Wellbore reamer

Abstract

A wellbore roller-reamer comprises a mandrel rotatable about a mandrel axis, and a first roller mounted around the mandrel and having an outer reaming surface for engaging a wall of a wellbore. The first roller is rotatable relative to the mandrel about a first roller axis which is offset from the mandrel axis such that, during use, rotation of the mandrel with the outer reaming surface engaged with a wall of the wellbore causes the first roller to be driven to rotate relative to the mandrel and ream the wall of the wellbore.

Claims

1. A wellbore roller-reamer, comprising: a mandrel rotatable about a mandrel axis; a first roller mounted around the mandrel, and comprising a plurality of rib structures extending outwardly of the first roller, wherein each rib defines a discrete portion of an outer reaming surface of the first roller for engaging a wall of a wellbore, wherein each of the plurality of rib structures extend helically and continuously along the length of the first roller; the first roller being rotatable relative to the mandrel about a first roller axis which is offset from the mandrel axis such that, during use, rotation of the mandrel with the outer reaming surface engaged with the wall of the wellbore causes the first roller to be driven to rotate relative to the mandrel and ream the wall of the wellbore, wherein the rib structures are separated by respective bypass recesses, the one or more bypass recesses extending helically along the length of the first roller.

2. The wellbore roller-reamer according to claim 1, wherein the mandrel comprises two axial sections with different outer dimensions and the first roller is mounted on the axial section of the mandrel with a reduced outer dimension.

3. The wellbore roller-reamer according to claim 1, comprising a first bearing sleeve which is mounted on the mandrel, wherein the first roller is mounted on the first bearing sleeve.

4. The wellbore roller-reamer according to claim 3, wherein the first bearing sleeve defines a varying circumferential wall thickness to facilitate the first roller being mounted and arranged in such a way that the first roller axis is offset form the mandrel axis.

5. The wellbore roller-reamer according to claim 3, wherein the first bearing sleeve defines an inner cylindrical surface and an outer cylindrical surface, wherein the inner and outer cylindrical surfaces are eccentrically arranged.

6. The wellbore roller-reamer according to claim 3, comprising at least one bearing element interposed between the first roller and the first bearing sleeve, wherein the at least one bearing element extends at least one of axially, circumferentially and spirally relative to the mandrel axis.

7. The wellbore roller-reamer according to claim 1, comprising a second roller having an outer reaming surface and mounted around the mandrel, wherein the second roller is rotatable relative to the mandrel about a second roller axis which is offset from the mandrel axis such that, during use, rotation of the mandrel with the outer reaming surface of the second roller engaged with a wall of the wellbore causes the second roller to be driven to rotate relative to the mandrel and ream the wall of the wellbore.

8. The wellbore roller-reamer according to claim 7, wherein the first and second roller axes are offset relative to each other and wherein the first and second rollers are axially distributed on the mandrel.

9. The wellbore roller-reamer according to claim 7, comprising a third roller having an outer reaming surface and mounted around the mandrel, wherein the third roller is rotatable relative to the mandrel about a third roller axis which is offset from the mandrel axis such that, during use, rotation of the mandrel with the outer reaming surface of the third roller engaged with a wall of the wellbore causes the third roller to be driven to rotate relative to the mandrel and ream the wall of the wellbore.

10. The wellbore roller-reamer according to claim 9, wherein the third roller axis is offset relative to the first and/or second roller axes such that the eccentricity of the first, second and/or third rollers is provided in different radial directions relative to the mandrel, and wherein the first, second and third rollers are axially distributed on the mandrel.

11. The wellbore roller-reamer according to claim 1, comprising a lubricant system for providing a lubricant to at least the first roller, the lubricant system comprising: a reservoir sleeve mounted around the mandrel to define a radial space between the mandrel and the reservoir sleeve, the radial space defining a lubricant reservoir; and a displacement mechanism to displace lubricant from the lubricant reservoir.

12. The wellbore roller-reamer according to claim 1, comprising an axial load mechanism to provide an axial load between components which are axially stacked on the mandrel.

13. The wellbore roller-reamer according to claim 1, wherein one end of the mandrel comprises a male threaded portion for facilitating coupling of the mandrel to a separate component the male threaded portion being provided adjacent a mounting surface of the mandrel, upon which mounting surface the first roller is mounted.

