GB2183693A

GB2183693A - Improvements in or relating to rotary drill bits

Info

Publication number: GB2183693A
Application number: GB08627050A
Authority: GB
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: EP0225082A2; GB8627050D0; GB8528299D0; EP0225082A3

Abstract

A rotary drill bit comprises a bit body having a leading face 11 and a gauge region,a plurality of blades 13 extending across the leading face of the bit body, a plurality of cutting elements 8 mounted along each blade, an exit channel 18 in the gauge region of the bit body between each pair of adjacent blades, a plurality of nozzles 19a, 19b, 19c, 19d in the leading face of the bit, each nozzle having a central axis which also forms the central axis of the jet of drilling fluid emerging from the nozzle, and a passage in the bit body for supplying drilling fluid to said openings. At least one nozzle is located between each pair of adjacent blades, 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 intersect the surface of the formation 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. <IMAGE>

Description

1 GB 2 183 693 A 1

SPECIFICATION

Improvements in or relating to rotary drill bits The invention relates to rota ry dri 11 bits for use in dril- 70 ling deep holes in subsurface formations.

In particular,the invention relatesto drill bits ofthe kind comprising a bit body having a leading faceand a gauge region, a plurality& blades each extending acrossthe leading face of the bit body awayfromthe axis of rotation thereof and towardsthe gauge re gion, each blade having an outer surface which, in use, faces the surface oftheformation being drilled and a front surface facing in the direction of normal forward rotation of the bit, a plurality of cutting el ements 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 bodyfor supplying drilling fluid to a plurality of openings in the leading face of the bit.

The aforesaid openings for drilling fluid are loc ated on the bit body between adjacent blades and are so located as to promote a flow of drilling fluid ac ross the front su rfaces of the blades and the cutting elements mounted thereon. The flow of drilling fluid cleans and cools the cutters and carries cuttings out wardly and upwardlythrough 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 substantiallythe same manner in each of the areas of the bit between two adjacent blades. This is because it has been con sidered desirableforthe flow overthefront surface of each blade to be substantiallythe same to provide 100 optimum cleaning and cooling of the cutters on the blade.

However,the present invention depends on the realisation that, contraryto what has previously been believed in relation to bits of thistype, the im pingement of thejet of drilling fluid on the surface of theformation itself plays an important part in the ef fective operation of the bit. It has previously been considered thatthe required cooling and cleaning objectives would be met by the emergence of the jet 110 of drilling fluid from the openings causing a general area of turbulentflow within the whole space between adjacent blades. The present invention, however, depends on the realisation thatthe direct im- pingement of a high velocity turbulent jet of drilling fluid on the surface of theformation itself performs a highly important function. The impingement of the jet on theformation at high velocity, particularly in a region on thefrontside of an advancing blade, causes effective cooling of theformation and this leadsto less hepting of the cutterswhich then act on theformation. This is believed to be more effective than the conventional method wherebythe primary cooling purpose of the drilling fluid isto cool the cut- tersthemseives.

Furthermore,the impingement of the high velocity turbulentjets on theformation serves to lift cuttings created bythe cutters and separatethem from the surface of theformation sothatthey become entrained in the flow of drilling fluid. In conventional arrangements there maybe a tendency, particularly in soft and sticky formations, for cuttings to beheld 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 orderto maintain a high velocity turbulent cohesive jet impinging on the surface of theformation 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 reasonsfor this is that if a greater numberof openings is provided they requireto be of smaller diameterto maintain the same overall flow rate and this leadstothe riskof 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 outto provide a construction of drill bitwhich 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 awayfrom the axis of rotation thereof and towards the gauge region, the number of blades being f rom 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 formsthe 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 bodyforsupplying 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 theformation being drilled at different distancesfrom the axis of rotation of the bit.

In use of the drill bit a jet of fluid emerges at high velocityfrom each opening and impinges on theformation in frontof a portion of the associated advancing blade. The length of the portion of the blade affected bythe jet is determined bythe 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 preferablythe dispositions of the openings are such thatthe jets from the openings between them sweep substantiallythe 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 anglesto the axis of rotation of the bit.

Preferably the central axis of each opening for dril- ling fluid is substantially parallel to the front surface 2 GB 2 183 693 A 2 of the adjacent blade. Preferably also the angular orientation of each opening is such thatthe central axis thereof is substantially at rightangles to the surface of theformation oppositethe opening (i.e. is less than 30'and preferably less than Wto the normal) sothatthejet of drilling fluid impinges substantially normally on to the surface of theformation.

