GB2360305A

GB2360305A - Friction reducing drillstring component

Info

Publication number: GB2360305A
Application number: GB0106480A
Authority: GB
Inventors: Gholam Hossein Rastegar
Original assignee: OFFSHORE RENTALS Ltd
Current assignee: OFFSHORE RENTALS Ltd
Priority date: 2000-03-16
Filing date: 2001-03-16
Publication date: 2001-09-19
Also published as: GB2360305A9; US20020129976A1; GB0006218D0; EP1162344A1; GB0106480D0

Abstract

A friction and/or torque reducing drillstring component has a one piece mandrel body 5 with a mandrel body recess 13c considerably smaller than mandrel upper neck 13a and mandrel body lower neck 13b, dressed with an outer sleeve 18 which is interlocked with a two piece inner bearing 20 through several integral dove-tailed splines 22b and grooves 22a. The combination of the outer sleeve 18 and inner bearing 20 is restricted in vertical movement over the said mandrel body 5 by an integral, optionally spirally, bladed first stop 15 and a removable second stop 16. The removable second stop 16 is locked onto the mandrel body upper neck 13a by means of threaded retaining bolts (24, fig 4). Once the second stop 16 is removed, the one piece outer sleeve 18 is retractable over the mandrel body upper neck 13a to allow the removal of the two piece inner bearing 20. A second inner bearing (155, fig 12) may also be provided.

