After the completion and the gas tightness test, the cavern is filled with gas. Gas filling is the last step in the construction of a cavern storage facility. It brings the cavern under gas pressure for the first time - all under consideration of technical and economic aspects for an optimal process.

To maintain or repair cavern storages, the cavern is flooded by replacing the stored gas with water or brine. Cavern flooding takes place, for example, as part of the backfilling of the cavern or also to prepare a recompletion measure of the well - i.e. a complete re-equipment - followed by a refilling with the storage medium.