WO2009120208A1

WO2009120208A1 - Coated cylinder for walking beam compressor

Info

Publication number: WO2009120208A1
Application number: PCT/US2008/058635
Authority: WO
Inventors: Ward S. Merrick
Original assignee: Oil Flow Usa, Inc.
Priority date: 2008-03-27
Filing date: 2008-03-28
Publication date: 2009-10-01
Also published as: US20090246049A1

Abstract

Various methods and device are provided for use in a walking beam compressor used in an oil well pump. In one embodiment, a walking beam compressor assembly is provided having a compressor configured to receive and compress gas. The compressor can be positioned around a piston rod movably disposed therethrough and can include a cylindrical housing having an interior surface that is coated with a self-lubricating composite material. The self-lubricating composite material can be impervious to gas such that it protects the interior surface of the cylindrical housing from corrosion by the gas. In one embodiment, the self-lubricating composite material can be a nickel ceramic composite. The cylindrical housing can be formed of any suitable material known in the art able to withstand pressure and heat within the housing, for example, a metallic material.

Description

COATED CYLINDER FOR WALKING BEAM COMPRESSOR

FIELD OF THE INVENTION The present invention relates to gas compressors to be used with oil wells, and in particular to a housing for use in a walking beam compressor and methods for manufacturing the same.

BACKGROUND OF THE INVENTION A common oil well pumping system includes a walking beam mounted upon a horizontally-axised, transverse pivot at the top of a Samson post. One end of the walking beam is connected to a pump rod and the other end is connected to the crank of a drive motor through a connecting rod. Rotation of the crank causes the walking beam to rock or oscillate in a vertical plane to raise and lower the pump rod. The rod- connected end of the walking beam is provided with the familiar "horse head" to keep the pump rod in alignment with the well axis. The opposite end of the walking beam carries a counterbalance weight to offset the weight of the pump rod and minimize the stress on the motor.

When pumping an oil well, both oil and gas may be produced and the capture of the gas is both profitable and better for the environment. Thus, an oil well pumping system can include a compressor unit mounted between the walking beam and a stationary part of the pumping unit for compressing the natural gas produced during the pumping of the oil. Such a compressor unit is called a walking beam compressor because it is activated by engaging a piston rod coupled to the walking beam. The rocking of the walking beam reciprocates the piston to effect intake and compression strokes. As a compressing mechanism compresses the gas, high pressure and firictional heat are created inside the compressor housing. Traditionally, the compressor housing has been formed from a composite wound fiberglass material that is insensitive to sour gas received into the housing. This fiberglass material, however, is unable to withstand the pressure and frictional heat for extended periods of time without failure, thus requiring frequent replacement of the compressor housing. Accordingly, there is a need for an improved housing for a walking beam compressor that is able to withstand high pressure, heat, and corrosive gas effects to eliminate the need for frequent and costly replacement.

SUMMARY OF THE INVENTION The present invention generally provides a housing for use in a walking beam compressor and methods for manufacturing the same. In one embodiment, a walking beam compressor assembly is provided having a compressor configured to receive and compress gas. The compressor can be positioned around a piston rod movably disposed therethrough and can include a metallic cylindrical housing having an interior surface that is coated with a self-lubricating composite material. The self-lubricating composite material can be impervious to gas such that it protects the interior surface of the metallic cylindrical housing from corrosion by the gas. In one embodiment, the self-lubricating composite material can be a nickel ceramic composite. The metallic cylindrical housing can be formed of any suitable metallic material known in the art able to withstand pressure and frictional heat within the housing, for example, steel and titanium.

The metallic cylindrical housing can have various shapes. In one embodiment, the housing can include proximal and distal cylindrical rims coupled to top and bottom end plates. In an exemplary embodiment, the top and bottom end plates can include circumferential grooves for receiving top and bottom o-rings therein to form a seal within the metallic cylindrical housing.

