WO2018132915A1

WO2018132915A1 - Sucker rod centralizer

Info

Publication number: WO2018132915A1
Application number: PCT/CA2018/050059
Authority: WO
Inventors: Mark Lea-Wilson; Shane Mcassey
Original assignee: Plainsman Manufacturing Inc
Current assignee: Plainsman Manufacturing Inc
Priority date: 2017-01-19
Filing date: 2018-01-19
Publication date: 2018-07-26
Anticipated expiration: 2019-07-19

Abstract

A centralizing sucker rod connector having a vaned sleeve mounted on a mandrel. The mandrel has a shoulder enclosed by the sleeve. One or more inserts included within the sleeve or the inner surface of the sleeve engage the mandrel and can contact the shoulder to bear an axial force. Box couplings connect the centralizing sucker rod connector to sucker rods. A retaining nut retains the sleeve and also has threads of a different pitch than an adjacent sucker rod box coupling to develop improved connection strength in that threaded connection as the retaining nut engages the box coupling.

Description

SUCKER ROD CENTRALIZER

TECHNICAL FIELD

[0001] Sucker rod centralizers.

BACKGROUND

[0002] Once a well has been established for the production of fluid hydrocarbons it is often necessary to pump the fluid out of the well when the fluid has a high viscosity or a relatively low pressure. Most artificial lift wells in the U.S. and Canada consist of a downhole pump attached to a surface power source by series of connected sucker rods. Each sucker rod is machined from a solid rod approximately 25 to 30 feet long with a central diameter between 5/8" and 1-1/8" with a threaded pin and shoulder at either end of the rod. A "sucker rod coupling" is a cylindrically internally threaded member and is used to connect segments of sucker rod together to create an assembly called a "sucker rod string". The sucker rod couplings are typically 4" long and have a larger outer diameter than the raised shoulders of the sucker rod.

[0003] The sucker rod string is fed through a concentric tubing string consisting of

30 foot sections of tubing which are threaded together and typically have a nominal inside diameter between 2-3/8" and 4-1/2". The function of the sucker rod string is to actuate the downhole pump to force fluid to the surface by pumping the fluid flow through the annulus formed by the sucker rod string and the tubing string. Progressing cavity pumps will rotate the sucker rod string and reciprocating pumps will move the sucker rod string up and down the axial direction of the sucker rod string.

[0004] When sucker rod string is rotated within a well that deviates from vertical, the string tends to lie on the one side of the tubing and the rod string rotates eccentrically about this point. This eccentric motion allows the steel sucker rod couplings, which have a larger outer diameter than the sucker rod, to slap and grind against the steel tubing causing wear and severe damage to the tubing wall. The resulting tubing wall failure is disastrous for the well operation and requires expensive repairs. It has become industry practice to centralize the rod string within the tubing with a soft non-metallic material to prevent steel -on- steel contact between the couplings and the tubing wall. This soft non-metallic centralizer, or guide, can be mounted on the rod string in a variety of methods. However, mounting the centralizer at the connecting point of a pair of sucker rods ensures that the large diameter couplings are prevented from contacting the tubing wall. If the centralizer were mounted on the narrow sucker rod stem in the center of the sucker rod the couplings might still contact the tubing wall.

[0005] The industry has recently been experimenting with high strength materials and alternative manufacturing techniques in the production of sucker rods resulting in the ability to apply higher amounts of torque to the rod string downhole. However, the same couplings and guides are being used to connect the rod string. In order for the centralizer mandrel to transmit the higher torque without material failure a greater bearing contact surface between the mandrel and the couplings was required. However, in a standard one- piece centralizer design as the bearing contact surface increases, the shoulder area formed by the interface of the mandrel and the couplings which fixes the soft non-metallic centralizer sleeve decreases and results in premature failure, axial travel of the sleeve and severe tubing wall damage.

[0006] U.S. Pat. No. 4,919,202 issued to Clintberg discloses a sucker rod guide bearing having a free spinning vaned sleeve of soft resilient material which is fixed by two large diameter washers and a mandrel which are attached to sucker rod couplings. However, the bearing surface formed between the mandrel and the free spinning washer does not maximize the contact area given that the diameter of the mandrel is less than that of the coupling. Consequently, the sucker rod guide bearing is not suitable for high torque applications. The metallic washer with a larger diameter than the coupling also introduces the likelihood of metal-metal contact with the tubing wall once the sleeve has been worn down. While the resulting metal-metal wear is generally less damaging, given the washer is softer than the tubing wall, the large diameter washer is undesirable as the large diameter and sharp edge are have the possibility to leave severe localized wear on the tubing.

[0007] US patent publication no. 2012/0193089 describes a previous solution to the problems described above. However, it is believed that the solution described in the present application will provide superior wear life and will better enable running "dry" without damage.

