Sucker Rod Coupling and Method of Wear Prevention in Driven Rotation of a Sucker Rod String in Production Tubing

Abstract

A sucker rod coupling features a coupler unit having internally threaded coupling sections at opposite ends for engaging sucker rod pins and one or two outer members extending about the coupler unit between the ends, each outer member being rotatable about the coupler unit and presenting contact surfaces facing outwardly at positions radially outward therefrom. Each outer member is positioned between a respective end of the coupler and a stop defining feature thereof, and a respective stop element is selectively deployable adjacent the respective end of the coupler on a side of the outer member opposite the stop-defining feature. The outer member prevents wear to the production tubing and the sucker rod string, is easily replaceable through manipulation of the stop element to allow sliding of the member off the unit and sliding of a new member thereon, and directly engages the sucker rods without needing additional threaded components.

Description

FIELD OF THE INVENTION

The present invention relates generally to a coupling arrangement for interconnecting adjacent sucker rods in a string of sucker rods and preventing wear of production tubing under driven rotation of the sucker rod string within a well bore.

BACKGROUND OF THE INVENTION

In pumping of fluids from a wellbore for production to the surface, a string of sucker rods connected end to end is used as a mechanical link between drive equipment at the surface and a downhole pump in the wellbore for driven operation thereof. Sucker rods are each externally threaded at pin ends of the rod and are conventionally interconnected by internally threaded box couplings each threadingly receiving ends of adjacent rods in the string. The present application is particularly concerned with wells using rotationally driven downhole pumps, where the sucker rod string is rotated to provide the rotational, not reciprocal, input required to operate this type of pump. A common problem in such installations is that the sucker rod string does not extend entirely linearly in the wellbore, and accordingly box couplings between the rods, which are of larger outer diameter than the rods themselves and thus form the radially outermost extents of the string, will tend to bump or rub against the production tubing wall during the driven rotation of the rod string and thus cause significant wear to the production tubing. Accordingly, some solutions for preventing or limiting this wearing of the production tubing have been previously proposed to avoid the need for costly repair or replacement of damaged tubing.

One prior art solution has been to bond elastomeric materials to the hard outer surfaces of sucker rod couplers to reduce wear to the tubing, which is more difficult and costly to replace than a coupler. However, the coating may quickly wear away, requiring frequent replacement or recoating of sucker rod couplers.

U.S. Pat. No. 4,757,861 and 4,919,202 each teach a cylindrical shaft-like body that has a vaned cylindrical wheel of elastomeric material disposed and freely rotatable thereabout. The ends of the body are externally threaded in order to each engage a box coupling receiving a sucker rod therein from the opposite end thereof. The wheel is of greater outer diameter than the box couplers and accordingly forms the only contact between the rod string and the production tubing or well casing, and due to the relative rotation allowed between the wheel and the central body, moves very slowly, if at all, under the driven rotation of the rod string. This lack of significant rotation and the use of elastomeric material minimizes wear to the production tubing or well casing.

However, these two prior art solutions each rely on a three-piece assembly to achieve both the wear prevention and rod coupling functions. In other words, the wear prevention structure needs is installed between adjacent sucker rods using a pair of box couplings. Installation thus requires threading of a box coupling on a sucker rod above the wear preventing structure, threading of the cylindrical body of the wear prevention structure to that box coupling, threading of a second box coupling onto the opposite end of the cylindrical body, and threading of the second box coupling onto the next sucker rod. It would be desirable to provide a sucker rod coupling and wear prevention arrangement that is easier to install in a sucker rod string.

In view of the forgoing and other shortcomings of the prior art, there is a desire for improvement in coupling of sucker rods and wear prevention in driven rotation of sucker rod strings in wellbores.

SUMMARY OF THE INVENTION

According to a first aspect of the invention there is provided a sucker rod coupling comprising:

a coupler unit defined by a unitary body structure having a central longitudinal axis passing therethrough and comprising first and second coupling sections defining opposite first and second ends of the coupler unit, each coupling section having internal box threading for selective threaded engagement with a respective sucker rod at an externally threaded pin end thereof; and

one or two outer members extending about the coupler unit between the first and second ends thereof, each outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis;

each outer member being disposed between a respective one of the first and second ends of the coupler unit and a respective stop-defining feature of the unitary body that projects radially outward further from the longitudinal axis than a portion of the coupler unit around which the outer member extends without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop-defining feature along the longitudinal axis; and

a respective stop element corresponding to each outer member and being selectively deployable adjacent the respective one of the first and second ends of the coupler unit on a side of the outer member opposite the stop-defining feature to project radially outward from an outer surfaces of the coupling section without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the deployed stop element, the outer member being slidable off the respective end of the coupler unit when the stop element is not deployed.

Preferably each outer member extends around the coupler unit at a respective one of the coupling sections at a position past which the internal box threading reaches along the longitudinal axis away from the respective end of the coupler unit.

