EP0225082A2

EP0225082A2 - Improvements in or relating to rotary drill bits

Info

Publication number: EP0225082A2
Application number: EP86308791A
Authority: EP
Inventors: John Fuller; Peter John Comber
Original assignee: NL Petroleum Products Ltd
Current assignee: NL Petroleum Products Ltd
Priority date: 1985-11-16
Filing date: 1986-11-12
Publication date: 1987-06-10
Also published as: GB2183693A; GB8627050D0; EP0225082A3; GB8528299D0

Abstract

A rotary drill bit comprises a bit body (10) having a leading face (11) and a gauge region (12), a plurality of blades (13) extending across the leading face (11) of the bit body (10), a plurality of cutting elements (8) mounted along each blade, an exit channel (18) in the gauge region (12) of the bit body (10) between each pair of adjacent blades (13), a plurality of nozzles (19a,19b,19c,19d) in the leading face (11) of the bit, each nozzle having a central axis (20) which also forms the central axis of the jet of drilling fluid emerging from the nozzle, and a passage (6) in the bit body (10) for supplying drilling fluid to said openings (19a-19d). At least one nozzle is located between each pair of adjacent blades (13), and the nozzles are inclined at different angles, or are otherwise differently located, so that, in use, the central axes of nozzles between different pairs of adjacent blades (13) intersect the surface of the formation (21) being drilled at different distances from the axis of rotation of the bit, so that the jets of drilling fluid emerging from the nozzles, between them, sweep over the whole of the surface of the formation as the bit rotates.

