Compensating Mechanical Seal For Use With A Downhole Electrical Submersible Pump

Abstract

An electrical submersible pumping system having a pump, a motor, a shaft connecting the pump and motor, and a mechanical seal assembly on the shaft. The mechanical seal assembly includes a sleeve circumscribing the shaft that is axially movable with respect to the shaft. The shaft is retained within a guide mount, an inner circumference of the guide mount extends radially outward to define a shoulder. An annular seat is disposed on the shoulder. One end of a resilient retention assembly couples on the outer surface of the sleeve with its other end compressively urged against the seat. A resilient member is compressively mounted on one end to the sleeve and on another end to the shaft at a location past the end of the sleeve distal from the seat.

Description

BACKGROUND

1. Field of Invention

The present disclosure relates in general to submersible well pumps, and in particular to a seal assembly used in combination with a shaft used to drive submersible well pumps.

2. Background of the Invention

In oil wells and other similar applications in which the production of fluids is desired, a variety of fluid lifting systems have been used to pump the fluids to surface holding and processing facilities. It is common to employ various types of downhole pumping systems to pump the subterranean formation fluids to surface collection equipment for transport to processing locations. One such conventional pumping system is a submersible pumping assembly which is immersed in the fluids in the wellbore. The submersible pumping assembly includes a pump and a motor to drive the pump to pressurize and pass the fluid through production tubing to a surface location. A typical electric submersible pump assembly (“ESP”) includes a submersible pump, an electric motor and a seal section interdisposed between the pump and the motor.

Shown in a side sectional view in FIG. 1, is a portion of a prior art electrical submersible pumping assembly (ESP) 5 with a seal assembly 11 for sealing around a pump shaft 9. In this example the shaft 9 extends through adjacent sections of the ESP 5. An annular guide 6 is shown coaxially disposed within a housing 7 for supporting the shaft 9 within the ESP 5. A bore 8 through the guide 6 provides for insertion of the shaft 9. Adjacent where the shaft 9 passes through the bore 8 is a circular groove having a bushing assembly 10 that circumscribes and supports the shaft 9.

The seal assembly 11 is set adjacent the bushing assembly 10 and mounted within the guide 6. The seal assembly 11 is made up of an annular seat 12 shown pressed against a shoulder formed in the bore 8. An O-ring 13 circumscribes the outer diameter surface of the seat 12 to provide a sealing surface between the seat 12 and the bore 8. An annular disk like runner 14 is shown urged against a side surface of the seat 12 and pushing the seat 12 into the shoulder in the bore 8. The runner 14 is mounted on the upper lateral surface of an annular bellows 15, where the bellows 15 also circumscribes the shaft 16. An O-ring 16 is shown providing a sealing surface between the bellows 15 and the shaft 9. A spring 17 is provided around the shaft 16 on the end of the bellows 15 opposite the runner 14 and is supported by a snap ring 18 set into the shaft 9. The spring 17 is typically pre-stressed so that it maintains an urging force on the bellows 15 and runner 14 to urge the seat 12 against the shoulder for forming a sealing surface between the shoulder and the seat 12. Because the shaft 9 may become heated and elongate; one drawback of this seal assembly 11 is the force of the spring 17 to compress the seat 12 against the shoulder is reduced with elongation of the shaft 9.

SUMMARY OF INVENTION

Disclosed herein is an example of an electrical submersible pumping assembly, having a housing member having a passage, a shaft extending through the passage, an annular member that fits over and rotates with the shaft and that is slidable along the shaft, a seat ring statically mounted to the housing member in the passage and encircling the shaft, a bellows having a first end fixed and sealed to the exterior of the sleeve and a runner on a second end that is urged by the bellows into sliding engagement with the seat ring, and an annular resilient assembly having a first end circumscribing and fixed to the shaft and a second end that urges the second end of the bellows toward the seat ring. The electrical submersible pumping assembly can also include an elastomeric seal between the annular member and the shaft; the annular member can be an elongate sleeve that extends past the first and second ends of the bellows. Axial grooves can be formed in the shaft and annular member, that can be registered, and a key selectively disposable in both the grooves so that the annular member rotates with shaft rotation. The annular resilient assembly can include a coil spring, and the second end of the annular resilient assembly can engage the first end of the bellows. Thermal growth of the shaft can cause the shaft to move along the shaft axis relative to the annular member; where the annular member remains substantially stationary relative to the seat ring. The first end of the resilient assembly can be made up of a collar retained by a snap ring set in the shaft.