Preferably each respective stop element comprises a ring releasably engagable around the coupler body adjacent the respective end of the coupler unit.

Preferably each ring is a snap ring engagable into a respective groove in the outer surface of the coupling section defining the respective end of the coupler unit.

The internal box threading of both coupling sections may be disposed within a common internal passage extending fully through the coupler unit along the longitudinal axis. A single internal thread in the common internal passage may define the box threading of both coupling sections. Is this right?

Each outer member may be defined by an outer race of a bearing assembly, the outer face closing fully about the coupler. Each bearing assembly may further comprise an inner race closing about the coupler, whereby the inner and outer races and roller elements therebetween are movable together along the longitudinal axis for selective removal of the bearing assembly from the coupler.

In use, the sucker rod coupling is coupled between adjacent sucker rods in a sucker rod string to form a section thereof, the adjacent sucker rods comprising upper and lower rods engaged to upper and lower ones of the coupling sections of the coupling unit and the sucker rod string being driven for rotation within production tubing in a wellbore, whereby contact of the contact surfaces of the outer member of the sucker rod coupling with an inner wall surface of the production tubing under driven rotation of the sucker rod string cooperates with allowed relative rotation between the outer member and the coupler to avoid direct contact between the production tubing and the rotating sucker rod string to prevent or limit wear to either thereof.

In one embodiment, there is only one outer member and only one respective stop element deployable adjacent a bottom end of the coupler unit, an upper one of the coupling sections having a larger outer diameter than a lower one of the coupling sections around which the outer member is positioned and a step in diameter between the coupling sections forming the stop-defining feature. Preferably the larger outer diameter of the upper coupling section of the coupler unit is equal to an outer diameter of a portion of the respective sucker rod to which the coupler unit is to be coupled. Preferably the larger diameter of the upper coupling section of the coupler unit is equal to the outer diameter of a pin connection shoulder of the respective sucker rod.

In another embodiment, the at least one outer member comprises separate first and second outer members spaced apart along the longitudinal axis and disposed adjacent the first and second ends of the coupler unit respectively. The coupler with two outer members preferably comprises a wrench engagable section defined between the first and second coupling sections, and the wrench engagable section preferably comprises opposing planar surfaces on opposite sides of the longitudinal axis.

According to a second aspect of the invention there is provided a method of operating and retrieving a sucker rod string within production tubing in a well bore, the method comprising:

providing a sucker rod coupling that is in accordance with the first aspect of the invention and has only one outer member and only one respective stop element deployable adjacent a bottom end of the coupler unit, an upper one of the coupling sections having a larger outer diameter than a lower one of the coupling sections around which the outer member is positioned and a step in diameter between the coupling sections forming the stop-defining feature, and the larger outer diameter of the upper coupling section of the coupler unit being equal to an outer diameter of a portion of the respective sucker rod to which the coupler unit is to be coupled;

installing the sucker rod coupling between the respective sucker rods by engaging the first and second coupling sections of the coupler unit to the respective sucker rods to form part of the sucker rod string from the coupler unit and the respective sucker rods engaged therewith;

driving rotation of the sucker rod string within the production tubing;

during driven rotation of the sucker rod string, using contact between the contact surfaces of each outer member of the sucker rod coupling and an inner wall surface of the production tubing to prevent contact of the production tubing with the rotating sucker rods and the coupler unit rotating therewith; and

after failure of the part of the sucker rod string at an upper one of the respective sucker rods between which the sucker rod coupling is installed, retrieving the sucker rod coupling and sucker rods therebelow by using the upper coupling section thereof of the coupling unit as a fish neck to grip the upper coupling section with a fishing tool dimensionally compatible with a sucker rod size of the sucker rod string.

According to a third aspect of the invention there is provided a sucker rod coupling comprising:

a coupler unit extending having a central longitudinal axis passing therethrough and comprising first and second coupling sections defining opposite first and second ends of the coupler unit, each coupling section being configured for selective attachment to a respective sucker rod; and

at least one outer member extending about the coupler unit between the first and second ends thereof, each outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis.

The at least one outer member may comprise first and second outer members spaced apart along the longitudinal axis and disposed adjacent the first and second ends of the coupler unit respectively, in which case first and second internal passages may extend into the first and second coupling sections from the first and second ends of the coupler unit respectively to engagingly receive ends of the respective sucker rods, the first and second outer members extending about the coupler unit at positions along the first and second internal passages respectively,

Preferably each internal passage is threaded for selective threaded engagement with a matingly threaded end of the respective sucker rod.

Preferably there are provided stops defined at ends of the first and second coupling sections opposite the first and second ends of the coupler unit and projecting radially outward from outer surfaces of the coupling sections where the outer members extend thereabout to limit sliding of the outer members toward one another along the longitudinal axis.

Preferably there are provided stop elements selectively deployable at positions between the first and second outer members and the first and second ends of the coupler unit to project radially outward from the outer surfaces of the coupling sections where the outer members extend thereabout to limit sliding of the outer members away from one another, the outer members being slidable off the ends of the coupler unit when the stop elements are not deployed.

