DOWNHOLE PUMP SEATING NIPPLE WITH PERFORATIONS

Abstract

A pump seating nipple for retaining a downhole pump assembly in a fixed position within a production tubing string has a generally cylindrical body defining a nipple bore for receiving the downhole pump assembly. The pump seating nipple attaches to the production tubing string. At the bottom end of the body, the nipple bore is open to the bore of the production tubing string. An upper portion of the body surface engages a pump assembly seating cup. The body has a lower skirt which defines openings which allow gas flow from the nipple bore into the casing annulus.

Description

FIELD OF THE INVENTION

The present invention relates to a pump seating nipple for retaining a downhole pump assembly in a production tubing string of an oil and gas well.

BACKGROUND OF THE INVENTION

Reciprocating downhole pump systems are used to elevate production fluids from an oil and gas well to the surface. A typical pump system includes a pump jack or other device at the ground surface that reciprocates an attached sucker rod alternately in upstrokes and downstrokes. The sucker rod is attached at its bottom end to a plunger that reciprocates within a hollow pump barrel of a downhole pump assembly. The plunger includes a travelling valve assembly (e.g., a ball and seat valve or a flapper valve) to regulate the flow of a production fluid from below to above the plunger, while the downhole pump assembly includes a standing valve assembly to regulate the flow of the production fluid into the barrel from the producing perforations of a well. A retaining device is needed to hold the barrel of the downhole pump assembly in a fixed position within the production tubing string as the travelling plunger moves up and down,

On the upstroke of the plunger, the travelling valve closes, so that the plunger lifts a column of production fluid in the pump barrel, upwards in the production string, towards the ground surface. Simultaneously, the standing valve is opened so that the plunger draws additional production fluid from the producing perforations of the well into the pump barrel below the plunger. On the downstroke of the plunger, the standing valve closes to prevent the production fluid below the plunger from flowing back into the production tubing. Simultaneously, the pressure exerted by the production fluid in the pump barrel below the travelling valve forces the traveling valve to open. This allows the production fluid to flow into the pump barrel above the plunger and charges the pump barrel with a new column of production fluid to be lifted on a subsequent upstroke.

The performance of the pump system may be adversely affected by a phenomenon known as “gas locking”, This occurs when gases dissolved in the production fluid breaks out of solution upon entering the relatively lower pressure environment of the wellbore. On the upstroke of the plunger, the gases flow upwards through the open standing valve into the pump barrel between the standing valve and the plunger. On the downstroke of the plunger, the gases are compressed between the closed standing valve and the plunger. On the following upstroke of the plunger, the compressed gas in the pump barrel between the traveling valve and the standing valve expands to fill the enlarged space. As such, the upstrokes and downstrokes of the plunger result in the repeated compression and expansion of trapped gas between the standing valve and the plunger. This interferes with the proper opening of the travelling valve, and the upward flow of production fluid into the barrel below the plunger. An associated problem is “fluid pounding,” which occurs when the space in the pump barrel below the plunger is partially filled with liquid and partially with gas such that the plunger forcefully enters the fluid level part way through the downstroke. This causes undesired vibrations, or “pounding”, through the production tubing string leading to mechanical failure and expedited wear.

Therefore, there is a need in the art for devices to retain a downhole pump assembly within a production tubing string and for devices that may ensure that a traveling valve assembly of a reciprocating downhole pump system opens and closes as intended.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a pump seating nipple for retaining a downhole pump assembly in a fixed position within a production tubing string. The production tubing string defines a production bore and is disposed within a casing string to define a casing annulus therebetween. The downhole pump assembly conventionally comprises a resilient seating cup, The pump seating nipple is insertable in the production tubing string and comprises a substantially cylindrical body having an outer surface, and an inner surface defining an internal nipple bore extending from a top end of the body to a bottom end of the body for receiving the downhole pump assembly at least partially therein. The nipple bore is in fluid communication with the production bore at the bottom end of the body. The body comprises an upper portion where the nipple bore defines a reduced diameter profile to engage the pump assembly seating cup to resist relative movement between the downhole pump assembly and the body and to prevent gas migration between the downhole pump assembly and the pump seating nipple. The pump seating nipple body comprises a lower skirt which has an inside diameter greater than an outside diameter of the pump, and which defines at least one opening extending through the skirt for fluid communication from the nipple bore to the casing annulus.

In one embodiment, the top end defines a top threaded surface for removable attachment of the top end to an upper joint, and the bottom end defines a bottom threaded surface for removable attachment of the bottom end to a lower joint.

In one embodiment, the nipple bore is chamfered at either or both an upper end or lower end of the nipple bore profile.

In one embodiment, the nipple bore profile is cylindrical, having a smaller internal diameter than the lower skirt.

