US20100096122A1

US20100096122A1 - Wellbore Cleaning Devices

Info

Publication number: US20100096122A1
Application number: US12/578,727
Authority: US
Inventors: Lisa L. Posevina; Gregory L. Hern; Paul L. Connell
Original assignee: Baker Hughes Inc
Current assignee: Baker Hughes Holdings LLC
Priority date: 2008-10-20
Filing date: 2009-10-14
Publication date: 2010-04-22

Abstract

Non-rotating tubular wellbore cleaning devices are described which include a central tool mandrel with radially surrounding stabilizers and a cleaning member subassembly. A rotational bearing is provided that is partially radially recessed, thereby improving the overall strength of the cleaning device.

Description

This application claims priority to U.S. Provisional Patent Application Ser. No. 61/106,674 filed Oct. 20, 2008 and U.S. Provisional Patent Application Ser. No. 61/149,632 filed Feb. 3, 2009.

BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates generally to systems and methods for cleaning the interior of tubular members. In particular aspects, the invention relates to methods and devices for scraping wellbore casing.
2. Description of the Related Art
Wellbore cleaning devices include casing scrapers and brushing devices. These mechanisms are used to remove mud, cement sheath, perforation burrs, rust, scale, paraffin, and other debris from the internal surface of wellbore casing. The casing scraper or brush is typically attached to a drill string for operation. The drill string and cleaning device are then disposed within the casing members to be scraped, and rotated.
Typical casing scrapers include a central scraping body and one or more scraping blades that extend radially outwardly therefrom. Conventional casing scrapers generally fall into one of two categories: rotating and non-rotating. With a rotating scraper, the scraping body and the scraping blades are securely affixed to each other so that both rotate with the drill string. In applications where the drill string is rotated for long periods of time, rotating scrapers can cause serious wear and damage to the interior surface of casing. With a non-rotating scraper, only the scraping body rotates with the drill string. The scraper blades are not affixed to the central scraping body, but are urged radially outwardly from it by compression springs in order to provide a force for removal of debris. An example of this type of arrangement is found in U.S. Pat. No. 7,311,141 issued to Tulloch et al.

SUMMARY OF THE INVENTION

The invention provides methods and devices for cleaning the interior of tubular members, such as casing members. Exemplary non-rotating tubular cleaning devices are described which include a central tool mandrel with radially surrounding stabilizers and a cleaning member subassembly. The cleaning member subassembly includes one or more scraper blades that are secured around the tool mandrel. In one embodiment, a scraper device is described wherein each scraper blade of a scraper blade subassembly includes a blade housing having blade windows. Scraper blades are retained within the blade housing so that the scraper blades are biased radially outwardly through the windows. In another embodiment, a brush-type wellbore cleaning device is described wherein the cleaning member subassembly includes a brush attachment having a central collar with cleaning bristles.
A rotation interface is disposed between the cleaning member subassembly and stabilizers and ensures that the stabilizers and cleaning members can rotate with respect to the mandrel. In preferred embodiments, the interface includes sets of rotational bearings or bushings, and preferably roller bearings that enable the cleaning member subassembly to easily rotate with respect to the tool mandrel. Exemplary rotation interfaces feature annular indentations and split ring and split sleeve components that fit into the indentations to allow portions of the rotation interface to be recessed radially inwardly.
The construction of the cleaning devices permit these tools to have improved strength and resistance to axial and torsional forces within the work string within which the cleaning device is used. The threaded connection of the tool mandrel largely governs the strength of the tool overall. The use of annular indentations and inner bearing race and rotational sleeve components permits the diameter of the threaded portion of the tool mandrel to be radially enlarged relative to the indentations. As a result, the cleaning tools are stronger and more resistant to axial and torsional stresses and forces.
In other aspects, the invention relates to improved tools for cleaning the interior of a surrounding tubular and wherein the rotation interface permits the central mandrel to rotate within the cleaning members. In various embodiments, the cleaning members may be scraper blades or brushes.

BRIEF DESCRIPTION OF THE DRAWINGS

The advantages and further aspects of the invention will be readily appreciated by those of ordinary skill in the art as the same becomes better understood by reference to the following detailed description when considered in conjunction with the accompanying drawings in which like reference characters designate like or similar elements throughout the several figures of the drawing and wherein:

FIGS. 1A-1C are a side, cross-sectional view of an exemplary scraper device constructed in accordance with the present invention.

