SUCKER ROD TERMINUS ASSEMBLY FOR UNDERGROUND WELLS

Abstract

A sucker rod terminus assembly is provided for use in downhole wells. The sucker rod terminus assembly includes a plurality of parallel composite strands forming an elongate rod and a metallic terminus fitting. The terminus fitting has a cavity with a proximal opening to receive the rod end. The cavity includes a plurality of frustum shaped chambers. Preferably, the frustum shaped chambers have different sizes or shapes wherein at least a frustum chamber's proximal end diameter, distal end diameter, or length is different than an adjacent frustum chamber's proximal end diameter, distal end diameter, or length. Even more preferably, each frustum chamber is diametrically larger than the frustum chamber positioned proximally to it. Preferably, the sucker rod assembly further includes a spreader plate, preferably made up of a plurality of pieces and a hardened material to affix the rod to the terminus fitting.

Claims

1. A sucker rod terminus assembly for underground wells comprising: a plurality of strands forming an elongate rod having first and second ends; a terminus fitting having a proximal end and a distal end and extending longitudinally to form a central axis, said terminus fitting having a central cavity coaxial to said terminus fitting's central axis, said central cavity extending to said terminus fitting's proximal end to form a proximal opening receiving said elongate rod within said cavity, said cavity including at least two frustum shaped chambers coaxially aligned with said cavity's central axis, wherein each of said frustum shaped chambers has a circular proximal end, a circular distal end, a length as measured from their proximal end to their distal end, and an axis coaxial to said central axis, said frustum shaped chambers distal ends having a diameter greater than the diameter of their proximal ends; and a hardened material within said cavity, said hardened material adhered to said strands and maintaining said strands in a splayed out condition in a widened orientation toward the terminus' distal end compared to where the strands pass through said terminus fitting's proximal opening so as to form an at least two frustum shaped plug which prevents said rod from withdrawing from said terminus fitting's proximal opening.

2. The sucker rod terminus assembly for underground wells of claim 1 wherein said at least two frustum shaped chambers include a first frustum shaped chamber and a second frustum shaped chamber, and the first and second frustum shaped chambers having different shapes wherein at least one of said first chamber's proximal end diameter, distal end diameter, or length is different than said second chamber's proximal end diameter, distal end diameter, or length.

3. The sucker rod terminus assembly for underground wells of claim 1 wherein said at least two frustum shaped chambers include a first frustum shaped chamber positioned proximally to a second frustum shaped chamber, and first frustum's proximal end diameter and distal end diameter are smaller that said length being different than the distal frustum's proximal end diameter, distal end diameter, or length.

4. The sucker rod terminus assembly for underground wells of claim 1 further comprising a first spreader plate positioned within said cavity, said first spreader plate having a plurality of holes receiving said plurality of strands so as to splay out said strands in a widened orientation toward the terminus' distal end compared to where the strands pass through said terminus fitting's proximal opening.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] FIG. 1 is an exploded perspective view of a sucker rod assembly;

[0033] FIG. 2 is a side cut-away view of a sucker rod terminus assembly;

[0034] FIG. 3 is an exploded cut-away view of a sucker rod terminus assembly;

[0035] FIG. 4 is a side cut-away view of a sucker rod terminus assembly illustrating a first cavity configuration;

[0036] FIG. 5 is a side cut-away view of a sucker rod terminus assembly illustrating a second cavity configuration;

[0037] FIG. 6 is a side cut-away view of a sucker rod terminus assembly illustrating a third cavity configuration;

[0038] FIG. 7 is a side cut-away view of a sucker rod terminus assembly illustrating injection of resin into the cavity;

[0039] FIG. 8 is an exploded perspective view of a spreader plate;

[0040] FIG. 9 is a perspective view of a spreader plate;

[0041] FIG. 10 is a top view of a first spreader plate;

[0042] FIG. 11 is a top view of a second spreader plate;

[0043] FIG. 12 is a top view of a third spreader plate;