According to a fourth aspect of the invention there is provided a method for preventing wear under driven rotation of a sucker rod string within production tubing in a well bore, the method comprising:

providing a sucker rod coupling comprising a coupler unit extending along a central longitudinal axis passing therethrough and comprising first and second coupling sections defining opposite first and second ends of the coupler unit, each coupling section being configured for selective attachment to a respective sucker rod; and at least one outer member extending about the coupler unit between the first and second ends thereof, each outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis;

installing the sucker rod coupling between the respective sucker rods by engaging the first and second coupling sections of the coupler unit to the respective sucker rods to form part of the sucker rod string from the coupler unit and the respective sucker rods engaged therewith; and

driving rotation of the sucker rod string within the production tubing;

during driven rotation of the sucker rod string, using contact between the contact surfaces of each outer member of the sucker rod coupling and an inner wall surface of the production tubing to prevent contact of the production tubing with the rotating sucker rods and the coupler unit rotating therewith.

Preferably the sucker rod coupling comprises a wrench engagable section defined between the first and second coupling sections at a position spaced from each outer member along the longitudinal axis and each coupling section of the coupler unit is threaded for engagement with a matingly threaded end of the respective sucker rod, the method comprising using a wrench to rotate the coupler unit about the longitudinal axis at the wrench engagable section to loosen or tighten threaded connection of the coupler unit within the rod string.

The wrench engagable section of the coupler unit may comprise opposing planar surfaces on opposite sides of the longitudinal axis. Alternatively, the wrench-engagable section may be circular in cross-section and engagable by a pipe wrench to effect rotation of the coupler unit.

BRIEF DESCRIPTION OF THE DRAWINGS

In the accompanying drawings, which illustrate exemplary embodiments of the present invention:

FIG. 1 is a side elevational view of a central body of a sucker rod coupling according to a first embodiment of the present invention.

FIG. 2 is an overhead plan view of the central body of the sucker rod coupling of FIG. 1.

FIG. 3 is a schematic illustration of the sucker rod coupling of FIG. 1 in use within a wellbore to couple together sucker rods in a string and prevent wear to the production tubing in which the sucker rods are used.

FIG. 4 is a perspective view of the central body of the sucker rod coupling of FIG. 1.

FIG. 5 is a perspective view of a sucker rod coupling according to a second embodiment of the present invention.

FIG. 6 is an exploded side elevational view of the sucker rod coupling of FIG. 5.

FIG. 7 is a schematic illustration of the sucker rod coupling of FIG. 5 in use within a wellbore to couple together sucker rods in a string and prevent wear to the production tubing in which the sucker rods are used.

DETAILED DESCRIPTION

FIG. 1 shows a central coupler unit 10 of a sucker rod coupling of a first embodiment of the present invention. The coupler unit 10 is defined by a single integral unitary body of solid material having an elongated shape oriented to lie lengthwise on a longitudinal axis 12 passing centrally therethrough. Along its length, the body 10 features a first coupling section 14 defining a planar first end 16 of the body, a second coupling section 18 defining an opposite planar second end 20 of the body and a middle wrench section 22 interconnecting the coupling sections along the longitudinal axis 12. Each coupling section 14, 18 features a cylindrical portion of the body that has been hollowed by formation of a bore 24 extending into the body from the respective planar end face of the body defined by that cylindrical portion in order to form an internal passage in the coupling section into which the end of a sucker rod can be inserted. The bore 24 has a circular cross section concentric with the circular cross section of the cylindrical portion into which it extends and, as shown in the partially sectioned illustration of FIG. 3, is threaded according to the thread pattern of an externally threaded male or pin end 26a of a conventional sucker rod 26 to facilitate threaded engagement of the sucker rod end 26a into the internally threaded female or box end section of the coupler body 10.

At a distance along the longitudinal axis 12 from each end face 16, 20 of the coupler body 10, the outer diameter of the coupling section 14, 18 increases by a single step to form a larger cylindrical portion 28 concentric and end-to-end with the smaller cylindrical portion 30 defining the respective end face 16, 20 of the coupler body 10. A shoulder formed at this change in diameter of each coupling section 14, 18 defines a ledge in the form of an annular stop face or surface 32 projecting radially outward from the smaller diameter portion 30 of the coupling section in a plane normal to the longitudinal axis 12. A circumferential groove 34 in the outer peripheral surface of the smaller diameter portion 30 of each coupling section 14, 18 extends fully therearound about the longitudinal axis at a location therealong a short distance inward from the respective end face 16, 20 of the coupler body 10.

