WO1993018321A1

WO1993018321A1 - Oil well plunger

Info

Publication number: WO1993018321A1
Application number: PCT/US1993/001708
Authority: WO
Inventors: Glen A. Weeks; Gary M. Miller; Stephen B. Ehlers
Original assignee: Seal Lift Corporation
Priority date: 1992-03-03
Filing date: 1993-03-02
Publication date: 1993-09-16

Abstract

An oil well plunger assembly (10) is provided which includes an elongated stem (12) having an upper portion (22) provided with an interiorly threaded bore (24) at an upper end thereof, and a plurality of equally spaced, axially extending flutes (26, 28, 30) defining a corresponding number of flow channels (32, 34, 36) therebetween; a lower coupler component (14) is secured to a lower end of the plurality of flutes. A seal assembly (16) is slidably received over the flutes and supported on the upper end face of the lower coupler (14). The seal assembly (16) includes a plurality of seal rings (52, 54, 56) seated on associated support rings (58), each support ring having a seal ring receiving surface. The seal receiving surface (64) is formed with a plurality of pressure ports (70) communicating the flow channels (32, 34, 36) the pressurization channel (80), and the number of pressure ports exceeds the number of flutes.

Description

OIL WELL PLUNGER

BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to an improved oil well pump or plunger, and specifically, to an improved reciprocating subsurface oil well plunger used to extract crude oil from subsurface oil formations. The plunger travels in a well barrel or cylinder of slightly larger diameter than the plunger and reciprocates in a vertical up and down motion.

Pumps of this type are generally known in the art, and typically include a ball valve assembly attached to the bottom of the plunger which closes on the up stroke of the pump to allow hydrostatic pressure from a column of fluid above the plunger to radially expand a plurality of seal rings supported on the plunger. This action seals off the barrel so that the fluid cannot pass between the plunger and the barrel, thereby causing the column of fluid to be lifted to the surface while drawing more fluid into the reservoir behind it. During the down stroke of the pump, the ball valve opens, relaxing the seal rings and allowing fluid to flow past the plunger. This reciprocating motion repeats itself several times per minute.

In one known construction, a fluted stem receives a plurality of annular seals supported by a radial shoulder of a lower portion of the stem, and held in place by a lock nut threadably received over the^'upper portion of the stem flutes. Fluid pressure from fluid in the flow channels (between the flutes) during the up stroke of the pump causes radial expansion of the seals into contact with the well bore wall or cylinder. Examples subsurface well pump constructions of this general type may be found in U.S. Patent Nos. 4,229,149; 4,395,204; and 4,762,476. Such constructions have not always proven completely satisfactory however.

A disadvantage of one known construction is the incorporation of four fluid channels as defined by four flutes in the stem. This arrangement tends to restrict flow into the plunger, and, because of the relatively few pressure ports by which the fluid is permitted to communicate with the seals, non-uniform pressure and hence non-uniform seal expansion may result. Moreover, a mechanical lock is required to prevent rotation of the seal rings relative to the stem during pumping. This is necessary to insure that the pressure ports maintain alignment with the fluid flow channels between the flutes, i.e., insuring that the pressure ports do not align themselves with the flutes and thereby preclude expansion of the rings.

Another disadvantage lies in the absence of a well defined, relatively large hydraulic pressurization channel on the inside surface of the seal ring, thereby also hindering uniformity of expansion. Another disadvantage lies in the fact that^' a pressure differential between the inside and outside surfaces of the seal ring may not always occur, and absent such a differential, the rings will not radially expand as intended.

Still another disadvantage of conventional pump constructions relates to the compression of the axially aligned seal rings after the locking nut is in place, because the seal ring itself was designed to be "taller", i.e., axially longer, than the underlying support ring surface. Thus, the seal elements themselves are sandwiched together under compression, thereby hindering free expansion and contraction of the seal rings during reciprocatory motion of the pump.

Finally, another disadvantage of prior pump constructions relates to the practice of injection molding the sealing rings, which practice does not lend itself to desired dimensional accuracies, again creating the potential for non-uniform expansion.

The present invention relates to an improved bottom hole or subsurface plunger for well bores which overcomes all of the above mentioned disadvantages of prior pump constructions.

