[directional casing drilling]

A method of drilling a wellbore, comprising:

• positioning a drilling tool connected to the end of a casing string in a wellbore, the drilling tool having a bit and a sleeve with extendable pads therein;
• passing a fluid through the tool;
• and
• diverting at least a portion of the fluid to the sleeve for selective extension of the pads whereby the tool drills in a desired direction.

A rotary steerable casing drilling system, comprising:

• a casing string for rotation of a drill bit;
• a tool collar comprising an interior, an upper end and a lower end, the upper end of the tool collar operatively coupled to the casing string;
• a bit shaft comprising an exterior surface, an upper end and a lower end, the bit shaft being supported within the tool collar for pivotal movement about a fixed position along the bit shaft;
• a variable bit shaft angulating mechanism, located within the interior of the tool collar, comprising a motor, an offset mandrel having an upper end and a lower end, and a variable offset coupling, having an upper end and a lower end, the motor attached to the upper end of the offset mandrel and adapted to rotate the offset mandrel, the upper end of variable offset coupling being uncoupleably attached to an offset location of the lower end of the offset mandrel, and the upper end of the bit shaft being rotatably coupled to the variable offset coupling;
• a torque transmitting coupling adapted to transmit torque from the tool collar to the bit shaft at the fixed position along the bit shaft;
• and
• a seal system adapted to seal between the lower end of the collar and the bit shaft.

A rotary steerable casing drilling system, comprising:

• a casing string for rotation of a drill bit;
• a control unit disposed in a drill collar, the control unit comprising
• an instrument carrier;
• a first impeller coupled to the instrument carrier;
• and
• a second impeller coupled to the instrument carrier,
• a pad section having at least one pad hydraulically extensible therefrom;
• and
• a valve system operatively coupled to the control unit and adapted to selectively conduct at least a portion of a drilling fluid to the at least one pad whereby the at least one pad moves between an extended position and a retracted position,
• wherein the control unit remains in a geo-stationary position and operates the valve system to modulate a fluid pressure supplied to the pad section in synchronism with rotation of the casing string so that the at least one pad is extended at the same rotational position so as to bias the drill bit in a selected direction.