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.

Desirabiythe location of each opening is such that its distancefrom the pointwhere the jet of drilling fluid impinges on the formation is less than five times the diameter of the opening. Preferably, said distance is lessthan fourtimes 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 forthe escape, through the associated exit channel, of cuttings produced bythe cutting elements. It is believed thatthis substantial clearance is one of the reasons forthe high penetration rates which drill bits of this kind may achieve in certain types of formation. It isthere- fore undesirableto 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 f rom the surface of the formation is achieved by providing each opening atthe 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 nearerthe formation. For example, the surface of the bit body may beformed with a projecting boss the opening being formed in the outer extremity thereof. In the case where the opening isformed in a separate nozzle, the nozzle may be an extended nozzle one end of which projects from the surface of the bit body 110 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 astungsten carbide.

Thefollowing is a more detailed description of embodiments of the invention, reference being madeto the accompanying drawings in which:

Figure 1 is a partsection, partside elevation of the body of a drill bit in accordancewith the invention, Figure2 is an end view of the bit body shown in Figure 1, Figures3to 6are half sectionsthrough the bit bodyshowing the location and orientation of the nozzles for drilling fluid, Figure 71s a longitudinal section through an alternative form of drill bit, Figure 8is an end viewof the drill bit of Figure 7, Figure9 is an end view of a furtherform of drill bit, and Figure 10is a half section through a still further form of drill bit, showing an extended nozzle.

Referring to Figures 1 to 6,there is shown the main bit body 10 of a rotary drill bitfor use in drilling deep holes in subsurface formations. The bit body 10 may beformed from steel and has a leading face 11 and a guage 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 foursuch blades spaced substantially equally around the central axis of rotation of the bit. Each blade has an outer surface 14which, in use of the bit, facesthe surface of theformation being drilled, and a front surface 15facing in the direction of normal forward rotation of the bit. A pluralityof cutting elements 8 are mounted on each blade 13 along thejunction between the outersurface 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 orothersuperhard material bonded to a less hard backing layer, such astungsten carbide. Each cutting element is bonded to a post7,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 mannerthe gauge region 12 of the bit is formed with abrasion elements 16 which may, for ex- ample, 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 orwear 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 ' 19b, 19c, and 19dre- spectively. Each nozzle communicates through a passagewith a central passage 6 in the bit body. In known manner, dril.ling fluid supplied under pressure through the central passage 6 emergesfrom the nozzles 19a- 19dforthe purpose of cleaning and cooling the cutting elements aswell as cooling the formation.

Figures 3to 6 are half-sections of the bit body through each of thefour nozzles 19a- 19dand 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 dril 1 ing f lu id which emerges under high pressu re f rom the nozzle. In Figures 3 to 6 the surface of the formation being dril led by the drill bit is indicated diag ram matically at 21.

The central axis of each nozzle lies in a plane which is su bstantial ly parallel to the f ront su rface 15 of the associated blade. It wil 1 be seen from Figures 3 to 6 that the central axes of the f ou r nozzles are inclined at different ang les to the central axis of rotation 22 of the bit a nd the effect of this ang u lar orientation, together with the location of the nozzles,Js thatthe jet of drilling fluid from each nozzle impinges on a different portion of the su rface 21, the portion of the surface on which the jet impinges in each case being 1 1 3 GB 2 183 693 A 3 indicated at 23. Due to radial ly outward dispersion of carbide or similar erosion-resistant material.

the jets, which increases with distance from the In the alternative arrangement shown in Fig ures7 nozzle opening, the diameter of the area of inf I uence and 8 the leading face 111 of the bit body is again of each jet is greater than the di am eter of the nozzle integrally formed with four blades 113 in generally opening, and the orientation of the nozzles is such 70 similarfashion to the arrangement of Figures 1 and thatthe four areas 23 of the formation on which the 2. In this case, however, there is spaced rearwardly jets impinge between them cover substantially the of certain of the cutting elements 108, with respectto whole of the formation from the gauge region to a the normal direction of forward rotation of the bit, an position close to the central axis 22 of the drill bit. abrasion element 126 which may, for example, com- The effect of this is that the four jets between them 75 prise a tungsten carbide stud impregnated with nat will, as the bit rotates, sweep out a total area exten- ural diamond particles and received in a socket in the ding over su bstantially the whole of the formation at blade.

