CA1254880A

CA1254880A - Rotary drill bits

Info

Publication number: CA1254880A
Application number: CA000519553A
Authority: CA
Inventors: John D. Barr; John Fuller; Malcolm R. Taylor
Original assignee: NL Petroleum Products Ltd
Current assignee: NL Petroleum Products Ltd
Priority date: 1985-10-01
Filing date: 1986-10-01
Publication date: 1989-05-30
Also published as: US4733735A; AU6320786A; EP0219992A2; EP0219992A3; EP0219992B1; DE3676271D1; AU581346B2; GB8524146D0

Abstract

ABSTRACT OF THE DISCLOSURE
A rotary drill bit comprises a bit body having a leading face and a gauge region, a number of blades on the leading face of the bit body, and a number of cutting element mounted along each blade. A passage in the bit body supplies drilling fluid to nozzles in the leading face of the bit body for cooling and cleaning the cutting elements. Each nozzle is so orientated, and the surface of the bit body in the region in front of each blade is so shaped, as to promote a vortex flow of drilling fluid around said region, with part of the periphery of the vortex extending across the cutting elements on the blade, so that fluid in the periphery of the vortex passes across the cutting elements mounted on each blade before escaping through an exit channel in the gauge region.

Description

Th~ lnv~ntioll ~ela~ .o rotary dr~L:l bl.t~; ~or u~e ln drllllng d~ep llole~ in ~ubsurf~ce ~rmA~.i.onf~
.Ln partic~llar, the lnvention rel~tes to drlll blts of the klnd compri~ing a blt body providing a lQadirlg faee, a gauye region,and an annular spac~e (known as the annulus ~ on the side of the gauge regi~n remote f rom the leadins~ ~ace, a number of blade~; on the leadlng face, each blade havlng an outer ~uxface whlah, in u~e, fAces the sur~ace of the formatlon being drilled and A ~ront ~urface facing in the direction of normal forw~rd rotation of the bit, a number of cutting elements ~ounted alon~ ~ach blade, a de~lvery pa~sage ln the bit body for ~upplyin~
drilling luid to a number of opening~ ln the leading fac~
of the ~lt, and a~ least one exlt pa~sage for returnlng ; said drilling fluid p~s~ the gauge region to the annulu~.
Sald openings are so located on the forward ~Lde of blade as ~o promote a flow o~ drillin~ ~luid acro~ th~
~ront surface of the blade and acro~s the cutting ~lemant~
20~ mounted on the blade~ ~he exit passage i~ u~ually ln th~
form of an exi~ channel or ~unk ~lot formed in the ou~r : sur~ace of tho gauge reglon, but the invention a~o in~lude arrangements wh~re oth~r ~orm~ o~ exlt p~
are employed.
~: 25 : A drill ~it o~ this kind i~ de~rlbed ln U.S.
: Patent Specificati~n No. 4,499,958. In the drill bit described in ~hat s~eclflc~tlon~ there ~re pro~vide~ ~our blades:and two openln~s ~or ~rilllng ~lui~ on the forw~rd ~' . . . .....
, : - . .;
.

~2~ ~X~ 3 side o~ ~ach l71aclel th~ operllngF~ being at dl~f~rLt. ril-llQI.
distanc~s frorn th~. axi~ o rotl~tion af ~he blt. rri~re arf3 p~ovid~d ~our ~unlc ;1O~ each of whi.ch ~xt:~nds, aro~ (l t~le p~rlphery o~ tll~ bi.~, ~rom the f.ront sur~ace o G~ch b1.~tl~
to a location ~paced a short di~ance ~rom ~he rear of thc next blade. Accordingly, almost the whole of the space between adjacen~ blade~ ls ln d.~r~ct co~nunloation wl~h the a~sociated junk slot. such an arxangement provicle~
substanti~l clearAnae and a large flow parh for the e~aape, through the junk ~lot, of cuttlngs produc~d by the cutting element~ and it i~ believed that this $~ one o~
the rea~on~ for the high pen~tration rate~ whlch drlll bits of this kind may achieve in certain typeB of ~orma~lon, Howe~er, a furt~er important function o~ the drillin~ fluid 1~ to aool the cutting element~ and ~he formation on which the cu~tin~ element~ are actin~, and wi~h the arrangement described ln U.S. SpecificAtion No.
4,499,958 suGh coollng may not b~ particularl~ effec~i~¢
in vie~ of t~le fact ~hat ~rilling fluid emer~ing from th~
nozzles in the ~it body aan Elow dlrectlY to the ~unk slot ~:withou~ providing su~ficient high velocity turbu~ent ~low o~ fluid over the cutting elements ~nd the ~ormation to provide e~fective cooling~
: ~ ~ The present inventlon provlde~ an improv~m3nt to 2S a drill ~ bit of the kind ~irst re~erred ~o, the improvemerlt comprising ~he provision of a structure which control~ the flow of drillin~ ~luid emer~in~ from the openin~ in ~he blt body in such mann~:r as to promote a controlled vortex ,.

