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Title:
MOTOR COMPENSATOR AND SHAFT SEAL MODULE ARRANGEMENT FOR ELECTRIC SUBMERSIBLE PUMPING SYSTEM
Document Type and Number:
WIPO Patent Application WO/2016/053658
Kind Code:
A1
Abstract:
A system and methodology are provided for improving the usefulness of certain types of motors and pumping systems in wells ranging from horizontal to vertical. The system and methodology facilitate oil volume change compensation while providing multiple shaft seals in an electric submersible pumping system. A compensator is combined with a shaft seal module, and both the compensator and the shaft seal module may be located between a submersible motor and a submersible pump. The compensator is able to balance pressure differentials between an interior of the motor and an exterior of the electric submersible pumping system without breathing through the shaft seal module.

Inventors:
WATSON ARTHUR (US)
Application Number:
PCT/US2015/051139
Publication Date:
April 07, 2016
Filing Date:
September 21, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
SCHLUMBERGER CA LTD (CA)
SCHLUMBERGER SERVICES PETROL (FR)
SCHLUMBERGER HOLDINGS
SCHLUMBERGER TECHNOLOGY BV (NL)
PRAD RES & DEV LTD
SCHLUMBERGER TECHNOLOGY CORP (US)
International Classes:
F04D29/66; F04D13/10; F04D29/10; F04D29/70
Foreign References:
US20100202896A12010-08-12
US20070277969A12007-12-06
US8408304B22013-04-02
US20110123374A12011-05-26
US20080286131A12008-11-20
Attorney, Agent or Firm:
STONEBROOK, Michael et al. (IP Administration Center of ExcellenceRoom 472, Houston Texas, US)
Download PDF:
Claims:
CLAIMS

What is claimed is:

1. A system for use in a well, comprising: an electric submersible pumping system deployed in a well, the electric pumping system comprising a submersible pump and a motor to power the submersible pump via a shaft;

a shaft seal module cooperating with the motor, the shaft seal module having a plurality of seals to seal the shaft; and

a compensator disposed between the shaft seal module and the motor, the compensator cooperating with the motor to compensate for differential pressures between an internal motor oil and an external well fluid by providing a passage directly to the well fluid without extending into the shaft seal module, the shaft seal module and the compensator being located at a common end of the motor such that the functions of sealing the shaft and compensating the motor oil are performed at the common end of the motor.

2. The system as recited in claim 1, wherein the shaft seal module and the

compensator are oriented generally vertically.

3. The system as recited in claim 1, further comprising a thrust section located above the motor to carry thrust loads transferred from the submersible pump.

4. The system as recited in claim 3, wherein the compensator is disposed above the thrust section and comprises a plurality of chambers.

5. The system as recited in claim 1, wherein the compensator comprises a metal bellows.

6. The system as recited in claim 1, wherein the compensator comprises a relief valve.

7. The system as recited in claim 1, wherein the compensator comprises a filter to prevent solids from interfering with operation of the compensator.

8. The system as recited in claim 1, wherein the shaft seal module comprises a

plurality of chambers for the plurality of seals.

9. The system as recited in claim 1, wherein the shaft seal module comprises a rotary filter.

10. A method, comprising : constructing a pumping system with a pump driven by a motor via a shaft; using a shaft seal module between the pump and the motor to provide a plurality of seals along the shaft; and

positioning a compensator between the pump and the motor to provide pressure compensation between an interior of the motor and an exterior of the pumping system independently of the shaft seal module.

11. The method as recited in claim 10, further comprising employing the pumping system downhole into a borehole.

12. The method as recited in claim 11, wherein using comprises providing the

plurality of seals in a plurality of shaft seal module chambers.

13. The method as recited in claim 11, wherein positioning comprises using a bellows to compensate for pressure differentials between an internal motor fluid and a surrounding well fluid.

14. The method as recited in claim 13, further comprising providing a relief flow path between the internal motor fluid and the surrounding well fluid, and locating a relief valve in the relief flow path.

15. The method as recited in claim 11 , further comprising coupling the shaft to a thrust section.

16. A system, comprising: a rotary filter for filtering solids from a fluid, the rotary filter comprising: a plurality of stationary rings; and

a plurality of rotatable rings which mate with the plurality of stationary rings in a non-contacting arrangement, the rotatable rings being rotatable by a shaft to centrifuge the solids into spaces disposed along the plurality of stationary rings.