Description

2360305 1 1 -Friction Reducing Drillstring Component" 2 3 This invention

relates to equipment used on a 4 drillstring to reduce the rotational friction 5 between the rotating drillstring and the borehole 6 wall. The said equipment is particularly useful in 7 the oil, gas and mining industries especially, but 8 not exclusively, for drilling of high angle, 9 horizontal and extended reach wells. 10 11 In order to drill a well, a drillstring is assembled 12 above a drill bit. The drillstring is used to 13 transfer the rotary motion from the surface 14 equipment to the drill bit, thereby causing the is drill bit to rotate and penetrate the sub surface 16 formation. However, the torque required at surface 17 to rotate the drill bit is substantially increased 18 due to the friction caused by contact between the 19 drillstring and the wall of the borehole. 20 Furthermore, the rotational contact between the 21 drillstring and the borehole wall causes wear on 2 1 drillstring as well as causing damage and wear to 2 the steel cased section of the borehole wall. 3 Conventionally, the drilling process also involves 4 pumping of drilling fluid down the bore through the 5 inside diameter of the drillstring to improve the 6 drilling performance of the bit, to assist with 7 cooling and lubrication of the bit as well as 8 providing the means to transfer the drill cuttings 9 to surface. Conveyance of the drill cuttings is a 10 function of well depth, well profile, shape and size 11 of drill cuttings, mechanical properties of the 12 drilling fluid and the capacity of surface mud 13 pumps. 14 is Conventional friction reducing drill pipe components 16 are shown, for example, in UK Patent nos. 2299598 17 and 2304763. 18 19 As those skilled in the art will appreciate, an 20 accumulation of drill cuttings in the well bore is a 21 major obstacle in any drilling operation as it can 22 increase downhole friction, thus increasing the 23 amount of torque required, and in some instances can 24 lead to the drillstring getting stuck in hole. For 25 these reasons, efficient drilling fluid circulation 26 is essential. 27 28 According to the present invention, there is 29 provided a component for forming part of a drill 30 string, the component comprising a mandrel having 31 couplings for connection with the drill string, a 3 1 bearing member mounted on the mandrel and a sleeve 2 member mounted on the bearing member. 3 4 Preferably, the bearing member is an inner bearing 5 member, and the sleeve member is an outer sleeve 6 member. 7 8 Preferably, the component further comprises first 9 and second retaining members for retaining the inner 10 bearing member, and the outer sleeve member on the 11 mandrel. Typically, the retaining members also 12 prevent longitudinal movement of the inner bearing 13 member, and the outer sleeve member, on the mandrel. 14 Typically, at least one of the first and second is retaining members is removable or retractable from 16 the mandrel, and more preferably, is removable or 17 retractable from the mandrel to permit the inner 18 bearing member, and the outer sleeve member, to be 19 removed from the mandrel. Most preferably, one of 20 the first and second retaining members is removable 21 from the mandrel by removing one or more fixture 22 devices, and typically, the other of the first and 23 second retaining members is integral with the 24 mandrel. 25 26 Preferably, the inner bearing member is provided in 27 at least two portions, the portions preferably when 28 brought together forming a substantially tubular 29 member. More preferably, there are two portions, 30 each portion comprising a half cylindrical member. 31 Preferably, the at least two portions are mounted in 32 a recess of the mandrel, the recess comprising a 4 1 reduced diameter portion with reference to the 2 diameter of the drill string, and particularly to 3 the diameter of the joints of the drill string. 4 Typically, the outer sleeve member is arranged 5 coaxially with the inner bearing member in use of 6 the component, and preferably, a selective locking 7 mechanism is provided to prevent relative rotational 8 movement between the inner bearing member and the 9 outer sleeve member in use of the component. The 10 selective locking mechanism may comprise a first 11 locking device provided on the inner bearing member 12 and a second locking device provided on the outer 13 sleeve member. Preferably, the first locking device 14 is provided on the outer surface of the inner is bearing member and the second locking device is 16 provided on the inner surface of the outer sleeve 17 member. More preferably, the first and second 18 locking devices interact with one another to provide 19 the locking action. Typically, the first and second 20 locking devices are formations provided on the 21 respective surfaces of the inner bearing member and 22 outer sleeve member, and more preferably, the 23 formations are arranged longitudinally at least 24 partly along the length of the respective inner 25 bearing member and outer sleeve member. Optionally, 26 a third locking device, which may be in the form of 27 a key, may be provided to interact with the first 28 and second locking devices to provide the locking 29 action. 30 31 Preferably, the component further comprises a second inner bearing member which is typically provided in 1 at least two portions, the portions preferably when 2 brought together forming a substantially tubular 3 member. More preferably, there are two portions, 4 each portion comprising a half cylindrical member. 5 Preferably, the at least two portions are mounted in 6 the same recess of the mandrel that the two portions 7 of the first inner bearing member are mounted. 8 Preferably, the first and second bearing members 9 each comprise a device which separates the outer 10 sleeve member from the mandrel. Typically the 11 separating device is a flange. 12 13 Preferably, the first inner bearing member is 14 capable of rotation with respect to the second inner is bearing member. 16 17 Preferably, a selective locking mechanism is 18 provided to prevent relative rotational movement 19 between the second inner bearing member and one of 20 the first and second retaining members in use of the 21 component. The selective locking mechanism may 22 comprise a first locking device provided on the 23 second inner bearing member and a second locking 24 device provided on the said one of the retaining 25 members. Preferably, the first locking device is 26 provided on the outer surface of the second inner 27 bearing member and the second locking device is 28 provided on the inner surface of the said one of the 29 retaining members. More preferably, the first and 30 second locking devices interact with one another to 31 provide the locking action. Typically, the first 32 and second locking devices are formations provided 6 1 on the respective surfaces of the second inner 2 bearing member and said one of the retaining 3 members, and more preferably, the formations are 4 arranged longitudinally at least partly along the 5 length of the respective second inner bearing member 6 and said one of the retaining members. Optionally, 7 a third locking device, which may be in the form of 8 a key, is provided to interact with the first and 9 second locking devices to provide the locking 10 action. 11 12 Preferably, the outer sleeve member is a one-piece 13 outer sleeve member. Preferably, the mandrel is a 14 onepiece or unitary mandrel body. is 16 The component may be dismantled by removing one of 17 the retaining devices and removing, if present, the 18 second inner bearing member, and then removing the 19 outer sleeve member over one end of the mandrel, and 20 then removing the first inner bearing member. A 21 section of the mandrel directly above and/or below 22 the first and/or second retaining member may be 23 spirally milled and fluted to provide integral 24 spiral blades. 25 26 Preferably, the mandrel, stops, outer sleeve member, 27 inner bearing member(s) and the retaining devices 28 are made of steel, but the inner bearing member(s) 29 and/or outer sleeve member may also be made from 30 high temperature/high impact/wear resistant 31 ceramics, such as alumina ceramic, polymers or 32 metals other than steel.