In one embodiment, the at least one opening comprises a plurality of openings, which may be arranged in a plurality of vertical columns circumferentially spaced apart on the skirt.

In another aspect, the present invention comprises a downhole assembly disposed within a casing string. The downhole assembly comprises a production tubing string, a downhole pump assembly, and a pump seating nipple. The production tubing string defines a production bore and is disposed within the casing string to define a casing annulus therebetween. The downhole pump assembly is disposed within the production bore and comprises a barrel with a perforated fitting for fluid communication from the production bore into the barrel, and an attached resilient seating cup. The pump seating nipple is disposed in the production tubing string. The pump seating nipple comprises a substantially cylindrical body comprising an outer surface, and an inner surface defining a nipple bore extending from a top end of the body to a bottom end of the body for receiving the downhole pump at least partially therein. The nipple bore is in fluid communication with the production bore at the bottom end of the body. The body comprises an upper portion that engages the seating cup to resist relative movement between the downhole pump assembly and the body and to prevent gas migration between the downhole pump assembly and the body. The body comprises a lower skirt which defines at least one opening extending from a lower portion of the inner surface to the outer surface for fluid communication from the nipple bore to the casing annulus. In one embodiment, the at least one opening is disposed above the perforated fitting.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described by way of an exemplary embodiment with reference to the accompanying simplified, diagrammatic, not-to-scale drawings. Any dimensions provided in the drawings are provided only for illustrative purposes, and do not limit the invention as defined by the claims. In the drawings:

FIG. 1 is a sectional, elevation view of a reciprocating downhole pump system incorporating one embodiment of the seating nipple of the present invention;

FIG. 2 is an expanded view of the portion of the system shown in FIG. 1 between lines A-A and B-B of FIG. 1;

FIG. 3 is a sectional, elevation view of the embodiment of the pump seating nipple of the present invention shown in FIG. 2; and

FIG. 4 is a photograph showing an external elevation view of an alternative embodiment of the pump seating nipple of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a pump seating nipple for retaining a downhole pump assembly in a production tubing string. When describing the present invention, all terms not defined herein have their common art-recognized meanings. To the extent that the following description is of a specific embodiment or a particular use of the invention, it is intended to be illustrative only, and not limiting of the claimed invention. The following description is intended to cover all alternatives, modifications and equivalents that are included in the spirit and scope of the invention, as defined in the appended claims.

FIGS. 1 and 2 show an embodiment of a reciprocating downhole pump system 100 incorporating one embodiment of the pump seating nipple 10 of the present invention. The pump system 100 includes production tubing string 102 defining a production bore 103. The production tubing string 102 is positioned inside the casing string 104 of a well bore, to define a casing annulus 105 therebetween, The pump seating nipple 10 forms part of the production tubing string 102 between an upper joint 106 and a lower joint 108. In the embodiment shown in FIGS. 1 and 2, the lower joint 108 is a tail joint terminating near the perforated zone of a formation that produces production fluid F. A packer 110 seals the casing annulus 105 to prevent upward flow of the production fluid F, thus diverting the production fluid F to flow upwards into the production tubing string 102.

A downhole pump assembly disposed within the production tubing string 102 includes a barrel 114 with a perforated fitting 112 and a standing valve assembly (not shown) that regulates the flow of production fluid F into the barrel 114. A motor 118 at the ground surface is attached to a sucker rod 120, which is in turn attached to the top end of a travelling plunger 122 having an internal travelling valve assembly (not shown), As the travelling plunger 122 moves alternately in upstrokes and downstrokes within the barrel 114, the standing valve assembly and travelling valve assembly open and close in a coordinated manner so that the travelling plunger 122 lifts production fluid F through the standing valve into the barrel 114, and up through the barrel 114 and the production tubing string 102 towards the ground surface.

While the plunger 122 reciprocates up and down within the barrel 114, the pump seating nipple 10 holds the downhole pump assembly in a fixed position within the production tubing string 102. In the embodiment shown in FIGS. 1 and 2, the downhole pump assembly has three externally attached annular seating cups 116a, 116b, 116c. Seating cups 116 suitable for use with pump seating nipples are known in the art and are commercially available. The seating cups 116 have an external diameter that is larger than the external diameter of the remainder of the downhole pump assembly, so that only the seating cups 116 contact an internal surface of the pump seating nipple 10 when the downhole pump assembly is positioned in the production tubing string 102. The seating cups 116 are made of a resilient material and thus bias themselves into sealing engagement with the surrounding inner surface of the pump seating nipple 10. Friction between the seating cups 116 and the inner surface of the pump seating nipple 10 are sufficient to resist the tendency of the downhole pump assembly to move vertically in response to forces imparted by the movement of the travelling plunger 122.

