DRILL PIPE WITH ROLLER ASSEMBLY

Abstract

A drill pipe assembly includes a tubular body and a roller assembly for reducing friction between the drill pipe and the inner wall of a wellbore. The tubular body includes a substantially cylindrical body outer surface defining roller pockets. Alternatively, the drill pipe assembly may have a sleeve that fits concentrically and rotatably around the tubular body, with the sleeve outer surface defining the roller pockets. Each roller pocket has a roller assembly that includes an axle having opposed ends retained by the tubular body or the sleeve. A roller is retained by and rotates on each axle, partially disposed in the roller pocket and partially projecting outwardly from the outer surface.

Description

FIELD OF THE INVENTION

The present invention is directed to the field of drill pipes used in drilling of oil and gas wellbores, and in particular to roller assemblies for facilitating the passage of drill pipes through wellbores.

BACKGROUND OF THE INVENTION

When drilling an oil and gas wellbore, it is conventional to use a drill string to conduct drilling fluid from the surface to a mud motor that drives a drill bit of the bottom hole assembly. The drill string may be made up of several segments of drill pipe, including segments known as pup joints, which may be irregular in length and typically shorter in length in comparison to standard length segments of drill pipe in the drill string. The path of the wellbore may be intentionally deviated from a vertical orientation to reach a formation that is horizontally displaced from the wellhead.

In the deviated portion of the wellbore, the drill string is not centralized in the wellbore. The weight of the drill string urges the drill string into contact with the bottom surface of the deviated portion of wellbore. Vertical undulations in the bottom surface of the deviated section of the wellbore are also common place, and may result in the drill string being “hung up” on the crests of the undulations. When withdrawing the drill string, the pup joints may be pulled upwards into contact with the top surface of the deviated portion of the wellbore. The resulting friction between the drill string and the bottom surface or top surface of the wellbore, as the case may be, can impede the movement of the drill string.

Accordingly, there is a need in the art for an apparatus that reduces friction between the drill string and the walls of the wellbore. Preferably, such a device is simple and economical to manufacture, and robust to withstand repeated use in drilling of oil and gas wellbores.

SUMMARY OF THE INVENTION

In one aspect, the present invention comprises a drill pipe assembly installable between an up-hole component and a down-hole component of a drill string, the drill string defining an axial direction and a transverse direction perpendicular thereto, the drill pipe assembly comprising:

• • (a) a tubular body comprising:
    • an up-hole end adapted for connection to the up-hole component, and a down-hole end adapted for connection to the down-hole component;
    • an inner surface defining an inner bore extending axially between the up-hole end and the down-hole end;
    • a substantially cylindrical body outer surface defining a plurality of inwardly extending roller pockets;
  • (b) for each of the plurality of roller pockets, a corresponding roller assembly comprising:
    • an axle having opposed ends each retained by the tubular body; and
    • a roller retained by the axle for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the body outer surface.

In one embodiment of the drill pipe assembly, the plurality of roller pockets are arranged in at least one row circumferential around the body outer surface. The at least one row may comprise a plurality of rows axially spaced apart from each other, and one of the roller pockets may be circumferentially offset from one of the roller pockets in one of the adjacent rows.

In one embodiment of the drill pipe assembly, the body outer surface further defines an access pocket circumferentially adjacent to one of the plurality of roller pockets and having an inwardly extending side wall; the body defines an aperture extending between an inwardly extending side wall of the one of the plurality of roller pockets and the side wall of the access pocket; and the axle is retained by the tubular body within the aperture. The access pocket circumferentially adjacent to the one of the plurality of roller pockets may be circumferentially adjacent to another one of the plurality of roller pockets.

In one embodiment of the drill pipe assembly, the roller has a barrel shape. Preferably, the barrel shape has a curvature closely matching the curvature of the body outer surface in a transverse plane.