7 2 Embodiments of the present invention will now be 3 described, by way of example only, with reference to 4 the accompanying drawings, in which:

6 Fig. 1 shows a cross sectional view of a 7 mandrel body forming part of a first embodiment 8 of the present invention; 9 Fig. 2 shows a side view of the mandrel body of Fig. 1 provided with an outer sleeve member and 11 a pair of inner bearing members together 12 forming the first embodiment of the present 13 invention; 14 Fig. 3 shows a cross-sectional plan view is through section 3-3 of the mandrel body, outer 16 sleeve member and inner bearing member of Fig.

17 2; 18 Fig. 4 shows a cross-sectional plan view 19 through section 4-4 of the mandrel body, and second retaining member of Fig. 2; 21 Fig. 5 shows a cross sectional view of a 22 mandrel body forming part of a second 23 embodiment of the present invention; 24 Fig. 6 shows a side view of the mandrel body of Fig. 5; 26 Fig. 7 shows a plan view through section C-C of 27 the mandrel body of Fig. 6; 28 Fig. 8 is a cross sectional view of one of a 29 pair of first inner bearing members for mounting on the mandrel body of Fig. 5; 31 Fig. 9 is a side view of the one f irst inner 32 bearing member of Fig. 8; 8 1 Fig. 10 is a first end view of the one first 2 inner bearing member of Fig. 8; 3 Fig. 11 is a second end view of the one first 4 inner bearing member of Fig. 8; Fig. 12 is a side view of one of a pair of 6 second inner bearing members for mounting on 7 the mandrel body of Fig. 5; 8 Fig. 13 is a cross sectional view of the one 9 second inner bearing member of Fig. 12; Fig. 14 is a f irst end view of the one second 11 inner bearing member of Fig. 12; 12 Fig. 15 is a second end view of the one second 13 inner bearing member of Fig. 12; 14 Fig. 16 is a side view of a locking ring for is mounting on the mandrel body of Fig. 5; 16 Fig. 17 is a first end view of the locking ring 17 of Fig. 16; 18 Fig. 18 is a second end view of the locking 19 ring of Fig. 16; Fig. 19 is a side view of an outer sleeve for 21 mounting on the mandrel body of Fig. 5; 22 Fig. 20 is a side view of a cross section 23 through the outer sleeve of Fig. 19; 24 Fig. 21 is a first end view of the outer sleeve of Fig. 19; 26 Fig. 22 is a side view of a rectangular 27 longitudinal groove formed on the inner bore of 28 the outer sleeve of Fig. 19; 29 Fig. 23 is a plan view of a cross section through the outer sleeve of Fig. 19; and 31 Fig. 24 shows a side view of a cross section 32 through the mandrel body of Fig. 5 provided 9 1 with an outer sleeve member and a pair of first 2 inner bearing members and a pair of second 3 inner bearing members together forming the 4 second embodiment of the present invention.

6 A mandrel body 5 forming part of a first embodiment 7 of a friction reducing drill string component 1 in 8 accordance with the present invention is shown in 9 Fig. 1. The mandrel body 5 comprises a male pin end 10 and female box end 11, both of which 10, 11 are 11 provided with standard API screw threads to permit 12 the mandrel body 5 to be included in a drill string 13 (not shown). The mandrel body 5 further comprises a 14 mandrel bore 12, mandrel body upper neck 13a, is mandrel body lower neck 13b and a mandrel body 16 recess 13c, a threaded bore 14 and an integral first 17 stop 15. Accordingly, the mandrel body 5 is a one 18 piece component. It should be noted that the first 19 stop 15 may be lengthened, and also that the first stop may be spirally milled on it's outer surface to 21 form integral blades proposed for hydra -mechanical 22 and hydra-dynamic drill cuttings bed removal.

