Small stop ring with solid cam ring

Abstract

This application relates to a small stop ring with a solid cam ring. A stop ring for installation onto a downhole pipe fitting includes: a cylindrical housing having a threaded inner surface and a tapered inner surface; a compressible slip ring having teeth formed in its inner surface and a pair of tapered outer surfaces; a solid cam ring having a tapered inner surface; and a cylindrical bolt having a threaded outer surface. The natural outer diameter of each ring is greater than the minor diameter of the threaded surface. Threading the threaded surface of the housing and the threaded surface of the bolt is operable to drive the tapered surfaces together, thereby compressing the slip ring such that the teeth engage the periphery of the pipe fitting.

Description

[0001] Disclosed Background

[0002] Disclosed Field

[0003] The present disclosure generally relates to a slimline stop collar with a solid cam ring.

[0004] Description of the Prior Art

[0005] US 4,101,179 discloses a rigid stabilizer sleeve having outwardly extending ribs that are slidably received on a drill collar. A pair of internal clamping rings are slidably received through each end of the rigid main sleeve. When a threaded end cap is screwed into the rigid main sleeve, an end clamp forces one of the pair of rings against the other ring, thereby creating a clamping effect whereby the stabilizer can be clamped at any desired position on the drill collar. The outer ring of the pair has grooves and ribs provided on its inner cylindrical surface; the end clamp portion received by the outer ring has ribs and grooves provided on its outer cylindrical surface. When the end cap receives the outer ring, the ribs and grooves of the end cap interlock with the grooves and ribs of the outer ring, respectively, whereby when the end cap is removed threadably from the rigid main sleeve, the outer ring follows the end cap and disengages from the inner ring, thereby releasing the pair of rings from the drill collar.

[0006] US 4,384,626 discloses a clamping stabilizer that fixes a drill string in a lateral position in a borehole. The stabilizer includes a clamping sleeve having slotted and tapered ends, a stabilizer body that houses the sleeve, and a tubular locking nut that is screwed into the body. The lower end of the stabilizer body is tapered internally to engage one tapered end of the clamping sleeve, while a ring adjacent to the locking nut engages the other tapered end. The tapers at both ends of the sleeve can be different to create a sequential locking effect. The full-length longitudinal slots in the sleeve increase the tolerance range of the object clamped by the stabilizer.

[0007] US 5,860,760 discloses a clamping device having an internal member and an external member. The internal member has a split that defines a first end and a second end. Also included is a selectively operable means for keeping the first end and the second end separated, thereby allowing the device to be placed around an object and allowing the first end and the second end to move towards each other such that the internal member clamps the object. At least a portion of the outer surface of the internal member cooperates with at least a portion of the inner surface of the external member in such a way that when a load is applied to the external member, the inner surface of the external member acts on the internal member, causing the internal member to compress, thereby increasing the clamping of the internal member on the object. The device is then locked in place on the object, and when the load is removed, the action of the external member on the internal member is reduced, thereby reducing the clamping of the internal member on the object and unlocking the device from the object.

[0008] U.S. Patent No. 8,832,906 discloses a stop collar assembled using a method that includes the steps of receiving a bore of a base having a set of fingers extending along an outer portion of a pipe fitting; receiving a bore of a sleeve onto the pipe fitting adjacent the set of fingers; and receiving the sleeve onto the set of fingers in an interference fit. In an alternative embodiment, the base includes a plurality of angularly distributed fingers and / or the base includes a gap to allow the base to conform to the pipe fitting. A fingerless base may cooperate with one or more individual fingers to form the base. In one embodiment of the method, the sleeve may be thermally expanded prior to the step of receiving the sleeve onto the set of fingers. The sleeve may be heated to expand the bore prior to being received onto the set of fingers.

[0009] U.S. Patent No. 9,598,913 discloses a wear band that includes a rotating element having a bore receivable onto a pipe fitting, the bore including a first bore portion and a second bore portion slidably receiving a first sleeve bearing and a second sleeve bearing, respectively. Outer surfaces of the sleeve bearings slidably engage the bore portions, and bores of the sleeve bearings slidably engage the pipe fitting. A first stop collar and a second stop collar may be received onto the pipe fitting to straddle the rotating element and the sleeve bearings therebetween to longitudinally secure the rotating element in place on the pipe fitting. The pipe fitting may be included within a string of pipe fittings entering a borehole or a bore of an installed casing (e.g., in a casing during drilling). The rotating element provides a stand-off between the pipe fitting and the walls of the bore, reducing frictional resistance to longitudinal sliding and also reducing frictional resistance to rotation of the string of pipe fittings within the bore.

