Note: Descriptions are shown in the official language in which they were submitted.
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DRILL STRING FITTING
This application is a division of Canadian Application
Serial No. 2,219,426, filed April 26, 1996.
Technical Field
The present invention relates to a fitting for reducing
friction between a drill string and the wall of a well.
More particularly, but not exclusively, in a first aspect
the present invention relates to a fitting having a
plurality of longitudinal recesses enabling lubrication
between the fitting and a drill string using drilling fluid.
According to a second aspect there is provided a fitting
having rotatable rollers to reduce both axial and rotational
friction. According to a third aspect there is provided a
fitting having an outer section rotatable relative to an
inner section secured about a drill string.
Background of the Invention
The depth to which and angle at which a well can be drilled
are often limited by the degree of friction experienced by
the drill string. The life of a drill string may also be
reduced due to friction. With increasing environmental
concerns it is also becoming less acceptable to reduce
friction by injecting chemicals down a well. Using
wellstream fluids as a lubricant results in drill string
wear due to particulate matter carried in the fluids.
Further, currently available similar fittings cannot be
rebuilt or reconditioned.
Disclosure of the Invention
In accordance with an embodiment of the present invention
there is provide a fitting for engagement with a drill
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string or further fitting comprising: an inner section for
se curement to a drill string or further fitting; an outer
section for securement about the inner section and rotatable
relative thereto; a bearing located between the inner
section and outer section; seals provided at either end of
the fitting between the inner section and outer section; and
pressure compensating means for maintaining the pressure
within the bearing substantially the same as the external
pressure; wherein the bearing comprises a layer of friction
reducing material.
Preferably, the pressure compensating is in the form of a
diaphragm.
In a preferred embodiment, the friction reducing material is
a plastics material, preferably a nylon.
In a preferred embodiment, the bearing comprises first
journal surfaces on the inner.and outer sections extending
in the axial direction of the fitting and second and third
journal surfaces on the inner and outer sections extending
radially outwards to restrict movement of the outer section
relative to the inner section in the axial direction.
A plurality of fins can be provided, said fins projecting
radially from the outer section, and being profiled to
reduce drag in the axial direction. Preferably, the fins
have a curved profile.
In a preferred embodiment, rollers are provided on the
periphery of the outer section to reduce friction in the
axial direction.
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Brief Description of the Drawings
Further aspects of the invention will become apparent from
the following description which is given by way of example
of possible embodiments with reference to the accompanying
drawings in which:
Figure 1: Shows a two part fitting having a polygonal bore.
Fi. ug re 2: Shows the interface between a drill string and the
interior polygonal bore of the fitting shown in
Figure 1.
IS
25
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Figure 3: Shows a section of drill string having
collars at either end for receiving the
fitting of Figure 1 therebetween.
Figure 4: Shows an end view of the fitting of
Figure 1.
Figure 5: Shows an end view of the fitting of
Figure 1 engaged with the sleeve shown in
Figure 3.
Figure 6: Shows a front view of the fitting of
Figure 1 showing a partial cross-
sectional view.
Figure 7: Shows a fitting having rotatable rollers
provided on the body thereof.
Figure 8: Shows a cross-sectional view of a
rotatable roller shown in Figure 7.
Figure 9: Shows a cross-sectional view of a roller
of a rotatable roller shown in Figure 7
or Figure 8.
Figure 10: Shows a perspective view of a fitting
according to a third embodiment.
Figure 11: Shows a cross-sectional view along the
axis of the fitting shown in figure 10.
Figure 12: Shows an enlarged view of the seal
arrangement shown in figure 11.
CA 02567346 2006-11-27
Best mode for carrvinQ out the invention
Referring firstly to Figures Z to 6, there is shown a
fitting for reducing friction on a pipe string. The
fitting comprises a body formed of two parts 1 and 2
which may be secured together by bolts which pass
through apertures 3. A plurality of rollers 4 are
provided about the outside of the fitting to reduce
longitudinal friction on the pipe string. The bore 5
of the body sections is polygonal so as to provide a
number of longitudinal recesses 6 between the body 1
and a sleeve 7.
Drilling pipe is usually forged from high tensile
steel. The outside surface is typically rough. The
preferred method of securing the fitting of the
invention to a drilling pipe is as follows. Firstly,
a section of the drilling pipe is machined so as to
have a relatively smooth outside surface. The two
halves 7a and 7b of the sleeve shown in Figure 3 are
then secured to the drilling pipe by bolts etc.
passing through the apertures of collars 8a, 8b, 9a
and 9b. Once the sleeve has been secured to a
section of pipe, the two halves 1 and 2 of the
fitting are secured about sleeve portions 7a and ?b
and secured by bolts passing through apertures 3.
Collars 8 and 9 restrict the longitudinal movement of
the fitting. The fitting is however free to rotate
about sleeve 7. Accordingly, friction due to
rotation of the drilling rig is minimised due to the
fluid lubricant provided in recesses 6 between body
sections 1 and 2 and sleeve 7. Axial friction is
reduced by rollers 4 which minimise friction between
the wall of the well and the fitting in the
longitudinal direction.