23 24 Fig. 2 illustrates the assembly arrangement of an outer sleeve 21, inner bearing members 20 and 26 retaining systems 15, 16 in place on the mandrel 27 body 5 to form the friction reducing drill string 28 component 1 in accordance with the present 29 invention. Also shown in Fig. 2 are a removable second stop 16 having circular access ports 17, a 31 one piece outer sleeve 18 which is preferably 32 provided with straight or spiral blades 21, a two- 1 piece inner sleeve 20 flanged at it's lower end, 2 longitudinal dovetailed grooves 22a formed on the 3 inner surface of the outer sleeve 18, and 4 longitudinal dove-tailed integral splines 22b formed 5 on the outer surface of the inner bearing members 6 20. The second stop 16 is in the form of an annular 7 ring 16. It should be noted that the dove-tailed 8 splines 22b and grooves 22a preferably do not extend 9 the entire length of the sleeves. 10 11 As shown in Figs. 2 and 3, the inner bearing members 12 20 are formed from two half-cylinder shaped inner 13 bearings 20a and 20b. 14 is In order to assemble the friction reducing drill 16 string component 1, the inner bearing members 20a, 17 20b and are positioned around the mandrel body 5 18 within the mandrel body recess 13c, such that the 19 f lange is arranged at the lower in use end of the 20 component 1. 21 22 Thereafter, the one piece outer sleeve 18 is slid 23 over the mandrel body upper neck 13a. After lining 24 up the dove- tailed grooves 22a with the dove-tailed 25 splines 22b, outer sleeve 18 will slide over the 26 inner bearing members 20 in a downward sliding 27 manner until the lower end of the outer sleeve 18 28 rests directly on top of the f langed end of the 29 inner bearing members 20. The second stop 16 is 30 then slid over the mandrel body upper neck 13a and 31 is lowered downwardly toward the outer sleeve 18 32 until each access port 17 lines up with it's 1 corresponding threaded bore 14. The second stop 16 2 is then secured on mandrel body upper neck 13a as 3 illustrated in Fig. 4. 4 5 As shown in Fig. 3, the dove-tailed fitting 6 arrangement of the outer sleeve 18 over the inner 7 bearing members 20 prevents relative circumferential 8 movement between the inner bearing members 20 and 9 the outer sleeve 18. 10 11 As shown in Fig. 4, the second stop 16 is secured to 12 the mandrel body upper neck 13a by means of a number 13 of threaded retaining bolts 24 protruding through 14 the respective circular access port 17, fitted and 15 screwed into each corresponding threaded bore 14 and 16 tightened to a specified torque. A locking clip 26 17 is then f itted into a locking clip recess 25 on each 18 circular access port 17, this being a secondary 19 safety measure to prevent the threaded locking bolt 20 24 from accidental unwinding and dislodgement. 21 22 When the outer sleeve 18 and inner bearing members 23 20a, 20b are mounted on the mandrel body 5, and 24 secured in position by the retaining devices 16, 15, 25 the outside diameter of the outer sleeve 18 is 26 sufficiently greater than the outside diameter of 27 the drill pipe tool joints (not shown) which form 28 the rest of the drill string. In this manner, when 29 the friction reducing drill string component 1 is 30 installed in the drill string, only the outer 31 surface of the outer sleeve 18 will contact the 32 wellbore wall and the drill pipe tool joint is not 12 1 in contact with the wellbore wall. During the 2 rotary drilling operation, the outer sleeve 18 is in 3 contact with the bore wall and does not rotate 4 whilst the mandrel body 5 rotates with the drillstring. Therefore there will be no rotational 6 contact between the drillstring and the wellbore 7 wall, and this ensures the protection of drillstring 8 as well as the steel cased section of the well 9 against damage and wear. On the other hand, the outside diameter of the mandrel body recess 13c here 11 referred to as ld, is smaller than the outside 12 diameter of drill pipe tool joint here referred to 13 as 'D. Hence, in rotary drilling mode the rotary 14 surface contact circumference of the drillstring is effectively reduced by n x (D-d) In other words, 16 the torque or friction created is reduced. In 17 addition, the first embodiment of the component 1 18 has the advantage that the pair of inner bearing 19 members 20 can be formed from a different, and preferably less expensive material, than the outer 21 sleeve 18 and in this manner, the inner bearing 22 members 20 can be designed to be sacrificed and 23 replaced when required.