17. The system as recited in claim 16, wherein the stationary rings are formed of porous carbide.

18. The system as recited in claim 16, wherein the stationary rings are arranged as interlocked stacked rings and the rotatable rings are arranged as interlocked stacked rings, the stationary rings having a compliant mounting.

19. The system as recited in claim 16, wherein the plurality of stationary rings

comprises dirt traps in the form of recesses which trap and hold the solids.

20. The system as recited in claim 16, further comprising an electric submersible pumping system having a motor protector, the rotary filter being disposed within the motor protector.

Description:
PATENT APPLICATION

MOTOR COMPENSATOR AND SHAFT SEAL MODULE ARRANGEMENT FOR ELECTRIC SUBMERSIBLE PUMPING SYSTEM

DOCKET NO.: IS 14.9354- WO-PCT INVENTORS: Arthur Watson

CROSS-REFERENCE TO RELATED APPLICATION

[0001] The present document is based on and claims priority to U.S. Provisional

Application Serial No.: 62/058,812 filed October 2, 2014, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] Electric submersible pumping (ESP) systems are used in a variety of well related applications and often comprise a submersible pump powered by a submersible motor which is protected by a motor protector. The traditional motor protector is located between the submersible pump and the submersible motor. The motor protector includes chambers which combine the functions of compensating for thermal expansion and contraction of motor oil, discharging motor oil into the well when the volume of motor oil exceeds the motor's capacity due to thermal expansion, and sealing of an internal driveshaft against leakage. Redundant relief valves and shaft seals are sometimes employed along the motor protector, but such redundancy involves adding compensating chambers and increasing protector length to handle thermal expansion of the additional motor oil.

[0003] In some designs suited to horizontal well applications, the function of compensating for motor oil expansion and contraction is performed in a motor compensator located below the submersible motor, i.e. farther into the well. The motor compensator in this type of application may have sufficient durability to enable the reduction or elimination of redundancy. Because there is no shaft below the motor, this type of pressure compensator may utilize a metal bellows comprising a single layer, thus enabling a shorter structure than that of other motor protectors. The functions of discharging excess oil and sealing the shaft are performed in a separate device, e.g. a shaft seal module, located above the motor at an opposite end of the motor from the motor compensator. Separating these functions permits redundancy of components that may be less durable in the separate device of much shorter length. A thrust section is positioned to absorb thrust resulting from operation of the submersible pump.

[0004] Such separation of functions is particularly useful in horizontal applications, e.g. steam assisted gravity drainage wells. If this horizontal-type system were installed in a non-horizontal well, the vertical distance between shaft seals above the motor and the motor compensator below the motor would introduce a pressure differential proportional to this distance and proportional to the difference in the densities of the well fluid and the motor oil. The reason for this is that the pressure in the motor is basically equalized with the pressure in the wellbore at the motor compensator. Going upward from that elevation, the pressures inside and outside the motor decrease according to the densities of the fluids. If the well fluid is denser than the motor oil (as is commonly the case) at the shaft seals, the pressure in the motor oil would be higher than the pressure in the wellbore. Because the leakage rate through the shaft seals is generally proportional to the pressure differential, higher pressure differentials would accelerate loss of motor oil, which could shorten the life of the motor. [0005] Regardless of the angle of the wellbore in relation to the earth, these types of horizontal systems with separation of functions involve well fluid passing over the entire length of the submersible motor as the well fluid travels from the compensator at one end of the motor to the shaft seals at the other end of the motor. If the clearance between the submersible motor and the surrounding well casing is small and the motor is long, this area flow can induce significant pressure drop in the well fluid while the motor oil does not experience this pressure drop. The resulting pressure differential on the shaft seals can accelerate loss of motor oil and thus shorten motor life.

[0006] In conventional ESP protectors, the substantial length of the protector when including redundant seals also produces a substantial pressure differential on the upper shaft seals. The pressure differential is due to both differential static head and pressure drop resulting from flow over the length of the motor protector. The substantial length of the motor protector in this type of application also increases the total axial deflection of the upper end of the shaft due to pump thrust carried by the thrust bearing in the lower end of the motor protector. Axial deflection can over-compress the shaft seals at the upper end of the motor protector, thus shortening seal life.