[0010] U.S. Patent No. 9,963,942 discloses a centralizer that includes a centralizer body in the form of a casing, liner, or the like used in drilling located at an outer surface of a pipe, the centralizer body formed with a plurality of outer centralizer vanes arranged in an inclined manner with respect to its longitudinal axis, wherein the centralizer body has a separate split inner tube fixed to the pipe string by a press fit, and low-friction inner surfaces of the centralizer body and the separate central tube facing each other are made of a low-friction material.

[0011] US 9,982,494 discloses an attachment device for an element arranged on a downhole tubular body, wherein an end portion of a sleeve arranged to surround a part of the tubular body includes an attachment portion. The attachment portion includes at least one clamping element arranged to be axially displaced by bringing an abutment surface into proximity with a conical abutment portion of a surrounding adapter sleeve.

[0012] US 2016 / 0376852 discloses a stabilizer assembly for a tubular member, including a stabilizer body sized to fit around the tubular member, a central portion having a radial protrusion, and a first end having a first threaded outer surface and a set of integrated first elastic members. A first nut member includes a proximal end and a central portion, the proximal end having a threaded inner surface configured to engage the first threaded outer surface of the stabilizer body, and the central portion having a first conical inner surface configured to engage the first elastic members of the stabilizer body. Screwing the first nut member onto the first end of the stabilizer body forces the first elastic members to engage the first conical inner surface of the first nut member, thereby radially bending the first elastic members to engage the tubular member. The inner surface of the distal end of each first elastic member may include a clamping portion.

[0013] US 2020 / 0109607 discloses a stop ring for installation on a downhole tubular, including: a cylindrical housing having a threaded inner surface and a conical inner surface; a compressible slip ring having teeth formed in its inner surface and a pair of conical outer surfaces; a compressible cam ring having a conical inner surface; and a cylindrical bolt having a threaded outer surface. The natural outer diameter of each ring is greater than the minor diameter of the threaded surface. Screwing the threaded surface of the housing and the threaded surface of the bolt is operable to drive the conical surfaces together, thereby compressing the slip ring such that the teeth engage the periphery of the tubular.

[0014] SUMMARY OF THE DISCLOSURE

[0015] The present disclosure generally relates to a small stop ring with a solid cam ring. In one embodiment, a stop ring for installation on a downhole tubular includes: a cylindrical housing having a threaded inner surface and a conical inner surface; a compressible slip ring having teeth formed in its inner surface and a pair of conical outer surfaces; a solid cam ring having a conical inner surface; and a cylindrical bolt having a threaded outer surface. The natural outer diameter of each ring is greater than the minor diameter of the threaded surface. Screwing the threaded surface of the housing and the threaded surface of the bolt is operable to drive the conical surfaces together, thereby compressing the slip ring such that the teeth engage the periphery of the tubular. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Thus, the above-described features of the present disclosure can be understood in detail, and a more specific description of the present disclosure briefly outlined above can be obtained by referring to the embodiments, some of which are illustrated in the accompanying drawings. However, it should be noted that the drawings only illustrate typical embodiments of the present disclosure and should not be considered as limiting its scope, since the present disclosure may admit other equally effective embodiments.

[0017] Figure 1A Shown is a centralizer equipped with a pair of small stop rings according to an embodiment of the present disclosure. Figure 1B Shown is the body of the centralizer mounted to a downhole tubular. Figure 1C Shown is one of the typical small stop rings used with an elastomeric centralizer rather than a (rigid) centralizer according to another embodiment of the present disclosure.

[0018] Figure 2 Shown is the arrangement of a typical small stop ring.

[0019] Figure 3A and Figure 3B Shown is the insertion of a solid cam ring into the housing of a typical small stop ring.

[0020] Figure 4A Shown is the insertion of a slip ring into the housing of a typical small stop ring. Figure 4B Shown is the screwing of a bolt into the housing of a typical small stop ring.

[0021] Figure 5A Shown is an assembled typical small stop ring in the disengaged position. Figure 5B and Figure 5C Shown is the operation of the locking system of a typical small stop ring.

[0022] Figure 6A and Figure 6B Shown is a typical small stop ring engaged with a downhole tubular. Figure 6C Shown is a typical small stop ring engaged with a second larger downhole tubular.

[0023] Figure 7A Shown is an alternative solid cam ring inserted into the housing of a typical small stop ring according to another embodiment of the present invention. Figure 7B Shown is the expansion of the alternative solid cam ring during the engagement of the slip ring with the downhole tubular. Detailed description

[0024] Figure 1A Illustrated is a centralizer 1 equipped with a pair of small stop rings 2a, 2b according to an embodiment of the present disclosure. Figure 1BIllustrated is the body 3 of the centralizer 1 installed to the downhole pipe fitting 4. The centralizer 1 may include a pair of small stop rings 2a, 2b, the body 3, a radial bearing 5, and a pair of thrust bearings 6a, 6b. Each stop ring 2a, 2b may be installed to the downhole pipe fitting 4, such as a casing or liner, and the stop rings may straddle both sides of the centralizer 3, thereby clamping the centralizer to the downhole pipe fitting. The body 3 may be cylindrical and have a plurality (four are shown) of blades 3b that form the periphery of the body 3 and extend helically along the body. The radial bearing 5 may be a split tube made of one or more materials (such as an internal material and an external material). The internal material of the radial bearing 5 may be a friction material, and the natural inner diameter of the radial bearing may be smaller than the outer diameter of the downhole pipe fitting 4, thereby forming an interference fit therewith. The external material of the radial bearing 5 may be a low-friction material to facilitate the rotation of the downhole pipe fitting 4 relative to the body 3. The inner portion of the body 3 may also be coated with a low-friction material. Each thrust bearing 6a, 6b may be made of a low-friction material and may be disposed between the radial bearing 5 and the corresponding stop ring 2a, 2b or between the body 3 and the corresponding stop ring.

[0025] Optionally, the radial bearing 5 may be a non-split tube. Optionally, the radial bearing 5 may be made entirely of a low-friction material.

[0026] Multiple centralizers 1 can each be installed along the string (e.g., casing string or liner string) of the downhole tubular 4, which string of the downhole tubular 4 is to be drilled into a wellbore (not shown) adjacent to an unstable or depleted formation. The centralizers 1 can be spaced apart at regular intervals along a portion of the string of the downhole tubular 4. Drilling the string of the downhole tubular 4 into a wellbore adjacent to an unstable or depleted formation is advantageous for using a drill string to prevent collapse or loss of drilling fluid due to the unstable or depleted formation. The string of the downhole tubular 4 can also include a casing bit that is screwed onto the bottom of the string of the downhole tubular 4 and can be rotated during drilling by a top drive, either directly or via a working drill string extending from the top of the string of the downhole tubular 4 to the top drive. During the drilling process, a drilling fluid such as mud can be pumped down through the borehole of the string of the downhole tubular 4, discharged from the casing bit, and returned to the surface through an annulus formed between the string of the downhole tubular 4 and the wellbore. The string of the downhole tubular 4 can have a premium connection to withstand the drilling torque applied thereto by the top drive. The string of the downhole tubular 4 can also include a floating collar positioned adjacent to the casing bit and a deployment assembly located at the upper end of the string of the downhole tubular 4, the deployment assembly including a hanger, a packer, and one or more wiper plugs. Once the string of the downhole tubular 4 is drilled in place, the hanger can be deployed, cement slurry can be pumped into the annulus, and the packer is deployed to install the string of the downhole tubular into the wellbore. The casing bit can then be drilled through to facilitate further drilling of the wellbore to a hydrocarbon bearing formation, such as crude oil and / or natural gas.

[0027] Figure 1C Shown is a typical one of the small stop rings 2a, 2b used with an elastomeric centralizer 7 rather than the (rigid) centralizer 1, in accordance with another embodiment of the present disclosure. The elastomeric centralizer 7 can include a pair of end rings 9a, 9b, a body 8, and the typical small stop ring 2. The body 8 can have a pair of end rings 8a, 8b and a plurality of bow springs 8s extending between the pair of end rings 8a, 8b. The bow springs 8s can be spaced apart around the body 8 at regular intervals, such as eight bow springs spaced at forty-five degree intervals. Bypass channels can be formed between the bow springs 8s to accommodate fluid flow through the annulus formed between the downhole tubular 4 and the wellbore. The bow springs 8s can be identical to each other and can move radially between an expanded position (shown) and a retracted position (not shown). The bow springs 8s can have a parabolic shape in the expanded position.

[0028] The body 8 can longitudinally extend when moving from the expanded position to the retracted position and longitudinally contract when moving from the retracted position to the expanded position. The bow springs 8s can be naturally biased towards the expanded position, and the expanded diameter of the centralizer 7 can correspond to the diameter of the wellbore. The engagement of the bow springs 8s with the wall of the wellbore can move the downhole pipe fitting 4 towards the central position within the wellbore to ensure a uniform cement sheath is formed around the downhole pipe fitting during the cementing operation. The body 8 can be formed from a single piece of spring steel by cutting out slots to form strips that will become the bow springs 8s. The body 8 can be formed into a tubular shape by rolling cut pieces and welding the seams of the end rings 8a, 8b together. The bow springs 8s can have a natural bias towards the expanded position by being held therein during the heat treatment of the body 8.

