WHEEL ASSEMBLY

Abstract

A wheel assembly and a method for detachably connecting the wheel assembly to a downhole tool to reduce friction between the downhole tool and a sidewall of a borehole through which the downhole tool is being transported. The wheel assembly may include a shaft configured to contact a sidewall of the downhole tool, a wheel rotatably connected to the shaft, and a fastener configured to extend into the sidewall of the downhole tool to detachably connect the shaft to the downhole tool.

Description

This application claims priority to and benefit from U.S. Provisional Patent Application No. 62 / 987,309, entitled Wheel Assembly, filed March 9, 2020, the entire disclosure of which is incorporated herein by reference. BACKGROUND OF THE INVENTION Wells are typically drilled into the Earth's surface or the seafloor to recover natural deposits of oil, gas, and other natural resources trapped within underground rock formations of the Earth's crust. Testing and evaluation of completed and partially completed wells has become routine to increase well production and investment returns. Downhole measurements of formation pressure, formation permeability, and the recovery of formation fluid samples can be useful in predicting the economic value, production capacity, and lifespan of geological formations. Well completion and stimulation operations, such as drilling and fracturing, can also be performed to optimize well productivity.Plugging and perforating tools can be used to place plugs within a wellbore to isolate portions of the hole and the surrounding rock formations from each other and to perforate the wellbore in preparation for fracturing. Each fracturing stage interval along the hole can be perforated with one or more perforating tools, forming one or more sets of drill tunnels along the hole. Intervention operations on completed wells, such as the installation, removal, or replacement of various production equipment, can also be performed as part of well workover, maintenance, or permanent abandonment operations. Testing, completion, intervention, and other downhole operations have become complicated as holes are drilled to greater depths and often include extensive horizontal or otherwise non-vertical (i.e., sidetracked) portions. Downhole tools conventionally used in vertical and near-vertical holes can encounter problems when used in non-vertical portions of a hole. Such downhole tools can be lowered into a hole as part of a tool string that uses gravity to facilitate transport or movement through the hole. ML / a / zuzz / ui i uo / In non-vertical holes, gravity can be overcome by frictional forces between the toolstring and the sidewalls of the hole, which resists movement of the toolstring through the hole. In addition to the increased friction due to a steeper horizontal gradient, the movement of a toolstring along a non-vertical portion of a hole can be further hampered by the presence of various obstacles. For example, washouts, sharp bends, misaligned tubular joints, transitions between casing, lining, and bare hole sidewalls, and other irregular surfaces can present increased resistance or impediments to the movement of the toolstring through the hole. Furthermore, particularly with openhole holes that are not lined with casing, the outer surface of the toolstring may stick to the sidewall of the hole, or an edge of the toolstring may sag or bind against imperfections along the sidewall of the hole. SUMMARY OF THE INVENTION This summary is provided to introduce a selection of concepts that are described in more detail below in the detailed description. This summary is not intended to identify essential features of the claimed subject matter, nor is it intended to be used as a contribution to limiting the scope of the claimed subject matter. The present disclosure features an apparatus comprising a wheel assembly configured to be removably connected to a downhole tool to thereby reduce friction between the downhole tool and a sidewall of a borehole through which the downhole tool is transported, the wheel assembly comprising: a shaft configured to contact a sidewall of the downhole tool; a wheel rotatably connected to the shaft; and a fastener configured to extend into the sidewall of the downhole tool to removably connect the shaft to the downhole tool. The present disclosure also features a method comprising connecting a wheel assembly to a downhole tool to reduce friction between the downhole tool and a sidewall of a hole through which the downhole tool is transported, wherein the wheel assembly comprises an axle and a wheel rotatably connected to the axle, and wherein connecting the wheel assembly to the downhole tool comprises inserting a wheel assembly into the wheel assembly. ΜΛ / a / ZUZZ / U 1 i uo / fastener at least partially in a side wall of the downhole tool for connecting the shaft to the downhole tool. The present disclosure also features an apparatus comprising a wheel assembly for a downhole tool, the wheel assembly operable to reduce friction between the downhole tool and a sidewall of a borehole through which the downhole tool is transported, and the wheel assembly comprising: a shaft comprising an outer circumferential groove and a pitch extending through the shaft; a wheel disposed about the shaft and comprising an inner circumferential groove, the outer circumferential groove and the inner circumferential groove collectively defining a circumferential space between the shaft and the wheel, and the pitch intersects the circumferential space; a plurality of ball bearings disposed within the circumferential space and configured to reduce friction between the shaft and the wheel;and a locking member disposed within the passage, wherein the locking member is movable within the passage between a first position in which the ball bearings can be inserted into the circumferential space through the passage and a second position in which the locking member prevents the ball bearings from exiting the circumferential space through the passage.; These and additional aspects of the present disclosure are set forth in the description that follows, and / or can be learned by one skilled in the art by reading the material herein and / or by practicing the principles described herein. At least some aspects of the present disclosure can be achieved by the means recited in the appended claims. BRIEF DESCRIPTION OF THE FIGURES This description is best understood from the following detailed description when read in conjunction with the accompanying figures. It is emphasized that, in accordance with standard industry practice, several elements are not drawn to scale. In fact, the dimensions of various elements may be arbitrarily increased or decreased for clarity of discussion. Figure 1 is a schematic view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 2 is a cross-sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 3 is a side view of the apparatus shown in Figure 2 according to one or more 3 ΜΛ / a / zuzz / ui i uor aspects of this description. Figure 4 is a cross-sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 5 is an axial view of the apparatus shown in Figure 4 in accordance with one or more aspects of the present disclosure. Figure 6 is a cross-sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 7 is an axial view of the apparatus shown in Figure 6 in accordance with one or more aspects of the present disclosure. Figure 8 is a cross-sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 9 is a side view of the apparatus shown in Figure 8 in accordance with one or more aspects of the present disclosure. Figure 10 is an axial sectional view of the apparatus shown in Figure 9 in accordance with one or more aspects of the present disclosure. Figure 11 is an axial sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 12 is a side view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 13 is an axial sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 14 is an axial sectional view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 15 is a schematic view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 16 is a perspective view of at least a portion of an example implementation of an apparatus according to one or more aspects of the present disclosure. Figure 17 is another perspective view of the apparatus shown in Figure 16 in accordance with one or more aspects of the present disclosure. Figure 18 is a side view of the apparatus shown in Figures 16 and 17 in accordance with one or more aspects of the present disclosure. Figure 19 is an exploded view of the apparatus shown in Figures 16-18 according to one ΜΛ / a / zuzz / ui i uo / or more aspects of the present description. Figure 20 is an axial view of the apparatus shown in Figures 16-19 in a stage of assembly operations. Figure 21 is an axial view of the apparatus shown in Figure 20 at a different stage of the assembly operations. Figure 22 is an axial sectional view of the apparatus shown in Figure 21 in accordance with one or more aspects of the present disclosure. Figure 23 is a perspective view of a portion of the apparatus shown in Figures 20-22 at a different stage of assembly operations. Figure 24 is a perspective sectional view of the apparatus shown in Figures 16-19 in a stage of connection operations. DETAILED DESCRIPTION It should be understood that the following description provides many different embodiments, or examples, for implementing different features of various embodiments. Specific examples of components and arrangements are described below to simplify the present description. These are, of course, mere examples and are not intended to be limiting. In addition, reference letters and / or numbers may be repeated in various examples throughout the present description. This repetition is for simplicity and clarity and does not in itself dictate a relationship between the various embodiments and / or configurations discussed.Furthermore, the formation of a first element on or in a second element in the description that follows may include embodiments in which the first and second elements are formed in direct contact, and may also include embodiments in which additional elements may be formed by interposing the first and second elements, such that the first and second elements may not be in direct contact. Terms such as upper, upward, above, lower, downward, and / or down are used herein to indicate relative positions and / or directions between apparatus, tools, components, parts, portions, members, and / or other elements described herein, as shown in the corresponding figures. Such terms do not necessarily indicate relative positions and / or directions when actually implemented. Such terms, however, may indicate relative positions and / or directions with respect to a pit when an apparatus is used in accordance with one or more aspects of the present disclosure or is otherwise arranged within the pit. For example, the term upper may mean in the MΛ / a / zuzz / ui i uo / wellhead direction and the term lower may mean in the downhole direction. Figure 1 is a schematic view of at least a portion of an exemplary implementation of a well placement system 100 in accordance with one or more aspects of the present disclosure, depicting an exemplary environment in which one or more aspects of the present disclosure may be implemented. The well placement system 100 is depicted in relation to a hole 102 formed by rotary and / or directional drilling and extending from the well placement surface 104 into a subterranean formation 106.A lower portion of the hole 102 is shown enlarged as compared to an upper portion of the hole 102 adjacent the wellsite surface 104 to allow for a larger and therefore more detailed depiction of various tools, tubulars, devices, and other objects disposed within the hole 102. The wellsite system 100 may be used to facilitate the recovery of oil, gas, and / or other materials that are trapped in the subterranean formation 106 via the hole 102. At least a portion of the hole 102 may be a cased hole 102 comprising a casing 108 secured with cement 109, and / or a portion of the hole 102 may be an openhole hole 102 lacking the casing 108 and cement 109.The well 102 may also or instead contain a fluid conduit (e.g., production tubing) (not shown) disposed within at least a portion of the casing 108 and / or an openhole portion of the well 102. Thus, one or more aspects of the present disclosure are applicable and / or readily adaptable for use in a cased hole portion of the well 102, an openhole portion of the well 102, and / or a fluid conduit disposed within a cased hole and / or openhole portion of a well 102. It is also noted that although the well placement system 100 is depicted as an onshore implementation, it should be understood that the aspects described below are generally applicable to offshore implementations as well. The wellsite system 100 includes surface equipment 130 located at the surface of the wellsite 104. The wellsite system 100 also includes or is operable in conjunction with a downhole intervention and / or sensor assembly, referred to as a tool string 110, transported into the borehole 102 via a transport line 120 operatively connected to one or more pieces of surface equipment 130. The transport line 120 may be operatively connected to a transport device 140 operable to apply an adjustable downwardly and / or upwardly directed force to the tool string 110 via the transport line 120 to transport the tool string 110 into the borehole 102. The transport line 120 may be or comprise coiled tubing, a wireline, a conductor cable, a slickline, a line multiple or an electronic line, among other examples.The transport device 140 may be, comprise, or