SUMMARY

[0008] There is provided a centralizer assembly comprising a mandrel having a first portion of a first diameter and a second portion of a second diameter, the first diameter larger than the second diameter, the first portion defining a shoulder adjacent to the second portion; and a sleeve mounted axially on the mandrel, the sleeve comprising an inner surface to forming a first radial bearing interface by contact with the first portion of the mandrel and a second radial bearing interface by contact with the second portion of the mandrel, the inner surface of the sleeve forming an inner shoulder disposed to contact the shoulder of the mandrel in use of the centralizer assembly.

[0009] In various embodiments, there may be included any one or more of the following features: the inner surface may comprise one or more inserts or may be a single insert shaped to conform with the first and second portions of the mandrel; the one or more inserts may comprise bronze; the one or more inserts may comprise oil-impregnated bronze; there may be a retaining element on the mandrel; the retaining element may be a nut; the nut and the mandrel may define threads to secure the nut to the mandrel with a threaded connection; the mandrel may further defines threads to secure the mandrel to a box coupling; the threads for securing the mandrel to the nut have a different pitch than the threads for securing the mandrel to the box coupling; there may be seals between the mandrel and the sleeve sealing at least a portion of an interface between the mandrel and the sleeve; there may be a pressure equalizing element connecting the at least a portion of the interface between the mandrel and the sleeve to an external surface of the centralizer assembly; the pressure equalizing element may comprise a passage through the sleeve; the pressure equalizing element may further comprise a piston within the passage.

[0010] These and other aspects of the device and method are set out in the claims, which are incorporated here by reference. BRIEF DESCRIPTION OF THE FIGURES

[0011] Embodiments will now be described with reference to the figures, in which like reference characters denote like elements, by way of example, and in which:

[0012] Fig. 1 is an end elevation view of a centralizer assembly;

[0013] Fig. 1 A is a section view taken along the A-A section lines of Fig. 1; and

[0014] Fig. 2 is a section view of another embodiment of a centralizer assembly.

DETAILED DESCRIPTION

[0015] Referring to Figs. 1 and 1A an embodiment of a centralizer assembly 10 comprises a sleeve 12 mounted axially on a mandrel 14. The mandrel has a first portion 16 of a larger diameter and a second portion 18 of a smaller diameter. The first portion defines a shoulder 20 adjacent to the second portion. The mandrel may be formed of any suitable material, for example case hardened and polished steel or chrome. The sleeve 12 has an inner surface that contacts the first portion 16 and second portion 18 of the mandrel 14, and may be formed of an outer sleeve 22 shown as having vanes 24 to space the centralizer from walls of a containing pipe (not shown) while allowing fluid flow and one or more inserts 26 (Fig. 1) or 44, 46 (Fig. 2), where the inserts 26, 44, 46 as the case may define the inner surface of the sleeve 12. The sleeve 12 may be formed from a relatively soft material in comparison to the pipe walls to act as a sacrificial wear surface, for example aluminum. The inserts, if present, are mounted between the outer sleeve 22 and the mandrel 14. The insert 26 shown in Figs. 1 and 1A is shaped to conform with the first and second portions 16, 18 of the mandrel 14. If inserts are not used, the inner surface of the single sleeve used for the sleeve 12 contacts the first and second portions of the mandrel 14. The inner surface of the sleeve 12, for example the one or more inserts, contacts the first portion 16 of the mandrel to form a first radial bearing interface 28 and contacts the second portion 18 of the mandrel to form a second radial bearing interface 30.

[0016] The insert 26 or the inserts 44, 46 or the inner surface of a single sleeve forming the sleeve 12 is also positioned so that it can contact the shoulder 20 to form an axial bearing interface. In use, it is expected that the centralizer will be exposed to hydrodynamic pressures from the downhole direction (corresponding to the downward direction in Fig. 1) pushing the sleeve uphole so that the shoulder formed by the inner surface of the sleeve 12 contacts the shoulder 20. An additional shoulder 32 is shown in Fig. 1 but the sleeve does not contact the additional shoulder 32 because the contact between or inner surface of the sleeve 12, formed by the insert 26 if present, and shoulder 20 prevents uphole motion of the sleeve to contact the additional shoulder 32. Thus the expected uphole axial load on the sleeve is borne by an interface internal to the centralizer which can be protected from wear-causing particles.

[0017] Seals 34 and 36 between the mandrel and the sleeve may seal at least a portion of an interface between the mandrel and the sleeve. The seals may seal against particulates such as sand while allowing fluid flow, or may seal against particulates and fluid flow. The seals may be, for example, energized wiper seals. In the embodiment shown in Figs. 1 and 1 A, the seals are mounted on the sleeve and the insert is wholly contained within the sealed volume. A seal retainer 38 is provided on one end of the sleeve. A pressure equalizing element may be provided to equalize hydrostatic pressure between the sealed volume and external fluid. In the embodiment shown, a passage 40 through the sleeve connects the sealed volume to an external surface to equalize the pressure. The passage may be filled with grease. A piston 42 may be included within the passage to prevent particulates or other contaminants from entering through the passage while still allowing pressure equalization. Threads 48 and 52 for connecting to box couplings, and nut 56 connected to the mandrel via threads 58, are described in relation to Fig. 2.

