WO2015120209A1

WO2015120209A1 - Power cable system and methodology

Info

Publication number: WO2015120209A1
Application number: PCT/US2015/014705
Authority: WO
Inventors: Bradley Matlack; Jason Holzmueller; Brandon NEAL; 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: 2014-02-06
Filing date: 2015-02-06
Publication date: 2015-08-13

Abstract

A technique facilitates construction of a power cable, such as a downhole electrical power cable for use with electrically powered systems. Construction of the power cable is accomplished with an external layer which does not use metallic, wrapped cable armor. The external layer may be extruded and has an exterior surface exposed to a surrounding environment. The external layer comprises a high temperature resin combined with a size disparate copolymer that creates amorphous regions in the extruded layer to restrict crack propagation.

Description

POWER CABLE SYSTEM AND METHODOLOGY

CROSS-REFERENCE TO RELATED APPLICATIONS

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

Application Serial No.: 61/936,840, filed February 6, 2014, which is incorporated herein by reference in its entirety.

BACKGROUND

[0002] In many hydrocarbon well applications, power cables are employed to deliver electric power to various devices. For example, electrical power cables may be used to provide power to electric submersible pumping systems and such power cables often are rated as 3 kV, 4 kV or 5 kV power cables. The power cables may be constructed in flat or round configurations. The round configurations are used in applications having sufficient room, while the flat configurations are used in applications subject to space constraints. [0003] Current electrical power cables for well applications often have an external armor to protect the cable from damage during handling, transport, equipment installation, and/or equipment removal from the wellbore. The armor also helps prevent the underlying cable layers from swelling and from incurring abrasion during operation. The armor is generally formed of a metallic strip or strips wrapped around the power cable. However, the wrapped metallic strip creates voids between overlapping portions of the metallic strip and the voids tend to collect well fluid after the electrical power cable has been installed downhole. When the power cable is removed from the wellbore, the well fluid trapped in these voids leaks or drips from the cable during transport and recycling, potentially causing damage. If the armor is omitted, the power cable is unprotected and well fluid can become trapped between power cable layers, e.g. inside a jacket layer, leading to similar leaks or drips during transport and recycling of the power cable.

SUMMARY

[0004] In general, a system and methodology are provided which facilitate construction of a power cable, such as a downhole electrical power cable for use with electric submersible pumping systems or other electrically powered systems. In embodiments, the construction of the power cable is accomplished with an external layer which does not use metallic, wrapped cable armor. The external layer may be extruded and has an exterior surface exposed to a surrounding environment. The external layer comprises a high temperature resin combined with a size disparate copolymer that creates amorphous regions in the extruded layer to, for example, restrict crack propagation.

[0005] 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

[0006] 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:

[0007] Figure 1 is a schematic illustration of a well system comprising an example of an electrical power cable coupled with an electric submersible pumping system deployed in a wellbore, according to an embodiment of the disclosure;

[0008] Figure 2 is a cross-sectional view of an example of an electrical power cable which may be used to supply electric power to an electrically powered system, according to an embodiment of the disclosure;

[0009] Figure 3 is a cross-sectional view of another example of an electrical power cable which may be used to supply electric power to an electrically powered system, according to an embodiment of the disclosure;

[0010] Figure 4 is a cross-sectional view of another example of an electrical power cable which may be used to supply electric power to an electrically powered system, according to an embodiment of the disclosure;

[0011] Figure 5 is a diagrammatic representation of a high temperature resin material which may be used in forming an external layer of the electrical power cable, according to an embodiment of the disclosure; and

[0012] Figure 6 is a diagrammatic representation of a size disparate copolymer material which may be combined with the high temperature resin material forming the external layer of the electrical power cable, according to an embodiment of the disclosure.

DETAILED DESCRIPTION

[0013] 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.

[0014] The present disclosure generally relates to a system and methodology for delivering electric power. The technique employs an electrical power cable constructed to enable operation in a variety of harsh environments, such as high heat, downhole environments associated with many types of well applications. By way of example, the electrical power cable has an electrical conductor surrounded by an insulation layer. The insulation layer and the electrical conductor are positioned within an external layer having an exterior surface exposed to the surrounding environment. In embodiments described herein, the external layer may be an extruded layer comprising a high temperature resin combined with a size disparate copolymer. The size disparate copolymer creates amorphous regions in the external layer to, for example, resist crack propagation in the external layer.