form at least a portion of a sheave or pulley, a winch, a hauling mechanism, an injection head, and / or other device coupled to the tool string 110 via the transport line 120. The transport device 140 may be supported above the hole 102 via a mast, a derrick, a crane, and / or other support structure 142. The surface equipment 130 may further comprise a reel or drum 146 configured to store thereon a coiled length of the transport line 120, which may be selectively spooled and unspooled by the transport device 140 to selectively transport the tool string 110 into, along, and out of the hole 102. Instead of or in addition to the transport device 140, the surface equipment 130 may comprise a winch transport device 144 comprising or operatively connected to the drum 146. The drum 146 may be rotated by a rotary actuator 148 (e.g., an electric motor) to selectively pay out and reel in the transport line 120 to apply an adjustable pulling force to the tool string 110 to selectively transport the tool string 110 into, along, and out of the hole 102. The transport line 120 may comprise one or more metal support wires or cables configured to support the weight of the downhole tool string 110. The transport line 120 may also comprise one or more insulated electrical and / or optical conductors 122 operable to transmit electrical power (i.e., electrical energy) and electrical and / or optical signals (e.g., downlink control data and / or uplink sensor data) between the tool string 110 and one or more components of the surface equipment 130, such as a power and control system 150. The transport line 120 may comprise and / or be operable in conjunction with communication means between the tool string 110, the transport device 140, the winch transport device 144, and / or one or more portions of the surface equipment 130, including the power and control system 150. The hole 102 may be plugged by a plurality (e.g., a stack) of fluid control devices 132, which may include a Christmas tree comprising fluid control valves, spools, and fittings operable individually and / or collectively to direct and control fluid flow out of the hole 102. The fluid control devices 132 may also comprise, or in lieu thereof, a blowout preventer (BOP) stack operable to prevent fluid flow out of the hole 102. ML / a / zuzz / ui i uo / of hole 102. Fluid control devices 132 may be mounted on top of a wellhead 134. The surface equipment 140 may further comprise a sealing and aligning assembly 136 mounted to the fluid control devices 132 and operable to seal the carrier line 120 during deployment, transport, intervention, and other wellsite operations. The sealing and aligning assembly 136 may comprise a lockout chamber (e.g., a lubricator, airlock, riser, etc.) mounted to the fluid control devices 132 and a stuffing box operable to seal around the carrier line 120 on top of the lockout chamber, although such details are not shown in Figure 1.The stuffing box may be operable to seal around an exterior surface of the conveying line 120, for example by annular gaskets applied around the surface of the conveying line 120 and / or by injecting a fluid between the exterior surfaces of the conveying line 120 and an interior wall of the stuffing box. The tool string 110 may be deployed or retrieved from the borehole 102 via the transport device 140 and / or the winch transport device 144, through the wellhead 134, the control devices 132, and / or the sealing and alignment assembly 136. The power and control system 150 (e.g., a control center) may be used to monitor and control various portions of the wellsite system 100. The power and control system 150 may be located at the surface of the wellsite 104 or in a structure located on the surface of the wellsite 104. However, the power and control system 150 may be located away from the surface of the wellsite 104. The power and control system 150 may include an electrical power source 152, a memory device 154, and a surface controller 156. The power source 152 (e.g., a battery, an electric generator, etc.)) may supply electrical power to various pieces of equipment in the well emplacement system 100, including the memory device 154, the surface controller 156, the tool string 110, the transport device 140, and / or the winch transport device 144. The surface controller 156 (e.g., a processing device, a computer, etc.) may store executable programs and / or instructions, including for implementing one or more aspects of the methods, processes, and operations described herein. The surface controller 156 may be communicatively connected to various pieces of equipment in the well emplacement system 100, so as to allow the surface controller 156 to monitor operations of one or more portions of the emplacement system. ML / a / zuzz / ui i uo / of well 100 and / or to provide automatic control of one or more portions of the well site system 100, including the tool string 110, the transport device 140 and / or the winch transport device 144. The surface controller 156 may also be used by well site personnel (i.e., a human operator) to manually control one or more portions of the well site system 100, including the tool string 110, the transport device 140 and / or the winch transport device 144. The surface controller 156 may include input devices for receiving commands from the well site personnel and output devices for displaying information to the well site personnel. The tool string 110 may be transported downhole 102 to perform various sampling, testing, intervention, and other downhole operations. The tool string 110 may further comprise one or more downhole tools 112 (e.g., devices, modules, replacement joints, etc.) operable to perform such downhole operations. The downhole tools 112 of the tool string 110 may include one or more of an acoustic tool, a wireline head, a casing collar locator (CCL), a cutting tool, a density tool, a depth correlation tool, a directional tool, an electrical power module, an electromagnetic (EM) tool, a formation testing tool, a fluid sampling tool, a gamma ray (GR) tool, a gravity tool, a formation logging tool,a hydraulic power module, a magnetic resonance tool, a formation measurement tool, a shakeout tool, a mechanical interface tool, a monitoring tool, a neutron tool, a nuclear tool, a drilling tool, a photoelectric factor tool, a plug, a plug setting tool, a porosity tool, a power module, a ram, a reservoir characterization tool, a resistivity tool, a seismic tool, a plotting tool, a surveying tool, and / or a telemetry tool, among other examples also within the scope of this disclosure. A plurality of wheel assemblies 114 may be connected to the tool string 110 to reduce friction between the tool string 110 and a side wall (e.g., an inner surface) of the hole 102, and thereby facilitate or assist with transporting the tool string 110 along the hole 102. As described herein, the side wall of the hole 102 may be ML / a / zuzz / ui i uor include a sidewall of rock formation 106 if hole 102 is an openhole hole, a sidewall of casing 108 along locations where casing 108 is installed in rock formation 106, or a sidewall of a fluid conduit if such a fluid conduit is installed within an openhole hole or casing 108. Wheel assemblies 114 may be or form a portion of tool string 110. Each wheel assembly 114 may comprise a shaft (not shown) and a wheel rotatably connected to the shaft. The shaft of each wheel assembly 114 may be removably connected to a corresponding downhole tool 112 to removably connect the wheel assembly 114 to the tool string 110. Each wheel assembly 114 may be removably connected to a body (e.g., a casing, a frame, a block, etc.) of a corresponding downhole tool 112 of the tool string 110. The wheel assemblies 114 may be connected to the tool string 110 when the wheel assemblies 114 are needed to assist in transporting the tool string 110 along the hole 102, and may be disconnected from the tool string 110 when the wheel assemblies 114 are not needed to assist in transporting the tool string 110 along the hole 102.The wheel assemblies 114 may be removably connected on opposite sides of the tool string 110. The wheel assemblies 114 may be connected to the tool string 110 at various axial (i.e., longitudinal) locations along the tool string 110, such as at a top (i.e., face up) end of the tool string 110, at a lower (i.e., downhole) end of the tool string 110, and / or at intermediate positions along the tool string 110. Although the tool string 110 is shown comprising wheel assemblies 114 at three locations along the series of tools 110, it should be understood that the wheel assemblies 114 may be removably connected to the tool string 110 at a smaller or greater number of locations. Figure 2 is a cross-sectional view of an exemplary implementation of a body 202 (e.g., a casing, a frame, a block, etc.) of a downhole tool of a tool string 200 in accordance with one or more aspects of the present disclosure. Figure 3 is a side view of the body 202 shown in Figure 2 in accordance with one or more aspects of the present disclosure. The tool string 200 may comprise one or more features and / or modes of operation of the tool string 110 described above and shown in Figure 1. The body 202 may be, comprise, or form at least a portion of a downhole tool 112 or other part of the tool string 110. Accordingly, the following description refers to Figures 1-3, collectively. A side wall (i.e., exterior surface) of the body 202 may comprise a mounting surface 204 configured to accommodate or otherwise facilitate removably connecting a wheel assembly to the body 202. The surface 204 may be recessed, extending inwardly of the body 202. The side wall of the body 202 may thus comprise a transition shoulder 214 between the recessed mounting surface 204 and a larger diameter portion of the body 202. The surface 204 may be substantially planar (i.e., flat) and / or comprise a substantially rectangular geometry. The body 202 may comprise one or more cavities 206 (e.g., openings, perforations) that partially extend into the side wall of the body 202. For example, the cavities 206 may extend into or beneath the surface 204 of the body 202.Each cavity 206 may be configured to accommodate or otherwise facilitate removably connected to a corresponding fastener of the wheel assembly. Each cavity 206 may be or comprise a threaded hole (i.e., threaded mounting hole) configured to threadably engage or otherwise receive a threaded fastener of the wheel assembly. The sidewall of the body 202 may further comprise one or more additional mounting surfaces 204 on the same and / or opposite side of the body 202. Each additional surface 204 may be configured to accommodate or otherwise facilitate removably connected a corresponding additional wheel assembly to the body 202. The opposing surfaces 204 may be or extend parallel to one another. The body 202 may further comprise one or more additional cavities 206 that partially extend into the sidewall of the body 202.For example, each additional cavity 206 may extend into or below surface 204 of body 202. Each additional cavity 206 may be configured to accommodate or otherwise facilitate detachable connection with a corresponding fastener of an additional wheel assembly. For example, each additional cavity 206 may be or comprise a threaded hole configured to threadably engage or otherwise receive a threaded fastener of an additional wheel assembly. Although cavities 206 are shown extending into the interior of body 202 along mounting surfaces 204, body 202 may not have mounting surfaces 204 that are recessed, and cavities 206 may extend into a round portion of the side wall of body 202. Figure 4 is a cross-sectional view of an exemplary implementation of a wheel assembly 220 in accordance with one or more aspects of the present disclosure. Figure 5 is a view MA / a / zuzz / ui i uo / side of wheel assembly 220 shown in Figure 4. Wheel assembly 220 may comprise one or more features and / or modes of operation of the wheel assemblies 114 described above and shown in Figure 1. Wheel assembly 220 may be removably connectable to body 202 of tool string 200 shown in Figures 2 and 3. Accordingly, the following description refers to Figures 1-5, collectively. The wheel assembly 220 may operate to reduce friction between the tool string 200 and a sidewall (i.e., inner surface) of the borehole 102 to facilitate downhole transport of the tool string 200. The wheel assembly 220 may comprise a shaft 222 configured to be removably connected to the body 202 of the tool string 200 and a wheel 224 rotatably connected to the shaft 222. At least a portion of the shaft 222 may have a cylindrical geometry, comprising opposing exterior surfaces 226, 228 (e.g., faces, flat surfaces, etc.) and an exterior circumferential surface 230 extending between the exterior surfaces 226, 228. The wheel assembly 220 may further comprise one or more fasteners 232 configured to engage (e.g., connect with, engage against, etc.) the shaft 222 and extend from the shaft 222. axis 222.Each fastener 232 may be configured to extend at least partially through the axle 222 and at least partially into the sidewall of the body 202 to removably connect the axle 222, and thus the wheel assembly 220, to the body 202. The axle 222 may comprise a plurality of holes, each of which extends between the exterior surfaces 226, 228 and each of which is configured to accommodate or receive a corresponding fastener 232. The axle 222 may comprise a shoulder (not shown) along each hole configured to engage (i.e., contact) a corresponding fastener 232. Each fastener 232 may comprise a head or other feature (not shown) having a shoulder (not shown) configured to engage (i.e., contact, engage against, etc.) a corresponding