Description

The invention relates to rotary drill bits for use in drilling deep holes in subsurface formations.
In particular, the invention relates to drill bits of the kind comprising a bit body having a leading face and a gauge region, a plurality of blades each extending across the leading face of the bit body away from the axis of rotation thereof and towards the gauge region, each blade having an outer surface which, in use, faces the surface of the formation being drilled and a front surface facing in the direction of normal forward rotation of the bit, a plurality of cutting elements mounted along each blade, an exit channel in the gauge region of the bit body between each pair of adjacent blades, and a passage in the bit body for supplying drilling fluid to a plurality of openings in the leading face of the bit.
The aforesaid openings for drilling fluid are located on the bit body between adjacent blades and are so located as to promote a flow of drilling fluid across the front surfaces of the blades and the cutting elements mounted thereon. The flow of drilling fluid cleans and cools the cutters and carries cuttings outwardly and upwardly through the exit channels in the gauge region.
Drill bits of the above-mentioned kind are normally substantially symmetrical and, conventionally, the openings are normally arranged in substantially the same manner in each of the areas of the bit between two adjacent blades. This is because it has been considered desirable for the flow over the front surface of each blade to be substantially the same to provide optimum cleaning and cooling of the cutters on the blade.
However, the present invention depends on the realisation that, contrary to what has previously been believed in relation to bits of this type, the impingement of the jet of drilling fluid on the surface of the formation itself plays an important part in the effective operation of the bit. It has previously been considered that the required cooling and cleaning objectives would be met by the emergence of the jet of drilling fluid from the openings causing a general area of turbulent flow within the whole space between adjacent blades. The present invention, however, depends on the realisation that the direct impingement of a high velocity turbulent jet of drilling fluid on the surface of the formation itself performs a highly important function. The impingement of the jet on the formation at high velocity, particularly in a region on the front side of an advancing blade, causes effective cooling of the formation and this leads to less heating of the cutters which then act on the formation. This is believed to be more effective than the conventional method whereby the primary cooling purpose of the drilling fluid is to cool the cutters themselves.
Furthermore, the impingement of the high velocity turbulent jets on the formation serves to lift cuttings created by the cutters and separate them from the surface of the formation so that they become entrained in the flow of drilling fluid. In conventional arrangements there may be a tendency, particularly in soft and sticky formations, for cuttings to be held down on the surface of the formation and even to be re-compacted into the surface or into balls of material which may eventually clog the cutters.
In order to maintain a high velocity turbulent cohesive jet impinging on the surface of the formation it has been found to be desirable to provide only a single large opening for drilling fluid in the area between adjacent blades. One of the reasons for this is that if a greater number of openings is provided they require to be of smaller diameter to maintain the same overall flow rate and this leads to the risk of the openings becoming blocked. However, the present invention may also be applicable to arrangements where more than one opening is provided between two adjacent blades.
The present invention sets out to provide a construction of drill bit which takes advantage of the above-mentioned advantageous effects of jet impingement on the formation.
According to the invention there is provided a drill bit comprising a bit body having a leading face and a gauge region, a plurality of blades each extending across the leading face of the bit body away from the axis of rotation thereof and towards the gauge region, the number of blades being from two to four inclusive, each blade having an outer surface which, in use, faces the surface of the formation being drilled and a front surface facing in the direction of normal forward rotation of the bit, a plurality of cutting elements mounted along each blade, an exit channel in the gauge region of the bit body between each pair of adjacent blades, a plurality of openings in the leading face of the bit, each opening having a central axis which also forms the central axis of the jet of drilling fluid emerging therefrom, at least one opening being located between each pair of adjacent blades, and a passage in the bit body for supplying drilling fluid to said openings, said openings being so located that, in use, the central axes of openings between different pairs of adjacent blades intersect the surface of the formation being drilled at different distances from the axis of rotation of the bit.
In use of the drill bit a jet of fluid emerges at high velocity from each opening and impinges on the formation in front of a portion of the associated advancing blade. The length of the portion of the blade affected by the jet is determined by the spread of the jet after leaving the opening. The different dispositions of the openings means that each jet sweeps a different annular area of the surface of the formation as the bit rotates, and preferably the dispositions of the openings are such that the jets from the openings between them sweep substantially the whole area of the surface of the formation between the axis of rotation of the bit and the gauge region.
There may be provided only a single opening for drilling fluid between each pair of adjacent blades.
In a preferred embodiment the central axes of the openings between different pairs of adjacent blades are inclined at different angles to the axis of rotation of the bit.
Preferably the central axis of each opening for drilling fluid is substantially parallel to the front surface of the adjacent blade. Preferably also the angular orientation of each opening is such that the central axis thereof is substantially at right angles to the surface of the formation opposite the opening (i.e. is less than 30° and preferably less than 15° to the normal) so that the jet of drilling fluid impinges substantially normally on to the surface of the formation.
In any of the above arrangements each said opening may be provided in a nozzle which is separately formed from the bit body and is mounted therein. For example, the nozzle may be removably secured within a socket in the bit body.
Desirably the location of each opening is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than five times the diameter of the opening. Preferably, said distance is less than four times the opening diameter and even more preferably less than three times said diameter.
One advantage of a drill bit of the basic kind to which the invention relates, as first referred to above, is that it may be designed to provide a substantial clearance in front of the blades carrying the cutting elements and hence a large flow path for the escape, through the associated exit channel, of cuttings produced by the cutting elements. It is believed that this substantial clearance is one of the reasons for the high penetration rates which drill bits of this kind may achieve in certain types of formation. It is therefore undesirable to achieve the desirable closeness of the openings to the surface of the formation by reducing the clearance between the surface of the bit body and the cutting elements on the forward side of each blade. Preferably, therefore, the required optimum distance of the openings from the surface of the formation is achieved by providing each opening at the extremity of a structure which projects from the main surface of the bit body on the forward side of each blade so as to bring the opening nearer the formation. For example, the surface of the bit body may be formed with a projecting boss the opening being formed in the outer extremity thereof. In the case where the opening is formed in a separate nozzle, the nozzle may be an extended nozzle one end of which projects from the surface of the bit body and is formed with the opening and the opposite end of which is secured in a socket in the bit body. In the latter case the extended nozzle is preferably formed from an erosion resistant material such as tungsten carbide.
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 part section, part side elevation of the body of a drill bit in accordance with the invention,
Figure 2 is an end view of the bit body shown in Figure 1,
Figures 3 to 6 are half sections through the bit body showing the location and orientation of the nozzles for drilling fluid,
Figure 7 is a longitudinal section through an alternative form of drill bit,
Figure 8 is an end view of the drill bit of Figure 7,
Figure 9 is an end view of a further form of drill bit, and
Figure 10 is a half section through a still further form of drill bit, showing an extend nozzle.