[0018] Referring to Fig. 2, another embodiment of a centralizer assembly 10 is shown. In this embodiment, inner surface of sleeve 12 comprises a first insert 44 in contact with the first portion of the mandrel and a second insert 46 in contact with the second portion of the mandrel. The second insert 46 contacts shoulder 20. In the embodiment shown in Fig.

2, seals 34 and 36 between the mandrel and sleeve are embedded in the inserts 44 and 46 respectively. The centralizer assembly here is shown connected via threads 48 to sucker rod

50 and threads 52 to sucker rod 54, forming box couplings, to enable the centralizer to act as a sucker rod coupling. A nut 56 is mounted on the mandrel via threads 58. The nut 56 is a retaining element which limits the motion of the sleeve in the downhole direction when no force pushing the sleeve uphole is present. The nut 56 may have a diameter equal to the outer diameter of the box coupling of sucker rod 54. This maximizes the bearing area resulting in the highest possible yield torque at the coupling-nut interface. In order to transmit this torque through the mandrel 14, threads 58 connecting the nut to the mandrel may have a different pitch than the threads 52 connecting the mandrel to sucker rod 54. As the coupling advances on the sucker rod threads and engages the nut the difference in thread pitch prevents the nut threads 58 from advancing axially at a specified pre-torque thereby transmitting the stress caused by the applied torque by the sucker rod axially through the nut threads to the body of the mandrel 14.

[0019] Insert 26, or inserts 44 and 46, may be formed of any suitable material, but bronze has been found experimentally to have particularly good wear characteristics. Oil impregnated bronze may be used if desired.

[0020] Immaterial modifications may be made to the embodiments described here without departing from what is covered by the claims.

[0021] The present disclosure was developed for applications with rotating sucker rod strings. It is discussed herein in connection with the problems associated with rotating sucker rod strings, particularly those applications which exert high torques on the sucker rod string downhole. However, the product can be used in reciprocating pumping also with the provision of an additional shoulder on the sleeve and mandrel.

[0022] In the claims, the word "comprising" is used in its inclusive sense and does not exclude other elements being present. The indefinite articles "a" and "an" before a claim feature do not exclude more than one of the feature being present. Each one of the individual features described here may be used in one or more embodiments and is not, by virtue only of being described here, to be construed as essential to all embodiments as defined by the claims.

Claims

[0001] THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVEPROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A centralizer assembly comprising:

a mandrel having a first portion of a first diameter and a second portion of a second diameter, the first diameter larger than the second diameter, the first portion defining a shoulder adjacent to the second portion; and

a sleeve mounted axially on the mandrel, the sleeve comprising an inner surface forming a first radial bearing interface by contact with the first portion of the mandrel and a second radial bearing interface by contact with the second portion of the mandrel, the inner surface of the sleeve forming an inner shoulder disposed to contact the shoulder of the mandrel in use of the centralizer assembly.

2. The centralizer assembly of claim 1 in which the inner surface of the sleeve is formed by one or more inserts.

3. The centralizer assembly of claim 2 in which the one or more inserts comprises a single insert shaped to conform with the first and second portions of the mandrel.

4. The centralizer assembly of claim 2 or claim 3 in which the one or more inserts comprise bronze.

5. The centralizer assembly of claim 4 in which the one or more inserts comprise oil- impregnated bronze.

6. The centralizer assembly of any one of claims 1-5 further comprising a retaining element on the mandrel.

7. The centralizer assembly of claim 6 in which the retaining element is a nut.

8. The centralizer assembly of claim 7 in which the nut and the mandrel define threads to secure the nut to the mandrel with a threaded connection.

9. The centralizer assembly of claim 8 in which the mandrel further defines threads to secure the mandrel to a box coupling.

10. The centralizer assembly of claim 9 in which the threads for securing the mandrel to the nut have a different pitch than the threads for securing the mandrel to the box coupling.

11. The centralizer assembly of any one of claims 1-10 further comprising seals between the mandrel and the sleeve sealing at least a portion of an interface between the mandrel and the sleeve.

12. The centralizer assembly of claim 11 further comprising a pressure equalizing element connecting the at least a portion of the interface between the mandrel and the sleeve to an external surface of the centralizer assembly.

13. The centralizer assembly of claim 12 in which the pressure equalizing element comprises a passage through the sleeve.

14. The centralizer assembly of claim 13 in which the pressure equalizing element further comprises a piston within the passage.