shoulder along the hole of the axle 222.Each fastener 232 may further comprise a shank configured to extend out of a corresponding bore of the shaft 222 and into a corresponding cavity 206 of the body 202 to engage the body 202 and thereby connect the shaft 222 to the body 202. The shank of each fastener 232 and each cavity 206 may be threaded (not shown), facilitating threaded engagement between each fastener 232 and a corresponding cavity 206, thereby removably connecting the shaft 222 to the body 202 of the tool string 200. Although the wheel assembly 220 is shown comprising four fasteners 232 arranged in a square pattern, it should be understood that the wheel assembly 220 may comprise one, two, three, five, six, or more fasteners 232 arranged in other patterns. Although the outer surfaces 204, 226 are shown to be substantially flat or planar, the outer surface 204 may be curved (e.g., round, convex, etc.) and the outer surface 226 may be curved (e.g., round, concave, etc.) in a manner complementary to the outer surface 204. The wheel 224 may extend around at least a portion of the axle 222. The wheel 224 may comprise an outer circumferential portion 234 (e.g., an end, an edge, an lip, etc.) configured to contact the sidewall of the pit 102, and thereby facilitate rolling of the wheel 224 along the sidewall of the pit 102. The wheel 224 may further comprise an inner circumferential surface 236 configured to contact or accommodate the outer surface 230 of the axle 222. The inner circumferential surface 236 may also be configured to contact a bearing (not shown) disposed between the inner circumferential surface 236 and the outer circumferential surface 230 to reduce friction between the wheel 224 and the axle 222. Figure 6 is a cross-sectional view of an exemplary implementation of a wheel assembly 240 in accordance with one or more aspects of the present disclosure. Figure 7 is a side view of the wheel assembly 240 shown in Figure 6. The wheel assembly 240 may comprise one or more features and / or modes of operation of the wheel assembly 220 described above and shown in Figures 4 and 5, even when indicated by the same reference numerals. The wheel assembly 240 may be removably connectable to the body 202 of the tool string 200 shown in Figures 2 and 3. Accordingly, the following description refers to Figures 1-7, collectively. The wheel assembly 240 may operate to reduce friction between the tool string 200 and a sidewall of the hole 102 to assist or facilitate downhole transport of the tool string 200. The wheel assembly 240 may comprise a shaft 222 configured to be removably connected to the body 202 of the tool string 200 and a wheel 244 rotatably connected to the shaft 222. The wheel assembly 240 may further comprise one or more fasteners 232 configured to engage (e.g., connect with, engage against, etc.) the shaft 222 and extend from the shaft 222. Each fastener 232 may be configured to extend at least partially through the shaft 222 and at least partially into a sidewall of the body 202 to removably connect the shaft 222 and thus the wheel assembly 240 to the body 202. The wheel 244 may extend around at least a portion of axis 222.The wheel 244 may comprise an outer circumferential portion 234 (e.g., an end, a rim, an edge, etc.) configured to contact a surface of the pit 102 to facilitate rolling of the wheel 244 along the surface of the pit 102. The wheel 244 may further comprise an inner circumferential surface 236 configured to contact or accommodate the outer surface 230 of the axle 222. The inner circumferential surface 236 may also be configured to contact a bearing (not shown) disposed between the inner circumferential surface 236 and the outer circumferential surface 230 to reduce friction between the wheel 244 and the axle 222. The wheel 244 may further comprise an intermediate portion 246 (e.g., a cap, a shroud, etc.) extending between the outer circumferential portion 234.The intermediate portion 246 may comprise a convex or otherwise outwardly extending outer surface configured to contact (e.g., roll over) the sidewall of the hole 102, such as when the tool string 200 rolls or otherwise rotates about its longitudinal central axis. The intermediate portion 246 may extend to overlie the outer surface 228 of the shaft 222. Figures 8, 9, and 10 are side, end, and axial section views, respectively, of the wheel assembly 240 shown in Figures 6 and 7 removably connected to the body 202 of the tool string 200 shown in Figures 2 and 3 in accordance with one or more aspects of the present disclosure. Accordingly, the following description refers to Figures 2, 3, and 6-10, collectively. The outer surface 226 of each wheel assembly 240 is shown disposed against (i.e., in contact with) a corresponding surface 204 of the body 202. Each fastener 232 may extend into and engage a corresponding cavity 206 of the body 202 to removably connect the shaft 222, and thus the wheel assembly 240, to the body 202 of the tool string 200. As shown in Figure 10, the cavities 206 may be located symmetrically with respect to a longitudinal central axis 203 of the body 202 and the tool string 200 such that the wheel assemblies 240 are connected symmetrically with respect to the central axis 203 and the body 202. For example, the wheel assemblies 240 may be connected to the body 202 such that the axes of rotation 245 of the wheels 244 extend through the shaft 222. central 203.Furthermore, the wheel assemblies 240 connected to the body 202 may collectively form or define an axial geometric profile having a geometric centerline 201, which may coincide with the center axis 203 and intercept the axes of rotation 245 when the wheel assemblies 240 are connected to the body 202. The geometric centerline 201 may be or define an axis of rotation of the body 202 and the wheel assemblies 240 connected to the body 202, such as when the tool string 200 and the wheel assemblies 240 collectively roll or otherwise axially rotate within the pit 102. Figure 11 is an axial sectional view of the wheel assemblies 240 shown in Figures 6 and 7 removably connected to a body 248 (e.g., a casing, block, frame, etc.) of the tool string 200 in accordance with one or more aspects of the present disclosure. The body 248 may be or form at least a portion of a downhole tool 112 or other portion of the tool string 110 shown in Figure 1. The body 248 may comprise one or more features and / or modes of operation of the body 202 of the tool string 200 described above and shown in Figures 2 and 3, even when indicated by the same reference numerals. Accordingly, the following description refers to Figures 1-3, 6, 7, and 11, collectively. A side wall (i.e., exterior surface) of the body 248 may comprise a plurality of mounting surfaces 204 and a plurality of cavities 206, each cavity 206 extending partially into the side wall of the body 248 below the surface 204 and configured to accommodate a corresponding fastener 232 to facilitate disassembly connecting the wheel assembly 240 to the body 248. An exterior surface 226 of each wheel assembly 240 is shown disposed against (i.e., in contact with) a corresponding surface 204 of the body 248. The surfaces 204 may be or extend at an angle (e.g., diagonally and / or non-parallel) with respect to each other and / or the cavities 206 may be located or extend asymmetrically with respect to the central axis 203 of the body 248.Thus, the wheel assemblies 240 may be connected asymmetrically with respect to the central axis 203 of the body 248, and the rotation axes 245 of each wheel 244 may extend at an angle (e.g., diagonally, non-parallel and / or non-collinear) with respect to each other. Each fastener 232 is shown extending into a corresponding cavity 206 of the body 248. Each fastener 232 may be coupled to the body 248 to removably connect the axle 222, and thus the wheel assembly 240, to the body 248. The wheel assemblies 240 may be connected to the body 248 such that the axes of rotation 245 of the wheels 244 intersect at a point below the central axis 203 or otherwise extend through the body 248 below the central axis 203 when the body 248 is oriented horizontally, as shown in Figure 11.Although the axes of rotation 245 of the wheels 244 may extend and / or intersect below the central axis 203, the axes of rotation 245 along or above the wheels 244, as indicated by the numerals 241, may be located at the same level (i.e., vertical position) equal to or higher than the central axis 203, as indicated on line 247. Figure 12 is a side view of an exemplary implementation of a body 252 (e.g., a housing, block, frame, etc.) of the tool string 200 according to one or more aspects of the present disclosure. Figure 13 is an axial sectional view of the wheel assemblies 240 shown in Figures 6-11 removably connected to the body 252 according to one or more aspects of the present disclosure. The assembly of body 252 and wheel assemblies 240 is shown disposed within an example borehole 102 through which the tool string 200 is transported. The body 252 may be or form at least a portion of a downhole tool 112 or other part of the tool string 110 shown in Figure 1. The body 252 may comprise one or more features of the bodies 202, 248 described above and shown in Figures 2, 3, and 8-11.Accordingly, the following description refers to Figures 1-3 and 6-13, collectively. A side wall (i.e., exterior surface) of the body 252 may comprise a plurality of mounting surfaces 204 and a plurality of cavities 206, each cavity 206 extending partially into the side wall of the body 252 below the surface 204 and configured to accommodate a corresponding fastener 232 to facilitate removably connecting the wheel assembly 240 to the body 252. The cavities 206 may be located symmetrically with respect to (e.g., on either side of) the body 252 and / or the central axis 203 of the body 252 and the tool string 200, such that the wheel assemblies 240 are connected symmetrically with respect to the body 252 and / or the central axis 203. For example, the wheel assemblies 240 may be connected to the body 252 such that the axes of rotation 245 of the wheels 244 extend or are at the same distance from the body 252. same level (i.e. vertical position) as the central axis 203. The body sidewall 252 may further comprise one or more cavities 256 (e.g., openings, holes, perforations, etc.) extending partially into the body sidewall 252 below each surface 204 in place of or in addition to the cavities 206. Each cavity 256 may be configured to accommodate or otherwise facilitate removably engaging a mating fastener 232 of the wheel assembly 240. For example, each cavity 256 may be a threaded hole configured to threadably engage or otherwise receive a threaded fastener 232 of the wheel assembly 240. The cavities 256 may be geometrically arranged (e.g., spaced) to align with mating fasteners 232 of the wheel assembly 240. The cavities 256 may be asymmetrically located (e.g., eccentrically, offset from, etc.).) with respect to the body 252 and / or 16 to the central axis 203, such that each wheel assembly 240 is connected asymmetrically with respect to the body 252 and / or the central axis 203. Therefore, when the wheel assemblies 240 are removably connected to the body 252 through the fasteners 232 that engage the cavities 256, the rotational axes 245 of the wheels 244 may be located above and therefore offset from the central axis 203 of the body 252 and the tool string 200 by an offset distance 205. The wheel assemblies 240 connected to the body 252 may collectively form or define an axial geometric profile having a geometric centerline 201. The geometric centerline 201 may be an axis of rotation of the body 252 and the wheel assemblies 240 connected to the body 252, such as when the tool string 200 and the wheel assemblies 240 collectively roll or axially rotate within the hole 102. Because each wheel assembly 240 is connected asymmetrically with respect to the body 252 and / or the central axis 203, the geometric centerline 201 may be offset from the central axis 203 by the offset distance 205.Accordingly, the center of mass of the body 252 (and the tool string 200) which approximately coincides with the central axis 203, may be located below the axes of rotation 245 of the wheels 244 and / or below the geometric center line 201, and thus displaced from the axes of rotation 245 and / or the geometric center line 201 by the offset distance 205, when the body 252 is oriented horizontally as shown in Figure 13. Figure 14 is an axial sectional view of the wheel assemblies 240 shown in Figures 6 and 7 removably connected to a body 254 (e.g., a housing, a block, a frame, etc.) of the tool string 200 in accordance with one or more aspects of the present disclosure. The body assembly 254 and wheel assemblies 240 are shown disposed within an exemplary borehole 102 through which the body assembly 254 and wheel assemblies 240 are transported. The body 254 may be or form at least a portion of a downhole tool 112 or other part of the tool string 110 shown in Figure 1. The body 254 may comprise one or more features and / or modes of operation of the bodies 202, 248, 252 of the tool string 200 described above and shown in Figures 2, 3 and 11-13, even when indicated by the same reference numerals.Accordingly, the following description refers to Figures 1-3 and 11-14, collectively. A side wall (i.e., exterior surface) of the body 254 may comprise a plurality of mounting surfaces 204 and a plurality of cavities 206, 256, each cavity 206, 256 extending partially into the side wall of the body 254 below the surface 204 and configured to accommodate a corresponding fastener 232 to facilitate removably connecting the wheel assembly 240 to the body 254. The exterior surface 226 