Sucker rod guide

Abstract

Apparatus for centering a sucker rod within tubing, comprising an elongate main body for engaging the sucker rod, defining a longitudinal axis and a circumferential direction around the longitudinal axis; and a plurality of vanes extending along the main body, the vanes being spaced apart in the circumferential direction. The main body defines an outer surface between the vanes, and each vane comprises two vane end sections that are separated by a vane mid-section. For each vane, the vane end sections extend generally longitudinally and are rotationally offset from one another in the circumferential direction.

Description

[0001] Sucker Rod Guide

[0002] The present invention relates to apparatus for centering sucker rods within pipes, such as tubing and casing used in the oil and gas industry.

[0003] A sucker rod is a rod, typically steel, threaded at each end for engagement in a string of such rods to form physical connection between a pump in the base of a well and a prime mover at ground level. The prime mover reciprocates the rod along its length so as to actuate the pump.

[0004] The string of sucker rods extends within the well tubing, and is generally centred by a plurality of guides. Each sucker rod may have one or more guides mounted thereon.

[0005] The guides extend outwardly from the sucker rod to contact the inner surface of the tubing, while leaving space for fluid to be pumped past the guide into or out of the well.

[0006] The guide itself should be strong enough to stably centre the sucker rod, and resist wear as it engages the inner surface of the tubing during the reciprocation of the sucker rod, while also minimising any resistance to the flow of fluid along the tubing.

[0007] One way to reduce resistance to the flow of fluid is to reduce the obstruction to the flow by manufacturing the apparatus from less material. However, such an apparatus would wear more quickly through use.

[0008] There are two commercially available products that provide advantageous sucker rod guides, Helix™ and TenFlow™.

[0009] Although these products have had success, there remains a need for a sucker rod guide that can provide advantageous flow characteristics and can be easily manufactured.

[0010] In the disclosure that follows, there is described apparatus for centering a sucker rod within tubing, comprising: an elongate main body for engaging the sucker rod (preferably, contacting the sucker rod), defining a longitudinal axis and a circumferential direction around the longitudinal axis; a plurality of vanes extending along the main body, the vanes spaced apart in the circumferential direction, wherein: the main body defines an outer surface between the vanes; each vane comprises two vane end sections, separated by a vane mid-section; and for each vane, the vane end sections extend generally longitudinally and are rotationally offset from one another around the longitudinal axis.

[0011] The vane mid-section extends helically around the longitudinal axis. The two vane end section are angled relative to the vane mid-section to extend generally longitudinally (i.e., the vane mid-section is at a greater angle to the longitudinal axis than the two vane end sections, which preferably extend close to parallel with the longitudinal axis).

[0012] When such a sucker rod guide is used, the fluid flow in use can generate less turbulence than prior art approaches, leading to lower fluid-induced wear of the sucker rod.

[0013] In addition, the apparatus in accordance with the present disclosure may be more robust, in particular, because the apparatus may have a large contact surface with the inner surface of the tubing.

[0014] Although it is not essential that such apparatus be manufactured by injection moulding, it is preferred. Equally, for ease of manufacturing by injection moulding, it is preferred that: when seen in cross-section perpendicular to the longitudinal axis, the vanes are not dovetail shaped, because such vanes necessitate a greater number of mould parts.

[0015] The vane end sections are preferably tapered such that they narrow in width (with width measured in the circumferential direction) from the mid-section to their terminal ends. This can increase the opening area at the ends of the apparatus for a flow of fluid, which in turn can reduce induced turbulence.

[0016] The vane mid-section may have a greater width in the circumferential direction than the vane end sections. This can increase the surface area of the apparatus for contact with the inner surface of the tube in which the sucker rod is guided. As a result, the wearable volume of the guide is increased.

[0017] The vane end sections may be tapered such that they reduce in radial height towards their terminal ends. The terminal ends can be located at the longitudinal ends of the main body. Each vane may comprise a longitudinally-extending crest, with the crest at the terminal ends of the vane end sections being curved in a plane extending through the longitudinal axis. Optionally, the terminal ends of the vane end sections are S-shaped in a side view (perpendicular to a plane extending through the longitudinal axis), with the terminal ends blending into the outer surface of the main body. Optionally, the terminal ends of the vane end sections are S-shaped in the side view to define a shoulder having a radius of 20mm to 40mm, with the terminal ends blending into the outer surface of the main body with a radius of between 12mm and 26mm.

[0018] Within the context of the present disclosure; in case a plane extends or passes through an axis, it may be understood that the axis is contained in the plane.

