Abstract: A choke device for controlling fluid flow, particularly in a modulated bias unit, drill bit or other item downhole drilling component, comprises a passage for the flow of fluid, a choke aperture separating an upstream portion of the passage from a downstream portion thereof, and an impingement surface located in the downstream portion of the passage opposite and spaced from the choke aperture, so that fluid flowing through the choke aperture impinges on the impingement surface. The impingement surface is formed from superhard material, such as polycrystalline diamond, and may comprise the front facing table of a two-layer polycrystalline diamond compact of the kind used as cutting elements in drag-type drill bits.

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 cutting structure for a rotary drag-type drill bit includes a preform cutting element mounted on a carrier which, in use, is mounted on the drill bit and comprises a front facing table of superhard material bonded to a less hard substrate. A portion of the carrier on which the preform cutting element is mounted is shaped, adjacent the cutting element, for engagement by a chip of formation material being removed by the cutting element from the formation being drilled so as to tend to break the chip away from the surface of the formation. A portion of the carrier, or a portion of the bit body itself, may also be shaped, adjacent the cutting element, to direct to a location in front of the cutting element a flow of drilling fluid which impinges on said surface so as to assist in chip removal.

Abstract: Apparatus for recompleting an oil and/or gas well includes a primary tubing hanger, and primary well tubing hung from the hanger within the well, and a communication/hanger nipple, located below the primary tubing hanger, which is suitable for receiving and locating a coiled tubing hanger. The communication/hanger nipple is run into the well as part of the initial completion in any situation where there is a potential requirement for a coiled tubing completion later in the life of the well but plays no part in the normal primary production operation of the well. However, should production fail for any reason, requiring coiled tubing recompletion, the communication/hanger nipple is available to support the coiled tubing and provide communication to the subsurface equipment without the necessity of modifying the primary tubing hanger.

Abstract: A preform element, for example for use as a cutting element on a rotary drag-type drill bit, includes a facing table of superhard material having a front face and a rear face bonded to the front face of a substrate which is less hard than the superhard material. The rear face of the facing table comprises a surface formed with a plurality of spaced protuberances and a plurality of spaced sockets, and the front face of the substrate comprises a surface which is bonded to the surface of the facing table and is formed with a plurality of spaced protuberances which are bonded within said sockets in the facing table, and a plurality of spaced sockets within which are bonded said protuberances on the facing table.

Abstract: A rotary drill bit, for drilling holes in subsurface formations, comprises a bit body, cutting structures mounted on the bit body, and a fluid supply system for supplying drilling fluid to the surface of the bit body, to cool and clean the cutting structures. The fluid supply system comprises a number of nozzles mounted in the bit body, a main passage in the bit body and a number of auxiliary passages leading from the main passage to the nozzles. Some or all of the passages are at least partly lined with an erosion-resistant lining material. The lining material may comprise a hard facing applied to the internal surface of a preformed passage or a rigid tube which itself defines the internal surface of the passage.

Abstract: A steerable rotary drilling system has a bottom hole assembly which includes, in addition to the drill bit, a modulated bias unit and a control unit, the bias unit comprising a number of hydraulic actuators around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole being drilled. Each actuator may be connected, through a control valve, to a source of drilling fluid under pressure and the operation of the valve is controlled by the control unit so as to modulate the fluid pressure supplied to the actuators as the bias unit rotates. If the control valve is operated in synchronism with rotation of the bias unit the thrust members impart a lateral bias to the bias unit, and hence to the drill bit, to control the direction of drilling.

Abstract: A preform element, such as a cutting element for a rotary drag-type drill bit, includes a facing table of superhard material having a front face, a peripheral surface, and a rear surface bonded to a substrate which is less hard than the superhard material. The rear surface of the facing table is integrally formed with a plurality of ribs which project into the substrate, and at least major portions of the ribs extend across the rear surface of the facing table in directions which are generally radial with respect to at least one point which is adjacent or outside the peripheral surface of the facing table.

Abstract: A drilling assembly for drilling holes in subsurface formations comprises a drill bit 10, a drive unit 12 including a housing and a rotor 11 operatively coupled to the drill bit to rotate the drill bit relative to the housing, and a modulated bias unit 14 coupled to rotate with the drive unit housing and apply a lateral bias thereto in synchronism with rotation of the housing. The modulated bias unit 14 comprises one or more hydraulic actuators including members 16 which, in use, bear against the sides of the borehole, and means for modulating the pressure of fluid supplied to the actuators in synchronism with rotation of a component of the drilling assembly, and in selected angular phase relation thereto, whereby each hydraulic actuator is actuated in a selected rotational position of the component.

Abstract: A cutter for a rotary drill bit comprises a cutting table of superhard material bonded to a less hard substrate, the cutting table having a front face and a peripheral edge at least a part of which defines a convexly curved cutting region. The substrate includes a portion which increases in lateral extent beyond the curved cutting region of the peripheral edge of the cutting table as it extends rearwardly . The rearward extent of the outer surface of said portion varies around the periphery of the cutting table, from a maximum adjacent the cutting region to a minimum diametrically opposite the cutting region. This renders the cutter more resistant to impact loads in the cutting region while, at the same time, allowing the opposite side of the cutter to be firmly mounted in a socket in the body of the drill bit.

Abstract: A drill bit comprises a main body part having a shank for connection to a drill string, an end face, an internal passage for supplying drilling fluid to the end face, a number of blades extending from the end face outwardly and longitudinally of the central axis of rotation of the bit, and a number of cutters mounted on each said blade. Each blade comprises a central metal core at least partly surrounded by solid infiltrated matrix material.