of each wheel assembly 240 is shown disposed against (i.e., in contact with) a corresponding surface 204 of the body 254. The surfaces 204 may be or extend at an angle (e.g., diagonal, non-parallel, etc.) with respect to each other and / or the cavities 206, 256 may be located asymmetrically with respect to the central axis 203 of the body 254.Thus, the wheel assemblies 240 may be connected asymmetrically with respect to the central axis 203 and the body 254, and the rotation axes 245 of each wheel 244 may extend at an angle (e.g., diagonally, non-parallel, non-collinear, etc.) with respect to each other. Each fastener 232 is shown extending into a corresponding cavity 256 of the body 254. Each fastener 232 may be coupled to the body 254 to removably connect the shaft 222, and thus the wheel assembly 240, to the body 254. The wheel assemblies 240 connected to the body 254 may collectively form or define an axial geometric profile having a geometric centerline 201. The geometric centerline 201 may be an axis of rotation of the body 254 and the wheel assemblies 240 connected to the body 254, such as when the tool string 200 and the wheel assemblies 240 collectively roll or otherwise axially rotate within the bore 102.The connection of the wheel assemblies 240 to the body 254 via the cavities 256 shifts or offsets the geometric centerline 201 from the center axis 203 of the body 254 by an offset distance 205. Accordingly, the center of mass of the body 254 (and the tool string 200) which is approximately coincident with the center axis 203, may be located below the geometric centerline 201 and thus offset from the geometric centerline 201 by the offset distance 205, when the body 254 is oriented horizontally as shown in Figure 14. As shown in Figures 10 and 11, the geometric centerline 201 and / or the axes of rotation 245 may coincide with the center axis 203 when the wheel assemblies 240 are connected to the body 202, 248 through the cavities 206. However, as shown in Figures 13 and 14, the geometric centerline 201 and / or the axes of rotation 245 may be offset from (e.g., located above) the center axis 203 by an offset distance 205 when the wheel assemblies 240 are connected to a corresponding body 252, 254 through the cavities 206, 256.The weight of the bodies 252, 254 forming the tool string 200 may be much (e.g., several times) greater than the collective mass of the wheel assemblies 240 and may be represented by a downward gravitational force 207 (i.e., weight) applied at the center of mass (i.e., center of gravity) of the tool string 200, which may substantially coincide 18 with the center axes 203 of the bodies 252, 254. Because the mass of the tool string 200 is much greater than the collective mass of the wheel assemblies 240, the displacement 205 between the center axis 203 and the geometric centerline 201 and / or the axes of rotation 245 creates a mechanical instability of the assembly of the series of tools 200 and the wheel assemblies 240 when the center of mass of the series of tools 200 and, therefore, the center axis 203 is not located directly below the geometric centerline 201 and / or the axes of rotation 245.Such mechanical instability may result in gravitational force 207 (i.e., weight of tool string 200) causing a torque 209 about geometric centerline 201 that drives rotation of tool string 200 and wheel assemblies 240 into a mechanically stable orientation in which center axis 203 is located directly below geometric centerline 201 and / or rotation axes 245. Torque 209 and thus the tendency of tool string 200 and wheel assemblies 240 to rotate (or roll) within hole 102 about geometric centerline 201 may be directly proportional to travel distance 205 between center axis 203 and geometric axis, centerline 201 and / or rotation axes 245. Accordingly, when the tool string assembly 200 and wheel assemblies 240 are oriented in their intended and most stable position within the hole 102, the center axis 203 is located directly below the geometric centerline 201 at its lowest position (i.e., closest to a lower side of the hole 102), as shown in Figures 13 and 14, and / or the rotation axes 245 or line 247 extend horizontally above the center axis 203, as shown in Figures 13 and 14. However, during downhole transportation, when the tool string assembly 200 and wheel assemblies 240 are not oriented in a mechanically stable position within the hole 102, the gravitational force 207 applied on the center axis 203 can cause a torque 209 about the geometric centerline 201 driving rotation. of the 200 series tool set and the 240 wheel assemblies to the most stable position.The present disclosure is further directed to wheel assemblies comprising shafts and wheels having different relative dimensions (e.g., diameter, length, width, etc.), which may be selected depending on the type of job and / or hole specifications. Figure 15 is an axial sectional view of a body 202 of a tool string 200 described above and shown in Figures 2 and 3, and a plurality of wheel assemblies 240, 260, 270, each configured to be removably connected to the body 202. Each of the wheel assemblies 260, 270 may comprise one or more features of the wheel assembly 240 as described above and shown in Figures 6 and 7. Accordingly, the following description refers to Figures 2, 3, 6, 7 and 15, collectively. The wheel assembly 240 may be removably connected to the body 202 of the tool string 200 via fasteners 232 that mate with corresponding cavities 206, as described above. The wheel assembly 260 may be similarly and removably connected to the body 202 of the tool string 200 via fasteners 232 that mate with corresponding cavities 206. However, the wheel assembly 260 may comprise a wheel 264 having an outer diameter that is substantially larger than the outer diameter of the wheel 244 of the wheel assembly 240. Thus, when the body 202 is oriented horizontally, the wheel assembly 260 may increase the vertical height of an assembly comprising the body 202 and the wheel assemblies 260, but not increase the horizontal width of the assembly comprising the body 202 and the wheel assemblies 260.The wheel assembly 270 may be removably connected to the body 202 of the tool string 200 via fasteners 276 that extend through a shaft 272 and mate with corresponding cavities 206. The shaft 272 may be substantially longer than the shafts 222 of the wheel assemblies 240, 260. The wheel assembly 270 may comprise a wheel 274 having an outside diameter that is substantially larger than the outside diameter of the wheel 264 of the wheel assembly 260. Thus, when the body 202 is oriented horizontally, the wheel assembly 270 may further increase the vertical height of an assembly comprising the body 202 and the wheel assemblies 270, and increase the horizontal width of the assembly comprising the body 202 and the wheel assemblies 270.The axle 272 may move the wheel 274 further from the body 202 such that the wheel 274 clears the transition shoulder 214 between the recessed mounting surface 204 and a larger diameter portion of the body 202 to prevent the wheel 274 from contacting the body 202. Prior to transporting the tool string 200 downhole, wellsite personnel (e.g., a field engineer) may select a wheel assembly 240, 260, 270 for connection to the body 202 or other body 248, 252, 254 within the scope of the present disclosure, based upon one or more factors, such as downhole operation (i.e., job) type and hole specifications (e.g., inclination, inside diameter, depth, etc.), among other examples. Furthermore, the wheel assemblies connected to the tool string 200 may be changed during a job or between jobs.For example, if the tool string 200 is not successfully transported downhole to the intended depth, the tool string 200 may be retrieved to the wellsite surface and one or more of the wheel assemblies may be disconnected and replaced with different wheel assemblies having different dimensions or other specifications. Additionally, if a job requires transporting the tool string 200 through different portions of the hole 102 and each portion has different specifications, the tool string 200 may be transported within a first portion of the hole 102 via a first set of wheels to perform downhole operations.The tool string 200 may then be retrieved to the surface of the well site 104, and the wheel assemblies may be disconnected and replaced with a second set of wheel assemblies having different dimensions or other specifications. The tool string 200 may then be transported into a second portion of the borehole 102 via the second set of wheel assemblies to perform downhole operations. Figure 16 is a perspective view of an exemplary implementation of a wheel assembly 300 in accordance with one or more aspects of the present disclosure. Figure 17 is a perspective view of a different side of the wheel assembly shown in Figure 16. Figure 18 is a side view of the wheel assembly 300 shown in Figures 16 and 17. Figure 19 is an exploded view of the wheel assembly 300 shown in Figures 16-18. The wheel assembly 300 may comprise one or more features and / or modes of operation of the wheel assemblies 114, 240 described above and shown in Figures 1, 6 and 7. The wheel assembly 300 may be removably connectable to the bodies 202, 248, 252, 254 of the tool string 200 shown in Figures 2, 3, and 11-14. The following description refers to Figures 1-3 and 16-19, collectively. The wheel assembly 300 may operate to reduce friction between a tool string 200 and a sidewall (i.e., inner surface) of a borehole 102 to facilitate downhole transport of the tool string 200. The wheel assembly 300 may comprise a shaft 302 removably connectable to a body 202 (or other body 248, 252, 254 shown in Figures 11-14) of the tool string 200 and a wheel 304 rotatably connected to the shaft 302. At least a portion of the shaft 302 may have a cylindrical geometry, comprising opposing exterior surfaces 312, 314 (e.g., faces, flats, etc.) and an exterior circumferential surface 316 extending between the exterior surfaces 312, 314. The exterior surface 312 may be configured to bear or make contact with the tool string 200. contact with a side wall (i.e., an outer surface) of the body 202, such as a mounting surface MA / a / zuzz / ui i uo / 204. The outer circumferential surface 316 may comprise an outer circumferential groove 318 (e.g., a channel, a race, etc.). The wheel assembly 300 may further comprise one or more fasteners 306 configured to engage (e.g., connect to, engage against, etc.) the shaft 302 and extend from the shaft 302. Each fastener 306 may be configured to extend at least partially through the shaft 302 and at least partially within the sidewall of the body 202 to removably connect the shaft 302 and thus the wheel assembly 300 to the body. Each fastener 306 may be configured to extend within a corresponding cavity 206 (or other cavity 256 shown in Figures 12-14) and engage the body 202 of the tool string 200 to removably connect the shaft 302 to the body 202.Shaft 302 may comprise a plurality of holes 320 (e.g., passageways), each extending axially through shaft 302 between opposing outer surfaces 312, 314 and configured to receive a corresponding fastener 306. Shaft 302 may comprise a shoulder 321 (i.e., a transition surface between a larger diameter portion of hole 320 and smaller diameter portions of hole 320) along each hole 320 configured to engage (e.g., contact, engage against, etc.) a corresponding fastener 306. Each fastener 306 may comprise a head 307 or other feature having a shoulder configured to engage (i.e., contact) a corresponding shoulder 321 along hole 320 of shaft 302.Each fastener 306 may further comprise a shank 309 configured to extend out of a corresponding hole 320 and into a corresponding cavity 206 of the body 202 to engage the body 202 and thereby connect the shaft 302 to the body 202. The shank 309 of each fastener 306 and each cavity 206 may be threaded, facilitating threaded engagement between each fastener 306 and a corresponding cavity 206 to removably connect the shaft 302 to the body 202 of the tool string 200. Although the shaft 302 is shown comprising four holes 320 arranged in a rectangular pattern, it should be understood that the shaft 302 may comprise one, two, three, five, six, or more holes 320 arranged in other patterns. The wheel 304 may extend around at least a portion of the shaft 302.The wheel 304 may comprise an outer circumferential portion 322 (e.g., an end, an edge, an edge) configured to contact a side wall of the pit 102, and thereby assist or facilitate rolling of the wheel 304 along the side wall of the pit 102. The wheel 304 may further comprise an inner circumferential surface 324 comprising an inner circumferential groove 326 (e.g., a channel, a raceway, etc.). The outer circumferential groove 318 of the axle 302 and the inner circumferential groove 326 of the wheel 304 may collectively form or otherwise define a circumferential space 328 (shown in Figure 22) (e.g., a ring-shaped or annular space or gap) between the axle 302 and the wheel 304. The wheel 244 may further comprise an intermediate portion 330 (e.g., a cap, a shroud) extending between the outer circumferential portion 322.The intermediate portion 330 may comprise a convex or otherwise outwardly extending outer surface configured to contact the sidewall of the pit 102, such as when the tool string 200 and wheel assemblies 300 collectively roll or rotate about a longitudinal axis (e.g., geometric centerline 201 shown in Figures 10, 11, 13 and 14) of the tool string 200 within the pit 102. The intermediate portion 330 may cover an end of the shaft 222, such as the outer surface 314 of the shaft 302. The wheel 304 may comprise a bore 332 (e.g., a passageway) extending