SUMMARY

[0007] In general, a system and methodology are provided for improving the usefulness of certain types of motors and pumping systems in, for example, non- horizontal wells. However, the system and methodology may be used in many types of wells oriented from horizontal to vertical. The system and methodology facilitate oil volume change compensation while providing a seal, e.g. multiple shaft seals, in a shaft seal module of an electric submersible pumping system without exposing the seal to increased pressure as with previous designs. A compensator is combined with a shaft seal module, and both the compensator and the shaft seal module may be located between a submersible motor and a submersible pump. The compensator is able to balance pressure differentials between an interior of the motor and an exterior of the electric submersible pumping system at a location near the shaft seals without breathing through the shaft seal module. Because the shaft seal module is much shorter than a conventional protector, the upper shaft seals are exposed to a smaller pressure differential than in a conventional protector. The shorter length of the shaft seal module also reduces the potential for axial shaft deflection at the upper shaft seals.

[0008] However, many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Certain embodiments of the disclosure will hereafter be described with reference to the accompanying drawings, wherein like reference numerals denote like elements. It should be understood, however, that the accompanying figures illustrate the various implementations described herein and are not meant to limit the scope of various technologies described herein, and:

[0010] Figure 1 is an illustration of an electric submersible pumping system disposed in a non-horizontal borehole, according to an embodiment of the disclosure;

[0011] Figure 2 is an illustration of an example of a shaft seal module and motor compensator for use in an electric submersible pumping system, according to an embodiment of the disclosure;

[0012] Figure 3 is an illustration of an example of a shaft seal module, according to an embodiment of the disclosure; and

[0013] Figure 4 is an illustration of an example of a filtration system which may be used for removing certain solids that enter the electric submersible pumping system, according to an embodiment of the disclosure. DETAILED DESCRIPTION

[0014] In the following description, numerous details are set forth to provide an understanding of some embodiments of the present disclosure. However, it will be understood by those of ordinary skill in the art that the system and/or methodology may be practiced without these details and that numerous variations or modifications from the described embodiments may be possible.

[0015] Embodiments described herein provide an architecture that facilitates the use of near-horizontal ESP features described above without the risk of shorter motor life due to accelerated shaft seal leakage. The functions of pressure compensating the motor oil and sealing the shaft are separate, but they are both located at the same end of the motor, e.g. above the motor. The structures described herein minimize the pressure gradient on the shaft seals by minimizing the vertical distance between the motor compensator, where the pressures are equalized, and the shaft seals. The design further reduces or eliminates pressure on shaft seals that would otherwise occur due to a pressure drop in the well fluid as it flows along the length of the motor.

[0016] According to an embodiment, a system and methodology are provided for improving the usefulness of certain types of motors and pumping systems in non- horizontal wells, e.g. vertical wells. However, the system and methodology may be used in wells having an orientation ranging from horizontal to vertical. The system and methodology facilitate oil volume change compensation/pressure compensation while providing separate sealing with respect to a driveshaft. For example, a separate shaft seal module may comprise multiple shaft seals and may be combined with a motor compensator in an electric submersible pumping system. Both the compensator and the shaft seal module may be located between a submersible motor and a submersible pump. The compensator is able to balance pressure differentials between an interior of the motor and an exterior of the electric submersible pumping system without breathing through the shaft seal module. [0017] Referring generally to Figure 1, an embodiment of a submersible pumping system 20, such as an electric submersible pumping system, is illustrated. Submersible pumping system 20 may comprise a variety of components depending on the particular application or environment in which it is used. Examples of components utilized in pumping system 20 comprise a submersible pump 22 powered by a submersible motor 24 via an internal shaft extending from the submersible motor 24 to the submersible pump 22.

[0018] In the embodiment illustrated, submersible pumping system 20 is constructed for deployment in a well 26 having a wellbore 28 drilled into a geological formation 30 containing desirable production fluids, e.g. petroleum. The wellbore 28 and the pumping system 20 are illustrated in a vertical orientation but may be arranged in other orientations ranging from horizontal to vertical. Depending on the application, the wellbore 28 may be lined with a wellbore casing 32. A plurality of perforations 34 may be formed through wellbore casing 32 to enable flow of fluids between the surrounding formation 30 and the wellbore 28.