In another aspect, the present invention comprises a drill pipe assembly installable between an up-hole component and a down-hole component of a drill string insertable in a wellbore, the drill string defining an axial direction and a transverse direction perpendicular thereto, the drill pipe assembly comprising:

• • (c) a tubular body comprising:
    • an up-hole end adapted for connection to the up-hole component, and a down-hole end adapted for connection to the down-hole component;
    • an inner surface defining an inner bore extending axially between the up-hole end and the down-hole end;
    • a substantially cylindrical body outer surface;
  • (d) a sleeve disposed concentrically around the tubular body between the up-hole end and the down-hole end, and comprising a substantially cylindrical sleeve outer surface defining a plurality of inwardly extending roller pockets;
  • (e) for each the plurality of roller pockets, a corresponding roller assembly comprising:
    • an axle having opposed ends each retained by the sleeve; and
    • a roller retained by the axle for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the sleeve outer surface.

In one embodiment of the drill pipe assembly, the sleeve comprises a first portion and a second portion releasably securable to the first portion, wherein each of the portions is semi-cylindrical.

In one embodiment of the drill pipe assembly, the body outer surface and the sleeve outer surface comprise abutting edges that are flush with each other. The sleeve may be disposed concentrically around a reduced portion of the tubular body having an outer diameter less than the outer diameter of the body outer surface.

In one embodiment of the drill pipe assembly, the sleeve is rotatable around the tubular body. The tubular body may define at least one aperture for fluid communication between the inner bore and an annular space between the tubular body and the sleeve.

In one embodiment of the drill pipe assembly, the plurality of roller pockets are arranged in at least one row circumferential around the sleeve outer surface. The at least one row may comprise a plurality of rows axially spaced apart from each other, and one of the roller pockets may be circumferentially offset from one of the roller pockets in one of the adjacent rows.

In one embodiment of the drill pipe assembly: the sleeve outer surface further defines an access pocket circumferentially adjacent to one of the plurality of roller pockets and having an inwardly extending side wall; the body defines an aperture extending between an inwardly extending side wall of the one of the plurality roller pockets and the side wall of the access pocket; and the axle is retained by the sleeve within the aperture. The access pocket circumferentially adjacent to the one of the plurality of roller pockets may be circumferentially adjacent to another one of the plurality of roller pockets.

In one embodiment of the drill pipe assembly, the roller has a barrel shape with a curvature closely matching the curvature of the sleeve outer surface in a transverse plane.

In another aspect, the present invention provides a sleeve assembly installable on a tubular body having an uphole end for connection to an up-hole component of a drill string and a down-hole end for connection to a down-hole component of a drill string, the drill string insertable in a wellbore and defining an axial direction and a transverse direction perpendicular thereto, the sleeve comprising:

• • (a) a sleeve disposable concentrically around the tubular body between the up-hole end and the down-hole end of the tubular body, and comprising a substantially cylindrical sleeve outer surface defining a plurality of inwardly extending roller pockets;
  • (b) for each of the plurality of roller pockets, a corresponding roller assembly comprising:
    • an axle having opposed ends each retained by the sleeve; and
    • a roller retained by for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the sleeve outer surface.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings, like elements are assigned like reference numerals. The drawings are not necessarily to scale, with the emphasis instead placed upon the principles of the present invention. Additionally, each of the embodiments depicted are but one of a number of possible arrangements utilizing the fundamental concepts of the present invention. The drawings are briefly described as follows:

FIG. 1 is a schematic side view of one embodiment of a drill string comprising a plurality of pup joints and a drill pipe assembly of the present invention in a deviated portion of a wellbore.

FIG. 2 is a perspective view of one embodiment of a drill pipe assembly of the present invention.

FIG. 3 is a side view of the embodiment of the drill pipe assembly of FIG. 2.

FIG. 4 is a sectional view of the drill pipe assembly of FIG. 3, along line A-A.

FIG. 5 is a sectional view of the drill pipe assembly of FIG. 3, along line B-B.

FIG. 6 is a detail view of the drill pipe assembly of FIG. 5, at portion C-C.

FIG. 7A is a side view, and FIG. 7B is an end view of the axle shown in FIG. 6.

FIG. 8A is a side view, and FIG. 8B is an end view of the roller shown in FIG. 6.

FIG. 9 is a perspective view of another embodiment of a drill pipe assembly of the present invention.

FIG. 10 is a perspective view of the sleeve shown in FIG. 9.

FIG. 11 is a side view of the drill pipe assembly of FIG. 9, along line A-A.

FIG. 12 is a sectional view of the drill pipe assembly of FIG. 11, along line A-A.