through the intermediate portion 330. The bore 332 may be offset from an axis of rotation 305 of the wheel 304.The hole 332 may be aligned with each of the holes 320 and each of the fasteners 306 (if located within a corresponding hole 320), one at a time, by rotating the wheel 304 relative to the axle 302. A fill plug 333 may be inserted into the hole 332 to allow injection and / or retention of grease or other lubricant within the space between the axle 302 and the wheel 304 to reduce friction between the axle 302 and the wheel 304. The wheel assembly 300 may further comprise a plurality of ball bearings 308 disposed within the circumferential space 328. The ball bearings 308 may be configured to reduce friction between the axle 302 and the wheel 304. The ball bearings 308 may also connect or lock the wheel 304 to the axle 302. For example, the ball bearings 308 disposed within the circumferential space 328 may contact and bear against opposite sidewalls or shoulders of the circumferential grooves 318, 326 to engage the wheel 304 to the axle 302, thereby preventing the wheel 304 from separating from the axle 302. The shaft 302 may further comprise a passageway 334 (e.g., a channel, a hole, a space, etc.) extending through or along the shaft 302 between the outer surface 312 and the circumferential outer surface 316 (along the circumferential outer groove 318). The passageway 334 may thus connect to or intercept the circumferential space 328. Accordingly, the passageway 334 may connect the space outside the outer surface 312 and the circumferential space 328, thereby forming a path between the space outside the outer surface 312 and the circumferential space 328. The passageway 334 may also extend through or along the axis 302 between the outer surface 314 and the circumferential outer surface 316 (along the circumferential outer groove 318).Accordingly, the passage 334 may connect the outer space to the outer surface 314 and the circumferential space 328, thereby forming a path between the space to the outer surface 314 and the circumferential space 328. The passage 334 may extend radially through or along the axis 302, such as perpendicular or otherwise laterally with respect to a central axis of the axis 302. The passage 334 may connect or intercept the outer circumferential groove 318 and the circumferential space 328 at a substantially right angle.For example, the passageway 334 may connect or intercept the outer circumferential groove 318 and the circumferential space 328 at an angle ranging from about 60 degrees to about 120 degrees, at an angle ranging from about 70 degrees to about 110 degrees, at an angle ranging from about 80 degrees to about 100 degrees, or at an angle ranging from about 85 degrees to about 95 degrees. The passageway 334 may connect or intercept the outer circumferential groove 318 and the circumferential space 328 at a right angle (i.e., at a 90 degree angle). The passageway 334 may also extend axially through the shaft 302 between the opposing outer surfaces 312, 314. However, the passageway 334 may extend axially toward the outer surface 312 of the shaft 302 without extending axially through the shaft 302 between the opposing outer surfaces 312, 314.The shaft 302 may further comprise a retaining member 336 that extends longitudinally along the passageway 334. For example, the retaining member 336 may be or comprise a groove (e.g., a track) that extends longitudinally along the passageway 334 or a protrusion (e.g., a rail, a ridge, etc.) that extends longitudinally along the passageway 334. The shaft 302 may further comprise a cavity 338 that extends axially (i.e., parallel with respect to the central axis of the shaft 302) in the outer surface 312 (or outer surface 314) of the shaft 302 below the outer surface 312. The cavity 338 may have an inner diameter greater than the width of the passageway 334. The cavity 338 may be located along or otherwise intercept the passageway 334. The wheel assembly 300 may further comprise a locking member 310 (e.g., a plug, a stopper, etc.) disposed within the passageway 334. The locking member 310 may be movable (e.g., slidable) within the passageway 334 between a first position in which the ball bearings 308 may be inserted into the circumferential space 328 through the passageway 334 and a second position in which the locking member 310 prevents the ball bearings 308 from exiting the circumferential space 328 through the passageway 334. The locking member 310 may comprise a retaining member 340 extending longitudinally along the locking member. 310 and configured to engage the retaining element 336 of the shaft 302. While engaged, the retaining features 336, 340 may allow the locking member 310 to move (e.g., slide) along the passageway 334 and to retain the locking member 310 within the passageway 334 or otherwise prevent the locking member 310 from moving out of the passageway 334. The retaining element 340 may be or comprise a slot (e.g., a track) extending longitudinally along the locking member 310 or a protrusion (e.g., a rail, a ridge, etc.) extending longitudinally along the locking member 310. The locking member 310 may form a portion of the outer circumferential groove 318 of the shaft 302 when the locking element 310 is in the second position, as shown in Figure 23.For example, the locking member 310 may comprise a slot 342 (e.g., a via) that forms a portion of the outer circumferential groove 318 of the shaft 302, and thus defines a portion of the circumferential space 328, when the locking element 310 is in its second position. The locking member 310 may further comprise a hole 344 that extends into or through the locking member 310. The hole 344 may be or comprise a threaded hole. Although the retaining member 336 is shown extending the entire length of the passageway 334, the retaining member 336 may not necessarily extend the entire length of the passageway 334. For example, the retaining member 336 may extend along a radially outward portion (i.e., closer to the surface 316) of the passageway 334, but not along a radially inward portion (i.e., closer to the central axis of the shaft 302) of the passageway 334. Such a configuration may allow the locking member 310 to be retained within the passageway 334 when the locking member 310 is in its second position and allow the locking member 310 to be withdrawn from the passageway 334 when the locking member 310 is in its first position. The wheel assembly 300 may further comprise a fastener 350 configured to engage the axle 302 and the locking member 310 to fixedly connect the locking member 310 in its second position within the passageway 334. The fastener 350 may be disposed within the cavity 338 of the axle 302 and extend into the bore 344 of the locking member 310 to fixedly connect the locking member 310 in its second position within the passageway 334. The fastener 350 may comprise a head 352 and a shank 354. The shank 354 may be inserted into the bore 344 to engage (i.e., connect) the fastener 350 to the retaining member 310 and the head 352 may be inserted into the cavity 338 to engage (i.e., connect or engage) the fastener 350 to the axle 302.The side walls of the cavity 338 may abut or otherwise contact the head 352 to prevent the fastener 350 and thus the locking member 310 from moving along the passageway 334 or otherwise relative to the axis 302, thereby fixedly engaging the locking member 310 in the second position within the passageway 334. The shank 354 may be a threaded shank and the bore 344 may be a threaded bore. Accordingly, the fastener 350 may be fixedly connected to the locking member 310 when the locking member 310 is in the second position within the passageway 334 by threadably engaging the shank 354 with the bore 344. The present disclosure is further directed to methods (e.g., operations, processes) of assembling (e.g., putting together, building, etc.) a wheel assembly, such as the wheel assembly 300 shown in Figures 16-19 in accordance with one or more aspects of the present disclosure. Figures 20 and 21 are side views of the wheel assembly 300 during different stages of assembly operations. Figure 22 is a cross-sectional view of the wheel assembly 300 shown in Figure 21. Figure 23 is a perspective view of the wheel assembly shown in Figures 20-22 at yet another stage of assembly operations. Accordingly, the following description refers to Figures 16-23, collectively. A method for assembling the wheel assembly 300 may comprise arranging the wheel 304 about the axle 302 to form the circumferential space 328 between the wheel 304 and the axle 302. As shown in Figure 20, the locking member 310 is movable (e.g., slidable) along the passageway 334 in a radially inward direction relative to the axle 302, as indicated by arrow 356, to its first position wherein the locking member 310 is located at a radially inward end of the passageway 334 (i.e., in a radially inward position relative to the axle 302), thereby opening (i.e., unlocking) the passageway 334 such that the ball bearings 308 may be inserted into the circumferential space 328 through the passageway 334, as indicated by arrow 358.Moving the locking member 310 along the passageway 334 may comprise sliding the locking member 310 along the retaining member 336 of the shaft 302 while the retaining member 336 engages the retaining member 340 of the locking member 310 to retain the locking member 310 within the passageway 334. If the shaft 302 does not comprise the retaining member 336 in the first position of the locking member 310, the locking member 310 may be removed from the passageway 334. When the locking member 310 is removed from the passageway 334 or is in the first position within the passageway 334, the ball bearings 308 may be inserted into the passageway 334 and moved into the circumferential space 328 through the passageway 334, as indicated by arrow 358. As shown in Figures 21 and 22, after all of the ball bearings 308 are inserted into the circumferential space 328, the locking member 310 can be moved (e.g., slid) along the passage 334 in a radially outward direction with respect to the shaft 302, as indicated by arrow 360, to its second position in which the locking member 310 is in a radially outward position with respect to the shaft 302 in which the locking member 310 is located at a radially outward end of the passage 334 to close (i.e., block) the passage 334 from the circumferential space 328 thereby preventing the ball bearings 308 from exiting the circumferential space 328 through the passage 334. The ball bearings 308 can reduce friction between the shaft 302 and the wheel 304 and prevent wheel separation. 304 of axle 302, thus connecting wheel 304 to axle 302. As shown in Figures 16 and 23, when the locking member 310 is moved to the second position along the passageway 334, the locking member 310 may then be fixedly connected or otherwise secured to the shaft 302 with the fastener 350, such as by inserting the fastener 350 at least partially into, through, or between the shaft 302 and the locking member 310. For example, the locking member 310 may be secured to the shaft 302 with the fastener 350 by inserting the head 352 of the fastener 350 into the cavity 338 extending in the shaft 302 along the passageway 334 while inserting the shank 354 of the fastener 350 into the hole 344 of the locking member 310. If the shank 354 and the hole 344 are threaded, the threaded shank 354 may threadably engage with the threaded hole 344 for fixedly connecting the fastener 350 with the locking member 310.The head 352 engages (i.e., locks against or contacts) the shaft (i.e., side walls of the cavity 338) to prevent the fastener 350 and thus the locking member 310 from moving from its second position. Accordingly, the fastener 350 may engage both the locking member 310 and the shaft 302 when the locking member 310 is in its second position to prevent the locking member 310 from moving along the passage from its second position to its first position. Furthermore, the locking element 310 may comprise a slot 342 (e.g., a track) that forms a portion of the outer circumferential groove 318 of the shaft 302 when the locking member 310 is in its second position. It should be noted that Figure 23 shows the wheel assembly 300 without the wheel 304 and ball bearings 308 to more clearly show the axle 302 and locking member 310 while in its second position. The present disclosure is further directed to methods (e.g., operations, processes) of removably connecting (e.g., coupling, clamping) a wheel assembly, such as wheel assembly 300 shown in Figures 16-23, to a sidewall (i.e., outside surface) of a downhole tool of a downhole tool string to reduce friction between the downhole tool and a sidewall (i.e., inside surface) of a hole to facilitate transporting the downhole tool. Figure 24 is a cross-sectional view of wheel assembly 300 removably connected to a body 362 of a downhole tool of a downhole tool string 360. Tool string 360 may comprise one or more features and / or modes of operation of tool strings 110, 200 described above and shown in Figures 1 and 2.Body 362 may comprise one or more features of bodies 202, 248, 252, 254 described above and shown in Figures 2, 3, 11, 13 and 14. An exemplary method may include positioning the wheel assembly 300 against a side wall of the body 362 of the tool string 360. For example, the surface 312 of the shaft 302 of the wheel assembly 300 may be disposed against or otherwise in contact with a corresponding mounting surface 364 of the body 362 such that each of the holes 320 of the shaft 302 is aligned with a corresponding one of the threaded holes 366 extending in the side wall of the body 362 along the surface 364. Thereafter, the fasteners 306 may be inserted