Also disclosed herein is an example of an electrical submersible pump assembly disposable within a wellbore that has a motor, a pump coupled to the motor, a shaft coupled to the pump and the motor, the shaft extending through a passage formed in a guide mount, a seat ring encircling the shaft and statically mounted in the guide mount, and a mechanical seal assembly. In one example, the mechanical seal assembly includes a runner coaxial to and having a side compressed against a side of the seat ring opposite the guide mount, a sleeve circumscribing the shaft and axially moveable thereon, an elastomeric seal member between the sleeve and shaft, a bellows circumscribing and coupled to the sleeve and having an end in compressive engagement with a side of the runner opposite the seat ring, and a resilient member compressively mounted on one end to a location on the sleeve and coupled on another end to a location on the shaft past the end of the sleeve distal from the seat, so that when the shaft axially expands compressive engagement of the annular seat is maintained. The bellows can include a retaining ring secured to the sleeve at a point between ends of the bellows. In an embodiment, the sleeve can be circumscribed by the seat ring. In an example embodiment, the end of the resilient member coupled to the shaft is set on a radial flange circumscribing the shaft and abutable with a lower surface of the sleeve, wherein the radius of the shaft increases at a location along the axis of the shaft to define a shoulder, so that when the shaft elongates, the shaft elongates through the sleeve to move the radial flange out of contact with the lower surface of the sleeve and abuts the shoulder against the upper surface of the sleeve. In an embodiment, a slot may be included on the sleeve inner circumference, a cavity formed in the shaft, and a key that is biased radially outward from the shaft and disposable in the cavity and the slot to rotationally couple the shaft and the sleeve. An o-ring seal can be disposed between an outer circumference of the seat and an inner circumference of the guide mount. A groove can be provided along a radius of the inner surface of the sleeve and an elastomeric member may be disposed in the groove. In an example, production tubing may be included having an end coupled to an end of the pump and an opposing end configured for attachment to a wellhead assembly. In another embodiment, an elastomeric seal can be included between the resilient retention member and the sleeve.

Yet further disclosed herein is a method of operating a centrifugal pump assembly having a housing member with a passage. The pump assembly may include a shaft driven by a motor that extends through the passage, a seat ring statically mounted in the housing member and surrounding the shaft, a bellows that rotates with the shaft and has a runner that engages the seat ring. The centrifugal pump assembly of the present method can include, mounting an annular member around the shaft for rotation with the shaft, but such that the shaft is movable along its axis relative to the annular member, connecting the bellows to the annular member on an end opposite the runner, providing a force that biases the annular member toward the seat ring, rotating the shaft, which in turn rotates the annular member and the bellows, and allowing the shaft to grow thermally, which moves portions of the shaft axially relative to the annular member and the bellows. In an embodiment of the method, the end of the bellows opposite the seat ring can remain at a constant distance from the seat ring as the portion of the shaft grows. In an example of the method, the biasing force onto the annular member and seat ring can be maintained as the shaft thermally elongates.

BRIEF DESCRIPTION OF DRAWINGS

Some of the features and benefits of the present invention having been stated, others will become apparent as the description proceeds when taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a side sectional view of an example of a prior art mechanical seal for an ESP.

FIG. 2 is a side schematic view of an example of an ESP in a wellbore.

FIG. 3A is an example of a mechanical seal for an ESP.

FIG. 3B is an example of the mechanical seal of FIG. 3A where the shaft has expanded.

While the subject device and method will be described in connection with the preferred embodiments but not limited thereto. On the contrary, it is intended to cover all alternatives, modifications, and equivalents, as may be included within the spirit and scope of the present disclosure as defined by the appended claims.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

The present invention will now be described more fully hereinafter with reference to the accompanying drawings in which exemplary embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the illustrated embodiments set forth herein; rather, these embodiments are provided so that this disclosure will be through and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout.