CA 02567346 2006-11-27
It ooo~ald 3~e possible to secure tho Fitting directl5~
about a section of pipe. This~wou3d however. not
reduces friction to the sane; extent a9 by providing
smooth GIGeVe ~ . Where a neat ruction of. pips is
5 being maaaufaCtllz~ed. IL, ma5~ of Cour~c be proi~tded with
a smooth section having gcparate col,ya~CS 8 and 9
i»teeaxally 1'ortned at either end l;horeof fo7~ f~;cciting
the fittiaag.
rlthough the interior bore 5 aL the fittialg has been
10 described an pn7.y~goril~l, it mill be appreciated that
ol:3aCr shapes of interndl borC (eg: ~i,riuBOidal~ may~ by
prcyvi.r3ed as long as suitable, r<:a~cases are provided
batw8ea the sleeveEt and bhe body Of. >~ho fitting to
m#,tZStttise friction. Tn same tipplication~e Bhm bore ~3
~.5 of the fitting rna~~ be t3piralled to uiiriiu~ise the
effect Of tZ'tenait3ona fxOttl orie receBB t0 tirioth.er and
to promote L'lu3d Flow through the fitting. Piltering
means, such. as trite a~ssh may prCferably be provided
at elLher and of the fitting to prevent large debris
20 ent$rsng the xeGesf3es.
Ia vie~rr~.nd' Figui~a S it x~,Zl bo seen thaC oaah roller
4 is secured to body i by a pin 10 passing through
roller 4 , Pin. io tltRy peas through apssrture 12 ilt
body 1 ~.nto Z~eCCss 11. 1'tte aperture 1.2 may bhen be
3s melded aloacd to preterit the pin 10 be l~omovad.
~to7,ler 4 tray preferablg be formed of a cQrarnic or
ieylcn material. GCratuic rnatexials have tlae advtiribage
that thoy exhibit exoellCnt wear px'opCrtiea and leave
a loov friction aeefficient. Newly developed aeramice
3o have .soCeptablt "duct3litg" properties and 8ro easily
formed. Ceravmics arc also very Etx~bl~ at high
temptxztturos and are sel# lulsricating, ~so do not
require oil-based lubricatioat. Cera~nica rnater~.a~la
axe riot susceptible to xheolagical fsiltire ar w~eld~,T7g
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either. One of the key advantages, however, is that
the density of ceramic materials is such that if a
roller breaks the pieces can be circulated out of the
well bore, unlike steel fragments which sink to the
bottom of the well and interfere with drilling.
As shown in Figure 6 a protective section 13 may be
provided between the collars 8a, 8b and 9a, 9b and
between the rollers 4 to create a smooth exterior
profile so that parts of the fitting do not catch as
the fitting is moved up and down in a well.
It is estimated that using fittings as herein before
described about drill pipe joints will reduce the
drag by at least 30%. This enables wells to be
drilled to greater displacements and at higher
angles. Further, expensive drill pipe is protected
and the fitting is exposed to most of the wear. The
fitting'is designed for easy retrofitting to existing
pipe and so avoids the need for large expenditure on
new pipe strings.
Figures 7 to 9 show a second embodiment of the
invention. The aim again is to reduce longitudinal
and rotational friction on a pipe string or fittings
employed therewith. A simple one part construction
is described although it will be appreciated that a
two part body as previously described, may be
employed.
Body 20 is provided with a plurality of rotatable
roller means 21, shown in more detail in Figure 8.
Rotatable roller means 21 are substantially
disc-shaped and have a cylindrical recess 22 located
at the centre thereof. Pin 23 of body 20 engages in
recess 22 so that the rotatable roller means 21 is
rotatable about pin 23. Circumferential flange 24 is
secured after roller means 21 has been inserted and
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retains the collar means 27, in place in use.
Circurnferential flange 24 may be se~_t~re~d fi:znly in
place by welding otc. The rotatak~lc rollers 25 ame
secured off-centre ir'Ot6 pin 23 so that the rotatahl.e
ro3ler means 21 gay be roCt2tod as it i.o eRposad to
different types o~ fi-icCj.01itx1 rOrce (i.e.
].Orig7.tudinal Or i"Ot&t;ianal) _
Front the above it will be apparent: that when bpdy 30
experiences peire Notation relative to the sra73 0~ a
10 vre:ll, xollera .~~ aat3.l riot bo able to rOt&l:e (in the
position shown in Ffgure 9) arid will cause the
rOtntable iroller means 21 to rotate 90° so that the
axeo OF the rollers are alfgned p~.t:h Lho axis o~ the
drilling rig. l'Phen iYl i:his positipn, the collars can
15 fro~ly rotate to minimise friot:ian. lateen the drill
str3.ngr is~ ~novcd purely in the longitudinal direetian.
the ro11ex8 will stay in the posir9,on a~ shown in
Pigurc 7 so That they may ~Lecly rotate to raduun
loxvgita~a~.rial friction. It v.ill be apprcoiated that
20 u~hCri t:hare is a combinar.~.ori Of rotational pl9d aicfa3.
movemem the axis pt the rol3era will he ~Ornavohere
beteateen the two positions desatibod abacus.