at least partially through the shaft 302 and inserted at least partially into the side wall of the body 362 to connect the wheel assembly 300 to the body 362.For example, wheel 304 may be rotated about rotational axis 305, as indicated by arrow 311, to align hole 332 extending through cap 330 of wheel 304 with a selected one of holes 320 of axle 302. One of fasteners 306 may then be inserted into the selected one of holes 320 through hole 332, as indicated by arrow 313, and positioned against threaded hole 366 of body 362. A torque tool (e.g., a hand wrench, an automated torque tool) (not shown) may then be inserted into hole 320 through hole 332 and engaged with head 307 of fastener 306. The torque tool may then be operated to rotate fastener 306 to threadably engage fastener 306 within threaded hole 366. until the shoulder of the head 307 of the fastener 306 makes contact with the shoulder 321 of the shaft 302.The wheel 304 may be further rotated to align the hole 332 extending through the cap 330 of the wheel 304 with another of the holes 320 of the axle 302. Then, another of the fasteners 306 may be inserted into the hole 320 through the hole 332 and threadably engage within the threaded hole 366. The above process may be repeated until each fastener 306 is threadably engaged in the body 362 to connect the axle 302 to the body 362. The fill plug 333 may be inserted into the hole 332 and then grease or other lubricant may be injected into the space between the axle 302 and the wheel 304, including the circumferential space 328, to lubricate the ball bearings 308 and various surfaces of the axle 302 and the wheel 304. In view of the entirety of the present disclosure, one of ordinary skill in the art will readily recognize that the present disclosure features an apparatus comprising a wheel assembly configured to be removably connected to a downhole tool to thereby reduce friction between the downhole tool and a sidewall of a borehole through which the downhole tool is transported, the wheel assembly comprising: a shaft configured to contact a sidewall of the downhole tool; a wheel rotatably connected to the shaft; and a fastener configured to extend into the sidewall of the downhole tool to removably connect the shaft to the downhole tool. The fastener may extend through at least a portion of the shaft and off the shaft. The fastener may be or comprise a threaded screw. The fastener may be or comprise a threaded fastener extending through at least a portion of the shaft and outward from the shaft, and the fastener may be configured to threadably engage a threaded hole extending in the sidewall of the downhole tool to removably connect the shaft to the downhole tool. The axle may comprise a first bore extending therethrough, the fastener may be disposed within and extending out of the first bore, the wheel may comprise a second bore configured to accommodate the fastener therethrough, and rotating the wheel relative to the axle may move the second bore into and out of alignment with the first bore. The first bore may be one of a plurality of first bores, the fastener may be one of a plurality of fasteners, and rotating the wheel relative to the axle may move the second bore one at a time into alignment with each of the first bores. Each of the first bore and the second bore may be offset from an axis of rotation of the wheel. The apparatus may further comprise the downhole tool, the fastener may be one of a plurality of fasteners, the downhole tool may comprise a plurality of threaded holes extending toward the sidewall of the downhole tool, and each fastener may threadably engage a corresponding threaded hole to removably connect the shaft to the downhole tool. The wheel assembly may be one of a plurality of wheel assemblies, and when the wheel assemblies are removably connected to the downhole tool: the wheel assemblies may collectively define an axial profile having an axis of rotation; and the axis of rotation may be offset from a central axis of the downhole tool. The wheel assembly may be one of a plurality of wheel assemblies, each wheel rotatable about an axis of rotation, and when the wheel assemblies are detachably connected to the downhole tool, the axes of rotation may be offset from a central axis of the downhole tool. The apparatus may further comprise the downhole tool, the fastener may be one of a plurality of fasteners, the downhole tool may comprise a plurality of mounting holes extending toward the sidewall of the downhole tool, the mounting holes may be located asymmetrically with respect to a central axis of the downhole tool, and each fastener may be coupled to a corresponding mounting hole to removably connect the wheel assembly to the downhole tool. The present disclosure also features a method comprising connecting a wheel assembly to a downhole tool to reduce friction between the downhole tool and a sidewall of a borehole through which the downhole tool is transported, the wheel assembly comprising an axle and a wheel rotatably connected to the axle, and connecting the wheel assembly to the downhole tool comprises inserting a fastener at least partially into a sidewall of the downhole tool to connect the axle to the downhole tool. The fastener may be a threaded fastener and inserting the fastener at least partially into the sidewall of the downhole tool may comprise threading the fastener into a threaded hole extending into the sidewall of the downhole tool to connect the shaft to the downhole tool. The fastener may be a threaded fastener, the downhole tool may comprise a threaded hole extending toward the sidewall of the downhole tool, the shaft may comprise a hole extending therethrough, the wheel may comprise a hole extending therethrough, the shaft hole and the inside diameter of the wheel may be offset from an axis of rotation of the wheel, and connecting the wheel assembly to the downhole tool may further comprise: disposing the shaft against the sidewall of the downhole tool such that the inside diameter of the shaft is aligned with the threaded hole; rotating the wheel relative to the shaft to align the hole in the wheel with the hole in the shaft; inserting the fastener into the threaded hole through the shaft hole and the wheel hole;and thread the fastener into the threaded hole to connect the shaft to the downhole tool.; Connecting the wheel assembly to the downhole tool may further comprise, before inserting the fastener at least partially into the sidewall of the downhole tool, inserting the fastener at least partially through the shaft. The fastener may be a threaded fastener, the downhole tool may comprise a threaded hole extending into the sidewall of the downhole tool, the shaft may comprise a hole extending therethrough, and connecting the wheel assembly to the downhole tool may further comprise: biasing the shaft against the sidewall of the downhole tool such that the hole in the shaft is aligned with the threaded hole; inserting the fastener into the threaded hole through the hole in the shaft;and threadably engaging the fastener within the threaded hole to connect the shaft to the downhole tool. The present disclosure also features an apparatus comprising a wheel assembly for a downhole tool, the wheel assembly operable to reduce friction between the downhole tool and a sidewall of a hole through which the downhole tool is transported, and the wheel assembly comprising: a shaft comprising an outer circumferential groove and a pitch extending through the shaft; a wheel disposed about the shaft and comprising an inner circumferential groove, the outer circumferential groove and the inner circumferential groove collectively defining a circumferential space between the shaft and the wheel, and the pitch intersects the circumferential space;a plurality of ball bearings arranged within the circumferential space and configured to reduce friction between the axle and the wheel; and a locking member disposed within the passageway, wherein the locking member is movable within the passageway between a first position in which the ball bearings can be inserted into the circumferential space through the passageway and a second position in which the locking member prevents the ball bearings from exiting the circumferential space through the passageway. The passage may extend laterally across the shaft. The passage may intersect the outer circumferential groove at an angle ranging from approximately 60 to 120 degrees. The first position may be a radially inward position of the locking member with respect to the axis, and the second position may be a radially outward position of the locking member with respect to the axis. The locking member may comprise a groove that forms a portion of the outer circumferential groove of the shaft when the locking member is in the second position. The axle may further comprise a first retaining element extending along the passageway, the locking member may comprise a second retaining element, and the first retaining element and the second retaining element may be coupled to retain the locking member within the passageway while allowing the locking member to move along the passageway between the first position and the second position. The wheel assembly may further comprise a fastener connected to the locking member when the locking member is in the second position, and the fastener may be coupled to the axle to prevent the locking member from moving along the passageway from the second position to the first position. The wheel assembly may further comprise a fastener that engages both the locking member and the axle when the locking member is in the second position to prevent the locking member from moving along the passage from the second position to the first position. The fastener may be a threaded fastener comprising a head and a threaded shank, and the threaded shank may threadably engage the locking member and the head may contact the axle to prevent the locking member from moving along the passage from the second position to the first position. The present disclosure also features a method comprising assembling a wheel assembly (e.g., operable to reduce friction between a downhole tool and a surface of a hole to facilitate transporting the downhole tool), wherein assembling the wheel assembly comprises: arranging a wheel about an axle to form a circumferential (e.g., substantially torus-shaped or otherwise toroidal) space between the wheel and the axle, wherein a passage extends through the axle and connects with the circumferential space; inserting ball bearings into the circumferential space through the passage; moving a plug along the passage to an end of the passage to close the circumferential space of the passage to prevent the ball bearings from exiting the circumferential space through the passage; and securing the plug to the axle with a fastener. The wheel assembly may further comprise a fastener, and the method may further comprise inserting the fastener at least partially into a sidewall of the downhole tool 32 to connect the wheel assembly to the downhole tool. Ball bearings can reduce friction between the axle and the wheel and prevent the wheel from separating from the axle. Moving the plug along the passage may comprise sliding the plug along the passage from a first position in which the ball bearings can be inserted into the circumferential space through the passage and a second position in which the plug is located at the end of the passage. Moving the plug along the passage may comprise sliding the plug along the passage from a radially inward position with respect to the axis in which the ball bearings can be inserted in the circumferential space through the passage to a radially outward position with respect to the axis in which the plug is located at the end of the passage. The shaft may further comprise a retaining element extending along the passageway, and moving the plug along the passageway may comprise sliding the plug along the retaining element to retain the plug within the passageway while sliding the plug along the passageway. Securing the plug to the shaft with the fastener may comprise inserting the fastener at least partially through the plug and the shaft. Securing the plug to the shaft with the fastener may comprise: inserting a head of the fastener into a cavity extending into the shaft and intersecting the passage; and while the head is in the cavity, threading a threaded shank of the fastener into a threaded hole extending into the plug. The shaft may further comprise: a circumferential outer surface comprising the outer circumferential groove; and an outer face surface configured to be disposed against the downhole tool, wherein the passage may extend through the shaft between the outer face surface and the circumferential outer surface. The foregoing describes the features of various embodiments so that a person skilled in the art can better understand aspects of the present disclosure. A person skilled in the art should appreciate that they can readily use the present disclosure as a basis for designing or modifying other processes and structures to accomplish the same purposes and / or achieve the same advantages of the embodiments introduced in the present disclosure. A person skilled in the art should also understand that such equivalent constructions do not depart from the scope of the present disclosure, and that they can make various changes, substitutions, and alterations in the present disclosure without departing from the spirit and scope of the present disclosure. The summary at the end of this description is provided to enable the reader to quickly ascertain the nature of the technical description. It is presented with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Claims