[0044] FIG. 13 is a top view of a fourth spreader plate;

[0045] FIG. 14 is a side view of a sucker rod terminus assembly including wear guides;

[0046] FIG. 15 is a side cut-away view of a sucker rod terminus fitting and connector member;

[0047] FIG. 16 is a side cut-away view of a sucker rod terminus assembly;

[0048] FIG. 17 is a side cut-away view of an additional embodiment of a sucker rod terminus assembly;

[0049] FIG. 18 is a side cut-away view of a sucker rod terminus assembly; and

[0050] FIG. 19 is a side cut-away view of a sucker rod terminus fitting.

DETAILED DESCRIPTION OF THE INVENTION

[0051] While the present invention is susceptible of embodiment in various forms, as shown in the drawings, hereinafter will be described the presently preferred embodiments of the invention with the understanding that the present disclosure is to be considered as an exemplification of the invention, and it is not intended to limit the invention to the specific embodiments illustrated.

[0052] With reference to the figures, the sucker rod assembly 10 includes a plurality of strands 20 forming an elongate rod 15. The sucker rod assembly 10 further includes a terminus fitting 30 having a central cavity 33, a spreader plate 22, and preferably a connection member 45. A plurality of sucker rod assemblies are connected together to form a sucker rod string 11 to connect a vertical lift surface device to a downhole pump unit.

[0053] As illustrated in FIGS. 1-19, the sucker rod terminus assembly 10 includes a plurality of generally round strands 20 that are bundled together to form the elongate rod 15. The tensile strength and stiffness of the composite rod assembly 15 is determined by the composite materials used for the individual strands 20, the size of the strands 20, and the number of strands 20 bundled together to make the rod 15. In preferred embodiment, the carbon composite sucker rod strands 20 are manufactured by the pultrusion process or variation thereof wherein high strength fibers are drawn through a resin bath to impregnate the fibers and then through heated dies and ovens to shape, consolidate and cure the strands 20 into generally round rods or similar shapes such as hexagons or octagons. Carbon fiber is the preferred material for the plurality of parallel strands 20, but fiberglass or other high strength fibers may also be utilized so long as they are tailored to meet the strength and stiffness requirements for the sucker rod assembly application.

[0054] The polymer matrix within the strands 20 may be epoxy, polyester, vinyl ester, cyanurate ester, benzoxyzene, phenolic or other suitable thermosetting resins. Thermoplastic polymer matrices such as PEI, PEEK, PPS or other suitable polymers may also be used by modifying the pultrusion process to heat, consolidate and shape, and chill the polymer and fiber matrix into usable composite strands. The fiber fraction of the strands 20 should be optimized for tensile strength, stiffness, durability and handling. The ideal size of the strands 20 is roughly from .sup.th inch diameter to 3/16.sup.th inch diameter although other sizes may be used, and the ideal size may be dependent on processing and assembly requirements.

[0055] Generally, the smaller the diameter of the strands, the faster it can be pultruded because of faster resin curing. A thick pultruded cross section is slow to cure. Additionally, a larger number of strands can be pultruded at the same time when they have a small diameter versus a large diameter. The cross sectional area of typical sucker rods can be pultruded at roughly 10 times the through-put speed when they are made as a plurality of strands versus as a monolithic rod, as such this lowers production cost. Even with the additional steps to cut and bundle the strands, the overall production cost of a carbon fiber composite sucker rod made from a plurality of strands is generally lower than an equivalent monolithic version. However, it is also necessary for the strands to be large enough in cross section for ease of handling and to lay straight in the tooling used for assembly of the sucker rod. Thus, the plurality of the strands 20 that make up the rod 15 should be straight and equal in length in order to maximize the overall strength of the rod 15. Unlike prior manufacturing processes, it is preferred that the strands 20 not be tensioned during assembly as that would be time consuming and costly.