14. The wellbore roller-reamer according to claim 13, wherein the male threaded portion defines an outer diameter which permits at least the first roller to slide over said male threaded portion to allow mounting of the first roller on the mandrel.

15. The wellbore roller-reamer according to claim 13, comprising a load sleeve defining a torque shoulder, wherein the load sleeve is mountable on the mandrel and securable adjacent the male threaded portion of the first end of the mandrel, such that the torque shoulder and the male threaded portion together define a pin connector to facilitate connection with a box connector of a separate component.

16. The wellbore roller-reamer according to claim 13, wherein the load sleeve is mountable on the mandrel after at least the first roller has been mounted on the mandrel.

17. A reamer roller assembly for a wellbore roller-reamer, comprising: a bearing sleeve defining a sleeve bore to permit mounting on a mandrel, wherein the bearing sleeve defines a sleeve bore axis; and a roller circumscribing the bearing sleeve, the roller comprising a plurality of rib structures extending outwardly of the first roller, wherein each rib defines a discrete portion of an outer reaming surface of the first roller for engaging a wall of a wellbore, wherein each of the plurality of rib structures extend helically and continuously along the length of the first roller; and wherein the roller is rotatable relative to the bearing sleeve about a roller axis, the sleeve bore axis and the roller axis being offset relative to each other; wherein the rib structures are separated by respective bypass recesses, the one or more bypass recesses extending helically along the length of the first roller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

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

(2) FIG. 1 is a diagrammatic illustration of a known roller reamer;

(3) FIG. 2 is a cross-section along line 2-2 of FIG. 1;

(4) FIG. 3 is a diagrammatic illustration of a wellbore roller-reamer in accordance with an example of the present disclosure;

(5) FIG. 4 is a cross-section along line 4-4 of FIG. 3;

(6) FIG. 5 is a perspective view of a wellbore roller-reamer in accordance with an example of the present disclosure;

(7) FIG. 6 is a sectional perspective view of the roller reamer of FIG. 5;

(8) FIG. 7 is an enlarged sectional view of roller assemblies of the roller reamer of FIG. 5;

(9) FIG. 8 is a sectional perspective view of a single roller assembly of the roller reamer of FIG. 5;

(10) FIG. 9 is a sectional and exploded view of the roller assembly of FIG. 8;

(11) FIG. 10 is a perspective view of a bearing assembly which forms part of the roller assembly of FIG. 8;

(12) FIG. 11 is an exploded view of the bearing assembly of FIG. 10;

(13) FIG. 12 is a perspective view of an alternative form of a bearing assembly;

(14) FIG. 13 is an exploded view of a mandrel and roller assemblies of the roller-reamer of FIG. 5;

(15) FIG. 14 is an enlarged sectional view of a lubrication system of the roller-reamer of FIG. 5;

(16) FIG. 15 is a complete exploded view of the roller-reamer of FIG. 5;

(17) FIG. 16 is a sectional perspective view of a roller-reamer according to an example of the present disclosure; and

(18) FIG. 17 is an exploded view of the roller-reamer of FIG. 16.

(19) FIG. 18 is an enlarged sectional view of a lubrication system of a roller-reamer according to an example of the present disclosure.

(20) FIG. 19 is a perspective view of a mandrel forming part of the lubrication system of FIG. 18.

(21) FIG. 20 is a sectional perspective view of a bearing sleeve of an individual roller assembly forming part of the lubrication system of FIG. 18.

(22) FIG. 21 an enlarged sectional perspective view of a portion of the lubrication system of FIG. 18.

DETAILED DESCRIPTION OF THE DRAWINGS

(23) An example wellbore roller-reamer, generally identified by reference numeral 22, is diagrammatically illustrated in FIG. 3 located within a wellbore 12, with FIG. 4 providing a cross-section through line 4-4 of FIG. 3. The roller-reamer tool 22 includes a tubular mandrel 24 which defines a mandrel axis 30, and is secured to a drill bit or bottom hole assembly 16 via a first connector 26, and to a drill string 14 via a second connector 28. The mandrel 24 and drill bit 16 are rotated by the drill string 14.

