SYSTEM CONTAINING EXPENDIBLE ISOLATION VALVE WITH FRANGIBLE SEALING MEMBER, SEAT ARRANGEMENT AND METHOD FOR USE

An isolation valve for a downhole well completion system having a one piece frangible, ceramic sealing element and an extrusion resistant resiliently faced valve seat and a method for the use thereof is presented. Said sealing element is biased to the closed position and rotatable within a sealing element chamber from an open position during run in to a closed position as a result of the withdrawal of a wash pipe and a protector tube from the valve bore. Said frangible sealing element cooperates with said extrusion resistant valve seat to provide a reliable pressure resistant seal. After recovery of completion fluids from the well bore and pressure testing of the production string, the frangible sealing element is shattered by impacting with a tooth-faced blind box hammer.