[0056] A minimum number of strands 20 are preferably bundled together to form a length of the elongate rod 15. As illustrated in FIG. 14, the bundle of strands 20 is preferably held together with composite wraps 50 spaced incrementally sufficient to hold the bundle of rods together, but allow them to flex between the wrap 50 if the rod experiences a compressive load. The spacing and the length of the incremental composite wraps 50 can be used to tailor the compressive stiffness of the overall carbon composite sucker rod 50. Spacing the composite wraps 50 and/or wear guides at approximately 10-30 times the bundle diameter is believed ideal to provide compressive dampening yet maintain the overall rod sufficiently stiff for handling. Even more preferably, the composite wraps 50 and/or wear guides (described below) are spaced at 15-25 times the bundle diameter, and the preferred distance between wraps or wear guides is approximately 20 times the bundle diameter.

[0057] The plurality of parallel strands 20 are preferably bundled in a generally polygonal or round package so the sucker rod assembly 10 can be progressively rotated in a well casing as typically done to prevent wear in one spot. It should be noted that the diameter of the carbon fiber sucker rod assembly 10 is significantly less than its equivalent steel counterpart. For example, the equivalent carbon fiber sucker rod assembly 10 replacing a 1 inch diameter steel sucker rod is just under 1 inch diameter.

[0058] The sucker rod assembly's terminus fittings 30 may be affixed at one or both ends of the sucker rod assembly 10. The terminus fittings 30 are preferably made of metal, and more preferably made of a high carbon steel. Other materials including carbon fiber may be employed. However, they are not preferred. Each terminus fitting 30 has a proximal end 31 and a distal end 32. A cavity 33 extends the length of the terminus fitting from its proximal end to its distal end so as to form a proximal opening 35 and a distal opening 36.

[0059] In embodiments illustrated in FIGS. 1-14, the terminus fitting's cavity 33 has a tapered construction so as to have a smaller diameter at its proximal opening 35 than toward its distal end to form a cavity that is conically shaped. In an embodiment illustrated in FIGS. 5 and 6, the central cavity has a conical section 37 towards the terminus fitting's proximal end 31 and a substantially cylindrical section 38 towards the terminus fitting's distal end 32. The cavity's proximal opening 35 is sized to receive one end of the elongate rod 15 and its individual strands 20. Preferably, the cavity's distal opening 36 includes a female thread 41 for affixing to a male threaded member 45.

[0060] To lock the strands 20 within the terminus fitting's cavity 33, the strands are splayed out so as to have a diameter at their distal ends greater than the terminus fitting's proximal opening 35. To maintain the strands 20 in a splayed out condition, the sucker rod assembly 10 preferably includes a spreader plate 22 positioned within the terminus fitting's cavity 33. The spreader plate is preferably planar and substantially round so as to define a central axis. In addition, the spreader plate 22 has a plurality of holes 23 for receiving the rod strands 20 so as to splay the strands in a widened orientation compared to where the strands enter the terminus fitting's proximal opening 35. To position the spreader plate within the terminus fitting's central cavity, the spreader plate has a diameter slightly smaller than the diameter fitting's cavity 33 where the spreader plate has been positioned within the cavity 33. Furthermore, preferably the spreader plate's central axis is coincident with the cavity's central axis. As would be understood by those skilled in the art, the diameter of a preferred spreader plate would be smaller when positioned within the cavity's conical section 37 than if the spreader plate 22 were positioned in the cavity's cylindrical section 38.

[0061] As illustrated in FIGS. 8-13, the preferred spreader plate 22 is constructed of two or more pieces 24 wherein the pieces can be arranged to adjoin one another to form a single spreader plate 22. Each of the spreader plate pieces 24 include an engagement edge 25 where it engages the engagement edge of an adjoining piece 24. Preferably these engagement edges 25 include indents 27 which align and adjoin indents formed in adjoining pieces to form holes 23 for receiving the rod strands 20. Moreover, the spreader plate pieces 24 also include a peripheral edge 26 where the pieces do not engage an adjoining spreader plate piece 24. It is preferred that these peripheral edges also include indents 27 sized for receiving a rod strand 20. As illustrated in FIGS. 2 and 3, strands within the peripheral edge indents are constrained by the terminus fitting's cavity sidewall. The peripheral edge indents 27 also maintain the strands 20 in a widened orientation compared to where the strands pass through the terminus fitting's proximal opening 35. The sucker rod assembly 10 may include any number of spreader plates so as to maintain the strands 20 properly aligned and positioned to prevent withdrawal of the elongate rod 15 from the terminus fitting 30. For example, FIG. 5 illustrates a sucker rod assembly 10 with two spreader plates 22.