(24) The wellbore roller-reamer 22 in the present example includes three axially arranged reamer rollers 32, 34, 36 (more or less rollers could be provided) which are rotatably mounted around (and thus circumscribe) the mandrel 24, wherein each roller 32, 34, 36 includes a respective reaming surface or structure 38, 40, 42 configured to engage and ream the wall of the wellbore 12. Each roller 32, 34, 36 defines a respective roller axis 44, 46, 48 (FIG. 4), about which axes the rollers 32, 34, 36 rotate. In the present example the roller axes 44, 46, 48 are each laterally offset from the mandrel axis 30, and also from each other. Specifically, the lateral offset between the roller axes 44, 46, 48 is such that these are evenly circumferentially distributed around the mandrel axis 30 (i.e., 120 degrees apart).

(25) The lateral offset of the various axes eccentrically arranges the individual rollers 32, 34, 36 relative to the mandrel 24 at a circumferential phasing, and thus establishes respective reaming contact points 50, 52, 54 between each roller 32, 34, 36 and the wall of the wellbore 12, with the contact points 50, 52, 54 being both circumferentially and axially distributed relative to each other. The provision of such axially and circumferentially distributed reaming contact points 50, 52, 54 may provide benefits over prior art designs. For example, the distributed contact points may assist to provide a degree of centralising of the wellbore roller-reamer 22 within the bore 12 during forming. Further, the roller-reamer 22 may provide a stabilising function, perhaps facilitating better control of the trajectory of the drill bit 16.

(26) It should be noted that the lateral offset between axes and the corresponding eccentric mounting of the rollers has been exaggerated in FIGS. 3 and 4 for illustration purposes.

(27) The offset between the mandrel axis 30 and the roller axes 44, 46, 48, combined with the contact with the bore wall, facilitates each roller 32, 34, 36 to be rotatably driven during rotation of the mandrel 24. In this case the rollers 32, 34, 36 and associated reaming contact points 50, 52, 54 will effectively orbit the wellbore 12, thus providing the mechanism by which the wellbore roller-reamer 22 effectively reams the wellbore 12. It will be appreciated that the established relative rotation between the mandrel 24 and rollers 32, 34, 36 is counter rotation, such that when the mandrel 24 rotates in a first direction, the rollers 32, 34, 36 are driven to rotate in a reverse second direction.

(28) By mounting the rollers around (i.e., circumscribing) the mandrel the rollers may thus be permitted to define a larger diameter, which may mitigate issues associated with smaller dimeter rollers in prior art reamers.

(29) A more detailed description of the roller reamer 22 will now be described, initially with reference to FIG. 5 which is a perspective view of the roller reamer 22, and FIG. 6 which is a part sectional view of the roller reamer 22 in FIG. 5.

(30) As noted above, the roller-reamer 22 includes a mandrel 24 which rotatably supports three axially distributed and eccentrically arranged rollers 32, 34, 36. One end of the roller reamer 22 includes the connector 28, specifically a box connector, which facilitates connection to a drill string (see 14 in FIG. 3). The roller-reamer 22 further includes a connector sub 56 which includes the connector 26, specifically a pin connector, which facilitates connection to a drilling BHA (see 16 in FIG. 3). The connector sub 56 is secured to the mandrel 24 via a threaded connection 58. Specifically, the end of the mandrel 24 includes a male pin thread 60 which is received within a female box connector 62 of the connector sub 56. The connector sub 56 may therefore be used to axially secure the various components on the mandrel 24. As such, the threaded connection 58 may function as a service connector/break within the roller-reamer 22, for example to facilitate assembly of components.

(31) In the present example the roller-reamer 22 further includes a lubrication system 64, which will be described in more detail below. The roller-reamer 22 further includes a spring assembly 66 interposed between the lubrication system 64 and connector sub 56. In this respect the spring assembly 66 is energised when the connector sub 56 is coupled to the mandrel 24, thus providing an axial pre-load between the mandrel 24, rollers 32, 34, 36 and lubrication system 64.