In an exemplary embodiment, the down hole pump or plunger comprises a constant diameter, elongated stem or body which is formed at one end with a cylindrical portion having an internally threaded bore for attachment to a conventional sucker rod

string extending through the working barrel in the usual manner. Below the internally threaded bore area, recessed channels are formed in the stem by three, equally spaced flutes extending axially to the opposite end of the stem. The lowermost ends of the stem flutes are threaded on their exterior surfaces to receive a cylindrical, lower coupler. The lower coupler, in turn, is provided with interior threads at its lowermost end to receive a conventional ball valve assembly. Use of three stem flutes provides greater flow through capability than conventional four-flute designs.

A plurality of annular seal assemblies are slidably received over the stem and seated on the upper end of the coupler, held in place by a lock nut threadably received on the fluted portion of the stem. Each seal assembly includes a support ring and a seal ring element. The support ring includes a cylindrical body portion with a radially outwardly extending flange at one end thereof. The seal ring is received snugly over the support ring body, into abutting relationship with a shoulder provided by the radial flange. The support ring body portion is also provided with a plurality of holes or pressure ports (for example, six) equally spaced about the support ring body, which allow oil flowing through the flute channels to exert pressure against the seal ring elements to thereby radially expand the seal ring elements against the barrel during the up stroke of the plunger. Each seal ring element is formed with an annular channel in its interior surface so as to be in communication with the pressure ports in the

support ring body to thereby insure uniform application of pressure, and hence expansion, of the seal ring.

By combining a three-flute design with six pressure ports, the need for a mechanical lock to prevent the support rings from rotating about the stem during pumping is eliminated since at least one pressure port will always be aligned with a fluid flow channel regardless of support ring rotation. Other configurations are possible, of course, which are nevertheless within the scope of this invention. For example, in the event a four-flute stem is used, eight pressure ports are provided.

The outer annular surface of each support ring radial flange is grooved in order to reduce the fluid pressure on the outside of the seal ring. In other words, in order for the seal ring element to function as intended, it is necessary to have lower pressure on the outer surface of the seal ring element than on the inner surface. As the fluid passes over the groove into a larger area, the pressure is reduced, thereby insuring that the rings will expand due to negative pressure differential between the inner and outer surfaces of the seal ring element.

In another aspect of the invention, the seal ring width is chosen to be slightly less than the length of the underlying body portion of the support ring. This is intended to allow the rings to "float" between adjacent support rings and thereby enhance the radial expansion and contraction movements of the seaJT"ring elements without undue friction when held in place by the lock nut.

Thus, in accordance with an exemplary embodiment of the invention, there is provided an oil well plunger assembly comprising: an elongated stem having an upper portion provided with an interiorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; a lower coupler component secured to a lower end of the plurality of flutes, the coupler having an upper end face; a seal assembly slidably received over the flutes and supported on the upper end face of the lower coupler; and a locking element secured to the flutes above the seal assembly; wherein the seal assembly comprises a plurality of axially adjacent seals, each seal comprising a support ring and a seal ring element, the support ring formed with, a seal ring element receiving surface and a radial flange providing an abutment shoulder for the seal ring element, the radial flange having a radial end face provided with an outwardly facing groove.

In another aspect of the invention, there is provided an oil well plunger assembly comprising: an elongated stem having an upper portion provided with anInteriorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; a lower coupler component secured to a lower end of the plurality of flutes, the coupler having an upper end face; a plurality of seals slidably received over the flutes and supported on the upper end face of the lower coupler, each seal including a support ring and a seal ring supported thereon, each support ring provided with a plurality of pressure ports for communicating the flow channels with a associated seal ring element; wherein the plurality of pressure ports is larger in number than the plurality of flutes.

In still another exemplary embodiment, the invention provides an oil well plunger assembly comprising: an elongated stem having an upper portion provided with an interiorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; a lower coupler component secured to a lower end of the plurality of flutes, the coupler having an upper end face; a seal assembly slidably received over the flutes and supported on the upper end face of the lower coupler, the seal assembly comprising a plurality of seal rings seated on associated support rings, each support ring having a seal ring receiving surface; and a locking element secured to the flutes above the seal assembly for retaining the seal assembly on the stem; wherein the seal element receiving surface has an axial length greater than a corresponding axial leηgth of the seal ring.