[0062] In an alternative embodiment not illustrated in the figures, the sucker rod assembly includes a plurality of annular spacers wherein an annular spacer is applied over the ends of each of the strands to maintain the strands in a splayed configuration. For this embodiment, the annular spacers may be positioned longitudinally upon the strands at approximately the same location so that the periphery of each annular spacer engages the periphery of an adjoin spacer. Alternatively, the annular spacers may be longitudinally positioned at different locations so that the periphery of an annular spacer engages adjoining strands.

[0063] As illustrated in FIGS. 5 and 6, the terminus fitting's tapered cavity 33 may include a conical section 37 and a cylindrical section 38. If it is desirable to minimize the size of the terminus fitting 30, the cavity's conical section 37 can be shorter in length provided the overall cavity length is retained. More specifically, shortening the length of the conical section 37 while retaining the overall length of the cavity 33 enables one to maintain the wedge effect of affixing the rod 15 to the terminus fitting 30 and thus maintain the overall adhesive shear strength of the wedge 21 to the rod 15 when the size of the fitting is constrained. For example, FIG. 7 illustrates a terminus fitting where the conical portion 37 is shorter than the cylindrical portion 38. Conversely, FIG. 6 illustrates a terminus fitting where the conical portion 37 is longer than the conical portion illustrated in FIG. 5.

[0064] The terminus fitting's cavity 30 (as illustrated in FIG. 7) is preferably injected or filled with a polymer material that adheres to the strands 20 and forms a mechanical tapered wedge 21 within the terminus fitting 30. The polymer material for the wedge 21 can be epoxy, phenolic or other thermosetting resin meeting the performance requirements. For extremely deep wells, a heat resistant ceramic material may be used within the terminus cone. In contrast to traditional potted steel wire rope terminations where resin or molten metal is poured into the open end of the terminus, the preferred method for assembling the carbon fiber sucker rod 10 is to inject the polymer or ceramic resin material directly into the terminus fitting 30. Preferably, an injection port 39 and vent port 40 are used for the resin material injection. The injection port 39 is provided to inject the polymer or ceramic resin into the fitting 30. The vent port provides a temporary vent and a sight window to show that adhesive has filled the cavity 30. Preferably, the polymer or ceramic material is injected into the injection port 39 while the terminus fitting 30 is lying in a horizontal position. It is important to assemble the composite sucker rod 10 in a horizontal position with the plurality of strands 20 supported substantially straight and in the desired bundle configuration with the terminus end fittings 30 properly aligned before the resin material is injected into the terminus fitting's injection port 39. It is also important for the splayed orientation of the strands 20 to be configured properly and consistent.

[0065] As illustrated in FIGS. 3-7, in a preferred embodiment, the sucker rod assembly 10 includes a threaded connection member 45 to interface with a standard sucker rod coupling that connects rod to rod to form a sucker rod string. In another embodiment, the threaded connection member 45 can be applied on only one end of the sucker rod 10 and no threaded connection member is affixed to the other end. This enables one sucker rod 10 to be coupled to another without the use of traditional sucker rod couplings. Instead, the connection member 45 of one sucker rod assembly 10 threads into the female threaded opening 36 of the other sucker rod assembly 10.