[0019] The S-shape can reduce friction with the inner surface of the tube, whilst blending into the main body in a manner that reduces unwanted turbulence, whilst simultaneously providing a shape that is more easily released from a mould during manufacture.

[0020] Each vane preferably extends away from the main body in a direction substantially perpendicular, and preferably exactly perpendicular, to a respective plane extending through the longitudinal axis. Each vane preferably tapers such that it reduces in width as it extends away, in the radial direction, from the main body (even a very minor taper can be of assistance for removal of an injection moulded vane from a mould). Optionally, each vane mid-section comprises a longitudinally-extending crest, and two longitudinally- extending sides; and for each vane, the longitudinally-extending sides are in parallel with each other in a cross-section through the longitudinal axis. Optionally, each vane comprises a longitudinally-extending crest and is no wider in the circumferential direction at its crest than at its base (put another way, each vane comprises a longitudinally-extending base for which the size of its base in the circumferential direction is greater than or equal to the size of its crest in the circumferential direction). Optionally, each vane comprises a longitudinally-extending crest, and two longitudinally-extending sides; and the two sides are sloped inwards or parallel in any cross-section perpendicular to the longitudinal axis. Vanes having such features can be manufactured by injection moulding using a simple mould. In particular, these features can improve the ease of removal of the manufactured item from the mould. Whilst very tapered vanes would be more easily removed from a simple mould (i.e., a mould with as few mould parts as possible), less tapered vanes will have a larger contact area with the inner surface of the tubing (reducing wear of the apparatus and / or the tubing), and so it is advantageous that the vanes be as wide as possible at their crests, while remaining easily removable from a simple mould. Preferably, each vane end section extends away from the main body in a plane of extension that is substantially, or exactly, parallel to and offset from a radial plane extending through the longitudinal axis. A radial plane is a plane that extends in the radial direction through the longitudinal axis (that is, the longitudinal axis lies in the radial plane).

[0021] Such a vane can be manufactured more easily by injection moulding, in contrast to a vane that has end sections extending exactly along the radial plane but offset from one another. If the two end sections of a single vane were to extend in different radial directions such that they diverge, then unless they were manufactured with a sufficient taper (which would reduce their contact area with the tube reducing their wear resistance), they would not be easily released from the mould after injection moulding.

[0022] By offset is meant that the direction of extension is in parallel with the radial plane, but is not coincident with the radial plane. The vane end section may be offset such there is a gap between the end section and the radial plane.

[0023] However, more preferably, each vane end section extends away from the main body along a plane of extension that is substantially parallel to and offset from a radial plane extending through the longitudinal axis, with the vane overlapping, or flush, with the radial plane.

[0024] The apparatus comprises at least three vanes to provide centering contact with the inner surface of the tube.

[0025] The apparatus preferably comprises four equally-spaced vanes. Such a configuration can be moulded using a two-part mould.

[0026] In cross-section perpendicular to the longitudinal axis, for each vane, the directions of extension through the two vane end sections intersect with the main body (that is, the directions in which the vanes extend away from the main body). The intersections are optionally rotationally offset from each other about the longitudinal axis of the main body by an angle in the range 20 to 65 degrees. This increases the contact surface with the inner surface of the tubing while reducing wear caused by inducing turbulence. In an end view along the longitudinal axis, the crests of the vanes preferably extend over an angular range of 30 to 70 degrees about the longitudinal axis. This has been found to provide a suitable amount of contact with the inner surface of the tubing while reducing wear caused by inducing turbulence.

[0027] For each vane, the vane end sections may join the mid-section via a radius in the range 100mm to 200mm. The maximum thickness of the mid-section of the vanes may be between 8mm and 16mm. The sides of the vane end sections preferably meet the main body with a radius of curvature of no less than 100mm, and preferably no more than 200mm. The main body may comprise two end portions in which the outer surface is radially tapered towards the terminal ends. Preferably, the end portions of the main body each include a ramp portions, and the outer surface of the main body is tapered with an angle of 1 to 5 degrees relative to the longitudinal axis in the ramp portions. The terminal ends of the two end portions may be tapered with an angle of 30 to 60 degrees relative to the longitudinal axis. Most preferably, the terminal ends meet the ramp portions at a radiused portion, the radiused portion having a radius in a plane passing through the longitudinal axis of between 10mm and 20mm. Such features can reduce turbulence.

[0028] The vanes are preferably spaced around the main body such that in an end view of the apparatus along the longitudinal axis they leave a gap and, more preferably, do not overlap. Most preferably, the vanes are spaced around the main body such that they leave a gap therebetween around the perimeter of the main body for providing an unobstructed linear flow path from one end of the main body to the other end.

