Patent Application
20160362939
The present invention relates generally to sucker rod engineering and design. More particularly, the present invention relates to a composite sucker rod assembly for use in down-hole vertical lift oil extraction.
Sucker rods for use with vertical lift rod pumps, also referred to as surface units, rocking horse, or pump jacks are typically made from individual lengths of steel rod sections that are connected together by threaded couplings. The individual sucker rods are typically 25 feet, 30 feet or 37.5 feet in length and are connected together with couplings to form a sucker rod string. A typical sucker rod string is from 700 to 10,000 feet or more in length. The sucker rod string connects the vertical lift surface device to the down-hole pump unit. Traditional metal sucker rods are heavy and subject to corrosion and fatigue failure, particularly at the threaded connections or due to stress corrosion cracking. An unexpected broken sucker rod due to corrosion and/or fatigue is expensive to remove and replace. Further, the weight of a metal sucker rod string limits its strength and fatigue life and can limit the depth which even large surface units can pump. The weight of a steel sucker rod string can also overload and reduce the life of the surface unit and its components. Monolithic fiberglass sucker rods have also been in use for some time. Fiberglass sucker rods do offer a weight reduction and corrosion resistance but have significant stretch and are prone to splitting and failing due to transient compression in the rod string.
Current sucker rod technology consists of wrought steel rods that are typically ¾ inch diameter, 7/8 inch diameter, 1 inch diameter, or 1 and 1/8 inch diameter. The ends of the rods are formed to include a wrench location and machined threads to interface with couplings that join the individual rods together. The typical steel sucker rod lengths are 25 feet and 30 feet. A string of segmented sucker rods is connected between the vertical lift pumping unit at the surface and the down-hole pump at or near the bottom of the oil well. Shorter rods often called “Pony Rods” are used to fine tune the overall length of the sucker rod string and the position of the pump down-hole. Sinker Bars (larger diameter heavy rods) are used at the bottom of the well to weight the entire string for the down stroke. The sucker rods reciprocate up and down in a tube that is typically steel and suspended in the wellbore or casing. No well is perfectly straight. Steel sucker rods are stiff and often cause excessive wear on the inside of the well casing where the well is not straight. Additionally, the flex in the string induced by pumping causes metal fatigue which can cause the sucker rod to fail. The highly corrosive environment worsens the frequency of rod failures.
Monolithic fiberglass sucker rods have been developed. The fiberglass rods have steel-end fittings bonded over the outside surface of each end of the monolithic fiberglass rod. Fiberglass sucker rods are typically larger in diameter compared to their steel counterparts. Fiberglass sucker rods have a lower tensile modulus than steel or carbon fiber and therefore exhibit more stretch than steel or carbon fiber. Fiberglass sucker rods are lighter than steel but have been known to suffer premature failure if subjected to any compression loading during the pumping cycle.
A carbon fiber composite sucker rod pultruded as a monolithic bar and meeting the typical requirements of a sucker rod would not be attractive because it would be subject to compression failures similar to fiberglass and it would be difficult to make the terminus end fitting match the strength potential of the carbon fiber composite mid-section since it would be merely glued on the outside of the monolithic rod versus tying into the majority of the fibers.
A continuous length steel sucker rod is also used in a small but increasing percentage of oil wells. Steel continuous length sucker rods require large diameter spools and special handling techniques. Continuous steel sucker rods are limited in the length that can be practically used due to weight, transportation and handling issues. Continuous length steel sucker rods are heavy, corrode, and are subject to fatigue failure.
Accordingly, it would be desirable to provide a sucker rod assembly that can meet or exceed all operational requirements and offer significant weight reduction, complete corrosion resistance, deeper pumping capability, less maintenance, longer life and overall improved oil production economics, thus having pumping performance and service life advantages over previous sucker rods.
The present invention addresses the aforementioned disadvantages by providing an improved sucker rod assembly for use in down-hole vertical lift oil extraction.
The sucker rod assembly of the present invention comprises a plurality of parallel composite strength elements, referred to herein as “strands” to create a light weight, corrosion and fatigue resistant sucker rod assembly. Preferably, the strands are made of carbon fiber, and will be described primarily as employing carbon fiber. However, other composite materials may be employed, and the invention is not intended to be limited to carbon fiber.
In a preferred embodiment, the sucker rod assembly strands are made of carbon fiber manufactured by the pultrusion process or variation thereof wherein high strength fibers are drawn through a resin bath to impregnate the fibers, and then drawn through heated dies and ovens to shape, consolidate and cure the strands into generally round or polygonal cross-sections such as hexagons or octagons. Carbon fiber is a preferred material for the sucker rod assembly 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. The fiber fraction of the strands should be optimized for tensile strength, stiffness, durability and handling. Additionally, the plurality of the strands that make up the sucker rod assembly should be straight and equal in length in order to maximize the overall strength of the sucker rod assembly.
