AU2013273635A1 - Polished rod protector and alignment sleeve - Google Patents

Abstract

The invention relates generally to a pumpjack (or beam pumping unit), and in particular to a sleeve for protecting a polished rod of a pumpjack from damage resulting from normal use. In one form, the pumpjack comprises a polished rod depending from a carrier structure, and the sleeve is slidably disposed over the polished rod and between the polished rod and the carrier structure so as to prevent contact between the polished rod and carrier structure, the sleeve being of such a length as to extend substantially between a bottom clamp for the polished rod, and either of a rod rotator or a top clamp for the polished rod.

Description

1 POLISHED ROD PROTECTOR AND ALIGNMENT SLEEVE TECHNICAL FIELD [0001] The invention relates generally to a pumpjack (or beam pumping unit), and in particular to a device for protecting a polished rod of a pumpjack from damage resulting from normal use. BACKGROUND [0002] A pump jack drives a reciprocating pump located downhole in a bore of a subterranean oil well by converting a rotary motion of a prime mover (ie a motor) into a vertical reciprocating motion which is used to drive the pump. [0003] More particularly, the prime mover of the pumpjack drives through a transmission which in turn drives a pair of cranks, which generally carry counterweights to assist the motor in lifting a heavy string of sucker rods which extend down to the pump. The cranks raise and lower one end of a walking beam which is pivotally supported on an A-frame. The distal end of the walking beam carries a curved metal box called a horse head or donkey head (so named due to its appearance). A steel cable - occasionally, fiberglass - called a bridle, connects the horse head to a polished rod, which acts as a piston that passes through a stuffing box seal located at a wellhead. [0004] The polished rod has a close fit with the stuffing box, so that it may move in and out of production tubing that runs to the bottom of the well and through which the liquid is produced. The bridle follows the curve of the horse head as it rises and falls to create a nearly vertical stroke. The polished rod carries the long string of sucker rods, which run through the tubing to the down-hole pump, usually positioned near the bottom of the well. [0005] In operation, the reciprocating sucker rods tend to rub against the inside of the production tubing, causing wear to the sucker rods, rod couplings, and tubing. This occurs particularly in the cases of slanted wells where the sucker rods tend to rest on the lower side of tubing. To limit or distribute the inevitable wear, a rod-rotator is used to incrementally rotate the polished rod each pump stroke. [0006] The polished rod is suspended by a polished rod clamp atop the carrier. The carrier bar is suspended from the horsehead of the pump jack by the cable bridle. The polished rod extends through the carrier bar. Misalignment of the polished rod and the carrier bar can result in contact between the carrier bar and polished rod. The rod-rotator is in turn supported by the carrier bar. Subsequent rotation of the polished rod results in circumferential scoring at the interface of the carrier bar and the polished rod.