With reference to FIG. 3, the final structure of the sucker rod coupling of the first illustrated embodiment is completed by installation of a bearing 36 and snap ring 37 on each coupler section 14, 18 of the coupler body 10. Each bearing 36 is of a conventional structure having an inner race member 38, an outer race member 40 and a plurality of rolling elements 42 disposed therebetween. Each bearing 36 is disposed about the smaller diameter portion 30 of the respective coupler section 14, 18 so that the annular or hollow cylindrical inner race member 38 is frictionally engaged with the outer peripheral surface of the coupling section at this small diameter portion thereof, and the annular or hollow cylindrical outer race member 40 is accordingly rotatable relative to the fixed-together inner race member and coupler body 10 about the longitudinal axis 12 due to the roller elements 42 between the races. The first illustrated embodiment features needle bearings having elongated cylindrical roller elements, but it will be appreciated that other known rolling element bearing types may alternatively be used to allow relative rotation between the outer race member and the coupler body 10. Furthermore, other embodiments may lack an inner race member engaged to the coupler body 10, and instead may have roller elements disposed directly between an outer race member and the coupler body 10, relying on outer surfaces of the coupler body to define the inner race of the bearing assembly.

The larger diameter portion 28 of each coupler section 14, 18 of the coupler body 10 locates the respective bearing 36 along the longitudinal axis 12 under sliding of the bearing 36 onto the coupler body 10 from the respective end 16, 20 thereof during assembly of the sucker rod coupling, this large diameter portion 28 acting as a stop to limit movement of the bearings toward each other and toward the middle wrench portion 22 of the coupler body 10 when the end face of the bearing reaches the ledge or stop surface 32 at the juncture of the small and large diameter portions of the respective coupling section of the coupler body 10. The snap ring of each coupling sections 14, 18 is then engaged into the groove 34 on the side of the respective bearing 36 opposite the large diameter stop-defining portion 28 of the coupling section 14, 18 to complete the positioning of the bearing 36 along the longitudinal axis 12 by blocking movement of the bearing 36 away from the middle section and the opposite bearing to the respective end 16, 20 of the coupler body 10. The snap rings 37 thus provide removable stop elements that can be installed and removed as needed to allow for possible removable of the bearings 36 if required, the installation of the snap ring 37 forming a stop deployed on the coupler body 10 to project radially outward from the outer peripheral surface of the smaller diameter portion 30 of the respective coupling section 14, 18 to block sliding movement of the installed bearing 36 past it along the longitudinal axis. It will be appreciated that other selectively deployable stop elements may be used in place of snap rings to position the bearings when deployed and allow removal of the bearings when not deployed. For example, the end of the coupling body could be externally threaded for engagement with an internally threaded nut or stop ring to allow installation and removal of the nut on the side of the bearing opposite the fixed or permanent larger diameter stop-defining portion 28 of the respective coupling section. However, the snap ring has the advantage that it will maintain it position along the longitudinal axis regardless of any inadvertent rotation thereof since the axial position of the snap ring is locked by its positive positioning within the groove. Also, use of an internally threaded nut or stop would require that such piece be sufficiently small so as not to project further from the coupling unit that the bearing to ensure that only the bearing contacts the production tubing surrounding the coupling.

FIG. 3 shows the sucker rod coupling in use within the bore 100 of a well. The threaded internal passage 24 of the first coupling section 14 has been engaged with the externally threaded pin end 26a at the bottom of a sucker rod 26 disposed above the coupling in the well bore 100, and the threaded internal passage of the second coupling section 18 has likewise been engaged with the externally threaded pin end at the top of a sucker rod disposed below the coupling in the well bore 100 so that the coupling body 10 acts to couple the two sucker rods together and accordingly forms part of the overall sucker rod string that is driven for rotation to operate a downhole pump. The bearings 36 of the coupling extend outwardly beyond any and all portions of the coupler body 10 in radial planes normal to the longitudinal axis 12 thereof. The outer peripheral surfaces of the outer race members of the bearings 36 facing outwardly away from the coupler body relative to the longitudinal axis 12 accordingly define the radially outermost extents of the coupling, and therefore define cylindrical contact surfaces that will contact the surrounding cylindrical inner wall surface of the production tubing 102 before any portion of the two sucker rods and the coupler body therebetween is allowed to reach the production tubing 102 under movement of this rod string portion out of alignment with a central axis of the section of the production tubing string 102. With frictional contact between the outer race of one of the bearings and the surrounding tubing wall 102 closing thereabout, the outer race is stationary with respect to rotation about the longitudinal axis while the inner race, and the coupler body 10 on which it is fixed, are rotated about the longitudinal axis 12 by the driven rotation of the sucker rods. Accordingly, there is no relative movement between the bearing contact surfaces that make contact with the production tubing, and so wear of the tubing that would otherwise occur under contact of any part of the spinning rod string with the production tubing is avoided. If the outer race of the bearing does rotate somewhat under the driven rotation of the string, it will be at significantly reduced speed compared to that of the string, and so the degree of wear is still reduced from what would occur without use of the coupling.