FIG. 13 is a side view of the tubular body shown in FIG. 9.

FIG. 14 is a sectional view of the tubular body shown in FIG. 13, along line A-A.

FIG. 15 is a sectional view of the drill pipe assembly of FIG. 9 along line B-B.

FIG. 16 is a detail view of the drill pipe assembly of FIG. 15, at portion C-C.

FIG. 17A is a side view, and FIG. 17B is an end view of the roller shown in FIG. 16.

DETAILED DESCRIPTION OF EMBODIMENTS

The invention relates to drill pipe used in drilling of wellbores such as oil and gas wellbores. When describing the present invention, all terms not defined herein have their common art-recognized meanings. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all combinations of features, alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.

The present invention is directed to a drill pipe assembly with a roller assembly. It will be understood that, in use, the drill pipe assembly is installed in a drill string between an adjacent up-hole component and an adjacent down-hole component, and that the drill string is inserted into a wellbore, which may be cased or uncased. As a non-limiting example, FIG. 1, shows the deviated portion of a wellbore 100 containing a drill string 102 which includes one of the drill pipe assemblies 10 of the present invention installed between an immediately adjacent up-hole pup joint 106 and a down-hole pup joint 108. As used herein, the term “axial” refers to the direction defined by that segment of the drill string, and the term “transverse” refers to a direction perpendicular to the axial direction. For example, in a portion of a drill string that is vertically oriented, the axial direction is vertical and the transverse direction is horizontal.

FIG. 2 shows one embodiment of a drill pipe assembly 10 of the present invention. In general, the drill pipe assembly 10 includes a tubular body 20 for conducting drilling fluid in a drill string, and one or more roller assemblies 50 for reducing friction between the tubular body 20 and the inner walls of a wellbore.

The tubular body 20 has an up-hole end 22, a down-hole end 24, an inner surface 26 that defines an inner bore 28, and a body outer surface 30. The tubular body 20 may have dimensions selected to suit a particular application, as will be understood by persons skilled in the art. For example, in the embodiment shown in FIG. 2, the tubular body 20 has a length of about 1500 millimeters, an outer diameter of about 130 millimeters and an internal diameter of about 75 millimeters. The tubular body 20 may be made of any suitably hard and durable material such as steel, and more particularly tool steel alloys exhibiting high hardness and resistance to abrasion. For example, a suitable tool steel alloy is marketed as Toolox 44™ (SSAB AB of Stockholm, Sweden) which, at 20 degrees Celsius, has a impact toughness of 18 on the Charpy-V scale as measured in accordance with EN 10 025, EN ISO 148, or EN 10 083 standards.

The up-hole end 22 and the down-hole end 24 of the body 20, are adapted for connection to an adjacent up-hole component and a down-hole component of a pipe string. The connection may comprise any suitable means known in the art. For example, in the embodiment shown in FIG. 2, the up-hole end 22 is a threaded box connection, while the down-hole end 24 is a threaded pin connection. In the embodiments shown, the connections selected for the up-hole end 22 and the down-hole end 24 preserve the substantially cylindrical shape of the body outer surface 30, so as to minimize irregularities that could impede movement of the body 20 within a wellbore.

The inner surface 26 defines the inner bore 28 for conducting drilling fluid. The inner bore 28 extends axially between the up-hole end 22 and the down-hole end 24. In the embodiment shown in FIG. 2, the inner surface 26 is substantially cylindrical in shape. In other embodiments, the inner surface 26 may be contoured as desired to define internal features of the inner bore 28 as are known to persons skilled in the art.

The body outer surface 30 presents a substantially cylindrical surface to the walls of the wellbore. In the embodiment shown in FIG. 2, the body outer surface 30 tapers gradually from a larger diameter at the midpoint of the body to a smaller diameter near the up-hole end 22 and the down-hole end 24 of the tubular body 20. Although the body outer surface 30 is substantially cylindrical, it defines one or more roller pockets 32 to partially receive the rollers 54 of the roller assembly 50. Further, the body outer surface 30 may also define one or more access pockets 36 positioned circumferentially adjacent to one of the roller pockets 32 to facilitate installation of the axles 52 of the roller assembly 50. As an example, the roller pockets 32 and the access pockets 36 may be formed by milling the body outer surface 30 of the tubular body 20, or cast forming the tubular body 20.

