WO2016028296A1

WO2016028296A1 - Multi-sector power cable

Info

Publication number: WO2016028296A1
Application number: PCT/US2014/051977
Authority: WO
Inventors: Stephen SKVARENINA; Mark A. Metzger
Original assignee: Schlumberger Canada Limited; Services Petroliers Schlumberger; Schlumberger Holdings Limited; Schlumberger Technology B.V.; Prad Research And Development Limited; Schlumberger Technology Corporation
Priority date: 2014-08-21
Filing date: 2014-08-21
Publication date: 2016-02-25

Abstract

A technique facilitates construction and use of power cables, such as power cables employed in downhole well applications. A power cable is formed with a plurality of conductors in which each conductor has sides extending outwardly from a center region of the power cable. The sides form an angle with respect to each other to facilitate a compact arrangement of electrical conductors. Additionally, the individual electrical conductors may be insulated, and the plurality of conductors may be surrounded with at least one outer protective layer.

Description

MULTI-SECTOR POWER CABLE

BACKGROUND

[0001] Hydrocarbon fluids such as oil can be pumped from a subterranean geologic formation, referred to as a reservoir, by operating an electric submersible pumping system disposed in a wellbore. The electric submersible pumping system comprises a submersible pump powered by an electric motor which receives power from a power cable routed downhole into the wellbore. The power cable comprises three electrical conductors which supply three-phase power to the submersible motor. The electrical conductors are round in cross-section and twisted around a central gap filled by a string to form a core. However, the structure of the conductors and the overall power cable often creates an inefficient use of space and also uses excess insulation materials or filler materials.

SUMMARY

[0002] In general, a system and methodology are provided for facilitating the construction and use of power cables, such as power cables employed in downhole well applications. A power cable is formed with a plurality of conductors in which each conductor has sides extending outwardly from a center region of the power cable. The sides form an angle with respect to each other to facilitate a compact arrangement of electrical conductors. Additionally, the individual electrical conductors may be insulated, and the plurality of conductors may be surrounded with at least one outer protective layer.

[0003] 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

[0004] 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:

[0005] Figure 1 is a front elevation view of an embodiment of an electric submersible system which receives power through a power cable, according to an embodiment of the disclosure;

[0006] Figure 2 is a cross-sectional view of an example of a power cable, according to an embodiment of the disclosure;

[0007] Figure 3 is a cross-sectional view of another example of a power cable, according to an embodiment of the disclosure; and

[0008] Figure 4 is a cross-sectional view of another example of a power cable, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0009] 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. [0010] The present disclosure generally relates to a system and methodology for facilitating the construction and use of power cables. The power cables may be used in a variety of applications including downhole well applications, e.g. providing power to electric submersible pumping systems. The power cable is useful in high-voltage applications and may be constructed as a power cable with an 8 kV rating or higher. However, the construction also may be used in power cables with lower ratings.

[0011] The power cable is formed with a plurality of conductors in which each conductor has sides extending outwardly from a center region of the power cable. The sides form an angle with respect to each other to facilitate a compact arrangement of electrical conductors. Additionally, the individual electrical conductors may be insulated, and the plurality of conductors may be surrounded with at least one outer protective layer, e.g. a barrier layer, a jacket layer, and/or an armor layer. The angle between sides is generally less than 180 degrees and often less than 150 degrees. To make efficient use of space within the power cable, the angle selected may be 360 degrees divided by the number of conductors in the power cable. For example, if the power cable employs three conductors, the angle may be approximately 120 degrees or if the cable employs four conductors, the angle may be approximately 90 degrees.

[0012] According to an embodiment, the power cable is constructed as a sector type power cable having three sectors of 120 degrees. A conductor formed with sides having an angle of approximately 120 degrees is located in each sector of the power cable, and each of the three conductors may be insulated and also protected with at least one semi-conductive layer. The three conductors may be twisted and then provided with a jacket layer and an armor layer to create a power cable with a generally round exterior. This same technique for construction also may be used for four conductor power cables or power cables having other numbers of conductors.

[0013] This type of construction removes the center void present in a

conventional power cable and reduces the final cable diameter. The reduced cable diameter facilitates a wider range of applications including a wider range of well applications, such as use of the cable in smaller wellbores without changing to a lower rated power cable. The smaller diameter construction for a given voltage rating also reduces material costs because the smaller diameter uses less material for various layers, such as barrier layers, jacket layers, and armor layers.