(32) Reference is now made to FIG. 7 which is an enlarged view of the roller-reamer 22 illustrated in FIG. 6, in the region of the rollers 32, 34, 36. The mandrel 24 includes a first axial section 68 which defines a first wall thickness T, and an adjacent second axial section 70 which defines a reduced wall thickness t, wherein the rollers 32, 34, 36 are each rotatably mounted around the second axial section 70. An annular shoulder 72 defines a stepped transition between the different wall thicknesses T, t, wherein the annular shoulder 72 includes a radiused root for stress management purposes. In the present example a spacer ring 74 is provided between roller 32 and the annular shoulder 72, wherein the spacer ring 74 matches the radiused profile of the shoulder 72. Furthermore, adjacent rollers 32, 34, 36 are separated by thrust rings 76, and similarly a thrust ring 76 is interposed between roller 32 and spacer ring 74, and between roller 36 and lubrication system 64.

(33) In the present example the rollers 32, 34, 36 are included as part of respective identical roller assemblies 78, 80, 82, which will now be described in detail. In this respect reference is now made to FIG. 8 which is a sectional view of roller assembly 78, and FIG. 9 which is an exploded sectional view of the same roller assembly 78.

(34) The roller 32 includes a series of rib structures 84 upon which are mounted a number of reaming/cutting inserts 86 formed from a suitably hard wearing material, such as tungsten carbide. In this respect the outer surfaces of the ribs 84 define discrete portions of a discontinuous outer reaming surface of the roller 32.

(35) The rib structures 84 are circumferentially separated by recesses 85 which each extend axially along the roller 32. The recesses 85 may be defined as bypass recesses in that they retain a degree of flow bypass area past the roller 32 when the wellbore roller-reamer 22 is in use. In this respect, and as noted above, by mounting the rollers around the mandrel 24 the rollers may be permitted to define a larger diameter than known roller-reamers. As a consequence, however, when the wellbore roller-reamer 22 is in use the rollers may occupy a substantial section of the bore, such that fluid bypass may be restricted. The provision of the bypass recesses 85 may address this possible restriction issue by providing a larger bypass flow area.

(36) The roller 32 is circumferentially and rotatably mounted on a bearing sleeve 88, with O-ring seals 90 provided therebetween. Thrust rings 76 are also mounted on the bearing sleeve 88, on opposing sides of the roller 86.

(37) A complete bearing sleeve 88 is illustrated in FIG. 10, reference to which is additionally made. The bearing sleeve 88 defines a cylindrical inner surface 92 which facilitates mounting of the roller assembly 78 on the mandrel 22. The bearing sleeve 88 also includes an outer generally cylindrical surface 94. The wall thickness of the bearing sleeve 88 varies, from its thickest region 96 to its thinnest region 98 on a diametrically opposing side. The nature of the variation in wall thickness is such that the inner and outer cylindrical surfaces 92, 94 are eccentrically arranged, with the inner surface 92 being generally concentric with the mandrel axis 30 (when mounted on the mandrel 24), and the outer surface 94 being generally concentric with the roller axis 44. As such, in the present example it is the variation in wall thickness and eccentricity of the bearing sleeve 88 which facilitates the lateral offset of the axes 30, 44.

(38) The bearing sleeve 88 further includes a longitudinal recess 100 on the inner surface 92, specifically at the location of the thickest wall region 96. As will be described in more detail below, the recess 100 facilitates alignment and rotatably securing the bearing sleeve 88 on the mandrel.

(39) The bearing sleeve 88 further includes a circumferential array of bearing pads 102 extending outwardly from the outer surface 94. The bearing pads 102 may be composed of a low friction material, and provide rotatable bearing engagement with the inner surface of the roller 32. The bearing pads 102 may be integrally formed with the bearing sleeve 88, as shown in FIG. 10, or alternatively may be provided as separate inserts mounted in pockets 104 formed in the outer surface 94 of the bearing sleeve 88, as illustrated in FIG. 11. In the examples of FIGS. 10 and 11, the individual bearing pads 102 extend axially. However, in a further example, as shown in FIG. 12, the bearing pads 102 may extend helically. In an alternative example (not illustrated) bearing pads may be provided on or in the inner surface of the roller 32. Furthermore, the radial extent of individual bearing pads may vary, which may provide eccentric mounting of the roller 32.