[0015] In embodiments described herein, the external layer is used in place of the traditional metallic, wrapped cable armor. The external layer may be constructed as a fluid impermeable, low surface energy material, e.g. fluoroplastic material. Because of the construction of the external layer, there are little or no absorbed or trapped fluids in the power cable that could otherwise leak or drip into the environment once the power cable is pulled to the surface after a well application. The external layer may be formed from non-metallic materials which reduce the cable weight and thus facilitate handling of the cable. The external layer also may be extruded in the form of, for example, a jacket, e.g. a polymeric jacket. The extrusion process enables a faster manufacturing process and thus increased throughput when manufacturing the electrical power cable. As described herein, the materials forming the external layer are selected to enable long-term durability of the cable in many harsh environments, including downhole well

environments.

[0016] In downhole, wellbore applications, the electrical power cable may be used with electric submersible pumping systems or other downhole systems. The cable is routed downhole along a tubing string and connected to the electric submersible pumping system or other suitable downhole system. In many applications, the power cable is coupled to the downhole system via a sealed connector, sometimes referred to as a pothead, to prevent intrusion of well fluids.

[0017] Referring generally to Figure 1, an embodiment of a well system is illustrated as comprising a downhole, electrically powered system, e.g an electric submersible pumping system. By way of example, the system may comprise a variety of electric submersible pumping system components deployed in a well string located in a wellbore. Electric power is delivered downhole into the harsh, subterranean environment via an electrical power cable which may be connected to the electric submersible pumping system via a pothead. The illustrated electric submersible pumping system or other types of well systems may comprise many types of components and may be employed in many types of applications and environments, including cased wells and open-hole wells. The well system also may be utilized in vertical wells or deviated wells, e.g. horizontal wells.

[0018] Referring again to Figure 1, a well system 20 is illustrated as comprising an electrically powered system 22 which receives electric power via an electrical power cable 24. By way of example, the electrically powered system 22 may be in the form of an electric submersible pumping system 26, and the power cable 24 is designed to withstand high temperature, harsh environments. 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.

[0019] In the example illustrated, electric submersible pumping system 26 is constructed 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 22) may be used in open hole wellbores or in other environments exposed to high temperatures and harsh conditions. 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 is 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. By way of example, the conveyance 44 may be coupled with the electrically powered system 22 via an appropriate tubing connector 48.

[0020] In the example illustrated, electric power is provided to submersible motor

30 by electrical power cable 24. 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.

[0021] As described in greater detail below, the electrical power cable 24 is designed to consistently deliver electric power to the electrically powered system 22, e.g. electric submersible pumping system 26, over long operational periods in environments subject to high temperatures, high pressures, deleterious fluids, and/or other harsh conditions. The power cable 24 is 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.

[0022] Depending on the application, the power cable 24 may comprise an individual electrical conductor protected by an insulation system and external layer; or the power cable 24 may comprise a plurality of electrical conductors protected by an insulation system and external layer. In various submersible pumping applications, the electrical power cable 24 is constructed to carry three-phase current delivered by three conductors. In such applications, submersible motor 30 comprises a three-phase motor powered by the three-phase current delivered via the three electrical conductors of electrical power cable 24.

[0023] Referring generally to Figure 2, an example of electrical power cable 24 is illustrated. In this example, the power cable 24 comprises at least one electrical conductor 56. In some embodiments, the power cable 24 comprises a plurality of the electrical conductors 56, such as the illustrated three electrical conductors 56. The plurality of electrical conductors 56 may be used to supply multiphase power, e.g. three- phase power, to downhole systems or other systems.

[0024] Within power cable 24, each conductor 56 may be surrounded by an insulation layer 58, and each insulation layer 58 may be surrounded by a barrier layer 60. The electrical power cable 24 further comprises an external layer 62, e.g. an external cable jacket, having an exterior surface 64 exposed to a surrounding environment 66, such as a surrounding high temperature, high pressure wellbore environment. Individual conductors 56 may be individually surrounded by the external layer 62, or the plurality of conductors 56 may be collectively surrounded by the external layer 62, as illustrated. Additionally, the cable 24 may be constructed to arrange the plurality of conductors 56 so as to present a generally flat configuration (as illustrated in Figure 2), a generally circular configuration, or another suitable cross-sectional configuration. [0025] As illustrated in Figure 3, for example, the cable 24 may comprise the plurality of conductors 56 arranged in a generally triangular pattern. Similar to the embodiment illustrated in Figure 2, each conductor 56 may be surrounded by selected layers, e.g. insulation layer 58 and barrier layer 60, and the plurality of conductors 56 may be surrounded collectively by the external layer 62. The external layer 62 may be constructed such that exterior surface 64 is circular in cross-section or is formed in another suitable shape. In some applications, the power cable 24 may comprise a single conductor 56, as illustrated in Figure 4. In this latter embodiment, the single conductor 56 also is surrounded by external layer 62 with selected layers, e.g. insulation layer 58 and barrier layer 60, positioned between the conductor 56 and the external layer 62.