24 Referring now to Figs. 5 to 24, a mandrel body 105 26 forming part of a second embodiment of a friction 27 reducing drill string component 100 in accordance 28 with the present invention is shown in Fig. 5. The 29 mandrel body 105 again comprises a male pin end 110 and female box end 111 in a similar fashion as the 31 mandrel 5. The mandrel body 105 also comprises a 32 mandrel bore 112, mandrel body upper neck 113a, 13 1 mandrel body lower neck 113b, and a mandrel body 2 recess 113c, a number of threaded bores 114 and an 3 integral first stop 115. It will be noted that the 4 integral first stop 115 formed in the mandrel body 5 105 is above the mandrel body recess 113c, whereas 6 the integral first stop 15 formed in the mandrel 7 body 5 of the first embodiment is below the mandrel 8 body recess 13c. Accordingly, the mandrel body 105 9 is again a one-piece component. The first stop 115 10 is spirally milled on its outer surface to form 11 integral blades 150 for hydra -mechanical and hydra12 dynamic drill cuttings bed removal. 13 14 Fig. 24 illustrates the assembly arrangement of an 15 outer sleeve 121, a pair of first inner bearing 16 members 120 flanged at their upper ends, a pair of 17 second inner bearing members 155 flanged at their 18 upper ends and retaining systems 115, 116 in place 19 on the mandrel body 105 to form the friction 20 reducing drill string component 100 in accordance 21 with the second aspect of the present invention.

