Drilling with casing and retrievable drill bit

A method of drilling a well with a well casing as an elongated tubular drillstem and a motor and bit assembly retrievable from the lower distal end of said drillstem without withdrawing said drillstem from a wellbore being formed by said motor and bit assembly and said drillstem, said method comprising the steps of:

• providing said casing as said drillstem including a sub disposed at said lower distal end and including means on said sub for engaging said motor and bit assembly to lock said motor and bit assembly to said drillstem to provide for drilling operations;
• providing a motor as a pressure fluid operated motor including means for rotating a bit without rotating said drillstem;
• providing a bit including cutter means radially movable with respect to the central longitudinal axis of said drillstem under the urging of pressure fluid to provide for cutting said wellbore and to provide for inserting and retrieving said bit through said sub;
• inserting said drillstem and said motor and bit as said motor and bit assembly into said wellbore and introducing pressure fluid into said drillstem to act on said motor and bit assembly to effect rotation of said bit and to extend said cutter means into a position for cutting said wellbore to a diameter greater than the diameter of said drillstem;
• removing said motor and bit assembly from said distal end of said drillstem upon completion of said wellbore without removing said drillstem from said wellbore;
• and
• leaving said drillstem in said wellbore to serve as said casing for said well.