. ` ~
, .a~

of ~low on the orw~I.d ~i.d~ o~ e~h blacl~ t~ ~I.ve gLeat~r velocity gradi.ent to the ~low ov~r the cutt~n~
~lements .lnd ~ er~by provid~ morc ~f~ive coolln~l o the cutting elementg a~d the forma~ion on which t:he~ a~e 5 ac~ting.
It Yhould be explalne~ that in mo~t conv~ntlonal drill bits o~ the kind first re~erred to above~ includin~
the type desoribed in U.S. Ratent Speai~icatlon No, 4,49~,958, the ~low o drllling fluid over th~ ~urace o ~he bit body ~nd cUtting element~ i~ comple~, an~ may be assumed ~that ~uch ~low will also involve ~he g~n~ration of on~ or many ~mall vortlce~, but in a ~enerally uncontrolled Inanner. The present lnvention, however, depend~ on the production of a con~rolled vortex, that i~

15 to say the conf igura~ion o:~ ~he bit body and the loc~tion ~ ~ of the openin~s therein for drillin~ fl~ld are ~uch a~
': inevitably to re~ult in the generation of at l~t one ma~or vortex in ~he reglon ad~acen~ the front ~urace of the ~ blade, the peripheral reglon o~ the vortex pa~in~

acros~ s~veral or all of the autting ~lement~ mounted on :
the~ bIade.

:

cordlng to one a~pe~t o the inventlon, in ~

:rotary drill bit of the kind firgt referre~ to, at l~R~t ~, : : :25 ~ne ~0~ the aforesaid openings is loc~ed in ~ r~gion Adjacent the front surface of a blade which ra~on 1~
bounded, when the blt i6 ln ~l~e, p~rtly b~ a ~u~ae porti~n o~ the bit body and partly by a sur ~ce porticn of :.
., ., :

: ~ .
:: : ` ~ :
::
. ~ ~

the fo~mation b~lnc3 dt~ clr ~he openin-J b~ n.~.l so orle:nt~tecl w;i~h re~ipec~ to t~l~ saitl sur~ACe port:l~n~; ar;
promote A vorteK f l.ow c~f ~lr.illirl~ :L'luld ArollrLr.l sa:L~I
region, with par~. of ~he E)exiph~ry o t.h~ vort:ex t~st~rldln~
across th~3 cut:tinS~ element~ on the bl~de, At lea~t part o~
said ~urfaee portion of the bit body which de1nes the af oresald region ~eln~ smooth:Ly and concave~ y curved ln manner to ~.cllltate the forrnation of ~;~id vortex, ~;sid exi'c passage being so locAted that f luld may escape f rom the periphery of ~che vortex lnto ~aid exit ~a~sage and thence to said ar~nuluS.
At lea~;t a por~lon of the vortex f low over ~aid sur~ace portion o~ the forma~ior~ may be in a direction ou~cwardly away frc~rn the central axis o~ rotatlon of the drill blt, and in this ca~e said exit passaçle may comprif;e an exit channe~ ~ormed ln th~ outer ~urf ace o~ the gaug~
reglon, which channel is located a~jacent th~ front surface o~ the bl~de whereby ~luid m~y escape direc~ly into said exit channel f rom the peripherY o th~ vor~ex a~er h~.ving pa~sed outwardly ~cros~: t~e cutting elementB .
Preferably, ~he par~ of :aid surface pc~rtion o~ the bit body; whlch i~ ad~acent saLld exit channel i~ incllned inwArdly ~;o as ~o f ace partly ~oward~ ~he ~ on~itudina:L
axis of rota~ion of the drill bit.
: ~ Accord~ng to a seaond a~pect of the invention, there is provided a rot~ry drill bi~ compri~ing a bl~ hody providing ~ leadin~ face, a gauge region, and ~n annulu~
on the side of ~he S~auge re~ion remot~: ~rom the leading ~ , .

, ~ ~ F~ .. S ~ ~} ~3(J~

face, ~ !lnmbeL of blacles on the l~din~ ~a~e, ~ach ~).l.a~
havin~ an outer ~r;urf~lc~ whl.ch, Ln u~ aGe~. the ~urfa~
of the ~orma~.ion being drilled an~ ront ~.urae~ ~acl.n~J
in the direction o~ norma~. forward rota~lon o~ the b~t, a numb~r of cut~ing ele~ent.~ mounted ~long each ~lade, a delivery pas~age in the bit body for ~upplying drilliny fluid to a number o openings ln the leadiny faae o~ th~
bit, and at lea~t one exit channel ormed in the outer surface o~ the gauCJe region for returning ~aid drillLn~

fluid pa5t the gauge region to the ~nnulu~ t at le~t one of the aforesald opening~ bein~ located in a x~lon adjacent the ~ron~ ~urface of a blade which region 1 bounded, when the ~ in u~e, par~ly by a surfac~
portion of the bit body and partly by a surface po~tion of the formation being drllled, the opening b~ing ~o orientated wlth respe~t to ~he ~aid Sur~ac~ portions a~ to promote a vor~ex ~low of drilling fluid around ~aid reglon, wi~h part of the perip~ery of the vortex extendin~
across the cutting element~ on the blAde, at leaet ~
portion o~ the vortex ~low over said ~urface por~ion 0 ~he ~orma~ion bein~ in a direc~ion out~rdly awa~ ~rom th~
central axi~ of rotation of ~he drill bit, wh~reby th~
fluid ~in the vor~eX reache~ the outer periphery of the drill bit lmmediately aft~r havlng passed outwardly acro~

the cutting elemerlts, there beln~ provided an exlt ohannel adjac~nt the ~ront sur~ace o~ the blade ~o that ~luid m~y e~cape directly into said exlt chann~l from the p~riph~ry o~ t~e vortex a~ter having pa~ed ~cro63 the ~uttin~