The above described invention overcomes the above described problems with conventional subsurface pumps, while significantly increasing pump reliability and efficiency. 8

^"Other objects and advantages of the present invention will become apparent from the detailed description which follows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGURE 1 is a perspective view of an exemplary plunger in accordance with the present invention;

FIGURE 2 is a side section view of the plunger illustrated in Figure 1;

FIGURE 3 is a side view of an elongated stem portion of the plunger illustrated in Figures 1 and 2;

FIGURE 4 is a bottom plan view of the elongated stem illustrated in Figure 3;

FIGURE 5 is a side sectional view of a lower coupling portion of the plunger illustrated in Figures 1 and 2;

FIGURE 6 is a side section view of a seal support ring of the type employed in the plunger construction illustrated in Figures 1 and 2;

^*" FIGURE 7 is a top plan view of the support ring illustrated in Figure 6;

FIGURE 8 is a side section view of a seal ring element of the type shown in the plunger construction illustrated in Figures 1 and 2; "-FIGURE 9 is an enlarged cross sectional view of the seal ring element illustrated in Figure 8;

FIGURE 10 is a side sectional view of a lock nut of the type used in the plunger construction illustrated in Figures 1 and 2; and

FIGURE 11 is a top plan view of the lock nut illustrated in Figure 10.

DETAILED DESCRIPTION OF THE DRAWINGS

Referring to Figure 1, the improved plunger of this invention is shown at 10, and generally includes an elongated stem component 12, a lower coupler 14 threadably secured to the lower end of the stem 12, and a seal assembly 16 comprising a plurality of annular seals (three in the exemplary embodiment) supported on an upper end face 18 of the coupler 14, and held in place by a lock nut 20 which is threadably secured to the stem 12.

With additional reference to Figures 2-4, the elongated stem 12 is generally cylindrical in shape and includes an upper portion 22 which is formed with an interior threaded bore 24 by which the stem may be attached to the lowermost sucker rod of a sucker string in the usual manner.

Below the upper end portion 22, the stem is formed with three equally spaced axially extending flutes 26, 28 and 30 which form therebetween three flow channels 32, 34 and 36. At the lowermost end of the fluted portion, each flute 26, 28 and 30 is formed with an exteriorly threaded section 38 by which the lower coupler 14 is threadably secured to the stem. In addition, intermediate portions of the respective flutes 26, 28 and 30 are also threaded as at 40 so as to enable the lock nut 20 to be secured to the stem. Between the threaded portions 38 and 40, there is a smooth axially extending surface 42 on each of the flutes, which surfaces slidably receive the individual seals of seal ring assembly 16. As best seen in Figure 3, the seal supporting surfaces 42 of the flutes have an outside diameter slightly greater than the diameter of the elongated stem in that portion above the intermediate threaded portions 40..

With reference now to Figures 1, 2 and 5, the lower coupler 14 is generally cylindrical in shape, the exterior surface of which is substantially smooth. The interior surface 44 of the coupler is provided at its upper end with an interiorly threaded portion 46 and at its lower end with a similar interiorly threaded portion 48. These threaded portions are separated by a reduced diameter smooth bore portion 50. The upper threaded portion 46 enables the lower coupler to be secured to the lower threaded portion 38 of the elongated stem 14, while the lower threaded portion 48 is adapted to receive a ball valve assembly (not shown) which those skilled in the art will appreciate may be any one of several commercially available ball valve assemblies. As such, the ball valve assembly per se forms no part of 11

this.invention and need not be described further herein.

With reference now to Figures 1, 2 and 6-9, the seal assembly 16 will be described in detail. As indicated above, in the exemplary embodiment, three annular seals 52, 54 and 56 are slidably received over the elongated stem 12 supported by the upper end face 18 of the lower coupler 14, and the smooth external surfaces 42 of flutes 26, 28 and 30. The annular seals 52, 54 and 56 are identical and, therefore, only one need be described in detail. Thus, for example, seal 52 comprises an annular support ring 58 and an annular seal ring element 60. The support ring 58, best seen in Figures 6 and 7, has a generally cylindrical shape with a smooth bore inner surface 62 of constant diameter. The outer surface of the support ring includes a first cylindrical portion 64 and an enlarged diameter portion which forms a radially outwardly extending flange 66 which provides an abutment shoulder 68 against which the seal ring element 60 abuts as will be described in further detail below.

The support ring 58 is provided with a plurality of pressure ports 70 (six preferred for a three flute stem, eight for a four flute stem), equally spaced aboμt the circumference of the support ring and axially, located so as to be substantially centered relative to the interior surface of the seal ring element as also described below. The end face 72 of the.radial flange 64 is formed with an annular groove 74 which, as noted above, and as further described below, causes a pressure differential between the inner and outer surfaces of the seal ring element 60 during pumping.