[0019] Submersible pumping system 20 is part of a well string 36 and may be deployed in wellbore 28 by a conveyance system 38. Conveyance system 38 may have various configurations and may comprise tubing 40, e.g. coiled tubing or production tubing, connected to submersible pump 22 by a connector 42. Power is provided to the submersible motor 24 via a power cable 44 routed downhole along the well string 36. When submersible motor 24 is operated to power submersible pump 22, well fluids, e.g. production fluids, may be drawn into the submersible pump 22 through a pump intake 46. The well string 36 is part of an overall well system 48, and the well string 36 extends downhole along wellbore 28 from surface equipment 50 positioned at a surface location 52. It should be noted that in a variety of applications the submersible pump 22 comprises a centrifugal pump. [0020] As explained in greater detail below, the pumping system 20 may be an electric submersible pumping system comprising additional components which provide sealing, pressure compensation, and/or thrust resistance. For example, the electric submersible pumping system 20 may include a thrust section 54 which resists thrust loads incurred as submersible pump 22 is operated to pump well fluids or other types of fluids. The electric submersible pumping system 20 also may comprise a compensator 56 which compensates for changes in motor oil volume and for pressure differentials which can occur between motor fluid within submersible motor 24 and surrounding wellbore fluids in an annulus 58 surrounding the electric submersible pumping system 20. Additionally, the pumping system 20 may comprise a shaft seal module 60 which provides a seal point or a plurality of seal points with respect to an internal shaft rotated to operate submersible pump 22. In the example illustrated, the compensator 56 and the shaft seal module 60 are independent components or modules disposed between submersible motor 24 and submersible pump 22.

[0021] It should be noted that many types of electric submersible pumping systems and other types of submersible pumping systems can benefit from the features described herein. Additionally, other components may be added to the pumping system 20, and other deployment systems may be used. Depending on the application, the production fluids may be pumped to a collection location through tubing 40 or through a portion of the annulus 58 around deployment system 38. The compensator 56 and the shaft seal module 60 also may utilize various components and techniques for providing the desired pressure compensation and internal sealing.

[0022] Referring generally to Figure 2, an embodiment of the compensator 56 is illustrated in greater detail. In this embodiment, the compensator 56 is positioned between thrust section 54 and shaft seal module 60. Figure 2 illustrates a portion of the electric submersible pumping system 20 starting from a head of the motor 24 and working upward to the pump 22. Above the submersible motor 24 is thrust section 54 for carrying thrust loads transferred from the submersible pump 22. The thrust section 54 comprises a lower thrust bearing 62 for carrying downward thrust, an upper thrust bearing 64 for carrying upward thrust, and a runner 66 between them that is joined to a shaft 68. The shaft 68 rotates in a shaft tube 70 and extends from submersible motor 24 to submersible pump 22 to power the submersible pump 22.

[0023] Above the thrust section 54, in this example, is the motor compensator 56 comprising one or more chambers 72 containing one or more corresponding pressure compensators 74. Multiple compensator chambers 72 may be arranged in parallel to provide greater compensation volume and/or in series to provide redundancy. The pressure compensator or compensators 74 may be formed from a variety of structures, such as elastomer bags or bellows, e.g. metal bellows. In the embodiment illustrated, the pressure compensator 74 is in the form of annular metal bellows having an annular inner bellows portion 76 joined with an annular outer bellows portion 78 to form a bellows interior 80. In another embodiment, the pressure compensator 74 may be in the form of multiple metal bellows arranged around the shaft 68 like bullets in a revolver. The structure of pressure compensator/metal bellows 74 provides high reliability and may provide greater displacement per unit length than can be achieved with parallel arrangements of metal bellows. However, embodiments described herein may utilize a single, serial, and/or parallel arrangement of metal bellows pressure compensators 74. If elastomer bags are used as pressure compensators 74, a series arrangement can be helpful in various applications.