In the first illustrated embodiment, the middle wrench section 22 of the coupler body 10 is concentric with the coupling sections and is square in cross-section with a corner-to-corner diameter less than the circular diameter of both the small and large diameter portions of the equally dimensioned coupling sections. This square wrench section provided two pairs 22a, 22b of parallel, planar opposing faces across the longitudinal axis 12, each pair of opposing faces thus defining wrench flats by which the wrench section can be engaged by opposing jaws of a wrench in order to rotate the coupler body 10 about its central axis 12 to effect tightening and loosening in threaded coupling and decoupling of the coupler body 10 with a sucker rod. It will be appreciated that other non-square cross-sections may be used in the wrench section of the coupling body while still presenting at least one pair of opposing planar surfaces or wrench flats. Alternatively, a circular or other curved peripheral shape may be used in the cross-section of the middle part of the coupler body, and still be engagable by a pipe wrench to effect rotation of the coupler body relative to a sucker rod in coupling or decoupling therefrom.

The coupler body is preferably a single integral unitary body of steel, for example 4140 HTSR steel machined to shape the different sections, but those of skill in the art will recognize alternate materials and production methods that may be used to form the coupler body having the different sections described. For example, a coupler body formed by multiple pieces rigidly fixed together during production of the coupling could similarly form a one-piece coupler unit for direct connection between sucker rods without additional coupling pieces separate from the coupler unit. Timken B-2420 and B-2824 are examples of bearings that may be used, and suitable dimensioning of stops and bearing-carrying portions of the coupler body for cooperation with such bearings is within the ambit of those skilled in the art. These differently sized exemplary bearings having different outer diameters illustrate how sucker rod couplings of the present invention may be produced in different sizes to better fit differently sized production tubing. The size of the bearing is selected to have an outer diameter less than the inner diameter of the production tubing, thereby leaving space between the bearing and the tubing wall through which the fluid being produced by operation of the downhole pump can pass, even when part of the bearing's outer surface is in contact with the tubing wall. Other bearings may be used, or sleeves or wheels of metal, plastic or other materials may be fitted about the coupler body using an interface other than rollers elements but of low enough friction between the sleeve and body to allow relative rotational motion therebetween about the longitudinal axis. The use of any such rotatable outer member disposed about a central body that not only forms the spinning core or shaft carrying the outer member but also forms coupling sections for direct connection to sucker rods without requiring separate additional couplers between the body and the sucker rods presents advantage over prior art arrangements requiring fastening together of multiple separate pieces to achieve both a wear preventing function and coupling of adjacent sucker rods.

Accordingly, embodiments using only one outer member rotatable relative to the central coupling body would still provide such advantage over the prior art, just as embodiments lacking a specific section for engagement by a wrench would share this advantage. The first illustrated embodiment provides further benefit by using two outer members at spaced positions along the central body to better resist deviation of the body's axis sufficiently out of line with the well bore axis to, and even further benefit by providing a central wrench engagable portion disposed between, and thus left uncovered and unobstructed by, the two outer members.

FIGS. 5 and 6 show a second embodiment sucker rod coupler that uses a single plastic sleeve to provide the contact area of the coupler with the production tubing instead of the two bearings of the first embodiment.

Carrying only a single sleeve, the coupler unit of this embodiment is significantly smaller than that of the first embodiment and has a simpler overall structure, meaning that the coupler may be produced at a lower cost and marketed as a more cost efficient option than the first embodiment.

With reference to the exploded view of the coupling in FIG. 6, the coupler unit 10′ of the second embodiment is again defined by a single integral unitary body of rigid material having an elongated shape oriented to lie lengthwise on a longitudinal axis 12′ passing centrally therethrough. Along its length, the body 10′ features a first coupling section 14′ defining a planar first end 16′ of the body and a second coupling section 18′ defining an opposite planar second end 20′ of the body. The second embodiment lacks the wrench section of the first embodiment. Each coupling section 14′, 18′ features a respective cylindrical portion of the body that has been hollowed by formation of a single bore 24′ extending fully through the body from the on planar end face thereof to the other to form a single internal passage into each end of which the pin end of a sucker rod can be received. The bore 24′ has a circular cross section concentric with the circular cross section of the cylindrical body portions through which it passes and, as shown in broken lines in FIG. 6, is threaded according to the thread pattern of an externally threaded male or pin end of a conventional sucker rod to facilitate threaded engagement of the pin ends of two sucker rods into the threaded internal passage from opposite ends of the coupler body 10′.

Still referring to FIG. 6, at a distance along the longitudinal axis 12′ from each end face 16′, 20′ of the coupler body 10′, the outer diameter of the coupling section 14, 18 features a single step change, decreasing from the upper first coupling section 14′ to the lower second coupling section 18′. A shoulder formed at this change in diameter of between the two coupling sections 14′, 18′ defines a ledge in the form of an annular stop face or surface 32′ projecting radially outward from the smaller diameter lower coupling section 18′ in a plane normal to the longitudinal axis 12′. A circumferential groove 34′ in the outer peripheral surface of the smaller diameter lower coupling section 18′ extends fully therearound about the longitudinal axis at a location therealong a short distance inward from the bottom end face 20′ of the coupler body 10′.