22 Also shown in Fig. 24 is a removable second stop 116 23 having circular access ports 117 (shown in Figs. 16 24 to 18), a one piece outer sleeve 118 which is provided with spiral blades 121. longitudinal 26 rectangular shaped grooves 122a formed on the inner 27 surface of the outer sleeve 118. and longitudinal 28 rectangular grooves 122b formed on the outer surface 29 of the first pair of inner bearing members 120, and longitudinal rectangular grooves 122c formed on the 31 outer surface of the second pair of inner bearing 32 members 155.The second stop 116 is in the form of 14 1 an annular ring 116, and is provided with 2 longitudinal rectangular grooves 122d formed on its 3 outer surface. It should also be noted that the 4 rectangular grooves 122a, 122b, 122c and 122d 5 preferably do not extend the entire length of the 6 respective outer sleeve 118, first pair of inner 7 bearing members 120, second pair of inner bearing 8 members 155 and second stop 116. 9 10 As shown in Figs. 8 to 11, the first pair of inner 11 bearing members 120 are formed from two half12 cylinder shaped inner bearings 120, and as shown in 13 Figs. 12 to 15, the second pair of inner bearing 14 members 155 are formed from two half-cylinder shaped is inner bearings 155. 16 17 In order to assemble the friction reducing drill 18 string component 100, the first pair of inner 19 bearing members 120 are positioned around the 20 mandrel body 105 within the mandrel body recess 21 113c, such that the flange is arranged at the upper 22 in use end of the component 100. A rectangular 23 longitudinal key (not shown) is then placed into 24 each groove 122b of the first pair of inner bearing 25 members 120. 26 27 Thereafter, the one piece outer sleeve 118 is slid 28 over the mandrel body lower neck 113b. After lining 29 up the rectangular grooves 122a with the rectangular 30 longitudinal keys, the outer sleeve 118 is slid over 31 the inner bearing members 120 in an upward sliding 32 manner until the upper end of the outer sleeve 118 is 1 rests directly against the underside of the flanged 2 end of the first pair of inner bearing members 120. 3 4 The second pair of inner bearing members 155 are 5 then positioned around the mandrel body 105 within 6 what is left open of the mandrel body recess 113c, 7 such that the f lange of the second pair of inner 8 bearing members 155 is arranged at the lower end of 9 the outer sleeve 118 and the f irst pair of inner 10 bearing members 120. 11 12 A rectangular longitudinal key (not shown) is then 13 placed into each groove 122c of the second pair of 14 inner bearing members 155. is 16 The second stop 116 is then slid over the mandrel 17 body lower neck 113b and, after lining up the 18 rectangular grooves 122d with the rectangular 19 longitudinal keys, the second stop 116 is slid over 20 the second pair of inner bearing members 155 in an 21 upward sliding manner toward the flange of the 22 second pair of inner bearing members 155 until each 23 access port 117 lines up with it's corresponding 24 threaded bore 114. The second stop 116 is then 25 secured on mandrel body lower neck 113b with 26 suitable threaded retaining bolts (not shown) and 27 associated locking clips (not shown). 28 29 As shown in Fig. 5, the mandrel body 115 is provided 30 with a further circumferential groove or recess 31 113d, around which a metal circlip (not shown) may 32 be fitted.This further metal circlip and recess 16 1 113d provides a tertiary safety mechanism to prevent 2 the dislodgement of the second retaining system (in 3 the form of the second stop 116) if the primary 4 safety mechanism (in the form of the bolts) and 5 secondary safety mechanism (in the form of the 6 associated locking clips) were to fail. 7 8 The rectangular fitting arrangement between the 9 grooves 122a of the outer sleeve 118, the 10 rectangular keys and the grooves 122b of the first 11 pair of inner bearing members 120 prevents relative 12 circumferential movement between the first pair of 13 inner bearing members 120 and the outer sleeve 118. 14 Also, the rectangular fitting arrangement between is the grooves 122d of the second stop 116, the 16 rectangular keys and the grooves 122c of the second 17 pair of inner bearing members 155 prevents relative 18 circumferential movement between the second pair of 19 inner bearing members 155 and the second stop 116. 20 21 Accordingly, the second embodiment of the component 22 100 has the advantage that the first 120 and second 23 155 pairs of inner bearing members can be formed 24 from a different, and preferably less expensive 25 material, than the outer sleeve 118 and in this 26 manner, the first 120 and second 155 pairs of inner 27 bearing members can be designed to be sacrificed and 28 replaced when required. In addition, when the outer 29 sleeve 121 contacts the wellbore wall, no portion of 30 the mandrel 115 is in direct contact with the outer 31 sleeve 118, and since the outer sleeve 118 is 32 preferably formed from a relatively hard wearing 17 1 material, the lifespan of the mandrel body 115 is 2 increased. In addition, it is only the first 120 3 and second 155 pairs of inner bearing members that 4 provide the bearing surfaces with the mandrel 115, 5 and so the material from which they are formed can 6 be chosen to be less likely to damage the mandrel 7 body 115. In other words, it is only the first 120 8 and second 155 pairs of inner bearing members that 9 are in direct contact with the mandrel body 115 and 10 the outer sleeve 121 is not in direct contact with 11 the mandrel body 115. 12 13 Thus, the embodiments of the present invention 14 provide a robust, fail safe mechanical. non-rotating 15 stand-off on the drillstring so as to remove the 16 rotational contact between the drillstring and the 17 bore wall and therefore prevent damage or wear of 18 drillstring and the cased section of the bore. The 19 embodiments described herein also provide a means to 20 reduce the rotational friction surface area of the 21 drillstring, and therefore reduce the torque 22 required to rotate the drill string at the surface. 23 Furthermore, the embodiments described herein also 24 provide a combined hydra -mechanical and hydra 25 dynamic means of agitating the cuttings bed in order 26 to improve the drilling fluid circulation. 27 28 Furthermore, the embodiments of the present 29 invention provide the advantage that they allow for 30 removal of the outer sleeve 18; 118 without 31 dismantling of the mandrel body 5; 115 or outer 32 sleeve18; 118 or heat expansion of the outer sleeve 18 1 18; 118 and yet allow the effective inside diameter 2 of the rotatable part of the component 1; 100 that 3 is the combination of the inner bearing member 20; 4 120 and the outer sleeve 18; 118 to be smaller than the outside diameter of the upper and lower ends of 6 the mandrel body 5; 115, hence providing a smaller 7 bearing surface area between the inner bearing 8 member 20; 120 and the mandrel body 5; 115 which 9 results in lowered friction and torque. These features make the embodiments of the present 11 invention a fail safe, easy to disassemble and re- 12 assemble drillstring component 1; 100 which reduces 13 drilling torque due to the reduced friction surface 14 area between the rotatable part of the component 1; 100 (the combination of the inner bearing member 20; 16 120 and the outer sleeve 18; 118) and the mandrel 17 body 5; 115. 18 19 Modifications and improvements may be made to the embodiments hereinbefore described without departing 21 from the scope of the invention. For instance, the 22 mandrel body 5; 115 may take the form of a full 23 length (range 1 being 20 foot in length, range 2 24 being 31 foot in length or range 3 being 40 foot in 25 length) drillpipe (not shown), or may take the form 26 of drillpipe pup joints (not shown) of any length.

19

Claims

1 CLAIMS:

2 3 1. A component for forming part of a drill string, 4 the component comprising a mandrel having couplings for connection with the drill string, a bearing 6 member mounted on the mandrel and a sleeve member 7 mounted on the bearing member.