In certain exemplary embodiments, the coating of the self-lubricating composite material disposed on the interior surface of the metallic cylindrical housing can have a thickness of between about 0.003 inches and 0.006 inches. The coated interior surface of the metallic cylindrical housing can have any inner diameter that is needed in a specific assembly or application. For example, in certain applications the inner diameter can be about 12 inches or about 14 inches. A person skilled in the art will appreciate that the cylinder can have any diameter, large or small, and the coating can have any thickness as needed.

In another embodiment, an oil well pump is provided having a walking beam configured for driving a rod and plunger system to pump oil out of the ground. A piston rod can be mated to the walking beam and can extend vertically therefrom. A compressor can be mounted on the piston rod, which can be configured for reciprocal longitudinal movement within the compressor. The compressor can be configured to receive and compress gas and can have a cylindrical housing defining an interior surface that can have a coating disposed thereon configured to prevent the cylindrical housing from excessive frictional wear and corrosion. In one embodiment, the coating can be a nickel ceramic composite and/or the coating can be self-lubricating. The cylindrical housing can be formed of any suitable material known in the art and able to withstand pressure and heat within the housing, such as a metallic material, e.g., steel or titanium.

In one embodiment, the coating of the self-lubricating composite material disposed on the interior surface of the metallic cylindrical housing can have a thickness of between about 0.003 inches and 0.006 inches. The coated interior surface of the metallic cylindrical housing can have any inner diameter that is needed in a specific assembly or application. For example, the inner diameter can be about 12 inches, 13 inches, and 14 inches. A kit containing housings of various sizes can also be provided. A person skilled in the art will appreciate that the cylinder can have any diameter, large or small, and the coating can have any thickness as needed.

Methods for manufacturing a walking beam compressor are also provided and can include coating an interior surface of a cylindrical casing with a self-lubricating composite material that is impervious to gas. The method can further include truing the coating on the interior surface such the cylindrical casing has a predetermined inner diameter, and coupling the coated cylindrical casing to a walking beam compressor. The self-lubricating composite material can be, for example, a nickel ceramic composite and can protect the interior surface of the metallic cylindrical casing from corrosion.

In one embodiment, the method can include positioning the coated cylindrical casing around a compressing mechanism. Top and bottom end plates can be coupled to top and bottom rims of the cylindrical casing. The method can further include positioning o-rings between the top and bottom end plates and the interior surface of the cylindrical casing to provide a fluid tight seal therebetween. The assembled walking beam compressor can be positioned around a piston rod extending from a walking beam for pumping oil.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which: - A -

FIG. 1 is a side view of an oil well pump, having one embodiment of a compressor coupled thereto;

FIG. 2 is a cross-sectional view of a cylindrical housing of the compressor of

FIG. 1;

FIG. 3A is a perspective transparent view of the cylindrical housing of FIG. 2;

FIG. 3B is a top view of the cylindrical housing of FIG. 3A, having a coating disposed on an interior surface thereof;

FIG. 4A is a photograph of a failed cylindrical housing formed from wound fiberglass;

FIG. 4B is a photograph of another failed cylindrical housing formed from wound fiberglass; and

FIG. 4C is a photograph of another failed cylindrical housing formed from wound fiberglass.

DETAILED DESCRIPTION OF THE INVENTION

Certain exemplary embodiments will now be described to provide an overall understanding of the principles of the structure, function, manufacture, and use of the devices and methods disclosed herein. One or more examples of these embodiments are illustrated in the accompanying drawings. Those skilled in the art will understand that the devices and methods specifically described herein and illustrated in the accompanying drawings are non-limiting exemplary embodiments and that the scope of the present invention is defined solely by the claims. The features illustrated or described in connection with one exemplary embodiment may be combined with the features of other embodiments. Such modifications and variations are intended to be included within the scope of the present invention. The present invention generally provides a housing for use in a walking beam compressor of an oil well pump. In particular, an improved housing for a walking beam compressor is provided having a coating disposed therein that is substantially impervious to gas, thus allowing the housing to be formed from a durable, more wear- resistant material, such as a metallic material. As a result, the housing is less susceptible to failure and can withstand the high pressure and frictional heater generated during operation. The coating can also be lubricating to facilitate movement of a piston through the compressor. In one embodiment, a walking beam compressor assembly is provided having a compressor configured to receive and compress gas. The compressor can be positioned around a piston rod movably disposed therethrough and can include a cylindrical housing having an interior surface that is coated with a self-lubricating composite material. The self-lubricating composite material can be impervious to gas such that it protects the interior surface of the cylindrical housing from corrosion by the gas. The cylindrical housing can be formed of any suitable metallic material known in the art able to withstand pressure and frictional heat within the housing. Exemplary materials include, by way of non-limiting example, steel and/or titanium.

FIG. 1 shows one embodiment of an oil well pump P having a compressor C mounted thereon. As shown, the oil well pump P generally includes a walking beam 10 pivotally mounted to a top of a Samson post 12 by a bearing 11. A horsehead 14 on one end of the walking beam 10 can be connected to a rod 16 for operating a downhole pumping system as is well understood in the oil production industry. A connecting rod 18 can be connected through a linkage 20 to a gear box 22 which drives the pump P. The compressor C can have a piston rod 24 attached at its upper end to a coupling 26 that is pivotally mounted in a bracket 28 and attached to the walking beam 10 by another bracket 30. The compressor C can also have a lower cover plate 34 with a lower support leg 32 coupled thereto and extending therebetween. A bottom portion of the support leg 32 can be pivotally connected to a bracket 38 attached to a leg of the Samson post 12 by a clamp 40. Additional clamps 42 can be provided at each end of clamp 40, as shown, to minimize possible movement of the clamp 40 along the leg of Samson post 12 during the pumping operation. It will be appreciated by those skilled in the art that the lower cover plate 34, and hence the bottom portion of the compressor, can be coupled to any stationary portion of the oil well pump P as needed. For example, the lower cover plate 34 can also be attached to a base 44, if desired. Exemplary oil well pumps and compressors are described in more detail in U.S. Patent No. 6,572,116 of Turiansky, U.S. Patent No. 6,164,935 of Turiansky, and U.S. Patent No. 6,305,918 of Turiansky, incorporated herein by reference in their entireties.

As further shown in FIG. 1, the compressor C can include a cylindrical housing 36 extending between the lower cover plate 34 and an upper cover plate or cap 46. As shown in more detail in FIG. 2, the cap 46 and the lower cover plate 34 can each have a circular shape with smaller diameter portions 25a, 25b that extend into open top and bottom ends of the cylindrical housing 36. The cap 46 and the lower cover plate 34 can also have larger diameter portions such that peripheral flanges 29a, 29b are formed to rest against top and bottom rims 41, 43 of the cylindrical housing 36. The cap 46 can be attached to the cylindrical housing 36 by one or more plurality of bolts 48 spaced about the peripheral flange 29a of the cap 46 and extending through the peripheral flange 29b of lower cover plate 34, as shown. Both the cap 46 and the lower cover plate 34 can also include peripheral recesses 53a, 53b formed in the smaller diameter portions 25a, 25b for receiving o-rings 50, 52 to form a fluid-tight seal between the smaller diameter portions 25a, 25b and the inner surface of cylindrical housing 36. As further shown, the cap 46 can include can include a central bore 55 formed therein for receiving a piston rod 24 that extends into the cylindrical housing. A piston rod seal 90 can be disposed within the central bore 55 and around the piston rod 24 for forming a seal between an interior chamber of the compressor and the piston rod 24. While not shown, it is well understood in the art that the cylindrical housing surrounds a compressing mechanism coupled to the piston rod 24 that is effective to use the longitudinal reciprocal motion of the piston rod 24 to receive and compress gas.

The cylindrical housing 36 is illustrated in more detail in FIG. 3A. The cylindrical housing 36 can have a generally tube-like structure with top and bottom rims 41, 43 that can be configured to mate with the lower cover plate 34 and the cap 46 as described above. The cylindrical housing thus has a sidewall 37 extending between the top and bottom rims 41, 43 and having an exterior surface 47 and an interior surface 45 defining a sidewall thickness t. The sidewall 47 can have any thickness t as needed for structural integrity and strength, and specific thicknesses will be described in more detail below. The tube-like structure allows the cylindrical housing 36 to be positioned concentrically around the piston rod 24.

It is known in the art to form compressor cylindrical housings of the type described herein from a composite wound fiberglass material. This wound fiberglass material, however, is unable to reliably withstand the high pressures inside the compressor chamber. Further, the pressure in combination with the frictional heat caused by the compressing mechanism causes the fiberglass walls to break down and ultimately fail over time. Thus, the cylindrical housing 36 disclosed herein can be formed of any suitable metallic material known in the art, including steel and titanium.

Both steel and titanium are able to withstand the pressure within the compressor without failing. Further, both materials are able to withstand heat much greater than the heat caused by the friction of the compressing mechanism. A person skilled in the art will appreciate that any metallic material known in the art that is able to withstand high pressures, as well as frictional heat, can be used to form the cylindrical housing.

In one embodiment shown in FIG. 3B, the cylindrical housing 36 can have a coating 39 disposed on the interior surface 37 thereof that is effective to protect the cylindrical housing 36 from corrosive effects caused by sour gas or gas containing significant amounts of hydrogen sulfide. The coating 39 can be self- lubricating to reduce friction between the compressing mechanism and the interior surface of the metallic cylindrical housing. Thus, the coating 39 can be formed of any material able to withstand the effects of a corrosive environment while protecting the interior surface 37 of the metallic cylindrical housing 36 from excessive friction and corrosive gas. For example, the coating 39 can be a nickel ceramic composite, such as NCC Coating® manufactured by Nickel Composite Coatings, Inc. The nickel ceramic composite can be layered onto the interior surface 37 of the cylindrical housing 36 to provide an impervious barrier between the gaseous environment inside the compressor and the interior surface of the cylindrical housing. Further, the nickel ceramic composite coating is self-lubricating and able to prevent excessive frictional wear. Thus, the metallic cylindrical housing in combination with the nickel ceramic coating prevents frequent repair and replacement of the cylindrical housing, as was the case with previous cylindrical housings formed of a wound fiberglass material. The cylindrical housing and the layered coating can have any size and thickness needed for a specific assembly and/or application. In general, an inner diameter of the cylindrical housing will be smaller than an outer diameter, defining a sidewall thickness t. The sidewall thickness t can vary depending on the strength and weight requirements of the system as well as the required length. The inner diameter and length of the cylindrical housing need only be large enough to contain the piston and enable the compressing mechanism to effectively compress the gas. The cylindrical housing in combination with the compressing mechanism can be made larger to effectively deal with larger quantities of gas or smaller to deal smaller quantities. Inner and outer diameters and lengths of the cylindrical housing can vary depending on the requirements needed, and a cylindrical housing made to one specific inner and outer diameter and/or length can be changed and adjusted in the field or in the shop as needed. Moreover, a kit of cylinders of differing sizes can be provided for selective use as desired. Further, the coating thickness can vary depending on the application and depending on the concentration of sour gas within a system. The coating can be made thicker and machined down to the required thickness and the interior surface can also be recoated with additional material to increase the thickness of the coating if needed.

In certain non-limiting exemplary embodiments, the cylindrical housing can be formed from steel machined to have an outer diameter of 12.355 inches and an inner, uncoated diameter of 11.998 inches. The inner diameter can receive a layer of coating and then be machined down such that the interior surface with the coating provides for an inner diameter of 12 inches. A cylindrical housing having a 12 inch interior diameter can have a length of 29 inches or a length of 45 inches. In another embodiment, the cylindrical housing can be formed of steel machined to have an outer diameter of 14.355 inches and an inner, uncoated diameter of 13.998 inches. The inner diameter can receive a layer of coating and then be machined down such that the coating provides for an inner diameter of 14 inches. A cylindrical housing having a 14 inch inner diameter can have a length of 45 inches or a length of 57 inches. The coating thickness can be between about 0.003 inches and 0.006 inches, and more preferably between about 0.004 inches and 0.005 inches. The coating can initially be layered with a thickness greater than that required and machined or trued down to the needed inner diameter. The sidewall thickness of the cylindrical housing can be between 0.349 inches and 0.352 inches and more preferably between about 0.350 inches and 0.351 inches. A person skilled in the art will appreciate that these dimensions are only exemplary in nature and the cylindrical housing can have any outer diameter, inner diameter, wall thickness, length, and coating thickness that is needed.

