In order to make available the millions of cubic metres of storage space proscribed necessary by law for an emergency stock of stored crude oil the standard practice of storing crude oil in salt caverns is used.
During geological processes that took place 250 million years ago, giant salt domes were formed. Inside these salt domes, large volume cavities are hollowed out. Salt domes are found at depths between 700 and 4,000 metres and are sometimes several kilometres in length and breadth. The cavities hollowed out in these domes contain volumes of several hundred thousand cubic metres. A sufficiently thick layer of salt serving as cladding around the caverns keeps them stable and safe.
In Rüstringen (Wilhelmshaven) and Friedeburg (Wittmund) there are cavern facilities belonging to NWKG – Nord West Kavernengesellschaft mbH and Storag Etzel GmbH, both of which are connected to the NWO tank farm in Wilhelmshaven. In the caverns in Rüstringen and Friedeburg there are around 15 million tonnes of crude oil set aside for long-term storage.
Storage in the caverns takes place via the NWO storage tanks exclusively. Whenever necessary, crude oil is removed exclusively under NWO’s control. The crude oil is taken from these caverns either to the refineries via the pipeline or transported further away by means of oil tankers. In addition crude oil from the tank in Ochtrup can be let into and taken out of the cavern facility in Epe (North-Rhine Westphalia).
Since NWO does not itself manage caverns, you can obtain more information on the subject directly from the companies named above.