GB2332691A

GB2332691A - Fluid directing cutting structure for drill bit

Info

Publication number: GB2332691A
Application number: GB9906511A
Authority: GB
Inventors: John Michael Fuller
Original assignee: Camco Drilling Group Ltd
Current assignee: Camco Drilling Group Ltd
Priority date: 1996-10-11
Filing date: 1997-10-10
Publication date: 1999-06-30
Anticipated expiration: 2017-10-10
Also published as: GB2332691B; GB9906511D0

Abstract

Cutting structure for a rotary drag-type drill bit comprising a cutting element 52 mounted on a member 53 on the drill bit. A portion of the member 55 is shaped to direct drilling fluid 57 to a location in front of the cutting element to facilitate the mechanical breaking of chips of the formation being drilled. The cutting element comprises a layer of superhard material bonded to a less hard substrate. The member may be a carrier or part of the bit body. The shaped surface is preferably smoothly and concavely shaped and may be wholly or partially faced with superhard material. A further element of superhard material bonded to a less hard substrate may be mounted on the member to form part of the shaped surface.

Description

"Improvements in or relating to cutting structures for rotary drill bits" The invention relates to cutting structures for rotary drag-type drill bits, for use in drilling or coring holes in subsurface formations, and ofthe kind comprising a bit body having a shank for connection to a drill string, a plurality of cutting structures at the surface of the bit body, and a passage in the bit body for supplying drilling fluid to the surface of the bit body for cooling and/or cleaning the cutters. Each cutting structure includes a preform cutting element comprising a front facing table of superhard material bonded to a less hard substrate. The cutting element may be mounted on a carrier, also of a material which is less hard than the superhard material, which is mounted on the body of the drill bit, for example, is secured within a socket on the bit body.

Alternatively, the cutting element may be mounted directly on the bit body, for example the substrate may be of suffiåent axial length that it may itself be secured within a socket on the bit body.

In drag-type drill bits of this kind the bit body may be machined from metal, usually steel, and sockets to receive the carriers or the cutting elements themselves are machined in the bit body. Alternatively, the bit body may be moulded from tungsten carbide matrix material using a powder metallurgy process.

Drag-type drill bits of this kind are particularly suitable for drilling softer formations. However, when drilling soft, sticky shale formations in a water based mud environment, and in other similar conditions, there may be a tendency for the shavings or chips of formation gouged from the surface ofthe borehole not to separate from the surface and to be held down on the surface of the formation by the subsequent passage over the shaving or chip of other cutters and parts of the drill bit. Also, there may be a tendency for such material to adhere to the surface of the bit body, a phenomenon known as "bit balling", eventually resulting in the bit becoming ineffective for further drilling.

The present invention provides arrangements whereby the hydraulic power of the drilling fluid supplied to the surface of the bit body may be employed to assist in the removal of cuttings from the formation or from the cutting elements.

According to the invention there is provided a cutting structure for a rotary dragtype drill bit including a preform cutting element mounted on a member on the drill bit and comprising a front facing table of superhard material bonded to a less hard substrate, wherein a portion of the member on which the preform cutting element is mounted is shaped, adjacent the cutting element, to direct to a location in front of the cutting element, with respect to the normal direction of forward movement of the cutting element in use, a flow of drilling fluid which impinges on said surface.

The member on which the preform element is mounted may comprise a carrier which is in turn mounted on the bit body, or may comprise a part of the bit body itself.

Preferably said shaped surface is formed on a portion of said member which overhangs the front surface of the facing table of the cutting element. Preferably the surface has an edge adjacent the cutting element, and an imaginary extension of the surface beyond said edge is spaced forwardly of the cutting element.

Preferably the shaped surface is smoothly and concavely curved as it extends towards the cutting element.

Said shaped surface may be hard faced, for example may have a surface coating of hard facing material applied thereto. Alternatively, the shaped surface may include a portion faced with superhard material. For example, a further preform compact, comprising a front facing table of superhard material bonded to a less hard substrate, may be mounted on the member so that the front face of the superhard material forms part of said shaped surface on the member.