With reference to FIG. 5, the final structure of the sucker rod coupling of the second illustrated embodiment is completed by installation of a sleeve 36′ and snap ring 37′ on the lower coupler section 18′ of the coupler body 10′. The plastic sleeve 36′ has a cylindrical outer surface closing around the longitudinal axis 12′ and a cylindrical inner bore centered thereon. The sleeve 36′ is disposed about the smaller diameter lower coupling section 18′ with the bore diameter of the sleeve 36′ slightly exceeding the outer diameter of the lower coupling section 18′ so that the sleeve 36′ is accordingly rotatable relative to the coupler body 10′ about the longitudinal axis 12′.

The larger diameter upper coupler section 14′ of the coupler body 10′ locates the sleeve 36′ along the longitudinal axis 12′ under sliding of the sleeve 36′ onto the coupler body 10′ from the bottom end 20′ thereof during assembly of the sucker rod coupling, this large diameter coupling section 14′ acting as a stop to limit movement of the sleeve toward the top end 16′ of the coupler body 10′ when the end face of the bearing reaches the ledge or stop surface 32′ at the juncture between the coupling sections 14′, 18′. The snap ring 37′ is then engaged into the groove 34′ on the side of the sleeve 36′ opposite the large diameter stop-defining upper coupling section 14′ to complete the positioning of the sleeve 36′ along the longitudinal axis 12′ by blocking movement of the sleeve 36′ away from the upper coupling section 14′ to the bottom end 20′ of the coupler body 10. The snap ring 37′ thus provides a removable stop element that can be installed and removed as needed to allow for possible removable of the sleeve 36′ by sliding off the bottom end of the coupling unit if required, the installation of the snap ring 37′ forming a stop deployed on the coupler body 10 to project radially outward from the outer peripheral surface of the smaller diameter lower coupling section 18′ to block sliding movement of the installed sleeve 36′ past it along the longitudinal axis.

FIG. 7 shows the sucker rod coupling in use within the bore of a well. The threaded internal passage 24′ of the coupling unit 10′ has been engaged at its top end with the externally threaded pin end 126a at the bottom of a sucker rod 126 disposed above the coupling in the well bore 100, and at its bottom end with the externally threaded pin end at the top of a sucker rod disposed below the coupling in the well bore 100 so that the coupling body 10 acts to couple the two sucker rods together and accordingly forms part of the overall sucker rod string that is driven for rotation to operate a downhole pump. The sleeve 36′ of the coupling extends outwardly beyond any and all portions of the coupler body 10′ in radial planes normal to the longitudinal axis 12′ thereof. The outer peripheral surfaces of the outer sleeve 36′ facing outwardly away from the coupler body relative to the longitudinal axis 12′ accordingly define the radially outermost extents of the coupling, and therefore define cylindrical contact surfaces that will contact the surrounding cylindrical inner wall surface of the production tubing 102 before any portion of the two sucker rods and the coupler body therebetween is allowed to reach the production tubing 102 under movement of this rod string portion out of alignment with a central axis of the section of the production tubing string 102. With frictional contact between the sleeve and the surrounding tubing wall 102 closing thereabout, the sleeve is stationary with respect to rotation about the longitudinal axis while the coupler body 10′ is rotated about the longitudinal axis 12′ by the driven rotation of the sucker rods. Accordingly, there is no relative movement between the sleeve contact surfaces that make contact with the production tubing, and so wear of the tubing that would otherwise occur under contact of any part of the spinning rod string with the production tubing is avoided. If the sleeve does rotate somewhat under the driven rotation of the string, it will be at significantly reduced speed compared to that of the string, and so the degree of wear is still reduced from what would occur without use of the coupling.

The second embodiment coupler thus operates similar to the first embodiment and shares the same advantage of direct coupling to the sucker rods it connects in order to avoid use of box connection pieces separate from the single body piece around which the outer member (whether a bearing or sleeve) rotates. The two illustrated embodiments also share the advantage that each such outer member is selectively removable from the coupler unit for replacement, by disengagement of the snap ring from the groove adjacent the end of the coupler unit to allow sliding of the outer member off that end of the unit. Both embodiments make use of the lower coupling section to not only provide the threaded coupling to the respective sucker rod, but also to provide a bearing or sleeve carrying portion of the coupler, with the first embodiment likewise having such dual functionality of the upper coupling section. This dual functionality provides material savings in reducing that size of the overall coupler, thus saving on production cost.