In the embodiment shown in FIG. 2 to FIG. 6, the body outer surface 30 defines a plurality of roller pockets 32 and circumferentially adjacent access pockets 36. The roller pockets 32 and access pockets 36 are arranged in four axially spaced apart rows. Each row has four roller pockets 32 and four access pockets 36, with one access pocket 36 between adjacent roller pockets 32. Each roller pocket 32 is a substantially rectangular prismatic depression in the body outer surface 30 with straight opposed side walls 34 extending inwardly from the body outer surface 30 towards the inner bore 28. Each access pocket 36 is a substantially triangular prismatic depression in the body outer surface 30, with side walls 38 converging inwardly from the body outer surface 30 towards the inner bore 28. As shown in FIG. 5, the roller pockets 32 and access pockets 36 are arranged so that the tubular body 20 has a cruciform shape in a transverse cross-section at the elevation of one of the rows. The cruciform shape is rotated by 45 degrees between successive rows to provide an even distribution of roller assemblies 50 over the tubular body 20. Further, the tubular body 20 defines an aperture 40 extending between one of the side walls 34 of the roller pocket 32 and one of the side walls 38 of an adjacent access pocket 36, to retain one of the axles 52 of the roller assembly 50. In other embodiments not shown, the roller pockets 32, their opposed side walls 34, and the access pockets 36 and their side walls 38 may have different shapes and configurations. The number of rows, and the number of roller pockets 32 and 36 may be fewer or greater in number depending on the selected size of the tubular body 20 and rollers 54, and the desired coverage of the rollers 54.

Each roller assembly 50 includes an axle 52 a roller 54. The ends of the axle 52 are retained by the tubular body 20, while the roller 54 is retained by the axle 52 for rotation in the axial direction. The roller 54 is disposed partially within the roller pocket 32, and partially projects outwardly from the body outer surface 30 of the tubular body 20 so as to contact and roll axially along the inner walls of a wellbore.

In the embodiment shown in FIGS. 7A and 7B, the axle 52 is formed by a substantially cylindrical member. The ends of the axle 52 are chamfered to assist insertion of the axle 52 through one of the apertures 40. The outer diameter of the axle 52 closely matches the size of the aperture 40 so that the axle 52 is retained within the aperture 40 by a friction fit, but in other embodiments, the axle 52 may be permitted to rotate within the aperture 40. As an example, the axle 52 may be made of a corrosion resistant metal alloy.

In the embodiment shown in FIGS. 8A and 8B, the roller 54 has a barrel shape with an outer diameter narrowing from the middle towards its ends. In one embodiment, as shown in FIG. 6, the curvature of the barrel 54 closely matches the curvature of the body outer surface 30 of the tubular body 20 in a transverse plane, and only a minor portion of the roller 54 projects outwardly from the body outer surface 30 of the tubular body. The roller 54 has a liner 56 with an inner diameter slightly larger than the outer diameter of the axle 52 to allow for rotation of the roller 54 when retained by the axle 52. As an example, the roller 54 may be made of a suitable hard and durable material such as the tool steel alloy that is used to make the tubular body 20, while the inner liner 56 may be made of the same metal alloy as the axle 52. In embodiments where the axle 52 rotates within the aperture 40, the roller 54 may be affixed to the axle 52.

FIG. 9 shows another embodiment of a drill pipe assembly 10 of the present invention. In general, the drill pipe assembly 10 includes a tubular body 20 for conducting drilling fluid in a drill string, a sleeve 25 that fits concentrically and rotatably around the tubular body 20, and one or more roller assemblies 50 to reduce friction between the tubular body 20 and sleeve 25 and the inner walls of a wellbore.

It will be appreciated that the embodiment of the drill pipe assembly 10 of FIG. 9 is similar to the embodiment of FIG. 2, with one difference being that, in the embodiment shown in FIG. 9, the roller pockets 32 and access pockets 36 are defined by the substantially cylindrical sleeve outer surface 31 of the sleeve 25, as opposed the body outer surface 30. As such, the roller assemblies 50 are directly attached to the sleeve 25, as opposed to the tubular body 20.