The following is a more detailed description of embodiments of the invention, by way of example, reference being made to the accompanying drawings in which: Figure 1 is a diagrammatic section through a cutting structure on a rotary dragtype drill bit, not in accordance with the present invention, Figures 2 and 3 are similar diagrammatic sections through cutting structures in accordance with the present invention, Figure 4 is an end view of a drill bit incorporating a different type of cutting structure according to the invention, Figure 5 is a diagrammatic section through a cutting structure of the type used on the drill bit of Figure 4, Figure 6 is a diagrammatic vertical half-section through the drill bit of Figure 5, and Figures 7 and 8 are diagrammatic sections through further forms of cutting structure according to the invention.

Referring to Figure 1, the body of the drill bit is formed, in well known manner, with a plurality of blades 10 extending generally outwardly away from the central longitudinal axis of rotation of the drill bit. Spaced apart side-by-side along the leading face of each blade is a plurality of cutting structures 11.

Each cutting structure comprises a cutting element 12 in the form of a circular tablet having a thin front cutting table 13 of polycrystalline diamond or other superhard material bonded in a high pressure, high temperature press to a substrate 14 of less hard material, such as cemented tungsten carbide. The cutting element 12 is brazed within a rebate 15 on a generally cylindrical carrier 16 which is also formed from cemented tungsten carbide.

The cylindrical carrier 16 is received within a correspondingly shaped socket or recess 17 in the blade 10. The carrier 16 will usually be brazed or shrink-fitted in the socket.

On the side ofthe cutting element 12 remote from its cutting edge 18, the carrier 16 is formed with a concave surface 19 which extends around a portion of the periphery ofthe cutting element 12 opposite its cutting edge 18. Alternatively the concave surface 19 may be cylindrical.

The edge of the curved surface 19 closest to the cutting element 12 meets the cutting element rearwardly of the front face of the facing table 13 and a tangent to the surface at that point is substantially parallel to the front face of the facing table. The curved surface 19 then extends to a region forwardly of the facing table 13 to a point where its tangent is substantially at right angles to the front face of the facing table.

Figure 1 shows the cutting structure in use gouging a shaving or chip 20 from the surface of the formation 21 of the borehole. As the chip 20 is lifted from the formation it passes upwardly across the front face of the cutting element 12, and when it engages the curved surface 19, the surface causes it to tend to break into fragments, as indicated diagrammatically 22. The chip is thus broken up and the particles can readily be washed away by the drilling fluid that is passing under pressure across the cutting structures, thereby reducing the tendency for cuttings to adhere to the cutting structures or to be held down on the surface of the formation. This arrangement is not in accordance with the present invention.

Figure 2 is another arrangement in which the cutting element 29 is mounted on a tungsten carbide carrier 30 which is received in a socket 31 in a blade 32 on the bit body. In this arrangement the carrier 30 is generally in the form of part of a sector of a circle and may be generally of the kind described in British Patent Specification No. 2298665. In this case also, the carrier 30 is formed with a shaped concave surface 33 on the side of the cutting element 29 opposite its cutting edge 34. In this case the surface 33 forms a continuation of the surface 35 on the carrier 30 to which the cutting element 29 is brazed.

Figure 3 shows a modification of the arrangement of Figure 2 where the shaped surface comprises two generally planar surfaces 36, 37 arranged at an angle to one another. The surface 37 comprises the front surface ofthe facing table 38 in a preform polycrystalline diamond compact 39 which is brazed into a suitably shaped recess on the carrier 40.

The compact 39 receives the direct impact of chips being removed from the formation and thus provides the cutting structure with substantial resistance to wear and erosion due to impact by the chips.

Figure 4 is an end view of a drill bit having a different form of cutting structure according to the invention In this case the bit body 41 is formed with two blades 42 as best seen in Figures 5 and 6, each blade 42 has two circular carriers 43 mounted side-byside thereon. Each carrier 43 is generally circular and is formed on its rear surface with a cylindrical stud portion 44 received in an appropriately shaped socket in the blade 42.

As best seen in Figure 6, each carrier 43 has mounted around the lowermost portion of its periphery a number of generally semi-circular preform cutting elements 45.