': : . ' : -~`

-6w ~ t.~

elcments, p~rt of .C3ai~ ~ur~ace port~n of t.he b.l.t k~c3tly which i~ ad~aaent ~a:ld exit ah~nnel bein~ lncl:i rLe inwardly so aS t~ ~ace p~rt~y tow~rd~ thQ lon~J.i~nc~..lrla~
~xi~ of rotatlon of the ~rlll blt~
The feature of p~rt o~ the surface portion o~
th~ bit body, adjacent ~he exit ch~nnel, belng inclined inwardly may be provided either in addltlon to or ~ an alt~rnative to ~e ~maoth curvature of ~he sur~ace port.ion of the bi~ body ln ~he previou~ly mentloned ~rran~m~nt~
where flulcl may e~aape directly into th~ ~xit channel ~rom the periphery of the voxtex. That is to say, if th~
surface o~ the bit ~ody 1~ inclined a~ ~eci~led adjacent the exit channel, it beco~es les~ neoes~ary ~ox ~he surface portion to be ~moothly curved and th~ vort~x may be adequately gener~ted by a more ~ngulAr configur~lon o~
the ~urface.
Arrang~ments in accordance wlth bo~h a~p~at~ o~
the invention provide two important maln advant~ga~. In order to provide e~flcien~ cooling ~nd cleaninc3 o~ ~e cuttin~ elemen~s ln a drill bit it i~ de~lrab~o th~t th~
drilling ~l~id flc~w~ ~aro~ the ~urfa~es of the cut~ln~
elements at hlgh velocity, ~hi~ re~uir~ a high vel~ci~y gradient ~n the ~luid a~acent the cu~ting elements~ which :in tur~ nece~ltates a very high veloCity at ~ di~tanae from the cut~ing elements and therefore a high volumetria ~Iow rate. In co~ventional drill bits, th~ drilling ~luid : normally flows only onae pa~ e~ch cu~ting ~l~ment an~
thus the thermal capa~ity of the ~luid i~ not ug~d r:~

~, :

-7~ S~

e~lciently in coo~.inc~ ~he el~rnent~. By rec.Lr~ula~.l.rl~ a high propo~tion of th~ ~luid in a controll~d vor.t~x however, ln ~ccord~nce w.ith th~ .inv~ntlo~ he recircUla~ed portlon of ~he fluid ~c~ on th~ cllttln-J
S elements mor~ ~han once, and consoquently pcrfoxm~ its cooling functi4n over ~ muah lon~er total effective flow path than is the case with conventional bit~. The coolin~
e~ficiency o~ the ~luld may thus be considerably ~nhanc~d, permitting lmproved utills~tlon of ~he ~vflll.abl~ ~low r~e of drilllng fluid which, ln any giv~n dri.lling situa~lon, is usually limited.
Furthermore, the centrifugal action o~ the vortex ten~s to cau~e cuttlng~ entrained in the drilllng ~luld to migrate to the out2r periphery o the vortex, from where they pass to the exlt pa~a~e and thence to ~he annulus. Conse~uently, the recirculated pvrtlon of th~
fluld ln the vortex is the inner, relatlVelY clean ~luid.
In the case where the exit pa~sa~e ~ompri~ an exit channel along the gau~e region of the hit, the exit 20 : channel may be shaped ~o a~ to lncre~e in cro~R-section : a~ it ex~end~ c~long ~he gauge region. A ~moothly ro~nded : edge region may be provlded between tho exit channel ~nd said sur~ace portion o~ the bit body.
Also in the arrangemen~s refe~red to abo~ in

2~5 which fluid esc~pes directly into the exit channel from the perlphery o~ the vor~ex, the cuttin~ element ar~
pre~erably so disposed ~hat said ~urface portion of th~
formation beln~ drilled i~ smoothly and conc~vely curved ~ ~J' `~ `

- `
. . .
.

~ t~

immediately a~ljace~lt st.ll~l exlt. ~hannel, ~n(1 sa~d e~lt;
channel exkends generfll1y ~.any~llkiall~ to saId c.lcjn~r~Y~y curved sur~ace por~.ion of the :eorm~tion~
~s an alternative to the exit pa~ cJ~ be.i.n(~ an 5 exi~ ~hannel alon~ ~he gauye region into which f~
passes directly from the perlphery of the vortex, the exit pass~ge may axtend th~ough ~he bit body from an openinc3 in said surace portion of the bit body.
In thi~ case at least ~ portion of the vortex flow over said sur~ace portlon of the form~tion i~
pxeferably ln a direction lnwardly towards the central axls o~ rota~ion of the drlll bit, ~nd said openlng in sald surface portion of tha bit body i~ ~o loaat~d that f1uid may escape ~hrough sai~ opening and into th~ ~c~pe passage ~ter having pasqed lnwardly ac~os~ the cu~tinU
element~. Thl~ ln~rd flow of drillin~ fluid may pr-ovid~
better cooling and cleaniny o~ cuttin~ element~ ne~rer the :outer periphery of the bit. ~he openlng through which drilling ~luid is delivered ~ px~ferab1Y so orienta~ed with respect to ~aid surfaae portion~ of the bit body ~nd formation as to be directed ~oward~ the viain~y of tha ~unction be~ween said sur~ace por~ions at ~he outer ,~
periphery of the bl~. As a resul~ th~ jet o~ drillin~
flu1d from ~he open1ng Wil1 lmplnge with hi~h v~locity on ~5 the ~eneral area where th~ outel-mo~t c~ttin~ ~lem@nt~ ~re located, these being the ~lem~nts ln respect o~ whi~h : adequate cooling and oleaning may be mo~t critio~l.