Abstract: A cutter assembly for a rotary drag-type drill bit includes a preform cutting element comprising a front facing table of polycrystalline diamond bonded to a tungsten carbide substrate, the cutting element being mounted on a tungsten carbide carrier which is received in a socket in the body of the drill bit. The carrier comprises a sector-shaped portion of a disc, and the cutting element is bonded to one of the straight edge surfaces of the carrier, adjacent the apex of the sector shape. The side surfaces of the carrier taper inwardly, as viewed in cross-section, as they extend towards the curved edge surface of the carrier.

Abstract: A modulated bias unit, for use in a steerable rotary drilling system, comprises a number of hydraulic actuators spaced apart around the periphery of the unit, each having a movable thrust member which is hydraulically displaceable outwardly for engagement with the formation of the borehole, and a control valve operable to bring the actuators alternately in succession into and out of communication with a source of fluid under pressure, as the bias unit rotates. The fluid pressure supplied to each actuator may thus be modulated in synchronism with rotation of the drill bit, and in selected phase relation thereto, so that each movable thrust member is displaced outwardly at the same rotational position of the bias unit so as to apply a lateral bias to the unit for the purposes of steering an associated drill bit.

Abstract: A rotary drill bit for drilling holes in subsurface formations comprises a bit body having a leading face and a gauge region, and a plurality of blades formed on the leading face of the bit body and extending outwardly away from the axis of the bit towards the gauge region so as to define a fluid flow channel between the leading edge of each blade and the trailing edge of the adjacent preceding blade. A plurality of cutting elements are mounted along the leading edge of each blade, and there is provided, in one or more of the channels, a main nozzle which directs fluid along the leading edge of one blade so as to clean and cool the cutting elements on it, and a subsidiary nozzle which is located and orientated so as to direct fluid along the trailing edge of the preceding blade in a direction opposite to the direction of flow from the main nozzle, so as to tend to enhance partial recirculation of fluid flow in the flow channel between the blades.

Abstract: A rotary drill bit for use in 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 a number of fluid channels leading towards the gauge region, a number of cutting elements mounted side-by-side along each blade, and a number of nozzles in the bit body for supplying drilling fluid to the fluid channels for cleaning and cooling the cutting elements. In at least one of the fluid channels, adjacent the gauge region, is an opening into an enclosed passage which passes internally through the bit body to an outlet which, in use, communicates with the annulus between the drill string and the wall of the borehole being drilled. The portion of the gauge region outwardly of the opening comprises a bearing surface which, in use bears against the wall of the bore hole and extends across the width of the channel.

Abstract: A preform cutting element for a drag-type rotary drill bit includes a facing table of polycrystalline diamond bonded to a less hard substrate, such as cemented tungsten carbide. The element is formed by first forming a solid substrate, and then applying an electron beam, laser, or other intense heating source to adjacent areas of the front surface of the substrate to melt the surface and form an array of holes or holes therein. A layer of polycrystalline diamond particles is applied to the substrate so that such particles fill the holes or holes, and the diamond layer and substrate are then subjected to pressure and temperature in a high pressure, high temperature press to bond the superhard layer to the substrate. The engagement of parts of the diamond table in the holes or holes in the substrate provides a mechanical interlock to improve the strength of the bond between the table and substrate.

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 each extending outwardly away from the central axis of rotation of the bit, a number of cutters mounted side-by-side along each blade, and a passage in the bit body for supplying drilling fluid to the surface of the bit for cleaning and cooling the cutters. The blades comprise alternating primary and secondary blades. The cutters on the primary blades are primary cutters which are located at different radial distances from the bit axis so as to define a cutting profile which, in use, covers substantially the whole of the bottom of the bore hole being drilled. At least the majority of the cutters on the secondary blades are secondary cutters each of which is located at substantially the same radial distance from the bit axis as an associated primary cutter on the preceding primary blade.

Abstract: A rotary drill bit comprises a bit body having a shank for connection to a drill string, a plurality of cutters mounted on the bit body, each cutter having a cutting face, and means for supplying drilling fluid to the surface of the bit body to cool and clean the cutters. At least some of the cutters are lateral cutters located to act sideways on the formation being drilled, and the cutting faces of such lateral cutters are orientated to exhibit negative side rake and negative top rake with respect to the surface of the formation. The negative side rake angle is greater than 20.degree. and may be as much as 90.degree., and the negative top rake angle is also more than 20.degree.. A single cutter may include two cutting faces at different negative side rake angles, e.g.

Abstract: A preform element, for example for use as a cutter in a rotary drill bit, includes a facing table of polycrystalline diamond bonded to a substrate of tungsten carbide. The rear surface of the facing table is integrally formed with a plurality of protuberances which project into the substrate and are spaced apart irregularly across the rear surface of the facing table. The protuberances may differ in cross-sectional shape and/or size, and the distribution of the different sizes and/or shapes may also be irregular. The protuberances may also project into the substrate to irregularly varying depths.

Abstract: A preform cutting element, for use on a rotary drill bit, includes a facing table of polycrystalline diamond bonded to a tungsten carbide substrate, a cutting edge being formed by part of the peripheral surface of the facing table. The rear surface of the facing table is integrally formed with a plurality of spaced elongate ribs which project into the substrate, at least the majority of the ribs being located in the vicinity of the cutting edge. The ribs may intersect the cutting edge and extend only part way across the facing table from the cutting edge. The ribs may vary in width and/or depth.