1. An apparatus comprising: a wheel assembly (240) configured to connect to a downhole tool (202) to thereby reduce friction between the downhole tool and a side wall of a borehole (102) through which the downhole tool is carried, wherein the wheel assembly comprises: a shaft (222) comprising: a first face (226); a second face (228); a circumferential surface (230) between the first face and the second face; and a bore (320) extending through the shaft between the first face and the second face; a wheel (224) rotatably connected to the shaft, wherein the wheel is disposed about the circumferential surface; and a threaded fastener (232) configured to: be disposed at least partially within the bore and extend out of the bore beyond the first face;and thread a threaded hole (206) extending into a side wall of the downhole tool to connect the shaft to the downhole tool, thereby connecting the wheel assembly to the downhole tool.

2. The apparatus according to claim 1, wherein the first face is configured to be placed against the side wall of the downhole tool such that the hole extending through the shaft is aligned with the threaded hole extending into the side wall of the downhole tool.

3. The apparatus according to claim 1, wherein: the hole extending through the shaft is one of a plurality of holes, each of which extends through the shaft between the first face and the second face; and the threaded fastener is one of a plurality of threaded fasteners, each configured to: be disposed at least partially within a corresponding hole of the holes and extend out of the corresponding hole of the holes beyond the first face; and thread-engage a corresponding threaded hole extending in the side wall of the downhole tool to connect the shaft to the downhole tool, thereby connecting the wheel assembly to the downhole tool.