[0024] In the embodiment illustrated in Figure 2, one side of the bellows 74, e.g. bellows interior 80, communicates with the motor 24 via a communication passage 82. The other side of bellows 74, e.g. the outside of bellows 74 within chamber 72, communicates to the wellbore 28 via a passage 84 extending to a pressure port 86 located along the exterior of compensator 56. Thus, the compensator 56 and its internal pressure compensator/bellows 74 breathes to the wellbore 28 and not through the shaft seal module 60. In other words, the pressure compensation between the internal fluid of submersible motor 24 and the external well fluid in the annulus surrounding pumping system 20 is achieved directly by the compensator 56 rather than through the shaft seal module 60. In this embodiment, the submersible motor 24 communicates with the interior 80 of the bellows 74 between the inner bellows portion 76 and outer bellows portion 78 via passage 82, and the wellbore 28 communicates with the exterior of the bellows 74 within a chamber 72 via passage 84.

[0025] In the embodiment illustrated, the pressure compensator, e.g. bellows, 74 may be located between an upper body 88 and a lower body 90 of compensator 56. The upper body 88 and the lower body 90 may be connected by an outer housing 92 which forms interior chamber or chambers 72 in cooperation with upper body 88, lower body 90, and shaft tube 70. By way of example, the bellows 74 may be suspended from the upper body 88. In some applications, bubbles can vent from the bellows 74 through a relief valve 94 disposed along a relief flow path 95. By way of example, the relief flow path 95 may be oriented so the bubbles can vent through the shaft seal module 60. Such venting may occur during oil filling and in the event gas is liberated from the oil during operation.

[0026] Well solids that enter the chamber 72 can settle out below the bellows 74.

Additionally, a filter 96 may be positioned at or along passage 84 to filter out solids from well fluid which enters passage 84 via port 86. The filter 96 may be constructed in a variety of configurations, such as the illustrated embodiment having a circular cross- section which provides a filtering surface along its circumference. The compensator 56 may further comprise one or more shaft seals 98, such as the shaft seal 98 illustrated as positioned proximate upper body 88.

[0027] In some applications, a relief valve, e.g. relief valve 94, also may be provided in cooperation with the motor compensator 56 to enable excess volume of oil to be discharged from the submersible motor 24 into the shaft seal module 60. The excess volume of oil entering the shaft seal module 60 is eventually discharged into the wellbore 28 through, for example, multiple redundant relief valves 100 (see schematic example illustrated in Figure 3). In some applications, this excess volume of oil is discharged through the shaft seal module 60 instead of directly to the wellbore 28 to provide redundancy of relief valves via the plurality of relief valves 100. Once the submersible motor 24 has reached maximum operating temperature and expelled excess oil, the relief valves 100 would not normally open again and there would be no further communication between the motor compensator 56 and the shaft seal module 60. In an embodiment, the relief valve or valves 94 also may be located in the upper body 88 above the metal bellows 74 to help vent gas liberated from the motor oil used within motor 24.

[0028] Referring again to Figure 2, the filter 96 may be provided within the motor compensator 56 to exclude solids, such as sand, from the chamber 72 outside the bellows 74. Otherwise, solids could lodge in crevices between portions, e.g. between diaphragms, of bellows portions 76, 78 and restrict the bellows 74 from fully collapsing. Hard solids, such as sand, could also deform the thin metal diaphragms/bellows portions of the bellows 74 if the bellows 74 is constructed as a metal bellows.

[0029] Depending on the application, the filter 96 may be located at the end of the chamber 72, either above or below the pressure compensator/bellows 74. By way of example, the filter 96 may be an annular pleated filter of sand screen material to maximize the filter element area per cubic inch of filter volume. In the illustrated example, this compact filter is attached to the lower body 90 below the pressure compensating bellows 74. The interior space of the filter 96 communicates downwardly through the body 90 below it, which in turn communicates to the wellbore 28 via passage 84 and external pressure port 86. This permits solids to drain from the filter 96 and back to the wellbore 28 instead of being trapped.

[0030] In another embodiment, the filter 96 may comprise a cylinder of sand screen material encircling the outer surface of the bellows 74. This type of filter 96 can be housed between two perforated metal housings, one inside the filter and the other outside the filter in, on, and/or outside the housing of chamber 72. In this embodiment, the filter 96 may include a longitudinal groove or channel for the power cable 44 so that the diameter of the chamber 72 and filter 96 may be maximized without causing undue interference with the cable 44. [0031] In the embodiment illustrated in Figures 2 and 3, the shaft seal module 60 is an independent module located above the motor compensator 56. By way of example, the shaft seal module 60 may comprise a plurality of redundant chambers 102, as illustrated schematically in Figure 3. Each of the redundant chambers 102 of the shaft seal module 60 may comprise a variety of components depending on the parameters of a given application. For example, each redundant chamber 102 may comprise a shaft seal 104 positioned about the shaft 68 to prevent interchange of motor oil and well fluid.