2 [0007] Examples of misalignment between the carrier bar and the polished rod include mechanical misalignment of the carrier bar, a slow or restricted downstroke and a resultant slackening of the cable bridle causing angular movement of the carrier bar, and a misaligned polished rod extending from the wellhead seal. [0008] The polished rod is expected to carry high cyclical loading so as to support rod string loads on the upstroke of about 13,000-40,000 pounds. If a polished rod were to fail at a stress riser, such as at a circumferential score, the rod string could fall into the well, potentially releasing well fluid (oil or gases) from the stuffing box seal and initiating an expensive recovery operation. [0009] Preventative maintenance regularly calls for replacement of scored polished rods before they fail, which is a costly exercise. As stated above, polished rod failure can result in the escape of oil and gas and force an expensive clean-up to the environment etc. and rod recovery process. [0010] It is against this background that the present invention has been developed. [0011] Certain objects and advantages of the present invention will become apparent from the following description, taken in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. SUMMARY [0012] According to a first aspect, there is provided a sleeve for a polished rod depending from a carrier structure of a pump jack, wherein in use, the sleeve is slidably disposed over the polished rod and between the polished rod and the carrier structure so as to prevent contact between the polished rod and carrier structure, the sleeve being of such a length as to extend substantially between a bottom clamp for the polished rod, and either of a rod rotator or a top clamp for the polished rod. [0013] In one form, the sleeve is of such a length as to extend above and below the carrier structure. [0014] In one form, the carrier structure comprises a carrier bar, and the sleeve is of such a length as to extend above and below the carrier bar. [0015] In one form, in an alternative, the carrier structure comprises a dynamometer which is supported on the carrier bar, and the sleeve is of such a length as to extend through both the dynamometer and the carrier bar. [0016] In one form, the sleeve is made of a nylon material. In one form, the sleeve is made of 3 [0017] In one form, the sleeve comprises an outer diameter adapted to fit within a bore of the carrier structure, and a bore through which the polished rod passes. [0018] In one form, the external diameter of the sleeve varies along its length. [0019] In one form, the dynamometer comprises a bore which is of a different diameter to that of the bore through the carrier bar, and the external diameter of the sleeve varies along its length accordingly. [0020] In one form, the external diameter of the sleeve is sized to match the dynamometer bore along that portion of its length for which it is to pass through the dynamometer. [0021] In one form, the external diameter of the sleeve is sized to match the carrier bar bore along that portion of its length for which it is to pass through the carrier bar. [0022] In one form, the sleeve comprises a ratio of length to external diameter which is in excess of 5 to 1. [0023] In one form, the sleeve comprises a ratio of length to external diameter which is within the range of 7 to 1 and 15 to 1. [0024] In one form, the sleeve comprises a ratio of length to external diameter which is 10 to 1. [0025] According to a second aspect, there is provided a sleeve for a polished rod depending from a carrier structure of a pump jack, wherein in use, the sleeve is slidably disposed over the polished rod and between the polished rod and the carrier structure so as to prevent contact between the polished rod and carrier structure, the sleeve being of a nylon material. [0026] According to a further aspect, there is provided an apparatus for preventing circumferential scoring of a reciprocating polished rod suspended by a carrier structure of a pump jack, the carrier structure comprising one or more stacked components including a top end for suspending the polished rod, a bore extending through the stacked components and through which the polished rod extends, and a bottom end from which the polished rod extends, the apparatus comprising a cylindrical sleeve having top and bottom ends, the sleeve having an outer dimension adapted to fit within the bore of the carrier structure and having a bore through which the polished rod passes slidably and rotatably, and the apparatus being of such a length as to extend substantially between a bottom clamp for the polished rod, and either of a rod rotator or a top clamp for the polished rod. [0027] A detailed description of one or more embodiments of the invention is provided below along with accompanying figures that illustrate by way of example the principles of the invention. While the 4 invention is described in connection with such embodiments, it should be understood that the invention is not limited to any embodiment. On the contrary, the scope of the invention is limited only by the appended claims and the invention encompasses numerous alternatives, modifications and equivalents. For the purpose of example, numerous specific details are set forth in the following description in order to provide a thorough understanding of the present invention. [0028] The present invention may be practiced according to the claims without some or all of these specific details. For the purpose of clarity, technical material that is known in the technical fields related to the invention has not been described in detail so that the present invention is not unnecessarily obscured. BRIEF DESCRIPTION OF DRAWINGS [0029] Embodiments of the present invention will be discussed with reference to the accompanying drawings wherein: [0030] Figure 1 is a schematic view of a conventional pumpjack for reciprocating a sucker rod string of a downhole pump; and [0031] Figure 2 is a partial cross-sectional view of a carrier structure of the pumpjack of Figure 1, the carrier structure comprising an embodiment of a sleeve of the invention installed within the carrier structure. [0032] In the following description, like reference characters designate like or corresponding parts throughout the figures. DESCRIPTION OF EMBODIMENTS [0033] Referring now to Figure 1, there is shown a conventional pumpjack unit 1 for driving a reciprocating pump 2 located downhole in a bore of a subterranean oil well 3. The pumpjack unit 1 comprises a prime mover 40 (a motor) which drives through a transmission 50 which in turn drives a pair of cranks 60, carrying counterweights 70 to assist the motor 40 in lifting a heavy string of sucker rods 8 which extend down to the pump 2. The cranks 60 raise and lower one end of a walking beam 5 which is pivotally supported at P on an A-frame 80. The distal end of the walking beam 5 carries a curved metal box called a horse head 4.

5 [0034] Cables 6a, 6b roll tangentially over the horsehead 4 as it reciprocates. A carrier bar 7 is hung from the cables 6a, 6b. A string of sucker rods 8 is suspended from the carrier bar 7. The string of sucker rods 8 extends down production tubing 13 to drive the pump 2. [0035] A polished rod 9 is connected to the top of the rod string 8. The polished rod 9 extends upwardly through a stuffing box seal 10 and through a bore 7a (see Figure 2) in the carrier bar 7. The weight of the polished rod 9 is borne by rod clamps 11, which bear against the carrier bar 7. [0036] The seal 10 is located atop wellhead 12 at the ground's surface. When the polished rod 9 and rod string 8 are reciprocated up and down, fluids are pumped up the production tubing 13 to the wellhead 12 and out of a flow tee 14 located below the seal 10. [0037] As shown in Figure 2, a rod-rotator 15 (known in the art and so not fully detailed in the drawings) is shown in a typical location above the carrier bar 7. The polished rod 9 extends through the rod-rotator 15, which in turn is supported by the carrier bar 7. [0038] As stated above, the polished rod 9 is suspended from the carrier bar 7 by the rod clamps 11. Reciprocation of the cables 6a, 6b and carrier bar 7 causes the rod 9 to reciprocate up and down. The rod rotator, a levelling plate (not shown), and a dynamometer (dyno) carrier structure 16 may also be installed on the carrier bar 7 between the top polished rod clamp 11 and the carrier bar 7. [0039] All of the components 7, 15, 16 stacked between the polished rod clamps 11 are referred to herein and collectively as the carrier structure. Each component 7, 15, 16 of the carrier structure has a bore 7a, 15a, 16a for passing the polished rod 9 there through. The significance of the carrier structure is that, for example, neither the dyno carrier structure 16 nor the carrier bar 7 are clamped or centralized to the polished rod 9. Accordingly, relative movement can occur between the polished rod 9 and the individual components of the carrier structure. [0040] With reference to Figure 2, it can be seen that contact between the carrier bar 7, dynamometer 16 and the polished rod 9 is prevented by employing a protective sleeve 18 manufactured according to the invention. [0041] The sleeve 18 is manufactured from Ertalon LFX blue nylon. Ertalon LFX is an internally lubricated cast nylon specifically developed for unlubricated moving parts. It provides high mechanical strength, good fatigue resistance, high mechanical damping ability, good sliding properties and excellent wear resistance.