[0029] For a better understanding of the invention, and to show how the same may be put into effect, reference will now be made, by way of example only, to the accompanying drawings in which:

[0030] Figure 1 shows a side view of a sucker rod guide installed on a sucker rod;

[0031] Figure 2 shows an end view along the longitudinal axis of the sucker rod guide of Figure 1 ; Figure 3 shows schematic representation of an end section in close up;

[0032] Figure 4 shows a cross-sectional view of the sucker rod guide through the line X-X in Figure 2;

[0033] Figure 5 shows a cross-sectional view of another sucker rod guide; and

[0034] Figure 6 shows comparative results for prior art sucker rod guides and an embodiment of a sucker rod guide in accordance with the invention. An embodiment of an apparatus 10 for centering a sucker rod 5 within tubing (not shown) in accordance with the invention is shown in Figure 1 .

[0035] The apparatus 10 can provide a sucker rod guide that can achieve advantageous fluid flow performance, while being easy to manufacture, in particular, by injection moulding.

[0036] Preferably, the apparatus 10 is axially fixed to the sucker rod 5. More preferably, the apparatus 10 is also rotationally fixed to the sucker rod 5.

[0037] The apparatus 10 comprises an elongate main body 30 and a plurality of radial vanes 20.

[0038] The main body 30 surrounds the sucker rod 5. The main body 30 defines an outer surface 31 that extends between the vanes 20. The outer surface 31 is preferably circular in crosssection, and may vary in radius along its length. However, any suitable shape of main body is considered.

[0039] The main body 30 has a cylindrical bore through which the sucker rod 5 penetrates. The main body 30 preferably has a thickness T of between 2mm and 10mm between the bore and the outer surface 31 (for example, at its thickest point, which would typically be its longitudinal mid-point).

[0040] The main body 30 is elongate and defines a longitudinal axis A-A, which when installed on a sucker rod 5 corresponds to the longitudinal axis of the sucker rod 5.

[0041] There is also defined a circumferential direction C-C around the longitudinal axis A-A.

[0042] As can be seen from Figure 4, the outer surface 31 of the main body 30 is curved such that the main body 30 is narrowest near its ends. Alternatively, other shapes of main body 30 are possible, such as that formed of two frusto-conical surfaces meeting at its longitudinal mid-point and tapering (for example, at an angle of 2 to 6 degrees) towards its ends.

[0043] More preferably, the main body 30 comprises two end portions 32a, 32b in which the outer surface is radially tapered towards the terminal ends 36a, 36b. In the specific embodiment shown, the end portions 32a, 32b of the main body 30 each include a ramp portion 38a, 38b. In the ramp portions 38a, 38b, the outer surface 31 of the main body 30 is tapered with an angle of 1 to 5 degrees relative to the longitudinal axis A- A.

[0044] The terminal ends 36a, 36b of the two end portions 32a, 32b are tapered with an angle 0 of 20 to 60 degrees relative to the longitudinal axis A-A.

[0045] The terminal ends 36a, 36b preferably meet the ramp portions 38a, 38b at a radiused portion 37a, 37b that blends the surface between them. The radiused portion 37a, 37b has a radius in a plane passing through the longitudinal axis A-A of between 10mm and 20mm.

[0046] The terminal ends 36a, 36b of the two end portions 32a, 32b preferably are located axially beyond the ends of the vanes 20.

[0047] The two end portions 32a, 32b of the main body 30 can be separated by a middle portion 34, which middle portion 34 can be cylindrical.

[0048] Although not essential, in preferred embodiments the two end portions 32a, 32b of the main body 30 meet the middle portion 34 at the same axial locations that the end sections 22a, 22b of the vanes 20 meet the mid-section 24 of the vanes 20 (the structure of each of the vanes 20 is discussed below).

[0049] The plurality of vanes 20 extend along the main body 30.

[0050] Each vane 20 extends along a majority of the length of the main body 30, such as at least 80% of the length of the main body 30.

[0051] The vanes 20 are spaced apart in the circumferential direction C-C. The vanes 20 are preferably equally spaced around the circumference of the main body 30.

[0052] The apparatus comprises at least three vanes, preferably at least four vanes. In a most preferred embodiment, there are four vanes, as depicted in the figures.

[0053] Each vane comprises two vane end sections 22a, 22b, and a vane mid-section 24. The two vane end sections 22a, 22b generally extend in parallel with the longitudinal axis A-A.

[0054] The vane end sections 22a, 22b extend generally longitudinally.