In the 1ast-mantioned arrang~ment~ th~ ~uraa~
.:

.
, :

portion O:e th~ bl~ body i.s pr~erab.LY smoc)t;hly ~In~
concavely curved i.m~ecl.late Ly ad;jacen~ 1 ope~ J .I.n~o the exi~ pas~ag~, an~ 9Ui~ pa~sag~ ~xtendr3, ~
initially, genera~lly tAngentially ko said concave:l.y aurv~d portion of t~e bit body.
In an~ o~ the Arrangement~ in accordance wi~h the invention pre~erably ~ubstantially the whole of th~
surface portion o~ the b.i~ body whlah bounds the a~ore~id reglon in which ~he vor~ex is formed is smoothly and concavely curv~d. Similarly, ~he cut~ing element~ ar~
preferably so disposed that sub~tantlally the whole of t~e ~urface portion of the formation wh~ Ch boundx the aforesai~ region in which the vor~ex is formed i~ al~o smo~thly and concavelY curved. Preferably a~o the sur~ace portions o~ the bit body and the f~r~ati~n ars o~
substantially equal and uni~orm curvature so that the region bounded thexeb~ i~ subs~antially circulAr.
~ In any o~ the Above arran~em~nt a numb~r of cutting elemen~s ma~ be mounted along the junction b~twee~
sald outer and front sur~ac~ of eaah bl~de. The number cutting ~lements are preferably arxanged in ~ gl~
row along each blade.
The xegion ad~acent the front sur:Eace of ~he I

blade within which the vor~ex i~ promot2d may b~ defin~d Z5 ~partly by a recessed por~ion of the lea~in~ f ace o~ th~
bit adjacent ~aid surface. For example, sald reces~d portion may b~ bounded par~ly by d ~all sur~ace ~pac~d ~orwardly away from sald fron~ sur~ace of the blade ~nd - L t) -6ub~tantlall.y p~rc~ thereto~

FicluLe 1 i~; ~ v~rtiaal .sect.Lorl throlly}l n dril:L
~it, S ~i.gure ~ an end vi~3w o~ the bit ~hown .In ~igure 1, and E'igure~ 3 and 4, 5 and ~, and 7 and ~ are slmllar views to Fl~ures 1 and 2 of alternativ~ forms of drill bit accordirlg to thP i~ven~lon.

Refexrlng to Figures 1 and 2, there i~ ~hown a ro~ary drill bit for u~e in drilling deep hole~ in subsurface formation~: comprising ~ blt body lO h~vin~
leading face 11 and a gauge reglon 12~
15The leAdin~ fa~e of the hit body 1~ lnteçlrally formed wlth blade; 1~. Af: best ~e:en ln Fl~ure 2 th~re ~re provided four such blades spa~ecl ~ub~tant.ially equ~lly around the central axls of rotation o~ the bit. However, any othex æuitable number o~ blades ma~ be employ~d, 20~: inaludiDg ~nly a sin~le blad~. Each blade ha~ an ou~er ~ur~ce 14 wh~ch, ~n U~e of the b~, f~ces the surface o~
the formation being drilled, and a ~ro~t 6urface lS f~c~n~
:; ln the direction of normal forward rotation of the blt.
: ~n the arrangemen~s shown the front urface 15 of each blade: lies in a substantlally f~at plane, but the invention lncludes wlthin ~t5 æcope arr~ngemen~s where the : ~front 6ur~ace is concavely or conv~xly cur~ed.
;~ A number of cuttlng element~ 1~ are mounted on , :

