EP0291314A2

EP0291314A2 - Cutting structure and rotary drill bit comprising such a structure

Info

Publication number: EP0291314A2
Application number: EP88304325A
Authority: EP
Inventors: John Denzil Barr; Malcolm Roy Taylor; Terry Richard Matthias; Michael Thomas Wardley; Michael Colin Regan
Original assignee: Reed Tool Co Ltd
Current assignee: Camco Drilling Group Ltd
Priority date: 1987-05-13
Filing date: 1988-05-12
Publication date: 1988-11-17
Also published as: EP0291314A3; GB8811390D0; GB8711255D0; GB2204625A

Abstract

A cutting structure, for use in a rotary drill bit for drilling or coring holes in subsurface formations, comprises an elongate stud 17 of hard material, such as cemented tungsten carbide, there being at least partly embedded in the stud, at one end thereof, one or more thermally stable polycrystalline diamond cutting elements 14, 15, 16. The diamond elements, which may be in the form of small rectangular blocks or cylinders, are bonded into the stud by a hot pressing or an infiltration process.

Description

The invention relates to rotary drill bits for use in drilling or coring deep holes in subsurface formations, and in particular relates to cutting structures for use in such drill bits.
Rotary drill bits of the kind to which the present invention is applicable comprise a bit body having a shank for connection to a drill string and an inner passage for supplying drilling fluid to the face of the bit. The bit body carries a plurality of cutters or cutting structures. The cutters may be so-called "preform" cutters one common form of which comprises a tablet, usually circular, made up of a hard facing layer of polycrystalline diamond and a backing layer of cemented tungsten carbide.
Usually, the bit body is machined from solid metal, usually steel, or is moulded using a powder metallurgy process in which tungsten carbide powder is infiltrated with metal alloy binder in a furnace so as to form a hard matrix. The maximum furnace temperature required to form the matrix may be of the order of 1100°C to 1170°C. Conventional two-layer preform cutters of the kind referred to above are not thermally stable at such temperatures and for this reason they normally require to be mounted on the bit body after it has been formed, and this may be a time-consuming and costly process. There are, however, available polycrystalline diamond cutter elements which are thermally stable at the infiltration temperature of matrix body bits. For example, such thermally stable cutter elements have been manufactured and sold by the General Electric Company under the trade mark "GEOSET" and by de Beers under the trade mark "SYNDAX 3". Reference in this specification to "thermally stable" cutting elements means elements which are thermally stable at the normal infiltration temperatures of matrix body bits.
One advantage of such thermally stable cutting elements is that they may be simply mounted on a matrix bit body by locating the cutters in the mould in which the matrix is formed so that they become partly embedded in the matrix as a result of the forming process.
Initially, it was the practice to use such thermally stable cutting elements in rotary drill bits in somewhat similar manner to that previously employed for natural diamonds. That is to say, the elements were so located in the mould that most of each cutting element became embedded in the matrix bit body with only a very small part of each element, if any, projecting from the surface of the bit body. The thermally stable elements were normally small in comparison to two-layer preform elements and a typical "GEOSET" element, for example, might be in the shape of an equilateral prismatic triangle having a side length of about 4mm and a depth of about 2.5mm. Other typical elements were cubic having a side length of from 2.5mm to 5mm.
It has been found, however, that problems can arise with such arrangements due to the small exposure of the thermally stable cutting elements. In view of the small exposure the clearance between the surface of the bit body and the surface of the formation being cut will also be small with the result that the available space for cooling and cleaning fluid to pass over the surface of the bit body is restricted. This can result in poor chip clearance from the face of the bit, and also poor cooling. It is therefore desirable to increase the amount of clearance between the surface of the bit body and the formation when using thermally stable cutting elements.
One solution offered to this problem has been to locate each thermally stable element so that a major portion thereof projects beyond the surface of the bit body, the projecting portion of each element being supported by some form of local projection of the matrix material of the bit body beyond the general level of the surface of the bit body. Such arrangements are described in U.S. Patents Nos. 4,529,047, 4,491,188 and 4,499,959.
Such arrangements, however, suffer from the disadvantage that the mounting of the cutting element to the bit body is necessarily weakened, when compared with the more deeply embedded arrangements, with the result that cutting elements may become detached and lost in use before they are extensively worn. Also, the extent of increased clearance which such arrangements can provide is still limited by the dimensions of the thermally stable cutting elements themselves.
