Storage facility types

Thanks to the favourable geological conditions in Germany, large quantities of gas can be stored economically and in an environmentally friendly way with very little impact on nature or the landscape. Storage in natural or artificial underground cavities is a tried and tested technology and, like storage in porous rock formations or depleted natural gas or oil fields, is safe, environmentally compatible and cost-effective.

First, it is necessary to distinguish above-ground and underground storage:

Above-ground storage facilities. Above-ground storage facilities are relatively small and can only play a minor local role in compensating for short-term demand peaks. The capacity available is scarcely adequate to compensate for major fluctuations in demand over the course of the day.

Underground storage facilities. Underground storage facilities are larger and are used for accommodating seasonal demand fluctuations as well as for short-term peak shaving.

There are two main types of underground storage facilities – artificial cavities in salt formations (cavern storage facilities) on the one hand and porous rock storage facilities, where gas is stored in natural pores in rock formations, either aquifers or depleted gas or oil fields, on the other hand. These types of storage facilities are based on different storage formations and mechanisms and may be located at depths between several hundred and up to 2,000 metres below the surface.

Cavern storage facilities

Cavern storage facilities consist of large caverns created by the targeted solution mining of salt formations. This process gives the caverns a cylindrical shape. They may have diameters of up to 100 metres, with heights ranging from 50 to 500 metres and geometric volumes of up to 800,000 cubic metres. The petrochemical properties of the salt ensure that the gas is sealed in naturally; there is therefore no need for an additional lining. At depths between 800 and 1,500 metres, gas can be stored at pressures of up to 200 bar.

The properties of cavern storage facilities not only allow the storage of large quantities of gas but also mean that gas can be rapidly injected and withdrawn from storage. These storage facilities are therefore especially well-suited for compensating for severe short-term demand fluctuations.

Porous rock storage facilities

In porous rock storage facilities, the natural gas is stored at high pressure in an underground storage formation. These storage facilities are mainly developed in aquifers, water-bearing sandstone formations with appropriate geophysical properties such as high permeability. Apart from these water-bearing formations, depleted oil and natural gas fields may also be used for storage. In this case, the suitability of the formation for gas storage has already been demonstrated by nature. These facilities feature gas-impermeable caprock and ensure naturally gas-tight storage.

Porous rock storage facilities are used for storing large quantities of gas but, as a result of their geophysical properties, the maximum injection and withdrawal rates are relatively low. Natural gas stored in facilities of this type is therefore used mainly to compensate for seasonal fluctuations in gas demand.