GB2338970A

GB2338970A - Friction reducing drill pipe component

Info

Publication number: GB2338970A
Application number: GB9915297A
Authority: GB
Inventors: Robert Patrick Appleton
Original assignee: Drilltech Services North Sea Ltd
Current assignee: Drilltech Services North Sea Ltd
Priority date: 1998-07-02
Filing date: 1999-07-01
Publication date: 2000-01-12
Also published as: GB9814230D0; GB9915297D0; WO2000001239A2; WO2000001239A3; AU4632299A

Description

2338970 FRICTION-REDUCING DRILL PIPE COMPONENT The present invention

relates to a drill- pipe component, and in particular to a component to be placed in a string of drill pipe to reduce the friction or drag between the string and the bore wall.

Where long holes or bores are drilled, such as in the oil and gas exploration and extraction indu-stries, the friction which occurs due to contact between the drill string and the bore wall may result in a substantial increase in the torque required to rotate the string and the drill bit. Such contact may also cause wear and damage to the steel casing used to line sections of the bore, and may conversely result in wear and damage to components of the drill string.

In an effort to avoid these difficulties there have been various proposals for friction reducing components to be mounted in or on the string. For examnle, the applicants produce a "torque reducing sub", as described in UK Patent Application GB 2 304 763, which component has proved effective in reducing the drag experienced by a rotat-ing drill string; testing has indicated that an appropriate number of such subs (ty pically 4-0 to 70) redUC- the torque required to rotate a drill string by 20 - 250i The sub comprises a mandrel which forms part of the string and a sleeve rotatably mounted on the mandrel, the sleeve 2 being of greater diameter than the dr''" L 1-, 01pe which forms the string. As the sleeve will tend to stop rotating on contact with the bore wall, this form o 'L sub is known as a "non-rotating" sub.

Advances in drilling and extraction techniques are resulting in a increasing demand for capability to drill highly deviated extended reach bores, and thus for high performance friction-reducing drill string components. The preferred form of the applicant's existing torque reducing sub features plane bearing surfaces. Although this provides a simple and robust construction, there is a limit to,the reduction in friction available from such a design.

It is known to provide friction-reducing subs with bearings which reduce friction between the sleeve and mandrel, although this increases the complexity and cost of the subs. Further, increasing complexity is often accompanied by increased unreliability, and a sub failure may result in considerable delay and expense for an operator; if a sub sleeve fails and detaches from the mandrel it may jam between the drill string and the bore wall, bringing the drilling operation to a halt and possibly preventing removal of the drill string from the bore.

It is among the objects of the present invention to obviate or alleviate these and other disadvantages of the PrLor art.

According to one aspect of the present invention, there is provided a f riction- reducing drill pipe component for forming part of a drill string, the component 3 comprising: a mandrel comprising a tu:bular body having first and second ends for connection to adjacent components of a drill string, and at least a first stop extending radially from the body; a sleeve rotatably mounted on the body; and a bearing arrangement provided between the sleeve and the body, at least one bearing set being provided between the sleeve and the stop to provide axial support for the sleeve.

Preferably, said at least one bearing set is adapted to provide radial support for the sleeve in addition to axial support, typically by locating the bearing between the sleeve and both the body and the stop. This configuration enables the at least one bearing set to support the sleeve against both axial and radial forces acting on the drill string, as are experienced, in use, when a rotating drill string is advancingthrough a bore, without requiring the provision of separate thrust bearings.

Preferably also, said at least one bearing set includes a first mandrel bearing race provided toward the first end of the mandrel, the bearing race being defined in part on the body and in part on the f irst stop, with a corresponding first sleeve race being defined on the sleeve, the bearing races serving to guide and retain a first set of ball bearings.

Preferably also, a second mandrel bearing race is provided on the mandrel body toward the second end thereof, with a corresponding second sleeve race on the sleeve, for 4 receiving a second set of bail bearings. Conveniently, the second races combine with the ball bearings to lock the sleeve axially on the mandre7.

Preferably also, at least one of the mandrel body and the sleeve is provided with a closeable opening whereby e 4 ball bearings may b _Lntroduced into bear 7 ng races between the sleeve and the mandrel. Most preferably, the opening is a keyway defined by corresponding grooves in the body and the sleeve. Alternatively, the opening may be defined solely by the sleeve. Preferably, the opening is toward the second end of the apparatus and permits bearings to be introduced into the second ball races. Preferably also, the apparatus further comprises a removable closure to ensure retention of ball bearings in the apparatus.