Figures 8 and 9 illustrate the annular seal ring element 60, the element having an annular shape and formed with a smooth exterior surface 76 and a grooved interior surface 78. More specifically, the interior surface is machined to provide a groove or pressurization channel 80 centered between the ends of the seal element. The seal element 60 may be constructed of a suitable thermoplastic material such as Arlon 1000™ or other suitable material which can be machined to very close tolerances thereby allowing the pressurization channel 80 to be precisely formed so that uniform expansion of the seal ring element 60 during pumping is insured. As indicated earlier, the pressure ports 70 formed in the support ring 58 will be centered relative to, and in fluid communication with, the pressurization channel 80 when the seal ring element 60 is press fit onto the support ring 58, with the end of the seal element engaged with the abutment shoulder 68 of the support ring 58.

It is to be noted further that the width (or axial length) of the cylindrical support portion 62 of the support ring 58 is slightly greater (for example, 0.505 + .002 inch) than the width (or axial length) of the seal ring element 60 (for example, 0.500 - .002 inch) so that when the seals 52, 54 and 56 of the seal assembly 16 are mounted in place on the elongated stem 12 and held there by the lock nut 20, the individual seal ring elements 60 will not be 13

tightly compressed between adjacent support ring radial flanges, ^'thereby permitting the seal ring elements 60 to radially expand and contract during pumping without substantial frictional interference.

Turning now to Figures 10 and 11, the lock nut 20 is also of substantially cylindrical shape having a generally smooth exterior surface 82, formed with opposed flats 84 which provide suitable tool engaging surfaces for tightening and loosening the lock nut. The interior surface of the lock nut 20 is threaded as shown at 86 thereby enabling the lock nut to be secured to the elongated stem 12 via threaded portions 40 on the flutes 26, 28 and 30.

After the lower coupler 14 has been secured to the elongated stem 12, the individual seals 52, 54 and 56 (each comprising a support ring 58 and seal ring element 60) are slidably received over the elongated stem (with the radial flange portion 66 of each support ring 58 facing upwardly), the seal assembly resting on the upper end face 18 of the lower coupler 14. It will be appreciated that the diameter of the flute surfaces 42 is closely matched to the interior diameter of the support rings 58 to permit sliding motion therebetween, but without any substantial play. For example, for a plunger intended for use with a 2.75 inch diameter well cylinder or barrel, the inner diameter of the support rings 58 may be 2.312 + .002 inches, while the diameter of the elongated stem 12 along the. support surfaces 42 may be 2.284 - .0094 inch. Further in this regard, the outer diameter of the lower coupler, 14

the.outer diameter of the seal ring elements, and the radial flange portion of the seal support rings may be 2.747 - .002 inches.

Dimensions for plunger components to be used with different well bore diameters, e.g., 2.0 or 2.5 inches, are adjusted accordingly.

In use, and during an upward pumping stroke, the ball valve is closed and hydrostatic pressure from the column of fluid above the ball valve and within the flow channels 32, 34 and 36, will be transmitted through the pressure ports 70 to the pressurization channels 80 of the respective seal ring elements 60, causing radially outward expansion of the individual seal ring elements 60 to thereby seal off the barrel so that no fluid is able to pass between the plunger and the barrel. As a result, the column of fluid is lifted to the surface while drawing more fluid into the cylinder or barrel behind it. During the down stroke, the ball valve will open, relaxing the seal ring elements 60 and allowing fluid to flow past the plunger between the plunger and the barrel.

During the initial upward movement, fluid will pass over the grooves 74 formed in the annular flanges 64 of the support rings 56, thus causing a decrease in the fluid pressure on the exterior surface of the seal ring elements. Because the interior pressure will be higher as a result of the fluid flowing in the pressurization channels 80, the seal ring elements 60 will reliably and uniformly expand as required to seal off the barrel. Further 15

in this regard, the carefully machined pressuri-zation channel 80 permits more uniform distribution of pressure and thus more uniform expansion of the seal ring elements than in prior known constructions.

With regard to materials of construction, the elongated stem 12, lower coupler 14, lock nut 20, and support rings 58 are preferably formed of a hardenable steel material, for example, 4140 steel alloy bar stock. This material is significantly stronger than the conventionally used aluminum bronze material, and thus allows cross sectional area reductions which further improve fluid flow capacity. In addition, the hardenable steel material (selected to have a Rockwell C-hardness of 40 or greater) is better suited to the extremely abrasive environment in which the plunger is used.

