Subsea casing drilling system

Abstract

In one embodiment, a casing bit drive assembly may be used with a casing drilling system. The casing bit drive assembly may include one or more of the following: a retrievable drilling motor; a decoupled casing sub; a releasable coupling between the motor and casing bit; a releasable coupling between the motor and casing; a cement diverter; and a casing bit.

1 . A casing drilling system, comprising:
 a casing;   a drilling member coupled to the casing;   a retrievable motor releasably coupled to the casing and includes a power section configured to rotate the drilling member relative to the casing; and   a releasable coupling assembly for coupling an output shaft of the motor to the drilling member, wherein the releasable coupling assembly includes:
 a coupling attached to the drilling member; and 
 a retractable dog configured to couple or decouple the output shaft to the coupling. 
   
     
     
         2 . The system of  claim 1 , wherein the motor includes a rotating portion and non-rotating housing, wherein the power section comprises an annular area between the rotating portion and a non-rotating portion. 
     
     
         3 . The system of  claim 2 , wherein the motor includes an arcuate recess formed in non-rotating housing, wherein a ball received at an end of the arcuate recess prevents relative rotation between the rotating portion and the non-rotating housing. 
     
     
         4 . The system of  claim 1 , further comprising a cement diverter for diverting cement from the power section of the drilling motor. 
     
     
         5 . The system of  claim 1 , wherein the releasable coupling assembly further comprising a biased sleeve configured to retain the dog in a retracted position. 
     
     
         6 . The system of  claim 1 , further comprising a locking mechanism to prevent relative rotation between drilling member and the casing. 
     
     
         7 . The system of  claim 6 , wherein the locking mechanism includes:
 a locking segment attached to the casing;   a first set of teeth formed on the locking segment; and   a second set of teeth formed on the drilling member, wherein the second set of teeth is engageable with the first set of teeth to prevent relative rotation between the casing and the drilling member.   
     
     
         8 . The system of  claim 6 , wherein the locking mechanism includes an arcuate recess formed between the casing and the drilling member, a ball received at an end of the arcuate recess prevents relative rotation between casing and the drilling member. 
     
     
         9 . The system of  claim 8 , further comprising a fluid path between a bore of the motor and the recess. 
     
     
         10 . The system of  claim 6 , wherein the locking mechanism includes:
 an upper sleeve attached to the casing, the upper sleeve having a first set of teeth; and   a lower sleeve releasably coupled the motor, the lower sleeve having a second set of teeth configured to mate with the first set of teeth,   wherein upon release, the lower sleeve is movable to engage the upper sleeve, thereby preventing relative rotation between casing and the drilling member.   
     
     
         11 . The system of  claim 1 , further comprising a second releasable coupling assembly for coupling the motor to the casing. 
     
     
         12 . A method of forming a wellbore in a formation, comprising:
 coupling a first casing to a second casing, the first casing having a motor for rotating the drilling member;   lowering the first casing and the second casing into the formation;   releasing the first casing from the second casing;   rotating the drilling member relative to the first casing to extend the wellbore;   supplying cement around the motor and into the wellbore;   detaching the motor from the drilling member by retracting a dog from engagement with the drilling member; and   retrieving the motor.   
     
     
         13 . The method of  claim 12 , wherein retracting the dog includes axially moving a mandrel coupled to the dog. 
     
     
         14 . The method of  claim 12 , further comprising preventing the retracted dog from re-extending. 
     
     
         15 . The method of  claim 12 , wherein the motor includes a rotatable member and a stationary member, and further comprising preventing the rotatable member from rotation. 
     
     
         16 . The method of  claim 15 , wherein prevention rotation of the rotatable member comprises landing a ball in a recess between the rotatable member and the stationary member. 
     
     
         17 . The method of  claim 12 , wherein supplying cement around the motor comprises diverting the cement through a bore in the motor. 
     
     
         18 . The method of  claim 12 , further comprising locking the drilling member from rotating relative to the first casing. 
     
     
         19 . The method of  claim 18 , wherein locking the drilling member from rotation includes engaging a first set of teeth of the first casing to a second set of teeth of the drilling member. 
     
     
         20 . The method of  claim 18 , where locking the drilling member includes moving a lower sleeve coupled to the motor toward an upper sleeve coupled to the first casing; and engaging a first set of teeth of the upper sleeve to a second set of teeth of the lower sleeve.