general security of supply; take up relatively small surface areas for the necessary operating equipment; provide the highest possible level of operating safety; and are also very environmentally friendly. Salt caverns are solution mined in thick salt formations - in particular in the numerous salt domes occurring in northern Germany - by the controlled solution of the salt with fresh water. The Nüttermoor location provided EWE Aktiengesellschaft, Oldenburg, with ideal conditions for constructing a gas storage: very good salt quality; a favourable location within the transport network; problem-free extraction of fresh water and disposal of brine into the Ems estuary. Boreholes to depths of up to 1400 m are drilled down to the planned roof position of the cavern. Solution mining pipes are then installed in the borehole. During solution mining, approx. 300 m³ fresh water are injected into the salt dome per cavern and hour. The salt dissolves in the fresh water and the resulting brine is pumped to the surface and disposed of. The cavern roof is protected from uncontrolled dissolution mining process by pumping in a protective fluid, usually liquefied gas, which floats on the surface of the brine. Below this protective blanket, the cavern can be solution mined in approximately cylindrical form in accordance with the rock mechanical and solution mining calculations and targets. Regular surveys of the cavern allow the progress of the solution mining and the height, depth, diameter and volume of the cavern to be monitored. The caverns in Nüttermoor are up to 420 m high and 80 m wide. During the first filling of gas in the cavern, the remaining brine is pushed out by the injected gas. The brine extraction string is then removed under pressure, after which the cavern is ready for operation. The surface gas operation facilities to inject and withdraw the gas consist of a number of plant components. In addition to the gas operations buildings, the main components are the compressor plant, the gas dehydration plant including regeneration, the electrical engineering/ measuring and control installation, as well as the metering and control plant. The storage is monitored from a central control room and usually remotely operated from the network control centre in Oldenburg. The Nüttermoor facility has a total of 16 caverns of which three are still in the process of construction. The total cavern volume is almost 8 Mio. m³ and can accommodate almost 1.0 Mrd. m³ (Vn) of natural gas, of which 80 % is working gas and 20 % the so called cushion gas - which is required to maintain the minimum operating pressure. The minimum operating pressure is approx. 30 bar, while the maximum pressure is approx. 150 bar. The Nüttermoor storage is one of the largest of its type in the world. It guarantees a significant part of the German energy supply.

Country: Germany
Region: Niedersachsen; Nüttermoor/Leer district (Lower Saxony)
Tunnel utilization: Utilitiy
Type of utilization: Storage of natural gas in salt caverns
Client: EWE Aktiengesellschaft, Oldenburg
Main construction method: Trenchless
Type of excavation: Sluice mining
Number of caverns: 16
Total cavern volume: 8.0 Mio. m³
Individual cavern volumes: 400,000- 700,000 m³
Cavern dimensions: Ø ≤ 80 m, height ≤ 420 m
Stored gas: approx 1.0 Bill. m³ (Vn)