FIG. 3 shows a cross-sectional view of one embodiment of the pump seating nipple 10 of the present invention in greater detail. The pump seating nipple 10 may be made of any suitably hard and durable material for use in a downhole environment such as, without limitation, a stainless steel alloy.

In general, the pump seating nipple 10 comprises a substantially cylindrical body. The body has a top end 12 that attaches to the upper joint 106 of the production tubing string 102, and a bottom end 14 that attaches to the lower joint 108 of the production tubing string 102. The attachment of the body to the upper joint 106 and the lower joint 108 may be either direct or indirect, and either permanent or removable. In one embodiment as shown in FIG. 3, each of the top end 12 and the bottom end 14 define a threaded surface for a direct removable connection to a compatible threaded connection formed on the upper joint 106 and the lower joint 108, respectively. In embodiments (not shown), the threaded surfaces of the top end 12 and the bottom end 14 may be formed on either a pin-style or box-style connection, wherein an external shoulder of the top end 12 and the bottom end 14 sealingly abuts an external shoulder of the upper joint 106 and the lower joint 108, respectively. In embodiments (not shown), the body may be attached to the upper joint 106 or the lower joint 108 by threaded collars.

The pump seating nipple 10 has an outer surface 16 and an inner surface 18. The outer surface 16 is exposed to the casing annulus 105. The inner surface 18 defines a nipple bore 20 extending from the top end 12 to the bottom end 14 that receives at least part of the downhole pump assembly. In one embodiment as shown in FIGS. 1 and 2, the nipple bore 20 permits through passage of the downhole pump assembly upon application of a downward force to the downhole pump assembly sufficient to overcome the friction between the seating cups 116 and the inner surface 18 of the body.

The body (10) has an upper portion 22 that defines an upper portion 24 of the nipple bore 20, and a lower skirt portion 26 that defines a lower portion 28 of the nipple bore 20. The upper portion 24 of the nipple bore 20 has an internal diameter less than an external diameter of the seating cups 116 attached of the downhole pump assembly so that the resilient seating cups 116 can be forcibly pushed into the nipple bore 20, and expand to engage the upper portion 22 of the inner surface 18.

The lower skirt 26 of the body has an inside diameter which is greater than the outside diameter of the pump assembly, and which defines at least one, and preferably a plurality of openings 30 that extend through to the outer surface 16, providing fluid communication to the casing annulus. The openings 30 permit gas to escape from the nipple bore 20 into the casing annulus 105. Although the shape and configuration of the openings is not an essential aspect, in one embodiment as shown in FIG. 3, the openings 30 have a rectangular shape and are arranged in four vertical columns of four openings 30, with the columns spaced circumferentially around the body at an angular separation of ninety degrees from each other. In an alternative embodiment as shown in FIG. 4, the openings 30 have a circular shape and are arranged in four vertical columns of five openings 30, with the columns spaced circumferentially around the body at an angular separation of ninety degrees from each other. In other embodiments (not shown), the shape, number and arrangement of the openings 30 may be different. The effective total opening size may be varied by varying the number and size of the openings.

In one embodiment as shown in FIG. 3, the lower skirt 28 of the nipple bore 20 has an internal diameter greater than the internal diameter of the upper portion 24 of the nipple bore 20. The enlarged diameter of the lower portion 28 of the nipple bore 20 relative to the upper portion 24 of the nipple bore 20 allows the inner diameter of the upper portion 24 of the nipple bore 20 be within very close tolerances (e.g., fractions of an inch) of the external diameter of the seating cups (116), which is only slightly larger (e.g., fractions of an inch) than the external diameter of the barrel 114, while still allowing for upward flow of gases within the lower skirt 28 of the nipple bore 20.

In one embodiment as shown in FIG. 3, the body defines an upper chamfer 32 between the top end 12 of the body and the upper portion 22 of the inner surface 18. Similarly, the body defines a lower chamfer 34 between the upper portion 22 of the inner surface 18 and the lower skirt 26 of the inner surface 18. The chamfers 32, 34 facilitate downward and upward passage, respectively, of the downhole pump assembly into the nipple bore 20.