In a preferred embodiment, the high strength carbon fibers within a polymer matrix are bundled together in parallel to form an elongate rod. Furthermore, by altering the number of strands allows for tailoring the mechanical properties of the sucker rod assembly and the sucker rod string. A larger bundle of strands is used for the sucker rods at the top of the well (near the surface) since the upper sucker rods must carry the weight of the entire sucker rod string. A smaller bundle of strands is used for the sucker rods near the bottom of the well since the tensile stress is lower, although the weight of the lifted oil must also be taken into account. The overall sucker rod string is configured to meet strength and longitudinal stiffness requirements and optimize pumping efficiency. A carbon fiber sucker rod assembly of this configuration has been demonstrated to be approximately one-fifth the weight of steel sucker rods while retaining comparable strength. As a result, the sucker rod assembly of the present invention will have pumping performance and service life advantages over conventional steel or monolithic fiberglass sucker rods and continuous length steel sucker rods.
The sucker rod assembly includes a terminus fitting at one end of the rod, and preferably at both ends of the rod. Preferably, the terminus fittings are made of metal such as a high carbon steel. However, other metals or materials may be employed. Each terminus fitting has a proximal end, a distal end, and a central cavity which extends to the terminus fitting's proximal end to form a proximal opening for receipt of the elongate rod into the cavity. The cavity flares outwardly from the fitting's proximal end toward said fitting's distal end. In a preferred embodiment, the terminus fitting's central cavity extends from the fitting's proximal opening to the terminus fitting's distal end to form a distal opening. The distal opening may include a female thread for affixing to a male threaded member.
The elongate rod's plurality of strands are splayed-out within the terminus fitting and encapsulated with a polymer resin or ceramic material which hardens within the terminus fitting's cavity to form a tapered wedge that holds the terminus fitting in place on the plurality of strands. The terminus polymer or ceramic wedge is cast by injecting the material into an injection port which projects through the side of the terminus fitting. When injected into the injection port, the material fills the space around the strands. A vent is provided to allow air to vent from the central cavity and to give a visual assurance that the tapered cavity is properly filled with material.
The tapered cavity is preferably conical and injected or filled with a polymer material that adheres to the strands to form a mechanical cone shaped wedge within the terminus fitting. The polymer material for the terminus wedge can be epoxy, phenolic or other thermosetting resin meeting the performance requirements. For extremely deep wells, a heat resistant ceramic material may be used for the terminus wedge. A preferred method for assembling the carbon fiber sucker rod assembly is to inject the polymer or ceramic material directly into the terminus fitting. Preferably, two ports in the terminus fitting are used for the wedge material injection. One port is an injection port to inject the polymer or ceramic into the fitting. The other port is a vent hole which provides a temporary vent and a sight window to show that adhesive resin has filled the tapered cavity. Preferably, the polymer or ceramic wedge material is injected into the terminus fitting while the terminus fitting is lying in a horizontal position.
Preferably, at least one spreader plate is positioned within the terminus fitting's cavity. The spreader plate is preferably planar and substantially round so as to define a central axis. Preferably, the spreader plate is positioned within the terminus fitting's central cavity with the spreader plate's central axis coincident with the cavity's central axis. Preferably, the spreader plate has a diameter slightly smaller than the diameter of the terminus fitting's cavity at the spreader plate's location within the central cavity. The spreader plate has a plurality of holes which receives the rod strands so as to splay out the strands in a widened orientation compared to where the strands enter the terminus fitting's proximal opening.
Preferably, the spreader plate is constructed of two or more pieces wherein each piece includes an engagement edge for engaging an engagement edge of an adjoining piece. Preferably, the pieces are held together to form a single spreader plate simply by the rod strands forcing the pieces radially together to engage one another. Also preferably, the engagement edges of the spreader plate pieces include one or more indents for engaging indents formed in the engagement edges of adjoining pieces so that adjoining indents of adjoining pieces form holes which receive the strands. In preferred embodiments, the spreader plate pieces also include a peripheral edge where the pieces do not engage an adjoining piece such as where the spreader plate periphery is adjacent to the terminus fitting's cavity wall. It is preferred that the peripheral edge of each piece include one or more indents for receiving and splaying out one or more strands in a widened orientation compared to where the strands pass through said terminus fitting's proximal opening.
In an alternative embodiment, an annular spacer is applied over the ends of the strands to maintain the strands in a splayed configuration within the terminus fitting while a polymer is injected into the fitting and cured. For this embodiment, it is preferred that the annular spacers are positioned longitudinally on the strands at approximately the same location so as to engage one another. Alternatively, the annular spacers may be longitudinally positioned at different locations so as to engage adjoining strands.
