All natural gas or liquefied petroleum gas which has previously been reduced to possession, and which is subsequently injected into an underground storage reservoir, shall at all times be deemed the property of the condemner, his heirs, successors or assigns; and in no event shall such natural gas or liquefied petroleum gas be subject to the right of the owner of the surface of said lands or of any mineral interest therein, under which said gas storage reservoir lies, or of any person other than the condemner, his heirs, successors and assigns, to produce, take, reduce to possession, waste, or otherwise interfere with or exercise any control thereover; Provided, that the condemner, his heirs, successors and assigns, shall have no right to natural gas or liquefied petroleum gas in any stratum, or portion thereof, which has not been condemned under the provisions of sections 57-601 to 57-609, or otherwise purchased.