In one embodiment, the sleeve 25 is removable from the tubular body 20. For example, in the embodiment shown in FIG. 9, the sleeve 25 is formed by a first portion 27, and a second portion 29. Each of the portions 27, 29 has a semi-cylindrical shape and collectively define the substantially cylindrical sleeve outer surface 31. The sleeve outer surface 31 defines bolt pockets 33 with apertures that receive bolts 35 that releasably secure portions 27, 29. The sleeve 25 may be made of the same material as the tubular body 20, such as a tool steel alloy.

In one embodiment, the body outer surface 30 and the sleeve outer surface 31 have abutting edges that are flush with each other to minimize irregularities that could interfere with the inner walls of a wellbore. For example, in the embodiment shown in FIGS. 11-14, the tubular body 20 has a reduced portion 21 having an outer diameter less than the outer diameter of a portion 23 of the tubular body 20 that defines body outer surface 30. The sleeve 25 fits concentrically around the reduced portion 21 and has a sleeve outer surface 31 with an outer diameter that is the substantially the same as the outer diameter of the body outer surface 30 at their abutting edges.

In one embodiment, the tubular body 20 defines one or more apertures 37 that allow communication of drilling fluid from the inner bore 28 to a space between the tubular body 20 and the sleeve 25. For example, in the embodiment shown in FIG. 11-14, the tubular body 20 has a plurality of apertures 37 distributed over the reduced portion 21 of the tubular body 20. The apertures 37 are relatively small so as to allow a low flow rate of drilling fluid from the inner bore 28 into the narrow annular space between the tubular body 20 and the sleeve 25.

In one embodiment, the roller 54 may have a textured surface to increase friction between the roller 54 and the inner wall of the wellbore. For example, in the embodiment shown in FIGS. 17A and 17B, the roller 54 has a plurality of grooves extending along the length of the roller 54.

In use, the drill pipe assembly 10 is installed in a drill string such as shown in FIG. 1. The up-hole end 22 attaches to an immediately adjacent up-hole component of the drill string, while the down-hole end 24 attaches to an immediately adjacent down-hole component of the drill string. As an example, the up-hole component and down-hole components may be other pup joints 106, 108, such that one drill pipe assembly 10 is installed in about every three or fourth adjacent lengths of pup joints. When the rollers 54 contact the inner walls of the wellbore, the rollers 54 rotate in the axial direction to facilitate the drill string being advanced or withdrawn from the wellbore. In the case of a drill pipe assembly 10 in accordance with the embodiment shown in FIG. 9, the tubular body 20 may also rotate within the rotatable sleeve 25, so as to allow for rotation of the drill string as may be desired in some directional drilling operations.

The relative rotation of the tubular body 20 and the sleeve 25 may be facilitated by the lubricating effect of the drilling fluid that flows under pressure from the inner bore 28 through apertures 37 and into the annular space between the tubular member 20 and the sleeve 25. The size and number of the apertures (37) are limited to provide a sufficient amount of lubrication, without appreciably reducing the volume or pressure of the drilling fluid passing through the tubular body. In alternative embodiment, the outer surface of the tubular body and/or the inner surface of the sleeve may be polished or coated to reduce friction. In a further alternative, seals (not shown) may be used to create a sealed annular lubricating chamber having a lubricant.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein.

Claims

1. A drill pipe assembly installable between an up-hole component and a down-hole component of a drill string insertable in a wellbore, the drill string defining an axial direction and a transverse direction perpendicular thereto, the drill pipe assembly comprising:

(a) a tubular body comprising: an up-hole end adapted for connection to the up-hole component, and a down-hole end adapted for connection to the down-hole component; an inner surface defining an inner bore extending axially between the up-hole end and the down-hole end; a substantially cylindrical body outer surface defining a plurality of inwardly extending roller pockets;

(b) for each of the plurality of roller pockets, a corresponding roller assembly comprising: an axle having opposed ends each retained by the tubular body; and a roller retained by the axle for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the body outer surface.

2. The drill pipe assembly of claim 1 wherein the plurality of roller pockets are arranged in at least one row circumferential around the body outer surface.

3. The drill pipe assembly of claim 2 wherein the at least one row comprises a plurality of rows axially spaced apart from each other.