[0055] The vane end sections 22a, 22b of each vane are rotationally offset from one another in the circumferential direction C-C. For example, as can be seen in the end view of Figure 2, one end section 22a meets the main body 30 offset in the anticlockwise direction from the other end section 22b.

[0056] All of the vane end sections 22a are offset relative to the opposite end section 22b in the same direction. In other words, in an end view, all of the near end sections 22a are offset one way (e.g. anti-clockwise) relative to the far end sections 22b.

[0057] In the end view of Figure 2, for each vane 20, the intersection of the centroidal planes (the centroidal plane being the plane through the centre of the end section, wherein the centroidal planes of the end sections of one vane are parallel with each other and parallel with a radial plane extending halfway between them) of the two vane end sections 22a, 22b with the main body 30 are rotationally offset from each other about the longitudinal axis of the main body 30 by an angle in the range 20 to 65 degrees.

[0058] Although each vane end sections 22a, 22b is rotationally offset from one another, they preferably do not extend away from the main body 30 in a radial line extending through where the vane end section 22a, 22b meets the main body 30.

[0059] In fact, it is preferable that each vane end section 22a, 22b extends away from the main body along a plane of extension that is substantially parallel to and transversely offset from a radial plane for that vane extending through the longitudinal axis. In this way, the plane of extension F-F for one end section 22a of a vane 20 is parallel to the plane of extension G- G for the other end section 22b of that vane 20.

[0060] In a plane perpendicular to the longitudinal axis A-A, the two vane end sections 22a, 22b are transversely offset along a line that is perpendicular to a radial line extending from the longitudinal axis A-A. One end section 22a is offset in one direction and the other end section 22b is offset in the opposite direction. The two vane end sections 22a, 22b may be offset perpendicular to a radial plane extending halfway between them.

[0061] In preferred embodiments, the planes of extension F-F, G-G for each vane 20 are spaced apart by a distance in the range 2mm to 12mm. As a result, the intersection of the centroidal planes of the two vane end sections 22a, 22b with the base are transversely offset about the longitudinal axis of the main body by a distance in the range 2mm to 6mm.

[0062] As can be seen in Figure 2, each vane comprises a longitudinally-extending crest 29, and two longitudinally-extending sides 28a, 28b.

[0063] The longitudinally-extending sides 28a, 28b of the vane end sections 20 preferably meet the main body 30 with a radius of curvature of no less than 1 mm to 6mm.

[0064] As can be seen in Figure 1 , when viewed in plan view (i.e., looking down on the crest 29), the vane end sections 22a, 22b are tapered such that they narrow in width (measured in the circumferential direction C-C) from the mid-section 24 to their terminal ends 20a, 20b.

[0065] In particular, each vane 20 narrows in the end sections 22a, 22b such that the distance between the its two longitudinally-extending sides 28a, 28b of that vane 20 reduces towards the respective terminal end 20a, 20b.

[0066] Also, in a plan view of the crest of each vane 20, a respective line of extension D-D, E-E extending in parallel to the longitudinal axis A-A but offset therefrom, extends within each end section 22a, 22b from its terminal end to where it meets the mid-section 24.

[0067] In other words, in plan view, a respective line of extension D-D, E-E extending in parallel to the longitudinal axis A-A but offset therefrom, extends between the two longitudinally- extending sides 28a, 28b over the longitudinal length of the end section 22a, 22b. As will be apparent, the lines of extension D-D and E-E are the plan view of the planes of extension F-F and G-G.

[0068] In each end sections 22a, 22b, the two longitudinally-extending sides 28a, 28b are angled relative to the line of extension D-D, E-E for that end section 22a, 22b. For one end section 22a, one of the longitudinally-extending sides 28a is an outer side, because it is further from the longitudinal axis than the other longitudinally-extending side 28b, which is the inner side. This is reversed at the opposite end of that vane, i.e. for the end section 22b, the longitudinally-extending side 28b is an outer side and the longitudinally-extending side 28a is the inner side.

[0069] For each end section 22a, 22b, the outer side is at a first angle to the line of extension D-D, E-E and the inner side is at a second angle to the line of extension D-D, E-E. The first angle is bigger than the second angle.

[0070] With reference to Figure 3, the example of end section 22b is shown in close up, with the outer side 28b depicted at a first angle, a, to the line of extension D-D and the inner side 28a is at a second angle, p, to the line of extension D-D, E-E. The first angle, a, is bigger than the second angle, p.

[0071] Preferably, the first angle is in the range 0 to 4 degrees. Preferably, the second angle is in the range 2 to 8 degrees.