Referring to Figures 1 to 6, there is shown the main bit body 10 of a rotary drill bit for use in drilling deep holes in subsurface formations. The bit body 10 may be formed from steel and has a leading face 11 and a gauge region 12.
The leading face 11 of the bit body is integrally formed with blades 13. As best seen in Figure 2, there are provided four such blades spaced substantially equally around the central axis of rotation of the bit. Each blade has an outer surface 14 which, in use of the bit, faces the surface of the formation being drilled, and a front surface 15 facing in the direction of normal forward rotation of the bit. A plurality of cutting elements 8 are mounted on each blade 13 along the junction between the outer surface 14 and the front surface 15. Each cutting element is in the form of a circular preform comprising a front hard facing layer of polycrystalline diamond or other superhard material bonded to a less hard backing layer, such as tungsten carbide. Each cutting element is bonded to a post 7, for example of tungsten carbide, received in a socket in the blade 13. The construction of such cutting elements is well known and will not be described in detail. The rear surface of each blade 13 is chamfered as indicated at 9.
In known manner the gauge region 12 of the bit is formed with abrasion elements 16 which may, for example, comprise tungsten carbide studs impregnated with natural diamond particles and received in sockets in the gauge portion.
The gauge portion comprises four axially extending kickers or wear pads 17 in which the abrasion elements are mounted, exit channels 18 being disposed between the kickers 17.
On the forward side of each blade 13 a nozzle is mounted in a socket in the bit body, the four nozzles being indicated at 19a, 19c, 19b, and 19d respectively. Each nozzle communicates through a passage with a central passage 6 in the bit body. In known manner, drilling fluid supplied under pressure through the central passage 6 emerges from the nozzles 19a - 19d for the purpose of cleaning and cooling the cutting elements as well as cooling the formation.
Figures 3 to 6 are half-sections of the bit body through each of the four nozzles 19a - 19d and showing the preferred position and orientation of each nozzle. The central axis of each nozzle is indicated at 20. The axis 20 also represents the central axis of the jet of drilling fluid which emerges under high pressure from the nozzle. In Figures 3 to 6 the surface of the formation being drilled by the drill bit is indicated diagrammatically at 21.
The central axis of each nozzle lies in a plane which is substantially parallel to the front surface 15 of the associated blade. It will be seen from Figures 3 to 6 that the central axes of the four nozzles are inclined at different angles to the central axis of rotation 22 of the bit and the effect of this angular orientation, together with the location of the nozzles, is that the jet of drilling fluid from each nozzle impinges on a different portion of the surface 21, the portion of the surface on which the jet impinges in each case being indicated at 23. Due to radially outward dispersion of the jets, which increases with distance from the nozzle opening, the diameter of the area of influence of each jet is greater than the diameter of the nozzle opening, and the orientation of the nozzles is such that the four areas 23 of the formation on which the jets impinge between them cover substantially the whole of the formation from the gauge region to a position close to the central axis 22 of the drill bit. The effect of this is that the four jets between them will, as the bit rotates, sweep out a total area extending over substantially the whole of the formation at the bottom of the hole. This means that substantially all the surface of the formation is subjected to direct impingement by a high pressure turbulent jet of drilling fluid with all the advantages this gives, as previously referred to. These advantages are in addition to the normal cooling and cleaning effects which would be provided by any nozzle delivering high pressure drilling fluid to the face of the drill bit regardless of the orientation of the nozzle.
Preferably the central axis of each nozzle is arranged as nearly as possible at right angles to the surface of the formation. It will be seen that in the case of the nozzles shown in Figure 5 the central axis is very close to being at right angles to the surface of the formation whereas, due to limitations imposed by the structure of the bit body, in the case of the nozzles shown in Figures 3, 4 and 6 the central axis is at a greater angle to the normal. Desirably the angle to the normal is not more than 30° and preferably is less than 15°.