[0066] Further, in a preferred embodiment, it is desirable to compress the hardened resin wedge 21 with the male threaded portion of the connection member 45 as a means to firmly hold the wedge 21 in position within the terminus fitting 30, especially when it is anticipated that the sucker rod assembly will experience compressive loads. The preferred method to compress the wedge 21 within the terminus 30 is to inject the polymer or ceramic resin into the terminus 30 with the threaded connection member 45 backed out slightly, for example, approximately to turn, from its final position or not fully torqued. As a result, the wedge 21 will be in-situ molded within the terminus 30. After the wedge 21 is cured, the threaded connection member 45 is fully screwed in place and torqued as appropriate. This method results in putting a pre-load on the wedge 21 which enhances its ability to handle cyclic tension and compressive loads. Another option is to use a dummy connection member (not shown) when the polymer or ceramic wedge is injected into the fitting 30. This dummy connection member can be slightly shorter than the final connection member 45 so a compressive load is applied to the wedge 21 when the final connection member 45 is installed.

[0067] As illustrated in FIG. 14, wear guides 50 and/or paraffin scrapers may be installed along the length of the sucker rod terminus assembly 10. Wear guides 50 are typically used only on sucker rods running in a deviated portion of the oil well. Traditional wear guides are made from a thermoplastic polymer and are pre-molded and snapped in place or injection molded directly onto the steel sucker rod. Traditional wear guides often do not stay in place during operation.

[0068] For a preferred sucker rod 10, a fiber filled composite wear guide 50 is molded directly onto the bundle of strands 20. This can be accomplished by infusion molding a relatively thick three dimensional fiber mat that is wrapped around the strands bundle. In a preferred example, the fiber form is a wear resistant spun polyester mat made by 3M that is from to inch thickness. In one example, a 3-4 inch wide by 9-12 inch long strip of inch thick spun polyester mat is wrapped around the plurality of strands 20 of the sucker rod assembly 10 at the location desired for the wear guide 50. A two piece mold is clamped around the wrapped fiber form. Thermosetting epoxy is injected into the mold through an injection port to flow through the porous spun polyester material. When cured, the mold is removed. The three dimensional spun polyester mat impregnated with epoxy forms a wear resistant composite particularly suited for application that is permanently bonded over the sucker rod assembly 10. Advantageously, as illustrated in FIG. 14, the wear guides 50 can also function as wraps incrementally spaced to provide the desired compressive dampening and rod stiffness, as described above. In another embodiment, woven fiberglass, carbon fiber or aramid fiber cloth tape can be convolutely wrapped with resin around the bundle of carbon fiber rods such that it functions both as a wear guide and the banding that holds the plurality of rods together.

[0069] As illustrated in FIGS. 15-19, in additional preferred embodiments, the terminus fitting's central cavity 33 includes a plurality of chambers 51 wherein each chamber is frustum shaped so as to have a proximal end having a small diameter d1, a distal end having a large diameter d2, and a length 1 between the proximal end and distal end. As illustrated in FIG. 19, it is preferred that frustum shaped chambers have different shapes and/or sizes wherein at least a frustum chamber's proximal end diameter, distal end diameter, or length is different than an adjacent frustum chamber's proximal end diameter, distal end diameter, or length. Even more preferably, each frustum chamber is diametrically larger than the frustum chamber positioned proximally to it. For example, for a three frustum chambered terminus fitting illustrated in FIGS. 15-19, it is preferred that the central frustum chamber 53 have diameters d1 and d2 which are larger than proximal frustum chamber 51, and that the distal frustum chamber 55 have diameters d1 and d2 which are larger than the central frustum chamber 53.

[0070] The terminus fitting 30 may be constructed in innumerable shapes and sizes as can be determined by those skilled in the art. For example, as illustrated in FIGS. 17 and 18, the terminus fitting's exterior proximal end 31 may be tapered. In addition, as illustrated in FIGS. 17 and 18, the terminus fitting's cavity 33 may include a cylindrical section 38 towards the terminus fitting's distal end 32.