[0072] The vane end sections 22a, 22b are also preferably tapered such that they reduce in radial height towards their terminal ends 20a, 20b.

[0073] In the end view of Figure 2, the crest 29 of each vane 20 extends over an angular range H of 30 to 70 degrees in the circumferential direction C-C.

[0074] For each vane, in the plan view of Figure 1 , the vane end sections 22a, 22b join the midsection 24 via a radius 23 in the range 100mm to 200mm.

[0075] The maximum thickness of the mid-section 24 of the vanes is between 8mm and 16mm. The maximum thickness being the distance between the two longitudinally-extending sides 28a, 28b. The vane end sections 22a, 22b are narrower than the midsection 24.

[0076] The crest 29 of each vane 20 at the terminal ends 20a, 20b of the vane end sections 22a, 22b form a curve 33 in a side view (perpendicular to a plane extending through the longitudinal axis A-A). Specifically, the terminal ends 20a, 20b are S-shaped in the side view. The S-shape blends the terminal ends 20a 20b into the outer surface 31 of the main body 30.

[0077] Preferably, the terminal ends 20a, 20b define a shoulder that extends to the highest point of the crest 29 via a curved section 33a with a radius of 20mm to 40mm, with the terminal ends 20a, 20b blending into the outer surface 31 of the main body 30 via a curved section 33b with a radius of between 12mm and 26mm.

[0078] Figure 5 shows a cross-sectional view of another embodiment of the sucker rod guide in accordance with the present invention. The embodiment of Figure 5 has a main body 30 comprising an envelope that is different from the embodiment shown in Figures 1 - 4. In particular, the end portions 32a, 32b of the main body 30 each include a ramp portion 38a, 38b. The ramp portions 38a, 38b adjoin a first radiused portion 37a, which first radiused portion adjoins a second radiused portion 39. The first radiused portion 37a is convex, and the second radiused portion 39 is concave. The second radiused portion 39 is connected to the sucker rod 5 by means of a tapered end portion 40. The tapered end portion 40 extends at an angle 0 of 20 - 60 degrees with respect to the longitudinal axis A-A. The second radiused portion 39 can help to reduce wear to the sucker rod 5 close to the sucker rod guide, as a turbulent flow may be guided away from the terminal end of the guide.

[0079] Returning to the preferred embodiment of Figure 2, it can be seen that the individual vanes 20 are spaced around the circumference of the main body 30 such that in an end view they do not overlap.

[0080] In particular, the vanes are spaced around the main body such that they leave a gap therebetween around the perimeter of the main body for providing an unobstructed longitudinal flow path from one end of the main body to the other end.

[0081] Preferably, the main body 30 and vanes 20 collectively form a unitary body. The unitary body may comprise or be formed of polymers and may be reinforced by fibers, such as glass fibers, and / or include other additives. Such a unitary body may be manufactured by injection moulding.

[0082] In some embodiments, each vane 20 extends away from the main body 30 in a mouldrelease direction in common with a radial line extending through the longitudinal axis A-A. In particular, the longitudinal side 28a of the vane end sections 22a, 22b may lie in the plane extending through the longitudinal axis A-A. The mould-release direction defines the direction that a mould for forming at least one of vanes 20 may be moved away from the longitudinal direction without catching on any part of the unitary body.

[0083] For this reason, each vane 20 is preferably no wider in the circumferential direction C-C at its crest 29 than at its base where it meets the main body 30.

[0084] That is, the two longitudinally-extending sides 28a, 28b are either sloped inwards (narrowing away from the base of the vane 20) or parallel in any cross-section perpendicular to the longitudinal axis A-A.

[0085] To minimise the wear of the apparatus 10, it is desirable to maximise the potential area of contact between the crest 29 and the tubing in which the pump rod 5 is to be deployed. As such, it is preferable that for each vane 20, in any cross-section through the apparatus 10, the longitudinally-extending sides 28a, 28b are parallel to the respective mould-release direction for that vane 20. It is preferred that there is a slight inward angle, such as from 85 to less than 90 degrees for removal from a mould, but it is possible in some cases to have a slight outward angle of up to 5 degrees without preventing removal from the mould (as such, the angle is preferably from 85 to 95 degrees).

[0086] There are two commercially available products that provide advantageous sucker rod guides, Helix™ and TenFlow™. In Figure 6, these product are compared with an embodiment of the invention, showing a graph of turbulence kinetic energy (Y-axis) against axial position (X-axis) of the respective apparatus. Examples A and B are TenFlow™ and Helix™, respectively. Example C is an embodiment of the present invention.