The present invention sets out to provide alternative methods for mounting thermally stable cutting elements on a bit body with increased clearance while at the same time maintaining strong attachment of the cutting elements.
According to the invention there is provided a rotary drill bit comprising a bit body having a shank for connection to a drill string, an inner passage for supplying drilling fluid to the face of the bit, and a plurality of cutting structures mounted on the bit body, at least one of said cutting structures comprising an elongate stud of hard material, one end of which stud is secured to the bit body and the opposite end of which projects from the bit body and has at least partly embedded therein at least one thermally stable polycrystalline diamond element.
The invention also includes within its scope a cutting structure, for use in a rotary drill bit of the kind referred to, comprising an elongate stud of hard material, there being at least partly embedded in the stud, at one end thereof, at least one thermally stable polycrystalline diamond element.
In arrangements according to the invention the thermally stable cutting elements are firmly held by embedding them in any desired manner in the ends of the studs, but at the same time the clearance between the formation and the main surface of the bit body is determined by the extent to which each stud projects from the bit body and not by the dimensions of the cutting elements themselves. The clearance may thus be selected to provide the required cooling and chip clearance.
The end of the stud which is secured to the bit body may be embedded in the bit body itself, or may be embedded in an extension thereof, or may be received and retained in a preformed socket in the bit body or an extension thereof.
Said extension of the bit body may comprise a blade upstanding from the main surface of the bit body and integral therewith or bonded thereto.
The invention is applicable to drill bits where the bit body is machined from steel or other metal, as well as to bits where the bit body is moulded using a powder metallurgy process of the kind described above. In the case of a steel body, sockets will usually be machined in the body to receive the studs which may be retained by brazing and/or shrink fitting or by any other suitable method. In the case of matrix bodied bits formed by a powder metallurgy process, the bit body may be preformed with sockets into which the studs of the cutting structures are subsequently mounted. However, since the cutting elements themselves are thermally stable at the temperatures involved the cutting structures, comprising the cutting elements and the studs into which the cutting elements are embedded, may be located in the mould so as to become embedded in the matrix in the course of the infiltration process.
The stud may be of any suitable hard material. For example, it may comprise refractory particles, such as cemented tungsten carbide, bonded by a metal, e.g. cobalt. The bonding may be performed by hot pressing or by infiltration. In the case of hot pressing the thermally stable cutting elements must be of such a kind that they will withstand the temperatures to which they will be subjected during the hot pressing process. Since this temperature is greater than the infiltration temperature normally used in the formation of matrix bodied bits, not all cutting elements generally referred to as thermally stable may be suitable for embedding in a cemented tungsten carbide stud. One suitable type of cutting element is that sold by de Beers under the trade name "SYNDAX 3". Cutting elements which are thermally stable at lower temperatures may be embedded in studs of matrix material similar to the material used for the bit body itself.
Each stud may project freely from the surface of the bit body, but the invention includes within its scope arrangements where the projecting portion of the stud is engaged and partly supported by a local raised portion of the bit body. For example, both in the case of a steel bodied bit and a matrix bodied bit, an extension of the bit body itself may engage and support the rearward surface of the stud with respect to the normal direction of travel of the cutting structure in use of the bit. For example, the bit body may be formed in conventional manner with a number of upstanding blades extending outwardly from the axis of rotation of the bit, the projecting portions of the studs being partly supported by the material of the bit body forming said blades.
The following is a more detailed description of embodiments of the invention, reference being made to the accompanying drawings in which:

Figure 1 is a side elevation of a cutting structure in accordance with the invention,
Figure 2 is an end elevation of the cutting structure of Figure 1,
Figure 3 is a scrap view in the direction of arrow A of Figure 1,
Figures 4 to 21 are diagrammatic sections through further forms of cutting structure according to the invention,
Figures 22 and 23 are a side view and end view respectively of a still further form of cutting structure, and
Figure 24 is a vertical section through a drill bit according to the invention.