FIG. 2 is a side, external view of the scraper device shown in FIGS. 1A-1C.

FIG. 3 is a side, cross-sectional view of an exemplary split sleeve used in the scraper device of FIGS. 1A-1C and 2, shown apart from the other components.

FIG. 4 is an axial cross-section taken along the lines 4-4 in FIG. 3.

FIG. 5 is a side, cross-sectional view of an exemplary spacer used in the scraper device of FIGS. 1A-1C and 2, shown apart from the other components.

FIG. 6 is an axial cross-section taken along the lines 6-6 in FIG. 5.

FIG. 7 is a side, cross-sectional view of an exemplary scraper blade sleeve used in the scraper device of FIGS. 1A-1C and 2, shown apart from the other components.

FIG. 8 is an axial cross-section taken along lines 8-8 in FIG. 7.

FIG. 9 is a further enlarged view of lower portions of the scraper device shown in FIGS. 1A-1C and 2.

FIG. 10 is an isometric view of an exemplary scraper blade used with the scraper device of FIGS. 1A-1C and 2, shown apart from other components of the scraper device.

FIG. 11 is an end view of the scraper blade shown in FIG. 10.

FIG. 12 is a cross-sectional view taken along the lines 12-12 in FIG. 11.

FIG. 13 is an isometric detail view of an exemplary inner bearing race used with the scraper device shown in FIGS. 1A-1C and 2.

FIG. 14 is an isometric view of an exemplary bearing used with the scraper device shown in FIGS. 1A-1C and 2.

FIGS. 15A-15C present a side, cross-sectional view of an exemplary cleaning device in accordance with the present invention and incorporating a brush-type cleaning assembly.