k~i~ It.~

each blade a l.ong th~ jun~,tl.on b~3twecn th~ otlt~-~r ~C,t~
and the ront ace 15 . Edc~h ~lt l~ing cl~rnerl~ m~ , as shown, ln th~ form of a cir~ul.ar pr~3~'0rm comprl,r;.1.lly ~
f ron~ har~ ~ac:Lng layer o~ polycry~tallln~ mon(l or ot~her superhard material bonded to ~ le~ hard ~acklng layer, SuCh a~ tung~;ten carbide. Each cut~in~ al~m~nl~ ma~
be bon~ed to a. post 17, ~or example o tun~ en c~rb:lde, recelved ln a socke~. ln the bl~de 13. The junctior between the outer surface 14 and the rear surface 9 o:E
10 each blade m~y be chamfered a~ shown, ~or example ~ 4S, to a line just rearward of the po~t 17.
In known m~nner the g~Luqe region 12 of the blt may be fcrmed with wear or abra~ n element~ 18 which may, for example, comprise ~unç~sten aarbide ~tud~ lmEsre~nd~ed 15 wi~h natural dlamorld particles and rec~ived ln ~;ocket~ .in the ~auge por~ion.
The cu~tln~ elemen~ hown ar~ only on~ ~xampl~
of the type of cut~in~ elem~nts wh~c}~ may be emplo~ed in drill bit ac~cording to the lnven~ion, and lt w~ b~
20 appreciated th~t the invention i~ applicable to drill bit~s inaorporating any o~he~ foxrn of sui~cabl~ cuttin~ element.
For example, ~ch~?re m~y extend 3.long each blade only a ~w lar~e cutt;lng ~lement~, or e~ren a ~in~la alon~at~ cu~n~
element provi~ only a singl~3 continUOU~ ~uttin~ ed~s.
The gaug~ portion compxi~e~ four axl~lly extending kiakers or wear pad~: 19 in whlch the abra~lon el~ment~ 18 ar~3 mounted, exlt channelS 20 being dispo~d be~ween adjace~nt Icick~rs ~g. ~aah klc~ser may be form~cl ,'~,', ~ ~j ~2~ S~L~ 3 wlth A SlCt ~0~1, the purpos~ of whlc~ , i.n known Inanrler, to allow dr.i~ rlg flui~l to ~low f~e~ly pae~ thc (.l:r.i~Ll. b.l~:
as it is in~ro~-lcccl .In~o th~ bol-~ hole or ~:L~hdra~1n ro~n t~e bore hole.
On the fo~ward side of each blade 13 ~he blt body is formed wlth ~ rec~ 27. A nozzle 21 i~. mount~d in a socket in the bit body at the botto~ oE each rece~
27. Each noz~le communicates throuyh a paSSAge 22 wlth a central delivery pas~a~e 2~ Drlllin~ ~luid suppll~d under pressure ~hrough the central pa~age 23 emerge~ from the nozzles 21 for the purpo~e of cleaning and coollng the cuttin~ elemen~ as well a~ coollng ~he formation.
In Figure 1, the ~urface o~ the formation being dr~ lled i~ indlcated ln dotted llne~ at 26. on ~he ~i~e of the gau~e region remote from ~he leading face 11 of th~
blt, the bit body i~ o~ reduced di~meter ~o ~ to provlde : an:ann~lar ~pace 1, known a~ the annulu~, between the blt body and the surrounding ~ormal:ion ~ur~ace 26. The exlt channel 20 provide~ co~muniaat:ion between the lsadln~ fac~
o~ the bit and the annul~.
A region Z~ ad~cent the front sur~ace 15 of : ~ each bIade is bounded partly by a porti~n of the ~urfac~
~26 c~ ~he ~ormation and partly by the smoothl~ and conc~vely curved bot~o~ ~urface 2~ o~ the rece~ ~7. Th~
w~ll 25 o$ the recess furth~s~ f~om the ~ron~ ~urf~ce lS
of the asEociated blade is substan~ially flat and par~llel to said fron~ surfflce. (In ~he ~e, mentioned earlier~
where the front sur~aae o~ the blade i~ curved, ~he ~p~ced - "

`

wa~l bounding the rece,~ may b~ :1.tnil~lrly curved ~.30 a~ ~0 be subst~n~l~J.ly par~lLeL to the blade ~ all pcin~s a1.on~J
its len~th.~ r~he a~ociat:ed exi~ Ghannel 7.0 ~cter~ 3 ~or th~ whole wi~h of the rece~ 27, a~ ~hown in E~'igure 2.
A~ be~t seen in F:lgure l, each nozzle 21 i~s ~o located in ~he region 29 and i~ ~o orlenta~ed (I.n ~h~
case subs~antlally parallel ~o the central axl~ of rotation o the drill bit) that drllllng 1uid emerg~ng under pres~ure from the nozY.le impinge~ on the ~urE~ce o the ~ormation and is deflect~d in a curved pa~h outwardly away from the axis of ~he bit in~o a vortex. The v~rtex will lie ln a plane generally parallel to the front ~urf~ce of the blade, the direction of ~low be.ln~
indicated generally by arrows 30. (The expreasion "generally parallel" i to be under~tood, in thl~ ~ontext, to lnclude arrangemen~ where th~ vo~tex i~ curved ~o follo~ ~he g~neral contour o~ a curve~ 6urface 15.) As the ~luid at the perlphery of the v~rtex flows outwardly across the leadi~g ~ace o~ the bl~de and across the pxeformed cu~tlng element~ mounted thereon, lt cools the cuttin~ element~ and the adjacent iormatlon ~nd al~o o~rries awa~ ~rom each cutting element ~h~ ~uttin~s which it ha~ removed ~rom the formatlon. Suah cut~ing~
are ~wept aroun~ the region 29 by the vort~x ~nd, c1ue to 2S the centri~ugal or cyclone effect thereof, ar~ maintained ln the outer peripheral region of the vor~ex.
As the voxtex reache~ the exit channel 20 it ;: meets an edge region 31 whRre the curved concav~ Gurf~c~

",~, .