With reference to FIG. 7, the second embodiment provides further advantage by having the outer diameter of the upper coupling section 14′ equal to the outer diameter of the pin shoulder 126b of the sucker rods 126 in the string. This way, should there be a failure at the pin connection 126a of the sucker rod 126 above the coupler to the coupler unit 10′, a conventional overshot fishing tool suitably dimensioned for compatibility in drawing out the size of sucker rod used in the string by its pin shoulder 126b can be used to fish out the coupler and the sucker rods connected below it by gripping the coupler unit 10′ at the outer peripheral surface of its upper coupling section 14′. This way, no new, different or specialized fishing tool is required to retrieve the remaining rod string portion stuck in the wellbore, as an existing sucker-rod fishing tool configured for the known sucker rod size can be employed in the conventional manner to grip the upper coupling section 14′ of the sucker rod coupler in the same manner as it would typically be used to grip the pin shoulder of one of the sucker rods. As shown in FIG. 7, the overall length of the coupler unit only slightly exceeds the combined length of the pins of the two sucker rods connected by it, which combines with the dual functionality of the lower coupling section 18′ to make efficient use of material in the smaller resulting coupling. The lower coupling section 18′ is just long enough to fit the axial length of the sleeve 36′ between the groove positioned at the bottom end of the coupler unit and the shoulder-like stop defined the joint of the two coupling sections 14′, 18′.

A prototype of the second embodiment coupler uses a roller-like piece of virgin ultra high molecular weight polyethylene (RecoTM UHMW-PE natural virgin from Redwood Plastics Corporation) to provide a sleeve having a high impact strength, high chemical and wear/abrasion resistance and low coefficient of friction, but it will be appreciated that sleeves of other materials may alternatively be employed. Likewise, although the illustrated sleeve 36′ features a continuously curved cylindrical outer surface, it will be appreciated that other sleeve shapes of non-circular cross section may be similarly employed to provide tubing contact surfaces radially outward from the rest of the coupler. For example, U.S. Pat. Nos. 4,757,861 and 4,919,202 show how a vaned wheel of elastomeric material or fluted and/or notched tubular sleeve of soft resilient abrasion resistant material may be used to contact the well tubing around a sucker rod string while providing significant open areas in the wheel or sleeve's cross section to ensure that fluid can flow past it. Such material and shape configurations may similarly be employed in the present invention in place of the illustrated second embodiment sleeve of substantially cylindrical shape (purely cylinder outer surface, except at short tapered end portions of the sleeve) or illustrated first embodiment bearing(s).

Since various modifications can be made in my invention as herein above described, and many apparently widely different embodiments of same made within the spirit and scope of the claims without department from such spirit and scope, it is intended that all matter contained in the accompanying specification shall be interpreted as illustrative only and not in a limiting sense.

Claims

1. A sucker rod coupling comprising:

a coupler unit defined by a unitary body structure having a central longitudinal axis passing therethrough and comprising first and second coupling sections defining opposite first and second ends of the coupler unit, each coupling section having internal box threading for selective threaded engagement with a respective sucker rod at an externally threaded pin end thereof; and

at least one outer member extending about the coupler unit between the first and second ends thereof, each outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis;

each outer member being disposed between a respective one of the first and second ends of the coupler unit and a respective stop-defining feature of on the unitary body that projects radially outward further from the longitudinal axis than a portion of the coupler unit around which the outer member extends without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop-defining feature along the longitudinal axis; and

a respective stop element corresponding to each outer adjacent the respective one of the first and second ends of the coupler unit on a side of the outer member opposite the stop-defining feature to project radially outward from an outer surfaces of the coupling section without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop element.

2. (canceled)

3. The sucker rod coupling according to claim 1 wherein each respective stop element comprises a ring releasably engagable around the coupler body adjacent the respective end of the coupler unit.

4. The sucker rod coupling according to claim 3 wherein each ring is a snap ring engagable into a respective groove in the outer surface of the coupling section defining the respective end of the coupler unit.

5. The sucker rod coupling according to claim 1 wherein an upper one of the coupling sections has a larger outer diameter than the portion of the coupler unit around which the outer member extends, and the stop defining feature is formed by a step in diameter between the upper coupling section and the portion of the coupler unit around which the outer member extends.

6. The sucker rod coupling according to claim 5 wherein the larger outer diameter of the upper coupling section of the coupler unit is equal to an outer diameter of a portion of the respective sucker rod to which the coupler unit is to be coupled to enable gripping the upper coupling section with a fishing tool dimensionally compatible with a sucker rod size of the sucker rod string.

7. The sucker rod coupling according to claim 6 wherein the larger diameter of the upper coupling section of the coupler unit is equal to the outer diameter of a pin connection shoulder of the respective sucker rod.

8. The sucker rod coupling according to claim 5 in combination with a sucker rod string, the sucker rod coupling being installed in the sucker rod string between adjacent sucker rods, the adjacent sucker rods comprising an upper rod engaged to the upper coupling section and a lower rod engaged to the lower coupling section.

9. The sucker rod coupling according to claim 1 wherein the internal box threading of both coupling sections is disposed within a common internal passage extending fully through the coupler unit along the longitudinal axis.

10. The sucker rod coupling according to claim 9 wherein a single internal thread in the common internal passage defines the box threading of both coupling sections.