[0029] After the body 8 has been formed, each end ring 9a, 9b can be inserted into the corresponding end rings 8a, 8b. Each end ring 9a, 9b can be formed to fit tightly within the end rings 8a, 8b. Then, each end ring 9a, 9b can be spot welded to the corresponding end rings 8a, 8b. The lips of each end ring 8a, 8b that extend through the corresponding rings 9a, 9b can be split into multiple tabs (before or after ring insertion), and the tabs can be bent over the corresponding end rings to mount the rings to the body 8 (in addition to spot welding). Before the centralizer 7 slides over the periphery of the downhole pipe fitting 4, the stop ring 2 can be positioned between the end rings 9a, 9b by inserting it into one of the slots between the bow springs 8s. The provision of the stop ring 2 can capture the centralizer 7 in place along the downhole pipe fitting 4 while allowing the body 8 to make limited longitudinal movement relative to the downhole pipe fitting 4 to accommodate movement between positions.

[0030] Optionally, instead of a single stop ring 2 located between them, the centralizer 7 can include a pair of small stop rings 2a, 2b straddling both sides of the end rings 8a, 8b.

[0031] Figure 2 The arrangement of a typical small stop ring 2 is shown. A typical stop ring 2 can include a bolt 10, a solid cam ring 11, a slip ring 12, a housing 13, and a locking system 14 ( Figure 5B ). Each of the components 10 - 14 can be made of metal or an alloy (such as steel). The locking system 14 can include a ratchet profile 13r of the housing 13 and a ratchet profile 10r of the bolt 10.

[0032] In addition, refer to Figure 3A, the housing 13 can be cylindrical and have a first portion 13a, a second portion 13b, a third portion 13c, and a fourth portion 13d. The first portion 13a has an increased inner diameter for accommodating the slip ring 12 and the cam ring 11. The second portion 13b has a decreased inner diameter for engaging with one of the thrust bearings 6a, 6b. The third portion 13c has a tapered inner surface connecting the first and second portions. The fourth portion 13d has a threaded 13t inner surface partially segmented by a ratchet profile 13r. The fourth portion 13d extends from the end of the housing to the first portion and has a ratchet profile along the housing portion. The ratchet profile 13r can include a series of circumferentially spaced and longitudinally extending catches, such as slots, for accommodating the tabs of the ratchet profile 10r of the bolt 10. The inner diameters of the first portion 13a and the second portion 13b can each be constant. The housing 13 can also have a plurality of holes formed through the wall of the first portion 13a to facilitate assembly (discussed below). The internal thread 13t of the fourth portion 13d can be used to mate with the threaded surface 10t of the bolt 10. The forms of the threads 13t, 10t can be lead screws for driving the slip ring 12 into engagement with the periphery of the downhole pipe fitting 4. The taper angle 13g relative to an axis parallel to the longitudinal axis of the downhole pipe fitting 4 can be in the range between five degrees and twenty-five degrees.

[0033] The slip ring 12 can have a central portion 12c (which has an outer surface with a constant diameter) and a pair of working portions 12w, each working portion having a tapered outer surface that slopes away from the central portion. The taper of each working portion 12w can correspond to the taper of the third portion 13c of the housing 13. The inner surface of each working portion 12w can have a plurality of circumferential teeth 12t (also called wickers) formed therein. Each tooth 12t can have a cross-sectional shape similar to a right triangle, and the hypotenuse of the teeth of each working portion 12w can slope towards the central portion 12c, thereby providing bi-directional clamping of the downhole pipe fitting 4. The slip ring 12 can be split (also called C-shaped) for compression between the (shown) natural position and the compressed position ( Figure 6B ). In the natural position, the outer diameter of the central portion 12c can be greater than the minor diameter of the threads 13t, 10t and approximately equal to (plus or minus 10%) the inner diameter of the first portion 13a of the housing 13.

[0034] Optionally, the slip ring 12 can be partially segmented by a plurality of slots that radially extend through its wall, each slot extending from one end of the slip ring along a respective working portion 12w and central portion 12c and terminating in another working portion before reaching the other end of the slip ring. Optionally, the teeth 12t of the slip ring 12 can all be inclined in the same direction, thereby providing only one-way clamping of the downhole pipe fitting 4, and the slip ring can have, for example, a direction indicator, such as an arrow, on its periphery by adhesion, engraving, or spraying. Optionally, the teeth 12t of the slip ring 12 can all be inclined away from the central portion.