In order to obtain the optimum effect of the impingement of the jet on the surface of the formation, it is desirable that the distance of the opening in each nozzle from the formation should not be greater than five times the diameter of the opening, preferably not more than four times the diameter, and more preferably not more than three times the diameter. If the nozzle is received in a socket in the bit body, as shown in Figures 3 to 6, the location of the surface 24 of the bit body in relation to the formation 21 will be determined by the required position of the nozzle. In other words, if it were wished to move the nozzles 19 closer to the formation 21 it would be necessary to bring the surface 24 closer to the formation to accommodate the nozzles. However, as previously mentioned, the location of the surface 24 determines the clearance on the front side of each blade carrying the cutting elements, and the large amount of clearance provided in the drill bit of this general type is believed to be one of the important contributing factors to the effectiveness of the bit. It may therefore be undesirable to reduce this clearance. Accordingly, the nozzles may be brought closer to the formation without reducing the overall clearance by locating each nozzle in a boss which is integral with the surface 24 of the bit body but which projects towards the formation. Alternatively, as shown in Figure 10, each nozzle may be in the form of an extended element 25 one end of which is secured within the socket in the surface 24 of the bit body and the other end of which projects away from the surface 24 towards the surface of the formation. Such projecting portion of the extended nozzle is preferably formed from tungsten carbide or similar erosion-resistant material.
In the alternative arrangement shown in Figures 7 and 8 the leading face 111 of the bit body is again integrally formed with four blades 113 in generally similar fashion to the arrangement of Figures 1 and 2. In this case, however, there is spaced rearwardly of certain of the cutting elements 108, with respect to the normal direction of forward rotation of the bit, an abrasion element 126 which may, for example, comprise a tungsten carbide stud impregnated with natural diamond particles and received in a socket in the blade.
On the forward side of each blade 113 a nozzle is mounted in a socket in the bit body, four nozzles being indicated at 119a, 119b, 119c and 119d respectively. As in the previously described arrangement, the central axes of these four nozzles are inclined at different angles to the central axis of rotation of the bit so that the jet of drilling fluid from each nozzle impinges on a different portion of the surface of the formation. In the arrangement of Figures 7 and 8, however, there is provided a further, fifth nozzle 127 which is located on the forward side of the same blade as the nozzle 119c but is located close to the central axis of the bit and is directed in a direction generally parallel to that axis. The object of the further nozzle 127 is to provide more effective cleaning and cooling of the cutting elements, and cooling of the formation, in the vicinity of the central axis of the bit.
The invention is applicable to drill bits having two, three or four blades, and Figure 9 shows an arrangement where the leading face of the bit body is integrally formed with only three blades 213 spaced equally around the central axis of rotation of the bit. Each blade has an outer surface 214 which faces the surface of the formation being drilled, and a front surface 215 facing in the direction of normal forward rotation of the bit. A plurality of cutting elements 208 are mounted along each blade 213, each cutting element being in the form of a circular polycrystalline diamond preform.
As in the previously described arrangements, on the forward side of each blade 213 a nozzle is mounted in a socket in the bit body, the three nozzles being indicated at 219a, 219b and 219c respectively. The central axes of the three nozzles are inclined at different angles to the central axis of rotation of the bit so that the jets of drilling fluid from the nozzles impinge on different portions of the surface of the formation being drilled.