Preferably, the closure is located on the mandrel body.

Preferably also, the sleeve is removable over the second end of the mandrel. This facilitates rapid and straightforward assembly and disassembly of the apparatus, and permits provision of a one-piece sleeve.

Preferably also, the mandrel body is of unitary construction, that is the body is formed of a single part.

A number of prior art mandrels for similar components are formed of two threaded parts; however, such mandrel forms increase the time required for assembly and disassembly of the apparatus, and increase the possibility of accidental disassembly of the component, which may occur during tripping out of a drill string when the drill pipe lengths are being separated. Also, the provision of threaded connections may require a greater wall thickness in the mandrel, producing a restriction in the mandrel internal diameter. Most oreferably, the stop is formed 4 ntegrally with the body, for example by machining the body and stop from a single piece of metal. Alternatively, the stop may be formed separately of the body and secured thereto.

A second stop may be provided toward --he second end of the mandrel. Preferably, the second stop is removable or retractable to enable the sleeve to be removed from the mandrel.

Preferably also, the bearing arrangement is adapted to be lubricated by bore fluid, that is the bearings are unsealed; bearing seals are typically formed from rubber compounds, which may deteriorate when exposed to the high temperatures found in many deeper wells.

Preferably also, the bearings are treated to resist wear. In one embodiment, bearing races are treated with INCLOY (Trade Mark) alloy, which is subject to work hardening as the ball bearings rotate in the races. in other embodiments, the races may be heat treated.

Conveniently, the sleeve comprises or at least carries a wear resistant, low friction coefficient material, such as a chromium carbide alloy, to minimise damage to the casing lining the bore, and also to resist wear where the bore is uncased. ARNCO 200 ST (Trade Mark) and ARMCO M (Trade Mark) alloys have been found to be particularly effective.

The sleeve will typically be formed predominately of steel, although plastics, rubbers, or indeed any appropriate material may be utilised.

The sleeve may have a plane outer surface or may be fluted. The provision of flutes tends to reduce the pressure losses in the drilling fluid passing up the annulus between the drill string and the bore wall. The flutes may be produced by addition of material to a substantially cylindrical sleeve, or ai-ternatively or in addition by machining or otherwise removing material from the sleeve surface.

These and other aspects of the present inVention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 shows a friction-reducing drill string component in accordance with an embodiment of the present is invention; Figure 2 shows a cross-section of the component of Figure 1; Figure 3 shows an enlarged cross-section of the sleeve of the component of Figure 1; Figures 4a and 4b show the locking key and stud of the component of Figure 1; and Figure 5 shows the mandrel of the component of Figure 1 in cross-section.

Referring firstly to Figure 1 of the drawings, this shows a friction-reducing drill string comnponant 10 in accordance with a preferred embodiment of the 'present invention. The component 10 comprises a unitary mandrel 15 having a generally cylindrical tubular body 16 with first 7 and second ends 12, 14 defining threaded box and pin connections for coupling to adjacent components of the drill string. Formed on the mandrel body 16 is a first stop 18 wh 4 ch serves to retain a rotatable unitary sleeve 20 on the body 16. The stop 18 and the upper end of the sleeve 20 present a tapering profile, to facilitate withdrawal of a string including a number of such components 10 from a bore.

Reference is now also made to Figure 2 of the drawings, which shows a cross-section of the component 10, illustrating the threaded box and pin connections 30, 32 and the mandrel through bore 40. Also shown in Figure 2 are the bearing sets 26, 28 located between the sleeve 20 and the mandrel 15. The upper set of bearings 26 is located so as to support the sleeve 20 both axially against the stop 18 and radially against the mandrel body 16. The lower set of bearings 28 support the sleeve 20 radially against the mandrel 16 and, as will be described, also serves to lock the sleeve 20 axially on the mandrel 15.

Both sets of bearings 26, 28 are located in respective ball races 34, 35 and 36, 37 (Figures 3 and 5), the upper mandrel race 35 extending radially outward between the mandrel body 16 and the stop 18.

The lower end of the sleeve 20 and the mandrel body 16, when in the relative -otar_ional positions shown in Figure 2, together define a key-way 38 which provides a port of entry through which ball bearings 28 may be introduced between the mandrel 15 and the sleeve 20. The 8 keyway 38 may be closed to prevent escape of ba'Ll bearings by a key 22, as illustrated in Figures 4a and 4b of the drawings. It will be observed that the upper face of the key is profiled to match the mandrel bearing race. The key 22 may be locked to the mandrel by a locking stud 24, as locking stud is illustrated in Figure 4b. Access to the I gained via a relief 42 in the sleeve 20; when the head of the stud 24 is accessible, the grooves 38a, 38b in the body and sleeve 20 will be aligned to define the keyway 38, allowing ball bearings to be inserted or removed.