8 9

2. A component as claimed in claim 1, wherein the bearing member is an inner bearing member, and the 11 sleeve member is an outer sleeve member, and the 12 component further comprises first and second 13 retaining members for retaining the inner bearing 14 member, and the outer sleeve member, on the mandrel.

is 16

3. A component as claimed in claim 2, wherein at 17 least one of the first and second retaining members 18 is removable or retractable from the mandrel, to 19 permit the inner bearing member, and the outer sleeve member, to be removed from the mandrel.

21 22

4. A component as claimed in either of claims 2 or 23 3, wherein the inner bearing member comprises at 24 least two portions, which when brought together, form a substantially tubular member.

26 27

5. A component as claimed in claim 4, wherein the 28 at least two portions are mounted in a recess of the 29 mandrel, the recess comprising a reduced diameter portion with reference to the diameter of the drill 31 string.

32 1

6. A component as claimed in any of claims 2 to 5, 2 wherein the outer sleeve member is arranged 3 coaxially with the inner bearing member in use of 4 the component.

6

7. A component as claimed in claim 6, wherein a 7 selective locking mechanism is provided to prevent 8 relative rotational movement between the inner 9 bearing member and the outer sleeve member in use of the component.

11 12

8. A component as claimed in claim 7, wherein the 13 selective locking mechanism comprises a first 14 locking device provided on the inner bearing member is and a second locking device provided on the outer 16 sleeve member.

17 18

9. A component as claimed in claim 8, wherein the 19 first locking device is provided on the outer surface of the inner bearing member and the second 21 locking device is provided on the inner surface of 22 the outer sleeve member.

23 24

10. A component as claimed in either of claims 8 or 9, wherein the first and second locking devices 26 interact with one another to provide the locking 27 action.

28 29

11. A component as claimed in any of claims 8 to 10, wherein the first and second locking devices are 31 formations provided on the respective surfaces of 32 the inner bearing member and outer sleeve member.

21 1

12. A component as claimed in claim 11, wherein 2 the formations are arranged longitudinally at least 3 partly along the length of the respective inner 4 bearing member and outer sleeve member. 5 6

13. A component as claimed in any of claims 10 to 7 12, wherein a third locking device is provided to 8 interact with the first and second locking devices 9 to provide the locking action. 10 11

14. A component as claimed in any of claims 2 to 12 13, further comprising a second inner bearing member 13 comprising at least two portions. 14 is

15. A component as claimed in claim 14, wherein the 16 portions when brought together form a substantially 17 tubular member. 18 19

16. A component as claimed in claim 15, wherein 20 there are two portions, each portion comprising a 21 half cylindrical member. 22 23

17. A component as claimed in any of claims 14 to 24 16, wherein the at least two portions are mounted in 25 the same recess of the mandrel that the two portions 26 of the first inner bearing member are mounted. 27 28

18. A component as claimed in any of claims 14 to 29 17, wherein the first and second bearing members 30 each comprise a device which separates the outer 31 sleeve member from the mandrel.

32 22 1

19. A component as claimed in any of claims 14 2 to 18, wherein the first inner bearing member is 3 capable of rotation with respect to the second inner 4 bearing member.

6

20. A component as claimed in any of claims 14 to 7 19, wherein a selective locking mechanism is 8 provided to prevent relative rotational movement 9 between the second inner bearing member and one of the first and second retaining members in use of the 11 component.

12 13

21. A component as claimed in any of claims 2 to 14 20, wherein the outer sleeve member is a one-piece is outer sleeve member.

16 17

22. A component as claimed in any of claims 2 to 18 21, wherein the component is dismantled by removing 19 one of the retaining devices and removing, if present, the second inner bearing member and then 21 removing the outer sleeve member over one end of the 22 mandrel, and then removing the first inner bearing 23 member. 24 25

23. A component as claimed in any preceding claim, 26 wherein a section of the mandrel directly above 27 and/or below the first and/or second retaining 28 member comprises spiral blades. 29 30

24. A component as claimed in any preceding claim, 31 wherein the mandrel is a one-piece mandrel body. 32 23 1

25. A torque reducing drillstring component 2 substantially as hereinbefore described with 3 reference to Figs. 1 to 4 of the accompanying 4 drawings. 5 6

26. A torque reducing drillstring component 7 substantially as hereinbefore described with 8 reference to Figs. 5 to 24 of the accompanying 9 drawings. 10 11