Referring to Figures 1 to 3: the cutting structure comprises a generally cylindrical circular cross-section stud 10 of cemented tungsten carbide hot pressed with cobalt. At one end, to be received in a socket in a bit body, the stud has a chamfered portion 11 and at the opposite end, which in use projects from the bit body, is formed with an end portion 12 of slightly reduced diameter. The end portion 12 has a curved upper surface 13 the generators of which are inclined to the axis of the stud as best seen in Figure 1.
Embedded in the upper part 12 of the stud are three cutting elements 14, 15 and 16 of thermally stable polycrystalline diamond material such as "SYNDAX 3". Each cutting element is in the form of a cube of side length 3mm. As best seen from Figures 2 and 3, one of the cutting elements 14 is located adjacent the upper curved surface of the stud part 12 where said surface forms an acute angle with the wall of the stud. This forms the leading part of the cutting structure with respect to the normal direction of movement of the structure during use.
The other two cutting elements 15 and 16 are disposed rearwardly of the leading cutting element 14 with respect to the normal direction of movement and are spaced apart laterally thereof.
The cutting structure may be received in a preformed socket in the surface of a matrix bodied or steel bodied bit. The stud may be shrink fitted and/or brazed within the socket and the surface of the stud is formed with an axially extending groove 17.
Alternatively, the cutting structure may be prelocated in a mould within which a matrix bodied bit is to be formed by infiltration, so as to be moulded into the bit body during its formation.
Figure 4 shows an alternative form of cutting structure where the stud 18 has one end received in the bit body 19 and the end thereof projecting from the bit body has cutting elements 20 embedded therein. In this case, the bit body, which may be formed from steel or from matrix, is formed with an upstanding blade 21 which provides additional support for the projecting portion of the stud 18.
In the embodiment of Figure 5, the blade 22 projects from the main surface of the bit body 23 to the full extent of the projection of the stud 24 so as to provide back support for the stud. In this case the forwardly facing projecting surface of the stud is curved as indicated at 25 and the thermally stable elements 26 are disposed around the curve.
In the arrangement of Figure 6 the elongate stud 27 is received in a socket which is inclined rearwardly with respect to the normal forward direction of travel of the cutting structure, the socket being formed in a blade 28 which projects from the general surface of the bit body.
Figure 7 shows an arrangement where a leading cutting structure 29 has spaced rearwardly thereof, with respect to the width of a blade 30, a second cutting structure 31, the projecting portion of each cutting structure having partly embedded therein a thermally stable cutting element as indicated at 32 and 33 respectively.
In the arrangement of Figure 8 the configuration is somewhat similar to that of Figure 7 but in this case the rearward cutting structure 34 is of a different shape and is impregnated with small natural diamonds 35 rearwardly of the thermally stable polycrystalline diamond cutting element 36. It is believed that the presence of natural diamonds embedded in the stud may prevent thermal cracking of the material of the stud. Natural diamonds may be embedded in the stud also in any of the other embodiments of the invention described.
In the embodiment of Figure 9, the cutting structure 37 in accordance with the present invention is disposed rearwardly of a conventional cutting structure of the kind comprising a two-layer polycrystalline diamond compact 38, for example of the conventional circular tablet form, bonded to an inclined surface on a stud 39. The cutting structure 37 according to the invention provides a back-up to the more conventional cutting structure since it is less liable to failure in use particularly when cutting harder formations. It is known to provide back-up for conventional two-layer cutters by means of studs impregnated with small natural diamonds, but the arrangement shown in Figure 9 has the advantage that the cutting structure according to the invention provides better cutting than such natural diamond impregnated studs. In this arrangement the cutting structure according to the invention may project from the surface of the bit body to substantially the same extent as the conventional cutter structure, as shown in Figure 9. Alternatively, however, it may project from the surface of the bit body to a greater or lesser extent. It will be appreciated that the cutting structure which projects from the bit body to the greater extent will normally provide the cutting action, whereas the cutting structure which projects to a lesser extent will only come into operation should the other cutting structure fail or wear or dig into the formation to such extent as to bring the other cutting structure into contact with the formation.
In the case of a steel bodied bit it may be desirable to provide a hard facing layer to protect the bit body from erosion in use. Figures 10 and 11 show such arrangements. In the arrangement of Figure 10 the hard facing layer 40 completely covers the stud 41 and thermally stable cutting element 42 whereas in the arrangement of Figure 11 the outer extremity of the stud 43, carrying the cutting element 44, projects clear of the hard facing layer 45. Since the cutting elements are thermally stable, this allows the cutting structures to be secured to the bit body before the hard facing is applied.
Figure 12 shows an arrangement where thermally stable cutting elements 46 and 47 are so located in the stud 48 as to be spaced apart one behind the other in the direction of movement of the cutting structure during drilling. The rearward cutting element 47 thus acts as a back-up for the forward cutting element 46. Figure 13 shows a modified arrangement where the forward cutting element 49 is located at a greater distance from the surface of the bit body 50 than the rearward cutting element 51, the stud 52 being stepped at its outer extremity. This arrangement has a similar effect to that shown in Figure 9 in that the rearward back-up cutting element only comes into operation under certain conditions.
