Casing drilling under reamer apparatus and method

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.

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.

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.

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.