[0032] According to an embodiment, the shaft seals 104 comprise mechanical shaft seals which each have a rotating part 106 attached to the shaft 68 and a rotationally stationary part 108 attached to a body 110 of the shaft seal module 60. Both the rotating part 106 and the stationary part 108 may be constructed with hard, flat seal faces that mate with each other. One of these two parts 106, 108 also may contain a spring element 112 that maintains sealing contact between the two faces over a range of axial shaft positions. In an example, the spring element 112 is attached to the rotationally stationary part 108 to minimize potential imbalance and vibration which could otherwise increase the leakage rate. A chamber compensator 114 may be used to compensate for thermal expansion and contraction of the motor oil contained between the shaft seals 104 and may be located above and/or below corresponding chambers 102. The chamber compensator 114 may comprise a single compensator or a plurality of chamber compensators 114 corresponding with the plurality of chambers 102.

[0033] By way of example, the chamber compensator(s) 1 14 may have one or more bellows 116, e.g. metal bellows. In an embodiment, the top chamber 102 breathes to the wellbore 28 via a passage 1 18 and each of the lower chambers 102 breathes to the chamber above it. The length or number of bellows 116 may be increased in the upper chambers 102 to handle the cumulative expansion of the oil in the lower chambers 102. In some applications, e.g. applications where cumulative oil volume can become excessive, a lower chamber 102 may breathe through a filter to the wellbore 28 instead of to the chamber 102 above it. In an example, multiple metal bellows 116 may be arranged around the shaft 68 like bullets in a revolver, the number of bellows being varied to accommodate cumulative oil volume. In another embodiment, the metal bellows 116 may comprise an annular metal bellows, concentric with the shaft 68. The length of the chambers 102 and the bellows 116 may be determined to appropriately accommodate the cumulative oil volume.

[0034] Each redundant chamber 102 of the shaft seal module 60 also may comprise the relief valve 100, as referred to above. The relief valves 100 are provided for discharge of excess oil during initial thermal expansion. In an embodiment, each relief valve 100 discharges to the chamber 102 above it, except the uppermost relief valve 100 may function to discharge excess oil directly to the wellbore 28 from the uppermost chamber 102 via passage 118. In some applications, the bellows 116 may be arranged to breathe to the wellbore 28 while each lower relief valve 100 discharges to the chamber 102 above it to provide redundancy.

[0035] The shaft seal module 60 also may comprise at least one filter 120, e.g. a plurality of filters 120, to protect the elements of the chamber(s) 102 from solids in the well fluid. In an example, at least one of the filters 120 comprises sand screen material shaped like a flat washer and located on the upper side of the corresponding body 110. Above the last body 110, another cylindrical filter may be incorporated to protect the topmost shaft seal 104.

[0036] One or more of the filters 120 may be provided below and/or above the shaft seal or shaft seals 104 for catching solids. An example of one type of filter 120 comprises a rotary labyrinth filter, as illustrated in Figure 4. In this embodiment, the filter 120 is constructed as a rotary filter comprising a labyrinth 122 of multiple rotatable rings 124 attached to the shaft 68 so as to rotate with the shaft. The rotating rings 124 mate with corresponding stationary rings 126 attached to a body structure, such as the adjacent body 110 of shaft seal module 60. The rotating rings 124 centrifuge solids into spaces, e.g. grooves, existing between the stationary rings 126 and these spaces effectively trap the solids. Accordingly, the rotating rings 124 and the stationary rings 126 effectively provide a rotating filter to remove particulates. Various rotating features, such as grooves, radial holes, vanes, or other suitable features also may be used to generate centrifugal action.