The use and operation of the embodiment of the pump seating nipple 10 shown in FIGS. 1-3 is now described. During the completion of the wellbore, the pump seating nipple 10 is attached the lower joint 108 and the upper joint 106 of the production tubing string 102 and lowered into the casing string 104. After the production tubing string 102 has been secured within the casing string 104, the downhole pump assembly is lowered into the production tubing string 102. When the downhole pump assembly reaches the depth of the pump seating nipple 10, it is forcibly pushed downwards against the pump seating nipple 10. The resilient seating cups 116 attached to the downhole pump assembly are thereby guided and compressed by the upper chamfer 32 into the nipple bore 20. The seating cups (116), by virtue of being compressed by the upper portion 22 of the inner surface 18, bias outwardly into sealing engagement with the upper portion 22 of the inner surface 18. Friction between the inner surface 18 and the seating cups 116 resist relative vertical movement between the downhole pump assembly and the pump seating nipple 10, thereby holding the downhole pump assembly in a fixed position despite forces imparted by the movement of the plunger 122. In one embodiment, when the downhole pump assembly is fixed in position by the pump seating nipple 10, the openings 30 are positioned above the perforated fitting 112 of the barrel 114.

In the event that any of the seating cups 116 is advanced below the upper portion 24 of the nipple bore 20, upon upward pulling of the downhole pump assembly, the seating cups 116 will be guided and compressed by the lower chamfer 34 to facilitate upward movement of the downhole pump assembly into the upper portion 24 of the nipple bore 20.

In use, the elevation of the production fluid F within the production bore 103 is preferably maintained at a level between the perforated fitting 112 of the pump assembly, and the openings 30 of the pump seating nipple 10. As shown by the solid arrow lines in FIG. 2, the production fluid F flows from the perforated zone of the formation into the relatively low pressure environment of the production bore 103. Dissolved gases in the production fluid F may break out of solution in the production bore 103 and rise to the level of the production fluid F within the production bore 103, where they are liberated. The liberated gases flow into the lower skirt 28, where further upward flow is prevented by the sealing relationship between the seating cups, the pump assembly and the upper portion 22 of the inner surface 18. Accordingly, the gases in the lower portion 28 of the nipple bore 20 flow through the openings 30 and into the casing annulus 105, where they may rise freely up towards the ground surface. In this manner, gas pressure which may evolve during pump seating may be relieved. This may encourage the gases to breakout of solution from the production fluid F and thus reduce the amount of dissolved gas that flows into the pump barrel 114 through the standing valve. Accordingly, the pump seating nipple 10 of the present invention may be used to help avoid gas locking phenomenon associated with a downhole reciprocating pump system 100.

As will be apparent to those skilled in the art, various modifications, adaptations and variations of the foregoing specific disclosure can be made without departing from the scope of the invention claimed herein.

Claims

1. A pump seating nipple for retaining a pump assembly in a fixed and sealed position within a production tubing string disposed within a casing string to define a casing annulus therebetween, the pump seating nipple being insertable in the production tubing string and comprising:

a substantially cylindrical body defining a nipple bore extending from a top end of the body to a bottom end of the body, wherein the body comprises an upper portion for receiving the pump assembly at least partially therein and a lower skirt which has an inside diameter larger than the pump assembly and which defines at least one opening extending through the lower skirt for fluid communication from the nipple bore to the casing annulus.

2. The pump seating nipple of claim 1 wherein the top end defines a top threaded surface for removable attachment of the top end to the upper joint, and the bottom end defines a bottom threaded surface for removable attachment of the bottom end to the lower joint.

3. The pump seating nipple of claim 1 wherein the body defines a chamfer between the top end of the body and an upper portion of an inner surface.

4. The pump seating nipple of claim 1 wherein the lower skirt has an internal diameter larger than the internal diameter of the upper portion of the body.

5. The pump seating nipple of claim 4 wherein the body defines a chamfer between the inside diameter of the upper portion and the inside diameter of the lower skirt.

6. The pump seating nipple of claim 1 wherein the at least one opening comprises a plurality of openings arranged in a plurality of columns or rows circumferentially spaced apart on the body.

7. A downhole assembly adapted to be disposed within a casing string and comprising:

(a) a production tubing string defining a production bore and disposed within the casing string to define a casing annulus therebetween;

(b) a downhole pump assembly disposed within the production bore comprising a barrel with a perforated fitting for fluid communication from the production bore into the barrel, and an attached resilient annular seating cup;

(c) a pump seating nipple disposed in the production tubing string, the pump seating nipple comprising a substantially cylindrical body comprising an outer surface, and an inner surface defining a nipple bore extending from a top end of the body to a bottom end of the body for receiving the downhole pump at least partially therein, wherein the nipple bore is in fluid communication with the production bore at the bottom end of the body; wherein the inner surface comprises an upper portion to engage the seating cup to resist relative movement between the downhole pump assembly and the body and to prevent gas migration between the downhole pump assembly and the body; and wherein the body comprises a lower skirt having an inside diameter greater than a pump outside diameter and which defines at least one opening extending from a lower portion of the inner surface to the outer surface for fluid communication from the nipple bore to the casing annulus, wherein the at least one opening is disposed above the perforated fitting.