In the arrangement shown in Figure 14 the cutting elements 53 embedded in the outer end of the stud 54 are disposed at different distances from the surface of the bit body 55. Such an arrangement increases the life of the cutting structure since as each outer cutting element wears away or fails, cutting is taken over by the next inward cutting element.
Cutting elements may be distributed in any manner throughout the projecting end of the stud and Figure 15 shows an arrangement where cutting elements 56 are dispersed throughout the outer part of the stud 57 and are spaced apart both in the direction of normal forward movement of the cutting structure and in a direction axially of the stud.
Figures 16 to 20 show diagrammatically other possible configurations of stud 58 and thermally stable cutting elements 59. The studs are shown as viewed in the direction of normal travel of the cutting structure during drilling. In the arrangement of Figure 20 the central cutting element 59 may be displaced rearwardly with respect to the two outer cutting elements. In operation, the two outer cutting elements then form spaced parallel cuts in the formation and the following central cutting element removes the strip of formation between the cuts. This is believed to be a particularly effective manner of cutting.
Rotary drill bits which employ polycrystalline diamond cutting elements often also employ abrasion elements comprising small natural diamonds embedded in a cylindrical stud of cemented tungsten carbide. The studs are located in sockets in the bit body and at least the outer portion of the stud has natural diamonds embedded in it. Such abrasion elements are often located in the gauge portion of the drill bit, but they may also be used on the face of the bit, for example as a back-up to the polycrystalline diamond cutters.
Such abrasion elements have the disadvantage that as the tungsten carbide wears away in use a situation is reached, for each embedded diamond particle and before the diamond itself has completely worn away, where the carbide surrounding the particle is no longer sufficient to hold it in place and the diamond particle becomes detached from the stud, leaving a small recess. This impairs the effectiveness of the abrasion element. Figure 21 shows a cutting structure in accordance with the present invention which may be used instead of abrasion elements using natural diamonds, and which may suffer to a lesser extent from the disadvantage just described.
Referring to Figure 21, at least the outer end of a cemented tungsten carbide stud 60 is impregnated with thermally stable polycrystalline diamond elements 61, each element being in the form of a small rod or cylinder, for example about ½mm in diameter and 1 to 2mm in length. The rods are randomly orientated within the tungsten carbide and, due to their shape, a large proportion of the rods are unlikely to become detached from the tungsten carbide until they have been substantially entirely worn away in use. It will be appreciated that the more nearly parallel a rod is to the longitudinal axis of the stud, the longer it will remain attached to the stud as the stud wears. Such an abrasion element may be used in any of the situations where natural diamond impregnated studs are normally used.
Figures 22 and 23 illustrate a further form of cutting structure in accordance with the invention. In this case the outer end of a cemented tungsten carbide stud 62 is formed with a frusto conical portion 63 and the thermally stable polycrystalline diamond element 64 comprises a generally circular section cylinder embedded in the stud coaxially therewith. The side edges of the outer end face of the element 64 are chamfered as indicated at 65 and 66.
In some of the above-described embodiments the thermally stable cutting elements are totally embedded in the studs, or have only their face remote from the bit body surface exposed, as shown for example in Figure 4. Such arrangements have the advantage that the elements are then held very securely, but the cutting efficiency of the elements may be reduced. Where cutting efficiency is more important than element retention, therefore, it may be preferred to embed the elements so that more of each element is exposed, particularly in the direction of cut, such as in the embodiment of Figure 6 where each element has its leading face exposed.
Figure 24 shows in section a typical full bore drill bit of the kind to which cutting structures of the present invention are applicable.
The bit body 70 may be formed of tungsten carbide matrix infiltrated with a binder alloy, or may be machined from metal, usually steel. The bit body has a threaded shank 71 at one end for connection to the drill string.
The operative end face 72 of the bit body is formed with a number of blades 73 radiating from the central area of the bit and the blades carry cutting structures 74 and 75 spaced apart along the length thereof.
The bit has a gauge section 76 including kickers which contact the walls of the borehole to stabilise the bit in the borehole. The gauge section 76 of the bit carries gauge cutters 76a of conventional form. A central channel 77 in the bit body and shank delivers drilling fluid through nozzles 78 in the end face 72, in known manner.
It will be appreciated that this is only one example of the many possible variations of the type of bit to which the invention is applicable.
The inner cutting structures 74 are of conventional form and each comprise a circular preform cutting element mounted on a stud located in a socket in the bit body. Each cutting element may comprise a thin facing layer of polycrystalline diamond bonded to a backing layer of tungsten carbide, the rear surface of the backing layer being bonded, for example by brazing, to a suitably orientated surface on the stud. Alternatively, each preform may comprise a circular unitary tablet of thermally stable polycrystalline diamond material bonded to the stud.
The outer cutting structures 75, in the example shown, are in accordance with Figures 1-3 described above. It will be appreciated, however, that cutting structures of any form in accordance with the present invention may be located in any suitable disposition on the bit body.

