Abstract: A downhole drilling apparatus may comprise a rotatable body with fixed cutting elements protruding from an exterior thereof. To form a subterranean borehole, the fixed cutting elements, spaced at a constant radius from a rotational axis of the body, may degrade an earthen formation as the body rotates. The body may also have a rotatable cutting element protruding from its exterior. To remove material from an interior wall of the borehole, the rotatable cutting element may be positioned in a first rotational orientation wherein it extends radially beyond the constant radius of the fixed cutting elements. An amount of material being removed may be altered by rotating the rotatable cutting element into a second rotational orientation wherein it remains radially within the constant radius.

Abstract: A downhole drilling apparatus may comprise a rotatable body with fixed cutting elements protruding from an exterior thereof. To form a subterranean borehole, the fixed cutting elements, spaced at a constant radius from a rotational axis of the body, may degrade an earthen formation as the body rotates. The body may also have a rotatable cutting element protruding from its exterior. To remove material from an interior wall of the borehole, the rotatable cutting element may be positioned in a first rotational orientation wherein it extends radially beyond the constant radius of the fixed cutting elements. An amount of material being removed may be altered by rotating the rotatable cutting element into a second rotational orientation wherein it remains radially within the constant radius.

Abstract: A cutting element for a rotary drill bit includes at least one insert of polycrystalline diamond of a kind incorporating a carbonate as a sintering binder-catalyst. The insert is mounted by being at least partly surrounded by a support body of conventional polycrystalline diamond of a kind incorporating a sintering binder-catalyst selected from cobalt and other iron group elements or alloys thereof. The insert and support body may be integrally bonded to a substrate during manufacture. Either the insert or support body may be pre-sintered or sintered during formation of the cutting element.

Abstract: A cutting structure for a rotary drag-type drill bit includes a cutting element mounted on a member on the bit body, which may be a carrier secured to the bit body or part of the bit body itself. The surface of the member on which the cutting element is mounted is formed with a groove, adjacent the cutting element. The downstream end of the groove is located near a nozzle in the bit body through which a jet of drilling fluid emerges, so that the groove directs to the front of the cutting element the flow of drilling fluid which impinges on the groove. An array of separate grooves may lead from the nozzle to different cutting elements. The flow of drilling fluid directed towards each cutting element serves to break up cuttings removed from the formation by the cutting element and to carry the cuttings away from the element.

Abstract: A method of determining wear characteristics of a rotary drag-type drill bit comprises the steps of: determining the location and shape of a datum profile for the cutters on the bit body: determining the location and shape of a reference profile located inwardly of the datum profile; and ascertaining the volume of superhard material in the cutters between the datum profile and the reference profile. The volume of superhard material in the cutters at discrete radial locations is then plotted against the radial distance of the material from the axis of rotation of the bit body. The predicted wear rate WR.sub.r of superhard material at radius r is also calculated as a function of the volume and the predicted wear rate is plotted against r. The type and location of the cutters may then be modified, if necessary, to give a wear rate which is substantially constant across the radius of the drill bit.

Abstract: Formation engaging elements are moveably mounted onto a drill bit. Such elements may be used to protect other rigidly mounted formation engaging elements from impacts that occur during use of the drill bit, or they may be used to alter the aggressiveness of the drill bit when used in directional drilling operations.

Abstract: A rotary drill bit, for drilling holes in subsurface formations, comprises a bit body having a shank for connection to a drill string, a number of circumferentially spaced blades on the bit body extending outwardly away from the central axis of rotation of the bit, and a number of cutters mounted side-by-side along the leading edge of each blade. The cutters include primary cutters having cutting edges which define a primary cutting profile and secondary cutters having cutting edges which define a secondary cutting profile which is disposed inwardly of the primary cutting profile with respect to the bit body. The secondary cutters may be on different blades from the primary cutters, or may be mounted on the same blades, rearwardly of the primary cutters. At least the majority of the cutters are located at different distances away from the bit axis, so that as the bit rotates each secondary cutter follows a path which lies intermediate the paths followed by two primary cutters.

Abstract: A torque transmitting device for use with a rotary drill bit connected to a drill collar, comprises a first member connected to the drill collar, a second member connected to the drill bit, and coupling means connecting the two members together for rotation about a common central axis. The coupling means permits limited relative rotation between the members about the axis, but provides a resistance to rotation of the first member relative to the second member in a forward drilling direction which is greater than its resistance to relative rotation in the reverse direction. The comparatively lower resistance to rotation in the reverse direction prevents momentary reverse rotation of the drill collar, due for example to torsional oscillations, being transmitted to the drill. bit. This reduces the likelihood of damage to the cutters on the drill bit, which might otherwise result from such momentary reverse rotation of the bit.

Abstract: A preform cutting element for a rotary drag-type drill bit comprises a front facing table of superhard material having a front surface, a peripheral surface, a rear surface bonded to a substrate of less hard material, and a cutting edge formed by at least part of the junction between the front surface and the peripheral surface. The front surface of the facing table is formed with a chip-breaking formation which is located adjacent the cutting edge and is shaped to deflect transversely of the front surface of the facing table cuttings which, in use, are removed by the cutting edge from the formation being drilled. The chip-breaking formation may comprise a peripheral groove or rebate, or an upstanding ridge or insert.

Abstract: A rotary drag-type drill bit, for drilling holes in subsurface formations, comprises a bit body having a leading face and a gauge region, a number of blades formed on the leading face of the bit and extending outwardly away from the axis of the bit so as to define between the blades fluid channels leading towards junk slots in the gauge region. Cutting elements are mounted along each blade, and nozzles in the bit body supply drilling fluid to the leading face of the bit for cleaning and cooling the cutting elements. At least some of said blades each have a leading edge which is non-linear, or convexly or concavely curved, as viewed axially of the bit, as it extends outwardly away from the axis of the bit. Blades of different shapes may be located alternately around the axis of the bit. The junk slots at the gauge region, and the kickers between which they are formed, may vary in width around the periphery of the bit, and may be inclined to the axis of the bit.