Abstract: A method for operating a dual drill string disposed in a wellbore, the string having a shutoff valve for at least a fluid return drill string therein proximate a bottom end thereof includes pumping fluid into the fluid return string such that a pressure therein is substantially equal to a fluid pressure in the wellbore. Circulation of fluid in the wellbore is initiated by pumping fluid into a fluid supply string of the dual drill string such that the shutoff valve on the fluid return string opens to enable the fluid leaving the wellbore to enter the fluid return string.

Abstract: The present invention relates to a system for transferring signals through a drill pipe system during drilling of a subsurface well. The drill pipe system comprises a first pipe (1) provided concentric inside a second pipe (2) by means of hanging devices (3, 3a). The first pipe (1) is electrically insulated from the second pipe (2). A first signal transceiver is electrically connected to the top of the drill pipe system. A second signal transceiver is electrically connected along or in the bottom of the drill pipe system. The first and second signal transceivers are electrically connected to the first and second pipes (1, 2) for transferring the signals through the drill pipe system.

Abstract: A method for operating a dual drill string disposed in a wellbore, the string having a shutoff valve for at least a fluid return drill string therein proximate a bottom end thereof includes pumping fluid into the fluid return string such that a pressure therein is substantially equal to a fluid pressure in the wellbore. Circulation of fluid in the wellbore is initiated by pumping fluid into a fluid supply string of the dual drill string such that the shutoff valve on the fluid return string opens to enable the fluid leaving the wellbore to enter the fluid return string.