[0035] The solid cam ring 11 can have a first portion 11a and a second portion 11b. The first portion 11a has a tapered inner surface for engaging one of the working portions 12w of the slip ring 12, and the second portion 11b has a reduced inner diameter for engaging the end of the bolt 10. The solid cam ring 11 can have a constant outer diameter (excluding the chamfers formed at each of its ends). The taper of the first portion 11a can correspond to the taper of the working portion 12w of the slip ring 12. By "solid" it is meant that the cam ring has a solid wall (without slots) and is not slotted. The metal or alloy of the cam ring 11 can have sufficient elasticity to allow the cam ring to be elastically compressed between a natural position (shown) and a compressed position ( Figure 3A ). In the natural position, the outer diameter of the cam ring 11 can be greater than the minor diameter of the threads 13t, 10t and less than or equal to the inner diameter of the first portion 13a of the housing 13.

[0036] The bolt 10 can be cylindrical and have a first portion 10a, a second portion 10b, and a shoulder 10s. The first portion 10a has a reduced outer diameter and threads 10t formed on its outer surface and extending from its end. The second portion 10b has an increased outer diameter, and a ratchet profile 10r is formed in the first portion. The shoulder 10s connects the first portion and the second portion. The bolt 10 can also have a plurality of holes formed through the wall of the second portion 10b to facilitate assembly (discussed below). The minor diameter of the threads 13t, 10t can be less than the inner diameter of the first portion 13a of the housing 13.

[0037] Also refer to Figure 5B to 5C, the ratchet profile 10r may include a circumferential row of openings and cantilever tabs disposed in the openings and radially extending outward when the cantilever tabs extend circumferentially through the openings. The ratchet profile 10r may be positioned adjacent to the threads 10t and positioned between the threads and the shoulder 10s. The ratchet profiles 10r, 13r may be configured to allow rotation in the tightening direction of the rotation of the bolt 10 relative to the housing 13, but prevent rotation in its loosening direction. This is because the natural effective diameter of the free end of the tab is greater than the major diameter of the thread surface 13t to ensure that the tab engages the slot of the ratchet profile 13r.

[0038] Figure 3A and 3B The insertion of the solid cam ring 11 into the housing 13 of a typical small retaining ring 2 is shown. To begin assembly, the cam ring 11 may be rotated so that its longitudinal axis 15c is perpendicular to the longitudinal axis 15h of the housing 13. The cam ring 11 may be compressed so that a portion of its outer diameter is less than or equal to the minor diameter of the threads 13t of the housing 13. The compressed cam ring 11 may then be inserted through the threads 13t into the hole of the first portion 13a of the housing 13 until the compressed cam ring engages the tapered third portion 13c of the housing. The compressed cam ring 11 may then be rotated again until its longitudinal axis 15c is parallel to the longitudinal axis 15h of the housing 13. This rotation may require some flexing of the cam ring 11. Once rotated into position, the cam ring 11 may then expand to its natural position (the compression is only elastic, not plastic) and slide along the hole of the first portion 13a of the housing 13 until the cam ring is adjacent to the housing threads 13t.

[0039] Optionally, the cam ring 11 may be inserted into the housing 13 via its non-threaded end adjacent to the second housing portion 13b rather than its threaded end adjacent to the fourth housing portion 13d. Optionally, the cam ring 11 may be partially deformed when inserted into the housing 13 and at least partially deformed back to its original shape of the cam ring before or during positioning parallel to the longitudinal axis 15h of the housing (the compression is partially plastic).

[0040] Figure 4AIllustrated is the insertion of the slip ring 12 into the housing 13 of a typical small retainer ring 2. Once the cam ring 11 has been correctly positioned within the housing 13, the slip ring 12 can be rotated such that the longitudinal axis 15s of the slip ring forms an acute angle with the longitudinal axis 15h of the housing 13. The slip ring 12 can then be inserted into the non-threaded end of the housing 13 adjacent the second housing portion 13b until the non-inserted end of the slip ring is adjacent the non-threaded end of the housing. The slip ring 12 can then be compressed such that the non-inserted end of the slip ring can slide beneath the inner surface of the second housing portion 13b, and then the non-inserted end of the slip ring can slide such that the slip ring is rotated into position along the bore of the first housing portion 13a and engages the cam ring 11 and the tapered surface portion of the third housing portion 13c.

[0041] Figure 4B Illustrated is the threading of the bolt 10 into the housing 13 of a typical small retainer ring 2. Once the slip ring 12 has been correctly positioned within the housing 13, the threads 10t of the bolt 10 can engage the housing threads 13t. The first torque bar 16a can be inserted into one of the holes of the second housing portion 13b, and the second torque bar 16b can be inserted into one of the holes of the second bolt portion 10b. Using the torque bars 16a, 16b, the bolt 10 can be rotated relative to the housing 13 in the tightening direction, thereby advancing the bolt toward the housing until the threaded end of the bolt is adjacent the cam ring 11 and the ratchet profile 10r of the bolt has begun to engage the ratchet profile 13r of the housing 13, thereby placing the typical small retainer ring 2 in the disengaged position.