11. The sucker rod coupling according to claim 1 wherein the at least one outer member comprises separate first and second outer members spaced apart along the longitudinal axis and disposed adjacent the first and second ends of the coupler unit respectively.

12. The sucker rod coupling according to claim 11 wherein the coupler comprises a wrench engagable section defined between the first and second coupling sections.

13. The sucker rod coupling according to claim 12 wherein the wrench engagable section comprises opposing planar surfaces on opposite sides of the longitudinal axis.

14. The sucker rod coupling according to claim 1 wherein each outer member is defined by an outer race of a bearing assembly, the outer face closing fully about the coupler and the bearing assembly further comprising an inner race closing about the coupler and roller elements between the inner and outer races.

15. (canceled)

16. The sucker rod coupling of claim 1 coupled between adjacent sucker rods in a sucker rod string to form a section thereof, the sucker rod string being driven for rotation within production tubing in a wellbore, whereby contact of the contact surfaces of the outer member of the sucker rod coupling with an inner wall surface of the production tubing under driven rotation of the sucker rod string cooperates with allowed relative rotation between the outer member and the coupler to avoid direct contact between the production tubing and the rotating sucker rod string to prevent or limit wear to either thereof.

17. A method of operating and retrieving a sucker rod string within production tubing in a well bore, the method comprising:

providing a sucker rod coupling comprising: a coupler unit defined by a unitary body structure having a central longitudinal axis passing therethrough and comprising upper and lower coupling sections defining opposite upper and lower ends of the coupler unit, each coupling section having internal box threading for selective threaded engagement with a respective sucker rod at an externally threaded pin end thereof; and an outer member extending about the coupler unit between the upper and lower ends thereof at a portion of the coupler unit of smaller diameter than the upper coupling section, the outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis;

installing the sucker rod coupling between the respective sucker rods by engaging the upper and lower coupling sections of the coupler unit to the respective sucker rods to form part of the sucker rod string from the coupler unit and the respective sucker rods engaged therewith, the upper coupling section of the coupler unit being equal in outer diameter to a portion of an upper one of the respective sucker rods to which the upper coupling section of the coupler unit is engaged;

driving rotation of the sucker rod string within the production tubing;

during driven rotation of the sucker rod string, using contact between the contact surfaces the outer member of the sucker rod coupling and an inner wall surface of the production tubing to prevent contact of the production tubing with the rotating sucker rods and the coupler unit rotating therewith; and

after failure of the part of the sucker rod string at the upper one of the respective sucker rods between which the sucker rod coupling is installed, retrieving the sucker rod coupling and sucker rods therebelow by using the upper coupling section of the coupling unit as a fish neck to grip the upper coupling section with a fishing tool dimensionally compatible with a sucker rod size of the sucker rod string.

18. The method according to claim 17 wherein the outer member of the sucker rod coupling is disposed between the lower end of the coupler unit and a respective stop-defining feature of the unitary body that projects radially outward further from the longitudinal axis than the portion of the coupler unit around which the outer member extends without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop-defining feature along the longitudinal axis, and there is provided a respective stop element adjacent the lower end of the coupler unit on a side of the outer member opposite the stop-defining feature to project radially outward from an outer surfaces of the lower coupling section without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the top element.

19. The method according to claim 17 wherein the upper coupling section of the coupler unit is equal in outer diameter to a pin connection shoulder of the upper one of the respective sucker rods.

20. The method according to claim 18 wherein the upper coupling section of the coupler unit is equal in outer diameter to a pin connection shoulder of the upper one of the respective sucker rods.

21. The sucker rod coupling according to claim 5 wherein there is only one outer member and only one respective stop element, which is adjacent a bottom end of the coupler unit.

22. A sucker rod coupling comprising:

a coupler unit defined by a unitary body structure having a central longitudinal axis passing therethrough and comprising first and second coupling sections defining opposite first and second ends of the coupler unit, each coupling section having internal box threading for selective threaded engagement with a respective sucker rod at an externally threaded pin end thereof; and

two outer members extending about the coupler unit between the first and second ends thereof, each outer member being rotatable about the central longitudinal axis relative to the coupler unit and presenting contact surfaces facing outwardly away from the coupler unit at positions radially outward therefrom relative to the central longitudinal axis;

each outer member being disposed between a respective one of the first and second ends of the coupler unit and a respective stop-defining feature of the unitary body that projects radially outward further from the longitudinal axis than a portion of the coupler unit around which the outer member extends without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop-defining feature along the longitudinal axis; and

a respective stop element corresponding to each outer member adjacent the respective one of the first and second ends of the coupler unit on a side of the outer member opposite the stop-defining feature to project radially outward from an outer surfaces of the coupling section without reaching past the contact surfaces of the outer member so as to block sliding of the outer member past the stop element;

wherein the unitary body of the coupler unit comprises a wrench engagable section defined at a position between the two outer members along the central longitudinal axis.