(40) As described previously, the roller assemblies 78, 80, 82 (FIG. 7) are configured identically. In this respect, the variation in lateral offset between the individual rollers 32, 34, 36 is achieved by varying the mounting alignment of the respective bearing sleeves 88 on the mandrel 24, as illustrated in FIG. 13, which is an exploded view of the mandrel 24 and roller assemblies 78, 80, 82. As described above, the bearing sleeve of each roller assembly includes a longitudinal recess 100. The roller assemblies 78, 80, 82 may thus be mounted onto the mandrel 24 such that the individual recesses 100 are engaged with respective keys 102 which are secured in any suitable way to the mandrel 24 at the desired circumferential spacing. In this way the roller assemblies may be mounted with a defined rotational offset, with the keys 102 also functioning to rotatably lock the bearing sleeves 88 to the mandrel 24.

(41) Reference is now made to FIG. 14 which is an enlarged view of the roller-reamer 22 illustrated in FIG. 6, in the region of the lubrication system 64. The lubrication system 64 includes a reservoir sleeve 106 mounted around the mandrel 24 and between roller assembly 82 and spring system 66. The reservoir sleeve 64 defines an annular space 110 with the outer surface of the mandrel 24, which is configured to accommodate a lubricant, such as grease, oil or the like. An annular piston 112 is sealably mounted in the annular spaces 110, and is acted upon by a spring 114, such that the spring 114 and piston 112 apply a positive pressure on the lubricant in the annular space 110. In this respect the lubricant may be displaced and fed towards the roller assemblies to provide suitable lubricating effect. A lubricant circuit communicates lubricant from the annular reservoir space 110 towards the roller assemblies. The lubricant reservoir may be defined by spaces etc. formed between different components of the roller-reamer 22. Further, the lubricant circuit may be provided by various grooves, ports, slots, annuli and the like throughout the assembly. An example form of a lubricant circuit will be provided later below.

(42) The nature of the present roller-reamer 22 is such that the volume of lubricant which can be accommodated represents a significant improvement over the prior art. Any variation in the required reservoir volume may be readily adjusted by simple selection of the length of mandrel 24 and reservoir sleeve 106.

(43) FIG. 15 is an exploded view of the roller reamer 22, which illustrates the sequence of assembly. In this respect, the sequence may involve mounting the spacer ring 75 on the mandrel 24 and installing the keys 106. The roller a roller assemblies 78, 80, 82 may then be mounted on the mandrel 24, with their alignment dictated by the position of the keys 106. The lubrication system 64 is then formed by mounting the piston 112, spring 115 and reservoir sleeve 106 on the mandrel 24, in addition to a suitable volume of lubricant. The spring system 66 is then mounted, and the connector sub secured to the mandrel via the male threaded portion 60, which functions to axially secure all components to the mandrel 24, with axial preloading provided by the spring system 66.

(44) In the example provided above the connector sub 56 is secured to the mandrel 24 via the male threaded portion 60 on the end of the mandrel. While this may be entirely sufficient in many circumstances, there may be requirements where a more robust connection is required, which includes a suitable thread torque shoulder against which the connector sub can rotationally and axially engage to provide a desired coupling torque. In this respect a further example wellbore roller-reamer 122 which includes such a facility is shown in FIGS. 16 and 17, reference to which is now made.

(45) FIG. 16 provides a sectional perspective view of the assembled roller-reamer 122, whereas FIG. 17 provides an exploded view of the roller-reamer 122. The example roller-reamer 122 in FIGS. 16 and 17 is similar in many respects to the example described above (roller-reamer 22), and as such for brevity identical components and features have been identified by the same reference numerals, with minimal additional description provided. Thus, the roller reamer 122 also includes: a mandrel 24 which includes a male threaded portion 60 at one end; roller assemblies 78, 80, 82 mounted on the mandrel 22 and located/aligned via keys 106; a lubrication system 64 formed from a reservoir sleeve 106, annular piston 112 and spring 114; a spring system 66; and a connector sub 56 connectable to the male thread portion 60 of the mandrel 24.

(46) In the present example, however, the roller-reamer 122 further includes a load sleeve 150 which is axially interposed between the spring system 66 and the connector sub 56, with the mandrel length being extended to accommodate. The load sleeve 150 comprises an axial torque shoulder 152 which is engaged by a corresponding torque shoulder 154 of the box connector 62 of the connector sub 56, thus providing a very robust and conventional pin and box type connection.