Claims

1. A drill bit comprising a bit body (10) having a leading face (11) and a gauge region (12), a plurality of blades (13) each extending across the leading face of the bit body away from the axis of rotation thereof and towards the gauge region (12), the number of blades (13) being from two to four inclusive, each blade having an outer surface (14) which, in use, faces the surface of the formation being drilled and a front surface (15) facing in the direction of normal forward rotation of the bit, a plurality of cutting elements (8) mounted along each blade (13), an exit channel (18) in the gauge region (12) of the bit body (10) between each pair of adjacent blades (13), a plurality of openings (19a-19d) in the leading face (11) of the bit, each opening having a central axis (20) which also forms the central axis of the jet of drilling fluid emerging therefrom, at least one opening being located between each pair of adjacent blades (13), and a passage (6) in the bit body for supplying drilling fluid to said openings, characterised in that said openings (19a-19d) are so located that, in use, the central axes of openings between different pairs of adjacent blades (13) intersect the surface of the formation being drilled at different distances from the axis of rotation of the bit.

2. A drill bit according to Claim 1, characterised in that there is provided only a single opening for drilling fluid between each pair of adjacent blades (13).

3. A drill bit according to Claim 1 or Claim 2, characterised in that the central axes (20) of the openings (19a-19d) between different pairs of adjacent blades (13) are inclined at different angles to the axis of rotation of the bit.

4. A drill bit according to any of Claims 1 to 3, characterised in that the central axis (20) of each opening for drilling fluid is substantially parallel to the front surface (15) of the adjacent blade.

5. A drill bit according to any of Claims 1 to 4, characterised in that the angular orientation of each opening is such that the central axis (20) thereof is substantially at right angles to the surface (21) of the formation opposite the opening (i.e. is less than 30° and preferably less than 15° to the normal) so that the jet of drilling fluid impinges substantially normally on to the surface of the formation.

6. A drill bit according to any of Claims 1 to 5, characterised in that each said opening (19a-19d) is provided in a nozzle which is separately formed from the bit body (10) and is mounted therein.

7. A drill bit according to Claim 6, characterised in that the nozzle is removably secured within a socket in the bit body (10).

8. A drill bit according to any of Claims 1 to 7, characterised in that the location of each opening (19a-19d) is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than five times the diameter of the opening.

9. A drill bit according to Claim 8, characterised in that the location of each opening (19a-19d) is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than four times the diameter of the opening.

10. A drill bit according to Claim 8, characterised in that the location of each opening (19a-19d) is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than three times the diameter of the opening.

11. A drill bit according to any of Claims 8 to 10, characterised in that each opening (19a-19d) is provided at the extremity of a structure (25) which projects from the main surface of the bit body (10) on the forward side of each blade (13) so as to bring the opening nearer the formation.

12. A drill bit according to Claim 11, characterised in that each opening (19a-19d) is formed in a separate nozzle, and the nozzle is an extended nozzle (25) one end of which projects from the surface of the bit body (10) and is formed with the opening and the opposite end of which is secured in a socket in the bit body (10).

13. A drill bit according to Claim 12, characterised in that the extended nozzle (25) is formed from an erosion resistant material.

14. A drill bit comprising a bit body (10) having a leading face (11) and a gauge region (12), a plurality of blades (13) each extending across the leading face of the bit body (10) away from the axis of rotation thereof and towards the gauge region (12), the number of blades (13) being from two to four inclusive, each blade having an outer surface (14) which, in use, faces the surface of the formation being drilled and a front surface (15) facing in the direction of normal forward rotation of the bit, a plurality of cutting elements (8) mounted along each blade, an exit channel (18) in the gauge region (12) of the bit body (10) between each pair of adjacent blades (13), a plurality of openings (19a-19d) in the leading face (11) of the bit, at least one opening being located between each pair of adjacent blades (13), and a passage (6) in the bit body (10) for supplying drilling fluid to said openings (19a-19d), characterised in that the location of each opening is such that its distance from the point where the jet of drilling fluid from that opening impinges on the formation (21) is less than five times the diameter of the opening.

15. A drill bit according to Claim 14, characterised in that the location of each opening is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than four times the diameter of the opening.

16. A drill bit according to Claim 14, characterised in that the location of each opening is such that its distance from the point where the jet of drilling fluid impinges on the formation is less than three times the diameter of the opening.

17. A drill bit according to any of Claims 14 to 16, characterised in that each opening is provided at the extremity of a structure (25) which projects from the main surface of the bit body (10) on the forward side of each blade so as to bring the opening nearer the formation.

18. A drill bit according to Claim 17, characterised in that each opening is formed in a separate nozzle, and the nozzle is an extended nozzle (25) one end of which projects from the surface of the bit body (10) and is formed with the opening and the opposite end of which is secured in a socket in the bit body (10).

19. A drill bit according to Claim 18, characterised in that the extended nozzle (25) is formed from an erosion resistant material.