Referring now to FIG. 2 a side sectional view example of an electrical submersible pumping system (ESP) 20 is shown disposed in a wellbore 22. In this example the wellbore 22 intersects a subterranean formation 24. The ESP 20 of FIG. 1 includes on its lower end a motor 26, a seal 28 attached to an upper end of the motor 26, and stacked above the seal section 28 is an optional separator 30. The ESP 20 further includes a pump 32 on the end of the separator 30 opposite this seal section 28. Wellbore fluids, shown illustrated by the arrows, enter the ESP 20 via a fluid inlet 34 is shown on the separator 30. After entering the fluid inlet 34 the wellbore fluids may be directed through the separator 30 and into the pump 32. The separator 30 can be used to remove or separate any vapor that may be mixed within the wellbore fluid and then forward the liquid within the fluid to the pump 32 and direct the separated gas or vapor to a bypass around the pump 32. The fluid inlet 34 can be positioned on the pump 32 in embodiments of the ESP 20 not including a separator 30. A shaft 33 for driving the pump 32 is shown in dashed line and coupled between the motor 26 and pump 32. The pump 32 pressurizes the wellbore fluid and directs it into production tubing 36 shown attached to one end of the pump 32. The production tubing 36 extends within the wellbore 22 and terminates at an upper end at a wellbore assembly 38. From the wellbore assembly 38, the produced wellbore fluid can be transmitted for subsequent processing.

Referring now to FIG. 3A, shown in side sectional view is an example of a seal assembly 58 for use with sealing around a shaft of an ESP. The shaft 33 is shown inserted into an axial bore 54 formed through a guide 52. A bushing 56 is schematically represented in the annular space between the shaft 33 and wall of the bore 54. Optionally, the bushing 56 may be two coaxially disposed bushing members, with one of the bushing members coupled and rotatable with the shaft 33, and the other bushing member coupled with and stationary with the guide 52. Optionally, a bearing assembly (not shown), in place of or in addition to the bushing 56, may be used for supporting the shaft 33 within the guide 52.

In the example of the seal assembly 58 of FIG. 3A, an annular seat 60 is shown set within a groove 62 that is formed on the inner wall of the guide 52. Below the bushing 56, the diameter of the bore 54 increases to define the groove 62. An O-ring 64, which may comprise an elastomeric material, is shown set in a groove 66 that is formed on the outer circumference of the seat 60. The O-ring 64 is shown contacting the inner wall of the bore 54 thereby forming a fluid seal between the seat 60 and the bore 54.

Further illustrated in FIG. 3A is a tubular sleeve 68 set over the shaft 33. The sleeve 68 is below a shoulder 69 formed on the outer surface of the shaft 33; the shoulder 69 is defined where the diameter of the shaft 33 decreases. A groove 70 is shown formed on the outer circumference of the shaft 33 along a region circumscribed by the sleeve 68. An O-ring 72 is set within the groove 70 so that fluid seal may be formed between the sleeve 68 and shaft 33. An annular runner 74 is shown set on a lateral side of this seat 60 and below the groove 62. In the embodiment shown, the runner 74 is supported on an upper surface of an annular bellows member 76 that circumscribes the sleeve 68. The bellows 76 shown includes a mid portion having a series of expandable folds and upper and lower annular rings 77, 79. Bellows 76 provides a bias or spring force, forcing the runner 74 against seat 60. The expandable folds of the bellows 76 can be metal or an elastomer. The upper ring 77 is the portion of the bellows 76 shown urging against the runner 74. The lower ring 79 is shown circumscribing a region of the sleeve 68 having a groove 78 along its outer circumference. A threaded screw 80 is shown in cross section inserted radially through the lower ring 79 and having an end projecting within the groove 78. Optionally, more than one screw 80 may be provided through the lower ring 79 at different points along its circumference. A seal (not shown) is provided on the ring 79 inner diameter and between the exterior of sleeve 68. By inserting the screw 80 into the lower ring 79 and into mating engagement with the groove 78, the bellows 76 is axially coupled with the sleeve 68.