[0071] As with embodiments described above, the rod strands 20 are positioned within the terminus fitting's central cavity 33 and the strands are splayed out so as to have a diameter at their distal ends greater than the terminus fitting's proximal opening 35. Preferably, the sucker rod assembly 10 includes one or more spreader plates 22 positioned within the terminus fitting's cavity 33. The spreader plates may be a one-piece construction. However preferably, the sucker rod assembly embodiments illustrated in FIGS. 15-19, include one or more spreader plates 22 constructed of two or more pieces 24 wherein the pieces can be arranged to adjoin one another to form a single spreader plate 22 as illustrated in FIGS. 8-13.

[0072] As with previous embodiments, the terminus fitting's cavity 30 is preferably injected or filled with a polymer material that adheres to the strands 20. The polymer material for the wedge 21 can be epoxy, phenolic or other thermosetting resin meeting the performance requirements. This terminus fitting construction having a plurality of frustum shaped chambers creates a resin wedge also having a double or triple (or even more) frustum wedge construction.

[0073] The sucker rod's terminus fitting 30 and resin wedge 21 with multiple frustum chambers 51 embodiment is not intended to be limited to two or three frustums as illustrated in FIGS. 15-19. Instead, the terminus fitting 30 and resin wedge may have four or more frustum chambers each preferably having a radius/diameter that is progressively larger from the proximal end to the distal end of the terminus fitting. However, in the preferred embodiment illustrated in FIGS. 15-19, the terminus fitting 30 and wedge 21 are constructed with three frustums chambers 51 with each frustum chamber progressively larger than the proximally adjacent frustum chamber.

[0074] Creating a multiple frustum shaped wedge in the metal terminus end fitting reduces the effect of the localized stress concentration at the nose of the terminus. The bulk modulus of the frustum is different at the terminus' proximal end 31 versus its distal end 32. At the proximal end 31, the wedge is made up of mostly strands 20 since the strands enter the fitting tightly grouped together. Hence, the bulk modulus at the proximal end of the wedge is predominately that of the composite strands. However, at the larger distal end of the wedge, the bulk modulus is comprised of a more equal ratio of strands and wedge polymer material. As a result, the bulk modulus at the large end of the frustum is significantly lower than at the small end of the frustum. In fact, the bulk modulus at the large end of the frustum is equal to the frustum polymer itself much like the spring constant of a series of springs with two different stiffness springs is equal to only the softer spring. Thus, there is often a 5:1 difference in the bulk modulus of the frustum at the small end versus the large end. Hence, there is not the same cushioning effect against a stress concentration for the strands at the nose of the frustum as there is at the large end of the frustum where the strands are surrounded with and spread within a lower modulus polymer. Additionally, the nose is more susceptible to compressing due to the wedge effect, thereby allowing axial displacement of the frustum. These conditions make the composite strands especially susceptible to a tri-axial stress concentration at the nose of the terminus fitting as the tensile load is increased. However, by including second and third frustum chambers 51 filled with polymer resin, as shown in FIGS. 15-19, the wedge construction provides a cushioning effect which reduces the stress concentration at the nose and allows for the stress to be spread over a greater percentage of the wedge and minimizes axial displacement of the wedge under tensile loads. Moreover, by altering the shapes and/or sizes of the frustum chambers, one is able to equalize the bulk modulus of the wedge throughout the terminus fitting's cavity.

[0075] Though not shown in FIGS. 15-19, the bundle of strands can be wrapped with a band of fiber composite material at the proximal end of the wedge in the proximal frustum. The band of hoop fibers reinforces the proximal frustum and helps to reduce the radial stress imposed by axial displacement of the frustum which works in conjunction with the softening effects of the double conical wedge.

[0076] While several particular forms of the invention have been illustrated and described, it will be apparent that various modifications can be made without departing from the spirit and scope of the invention. Therefore, it is not intended that the invention be limited except by the following claims. Having described my invention in such terms so as to enable person skilled in the art to understand the invention, recreate the invention and practice it, and having presently identified the presently preferred embodiments thereof we claim: