SUCKER ROD ASSEMBLY

[0001] The present invention relates in general to sucker rods and sucker rod assemblies for use in oil wells and other wells, and to methods for using or assembling the sucker rods.

[0002] Oil is removed from the ground using a pump-jack. This equipment is mounted on the surface of the earth above an oil reservoir. The pump-jack is connected to a down-hole pump located at the bottom of an oil well by a string of interconnected sucker rods, which extends inside a production tubing. Through the action of the pump-jack, oil is pumped from the reservoir to the surface for collection.

[0003] A sucker rod is typically a rod having a length of between 24 and 32 feet and a diameter of 0.5 to 2 inches. During pumping, the string of sucker rods performs a reciprocating or alternative movement, which may produce deflections of the string. The sucker rods are thereby subjected to wear due to frictional contact with the inner wall of the production tubing. Even though the fluid environment serves as a lubricant, abrasion does occur over the surface of the sucker rods. Additionally, tools used for assembling sucker rods into a string may also cause tearing of the rod surface.

[0004] In some oil wells, the fluid includes dissolved salts and undissolved minerals which may have an additional abrasive or corrosive effect on the sucker rod surface. The presence of hydrogen sulfide (H₂S), sulfurs (HS, S), water, salty water, hydrogen ions, CO₂ in aqueous solution, and other corrosive chemical compounds, also weaken the sucker rods structure, thereby reducing their fatigue limit. When the attack is particularly harsh, sucker rods break.

[0005] When a rod fails, the whole sucker rod string needs to be pulled from the well and inspected, and defective rods must be replaced. This procedure increases costs when it becomes frequent. Additional costs related to corrosion problems result in losses in production, added costs for new materials, and increased pulling costs.

[0006] Therefore, it is desirable to provide a sucker rod or sucker rod assembly capable of reducing friction and/or resisting corrosion in environments like those found in oil wells.

[0015] Throughout the following description, specific details are set forth in order to provide a more thorough understanding of the invention. However, the invention may be practiced without these particulars. In other instances, well known elements have not been shown or described in detail to avoid unnecessarily obscuring the invention. Accordingly, the specification and drawings are to be regarded in an illustrative, rather than a restrictive, sense.

[0016] One aspect of the invention relates to sucker rods and sucker rod assemblies. FIG. 1 shows a sucker rod assembly 100 according to an example embodiment of the present invention. FIG. 2 shows the components of sucker rod assembly 100 in an unassembled configuration. Sucker rod assembly 100 comprises a sucker rod 102. Sucker rod 102 comprises a rod body 104 and two end portions 106. In some embodiments, sucker rod 102 has a length in the range of 24 to 32 feet, and a diameter of 0.5 to 2 inches. The break lines in FIG. 1 (and also FIG. 2) indicate that rod body 104 may comprise a portion between the break lines which is not shown in order to shorten the view. The portions of sucker rod 102 to the left of the break lines are shown in a partially sectional view. The portion of sucker rod 102 to the right of the break lines are shown in a side elevation view.

[0017] Each end portion 106 comprises a male end section 108, a shoulder section 110, a tool engagement section 112, and a tapered enlargement section 113. Male end section 108 may be connectable to a coupling (which is a tubular connector typically having internal threads used to join two sucker rods together) or some other component which has a female end section. Male end section 108 may be threaded. Shoulder section 110 comprises an abutment face. When the sucker rod is connected to a coupling, the abutment face of the shoulder section abuts an axial face of the coupling. Tool engagement section 112 comprises a set of flats suitable for engagement by a sucker rod turning or holding tool (e.g., power tongs or wrench) used for turning a sucker rod or holding a sucker rod still when assembling sucker rods into a string. Tapered enlargement section 113 can be gripped by a lifting tool such as a sucker rod hanger or a sucker rod elevator, which is used to lift a sucker rod.

[0018] Sucker rod assembly 100 also comprises two end fittings 114 which are connectable to the two ends of sucker rod 102. Each end fitting 114 comprises a male end section 116, a shoulder section 118, a middle section 120, and a female end section 122. Male end section 116 may be threaded. Male end section 116 of end fitting 114 may have the same or similar shape or dimensions as male end sections 108 of sucker rod 102. Male end section 116 is used to connect to a coupling that has a female end section. Shoulder section 118 comprises an abutment face which abuts an axial face of a coupling when the end fitting is connected to a coupling. Shoulder section 118 comprises at least two flat sides suitable to be engaged by a sucker rod turning or holding tool (e.g., power tongs or wrench). In some embodiments, the cross-section of shoulder section 118 has two flat sides and two curved sides. In some embodiments, the cross-section of shoulder section 118 has a square, rectangular, hexagonal, or some other suitable shape. The flat sides of shoulder section 118 allows end fitting 114 to be turned or held still by a sucker rod turning or holding tool (e.g., power tongs or wrench). In some embodiments, shoulder section 118 may be solid (i.e., without a hollow channel therein). Middle section 120 can be gripped by a lifting tool such as a sucker rod hanger or a sucker rod elevator. Female end section 122 is used to connect to male end section 108 of sucker rod 102.

[0019] Sucker rod assembly 100 may also comprise a coupling 124. Coupling 124 may be a tubular connector having internal threads. Coupling 124 may have two female end sections 126, with each female end section at one end. In conventional use, coupling 124 can be connected to the male end sections of two adjacent sucker rods, thereby joining two sucker rods together. In this example embodiment, one female end section 126 of coupling 124 is connectable to male end section 116 of end fitting 114 in one sucker rod assembly, and the other female end section 126 of coupling is connectable to male end section 116 of end fitting 114 in another sucker rod assembly, thereby joining two adjacent sucker rod assemblies together. When pluralities of sucker rods, end fittings and couplings are assembled into a string, the string has the repeating pattern of: coupling, end fitting, sucker rod, end fitting, coupling, end fitting, sucker rod, and end fitting.

[0020] In some embodiments, end fittings 114 may be fixedly connected to sucker rod 102 using specialized tools in a manufacturing plant. In these embodiments, the manufacturing plant can produce and ship to the oil production site a fixed assembly comprising sucker rod 102 and two end fittings 114 fixedly connected thereto. In these embodiments, the connection between end fitting 114 and sucker rod 102 is not reversible, in the sense that a worker at the oil production site cannot disconnect end fitting 114 from sucker rod 102. For example, in some embodiments, end fitting 114 and sucker rod 102 of one fixed unit are not free to rotate relative to one another. At the oil production site, the fixed assembly comprising sucker rod 102 and two end fittings 114 is further coupled to coupling 124 in order to form a string of sucker rods. The connection between end fitting 114 and coupling 124 may be reversible, in the sense that a worker at the oil production site can disconnect coupling 124 from end fitting 114.

[0021] Sucker rod 102 may comprise a corrosion-resistant coating 128. The entire external surface of sucker rod 102, except for the two male end sections, may be covered by corrosion-resistant coating 128. Coating 128 may extend from shoulder section 110 at one end of sucker rod 102 to shoulder section 110 at the other end of sucker rod 102. Coating 128 may comprise a circumferential coating along the entire length of sucker rod 102, except for the end sections.

[0022] Coating 128 may comprise a friction-resistant coating material. The coating material may be a polymeric material comprising either a thermoplastic material or a thermoset material or both. Coating 128 may be formed of co-polymers, homo-polymers, composite polymers, or co-extruded composite polymers. The term “co-polymers” refers to materials formed by mixing two or more polymers, “homo-polymers” refers to materials formed from a single polymer, and “composite polymers” refers to materials formed of two or more discrete polymer layers that can either be permanently bonded or fused.

[0023] In some embodiments, coating 128 may comprise polyethylene. For example, coating 128 may comprise high-density polyethylene (HDPE) or cross-linked polyethylene (PEX). Polyethylene in general has several advantages over other materials such as polyurethane. For example, polyethylene has a lower coefficient of friction than polyurethane, it is easier to manufacture, it is easier to recycle than thermoplastic polyurethane, and it is less costly.

[0024] In some embodiments, coating 128 may comprise high-strength resin material. In some embodiments, coating 128 may comprise polyvinylidene fluoride (PVDF), ethylene tetrafluoroethylene (ETFE), polytetrafluoroethylene (PTFE), polyphenylensulfide (PPS), polyamide, polyester, polyethersulfone, polyethylene terephthalate (PET), polypropylene, polystyrene, epoxy, or a combination thereof.

[0025] Tool engagement sections 112 and tapered enlargement sections 113 of sucker rod 102 are also covered by coating 128. In conventional sucker rods, the tool engagement sections are generally exposed (i.e., not covered by a corrosion-resistant coating). This is because the tool engagement sections of conventional sucker rods need to be engaged by a sucker rod turning or holding tool (when sucker rods are assembled to form a string) which would damage any coating that covers the tool engagement sections. In contrast, in the present disclosure, the sucker rod assembly comprises add-on end fittings which comprise shoulder sections that comprise flat sides suitable for engagement by sucker rod turning or holding tools. In the present disclosure, it is the shoulder sections of the end fittings, not the tool engagement sections of the sucker rods, that are engaged by sucker rod turning or holding tools.

[0026] In some embodiments, the end fittings are made of stainless steel. In other embodiments, end fittings are covered with stainless steel using a method such as spray welding or spray coating. Therefore, the end fittings can have a stainless steel surface, which is corrosion resistant. In some embodiments, the end fitting may comprise a surface or coating of a corrosion-resistant material, as described above for coating 128 of sucker rod 102.

[0027] Assembly 100 may also comprise two or more centralizers 130 which are interspaced along the length of rod body 104 of sucker rod 102. Each centralizer 130 encircles rod body 104 of sucker rod 102. The function of centralizers 130 is to centralize sucker rods 102 within a production tubing and to reduce frictional forces between the production tubing and sucker rods 102.

[0028] FIG. 3 shows a sucker rod assembly 101 according to another example embodiment of the present invention. FIG. 4 shows the components of sucker rod assembly 101 in an unassembled configuration. Sucker rod assembly 101 comprises a sucker rod 102. Sucker rod 102 comprises a rod body 104 and two end portions 106. In some embodiments, sucker rod 102 has a length in the range of 24 to 32 feet, and a diameter of 0.5 to 2 inches. The break lines in FIG. 3 (and also FIG. 4.) indicate that rod body 104 may comprise a portion between the break lines which is not shown in order to shorten the view. The portions of sucker rod 102 to the left of the break lines are shown in a partial sectional view. The portion of sucker rod 102 to the right of the break lines are shown in side elevation view.

[0029] Each end portion 106 comprises a male end section 108, a shoulder section 110, a tool engagement section 112, and a tapered enlargement section 113. Male end section 108 may be connectable to a coupling or some other component that has a female end section. Male end section 108 may be threaded. Shoulder section 110 comprises an abutment face which abuts an axial face of a coupling when the sucker rod is connected to a coupling. Tool engagement section 112 comprises a set of flats suitable to be engaged by a sucker rod turning or holding tool used for turning sucker rods or holding sucker rods still. In FIG. 3, one end of sucker rod 102 is connected to coupling 124 and the other end of sucker rod 102 is connected to end fitting 114.

[0030] Sucker rod assembly 101 also comprises an end fitting 114 which is connectable to an end of sucker rod 102. In FIG. 3, end fitting 114 is shown connected to the right side of sucker rod 102. End fitting 114 comprises a male end section 116, a shoulder section 118, a middle section 120, and a female end section 122. Male end section 116 of end fitting 114 is connectable to a coupling. Shoulder section 118 comprises an abutment face which abuts an axial face of a coupling when the end fitting is connected to a coupling. Shoulder section 118 comprises at least two flat sides suitable to be engaged by a sucker rod turning or holding tool. Middle section 120 can be gripped by a lifting tool such as a sucker rod hanger or a sucker rod elevator. Female end section 122 of end fitting 114 is connectable to male end section 108 of sucker rod 102.

[0031] Sucker rod assembly 101 may also comprise a coupling 124. In FIG. 3, coupling 124 is shown connected to the left side of sucker rod 102. Coupling 124 has two female end sections 126. Female end section 126 is connectable to male end section 108 of sucker rod 102 or male end section 116 of end fitting 114. In some embodiments, in order to form a string of sucker rods, one female end section 126 of coupling 124 is connectable to male end section 108 of sucker rod 102 and the other female end section 126 of coupling 124 is connectable to male end section 116 of end fitting 114 of an adjacent sucker rod assembly. When assembled into a string, the string has the repeating pattern of: coupling, sucker rod, end fitting, coupling, sucker rod, and end fitting.

[0032] In some embodiments, end fittings 114 and coupling 124 may be fixedly connected to sucker rod 102 using specialized tools in a manufacturing plant. Therefore, in these embodiments, the sucker rod assembly comprising sucker rod 102 and end fittings 114 and coupling 124 fixedly connected thereto can be shipped to the oil production site as one unit. For example, in some embodiments, end fitting 114, sucker rod 102, and coupling 124 of one fixed unit are not free to rotate relative to one another. At the oil production site, a worker can couple coupling 124 of one assembly to end fitting 114 of an adjacent assembly in an end-to-end fashion, in order to form a sucker rod string.

[0033] Assembly 101 may also comprise two or more centralizers 130 which are interspaced along the length of rod body 104 of sucker rod 102. The function of centralizers 130 is to centralize sucker rods 102 within a production tubing and to reduce frictional forces between the production tubing and sucker rods 102.

[0034] As mentioned above, sucker rod 102 may comprise corrosion-resistant coating 128.

[0035] One aspect of the invention relates to sucker rods having shoulder sections having special features. In some embodiments, shoulder section 110 of sucker rod 102 may comprise a recessed shoulder 132. Recessed shoulder 132 is filled with coating 128 to provide for a better seal for sucker rod 102 and to form a tight fit with coupling 124 or end fitting 114 to prevent infiltration of corrosive media to sucker rod 102. In some embodiments, shoulder section 110 of sucker rod 102 may also comprise a recessed groove 134. Recessed groove 134 is also filled with coating 128, and functions to prevent infiltration of corrosive media to sucker rod 102. An example embodiment of a portion of a sucker rod having recessed shoulder 132 and recessed groove 134 is shown in FIG. 5.

[0036] FIG. 6 shows a sucker rod assembly 200 according to another example embodiment of the present invention. FIG. 7 shows the components of sucker rod assembly 200 in an unassembled configuration. Sucker rod assembly 200 comprises a sucker rod 202. Sucker rod 202 may comprise some or all of the features of sucker rod 102 as described above.

[0037] Sucker rod assembly 200 also comprises two different end fittings 214 and 215 which are connectable to the two ends of sucker rod 102. End fitting 214 comprises a male end section 216 and a female end section 222. Male end section 216 may be threaded. The outer surface of female end section 222 comprises at least two flat sides suitable to be engaged by a sucker rod turning or holding tool (e.g., power tongs or wrench). The flat sides on the outer surface of end fitting 214 allows end fitting 214 to be turned or held still by a sucker rod turning or holding tool (e.g., power tongs or wrench).