FIG. 16 is an axial cross-section taken along lines 16-16 in FIG. 15A.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1A-1C and 2 illustrate a first exemplary wellbore cleaning device constructed in accordance with the present invention. The first cleaning device is in the form of an exemplary tubular scraper device or tool 10 that is useful for incorporation into a wellbore work string and disposed within a wellbore. The scraper device 10 includes a generally cylindrical tool mandrel, generally indicated at 12. The tool mandrel 12 defines a central flowbore 14 along its length. The upper end of the tool mandrel 12 preferably includes a box-type threaded connection 16 so that the scraper device 10 may be secured to other portions of a wellbore work string (not shown). As shown in FIG. 1C, the lower to end of the tool mandrel 12 is secured by a threaded connection 18 to a bottom sub 20.
The tool mandrel 12 presents an outer radial surface having a number of different diameter portions. There is an upper, enlarged-diameter portion 22 and a reduced diameter lower shaft, generally shown at 24. The lower shaft 24 includes a plurality of annular indentations 26, 28, 30, 32, 34, 36, 38 which are preferably spaced apart from one another along the length of the lower shaft 24. The indentations 26, 28, 30, 32, 34, 36, 38 have a diameter that is less than the diameter of the lower shaft 24.
An upper wear ring 40 surrounds the lower shaft 24 immediately below the upper enlarged diameter portion 22. An upper stabilizer 42 surrounds the lower shaft 24 below the wear ring 40. A cleaning member subassembly or scraper blade subassembly, generally indicated at 44, is located below the upper stabilizer 42 on the lower shaft 24. Lower stabilizer 46 surrounds the lower shaft 24 below the scraper blade subassembly 44. The upper and lower stabilizers 42, 46 are of a type known in the art and function to centralize the scraper blade subassembly 44 within a surrounding casing member. Lower wear ring 48 is disposed below the lower stabilizer 46 and on the bottom sub 20.
The scraper blade subassembly 44 includes an outer tubular cleaning member housing, or blade housing 50 which radially surrounds the lower shaft 24 of the tool mandrel 12. The blade housing 50 defines a plurality of cleaning member windows, or blade windows 52. The construction of the blade housing 50 may be better understood by further reference to FIGS. 7 and 8, which show the blade housing 50 apart from the other components of the scraper device 10. As shown there, the blade housing 50 includes a central axial bore 54 along its longitudinal length. The bore 54 includes an upper, enlarged diameter bearing chamber 56 and a reduced diameter engagement section 58. The bearing chamber 56 has a smooth, cylindrical shape. However, the engagement section 58 preferably includes a plurality of radially inwardly directed engagement flats 60. FIG. 8 shows the engagement section 58 having a hexagonal shape which provides six flats 60. However, other suitable cross-sectional shapes may also be used (i.e., pentagon, square), and there may be more or fewer than six engagement flats 60. In the exemplary embodiment shown in FIGS. 1A-1C and 7, the bore 54 of the blade housing 50 also includes two radially-enlarged blade chambers 62 and 64 which are separated by a radially inwardly-projecting annular flange 66. The blade chambers 62, 64 contain the blade windows 52. In addition, the bore 54 of the blade housing 50 contains a lower, enlarged diameter bearing chamber 68.
Cleaning members in the form of scraper blades 70 are disposed radially within the blade housing 50. FIGS. 10, 11 and 12 depict an exemplary scraper blade 70. Each scraper blade 70 includes a blade body 72 which presents radially outward-facing scraping surfaces 74. The radially interior face 76 of the scraper body 72 is radially curved to generally match the curvature of the tool mandrel 12. A spring-retaining recess 78 is formed within the interior face 76 (see FIG. 12). Retaining flanges 80 extend laterally outwardly from the blade body 72. When a blade 70 is disposed within a window 52 of the blade housing 50, the retaining flanges 80 prevent the blade 70 from falling radially outside of the window (see FIGS. 1A and 1B). Compression springs 82 reside within the spring-retaining recess 78 of each blade 70 and bias the scraper blade 70 radially outwardly from the tool mandrel 12. The configuration of the compression springs 82 are adapted to allow for the exertion of a symmetrical force between the scraper blade 70 and rotation sleeve 104.
A rotation interface, generally indicated at 84 in FIGS. 1A-1C, is disposed radially between the lower shaft 24 and the surrounding stabilizers 42, 46 and scraper blade subassembly 44. The rotation interface 84 allows the stabilizers 42, 46 and the scraper blade subassembly 44 to rotate freely around the lower shaft 24. In one embodiment, the rotation interface 84 includes a plurality of rotational bearings that are in the form of roller bearing sets 86. In the exemplary embodiment depicted in FIGS. 1A-1C, there are six roller bearing sets 86. However, there may be more or fewer than six sets. Each of the roller bearing sets 86 is made up of an inner bearing race 88, an outer bearing race 90, and a plurality of rollers 92 that are disposed in between the inner and outer bearing races 88, 90. Alternatively, a bushing may be used in place of outer bearing race 90, rollers 92 and spacer 116. The rollers 92 are preferably cylindrically shaped members, as illustrated in FIG. 14. However, spherical roller bearings might also be used. The inner bearing race 88 of each roller bearing set 86 is preferably made up of two halves 94, 96, as illustrated in FIG. 13. Alternatively, if desired, an inner bearing race 88 could also be made up of three or more separate race portions which could be assembled within an indentation 26, 28, 30, 34, 36, or 38 to make up a complete annular bearing race. When the roller bearing set 86 is assembled, the rollers 92 will rotate upon the outer radial surface 98 of the inner bearing race 88 and, due to rolling contact of the rollers 92 with both the inner and outer bearing races 88, 90, the bearing races 88, 90 will easily rotate with respect to one another. The outer bearing races 90 of the roller bearing sets 86 are in contact with, and preferably secured to portions of either the scraper blade subassembly 44 or the stabilizers 42, 46. FIG. 9 shows, for example, that the outer bearing race 90 of the roller bearing set 86 that is mounted within indentation 34 is in contact with the surrounding scraper blade housing 50 and is secured in place against the scraper blade housing 50 by spacers 116 on each axial side. As a result, the scraper blade housing 50 will rotate about the tool mandrel 12 with the outer bearing race 90. Similarly, the outer bearing races 90 of the roller bearing sets 86 that are located in indentations 36 and 38 are in contact with the lower stabilizer 46 so that the lower stabilizer 46 will rotate about the tool mandrel 12 with those outer bearing races 90. Alternative cleaning elements may be used in place of scraper blades 70, such as magnets or brushes. This may be achieved by removing outer bearing races 90, rotation sleeve 104 and scraper blade subassembly 44, and engaging the alternative cleaning element to the inner bearing race 88.