[0087] As can be seen, in the graphs corresponding to the prior art guides, there is a significant spike in turbulence at the downstream end of the guide. This spike can lead to the eventual erosion and / or corrosion of the sucker rod.

[0088] The inventors have recognised that the helical shape of the Helix™ guide of the prior art makes it very difficult to form such a guide using injection moulding. This is because, at every point along its length, the vanes of the guide extends away from the longitudinal axis along a different radial direction. As such, a single mould could not be provided to form each vane of the guide without undue complexity.

[0089] As can be seen from Figure 6, the flow results for the embodiment in accordance with the present invention are better than either prior art guide.

[0090] It is possible to manufacture the apparatus 10 by injection moulding, with one mould per vane 20. The mould removal direction for each vane 20 would be the radial direction. Since the vanes 20 all extend away from the main body in the planes of extension F-F and G-G, the radial removal of the mould will not be hindered by the shape of the apparatus 10. In relation with mould removal, it is noted that although preferable for the moulded component to have parallel sides or an inward angle with respect to the direction of removal of the mould, it is possible (depending on material of the component and the material of the mould) to remove moulds from shapes that have a small (up to 5 degree) outward angle with respect to the removal direction, since the mould and moulded component can deform during mould removal.

[0091] Most preferably, the apparatus 10 has exactly four vanes 20 spaced at 90 degree intervals about the longitudinal axis A-A. It is preferable to manufacture this specific apparatus 10 by injection moulding, with just two half-moulds. Each of the half-moulds would form a first vane 20 in its entirety and half a vane 20 on either side of the first vane 20.

[0092] With reference to Figure 1 , if the half-moulds were to meet in the plane through the longitudinal axis A-A and extending perpendicular to the page (with one to the left and the other to the right on the page), the first vane 20 for the upper half of the mould would be the leftmost on the page, and would form the upper half of the vane 20 shown in plan view.

[0093] As can be seen from Figure 1 , although the plane of extension of each end section 22a, 22b is transversely offset from a radial plane through the longitudinal axis A-A, the end sections 22a and 22b preferably overlap the radial plane (the radial plane that is parallel to the plane of extension). In this way, the half-moulds can meet to define therebetween the vanes 20 that lie in the plane in which the two half-moulds meet.

[0094] The following clauses define preferred embodiments of the invention: Clause 1 . Apparatus for centering a sucker rod within tubing, comprising: an elongate main body for engaging the sucker rod, defining a longitudinal axis and a circumferential direction around the longitudinal axis; a plurality of vanes extending along the main body, the vanes spaced apart in the circumferential direction, wherein: the main body defines an outer surface between the vanes; each vane comprises two vane end sections, separated by a vane mid-section; and for each vane, the vane end sections extend generally longitudinally and are rotationally offset from one another in the circumferential direction.

[0095] Clause 2. The apparatus of clause 1 , wherein the vane end sections are tapered such that they narrow in width in the circumferential direction from the mid-section to their terminal ends.

[0096] Clause 3. The apparatus of clause 1 or clause 2, wherein the vane mid-section has the same or a greater width in the circumferential direction than the widest part of the vane end sections.

[0097] Clause 4. The apparatus of any preceding clause, wherein the vane end sections are tapered such that they reduce in radial height towards their terminal ends.

[0098] Clause 5. The apparatus of any preceding clause, wherein each vane extends away from the main body in a direction substantially or exactly perpendicular to a respective plane extending through the longitudinal axis. In particular, the longitudinal axis extends in the respective plane.

[0099] Clause 6. The apparatus of clause 5, wherein: each vane mid-section comprises a longitudinally-extending crest, and two longitudinally-extending sides; and for each vane, the longitudinally-extending sides are in parallel in a cross-section through the longitudinal axis.

[0100] Clause 7. The apparatus of any preceding clause, wherein each vane end section extends away from the main body along a plane of extension that is substantially parallel to and offset from a radial plane extending through the longitudinal axis. Clause 8. The apparatus of any preceding clause, wherein: each vane comprises a longitudinally-extending crest; and each vane is no wider in the circumferential direction at its crest than at its base.

[0101] Clause 9. The apparatus of any preceding clause, wherein: each vane comprises a longitudinally-extending crest, and two longitudinally-extending sides; and the two sides are sloped inwards or parallel in any cross-section perpendicular to the longitudinal axis.

[0102] Clause 10. The apparatus of any preceding clause, wherein the apparatus comprises at least three vanes, preferably at least four vanes.

[0103] Clause 11 . The apparatus of any preceding clause, wherein in cross-section, for each vane, the intersection of the centroidal planes of the two vane end sections with the main body are rotationally offset about the longitudinal axis of the main body by an angle in the range 20 to 65 degrees.

[0104] Clause 12. The apparatus of any preceding clause, wherein in an end view along the longitudinal axis, the crests of the vanes extend over an angular range of 30 to 70 degrees about the longitudinal axis.

[0105] Clause 13. The apparatus of any preceding clause, wherein for each vane, the vane end sections join the mid-section via a radius in the range 100mm to 200mm.

[0106] Clause 14. The apparatus of any preceding clause, wherein the maximum thickness of the mid-section of the vanes is between 8mm and 16mm.

[0107] Clause 15. The apparatus of any preceding clause, wherein each vane comprises a longitudinally-extending crest; and the crest at the terminal ends of the vane end sections are curved in a plane extending through the longitudinal axis.

[0108] Clause 16. The apparatus of any preceding clause, wherein the terminal ends of the vane end sections are S-shaped in a side view, with the terminal ends blending into the outer surface of the main body. Clause 17. The apparatus of any preceding clause, wherein the terminal ends of the vane end sections are S-shaped in a side view to define a shoulder having a radius of 20mm to 40mm, with the terminal ends blending into the outer surface of the main body with a radius of between 12mm and 26mm.

[0109] Clause 18. The apparatus of any preceding clause, wherein the main body comprises two end portions in which the outer surface is radially tapered towards the terminal ends. In particular, the outer surfaces are tapered such to reduce in diameter towards the terminal ends of the main body.

[0110] Clause 19. The apparatus of any preceding clause, wherein the end portions of the main body each include a ramp portions; and the outer surface of the main body is tapered with an angle of 1 to 5 degrees relative to the longitudinal axis in the ramp portions.

[0111] Clause 20. The apparatus of any preceding clause, wherein the terminal ends of the two end portions are tapered with an angle of 30 to 60 degrees relative to the longitudinal axis. In particular, the terminal ends of the two end portions are tapered with an angle of 30 to 60 degrees relative to the longitudinal axis so as to reduce in diameter towards the terminal ends of the end portions.

[0112] Clause 21 . The apparatus of any preceding clause, wherein the terminal ends meet the ramp portions at a radiused portion in a plane passing through the longitudinal axis. In particular, the radiused portion has a radius of between 10mm and 30mm.

[0113] Clause 22. The apparatus of any preceding clause, wherein the terminal ends of the end portions meet the ramp portions at a concave radiused portion. In particular, the concave radiused portion has a radius of 15mm to 30mm. The radiused portion has a radius in a plane extending through the longitudinal axis.

[0114] Clause 23. The apparatus of any preceding clause, wherein the terminal ends of the end portions adjoin the ramp portions via a first radiused portion and a second radiused portion. In particular, the first radiused portion is convex, and the second radiused portion is concave, the second radiused portion being located closer to the terminal end of the main body than the first radiused portion. Clause 24. The apparatus of any preceding clause, wherein the vanes are spaced around the main body such that in an end view of the apparatus along the longitudinal axis they do not overlap with each other.

[0115] Clause 25. The apparatus of any preceding clause, wherein the vanes are spaced around the main body such that in an end view of the apparatus along the longitudinal axis they leave a gap in the circumferential direction.

[0116] Clause 26. The apparatus of any preceding clause, wherein the vanes are spaced around the main body such that they leave a gap therebetween around the perimeter of the main body for providing an unobstructed longitudinal flow path from one end of the main body to the other end.

[0117] Clause 27. The apparatus of any preceding clause, further comprising a sucker rod, wherein the main body is axially and rotationally fixed to the sucker rod.

[0118] Clause 28. The apparatus of any preceding clause, wherein the longitudinally-extending sides of the vane end sections meet the main body with a radius of curvature of no less than 100mm.

[0119] Clause 29. Apparatus for centering a sucker rod within tubing, comprising: an elongate main body for engaging the sucker rod, defining a longitudinal axis, a circumferential direction around the longitudinal axis, and a radial direction perpendicular to the longitudinal axis and the circumferential direction; a plurality of vanes extending along the main body, the vanes spaced apart in the circumferential direction, wherein: the main body defines an outer surface between the vanes; each vane comprises two vane end sections, separated by a vane mid-section; and for each vane, the vane end sections extend from the vane mid-section generally parallel to the longitudinal axis and are rotationally offset from one another in the circumferential direction.