Preliminary testing of the above described exemplary embodiment of the invention has resulted in no failures due to base metal errosion as a result of the abrasive fluid, while increases in production ranging from 10 to 30% have been realized. Seal ring elements have exhibited uniform wear characteristics and have reliably functioned in their intended manner.

While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements.,included within the spirit and scope of the appended claims.

Claims

WHAT-IS CLAIMED IS:

1. An oil well plunger assembly comprising: an elongated stem having an upper portion provided with an interiorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; a lower coupler component secured to a lower end of the plurality of flutes, said coupler having an upper end face; a seal assembly slidably received over said flutes and supported on said upper end face of said lower coupler; and a locking element secured to said flutes above said seal assembly; wherein said seal assembly comprises a plurality of axially adjacent seals, each seal comprising a support ring and a seal ring element, said support ring formed with a seal ring element receiving surface and a radial flange providing an abutment shoulder for said seal ring element, said radial flange having a radial end face provided with an outwardly facing groove.

2. The assembly of claim 1 wherein said seal ring element receiving surface has an axial length greater than a corresponding axial length of said seal ring element.

3. The assembly of claim 1 wherein»said seal ring element is formed with an annular pressurization channel on an interior surface thereof, and said seal element receiving surface is formed with a plurality of pressure ports communicating said flow channels and said pressurization channel.

4. The assembly of claim 1 wherein said plurality of flutes comprises three.

5. The assembly of claim 1 wherein said elongated stem, lower coupler and support rings are constructed of hardenable steel.

6. The assembly of claim 5 wherein said hardenable steel comprises 4140 steel alloy.

7. The assembly of claim 1 wherein said seal elements are constructed of a thermoplastic material.

8. The assembly of claim 2, wherein said seal ring element is formed with an annular pressurization channel on an interior surface thereof, and said seal element receiving surface is formed with a plurality of pressure ports communicating said flow channels and said pressurization channel.

9. The assembly of claim 3 wherein the number of pressure ports exceeds the number of flutes.

..

10. An oil well plunger assembly comprising: an elongated stem having an upper portion provided with an interiorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; 19

--a lower coupler component secured to a lower end of the plurality of flutes, said coupler having an upper end face; a plurality of seals slidably received over said flutes and supported on said upper end face of said lower coupler, each seal including a support ring and a seal ring supported thereon, each support ring provided with a plurality of pressure ports for communicating said flow channels with an associated seal ring element; wherein said plurality of pressure ports is larger in number than said plurality of flutes.

11. The assembly of claim 10 wherein said support ring includes a seal ring receiving surface which has an axial length greater than a corresponding axial length of said seal ring.

12. The assembly of claim 10 wherein said plurality of flutes comprises three, and said plurality of pressure ports comprises six.

13. The assembly of claim 10 wherein said plurality of flutes comprises four, and said plurality of pressure ports comprises eight.

14. The assembly of claim 10 wherein said elongated stem, lower coupler and support rings are constructed of hardenable steel.

15. The assembly of claim 10 wherein said hardenable steel comprises 4140 steel alloy bar stock. 20

^'16. The assembly pf claim 10 wherein said seal ring is formed with an annular pressurization channel on an interior surface thereof communicating with said flow channels by means of said pressure ports.

17. An oil well plunger assembly comprising: an elongated stem having an upper portion provided with an interiorly threaded bore at an upper end thereof, and a plurality of equally spaced, axially extending flutes defining a corresponding number of flow channels therebetween; a lower coupler component secured to a lower end of the plurality of flutes, said coupler having an upper end face; a seal assembly slidably received over said flutes and supported on said upper end face of said lower coupler, said seal assembly comprising a plurality of seal rings seated on associated support rings, each support ring having a seal ring receiving surface; and a locking element secured to said flutes above said seal assembly for retaining said seal assembly on said stem; wherein said seal element receiving surface has an axial length greater than a corresponding axial length of said seal ring.

^** 18. The assembly of claim 17 wherein said seal ring is formed with an annular pressurization channel on an interior surface thereof, and said seal receiving surface is formed with a plurality of pressure ports communicating said flow channels and said pressurization channel. 21

'19. The seal assembly of claim 18 wherein the number of pressure ports exceeds the number of flutes.

20. The assembly of claim 19 wherein each of said support rings is also formed with a radially outwardly directed flange including a radial end face provided with an outwardly facing groove.