FIGS. 15A-15C and 16 depict an alternative exemplary cleaning tool 10′ configured with an alternative cleaning member. The cleaning member of the cleaning tool 10′ is in the form of a brush 101 wherein cleaning brush bristles extend radially outwardly from a central collar. In this instance, the rotation interface includes bearing races 88, which are disposed between the mandrel 12 and the brush 101.
Referring once again to the scraper-type cleaning tool 10 shown in FIGS. 1A-1C and 2-14, the rotation interface 84 also includes a split rotation sleeve 104 which underlies scraper blades 70 of the scraper device 10. An exemplary rotation sleeve 104 is depicted in detail in FIGS. 3 and 4 wherein it can be seen that the sleeve 104 is preferably made up of two sleeve halves 106, 108. If desired, there may be more than two sleeve halves 106, 108 which can be assembled about the lower shaft 24 to form a complete or substantially complete annular sleeve 104. The rotation sleeve 104 preferably presents a smooth cylindrical outer radial surface 110 along most of its length. One axial end of the rotation sleeve 104 includes an outer interengagement surface 112 that presents engagement flats 114. In the exemplary embodiment shown in FIG. 4, there are six engagement flats 114. However, there may be more or fewer than six, if desired. Alternatively, the interengagement surfaces 112, 58 may comprise teeth as opposed to engagement flats, so long as both surfaces are complimentary to one another. The engagement flats 114 of the split sleeve 104 are shaped and sized to abut the engagement flats 60 of the blade housing 50. This complimentary engagement permits the rotation sleeve and the blade housing 50 to rotate together without the need to affix them to one another with a fastener or otherwise. The rotation sleeve 104 halves 106, 108 are placed radially around the shaft portion 24 of the tool mandrel 12, and will readily rotate about the mandrel 12.
In preferred embodiments, spacer rings 116 are located between roller bearing sets 86 under the stabilizers 42, 46. The spacer rings 116 serve to retain the roller bearing sets 86 in axial spaced relation to one another. FIGS. 5 and 6 illustrate an exemplary spacer ring 116 apart from the other components of the scraper device 10.
As best seen in the enlarged view provided by FIG. 9, roller bearing sets 86 are preferably abutted by elastomeric lip seals 122 of a type known in the art for creating a fluid seal against the bearing set 86. In addition, the lip seals 122 will drag on the shaft portion 24 of the tool mandrel 12 to prevent the scraper blade subassembly 44 and stabilizers 42, 46 from floating freely with respect to the tool mandrel 12. The retaining ring 124 and spacer 116 mechanically secure the roller bearing set 86 in place axially. The fluid seal 122 prevents or limits the escape of lubricant from the bearing set 86. In an alternative embodiment, the roller bearing sets 86 may be replaced by an annular bushing.
Removable pipe plugs 130 are preferably provided in each of the stabilizers 42, 46 and the blade housing 50. The pipe plugs 130 are preferably removably secured by threading and may be removed to allow lubricant to be supplied to the roller bearing sets 86.
To assemble the scraper device 10, the inner bearing races 88 for each of the roller bearing sets 86 are placed into the indentations 26, 28, 30, 34, 36, 38. This is possible because the inner bearing races 88 are each formed of multiple components (i.e. halves 94, 96) which can be assembled within the indentations to form a complete annular bearing race 88. Stabilizers are preassembled with lip seals 122, outer bearing races 90 with rollers 92, spacer ring 116 and retaining ring 124. The upper stabilizer 42 is slid onto the shaft 24 to a position wherein it abuts the upper wear ring 40. Springs 82 are installed in spring retaining recesses 78. Spacer 116, lip seals 122 and outer bearing race 90 with rollers or annular bushing 92 for blade housing 50 are slid onto shaft 24. The rotation sleeve 104 is assembled around the shaft 24 in indentation 32. The scraper blades 70 are disposed into the windows 52 of the blade housing 50. Thereafter, the blades 70, springs 82, and blade housing 50 are slid onto the shaft 24. The engagement section 58 of the blade housing 50 is positioned onto the outer surface 112 of the rotation sleeve 104 so that the engagement flats 114 of the split sleeve 104 are interengaged with the engagement flats 60 of the blade housing 50. As a result of this interengagement, the blade housing 50 and split sleeve 104 will rotate as one about the shaft 24 of the tool mandrel 12. Spacer 116, lip seals 122, and outer bearing race 90 with roller 92 are slid onto shaft 24, and pushed inside of blade housing 50. The lower stabilizer assembly 46 is then slid onto the shaft 24. Thereafter, the wear ring 48 and bottom sub 20 are secured to the shaft 24. It will be appreciated that the rotation interface 84 permits the stabilizers 42, 46 and the scraper blade subassembly 44 to rotate freely about the tool mandrel 12.
The internal diameters of the stabilizers 42, 46 and the blade housing 50 are slightly larger than the external diameter of the threaded portion 18 of the tool mandrel shaft 24. The internal diameters of the split bearing races 88 are smaller than the diameter of the threaded portion 18. The use of split bearing races 88 reduces the amount of wear and frictional heat sustained on the surface of the mandrel 12, when compared to the amount of wear and frictional heat a person of ordinary skill in the art would expect to occur if the stabilizers 42, 46 and blade housing 50 were allowed to rotate on the surface of the mandrel 12, by allowing for rotation about the split bearing races 88. As FIG. 9 depicts, the outer diameter D1 of each of the indentations (as illustrated at indentation 38) is less than the outer diameter D2 of the shaft 24 at the point where the threaded connection 18 begins. Diameter D2 is essentially the diameter of the shaft portion 24 where there are no indentations 26, 28, 30, 32, 34, 36 and 38. The inventors have determined that the strength of a scraper device within a work string and its resistance to damage from axial and torsional stresses is largely a function of the strength of the threaded connection 18. The provision of split inner bearing races 88 and rotation sleeve 104, which reside in a radially recessed manner within the indentations 26, 28, 30, 32, 34, 36 and 38, allows the threaded connection portion 18 of the shaft portion 24 to be provided with a larger diameter, thereby increasing the strength of the connection to bottom sub 20, the overall strength of the tool 10 and the resistance to damage from applied forces within a wellbore. As a result, the threaded connection 18 substantially approximates full gauge (D2) while at least a portion of the rotational interface is disposed upon the shaft portion 24 radially within the full gauge diameter D2 by being recessed at less than full gauge (to the depth D1 of the indentations 26, 28, 30, 32, 34, 36 and 38).
The foregoing description is directed to particular embodiments of the present invention for the purpose of illustration and explanation. It will be apparent, however, to one skilled in the art that many modifications and changes to the embodiment set forth above are possible without departing from the scope and the spirit of the invention.