Claims

1. A cutting structure, for use in a rotary drill bit for drilling or coring holes in subsurface formations, comprising an elongate stud of hard material, there being at least partly embedded in the stud, at one end thereof, at least one thermally stable polycrystalline diamond element.

2. A cutting structure according to Claim 1, wherein the stud comprises refractory particles, bonded by a metal.

3. A cutting structure according to Claim 2, wherein the stud comprises cemented tungsten carbide bonded with cobalt.

4. A cutting structure according to Claim 2 or Claim 3, wherein the bonding is performed by hot pressing, the thermally stable cutting elements being of such a kind as to withstand the temperatures to which they are subjected during the hot pressing process.

5. A cutting structure according to Claim 2 or Claim 3, wherein the bonding is performed by infiltration.

6. A cutting structure according to any of Claims 1 to 5, wherein each thermally stable polycrystalline diamond element comprises a substantially rectangular block of thermally stable polycrystalline diamond.

7. A cutting structure according to any of Claims 1 to 5, wherein each thermally stable polycrystalline diamond element comprises a circular cross-section cylinder of thermally stable polycrystalline diamond.

8. A cutting structure according to any of Claims 1 to 6, wherein the elongate stud of hard material provides a cutting edge which, in use, faces in the forward direction of travel of the cutting structure, and wherein at least one thermally stable polycrystalline diamond element defines part of the cutting edge of the cutting structure.

9. A cutting structure according to any of Claims 1 to 8, including a plurality of thermally stable polycrystalline diamond elements spaced apart in the normal direction of forward travel of the cutting structure in use.

10. A cutting structure according to any of the preceding claims including a plurality of thermally stable polycrystalline diamond elements spaced apart transversely of the normal direction of forward travel of the cutting structure in use.