28 of the bl.~ ~ocly m~et.s the bo~torn wflll. 37 o:~ the ~1Cit channel 2~.
A~acent the edye r~gio~ he ~ur~c~ ~ort..i.on 2B
o~ ~he ~it bo~y may be inclined inwardly at about 45 130 as to ~ace par~ly towards the lon~ltudinal axl6 of th~
bit, ~s shown. O~her angle~ o~ inclination may ~ used, but in order to promote ~he vortex ~h~ ~ngle is preer~hly alway~ inclined inwardly. The edge region has the efect o~ dividing ~he ~low ln the vor~ex ~o th~t ~n ollter portlon, carrylng a higher proportion of cutting~, ~xits through the exit ahannel 20 where2s ~he cleaner inner por~on ls re-clrclllated in the vortex around th~ curved concave portion 28 o~ the hit body.
In the arrangament ~hown the ed~e portion 31 i~
~ 15 sharply an~led but the ~dge may be round~d a~ indic~ted in ; dotted lines at 31a.
The exit ahannel 20 may in~rease in area, a~
shown, as it extends away fxom the re~ion 29.
It is preferred to prov~de only one nozzle on ~he forward slde o~ ~ach blade ~ince th~ s~ngle nozzle aan ' : be of compara~ively large ~perture dl~meter with les~ rl~
., ; of blockage ~han if two or more noz~ were u~ed, ~in~
such no~zzles would have to be oP ~maller aperture.
However, ~he inventlon Lncludes within its ~cope arrangement~ in whlc~ more than one nozzle ~re u~ed O
Al60 the num~cr and conflguratlorl o~ the blade~ ma~ be alter~d without depar~ing ~rom the scope of the invention, a~ may be the type and a~rang~ment o~ the cuttln~ elem~nt~

, -~.5~ :

on the blades.
Figure~ 3 and 4 ~how A l!lodi~i~d ar~;~ln~lern~L~t ;ltl which, in or~er to enhAnce ~h~ ~nerat1On o~ ~ vor~ 1n the regio~ 12~, the. confiyuration o~ ~he hlade~ L13 un~l S the location of the cuttin~ element~ is such thut the surface 126 o~ ~he .~rmation, cut by the cutting ~lem~nt~
on the blade, forms a smooth continuation of the conce~v~
surface 12~ of the recess 127. To enhan~e the g~n~r~tlon of d vortex the c~ncave surface 128 of ~he bit bo~y ~nd the surrounding sur~ace 12~ of the ~ormation to~e~her approximate to a circle. The proile of th~ formation sur~ace lmmedlately ad~acent the exit channel 120 ls thu~
smoothly a~ concavely curved and the ~xlt cha~nel 1~0 extends tangentially thereto.
lS In order ~o minimise leak~ge of drlllin~ fluld from the reces~ 127 across the leading face 111 o~ the bl~
body, an ups~andin~ fence 109 is formed alon~ th~ upper edge of ~he wall o~ ~he rece~s 127 oppo~ite the blAde 113, the ~ence extending also around the end of th~ r~c~s~
contalnlng ~he nozzl~ and ~olning the ~la~e 113. ~h~
fence ~09 eng~ge~ th~ ~urfac~ of the formation bein~
drilled to m1nimise leaka~ o~ drillin~ fluid ~rom or to the reces~ 127 and acroS~ the leadin~ ~ac~ of the ~it, thereby as~i~ting in main~alniny the vortex and ~n~uring that most o~ t~e drillinq ~luid e~caPing from ~he res~
127 pa~ses ~irec~ly ~o the corre~pondlng exlt ch~nnel 120.
In order ~o provlde a more effective ~eal agaln~t the ~ormatlon, ~ fence 109 could compri~e ~ se~arate ol~ment , of ~lexible mat:~3ri~l ~ecured to t~ha b.i~ bod~.
As wlll b~ ~een ~rom F~yure 3 ~h~r~ i J :I. b~3 small lea}cag~ pflth~ :~or ~luid betwe~n the ~la(le 113 a~ld the surface of the formatlon 126, between the c:ut~ s~
5 elemen~c~ 116, but ~hi~ lealcage 1~; ~;m~ll and t;he l~akag~
space wl 1~ ~ecome smaller as the cutter~ become worn.
As p~evlou~ly explained, an ob~ect o~ the invention is to ensure that c~rll~inçl fluid escape~ to th~
exit channel 20 or 120 rom the p~ri~h~3ry o:E the vorte~s ~o 10 that the proportion of ~luid e~;caplng to the exit channel carries with it the h.iyh proportion of cuttin~s w~ich ar~
entrained in the peri.ph~ral region of the vortex due to centri~ugal :~orce, ~he proport~on of drlllin~ ul~ whiah is recirculated in the vortex en~cr~inlrly a much ~m~ller 15 proportion o:E cutting~. In order to enhanc~ t}le vor~x flow, it may be deslrable ~o allow a proE?ortlon of th~
Comparatively clean drilling ~lui~ to e~cape ~rom ~he eneral regi.on o:~ ~he vortex. Accordingly, l~h~re may optiona~lly be provided ~or th~ E~ purpose a circular ex~t 20 pas~age :leading f rom ~h~ central region o~ the vortex A
Such~ passages are, for example, lndlaated at 207 ln Figure~ 5 and 6, ~he drlll bit shc:wrl in tho~e ~l~ure~
being othe~wi~;~ similar ~co tha~ o ~lgure~ 3 ~nd 4 . P,~
best~s~en i n Flgure 6 each exit pas~;age 207 ~xten~ f~om an outle~c 20~ :i n the W~ of the r~ess 227 adiacent ~he blade il3 ~.nd extends through the maln ~ody o~ the bit to open ~nto an exit channel 205 in ~he gau~e r~gion, th~
exit channelE~ ~05 bein~ loca~ed around th~ ~au~e~ region t~

