Centered-leg roller cone drill bit

摘要

A drill bit including a roller cone and fixed cutters positioned external to the roller cone and radially from the bit axis of rotation. The roller cone is located so that a drill diameter of the cone is substantially concentric with an axis of rotation of the bit. The fixed cutters can be made of tungsten carbide, polycrystalline diamond, boron nitride, or any other superhard material. The fixed cutters are positioned to either maintain the hole diameter drilled by the roller cone or to drill a larger diameter hole than the hole drilled by the roller cone. The single roller cone may be located in the center of a multi-cone bit arrangement or in the center of a PDC bit to assist in drilling the center of a wellbore. The single roller cone may be used to form a bi-center bit in combination with a reaming section. The single roller cone may also be located on an independent sub that is removably attached to the bit body.