Any importer of natural gas may enter into an exchange by displacement agreement without the prior authorization of the Assistant Secretary when the net effect of the exchange is no different than under the importer's existing authorization. An exchange by displacement is an arrangement whereby authorized imported volumes are displaced by other gas for purposes of storage or flexibility. The term of the exchange agreement may not exceed five (5) years, the volumes imported may not exceed the importer's existing import authorization, and no actual natural gas may flow across the United States border under the terms of the exchange agreement. Any importer who enters into an exchange agreement pursuant to this section shall file with FE within fifteen (15) days after the start up of the exchange, a written description of the transaction, the exact volume of natural gas to be displaced, the name of the purchaser, and the import authorization under which the exchange is being carried out.