| abstract |
Casing is run into a well bore hole on a running pipe string. Fluid motor and drill apparatus is supported in the casing, with the drill extending below the lower end of the casing to drill the bore hole in advance of the casing. For subsea drilling operations, the casing is suspended from a riser housing which lands on a subsea base, and the running pipe is released from the riser housing to enable retrieval of the motor and drill assembly. Plural motors are employed for drilling large holes. |