Rotary drill bits
AssigneeCamco Drilling Group Limited
InventorJohn M. Clegg
Life of this patent
Estimating the term…
Abstract
A rotary drill bit comprises a bit body carrying a plurality of primary preform cutting elements defining a primary cutting profile. The bit includes means to apply a lateral imbalance force to the bit as it rotates, and a portion of the outer periphery of the bit body includes a low friction bearing surface so located as to transmit the lateral force to the formation. There are associated with some of the primary cutting elements respective secondary elements spaced inwardly of the cutting profile defined by the primary cutting elements, but the portion of the periphery of the bit body where the bearing surface is located is substantially free of such secondary elements. The arrangement enhances the anti-whirl characteristics of the bit.
Claims16
A rotary drill bit comprising a bit body having a shank for connection to a drill string and a passage for supplying drilling fluid to the face of the bit, the bit body having a central longitudinal axis and carrying a plurality of primary cutting elements defining a primary cutting profile, at least some of the primary cutting elements each comprising a preform cutting element having a superhard front cutting face, the bit including means to apply a resultant lateral force to the bit as it rotates in use, and a portion of the outer periphery of the bit body including at least one low friction bearing means so located as to transmit said resultant lateral force to the part of the formation which the bearing means is for the time engaging, there being associated with at least certain of said primary cutting elements respective secondary elements spaced inwardly of said primary cutting profile, each primary cutting element having an operative cutting edge portion, and at least certain of said respective secondary elements each having an outer surface portion located at substantially the same radial distance from the central longitudinal axis of the bit as a radially outer part of the operative cutting edge portion of its respective associated primary cutting element.
A rotary drill bit comprising a bit body having a shank for connection to a drill string and a passage for supplying drilling fluid to the face of the bit, which carries a plurality of primary cutting elements defining a primary cutting profile, at least some of the primary cutting elements each comprising a preform cutting element having a superhard front cutting face, there being associated with at least certain of said primary cutting elements respective secondary elements each spaced inwardly of said primary cutting profile and rearwardly from its respective associated primary cutting element, with respect to the normal direction of rotation of the drill bit, said inward spacing having a vertical and a radial component, each secondary element being s shaped and located as substantially to compensate for said radial component of the inward spacing of the secondary, element from the primary profile, whereby radially outer parts of formation-engaging surfaces on said primary and secondary elements are at substantially the same radial location in spite of the inward spacing of the secondary element from its associated primary cutting element.
Dependencies are inferred from the claim text.