11. A cutting structure according to any of the preceding claims including a plurality of thermally stable polycrystalline diamond elements spaced apart longitudinally of the elongate stud.

12. A cutting structure according to any of the preceding claims including a plurality of elongate thermally stable polycrystalline diamond elements randomly orientated within the elongate stud.

13. A cutting structure according to any of Claims 1 to 5, wherein the elongate stud is substantially circular in cross-section and is formed with a frusto conical end surface, there being provided a thermally stable polycrystalline diamond element embedded within the stud and coaxial therewith adjacent the apex plane of the frusto conical surface.

14. A rotary drill bit comprising a bit body having a shank for connection to a drill string, an inner passage for supplying drilling fluid to the face of the bit, and a plurality of cutting structures mounted on the bit body, at least one of said cutting structures comprising an elongate stud of hard material, one end of which stud is secured to the bit body and the opposite end of which projects from the bit body and has at least partly embedded therein at least one thermally stable polycrystalline diamond element.

15. A rotary drill bit according to Claim 14, wherein the end of the stud which is secured to the bit body is embedded in the bit body itself, or in an extension thereof.

16. A rotary drill bit according to Claim 14, wherein the end of the stud which is secured to the bit body is received and retained in a preformed socket in the bit body or an extension thereof.

17. A rotary drill bit according to Claim 15 or Claim 16, wherein said extension of the bit body comprises a blade upstanding from the main surface of the bit body.

18. A rotary drill bit according to any of Claims 14 to 17, wherein the bit body is machined from steel.

19. A rotary drill bit according to any of Claims 14 to 17, wherein the bit body is moulded using a powder metallurgy process.

20. A rotary drill bit according to any of Claims 14 to 19, wherein the stud comprises refractory particles, bonded by a metal.

21. A rotary drill bit according to Claim 20, wherein the stud comprises cemented tungsten carbide bonded with cobalt.

22. A rotary drill bit according to Claim 20 or Claim 21, wherein the bonding is performed by hot pressing, the thermally stable cutting elements being of such a kind as to withstand the temperatures to which they are subjected during the hot pressing process.

23. A rotary drill bit according to Claim 20 or Claim 21, wherein the bonding is performed by infiltration.

24. A rotary drill bit according to any of Claims 14 to 23, wherein the projecting portion of the stud is engaged and partly supported by a local raised portion of the bit body.

25. A rotary drill bit according to Claim 24, wherein the bit body is formed with a number of upstanding blades extending outwardly from the axis of rotation of the bit, the projecting portions of the studs being partly supported by the material of the bit body forming said blades.

26. A rotary drill bit according to any of Claims 14 to 25, wherein the cutting structure has an arcuate face facing in the normal forward direction of travel of the cutting structure in use, and includes a plurality of thermally stable polycrystalline diamond elements disposed along said face in the direction of the length of the stud, the elements being disposed at varying angles to the surface of the bit body by virtue of the curvature of the face of the stud.

27. A rotary drill bit according to any of Claims 14 to 26 wherein the elongate stud is inclined rearwardly with respect to the normal forward direction of travel of the cutting structure in use.

28. A rotary drill bit according to any of Claims 14 to 27, wherein there is mounted in the bit body, rearwardly of the cutting structure with respect to the normal direction of forward travel of the cutting structure, a back-up abrasion element comprising an elongate stud secured to the bit body and having a projecting portion in which are at least partly embedded a plurality of superhard abrasion elements.

29. A rotary drill bit according to Claim 28 where the superhard abrasion elements are selected from natural diamonds and thermally stable polycrystalline diamond elements.

30. A rotary drill bit according to any of Claims 14 to 29, wherein the bit body is formed with a hard facing layer surrounding each cutting structure.

31. A rotary drill bit according to any of Claims 14 to 30, wherein the cutting structure includes a plurality of thermally stable polycrystalline diamond elements spaced apart in the normal direction of forward travel of the cutting structure in use, rearward elements being closer to the surface of the bit body than forward elements.

32. A cutting structure substantially as hereinbefore described with reference to any of Figures 1 to 23 of the accompanying drawings.