A key 82 is illustrated set within a cavity 84 that is formed axially along a portion of the outer surface of the shaft 33. The cavity 84 includes end portions 85 shown extending into the shaft 33 past the middle portion of the cavity 84. In the example of FIG. 3A, the key 82 has a generally U shaped configuration with a crown 88 extending along its midsection between its ends 83. The crown 88 projects past the radius of the shaft 33 and into a slot 90 formed along an inner wall of the sleeve 68. The slot 90 is a narrow groove shown extending substantially parallel with the axis A_x of the shaft 33. The ends 83 are oriented transverse to the midsection and project radially inward within the shaft 33. Springs 86 are shown located around each end 83 of the key 82 and set within the end portions 85 of the cavity 84 that press the key 82 towards the sleeve 68 engaging the crown 88 within the slot 90. Accordingly, as the springs 86 urge the key out from the cavity 84 into the slot 90, portions of the key 82 project into the corresponding slot 90 and cavity 84 thereby coupling the sleeve 68 and shaft 33 for rotational movement.

A coil spring 98 is illustrated depending downward from the bellows 76 and circumscribing the sleeve 68. Supporting the bottom end of the spring 98 is an annular collar 92 having a base portion 93 that projects radially outward from the shaft 33. The collar 92 is supported along the shaft 33 by a snap ring 94 that circumscribes the shaft 33 and set in a groove 96 formed on the outer circumference of the shaft 33.

Referring to FIG. 3B, an example configuration of the seal assembly 58 is illustrated with the shaft 33 elongated relative to guide 52 such as from an increase in temperature. As shown, the lengthening of the shaft 33 causes the shoulder 69 on the outer surface of the shaft 33 to relocate downward and contact the upper end of the sleeve 68. Elongation of the shaft 33 also downwardly moves the snap ring 94, the collar 92, and lower end of the spring 98 in unison with shaft 33. The spring 98, although decompressed by downward movement of the collar 92, still maintains a compressive force against the bellows 76 that is in turn translated to the runner 74. This perpetuates the upward urging force against the seat 68 and maintains a liquid seal around the seat 60. Shaft 33 moves downward relative to sleeve 68, and sleeve 68 remains at the same position relative to guide 52. Additionally, the sleeve 68 is retained to the shaft 33 and rotational movement by the key 82 within the slot 90. Bellows 76 remains the same axial length because the distance from ring 79 to ring 77 remains the same. The spring force provided by the resiliency of bellows 76 remains the same even though shaft 33 has grown in length. The spring 98 can be separate from the bellows 76 and compressible between the base portion 93 and base ring 79 without being attached to the base ring 79. Optionally, the spring 98 can integrated into a modular unit with the bellows 76. For example, the upper end of the spring 98 can couple or attach to the base ring 79 lower surface, or can extend past the lower surface of the base ring 79 and couple within or above the base ring 79.

It is understood that variations may be made in the above without departing from the scope of the invention. While specific embodiments have been shown and described, modifications can be made by one skilled in the art without departing from the spirit or teaching of this invention. The embodiments as described are exemplary only and are not limiting. Many variations and modifications are possible and are within the scope of the invention. Accordingly, the scope of protection is not limited to the embodiments described, but is only limited by the claims that follow, the scope of which shall include all equivalents of the subject matter of the claims.

Claims

1. An electrical submersible pumping assembly, comprising:

a housing member having a passage;

a shaft extending through the passage;

an annular member that fits over and rotates with the shaft and that is slidable along the shaft;

a seat ring statically mounted to the housing member in the passage and encircling the shaft;

a bellows having a first end fixed and sealed to the exterior of the sleeve and a runner on a second end that is urged by the bellows into sliding engagement with the seat ring; and

an annular resilient assembly having a first end circumscribing and fixed to the shaft and a second end that urges the second end of the bellows toward the seat ring.

2. The electrical submersible pumping assembly of claim 1, further comprising an elastomeric seal between the annular member and the shaft and wherein the annular member comprises an elongate sleeve that extends past the first and second ends of the bellows.