Methods for manufacturing a walking beam compressor are also provided. In one embodiment, an interior surface of a metallic cylindrical housing or casing can be coated with a self-lubricating composite material that is impervious to gas, such as a nickel ceramic composite material. A metallic cylindrical casing can be prepared having an inner diameter greater than that needed in the assembled compressor. The metal can be machined down to receive the coating over the entire interior surface thereof. Once applied, the coating can be machined down or trued such that the metallic cylindrical casing has a predetermined inner diameter, as well as a predetermined coating thickness. The coated metallic cylindrical casing can be coupled to a walking beam compressor such that the cylindrical casing concentrically surrounds a compressing mechanism. As explained above, top and bottom end plates can be coupled to top and bottom rims of the metallic cylindrical casing. Connecting rods can be placed between the top and bottom end plates to secure the plates to the cylindrical housing. In one embodiment, o-rings can be positioned between the top and bottom end plates and the interior surface of the metallic cylindrical casing to provide a fluid tight seal therebetween. The assembled walking beam compressor can be positioned around a piston rod extending from a walking beam to receive and compress gas.

Once assembled, the coated cylindrical housing will have lubrication effective to reduce friction within the chamber and withstand heat created by any remaining friction produced by the piston. Further, the coating with protect the cylinder walls from corrosion or other negative effects from the sour gas within the chamber. The coated cylindrical housing formed from a metallic material will be able to withstand the high pressures within the chamber over long periods of time. All of these advantages will increase the useful life of the compressor as compared to typical walking beam compressors formed from wound fiberglass materials.

FIGS. 3 A -3 C show photographs of compressor cylindrical housings formed of wound fiberglass material that failed in use and were replaced. As can be seen from the pictures, the pressure inside the chamber in combination with heat and friction from the compressing mechanism caused significant damage to both exterior and interior surfaces of the cylindrical housing. In particular, FIG. 3A illustrates an exterior surface of the wound fiberglass cylindrical housing that has failed due to pressure and frictional heat. The picture shows that the wound fiberglass is disintegrating from an interior surface through the wall thickness to the exterior surface. FIGS. 3B and 3C shows the damaged interior surface of the wound fiberglass cylinders. In particular, the break down and failure of the interior wall surface from frictional wear and pressure can be seen in the streaking and the wide gash. As an example of the statistics and rate of failure, out of 131 wound fiberglass compressor cylinders installed in oil well pumps, over 20 cylinders failed to the point of requiring a new cylinder be installed. Each time this occurs, the compressor does not function until the cylinder is replaced and the compressor is rebuilt, costing valuable time and money, as well as wasting gas that is not extracted because of the failure. The failures often occur soon after the woven fiberglass cylinder is installed, sometimes in less than 2 months from the date of installation. Substituting a nickel ceramic coated metallic cylindrical housing, such as those disclosed herein, for the woven fiberglass cylindrical housings prevents this type of failure and allows for prolonged use in the field. The metal cylindrical housing is able to withstand the frictional heat and high pressures associated with conditions in the compressor. The nickel ceramic composite coating is able to protect the interior surface of the metallic cylinder from the corrosive effects of sour gas as well as reduce excessive friction. Thus far, there have been no signs of corrosion or possible failure of a coated metallic cylindrical housing when it is used in place of the wound fiberglass cylinder. Accordingly, a novel cylindrical housing and method of assembling a walking beam compressor has been shown that will prevent the costly and time consuming task of repairing and replacing traditional fiberglass cylinders.

One skilled in the art will appreciate further features and advantages of the invention based on the above-described embodiments. Accordingly, the invention is not to be limited by what has been particularly shown and described, except as indicated by the appended claims. All publications and references cited herein are expressly incorporated herein by reference in their entirety.

