Patent ID: 7182153

Claim:
An apparatus to install a casing string into a borehole while it is being drilled, the casing having an internal diameter and an external diameter, the apparatus comprising: a casing latch installed at a distal end of the casing string, the casing latch having a pass-through diameter smaller than the casing internal diameter, the casing latch configured to releaseably connect to a flexible drill collar assembly; the flexible drill collar assembly having an enlargement tool and an articulated joint, the articulated joint adapted to position the enlargement tool in a first position that is in axial alignment with the axis of rotation of the casing string and a second position that is eccentric with respect to the axis of rotation of the casing string; and a drill bit coupled to the enlargement tool such that when the enlargement tool is in its second, eccentric, position, the drill bit drills a borehole large enough to provide clearance for the casing string and when the drill bit is in its first, axial, position, the drill bit is removable through the casing string.