As noted above, the mandrel 15 and sleeve 20 are of unitary construction, and thus may be robust-- and each machined from a single piece of metal. To assemble the component, the sleeve 20 is placed over the lower second end of the mandrel and lifted towards the stop 18. Before the upper end of the sleeve 20 contacts the stop 18, the appropriate number of ball bearings 26 are loaded between the sleeve 20 and stop 18, and the stop 18 then raised further to trap the bearings 26 between the races 34, 35.

The sleeve 20 is then aligned on the mandrel 15 as illustrated in Figure 2, and the appropriate number of ball bearings 28 loaded between the races 36, 37 via the keyway 38. The key 22 is then located in the mandrel keyway groove 38a and the stud 24 secured to hold the key 22 on ?C; the mandrel 15.

Disassembly of the component is simply the reverse of the above procedure.

It will be apparent that the com-oonent is of 9 relatively s i mL,'- e construction, mini-nising cost and assembly time, and also facilitating provision of a reliable drill s=Jng component. The construction of the component also facilitates rapid inspection, refurbishment and repair, which is important when large numbers of components have been returned from one drilling operation and it is desired to make the compone-i--s available for another operation as qU 4 -Ickly as possible. The bearings are unsealed, such that no seals are required to be provided or maintained, or lubricating fluids provided or a(commodated.

Also, the configuration of the upper bearing allows the bulk of the axia7 forces experienced by the sleeve 20, as the drill string advances through the bore, to be borne by the bearing and the stop 18, such that no separate thrust bearing is required. Also, the use of the lower bearings as a sleeve lock obviates the requirement to provide a separate sleeve retaining arrangement. Despite its simple construction, a drill string including the appropriate number of components!0 will reduce the torque necessary to rotate a drill string in a deviated bore by 45 - 50-06.

It will apparent to the person of skill in the art that the foregoing is for illustrative purposes only, and that various im-provements and modifications may be made thereto without departing from the scope of the invention.

Claims

1. A friction-reducing drill pipe component for forming part of a drill string, the component comprising: a mandrel comprising a tubular body having first and second ends for connection to adjacent components of a drill string, and at least a first stop extending radially from the body; a sleeve rotatably mounted on the body; and a bearing arrangement provided between the sleeve and the body, at least one bearing set being provided between the sleeve and the stop to provide axial support for the sleeve.

2. The component of claim 1, wherein said at least one bearing set is adapted to provide radial support for the sleeve as well as axial support.

3. The component of claim 2, wherein said at least one bearing set is located between the sleeve and both the body and the stop.

4. The component of claim 2 or 3. wherein said at least one bearing set includes a first mandrel bearing race provided toward the first end of the mandrel, the bearing race being def ined in part on the body and in part on the f irst stop, with a corresponding f irst sleeve bearing race being defined on the sleeve, the bearing races serving to guide and retain a first set of ball bearings.

11 S. The component of (--Iaim 4, wherein a second mandrel bearing race is provided on the mandrel body toward the second end thereof, with a corresponding second sleeve bearing race on the sleeve, for receiving a second set of ball bearings.

6. The component of claim 5, wherein the second races combine with the second set of ball bearings to lock the sleeve axially on the mandrel.

7. The component of claim 4, 5 or 6, wherein at least one of the mandrel body and the sleeve is provided with a closeable opening whereby ball bearings may be introduced into bearing races between the sleeve and the mandrel.

8. The component of claim 7, wherein the opening is a keyway defined by corresponding grooves in the body and the sleeve.

9. The component of claim 7 or 8, wherein the opening is toward the second end of the apparatus and permits bearings to be introduced into the second ball races.

10. The component of claim 7, 8 or 9, wherein the apparatus further comprisps a removable closure to ensure retention of ball bearings in the apparatus.

11. The component of claim 10, wherein the closure is 12 located on the mandrel body.

12. The component of any of the preceding claims, wherein the sleeve is removable over the second end of the mandrel.

13. The component of any of the preceding claims, wherein the sleeve is a one-piece sleeve.

14. The component of any of the preceding claims, wherein the mandrel body is of unitary construction. -