[0042] Figure 5A Illustrated is the assembled typical small retainer ring 2 in the disengaged position. The torque bars 16a, 16b can be removed, and the disengaged retainer ring 2 can then be slid onto the downhole tubular 4 until the non-threaded end of the housing 13 engages one of the thrust bearings 6a, 6b.

[0043] Figure 6A and 6BShows a typical small retainer ring 2 engaged with a downhole fitting 4. Once the disengaged retainer ring 2 has been positioned along the downhole fitting 4, the torque rods 16a, 16b can be reinserted, and the bolt 10 can be further rotated in the tightening direction relative to the housing 13, thereby further advancing the bolt into the housing. During continued rotation of the bolt 10 relative to the housing 13, the threaded end of the bolt can engage the non-tapered end of the cam ring 11 and drive the cam ring towards the slip ring 12. During continued rotation of the bolt 10 relative to the housing 13, the tapered first portion 11a of the cam ring 11 can slide on the adjacent working portion 12w of the slip ring 12 until its mating tapered surfaces engage, thereby driving the distal surface of the slip ring 12 into engagement with the mating tapered surface of the third portion 13c of the housing. During continued rotation of the bolt 10 relative to the housing 13, the tapered first portion 11a of the cam ring 11 can continue to slide on the adjacent working portion 12w of the slip ring 12, and the slip ring can continue to advance along the tapered inner surface of the third portion 13c of the housing, thereby radially compressing the slip ring 12 towards the periphery of the downhole fitting 4. The radial compression of the slip ring 12 can continue until its teeth 12t engage and penetrate the periphery of the downhole fitting 4, thereby longitudinally and torsionally mounting the retainer ring 2 to the downhole fitting.

[0044] In addition, during continued rotation of the bolt 10 relative to the housing 13, the tabs of the ratchet profile 10r can engage the slots of the ratchet profile 13r. Since the bolt 10 is rotated in the tightening direction, the engaging end of each tab can enter and exit the corresponding slot before the free end of the tab, thereby allowing the walls of the slot to compress the tab such that rotation in the tightening direction is unhindered. The operation of the locking system 14 prevents the bolt 10 from rotating in the loosening direction during deployment of the centralizer 1, which rotation may be caused by vibration. Depending on the relative positions of the bolt 10 and the housing 13 when the slip ring 12 is fully engaged, there may be some acceptable clearance until the ratchet profiles 10r, 13r engage.

[0045] Optionally, the retainer ring 2 can be installed on the downhole fitting 4 with the bolt 10 positioned adjacent to one of the thrust bearings 6a, 6b instead of the housing 13 being positioned adjacent to one of the thrust bearings 6a, 6b.

[0046] Advantageously, using a solid cam ring 11 instead of a slotted or grooved cam ring provides a stronger retainer ring 2 because the cam ring serves as a hoop stress support member, thereby strengthening the thinner first portion 13a of the housing 13. The radial clearance that necessarily results from using a slotted cam ring is eliminated. At the engagement location of the retainer ring 2, the cam ring 11 can be loaded primarily or only within the elastic range such that the equivalent tensile stress is less than or equal to the yield strength of the cam ring material.

[0047] Figure 6C shows a typical small stop ring 2 engaged with a second larger downhole fitting 17. The stop ring 2 can accommodate dimensional variations of the downhole fittings 4, 17 such that Figure 6B shows the maximum clearance between the outer surface of the downhole fitting 4 and the inner diameter of the second housing portion 13b that can be used therewith, while Figure 6C shows the minimum clearance between the outer surface of the second downhole fitting 17 and the inner diameter of the second housing portion 13b that can be used therewith.

[0048] Figure 7A shows an alternative solid cam ring 18 inserted into a typical small stop ring housing 13 according to another embodiment of the present invention. The alternative cam ring 18 can replace the cam ring 11, thereby forming an alternative typical stop ring. The alternative typical stop ring can include bolts 10, an alternative solid cam ring 18, a slip ring 12, a housing 13, and a locking system 14( Figure 5B ). The alternative cam ring 18 can have an outer diameter smaller than that of the cam ring 11, thereby forming a clearance 19 between its outer surface and the inner surface of the first portion 13a of the housing 13. For illustrative purposes, Figure 7B the dimensions and expansion of the clearance 19 shown therein may be exaggerated. In addition to the smaller outer diameter, the alternative cam ring 18 can be similar or identical to the cam ring 11. The reduced outer diameter of the alternative cam ring 18 can be greater than the minor diameter of the threads 13t, 10t and less than the inner diameter of the first portion 13a of the housing 13, such as less than or equal to 99%, 98%, 97%, 96%, 95%, 94%, 93%, 92%, 91% or 90% of the inner diameter of the first portion 13a of the housing 13.