[0120] Clause 30. The apparatus of clause 29, wherein: each vane end section extends away from the main body in a plane of extension that is: substantially parallel to a radial plane extending in the radial direction through the longitudinal axis; and offset along a line perpendicular to the radial plane.

[0121] Clause 31 . The apparatus of any preceding clause, wherein, for each vane: the vane mid-section extends helically around the longitudinal axis; and the two vane end sections extend at an angle to the vane mid-section.

[0122] The terms "a" or "an", as used herein, are defined as one or more than one. The terms multitude or plurality, as used herein, is defined as two or more than two. The term another, as used herein, is defined as at least a second or more. The terms including and / or having, as used herein, are defined as comprising (i.e., open language, not excluding other elements or steps). Any reference signs in the claims should not be construed as limiting the scope of the claims or the invention.

[0123] It will be apparent to those skilled in the art that various modifications can be made to the shown apparatus according to the invention without departing from the scope as defined in the claims.

Claims

CLAIMS1 . Apparatus for centering a sucker rod within tubing, comprising: an elongate main body for engaging the sucker rod, defining a longitudinal axis and a circumferential direction around the longitudinal axis; a plurality of vanes extending along the main body, the vanes spaced apart in the circumferential direction, wherein: the main body defines an outer surface between the vanes; each vane comprises two vane end sections, separated by a vane mid-section; and for each vane, the vane end sections extend generally longitudinally and are rotationally offset from one another in the circumferential direction.

2. The apparatus of claim 1 , wherein the vane end sections are tapered such that they narrow in width in the circumferential direction from the mid-section to their terminal ends.

3. The apparatus of claim 1 or claim 2, wherein the vane mid-section has the same or a greater width in the circumferential direction than the widest part of the vane end sections.

4. The apparatus of any preceding claim, wherein each vane extends away from the main body in a direction substantially perpendicular to a respective plane extending through the longitudinal axis.

5. The apparatus of claim 4, wherein: each vane mid-section comprises a longitudinally-extending crest, and two longitudinally-extending sides; and for each vane, the longitudinally-extending sides are in parallel in a cross-section through the longitudinal axis.

6. The apparatus of any preceding claim, wherein each vane end section extends away from the main body along a plane of extension that is substantially parallel to and offset from a radial plane extending through the longitudinal axis.

7. The apparatus of any preceding claim, wherein: each vane comprises a longitudinally-extending crest; andeach vane is wider, or of equal width, in the circumferential direction at its base than at its crest.

8. The apparatus of any preceding claim, wherein: each vane comprises a longitudinally-extending crest, and two longitudinally- extending sides; and the two sides are sloped inwards or parallel in any cross-section perpendicular to the longitudinal axis.

9. The apparatus of any preceding claim, wherein the apparatus comprises at least three vanes, preferably at least four vanes.

10. The apparatus of any preceding claim, wherein in cross-section, for each vane, the intersection of the centroidal planes of the two vane end sections with the main body are rotationally offset about the longitudinal axis of the main body by an angle in the range 20 to 65 degrees.1 1 . The apparatus of any preceding claim, wherein in an end view along the longitudinal axis, the crests of the vanes extend over an angular range of 30 to 70 degrees about the longitudinal axis.

12. The apparatus of any preceding claim, wherein each vane comprises a longitudinally- extending crest; and the crest at the terminal ends of the vane end sections are curved in a plane extending through the longitudinal axis.

13. The apparatus of any preceding claim, wherein the terminal ends of the vane end sections are S-shaped in a side view, with the terminal ends blending into the outer surface of the main body.

14. The apparatus of any preceding claim, wherein the main body comprises two end portions, and the terminal ends of the two end portions are tapered with an angle of 30 to 60 degrees relative to the longitudinal axis.

15. The apparatus of any preceding claim, wherein the vanes are spaced around the main body such that in an end view of the apparatus along the longitudinal axis they do not overlap with each other.

16. The apparatus of any preceding claim, wherein the vanes are spaced around the main body such that in an end view of the apparatus along the longitudinal axis they leave a gap in the circumferential direction.

17. The apparatus of any preceding claim, wherein the vanes are spaced around the main body such that they leave a gap therebetween around the perimeter of the main body for providing an unobstructed longitudinal flow path from one end of the main body to the other end.

18. The apparatus of any preceding claim, wherein the main body comprises two end portions, the end portions each include a ramp portion; and the outer surface of the main body is tapered with an angle of 1 to 5 degrees relative to the longitudinal axis in the ramp portions.

19. The apparatus of claim 18, wherein the terminal ends of the end portions meet the ramp portions at a concave radiused portion.

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