Each cutting element 45 comprises a facing table of polycrystalline diamond bonded to a substrate of tungsten carbide and is brazed within a suitably shaped socket 46 in the circular carrier 43. The front face of the carrier 43 is formed with a part-spherical concave surface 47 which performs two functions. It acts in similar fashion to the concave surfaces 19, 28, 33 in the arrangements of Figures 1 and 2, but it also directs a jet of drilling fluid 48 from a nozzle 49 associated with the carrier downwardly past the cutting element 45 and on to the formation in front of the cutting element. This also serves to clean the chips of formation from the front of the cutting elements 45 as they are broken up by the curvature 47 in the front face of the carrier.

As best seen in Figure 6, the shape of the carriers 43 forms two part-circular groove side-by-side in the formation 50 and the nozzle 49 is so located that the jet 48 of drilling fluid flows around the bottom of the grooves in the formation and sweeps across the cutting elements 45 as indicated by the arrows 51.

Figure 7 is a diagrammatic section through a cutting structure comprising a polycrystalline diamond preform element 52 mounted on a cemented tungsten carbide carrier 53 which is received in a socket in the bit body (not shown). In this case a portion ofthe carrier on the side ofthe cutting element 52 remote from its cutting edge is formed with a concavely curved surface 55 an imaginary extension of which, as indicated in dotted lines at 56, is spaced forwardly ofthe cutting element 52. In this case a jet 57 of drilling fluid is directed downwardly by the curved surface 55 so as to impinge on chips 58 of formation being raised from the surface of the borehole by the cutting element 52 and breaks the chips away from the cutting element and from the surface of the formation as a result of the hydraulic pressure.

Figure 8 shows a modified arrangement where the hydraulic effect of Figure 7 is combined with the mechanical effect of Figures 1-3. In this case the edge 59 of the concavely curved surface 55 is located forwardly of the front surface of the cutting element 52 so that the chips of formation 58 impinge on the undersurface 60 and are thus mechanically broken up in addition to the braking up effect of the jet 57 of drilling fluid.

In the arrangements of Figures 7 and 8, a PDC element may be set into the surface 55 to resist erosion of the surface by the jet of drilling fluid.

In any ofthe arrangements in accordance with the present invention, the interface between the facing table and substrate of the cutting element may be non-planar and configured, instead of being substantially flat, so as to improve the bond between the facing table and substrate and also to provide other advantages, as is well known in the art. Alternatively or in addition, there may be provided between the facing table and the substrate a transition layer which may, for example, have certain characteristics, such as hardness, which are intermediate the corresponding characteristics of the facing table and substrate.

The arrangements described above, and shown in the drawings, are also described and illustrated in British Patent Application No. 9721408.4, the claims of which differ in scope from the claims of the present application.

Claims

CLAIMS 1. A cutting structure for a rotary drag-type drill bit including a preform cutting element mounted on a member on the drill bit and comprising a front facing table of superhard material bonded to a less hard substrate, wherein a portion of the member on which the preform cutting element is mounted is shaped, adjacent the cutting element, to direct to a location in front of the cutting element, with respect to the normal direction of forward movement of the cutting element in use, a flow of drilling fluid which impinges on said surface.
2. A cutting structure according to Claim 1, wherein the shaped member on which the preform element is mounted comprises a carrier which is, in use, mounted on the bit body.
3. A cutting structure according to Claim 1, wherein the shaped member on which the preform element is mounted comprises a part of the bit body itself.
4. A cutting structure according to any of Claims 1 to 3, wherein said shaped surface is formed on a portion of said member which overhangs the front surface of the facing table of the cutting element.
5. A cutting structure according to Claim 4, wherein said shaped surface has an edge adjacent the cutting element, and an imaginary extension of the surface beyond said edge is spaced forwardly of the cutting element.
6. A cutting structure according to any of Claims 1 to 5, wherein the shaped surface is smoothly and concavely curved as it extends towards the cutting element.
7. A cutting structure according to any of Claims 1 to 6, wherein the shaped surface is hard faced.
8. A cutting structure according to any of Claims 1 to 6, wherein the shaped surface includes a portion faced with superhard material.
9. A cutting structure according to Claim 8, wherein a further preform compact, comprising a front facing table of superhard material bonded to a less hard substrate, is mounted on the member so that the front face of the superhard material forms part of said shaped surface on the member.
10. A cutting structure for a rotary drag-type drill bit, substantially as hereinbefore described with reference to any of the accompanying drawings.