[0049] Optionally, the reduced outer diameter of the alternative cam ring 18 can be greater than the minor diameter of the threads 13t, 10t and less than or equal to the major diameter of the threads 13t, 10t.

[0050] Figure 7BShows the expansion of an alternative solid cam ring 18 during engagement of the slip ring 12 with the downhole fitting 4. The natural position of the alternative solid cam ring 18 is shown in dashed lines. As the bolt 10 continues to rotate relative to the housing 13, the threaded end of the bolt can engage the non-tapered end of the alternative solid cam ring 18 and drive the cam ring towards the slip ring 12. During continued rotation of the bolt 10 relative to the housing 13, the tapered first portion of the cam ring 18 can slide on the adjacent working portion 12w of the slip ring 12 until its mating tapered surfaces engage, thereby driving the distal surface of the slip ring 12 into engagement with the mating tapered surface of the third portion 13c of the housing. During continued rotation of the bolt 10 relative to the housing 13, the tapered first portion 11a of the cam ring 18 can continue to slide on the adjacent working portion 12w of the slip ring 12, and the slip ring can continue to advance along the tapered inner surface of the third portion 13c of the housing, thereby radially compressing the slip ring 12 towards the periphery of the downhole fitting 4 and radially expanding the cam ring 18. The radial compression of the slip ring 12 can continue until its teeth 12t engage and penetrate the periphery of the downhole fitting 4, thereby longitudinally and torsionally mounting the alternative stop ring to the downhole fitting.

[0051] Advantageously, the radial expansion of the alternative solid cam ring 18 increases the preload or strain in the alternative stop ring. The cam ring 18 can act as an annular spring, thereby ensuring that the slip ring 12 maintains its grip on the fitting 4. The cam ring 18 can even be expanded beyond its yield strength, thereby strain hardening the cam ring.

[0052] While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the present disclosure may be devised without departing from the basic scope thereof, and the scope of the invention is determined by the appended claims.

[0053] The present invention also relates to the following aspects:

[0054] 1. A stop ring for installation on a downhole fitting, the stop ring comprising:

[0055] A cylindrical housing having a threaded inner surface and a tapered inner surface;

[0056] A compressible slip ring having teeth formed in its inner surface and a pair of tapered outer surfaces;

[0057] A solid cam ring having a tapered inner surface; and

[0058] A cylindrical bolt having a threaded outer surface,

[0059] Wherein:

[0060] The natural outer diameter of each ring is greater than the minor diameter of the threaded surface, and

[0061] Turning the threaded surface of the housing and the threaded surface of the bolt are operable to drive the conical surfaces together, thereby compressing the slip ring such that the teeth engage the periphery of the fitting.

[0062] 2. The stop ring according to aspect 1, wherein the solid cam ring is made of an elastic material to allow its elastic compression.

[0063] 3. The stop ring according to aspect 1, wherein the slip ring is slotted.

[0064] 4. The stop ring according to aspect 1, wherein the conical surfaces have respective angles relative to the longitudinal axis of the fitting, and the angles each range between five degrees and twenty-five degrees.

[0065] 5. The stop ring according to aspect 1, wherein:

[0066] The slip ring has a central portion and a pair of working portions, the central portion having an outer surface of constant diameter,

[0067] Each working portion has one of the conical outer surfaces that slopes away from the central portion,

[0068] Each working portion has some of the teeth.

[0069] 6. The stop ring according to aspect 1, further comprising a locking system that is operable to prevent the threaded surfaces of the housing and the bolt from loosening.

[0070] 7. The stop ring according to aspect 6, wherein the locking system includes:

[0071] A ratchet profile formed in the bolt adjacent the threaded surface of the bolt, and

[0072] A ratchet profile formed in the housing that is configured to engage the ratchet profile of the bolt when the threaded surfaces of the bolt and the housing are screwed together.

[0073] 8. The stop ring according to aspect 7, wherein the ratchet profile of the housing is a plurality of slots formed through the wall of the housing and partially dividing the threaded inner surface.

[0074] 9. The stop ring according to aspect 1, wherein:

[0075] The housing has a first portion having a constant inner diameter for receiving the cam ring,

[0076] A gap is formed between the outer surface of the cam ring in its natural position and the inner surface of the first part of the housing.

[0077] 10. The stop ring according to aspect 9, wherein the natural outer diameter of the cam ring is less than or equal to 95% of the inner diameter of the first part of the housing.