6 [0042] The sleeve 18 is generally cylindrical, and comprises a lengthwise extending through bore 20 having a diameter adapted to slidably fit over the polished rod 9, and a stepped outer diameter having diameters 20a and 20b which are adapted to slidably fit the bores 7a and 16a respectively of each of the carrier bar 7 and dynamometer 16 of the carrier structure. [0043] When the polished rod 9 is installed through the bore 20 of the sleeve 18, the polished rod 9 cannot come into contact with any part of the carrier bar 7 or dynamometer 16, particularly an edge of the carrier bar 7, and thus prevents circumferential scoring of the polished rod 9 when it is rotated by the rod rotator 15. [0044] It can be seen then that the present invention maintains the polished rod of a pumpjack in a good, fatigue-resistant condition. This significantly reduces the failure rate of polished rods, thus avoiding the high turnaround cost and associated potential for the release of well fluid which is associated with polished rod failure. [0045] Throughout the specification and the claims that follow, unless the context requires otherwise, the words "comprise" and "include" and variations such as "comprising" and "including" will be understood to imply the inclusion of a stated integer or group of integers, but not the exclusion of any other integer or group of integers. [0046] The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement of any form of suggestion that such prior art forms part of the common general knowledge. [0047] It will be appreciated by those skilled in the art that the invention is not restricted in its use to the particular application described. Neither is the present invention restricted in its preferred embodiment with regard to the particular elements and/or features described or depicted herein. It will be appreciated that the invention is not limited to the embodiment or embodiments disclosed, but is capable of numerous rearrangements, modifications and substitutions without departing from the scope of the invention as set forth and defined by the following claims.

Claims (15)

1. A sleeve for a polished rod depending from a carrier structure of a pump jack, wherein in use, the sleeve is slidably disposed over the polished rod and between the polished rod and the carrier structure so as to prevent contact between the polished rod and carrier structure, the sleeve being of such a length as to extend substantially between a bottom clamp for the polished rod, and either of a rod rotator or a top clamp for the polished rod.

2. The sleeve of claim 1, wherein the sleeve is of such a length as to extend above and below the carrier structure.

3. The sleeve of claim 1, wherein the carrier structure comprises a carrier bar, and the sleeve is of such a length as to extend above and below the carrier bar.

4. The sleeve of claim 3, wherein the carrier structure further comprises a dynamometer which is supported on the carrier bar, and the sleeve is of such a length as to extend through both the dynamometer and the carrier bar.

5. The sleeve as in any one of the preceding claims, wherein the sleeve is made of a nylon material.

6. The sleeve as in any one of the preceding claims, wherein the sleeve is made of Ertalon LFX blue nylon.

7. The sleeve as in any one of the preceding claims, wherein the sleeve comprises a bore through which the polished rod passes, and an external diameter adapted to fit within a bore of the carrier structure.

8. The sleeve of claim 7, wherein the external diameter of the sleeve varies along its length.

9. The sleeve of claim 8, wherein the dynamometer comprises a bore which is of a different diameter to that of the carrier bar bore, and the external diameter of the sleeve varies along its length accordingly.

10. The sleeve of claim 9, wherein the external diameter of the sleeve is sized to fit in the dynamometer bore along that portion of its length for which it is to pass through the dynamometer.

11. The sleeve of claim 9, wherein the external diameter of the sleeve is sized to fit in the carrier bar bore along that portion of its length for which it is to pass through the carrier bar. 8

12. The sleeve as in any one of the preceding claims, wherein the sleeve comprises a ratio of length to external diameter which is in excess of 5 to 1.

13. The sleeve of claim 12, wherein the sleeve comprises a ratio of length to external diameter which is within the range of 7 to 1 and 15 to 1.

14. The sleeve as in either of claims 12 or 13, wherein the sleeve comprises a ratio of length to external diameter which is 10 to 1.

15. A sleeve for a polished rod depending from a carrier structure of a pump jack, wherein in use, the sleeve is slidably disposed over the polished rod and between the polished rod and the carrier structure so as to prevent contact between the polished rod and carrier structure, the sleeve being of a nylon material.