Claims

1. A wellbore cleaning device comprising:

a tool mandrel having a shaft portion;

at least one cleaning member mounted to said mandrel for cleaning a surrounding tubular member;

a rotation interface between the cleaning member and said mandrel to permit the mandrel to rotate with respect to the cleaning member, the rotation interface comprising:

an indentation within and said mandrel; and

a bearing at least partially disposed within the indentation, the bearing allowing the mandrel to rotate inside said cleaning member, the bearing including a to rotation sleeve radially surrounding and rotatable with respect to the shaft portion.

2. The wellbore cleaning device of claim 1 wherein the bearing comprises a roller bearing set comprising:

a radially inner bearing race that is seated within the indentation, the inner bearing race being formed of multiple race portions that are assembled within the indentation to form a complete annular bearing race;

an outer bearing race radially surrounding the inner bearing race and the roller; and

at least one roller disposed between the inner and outer bearing races to permit the inner and outer bearing races to rotate with respect to each other.

3. The wellbore cleaning device of claim 1 wherein the bearing comprises an annular bushing.

4. The wellbore cleaning device of claim 1 further comprising a stabilizer rotationally mounted on the shaft portion of the tool mandrel.

5. The wellbore cleaning device of claim 1 further comprising:

a cleaning member housing that radially surrounds the shaft portion of the tool mandrel and has a cleaning member window defined therein; and

the cleaning member being disposed radially within the housing with a portion of the cleaning member being biased radially outwardly through the window.

6. The wellbore cleaning device of claim 4 wherein the rotation sleeve is not secured to the cleaning member housing by a fastener.

7. The wellbore cleaning device of claim 6 wherein the rotation interface further comprises a locking interengagement between the rotation sleeve and the cleaning member housing, the interengagement allowing the shaft portion to rotate inside the rotation sleeve and cleaning member housing.