[0014] Referring generally to Figure 1, an embodiment of a power cable 20 is illustrated as employed in a well application. However, the power cable 20 may be used in a variety of other types of applications including non-well applications. In the example illustrated in Figure 1 , a well system 22 is illustrated as comprising an electrically powered system 24 which receives electrical power via the power cable 20. By way of example, the electrically powered system 24 may be in the form of an electric submersible pumping system 26, and the power cable 20 is constructed in a space efficient manner. Although the electric submersible pumping system 26 may have a wide variety of components, examples of such components comprise a submersible pump 28, a submersible motor 30, and a motor protector 32.

[0015] In the example illustrated, electric submersible pumping system 26 is designed for deployment in a well 34 located within a geological formation 36 containing, for example, petroleum or other desirable production fluids. A wellbore 38 may be drilled and lined with a wellbore casing 40, although the electric submersible pumping system 26 (or other type of electrically powered system 24) may be used in open hole wellbores or in other surface or subsurface environments. In the example illustrated, however, casing 40 is perforated with a plurality of perforations 42 through which production fluids flow from formation 36 into wellbore 38. The electric submersible pumping system 26 may be deployed into the wellbore 38 via a conveyance or other deployment system 44 which may comprise tubing 46, e.g. coiled tubing or production tubing, or other suitable conveyance systems. By way of example, the conveyance 44 may be coupled with the electrically powered system 24 via an appropriate connector 48. [0016] In the example illustrated, electric power is provided to submersible motor

30 by power cable 20. The submersible motor 30, in turn, powers submersible pump 28 which draws in fluid, e.g. production fluid, into the pumping system through a pump intake 50. The fluid is produced or moved to the surface or other suitable location via tubing 46. However, the fluid may be pumped to other locations along other flow paths. In some applications, for example, the fluid may be pumped along an annulus surrounding conveyance 44. In other applications, the electric submersible pumping system 26 may be used to inject fluid into the subterranean formation or to move fluids to other subterranean locations.

[0017] As described in greater detail below, the electric power cable 20 has a space efficient construction. The construction also enables higher ratings, e.g. higher voltage ratings, with respect to power cable 20 for a given power cable diameter. The power cable 20 may be connected to the corresponding, electrically powered component, e.g. submersible motor 30, by a suitable power cable connector 52, e.g. a suitable pothead. The cable connector 52 provides sealed and protected passage of the power cable conductor or conductors through a housing 54 of submersible motor 30. Depending on the application, the power cable 20 may comprise an individual electrical conductor protected by an insulation system or a plurality of electrical conductors protected by the insulation system. In various submersible pumping applications and other applications, the submersible motor 30 may be powered by three-phase current delivered through three electrical conductors of power cable 20.

[0018] Referring generally to Figure 2, an example of power cable 20 is illustrated in cross-section. In this example, power cable 20 comprises a plurality of conductors 56 and each conductor 56 comprises sides 58 which extend outwardly from a center region 60 of the power cable 20 to form an angle 62 with respect to each other. The sides 58 of each conductor 56 comprise surfaces which separate from each other as they move outwardly to an outer surface 64 extending between the sides 58. In some embodiments, the outer surface 64 may be an arcuate surface, e.g. a section of a circle, that extends between the sides 58. In some applications, the sides 58 comprise generally flat surfaces.

[0019] The size of angle 62 may be selected according to the construction of the overall power cable 20 and/or according to the number of conductors 56 disposed within the electric power cable 20. By way of example, the angle 62 between sides 58 is generally less than 180 degrees and often less than 150 degrees. To make efficient use of space within the power cable 20, the selected angle 62 may be 360 degrees divided by the number of conductors 56 in the power cable 20. For example, if the power cable 20 employs three conductors 56, the angle 62 may be approximately 120 degrees or if the power cable 20 employs four conductors 56, the angle 62 may be approximately 90 degrees.

[0020] In the example illustrated, the power cable 20 further comprises an insulation layer 66 disposed around each conductor 56. A semi-conductive layer 68 or a plurality of semi-conductive layer 68 also may be disposed around each conductor 56. By way of example, a semi-conductive layer 68 may be positioned around each electrical conductor 56 between the conductor 56 and the corresponding insulation layer 66. In some embodiments, the semi-conductive layer 68 may be positioned around each electrical conductor 56 along an exterior of the insulation layer 66. Additionally, a plurality of semi-conductive layer 68 may be employed and may be positioned along both the interior and the exterior of the insulation layer 66.

