Abstract: The present invention addresses this need in the art by providing a cutter insert comprising a plug section and a cutter pedestal. The cutter insert is preferably formed of tungsten carbide, except for two exterior surfaces covered with PDC. The plug section may be circular or oval in cross section perpendicular to the axis of the insert. The plug section and the pedestal each defines a shoulder which is coated with a PDC layer. In this way, two cutting surfaces are applied to the formation, enhancing the cutting ability of the insert.

Abstract: 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.