8. The wellbore cleaning device of claim 7 wherein the locking interengagement comprises:

a radially outwardly-facing engagement surface on the rotation sleeve; and

a radially inwardly-facing engagement surface on the cleaning member housing that is shaped and sized to be generally complimentary to the engagement surface of the rotation sleeve.

9. The wellbore cleaning device of claim 8 wherein the inwardly and outwardly facing engagement surfaces each comprise a plurality of engagement flats.

10. The wellbore cleaning device of claim 1 wherein there are a plurality of indentations and a plurality of bearings, each of the bearings being disposed within a different indentation.

11. The wellbore cleaning device of claim 1 further comprising one or more spacers radially surrounding the shaft portion to secure the bearing in place upon the shaft portion.

12. The wellbore cleaning device of claim 1 wherein the cleaning member comprises a scraper blade.

13. The wellbore cleaning device of claim 1 wherein the cleaning member comprises a brush.

14. The wellbore cleaning device of claim 12 wherein the scraper blade is biased radially outwardly from the rotation sleeve by a spring.

15. A wellbore cleaning device comprising:

a tool mandrel having a shaft portion;

a cleaning member subassembly radially surrounding the shaft portion, the subassembly having at least one cleaning member for cleaning a surrounding tubular member;

a rotation interface between the scraper blade subassembly and shaft portion to permit the tool mandrel to rotate within the scraper blade subassembly, the rotation interface comprising:

an indentation within the shaft portion; and

a bearing set at least partially disposed within the indentation, the roller bearing set allowing the shaft portion to rotate within the cleaning member subassembly, the roller bearing set comprising:

an outer bearing race radially surrounding the inner bearing race and being in contact with the cleaning member subassembly so that the cleaning member subassembly rotates with the outer bearing race; and

at least one bearing member disposed between the inner and outer bearing race to permit the inner and outer bearing races to rotate with respect to each other.

16. The wellbore cleaning device of claim 15 wherein the cleaning member subassembly comprises:

a cleaning member that is disposed radially within the housing with a portion of the cleaning member being biased radially outwardly through the window.

17. The wellbore cleaning device of claim 16 wherein the rotation interface further comprises:

a rotation sleeve radially surrounding the shaft portion and rotatable with respect to the shaft portion; and

a locking interengagement between the rotation sleeve and the cleaning member housing, the interengagement causing the shaft portion to rotate within the rotation sleeve and cleaning member housing.

18. The wellbore cleaning device of claim 16 wherein the locking interengagement comprises:

a radially outwardly-facing engagement surface on the rotation sleeve; and

19. The wellbore cleaning device of claim 18 wherein the inwardly-facing and outwardly-facing engagement surfaces each comprise a plurality of engagement flats.

20. The wellbore cleaning device of claim 15 further comprising one or more spacers radially surrounding the shaft portion to secure the roller bearing set in place upon the shaft portion.

21. The wellbore cleaning device of claim 15 further comprising a plurality of stabilizers rotationally mounted on the shaft portion of the tool mandrel.

25. The wellbore cleaning device of claim 15 further comprising a plurality of stabilizers rotationally mounted upon the tool mandrel.

26. The wellbore cleaning device of claim 17 wherein the rotation sleeve is made up of a plurality of sleeve portions that are assembled about the shaft portion within an indentation to form a substantially complete annular sleeve.

27. The wellbore cleaning device of claim 17 wherein the rotation sleeve is not affixed to the cleaning member housing.

28. The wellbore cleaning device of claim 15 wherein the bearing member of the bearing set comprises an annular bushing.

29. The wellbore cleaning device of claim 15 wherein the bearing member of the bearing set comprises a roller element.

30. A wellbore cleaning device comprising:

a tool mandrel having a shaft portion;

an indentation within the shaft portion of said mandrel; and

a bearing at least partially disposed within the indentation, the bearing allowing the mandrel to rotate inside said scraper blade, the bearing including a rotation sleeve radially surrounding and rotatable with respect to the shaft portion.

31. The cleaning device of claim 30 wherein the cleaning member comprises a scraper blade.

32. The cleaning device of claim 31 wherein the cleaning member is a brush.

33. The cleaning device of claim 30 wherein:

the mandrel presents a threaded connection portion for attachment of the mandrel to an adjoining sub, the connection portion having a first diameter; and

the indentation has a second diameter which is less than the first diameter, thereby permitting the cleaning device to have a greater tool strength.