[0037] According to an embodiment, the stationary rings 126 may be formed of a porous material, e.g. porous carbide. The rotating rings 124 and/or other suitable features act as a centrifugal or axial pump to pump liquid through the porous stationary rings 126 or through other types of filters to filter out solids. In some applications, faces of each stationary ring 126 may feature a recess 128 to trap and hold solids. The outer diameter of the rotating rings 124 may be larger than the inner diameter of the stationary rings 126 so they mesh to form the labyrinth 122 when multiple sets are stacked. In some applications, stacking smaller parts to form grooves is helpful in avoiding larger carbide pieces which have a tendency to create stress concentrations that can lead to cracking. As illustrated, the rotatable rings 124 may be constructed as interlocking stacked rings. Similarly, the stationary rings 126 may be constructed as interlocking stacked rings. Rings 124 may be non-contacting rings with respect to rings 126, and both sets of rings 124, 126 may be formed of carbide or another suitable material.

[0038] In an embodiment, the stationary rings 126 are mounted on compliant material to facilitate a close running clearance 129 between the rotating rings 124 and stationary rings 126 without generating high contact forces or friction due to slight eccentricity. The compliant mounting may comprise dampers or springs composed of elastomer, polymer or metal, such as o-rings or spring-energized polymer lip seals. The compliant mounting may be housed in a recess near the outer edge of the stationary rings 126. In an example, the stationary rings 126 are prevented from rotating with respect to the body 1 10 by, for example, at least one lock ring 130.

[0039] In this example, the rotating rings 124 are driven via the shaft 68 by, for example, a keyless bearing drive ring 132 that engages the end face of the rotating rings 124. The drive rings 132 may be secured to shaft 68 via a suitable key 134 or other structure and to each other by keyless drive tabs 136 disposed between sequential rotating rings 124. By way of example, the rotating rings 124 and/or stationary rings 126 may be formed of ceramic carbide, such as silicon carbide or tungsten carbide. The stationary rings 126 may be sealed with respect to the surrounding body, e.g. body 110, by suitable seals 138, e.g. O-ring seals.

[0040] In some embodiments, an additional structure or structures may be used to help stabilize the shaft 68 and to minimize vibration of the shaft 68. For example, a radial bearing or bearings 140 may be provided to stabilize the shaft 68. The bearing or bearings 140 also serve to minimize vibration and thus reduce the potential for shaft seal damage and leakage. In an example, each bearing 140 comprises a keyless carbide bearing. A stationary cylinder 142 is attached to the body, while a rotating cylinder 144 is attached to the shaft 68. Relative rotation of each bearing element 142, 144 with respect to its associated non-bearing component (body or shaft) may be prevented by a suitable abutment. For example, a projection may be attached to the non-bearing component for engagement with a corresponding recess in an end of the adjacent bearing element 142 or 144. The recess may be formed without sharp corners to help minimize stress concentrations.

[0041] In embodiments described herein, the shaft seal module 60 may be located above the submersible pump 22. Certain characteristics of embodiments described herein are derived from the relationship of the shaft seal module 60 and the motor compensator 56. For example, the shaft seal module 60 and the motor compensator 56 may be located at or near the same elevation at the same end of the submersible motor 24. Also, embodiments of the motor compensator 56 do not breathe into the shaft seal module 60 during thermal cycling. For example, the motor compensator 56 does not breathe into the differential pressure chamber compensators 114 of the shaft seal module 60 during thermal cycling.

[0042] Depending on the application, embodiments described herein may have other characteristics. For example, the thrust section 54 or an additional thrust section may be located between the motor compensator 56 and the shaft seal module 60. The thrust section also may be located at an opposite end of the submersible motor 24 relative to the motor compensator 56 and the shaft seal module 60. The string of equipment may be inverted such that the submersible motor 24 is on top and the submersible pump 22 is on the bottom.

[0043] In some applications, the motor compensator 56 may not be concentric with the shaft seal module 60 and may not contain shaft 68. Additionally, the motor compensator 56 may be positioned at other locations near the same elevation as the shaft seal module 60. For example, the motor compensator 56 may be located outside of a seabed capsule and connected to the motor 24 by tubing. The string of equipment also may be oriented at many angles in relation to the earth. Generally, the components and systems described above facilitate use of the electric submersible pumping system 20 in boreholes 28 while oriented at a desired angle ranging from horizontal to vertical.

[0044] Although a few embodiments of the disclosure have been described in detail above, those of ordinary skill in the art will readily appreciate that many modifications are possible without materially departing from the teachings of this disclosure. Accordingly, such modifications are intended to be included within the scope of this disclosure as defined in the claims.