3. The electrical submersible pumping assembly of claim 1, further comprising registrable axial grooves respectively in the shaft and in the annular member and a key selectively disposable in both the grooves so that the annular member rotates with shaft rotation.

4. The electrical submersible pumping assembly of claim 1, wherein the annular resilient assembly comprises a coil spring and the second end of the annular resilient assembly engages the first end of the bellows.

5. The electrical submersible pumping assembly of claim 1, wherein thermal growth of the shaft causes the shaft to move along an axis of the shaft relative to the annular member, which remains substantially stationary relative to the seat ring.

6. The electrical submersible pumping assembly of claim 1, wherein the first end of the resilient assembly comprises a collar retained by a snap ring set in the shaft.

7. An electrical submersible pump assembly disposable within a wellbore comprising:

a motor;

a pump coupled to the motor;

a shaft coupled to the pump and the motor and extending through a passage formed in a guide mount;

a seat ring encircling the shaft and statically mounted in the guide mount; and

a mechanical seal assembly comprising: a runner coaxial to and having a side compressed against a side of the seat ring opposite the guide mount, a sleeve circumscribing the shaft and axially moveable thereon, an elastomeric seal member between the sleeve and shaft, a bellows circumscribing and coupled to the sleeve and having an end in compressive engagement with a side of the runner opposite the seat ring, and a resilient member compressively mounted on one end to a location on the sleeve and coupled on another end to a location on the shaft past the end of the sleeve distal from the seat, so that when the shaft axially expands compressive engagement of the annular seat is maintained.

8. The electrical submersible pump assembly of claim 7, wherein the bellows comprises a retaining ring that is secured to the sleeve at a point between ends of the sleeve.

9. The electrical submersible pump assembly of claim 7, wherein the sleeve is circumscribed by the seat ring.

10. The electrical submersible pump assembly of claim 7, wherein the end of the resilient member coupled to the shaft is set on a radial flange circumscribing the shaft and abutable with a lower surface of the sleeve, wherein the radius of the shaft increases at a location along the axis of the shaft to define a shoulder, so that when the shaft elongates, the shaft elongates through the sleeve to move the radial flange out of contact with the lower surface of the sleeve and abuts the shoulder against the upper surface of the sleeve.

11. The electrical submersible pump assembly of claim 7, further comprising a slot on the sleeve inner circumference, a cavity formed in the shaft, and a key that is biased radially outward from the shaft and disposable in the cavity and the slot to rotationally couple the shaft and the sleeve.

12. The electrical submersible pump assembly of claim 7, further comprising an o-ring seal between an outer circumference of the seat and an inner circumference of the guide mount.

13. The electrical submersible pump assembly of claim 7, further comprising a groove provided along a radius of the inner surface of the sleeve and an elastomeric member disposed in the groove.

14. The electrical submersible pump assembly of claim 7, further comprising production tubing having an end coupled to an end of the pump and an opposing end configured for attachment to a wellhead assembly.

15. The electrical submersible pump assembly of claim 7, further comprising an elastomeric seal between the resilient retention member and the sleeve.

16. A method of operating a centrifugal pump assembly having a housing member with a passage, a shaft driven by a motor and extending through the passage, a seat ring statically mounted in the housing member and surrounding the shaft, a bellows that rotates with the shaft and has a runner that engages the seat ring, the improvement comprising:

mounting an annular member around the shaft for rotation with the shaft, but such that the shaft is movable along an axis of the shaft relative to the annular member;

connecting the bellows to the annular member on an end opposite the runner;

providing a force that biases the annular member toward the seat ring;

rotating the shaft, which in turn rotates the annular member and the bellows; and

allowing the shaft to grow thermally, which moves portions of the shaft axially relative to the annular member and the bellows.

17. The method of claim 16, wherein the end of the bellows opposite the seat ring remains at a constant distance from the seat ring as the portion of the shaft grows.

18. The method of claim 16, wherein the biasing force onto the annular member and seat ring is maintained as the shaft thermally elongates.