It is understood and agreed that one (1) year after the expiration of the primary term of this lease, upon the expiration of any extension or renewal, or after cessation of operations as provided herein, whichever occurs last, Lessee shall release all rights lying below the stratigraphic equivalent of one hundred feet (100') below the base of the deepest producing formation in any well drilled on the leased premises or on lands with which the leased premises has been pooled or unitized.