(47) There are multiple possible options to facilitate suitable mounting and connection of the load sleeve 150 on/to the mandrel 24. In the present example, a split load ring 156 is axially secured to the mandrel 24 via complementary circumferential grooves 158 and ribs 160. Mounting of the load sleeve 150 on the mandrel 24 and over the split load ring 156 effectively holds the split load ring 156 together, with axial load transfer between the load sleeve 150 and the split load ring 156 being achieved via a shoulder 162 internally of the load sleeve 150.

(48) A number of circumferentially distributed keys 164 are mounted in corresponding slots 166 in the mandrel 24, and become received into complementary slots 168 formed in the inner surface of the load sleeve 150 as the sleeve 150 is mounted onto the mandrel 24. Once assembled as such, the load sleeve 150 also becomes rotatably secured to the mandrel 24, and thus capable of resisting torque applied during connection with the connector sub 56.

(49) In order to ensure sealing integrity, a pair of O-rings 170 is provided between the load sleeve 150 and the mandrel 24.

(50) The load sleeve 150 may thus be absent during the process of installing the roller assemblies 78, 80, 82, and the various other components, onto the mandrel 24.

(51) Following assembly of the various components, the load sleeve 150 may be installed, effectively permitting the construction of a more convention pin connector to be achieved.

(52) As noted above, a lubricant circuit is provided to ensure appropriate delivery of lubricant from the lubricant reservoir to the rollers. An example of such a lubricant circuit will now be provided with reference to FIGS. 18 to 21.

(53) FIG. 18 is an enlarged perspective sectional view of a portion of a wellbore roller-reamer 222, specifically in the region of a lubrication system 264 of the roller-reamer 222. In this respect the roller-reamer 222 is similar in most respects to roller-reamer 22, and as such like features share like reference numerals, incremented by 200. Due to the significant similarities a full description of all features of roller-reamer 222 will not be repeated, for brevity.

(54) A reservoir 210 of the lubrication system 264 is provided by an annular space created between an inner surface of a reservoir sleeve 206 and an outer surface of a mandrel 224. Lubricant is communicated from the lubrication reservoir 210 to multiple roller assemblies (only one roller assembly 282 is partially shown in FIG. 18) via a communication path which will now be described.

(55) In the present example, a spring 214 and piston 212 create a relatively low differential pressure on the lubricant within the lubrication reservoir 210 (e.g. 5 to 10 psi). This differential pressure causes lubricant to be driven from the lubrication reservoir 210 to a groove or slot 180 provided along part of the mandrel 224.

(56) FIG. 19 shows the mandrel 224 in isolation, illustrating the axial direction of the groove or slot 180 along the mandrel 224. In alternative examples the groove or slot 180 may follow an alternative path, such as a helical path. The groove or slot 180 is provided in this manner to provide lubricant to all roller assemblies of the wellbore roller-reamer 222.

(57) FIG. 20 shows a perspective cross-sectional view of a bearing sleeve 288 of roller assembly 282, which defines an annular groove 182 in its internal surface 292. This annular groove 182 provides a means of communication with the lubricant groove or slot 180 of the mandrel 224.

(58) The bearing sleeve 288 further includes a radial port 184 which provides communication between the internal annular groove 182 of the bearing sleeve 288 and an outer surface 294 of the bearing sleeve 288. Although a single radial port 184 is provided it should be understood that any number of ports may be provided. The grove or slot 180, annular groove 182 and radial port 184 thus permit lubricant to be delivered between the outer surface 294 of the bearing sleeve 288 and inner surface of the associated outer roller (not shown in FIG. 20).

(59) FIG. 21 illustrates lubricant circuit described above delivering lubricant to multiple rollers (280, 282).

(60) The present example roller-reamer 22 also includes a spring assembly 266 interposed between the lubrication system 264 and a connector sub 256. As before, the spring assembly 266 is energised when the connector sub 256 is coupled to the mandrel 224, thus providing an axial pre-load between different components mounted on the mandrel 224. This preload may provide sufficient pressure contact between adjacent components to retain the lubricant within the system. Alternatively, seals may be provided (such as face seals or radial seals) between the components to seal the lubricant within the system.

(61) It should be understood that the descriptions provided here are merely exemplary of the present disclosure, and that various modifications are possible. For example, while the examples provided above include roller assemblies which include rollers mounted on respective bearing sleeves, the bearing sleeves may be omitted and the rollers mounted directly on the mandrel. Further, a single bearing sleeve may be provided to accommodate two or more rollers.