the bottom of the hole. This means that substantially On the forward side of each blade 113 a nozzle is all the surface of the formation is subjected to direct mounted in a socket in the bit body, four nozzles impingement by a high pressure turbulentjet of dril- 80 being indicated at 11 9a, 11 9b, 11 9c and 11 9dre ling fluid with all the advantages this gives, as pre- spectively. As in the previously described arrange viously referred to. These advantages are in addition ment, the central axes of these four nozzles are in to the normal cooling and cleaning effects which clined at different angles to the central axis of would be provided by any nozzle delivering high rotation of the bit so thatthejet of drilling fluidfrom pressure drilling fluid to the face of the drill bit re- 85 each nozzle impinges on a different portion of the gardless of the orientation of the nozzle. surface of the formation. In the arrangement of Fig Preferably the central axis of each nozzle is arran- ures 7 and 8, however, there is provided a further, ged as nearly as possible at right angles to the sur- fifth nozzle 127 which is located on the forward side face of the formation. It wil 1 be seen that in the case of of the same blade as the nozzle 11 9c but is located the nozzles shown in Figure 5 the central axis is very 90 close to the central axis of the bit and is directed in a close to being at right angles to the surface of the direction generally parallel to that axis. The object of formation whereas, due to limitations imposed by the further nozzle 127 is to provide more effective the structure of the bit body, in the case of the nozzles cleaning and cooling of the cutting elements, and shown in Figures 3,4 and 6the central axis is at a cooling of theformation, in the vicinity of the central greater angle to the normal. Desirablythe angleto 95 axis of the bit.

the normal is not more than 30'and preferably is less The invention is applicable to drill bits having two, than 150. three orfour blades, and Figure 9shows an arrange In orderto obtain the optimum effect of the immentwherethe leading face of the bit body is integr pingement of thejet on the surface of theformation, allyformed with onlythree blades 213 spaced equ it is desirable thatthe distance of the opening in each 100 ally around the central axis of rotation of the bit. Each nozzlefrom theformation should not be greaterthan blade has an outer surface 214which facesthe sur five times the diameter of the opening, preferably face of theformation being drilled, and a frontsur not morethan fourtimesthe diameter, and more face 215facing in the direction of normal forward rot preferably not more than threetimes the diameter. If ation of the bit. A plurality of cutting elements 208 the nozzle is received in a socket in the bit body, as 105 are mounted along each blade 213, each cutting el shown in Figures 3to 6, the location of the surface 24 ement being in theform of a circular poiycrystailine of the bit body in relation to theformation 21 will be diamond preform.

determined bythe required position of the nozzle. In As inthe previously described arrangements otherwords, if itwerewished to movethe nozzles 19 theforward side of each blade 213 a nozzle is moun closerto the formation 21 itwould be necessaryto 110 ted in a socket inthe bit body,thethree nozzles being bring the surface 24 closerto the formation to ac- indicated at 219a, 219b and 219c respectively. The commodate the nozzles. However, as previously central axesof thethree nozzles are inclined atdif mentioned,the location of the surface 24determines ferent angles to the central axis of rotation of the bit the clearance on thefrontside of each bladecarrying sothatthejets of drilling fluidfrom the nozzles im- the cutting elements, and the large amountof clear- 115 pinge on different portions of the surface of theform ance provided in the drill bit of this general type is ation being drilled.

