E.ON Földgáz Storage Zrt. has four underground natural gas storage sites where the gas is being stored in depleted gas fields.
Only those underground formations were suitable for natural gas storage where gas can be injected into the stone layers by around 160 bar, maximum by 210 bar. This is mostly the case if the storage layers are not deeper than 2000-2500 meters and the stone formation is permeable enough.
A further requirement is that the rock layers surrounding the reservoir are impassable for the gas, thus preserving the volumes injected, while the storage stone layers are to be steadfest enough to endure the continuous flow of gas in and out.
The four underground storage sites of E.ON Földgáz Storage Zrt. are to be found in Zsana, Hajdúszoboszló, Pusztaederics, and Kardoskút.