4. The apparatus according to claim 3 wherein: the wheel comprises a hole (332) extending through it; and each of the holes extending through the axle and the hole extending through the wheel are offset from a rotation axis (305) of the wheel such that as the wheel is rotated about the axle, the hole extending through the wheel is moved one by one into alignment with each of the holes extending through the axle.

5. The apparatus according to claim 1, wherein: the wheel assembly is one of a plurality of wheel assemblies; and when the wheel assemblies are connected to the downhole tool: the wheel assemblies collectively define an axial profile having a geometric centerline (201); and the geometric centerline is offset (205) from a longitudinal centerline (203) of the downhole tool.

6. The apparatus according to claim 1, wherein: the wheel assembly is one of a plurality of wheel assemblies; each wheel of the wheel assemblies rotates about an axis of rotation (245); and when the wheel assemblies are connected to the downhole tool, each axis of rotation is offset (205) from a longitudinal central axis (203) of the downhole tool.

7. The apparatus according to claim 1, wherein: the wheel assembly is one of a plurality of wheel assemblies; each wheel of the wheel assemblies rotates about an axis of rotation (245); and when the wheel assemblies are connected to the downhole tool, the axes of rotation extend at an angle to each other such that the axes of rotation are not parallel to each other.

8. The apparatus according to claim 1 further comprising the downhole tool, wherein: the hole extending through the shaft is one of a plurality of holes, each of which extends through the shaft between the first face and the second face; the threaded hole extending into the side wall of the downhole tool is one of a plurality of threaded holes, each of which extends into the side wall of the downhole tool; the threaded holes (256) extending into the side wall of the downhole tool are asymmetrically located with respect to a longitudinal central axis (203) of the downhole tool;The threaded fastener is one of a plurality of threaded fasteners, each configured to: be disposed at least partially within a corresponding hole of the holes extending through the shaft and extend out of the corresponding hole of the holes extending through the shaft beyond the first face; thread a corresponding hole of the threaded holes extending in the side wall of the downhole tool to connect the shaft to the downhole tool to thereby connect the wheel assembly to the downhole tool.

9. The apparatus according to claim 1 further comprising the downhole tool, wherein: the hole extending through the shaft is one of a plurality of holes, each of which extends through the shaft between the first face and the second face; the side wall of the downhole tool comprises a mounting surface (204) configured to contact the first face of the shaft and having: a first set of threaded holes (206) extending into the mounting surface; and a second set of threaded holes (256) extending into the mounting surface;and the threaded fastener is one of a plurality of threaded fasteners, each configured to: be disposed at least partially within a corresponding hole of the holes extending through the shaft and extend out of the corresponding hole of the holes extending through the shaft beyond the first face; and thread-engage the corresponding hole of the threaded holes of one of: the first set of threaded holes extending into the mounting surface to connect the wheel assembly to the downhole tool in a first relative position; and the second set of threaded holes extending into the mounting surface to connect the wheel assembly to the downhole tool in a second relative position.

10. A method comprising: connecting a wheel assembly (240) to a downhole tool (202) to reduce friction between the downhole tool and a side wall of a borehole (102) through which the downhole tool is carried, wherein the wheel assembly comprises: a shaft (222) comprising: a first face (226); a second face (228); a circumferential surface (230) between the first face and the second face; and a hole (320) extending through the shaft between the first face and the second face; and a wheel (224) rotatably connected to the shaft, wherein the wheel is arranged around the circumferential surface;wherein connecting the wheel assembly to the downhole tool comprises: arranging the wheel assembly along a side wall of the downhole tool such that the first face is oriented towards the side wall of the downhole tool and the shaft hole is aligned with a threaded hole (206) extending into the side wall of the downhole tool; inserting a threaded fastener (232) into the threaded hole of the downhole tool through the shaft hole; and threading the threaded fastener to the threaded hole of the downhole tool to connect the shaft to the downhole tool, thereby connecting the wheel assembly to the downhole tool.

11. The method of claim 10, wherein: the shaft hole is one of a plurality of holes, each of which extends through the shaft between the first face and the second face; and connecting the wheel assembly to the downhole tool comprises: arranging the wheel assembly along the side wall of the downhole tool such that the first face faces the side wall of the downhole tool and each of the shaft holes is aligned with a corresponding threaded hole extending into the side wall of the downhole tool; inserting a threaded fastener into each threaded hole of the downhole tool through a corresponding hole in the shaft holes;and thread each threaded fastener to a corresponding threaded hole of the downhole tool to connect the shaft to the downhole tool, thereby connecting the wheel assembly to the downhole tool.

12. The method of claim 10, wherein: the wheel comprises a bore (332) extending through it; wherein the shaft bore and the wheel bore are offset from a rotation axis (305) of the wheel; and connecting the wheel assembly to the downhole tool further comprises: before inserting the threaded fastener into the threaded hole of the downhole tool through the shaft bore, rotating the wheel about the shaft to align the wheel bore with the shaft bore; and inserting the fastener into the shaft bore through the wheel bore.

13. The method of claim 10, wherein: the wheel assembly is one of a plurality of wheel assemblies; and the method further comprises connecting the wheel assemblies to the downhole tool such that: the wheel assemblies collectively define an axial profile having a geometric centerline (201); and the geometric centerline is offset (205) from a longitudinal centerline (203) of the downhole tool.

14. The method of claim 10, wherein: the wheel assembly is one of a plurality of wheel assemblies; and the method further comprises connecting the wheel assemblies to the downhole tool such that the rotation axes (245) of the wheels of the wheel assemblies are offset (205) from the longitudinal center axis (203) of the downhole tool.

15. The method of claim 10, wherein: the shaft hole is one of a plurality of holes, each of which extends through the shaft between the first face and the second face; the side wall of the downhole tool comprises a mounting surface (204) having: a first set of threaded holes (206) extending into the mounting surface; and a second set of threaded holes (256) extending into the mounting surface; and the connection of the wheel assembly to the downhole tool comprises: arranging the wheel assembly along the mounting surface so that the shaft holes align with one of the first set of threaded holes extending into the mounting surface and the second set of threaded holes extending into the mounting surface;Insert threaded fasteners into the aligned set of the first set of threaded holes and the second set of threaded holes through the shaft holes; and thread each threaded fastener to a corresponding threaded hole of the aligned set of the first set of threaded holes and the second set of threaded holes to connect the shaft to the downhole tool, thereby connecting the wheel assembly to the downhole tool.

16. An apparatus comprising: a wheel assembly (300) for a downhole tool (362), wherein the wheel assembly functions to reduce friction between the downhole tool and a side wall of a borehole (102) through which the downhole tool is carried, and wherein the wheel assembly comprises: a shaft (302) comprising an outer circumferential groove (318) and a channel (334) extending through the shaft; a wheel (304) disposed about the shaft and comprising an inner circumferential groove (326), wherein the outer circumferential groove and the inner circumferential groove collectively define a circumferential space (328) between the shaft and the wheel, and wherein the channel intersects the circumferential space; a plurality of ball bearings (308) disposed within the circumferential space and configured to reduce friction between the shaft and the wheel;and a locking member (310) disposed within the channel, wherein the locking member can slide within the channel between a first position in which the ball bearings can be inserted into the circumferential space through the channel and a second position in which the locking member prevents the ball bearings from leaving the circumferential space through the channel.

17. The apparatus according to claim 16 wherein the first position is a radially inward position (356) of the locking member with respect to the axis, and wherein the second position is a radially outward position (360) of the locking member with respect to the axis.

18. The apparatus according to claim 16 wherein: the shaft further comprises a first retaining element (336) extending along the channel; the locking member comprises a second retaining element (340); and the first retaining element and the second retaining element are coupled to retain the locking member within the channel while allowing the locking member to slide along the channel between the first position and the second position.

19. The apparatus according to claim 16, wherein the wheel assembly further comprises a fastener (350) that engages both the locking member and the axle when the locking member is in the second position to prevent the locking element from sliding along the channel from the second position to the first position.

20. The apparatus according to claim 19, wherein the fastener is a threaded fastener comprising a head (352) and a threaded stem (354), and wherein the threaded stem is threaded to the locking member and the head contacts the shaft to prevent the locking member from sliding along the channel from the second position to the first position.

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