Re~arring to Figures 10 to 12 a third srnbo3iment vti.ll
be d~acribed. The fitting of the third ernbo3iment
3~ comprises tin ixrner section 30 arid an outer BeCtion 3i
which is xotRtab3.e about inner seCLiOn 30, inner
setCLieri 30 is adapted to be se0ared about a drill
pipe orhich passes Through bore 33. Inner section 30
may be ef taro part eonatrnot~,on (9imilar to that
30 sfzamn in figufe 3) tvhere the two partG are secured
tagethgr by bolts or similar fa$tening mesas. Outer
section 37. may similarly be of tvro part comstxuctiot~
arid b~ assured about irinGr section 30, Outer section
3l is provided with a plurality of fins 33 extending
3s radia.l3y i'ratrt body 34.
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Figure 11 shows a cross-sectional view along the axis
of the fitting shown in figure 10. In this case the
fitting is secured to a drill pipe 35. A layer of
friction reducing material 36 is provided between
faces 42 to 47 to reduce friction as outer section 31
rotates about inner section 30. Layer.36 will
preferably be formed of a plastics material such as
nylon (zytel 70633L for example).
Seals 37 and 38 are provided at either end of the
bearing formed by the inter-engaging faces 42 to 47
of inner section 30 and outer section 31 and friction
reducing layer 36. These seals serve to prevent the
ingress of fluid from a well into the bearing. This
greatly reduces friction on bearing surfaces, thus
reducing wear and decreasing the torque required to
drive a drill string.
Due to the.sealed nature of the bearing a pressure
compensating system 39 is provided to compensate the
pressure within the bearing as the external pressure
varies. The pressure compensating system comprises a
diaphragm 40 containing grease within region 41 which
moves in and out of the bearing as external pressure
varies. This prevents external fluid being drawn
into the bearing as the external pressure increases.
The bearing journals 42 and 43 are preferably
precision ground. Bearing sleeves may be provided if
required. Sections 44 and 45, and 46 and 47 of the
bearing minimise friction when the outer section 31
~is forced in the axial direction relative to the
inner section 30.
Referring now to figure 12, seal 37 is shown in
detail. The seal is seen to include a resilient seal
48 located within a recess 49 in outer section 31.
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3aal 48 it pxetcrab7.y formed of ~a fibre reinforced
p'1 FE .
she profile of the Eina 33 is shos~rn to xte penti-
circular is tigm'~CS 10 atld 11. It is to be
appreciatsd that Other profiles txlriy be employed tY]7p.ch
reduce drag in the axial dixection. The ourved
grofile shot9t5 is preferred sup tn 3t~: cifag reduction
:in bdth dl,ractiane. It is to be appreciated Chat
rollers cars,ld be pi-aviaed upori fins 31 to assist in
thr_> rrdttGrS.on of asa.al drag. ThP fi.na arw pr~~.fe~zaWly
coated with Q ccrautio aOaLirig suLh u3 CERl~i-I(OTE"'.
Bearing surfaces 42 to 4T are preferably coated ~rr~,t]t
a hard mat~rinl such as TeChnogeriiec "Ceclmepoudre" or
similar. Channels axe p~ceferably provided in bearing
t~urfdC:ea a2 and h3 to facilitate the floor o~
lubricant. These channels orill preferably be sern~,-
cirGttlar in pro~i7,e and o~il~. preferably spiral alonq
the lenqti~. of the jotfrnals (similar to the rece8se8 G
eh4wi7 is figure a1.
2o Thisr fitting tttay bt mounted dircotly amto a drill
pipe during product~.on or tray be retrafittad to art
existing drill pips. Alternativell~, the fl.tting flay
be pravidEd on its otrn sepa~ratn ~sub~ or mandrill, in
ovhich case the "sub" or tuandrill may be ACreNed into
the drill etririg bett<'ecct Cwo lengths of drill pipe.
It rovill thus be seen that the imrentian pi~OVidts S
... numbVr of simple inexpensive fittings for reducing
the friction experienced 3tetsceea a drill. Btx'ing tW d
the wall of a yrell. Tits iitainga may ba use3 to
protect the ~ointa of pipe strings ox f3Gt~.ng toCls
as required. The SnvenGion rcduCes friction and tlxus
the required torque to dr~.l,1 a o?ell. RaduCtfaw of
frl4tion slab rvduCda drill string vibration and thus
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fatigue in the drill string. The invention also
minimises environmental damage by using a water-based
mud lubricant.
Where in the foregoing description reference has been
made to integers or components having known
equivalents then such equivalents are herein
incorporated as if individually set forth.
Although this invention has been described by way of
example and with reference to possible embodiments
thereof, it is to be appreciated that improvements
andJor modifications maybe made thereto without
departing from the scope of the invention as defined
in the claims.
Industrial apglicabilitv
The present invention may find particular application
in the reduction of friction experienced by drilling
strings.
