Casing drilling under reamer apparatus and method

Abstract

A method to drill a wellbore includes positioning a cutting structure proximal to a distal end of a drilling string, deploying a bottom hole assembly through a central bore of the distal end of the drilling string and the cutting structure, engaging the cutting structure with the bottom hole assembly, and rotating the cutting structure with the bottom hole assembly. An under reamer assembly includes a reamer shoe positioned proximal to a distal end of a drilling string and a cutting structure coupled to the reamer shoe, wherein the cutting structure is configured to be engaged by a bottom hole assembly, and wherein the cutting structure is configured to enlarge a pilot bore cut by a drill bit of the bottom hole assembly.

What is claimed is: 
     
         1 . An apparatus to drill a wellbore, the apparatus comprising:
 a cutting structure attached to a distal end of a drilling string; and   a bottom hole assembly including a drill bit, a reamer drive sub, and a downhole motor;
 the bottom hole assembly configured to pass through a central bore of the drilling string and the cutting structure; 
 the reamer drive sub configured to releasably engage the cutting structure, and 
 the bottom hole assembly configured to rotate the cutting structure through the reamer drive sub; 
   wherein, when engaged, the cutting structure is axially decoupled from the drilling string.   
     
     
         2 . The apparatus of  claim 1 , wherein the bottom hole assembly is configured to pass through a central bore of the drilling string and releasably engage a lock nipple of the drilling string. 
     
     
         3 . The apparatus of  claim 2 , further comprising a delivery conduit selected from the group consisting of wireline, coiled tubing, and drill pipe to deploy and retrieve the bottom hole assembly to and from the lock nipple of the drilling string. 
     
     
         4 . The apparatus of  claim 1 , wherein the downhole motor is configured to rotate both the cutting structure and the drill bit. 
     
     
         5 . The apparatus of  claim 1 , wherein the cutting structure is free to rotate relative to the drilling string in a decoupled state and restricted from rotating relative to the drilling string in a coupled state. 
     
     
         6 . The apparatus of claim I, wherein the drilling string comprises one of a casing string and a liner string. 
     
     
         7 . A method to drill a wellbore, the method comprising:
 positioning a cutting structure proximal to a distal end of a drilling string;   deploying a bottom hole assembly through a central bore of the distal end of the drilling string and the cutting structure;   engaging the cutting structure with the bottom hole assembly;   axially decoupling the cutting structure from the drilling string; and   rotating the cutting structure with the bottom hole assembly.   
     
     
         8 . The method of  claim 7 , further comprising engaging a lock nipple of the drilling string with the bottom hole assembly. 
     
     
         9 . The method of  claim 7 , further comprising recoupling the cutting structure to the drilling string. 
     
     
         10 . The method of  claim 9 , further comprising disengaging the cutting structure from the bottom hole assembly and retrieving the bottom hole assembly. 
     
     
         11 . The method of  claim 8 , further comprising disengaging the lock nipple of the drilling string and retrieving the bottom hole assembly. 
     
     
         12 . The method of  claim 7 , further comprising reaming, under reaming, or drilling a pilot bore formed by a drill bit of the bottom hole assembly. 
     
     
         13 . The method of  claim 7 , further comprising rotating a drill bit of the bottom hole assembly and the cutting structure with a downhole motor of the bottom hole assembly. 
     
     
         14 . An under reamer assembly to be used in a drilling operation, the under reamer assembly comprising:
 a reamer shoe configured to be positioned proximal to a distal end of a drilling string; and   a cutting structure releasably coupled to the reamer shoe, wherein the cutting structure is configured to be engaged by a bottom hole assembly, decoupled from the reamer shoe, and axially displaced from the drilling string;   wherein the cutting structure is configured to enlarge a pilot bore cut by a drill bit of the bottom hole assembly.   
     
     
         15 . The under reamer of  claim 14 , wherein the cutting structure is configured to be recoupled to the reamer shoe. 
     
     
         16 . The under reamer of  claim 14 , wherein, when engaged, a downhole motor of the bottom hole assembly operatively simultaneously rotates the drill bit and the cutting structure. 
     
     
         17 . The under reamer of  claim 14 , wherein the cutting structure, reamer shoe, and drilling string have a clearance diameter through which the bottom hole assembly may be deployed to and retrieved from the distal end of the drilling string. 
     
     
         18 . An apparatus to drill a wellbore, the apparatus comprising:
 a drilling string;   a bottom hole assembly including a drill bit, a reamer drive sub including one or more torque dogs, and a downhole motor;   a reamer shoe assembly having:
 a sleeve rotatably attached to a distal end of the drilling string; 
 a cutting head, configured to be rotated by the reamer drive sub, having one or more inner recesses configured to be releasably engaged by the one or more torque dogs of the reamer drive sub; and 
 a biasing spring and a bushing intermediate the cutting head and the distal end of the drilling string configured to permit relative rotation and axial movement between the cutting head and the drilling string. 
   
     
     
         19 . The apparatus of  claim 18 , wherein the bottom hole assembly is configured to pass through a central bore of the drilling string and the reamer shoe and releasably engage a lock nipple of the drilling string. 
     
     
         20 . The apparatus of  claim 18 , wherein the downhole motor is configured to rotate both the cutting structure and the drill bit. 
     
     
         21 . The apparatus of  claim 18 , wherein the drilling string comprises one of a casing string and a liner string. 
     
     
         22 . A method to drill a wellbore, the method comprising:
 disposing a reamer shoe assembly proximal to a distal end of a drilling string, the reamer shoe configured to rotate freely with respect to and move axially relative to the drilling string;   deploying a bottom hole assembly through a central bore of the distal end of the drilling string and the reamer shoe assembly;   releasably engaging and rotating the reamer shoe assembly with the bottom hole assembly.   
     
     
         23 . The method of  claim 22 , further comprising engaging a lock nipple of the drilling string with the bottom hole assembly. 
     
     
         24 . The method of  claim 23 , further comprising disengaging the lock nipple of the drilling string and retrieving the bottom hole assembly. 
     
     
         25 . The method of  claim 22 , further comprising disengaging the reamer shoe assembly and retrieving the bottom hole assembly. 
     
     
         26 . The method of  claim 22 , further comprising reaming, under reaming, or drilling a pilot bore formed by a drill bit of the bottom hole assembly. 
     
     
         27 . The method of  claim 22 , further comprising rotating a drill bit of the bottom hole assembly and the cutting structure with a downhole motor of the bottom hole assembly. 
     
     
         28 . An under reamer assembly to be used in a drilling operation, the under reamer assembly comprising:
 a sleeve configured to be attached to a distal end of the drilling string;   a cutting head attached to the sleeve, the cutting head configured to be rotated by a reamer drive sub and comprising one or more inner recesses configured to be releasably engaged by one or more torque dogs of the reamer drive sub;   a biasing spring and a bushing configured to be disposed intermediate the cutting head and the distal end of the drilling string, the biasing spring and bushing permitting relative rotation and axial movement between the cutting head and the drilling string.   wherein the cutting head is configured to enlarge a pilot bore cut by a drill bit of a bottom hole assembly.   
     
     
         29 . The under reamer of  claim 28 , wherein the reamer shoe assembly has a clearance diameter through which the bottom hole assembly may be deployed to and retrieved from the distal end of the drilling string. 
     
     
         30 . The apparatus of  claim 28 , wherein the drilling string comprises one of a casing string and a liner string.