CA2567346C - Drill string fitting - Google Patents

Abstract

A fitting for engagement with a drill string or further fitting comprising an inner section for securement to a drill string or further fitting and an outer section for securement about the inner section and rotatable relative thereto. A bearing is located between the inner section and outer section. Seals are 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. The bearing comprises a layer of friction reducing material.

Description

, , ,i ~ i ~. "~ , " , 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

- 2 -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.

CA 02567346 2006-11-27 ,

- 3 -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

- 4 -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.

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.

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 CA 02567346 2006-11-27 , _ 7 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 _ g 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.

i i il ~ i n i ii i ii _ g _ 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.

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 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.

Claims (8)

CLAIMS:

1. A fitting for engagement with a drill string or further fitting comprising:
an inner section for securement to a drill string or further fitting;
an outer section for securement about said 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.

2. The fitting as claimed in claim 1, wherein the pressure compensating means is in the form of a diaphragm.

3. The fitting as claimed in claim 1 or 2, wherein the friction reducing material is a plastics material.

4. The fitting as claimed in claim 1, 2 or 3, wherein the friction reducing material is nylon.

5. The fitting as claimed in any one of claims 1 to 4, wherein the bearing comprises first journal surfaces on said inner and outer sections extending in the axial direction of said fitting and second and third journal surfaces on said inner and outer sections extending radially outwards to restrict movement of said outer section relative to said inner section in the axial direction.

6. The fitting as claimed in any one of claims 1 to 5, wherein a plurality of fins project radially from said outer section which are profiled to reduce drag in the axial direction.

7. The fitting as claimed in claim 6, wherein the fins have a curved profile.

8. The fitting as claimed in any one of claims 1 to 7, wherein rollers are provided on the periphery of said outer section to reduce friction in the axial direction.