[0078] 11. The stop ring according to aspect 9, wherein the natural outer diameter of the cam ring is less than or equal to the major diameter of the threaded surface.

[0079] 12. A centralizer, comprising:

[0080] A body having a plurality of vanes forming its periphery; and

[0081] A pair of stop rings according to aspect 1, each ring for mounting the body of the centralizer to a downhole tubular.

[0082] 13. A centralizer, comprising:

[0083] A body having a plurality of bow springs forming its periphery; and

[0084] A stop ring according to aspect 1, which is used to mount the body of the centralizer to a downhole tubular by being disposed between the ends of the body.

[0085] 14. A method of assembling the stop ring according to aspect 1, comprising:

[0086] Rotating the solid cam ring such that its longitudinal axis is perpendicular to the longitudinal axis of the housing;

[0087] Compressing the solid cam ring and inserting the compressed cam ring through the inner surface of the housing; and

[0088] After insertion, rotating the cam ring until its longitudinal axis is parallel to the longitudinal axis of the housing.

Claims

1. A stop collar for installation onto a downhole pipe fitting, the stop collar comprising: A cylindrical housing having a threaded inner surface and a tapered inner surface; A compressible slip ring having teeth formed in its inner surface and a pair of tapered outer surfaces; A solid cam ring having a tapered inner surface; And A cylindrical bolt having a threaded outer surface, Wherein: The natural outer diameter of each of the slip ring and the solid cam ring is greater than the minor diameter of the threaded inner surface and the threaded outer surface, Threading the threaded inner surface of the housing and the threaded outer surface of the bolt is operable to drive together the tapered inner surface of the housing, the tapered outer surface of the slip ring, and the tapered inner surface of the solid cam ring, thereby compressing the slip ring such that the teeth engage the periphery of the downhole pipe fitting, and The solid cam ring has a solid wall without slots and without slits.

2. The stop ring according to claim 1, wherein, The solid cam ring is made of an elastic material to allow its elastic compression.

3. The stop ring according to claim 1, wherein, The slip ring is slotted.

4. The stop ring according to claim 1, wherein, The tapered inner surface of the housing, the tapered outer surface of the slip ring, and the tapered inner surface of the solid cam ring have respective angles relative to the longitudinal axis of the downhole pipe fitting, and the angles are each in the range between five degrees and twenty-five degrees.

5. The stop collar according to claim 1, wherein: The slip ring has a central portion and a pair of working portions, the central portion having an outer surface with a constant diameter, Each working portion has one of the pair of tapered outer surfaces that slopes away from the central portion, Each working portion has some of the teeth.

6. The stop collar according to claim 1, further comprising a locking system operable to prevent the threaded inner surface of the housing and the threaded outer surface of the bolt from loosening.

7. The stop collar according to claim 6, wherein, The locking system comprises: A ratchet profile formed in the bolt adjacent to the threaded outer surface of the bolt, and A ratchet profile formed in the housing configured to engage the ratchet profile of the bolt when the threaded outer surface of the bolt and the threaded inner surface of the housing are threaded together.

8. The stop ring according to claim 7, wherein The ratchet profile of the housing is a plurality of slots formed through the wall of the housing and partially dividing the threaded inner surface of the housing.

9. The stop collar according to claim 1, wherein: The housing has a first portion having a constant inner diameter for receiving the solid cam ring, A gap is formed between the outer surface of the solid cam ring in its natural position and the inner surface of the first portion of the housing.

10. The stop ring according to claim 9, wherein, The natural outer diameter of the solid cam ring is less than or equal to 95% of the inner diameter of the first portion of the housing.

11. The stop collar according to claim 9, wherein, The natural outer diameter of the solid cam ring is less than or equal to the major diameter of the threaded inner surface and the threaded outer surface.

12. A centralizer comprising: A body having a plurality of vanes forming its periphery; And A pair of stop collars according to any one of claims 1-11, each stop collar for mounting the body to a downhole pipe fitting.

13. A centralizer comprising: A body having a plurality of bow springs forming its periphery; and A stop ring according to any one of claims 1 - 11, for mounting the body to a downhole tubular by being disposed between ends of the body.

14. A method of assembling a stop ring according to any one of claims 1 - 11, comprising: Rotating the solid cam ring such that its longitudinal axis is perpendicular to the longitudinal axis of the housing; Compressing the solid cam ring and inserting the compressed solid cam ring through the inner surface of the housing; and After insertion, rotating the solid cam ring until the longitudinal axis of the solid cam ring is parallel to the longitudinal axis of the housing.

15. A centralizer, comprising: A body having a plurality of bow springs forming its periphery; and A pair of stop rings according to any one of claims 1 - 11, each stop ring for mounting the body to a downhole tubular.

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