Claims

What is claimed is:

1. A walking beam compressor assembly, comprising: a compressor configured to receive and compress gas, the compressor being positioned around a piston rod movably disposed therethrough and including a metallic cylindrical housing having an interior surface that is coated with a self-lubricating composite material that is impervious to gas such that the self-lubricating composite material protects the interior surface of the metallic cylindrical housing from corrosion by the gas.

2. The walking beam compressor assembly of claim 1, wherein the self-lubricating composite material comprises a nickel ceramic composite.

3. The walking beam compressor assembly of claim 1, wherein the metallic cylindrical housing is formed from steel.

4. The walking beam compressor assembly of claim 1, wherein the coating of the self-lubricating composite material disposed on the interior surface of the metallic cylindrical housing has a thickness in the range of about 0.003 inches and 0.006 inches.

5. The walking beam compressor assembly of claim 1, wherein an inner diameter of the coated interior surface of the metallic cylindrical housing is about 12 inches.

6. The walking beam compressor assembly of claim 1, wherein an inner diameter of the coated interior surface of the metallic cylindrical housing is about 14 inches.

7. The walking beam compressor assembly of claim 1, wherein the metallic cylindrical housing includes proximal and distal cylindrical rims coupled to top and bottom end plates.

8. The walking beam compressor assembly of claim 7, wherein the top and bottom end plates include circumferential grooves for receiving top and bottom o-rings therein to form a seal within the metallic cylindrical housing.

9. An oil well pump, comprising: a walking beam configured for driving a rod and plunger system to pump oil out of the ground; a piston rod mated to the walking beam and extending vertically therefrom; and a compressor mounted on the piston rod and having a cylindrical housing defining an interior surface, the interior surface having a coating disposed thereon and configured to prevent the metallic cylindrical housing from excessive frictional wear and corrosion.

10. The oil well pump of claim 9, wherein the coating is a nickel ceramic composite.

11. The oil well pump of claim 9, wherein the coating is a self- lubricating material.

12. The oil well pump of claim 9, wherein the cylindrical housing is metallic.

13. The oil well pump of claim 12, wherein the metallic cylindrical housing is formed from steel.

14. The walking beam compressor assembly of claim 9, wherein the coating of the self-lubricating composite material disposed on the interior surface of the cylindrical housing has a thickness of between about 0.003 inches and 0.006 inches.

15. The walking beam compressor assembly of claim 9, wherein an inner diameter of the coated interior surface of the cylindrical housing is selected from the group consisting of about 12 inches, 13 inches, and 14 inches.

16. The oil well pump of claim 9, wherein the piston rod is configured for reciprocal longitudinal movement within the compressor.

17. The oil well pump of claim 9, wherein the compressor is configured to receive and compress gas.

18. The oil well pump of claim 9, wherein the metallic cylindrical housing includes proximal and distal cylindrical rims coupled to top and bottom end plates.

19. The oil well pump of claim 18, wherein the top and bottom end plates include circumferential grooves for receiving top and bottom o-rings therein to form a seal within the cylindrical housing.

20. A method of manufacturing a walking beam compressor, comprising: coating an interior surface of a cylindrical casing with a self-lubricating composite material that is impervious to gas; truing the coating on the interior surface such the metallic cylindrical casing has a predetermined inner diameter; and coupling the coated metallic cylindrical casing to a walking beam compressor.

21. The method of claim 20, further comprising positioning the coated cylindrical casing around a compressing mechanism.

22. The method of claim 20, further comprising coupling top and bottom end plates to top and bottom rims of the cylindrical casing.

23. The method of claim 22, further comprising positioning o-rings between the top and bottom end plates and the interior surface of the cylindrical casing to provide a gas tight seal therebetween.

24. The method of claim 20, further comprising positioning the assembled walking beam compressor around a piston rod extending from a walking beam.

25. The method of claim 20, wherein the self-lubricating composite material is a nickel ceramic composite that protects the interior surface of the cylindrical casing from corrosion.