[0021] Referring again to Figure 2, a barrier layer 70 also may be disposed around each electrical conductor 56. By way of example, the barrier layer 70 may be positioned against the exterior of insulation layer 66 or against the exterior of the semi- conductive layer 68 located along the exterior of insulation layer 66 in embodiments employing the semi-conductive layer 68 at this location. Each of the layers surrounding the individual electrical conductors 56 may be constructed to follow the contour of the corresponding electrical conductor 56 so as to meet in center region 60 without employing a central gap or an additional core, e.g. string, within the central gap. This construction provides a very space efficient package and enables a reduced diameter power cable for a given power/voltage rating.

[0022] In addition to barrier layer 70, the electrical power cable 20 may comprise additional protective layers. For example, the power cable 20 may comprise a jacket layer 72 disposed around the barrier layer 70 and enclosing, e.g. encircling, the plurality of conductors 56. Additionally, the power cable 20 may comprise an armor layer 74 also disposed around the plurality of conductors 56. In the illustrated example, the armor layer 74 is disposed along the exterior of the jacket layer 72.

[0023] The size of the power cable components, materials selected, configuration of the components, and arrangement of the components may be adjusted according to the parameters of a given application. By way of example, the electrical conductors 56 may be formed of copper or another suitable conductive material, and the copper or other material may be drawn and roll formed to provide the desired surfaces/sides 58 and angles 62. However, other techniques may be used to construct the electrical conductors 56 in the desired shape and size. Additionally, the cross-sectional area of each conductor 56 may be equivalent to the American Wire Gauge cross-sectional area appropriate for minimizing conductor resistance losses.

[0024] In some applications, an alloy coating can be added to each conductor 56 for corrosion resistance. Additionally, the semi-conductive material layers 68 may be added and utilized as stress control layers. The barrier layer 70 may be formed from lead tape or an extrusion. The insulation layer 66 may be formed from a variety of elastomeric materials used in electrical power cables. Additionally, the jacket layer 72 may be formed from a variety of elastomeric materials, composite materials, or other suitable materials. The armor layer 74 may be formed from various metallic materials, composite materials, or other suitable materials.

[0025] Depending on the application, the power cable 20 may be constructed by twisting together the three conductors 56 with the corresponding layers disposed around each conductor 56. The three conductors 56 are twisted to form a core with a generally circular cross-section which can be enclosed with protective layers, such as jacket layer 72 and armor layer 74. The sector type construction utilizing sectors 76 generally matching the shape of conductors 56 and their angled sides 58 removes the interstice that would otherwise exist between the three conductors 56.

[0026] After twisting the three conductors 56 and the associated layers around each individual conductor 56, the jacket layer 72 can serve to bind the conductors 56 together for subsequent processing. The jacket layer also may serve to cushion the internal layers during the armoring process, to provide additional fluid and gas resistance, and/or to protect the internal components from damage during handling. The outer armor layer 74 can be applied as a formed metallic tape, as multiple layers of heli-axial wire, or according to other suitable techniques. The armor layer 74 provides further damage resistance as the power cable 20 is installed and also provides swell containment once the power cable 20 is placed in service in, for example, a downhole environment.

[0027] Referring generally to Figure 3, another embodiment of power cable 20 is illustrated. In this embodiment, instead of placing barrier layer 70 around each individual electrical conductor 56, the barrier layer 70 is disposed around the plurality of insulated, electrical conductors 56. For example, the barrier layer 70 may be generally circular in cross-section (or another suitable cross-sectional shape) and disposed along the radial exterior of insulation layers 66. For example, the barrier layer 70 may be disposed directly against the radially outer surface of the plurality of insulation layers 66 or against the exterior of the semi-conductive layers 68 disposed along the exterior of each of the insulation layers 66 when external semi-conductive layers 68 are employed in the structure. In this example, the conductors 56 may be twisted before applying barrier layer 70.

[0028] By employing barrier layer 70 in a form which encircles the conductors 56 electrically, the overall diameter of the power cable 20 can be further reduced. Similar protective layers, such as jacket layer 72 and armor layer 74, may be disposed around the barrier layer 70.

[0029] Referring generally to Figure 4, another embodiment of power cable 20 is illustrated. This latter embodiment is similar to the embodiment described with reference to Figure 3, except that four electrical conductors 56 have been provided in the power cable 20 instead of the three electrical conductors 56 illustrated in Figures 2 and 3. In this latter embodiment, similar arrangements of insulation layers 66 and semi-conductive layers 68 may be used around each of the conductors 56. In some embodiments, the barrier layer 70 may be employed around individual conductors of the four electrical conductors 56, similar to the embodiment illustrated in Figure 2. Similar arrangements of additional protective layers, such as jacket layer 72 and armor layer 74, also may be positioned around the plurality of electrical conductors 56. Depending on the application, the four electrical conductors 56 may again be twisted and then enclosed with, for example, barrier layer 70, jacket layer 72, and/or armor layer 74.