Claims

believedto be one of the important contributing fac- CLAIMS tors to the

effectiveness of the bit. It maytherefore be undesirableto reduce this clearance. Accordingly, 1. A drill bit comprising a bit body having a lead the nozzles maybe brought closer to the formation 120 ing face and a gauge region, a plurality of blades without reducing the overall clearance by locating each extending acrossthe leading face of the bit each nozzle in a boss which is integral with thesur- body awayfrom the axis of rotation thereof andtow face 24 of the bit body butwhich projects towards the ardsthe gauge region,the numberof blades being formation. Alternatively, asshown in Figure 10, each from twotofour inclusive, each blade having an nozzle may be in the form of an extended element 25 125 outer surface which, in use, faces the surface of the one end of which is secured within the socket in the formation being drilled and a front surface facing in surface 24 of the bit body and the other end of which the direction of normal forward rotation of the bit, a projects awayfrom the surface 24towards the sur- plurality of cutting elements mounted along each face of the formation. Such projecting portion of the blade, an exit channel in the gauge region of the bit extended nozzle is preferably formed from tungsten 130 body between each pair of adjacent blades, a plura- 4 GB 2 183 693 A 4 lity 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 there from, at least one opening being located between each pair of adjacent blades, and a passage in the bit bodyfor supplying drilling fluid to said openings, said openings being so located that, in use, the cen tral axes of openings between different pairs of adja cent blades intersectthe surface of theformation being drilled at different distancesfrom the axis of rotation of the bit.
2. A drill bit according to Claim 1, wherein there is provided only a single opening for drilling fluid be tween each pair of adjacent blades.
3. A drill bit according to Claim 1 or Claim 2, wherein the central axes of the openings between different pairs of adjacent blades are inclined at dif ferent angles to the axis of rotation of the bit.
4. A drill bitaccording to any of Claims 1 to 3, wherein the central axis of each opening for drilling fluid is substantially parallel to the front surface of the adjacent blade.
5. Adrill bit according to any of Claims 1 to4, wherein the angular orientation of each opening is such thatthe 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 lYto the normal) so thatthe jet of drilling fluid impinges substantially normally onto the surface of theformation.
6. Adrill bitaccordingtoanyof Claims 1 to5, wherein each said opening is provided in a nozzle which is separately formed from the bit body and is mountedtherein.
7. A drill bit according to Claim 6, wherein the 100 nozzle is removably secured within a socket in the bit body.
8. A drill bitaccording to any of Claims 1 to 7, wherein the location of each opening is such that its distancefrom the point where the jet of drilling fluid impinges on the formation is less than five timesthe diameter of the opening.
9. A drill bit according to Claim 8, wherein the location of each opening is such that its distance from the pointwhere the jet of drilling fluid impinges on theformation is less than fourtimes the diameter of the opening.
10. A drill bit according to Claim 8, wherein the location of each opening is such that its distance from the point where the jet of drilling f luid impinges on the formation is less than three times the diame ter of the opening.
11. A drill bit according to anyof Claims 8to 10, wherein each opening is provided atthe extremity of a structure which projects from the main surface of the bit bodyon theforward side of each blade so as to bring the opening nearer the formation.
12. A drill bit according to Claim 11, wherein each opening is formed in a separate nozzle, and the nozzle is an extended nozzle one end of which pro jectsfrom the surface of the bit body and isformed with the opening and the opposite end of which is secured in a socketin the bit body.
13. A drill bit according to Claim 12, wherein the extended noizie is formed from an erosion resistant material.
14. A drill bit comprising a bit body having a leading face and a gauge region, a plurality of blades each extending acrossthe leading face of the bit body awayfrom the axis of rotation thereof and towards the gauge region, the number of blades being from two to four inclusive, each blade having an outersurface which, in use, facesthe 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, at least one opening being located between each pair of adjacent blades, and a passage in the bit bodyfor supplying drilling fluid to said openings, the location of each opening being such that its distance from the point where the jet of drilling fluid from that opening impinges on the formation is less than five times the diameter of the opening.
15. A drill bit according to Claim 14, wherein 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 fourtimes the diameter of the opening.
16. A drill bit according to Claim 14, wherein the location of each opening is such that its distance from the pointwhere the jet of drilling fluid impinges on theformation is less than three times the diameter of the opening.
17. A drill bit according to any of Claims 14to 16, wherein each opening is provided at the extremity of a structure which projects from the main surface of the bit body on theforward side of each blade so as to bring the opening nearer the formation.
18. A drill bit according to Claim 17, wherein each opening is formed in a separate nozzle, and the nozzle is an extended nozzle one end of which pro- jects 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.
19. A drill bit according to Claim 18, wherein the extended nozzle is formed from an erosion resistant material.
20. A drill bit substantially as herein before described with reference to Figures 1 to 6, Figures 7 and 8, Figure 9 or Figure 10 of the accompanying drawings.

Printed for Her Majesty's Stationery Office by Croydon Printing Company (UK) Ltd,4187, D8991685. Published by The Patent Office, 25 Southampton Buildings, London, WC2A 'I AY, from which copies maybe obtained.

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