:~
. :

-17 ~ ~.3~.'t~

alternutely wlth ~he ~xit cha~nel~ 220 wl~il whl.cil t~ e re~e~e~ 2?.7 ~O~ cli~
~ n ~ rr~rl(J~rn~nt~ cl~ .ib~d ~ov~ ,f~
27, 127 or ~2 7 in fxont~ of eaah hla~ dLxo~:i.ly, a~:
the periphery oE ~he bit r i~to the a~soclated exit ch~lnrlel 20, 120 or 220, and thence to the annulu~. Figur~ 7 and 8 ~how a rnodified, ~wo~laded, axx~ny~m~nt where ~uch exlt channels ar~ not provided, and co~munlcation b~w~ ah reoess 327 and the ~nmllus 301 is by mean~ of an op~ning 303 in the curved hottom wall 328 of -the rec~s 327, wh~ch opening oommunicfltes with the annulu~ 301 throu~h an exl~
pa~age 302 whlch extend~ throu~h the b1t body it~el~.
In this arrang~m~nt each nozzle 321 ia ~o lo~ated that the ~ortex rotate~ cloc~wi~e a3 viewed ln Figure 7, so tha~ the portion of the vortex f low whlah i8 over the ~ormation and cu~ting element~ i~ in a d~r~ction inwaxdly toward~ the central ~xis o~ rotation of ~h~ drlll bit. The nozzle is also direct~d gen~rally tangen~i~lly to the curved surface 328 of the ~it body so ~ to imping~
on the ormation 32~ in the vlalni~y of the junction hetween the ~it body ~urfac~ 328 and ~he ~orm~tion. Thi~
ensure~ ~h~t the out~rmost c~ttl~ element~ 31~ of th~ bit are ubjecte~ to the ~igh veloci~y je~ o~ drilllng ~luid immediately ~fte~ it emerges f~om ~he nozzle 321~ .
25~ The exit opening 303 i~ ~o located ln the 6urface portion 328 of the bit body that fluld at the periphery of the vortex m~y escape through the openin~
303, into the paY~eoe 302, end thenoa lnto the annulu TOTRL P.20 ~;S~

, , ' .
,, ~ "

~,3t~ f~

301, ~f ter hAvlnc,~ pA;~ied inwardly ~laro~ the cut ti~
el~m~nt~; 3 lii . rrO faailit.at~ eJuch ~3c~pa the ~)ntJ~ e :~02 ext~?nd~ tan~n~.ia:l :Ly erom th~ ~uriace p~r~loii 3~ f the bit body. ~rhe nozzle 321 al~o ~x~n~ t.anfJen~ P.~ ~.o tho S ~urface portion to Ea~ .aLt~e the g~ rAtLon oi ~;h~
vortex .
Fluid aarrying the bulk of the cuttin~B thu~
escapes f rom the ~eriphery o~ the vor~ex throuçlh th~
opening 303 leaving the relatively al~an dxilling f lllltl to 10 be recirculated in the vortex.

: 20 2S .

'~

~3 ~~;' . .

:: .. .

Claims

1. A rotary drill bit comprising a bit body providing a leading face, a gauge region, and annulus on the sides of the gauge region remote from the leading face, a number of blades on the leading face, 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 number of cutting elements mounted along each blade, a delivery passage in the bit body for supplying drilling fluid to a number of openings in the leading face of the bit, and at least one exit passage for returning said drilling fluid past the gauge region to the annulus, at least one of the aforsaid openings being located in a region adjacent the front surface of a blade which region is bounded, when the bit is in use, partly by a surface portion of the bit body and partly by a surface portion of the formation being drilled, the opening being so orientated with respect to the said surface portions as to promote a vortex flow of drilling fluid around said region, with part of the periphery of the vortex extending across the cutting elements on the blade, at least part of said surface portion of the bit body which defines the aforesaid region being smoothly and concavely curved in a manner to facilitate the formation of said vortex, said exit passage being so located that fluid may escape from the periphery of the vortex into said exit passage and thence to said annulus.

2. A rotary drill bit according to Claim 1, wherein at least a portion of the vortex flow over said surface portion of the formation is in direction outwardly away from the central axis of rotation of the drill bit, and wherein said exit passage comprises an exit channel formed in the outer surface of the gauge region, which channel is located adjacent the front surface of the blade whereby fluid may escape directly into said exit channel from the periphery of the vortex after having passed outwardly across the cutting elements.

3. A rotary drill bit according to Claim 2, wherein the part of said surface portion of the bit body which is adjacent said exit channel is inclined inwardly so as to face partly towards the longitudinal axis of rotation of the drill bit.

4. A rotary drill bit according to Claim 2, wherein the exit channel is shaped so as to increase in cross-section as it extends along the gauge region of the drill bit.

5. A rotary drill bit according to Claim 2, wherein a smoothly rounded edge region is provided between the exit channel and said surface portion of the bit body.

