A roller cone bi-center bit for economically drilling an enlarged borehole below
casing in earth formation is provided. The bi-center bit includes a rolling cone
cutter or other appropriate cutter to enlarge a pilot bore also made by rolling
cone or other type of cutters. The bit comprises a single-diameter body with a
recess to accommodate the trailing cutter which enlarges the pilot bore. The bi-center
bit may also provide the ability to change out the cutters efficiently in the field.
The cutters are oriented to enhance drilling out the cement plug at the bottom
of the casing. The cone cutter may be also be mounted on segments which are designed
to be easily removed for replacement or adjustment in position in the field.