[0038] End fitting 215 comprises two female end sections 250 and 252, and a middle section 254. Female end section 250 is connectable to one end of sucker rod 202. Female end section 252 is connectable to male end section 216 of end fitting 214 (of an adjacent sucker rod assembly 200). Therefore, it is possible to assemble pluralities of sucker rod 202, end fittings 214 and 215 into a string of sucker rods without the use of couplings. The string according to this embodiment has the repeating pattern of {end fitting 215, sucker rod 202, end fitting 214, end fitting 215, sucker rod 202, end fitting 214}. The outer surface of female end section 252 comprises at least two flat sides suitable to be engaged by a sucker rod turning or holding tool (e.g., power tongs or wrench). The flat sides allows end fitting 215 to be turned or held still by a sucker rod turning or holding tool (e.g., power tongs or wrench). Middle section 254 is narrower than the two female end sections 250 and 252, and can be gripped by a lifting tool such as a sucker rod hanger or a sucker rod elevator. End fittings 214 and 215 may be fixedly attached to sucker rod 202.

[0039] The sucker rods and the sucker rod assemblies of the present disclosure have a number of advantages. For example, in some embodiments, the entire sucker rod (except for the two end sections) is coated with corrosion-resistant coating. The corrosion-resistant coating functions to prevent corrosive media from contacting the sucker rod, including the shoulder sections, the tool engagement sections and the rod body. The two end sections of the sucker rod that are not coated with corrosion- resistant coating can be coupled with, and shielded by, either the end fitting or the coupling, and therefore are also protected from corrosive media. The end fittings and the couplings may be made of a corrosion-resistant material or have a corrosion resistant surface or coating, so they can be corrosion-resistant. Because the end fitting attached to one or both ends of the sucker rod provides a section that has flat sides, a worker can use a sucker rod turning or holding tool (e.g., power tongs or wrench) to engage the end fitting to tighten the sucker rod assembly in order to form a sucker rod string. This way, the sucker rod turning or holding tool does not need to engage the tool engagement sections of the sucker rods, and thereby avoids damaging the coating on the sucker rods.

[0040] Also the attachment of the end fitting to one or both ends of the sucker rod can increase the life of the sucker rod, and increase the efficiency of assembling a string of sucker rods at the oil production site. Compared to a sucker rod, the end fitting is relatively short and can be manufactured relatively inexpensively. For example, the end fitting may have a length of 5 to 25 inches. Also, the end fittings can be made to be corrosion-resistant, as the end fittings can be made with or coated with a corrosion-resistant material, e.g., stainless steel.

[0041] One aspect of the invention relates to a method of assembling a sucker rod assembly. In one embodiment, the method comprises providing a sucker rod. The sucker rod may be a sucker rod comprising some or all the features as disclosed above in the present disclosure. The sucker rod may have two end sections. The method further comprises connecting an end fitting to each one of the two end sections of the sucker rod to form a sucker rod unit. The end fitting may comprise some or all the features as disclosed above in the present disclosure. The end fitting may be connected to the end sections of the sucker rod either reversibly or irreversibly. When the end fitting is connected to the end section of the sucker rod irreversibly, a worker at an oil production site cannot disconnect the end fitting from the sucker rod. The method may further comprise connecting a coupling to end fittings of two sucker rod units to join two sucker rod units together, in order to form a string of sucker rods.

[0042] In one embodiment, the method comprises providing a sucker rod. The sucker rod may be a sucker rod comprising some or all the features as disclosed in the present disclosure. The sucker rod may have two end sections. The method further comprises connecting an end fitting to one of the end sections of the sucker rod and connecting a coupling to another one of the end sections to form a sucker rod unit. The end fitting may comprise some or all the features as disclosed above in the present disclosure. The end fitting and the coupling may be connected to the end sections of the sucker rod either reversibly or irreversibly. When the end fitting and the coupling are connected to the end sections of the sucker rod irreversibly, a worker at an oil production site cannot disconnect the end fitting from the sucker rod. The method may further comprise joining two sucker rod units end to end, in order to form a string of sucker rods.

[0043] As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention. For example, the end sections of the sucker rod may comprise two male end sections, two female end sections, or one male end section and one female end section. The end fitting may comprise a male end section and a female end section, or two male sections, or two female end sections, depending on the configuration of the sucker rod and/or the coupling. The scope of the claims should not be limited by the preferred embodiments set forth in the examples, but should be given the broadest interpretation consistent with the description as a whole.