6. A rotary drill bit according to Claim 2, wherein the cutting elements are so disposed that said surface portion of the formation being drilled is smoothly and concavely curved immediately adjacent said exit channel, and said exit channel extends generally tangentially to said concavely curved surface portion of the formation.

7. A rotary drill bit according to Claim 1, wherein said exit passage extends through the bit body from an opening in said surface portion of the bit body, whereby fluid may escape through said passage and into the annulus from the periphery of the vortex.

8. A rotary drill bit according to Claim 7, wherein at least a portion of the vortex flow over said surface portion of the formation is in a direction inwardly towards the central axis of rotation of the drill bit, and wherein said opening in said surface portion of the bit body is so located that fluid may escape through said opening and into the exit passage after having passed inwardly across the cutting elements.

9. A rotary drill bit according to Claim 8, wherein said opening through which drilling fluid is delivered is so oriented with respect of said surface portions of the bit body and formation as to be directed towards the vicinity of the junction between said surface portions at the outer periphery of the bit.

10. A rotary drill bit according to Claim 7, wherein said surface portion of the bit body is smoothly and concavely curved immediately adjacent said opening into the exit passage, and said passage extends, at least initially, generally tangentially to said concavely curved portion of the bit body.

11. A rotary drill bit according to Claim 1, wherein substantially the whole of the surface portion of the bit body which bounds the aforesaid region in which the vortex is formed is smoothly and concavely curved.

12. A rotary drill bit according to Claim 1, wherein the cutting elements are so disposed that substantially the whole of the surface portion of the formation which bounds the aforesaid region in which the vortex is formed is smoothly and concavely curved.

13. A rotary drill bit according to Claim 12, wherein said surface portions of the bit body and the formation are of substantially equal and uniform curvature so that the region bounded thereby is substantially circular.

14. A rotary drill bit according to Claim 1, wherein a number of cutting elements are mounted along the junction between said outer and front surfaces of each blade.

15. A rotary drill bit according to Claim 1, wherein said number of cutting elements are arranged in a single row along each blade.

16. A rotary drill bit according to Claim 1, wherein the region adjacent the front surface of the blade within which the vortex is promoted is defined partly by a recessed portion of the leading face of the bit adjacent said surface.

17. A rotary drill bit according to Claim 16 wherein said recessed portion is bounded partly by a wall surface spaced forwardly away from said front surface of the blade and substantially parallel thereto.

18. A rotary drill bit comprising a bit body providing a leading face, a gauge region, and an annulus on the side of the gauge region remote from the leading face, a number of blades on the leading face, 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 number of cutting elements mounted along each blade, a delivery passage in the bit body for supplying drilling fluid to a number of openings in the leading face of the bit, and at least one exit channel formed in the outer surface of the gauge region for returning said drilling fluid past the gauge region to the annulus, at least one of the aforesaid openings being located in a region adjacent the front surface of a blade which region is bounded, when the bit is in use, partly by a surface portion of the bit body and partly by a surface portion of the formation being drilled, the opening being so orientated with respect to the said surface portions as to promote a vortex flow of drilling fluid around said region, with part of the periphery of the vortex extending across the cutting elements on the blade, at least a portion of the vortex flow over said surface portion of the formation being in a direction outwardly away from the central axis of rotation of the drill bit, whereby the fluid in the vortex reaches the outer periphery of the drill bit immediately after having passed outwardly across the cutting elements, there being provided an exit channel adjacent the front surface of the blade so that fluid may escape directly into said exit channel from the periphery of the vortex after having passed across the cutting elements, part of said surface portion of the bit body which is adjacent said exit channel being inclined inwardly so as to face partly towards the longitudinal axis of rotation of the drill bit.

19. A rotary drill bit according to Claim 18, wherein the exit channel is shaped so as to increase in cross-section as it extends along the gauge region of the drill bit.

20. A rotary drill bit according to Claim 18, wherein a smoothly rounded edge region is provided between the exit channel and said surface portion of the bit body.

21. A rotary drill bit according to Claim 18, wherein the cutting elements are so disposed that said surface portion of the formation being drilled is smoothly and concavely curved immediately adjacent said exit channel, and said exit channel extends generally tangentially to said concavely curved surface portion of the formation.

22. A rotary drill bit according to Claim 18, wherein substantially the whole of the surface portion of the bit body which bounds the aforesaid region in which the vortex is formed is smoothly and concavely curved.

23. A rotary drill bit according to Claim 18, wherein the cutting elements are so disposed that substantially the whole of the surface portion of the formation which bounds the aforesaid region in which the vortex is formed is smoothly and concavely curved.

24. A rotary drill bit according to Claim 23, wherein said surface portions of the bit body and the formation are of substantially equal and uniform curvature so that the region bounded thereby is substantially circular.

25. A rotary drill bit according to Claim 18, wherein a number of cutting elements are mounted along the junction between said outer and front surfaces of each blade.

26. A rotary drill bit according to Claim 18, wherein said number of cutting elements are arranged in a single row along each blade.

27. A rotary drill bit according to Claim 18, wherein the region adjacent the front surface of the blade within which the vortex is promoted is defined partly by a recessed portion of the leading face of the bit adjacent said surface.

28. A rotary drill bit according to Claim 27, wherein said recessed portion is bounded partly by a wall surface spaced forwardly sway from said front surface of the blade and substantially parallel thereto.