4. The drill pipe assembly of claim 3 wherein one of the roller pockets is circumferentially offset from one of the roller pockets in one of the adjacent rows.

5. The drill pipe assembly of claim 1 wherein:

the body outer surface further defines an access pocket circumferentially adjacent to one of the plurality of roller pockets and having an inwardly extending side wall;

the body defines an aperture extending between an inwardly extending side wall of the one of the plurality of roller pockets and the side wall of the access pocket; and

the axle is retained by the tubular body within the aperture.

6. The drill pipe assembly of claim 5 wherein the access pocket circumferentially adjacent to the one of the plurality of roller pockets is circumferentially adjacent to another one of the plurality of roller pockets.

7. The drill pipe assembly of claim 1 wherein the roller has a barrel shape with a curvature closely matching the curvature of the body outer surface in a transverse plane.

8. A drill pipe assembly installable between an up-hole component and a down-hole component of a drill string insertable in a wellbore, the drill string defining an axial direction and a transverse direction perpendicular thereto, the drill pipe assembly comprising:

(a) a tubular body comprising: an up-hole end adapted for connection to the up-hole component, and a down-hole end adapted for connection to the down-hole component; an inner surface defining an inner bore extending axially between the up-hole end and the down-hole end; a substantially cylindrical body outer surface;

(b) a sleeve disposed concentrically around the tubular body between the up-hole end and the down-hole end, and comprising a substantially cylindrical sleeve outer surface defining a plurality of inwardly extending roller pockets;

(c) for each of the plurality of roller pockets, a corresponding roller assembly comprising: an axle having opposed ends each retained by the sleeve; and a roller retained by the axle for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the sleeve outer surface.

9. The drill pipe assembly of claim 8 wherein the sleeve comprises a first portion and a second portion releasably securable to the first portion, wherein each of the portions has a semi-annular shape in a transverse plane.

10. The drill pipe assembly of claim 8 wherein the body outer surface and the sleeve outer surface comprise abutting edges that are flush with each other.

11. The drill pipe assembly of claim 10 wherein the sleeve is disposed concentrically around a reduced portion of the tubular body having an outer diameter less than the outer diameter of the body outer surface.

12. The drill pipe assembly of claim 8 wherein the sleeve is rotatable around the tubular body.

13. The drill pipe assembly of claim 12 wherein the tubular body defines at least one aperture for fluid communication between the inner bore and an annular space between the tubular body and the sleeve.

14. The drill pipe assembly of claim 8 wherein the plurality of roller pockets are arranged in at least one row circumferential around the sleeve outer surface.

15. The drill pipe assembly of claim 14 wherein the at least one row comprises a plurality of rows axially spaced apart from each other.

16. The drill pipe assembly of claim 15 wherein one of the roller pockets is circumferentially offset from one of the roller pockets in one of the adjacent rows.

17. The drill pipe assembly of claim 8 wherein:

the sleeve outer surface further defines an access pocket circumferentially adjacent to one of the plurality of roller pockets and having an inwardly extending side wall;

the body defines an aperture extending between an inwardly extending side wall of the one of the plurality roller pockets and the side wall of the access pocket; and

the axle is retained by the sleeve within the aperture.

18. The drill pipe assembly of claim 17 wherein the access pocket circumferentially adjacent to the one of the plurality of roller pockets is circumferentially adjacent to another one of the plurality of roller pockets.

19. The drill pipe assembly of claim 8 wherein the roller has a barrel shape with a curvature closely matching the curvature of the sleeve outer surface in a transverse plane.

20. A sleeve assembly installable on a tubular body having an uphole end for connection to an up-hole component of a drill string and a down-hole end for connection to a down-hole component of a drill string, the drill string insertable in a wellbore and defining an axial direction and a transverse direction perpendicular thereto, the sleeve assembly comprising:

(a) a sleeve disposable concentrically around the tubular body between the up-hole end and the down-hole end of the tubular body, and comprising a substantially cylindrical sleeve outer surface defining a plurality of inwardly extending roller pockets;

(b) for each of the plurality of roller pockets, a corresponding roller assembly comprising: an axle having opposed ends each retained by the sleeve; and a roller retained by for rotating axially relative to the tubular body, partially disposed within the roller pocket and partially projecting outwardly from the sleeve outer surface.