[0030] In some applications, the fourth electrical conductor 56 may be used as a ground wire 78 or as an injection tube. It should be noted that the number of electrical conductors 56 can be greater or lesser than the number illustrated and described with reference to Figures 2-4. The use of angular sectors 76 which fit tightly together at center region 60 provides improved space efficiency for power cables 20 with various numbers of electrical conductors 56. In some applications, one or more of the angular sectors 76 may be used to accommodate other features, such as control lines, communication lines, injection tubes, and/or other features.

[0031] As described herein, electric power cable 20 may be constructed for use with many types of systems and components. The power cable 20 may be used to power electric submersible pumping systems 26 or other downhole systems and components. Additionally, the power cable 20 may be used in a variety of surface applications which may be well related or non-well related applications. The power cable 20 may be constructed with sectors 76 having a variety of layers and configurations in combination with various types, numbers and arrangements of protective layers.

[0032] Additionally, the power cable 20 may be used in high-voltage applications to facilitate supply of high- voltage power with a power cable having a relatively small size, e.g. small diameter. For example, the power cable 20 may be used with high- voltage electric submersible pumping systems rated at 8 kV or higher. However, the structure of power cable 20 also makes the power cable useful with lower voltage systems due to the space efficiency of the cable. For example, the power cable 20 can be constructed as a round power cable having a smaller diameter for use in tighter spaces between production tubing and casing in various downhole applications.

[0033] 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.

Claims

CLAIMS What is claimed is:

1. A system for conveying electric power, comprising:

a power cable having:

a plurality of conductors, each conductor having sides which extend outwardly from a center region of the power cable, the sides forming an angle with respect to each other of less than 150 degrees; a semi-conductive layer disposed about each conductor;

an insulation layer disposed about each conductor; and a barrier layer disposed around the conductors.

2. The system as recited in claim 1, wherein the plurality of conductors comprises three conductors and the angle is approximately 120 degrees.

3. The system as recited in claim 1, wherein the plurality of conductors comprises four conductors and the angle is approximately 90 degrees.

4. The system as recited in claim 1, wherein each conductor comprises an outer surface which is arcuate and extends between the sides.

5. The system as recited in claim 1, wherein the sides are generally flat surfaces extending outwardly from the center region.

6. The system as recited in claim 1, further comprising a jacket layer disposed around the barrier layer.

7. The system as recited in claim 6, further comprising an armor layer disposed around the jacket layer.

8. The system as recited in claim 1, wherein the barrier layer is disposed fully around each conductor.

9. The system as recited in claim 1, wherein the semi-conductive layer is disposed inwardly of the insulation layer.

10. The system as recited in claim 1, wherein the semi-conductive layer is disposed outwardly of the insulation layer.

11. The system as recited in claim 1 , wherein the semi-conductive layer comprises a plurality of semi-conductive layers with at least one semi-conductive layer disposed inwardly of the insulation and at least one semi-conductive layer disposed outwardly of the insulation layer.

12. A system, comprising: an electric submersible pumping system having:

a submersible motor;

a submersible pump powered by the submersible motor; and a motor protector coupled to the submersible motor; and a power cable mounted to the submersible motor, the power cable having: a plurality of conductors, each conductor having sides which extend outwardly from a center region of the power cable, the sides forming an angle with respect to each other of less than 150 degrees; and an insulation layer disposed about each conductor.

13. The system as recited in claim 12, wherein the plurality of conductors comprises at least three conductors for delivery of three-phase power to the submersible motor.

14. The system as recited in claim 12, wherein the plurality of conductors comprises three conductors and the angle is approximately 120 degrees.

15. The system as recited in claim 14, wherein each conductor is surrounded by a semi-conductive layer.

16. The system as recited in claim 15, wherein each conductor comprises a barrier layer positioned around the insulation layer.

17. The system as recited in claim 15, further comprising a jacket layer disposed around the plurality of conductors and an armor layer disposed about the jacket layer.

18. A method, comprising : forming a power cable with a plurality of conductors in which each conductor has sides extending outwardly from a center region of the power cable, the sides forming an angle with respect to each other of less than 180 degrees; insulating each conductor;

twisting the plurality of conductors; and

providing the plurality of conductors with at least one outer protective layer.

19. The method as recited in claim 18, further comprising coupling the power cable to a submersible motor of an electric submersible pumping system.

20. The method as recited in claim 18, wherein forming comprises selecting three conductors with each of the three conductors having an angle between sides of approximately 120 degrees or less.