The sucker rod assembly includes a connection member for connecting to other sucker rod assemblies or other equipment. A preferred connection member has a male threaded end which affixes to the terminus fitting's female thread. Preferably, the connection member projects into the cavity sufficient such that the connection member engages the tapered wedge to place the wedge in a state of compression. This construction results in putting a pre-load on the tapered wedge which enhances its ability to handle cyclic tension and compressive loads.
The preferred method to compress the wedge within the terminus fitting is to inject the polymer or ceramic material into the terminus with the threaded connection member backed out slightly from its final (not fully torqued) position. After the wedge is cured, the threaded connection member is fully screwed in place and torqued as appropriate. Another option is to use a dummy connection member when the polymer or ceramic wedge is injected into the fitting. This dummy connection member can be slightly shorter than the final connection member so a compressive load is applied to the wedge when the final connection member is installed.
A minimum number of strands are preferably bundled together to form a length of the composite sucker rod assembly. The plurality of parallel strands may be fully over-wrapped with an encapsulating layer of composite or polymer material that holds the bundle together and provides a wear resistant covering. The over-wrap may also be spaced incrementally to keep the bundle together, thereby increasing the overall stiffness of the sucker rod assembly and providing tailored dampening for compressive loads. The bundle of strands is preferably held together with a composite wrap spaced incrementally sufficient to hold the bundle of rods together but allow them to flex between the wrap if the rod experiences a compressive load. The spacing and the length of the incremental composite wraps can be used to tailor the compressive stiffness of the overall carbon composite sucker rod assembly.
The plurality of parallel strands are preferably bundled in a generally polygonal or round package so the sucker rod assembly can be progressively rotated in a well tubing as typically done to prevent wear in one spot. It is also necessary for the strands to splay-out evenly in the terminus without crossing one strand over another.
Wear guides and paraffin scrapers may be installed along the length of the composite sucker rod assembly after it is assembled. Wear guides are typically used only on sucker rods running in a deviated portion of the oil well. A preferred method is to mold a fiber filled composite wear guide directly onto the bundle of strands. This can be accomplished by infusion molding a relatively thick three dimensional fiber mat that is wrapped around the strands bundle. A two piece mold is clamped around the wrapped fiber form. Thermosetting epoxy is injected into the mold and flows 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. Advantageously, the wear guides can also function as wraps incrementally spaced to provide the desired compressive dampening and rod stiffness, as described above. A preferred method is to mold the composite wear guide over an incrementally spaced band in order to maintain the desired band spacing.
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 band and the banding that holds the plurality of rods together.
Other features and advantages of the present invention will be appreciated by those skilled in the art upon reading the detailed description which follows with reference to the attached drawings.
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.
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 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 down-hole pump unit.
As illustrated in
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 118th inch diameter to 3/16th inch diameter although other sizes may be used and the ideal size may be dependent on processing and assembly requirements.
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. If one strand is shorter than the others in the bundle, then that strand is loaded more than the others and would fail prematurely under a tensile load condition.
Experience has shown that it is preferred that the strands 20 be approximately 1/8 inch or larger in diameter to be stiff enough to be assembled in typical assembly tools maintaining equal length and straightness of the strands 20 without methods to pre-tension the strands. Unlike prior manufacturing processes, tensioning the strands 20 during assembly is not necessary as that would be time consuming and costly.
A minimum number of strands 20 are preferably bundled together to form a length of the elongate rod 15. As illustrated in
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 1-1/8 inch diameter steel sucker rod is just under 1 inch diameter.
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 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. The cavity 33 has a tapered construction so as to have a smaller diameter at its proximal opening 35 than toward its distal end. In a preferred embodiment, 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.
To lock the strands 20 within the terminus fitting's cavity 33, the strands are splayed out so as to have a diameter greater than the terminus fitting's proximal opening 35. To maintain the strands 20 in a splayed out condition, the sucker rod assembly 10 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.
As illustrated in
In an alternative embodiment, the sucker rod assembly includes a plurality of annular spacers wherein an annular spacer is applied over the ends of each 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.
As illustrated in
The terminus fitting's cavity 30 (as illustrated in
As illustrated in
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 1/8 to ½ 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.
As illustrated in
For a preferred sucker rod 10 of the present invention, 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 ¼ to 3/8 inch thickness. In one example, a 3-4 inch wide by 9-12 inch long strip of ¼ 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
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:
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US14/65018 | 11/11/2014 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 61903194 | Nov 2013 | US | |
| 62003437 | May 2014 | US |