[0026] By way of example, each electrical conductor 56 may be formed from a suitably conductive material, such as a high purity copper, and may be formed as a solid conductor, stranded conductor, or compacted stranded conductor. Stranded and compacted stranded conductors provide improved flexibility in some applications. Each conductor 56 also may be coated with a corrosion resistant coating 68 to reduce or prevent conductor degradation from hydrogen sulfide gas or other substances which can occur in downhole environments. Examples of such a corrosion resistant coating 68 include tin, lead, nickel, silver, and/or other corrosion resistant metals, alloys, or other suitable materials.

[0027] In some applications, a conductor shield 70 may be located around each electrical conductor 56 (see, for example, Figures 2-4). The conductor shield 70 may comprise a semiconductive layer which controls electrical stress in the power cable 24 to minimize the chance of undesirable discharge. By way of example, the conductor shield 70 may be between 0.002 inches and 0.020 inches in thickness and have a resistivity less than 500 ohm-cm. The layer 70 may be bonded to the conductor 56 and/or to insulation layer 58 to further reduce or block gas migration. Sometimes, the conductor shield layer 70 may be formed as a strippable layer to provide easy access to the conductor. [0028] The conductor shield 70 may be comprised of, for example, a

semiconductive tape wrap or an extruded semiconductive polymer. Additionally, the conductor shield 70 may be a layer of elastomer or thermoplastic co-extruded with the insulation layer 58 to enable cross-linking with the insulation layer. The cross-linking reduces the chance of void formation at the interface between conductor shield 70 and insulation layer 58. Specific examples of materials used to form conductor shield 70 include elastomer compound, e.g. ethylene propylene diene monomer (EPDM) or polyetheretherketone (PEEK), loaded with conductive fillers. Depending on the application, the conductor shield 70 and insulation layer 58 may use the same base material.

[0029] For example, the insulation layer 58 may be formed from ethylene propylene diene monomer (EPDM), e.g. oil and decompression resistant EPDM, or polyetheretherketone (PEEK). The insulation layer 58 may be adhered or bonded to the conductor shield 70, although some applications may utilize an insulation layer 58 which is continuous with the insulation shield but not completely bonded. In some

embodiments, constructing the insulation layer 58 with polyetheretheretherketone provides good mechanical properties and damage resistance during cable installation and cable operation. The relatively high stiffness of polyetheretheretherketone facilitates sealing over cable members at cable termination points, e.g. motor pothead, well connectors, feed-throughs, and other termination points, and this provides the power cable 24 as well as the overall system with increased reliability.

[0030] In some applications, an insulation shield 72 is applied over the insulation layer 58 to reduce electrical stresses in the cable 24. The insulation shield 72 may be a semiconductive layer having a resistivity less than 5000 ohm-cm The insulation shield 72 also may be bonded to the insulation layer 58 or it may be strippable to enable ends of the insulation shield 72 to be stripped away. However, some adhesion between the layers may be helpful in preventing voids or defects in the power cable 24. The insulation shield 72 may be formed with a semiconductive tape or a semiconductive polymer. In some applications, the conductor shield 70 and the insulation shield 72 are co-extruded with the insulation layer 58 to ensure complete contact between the corresponding surfaces. Depending on the application, the insulation shield 72 and the conductor shield 70 may be formed of similar materials.

[0031] In some applications, a conductive layer 74 may be located outside of the insulation shield 72 to serve as a ground plane. The conductive layer 74 may be used to isolate the phases of the power cable 24 from each other. Examples of materials used to form conductive layer 74 include copper, aluminum, lead, or other conductive materials applied to insulation shield 72 as tape, braid, paint, extrusion, or other suitable structure. The conductive layer 74 also can be used as a barrier to downhole gas and fluids, thus protecting the radially inward layers of power cable 24.

[0032] The barrier layer 60 further protects the power cable 24 from corrosive downhole gases and fluids. Additional barrier layers 60 may be added to power cable 24 when the power cable 24 is to be used in certain environments. By way of example, barrier layer 60 may be formed of extruded layers or tape layers of fiuoropolymers, lead, or other materials and structures able to protect the cable 24 against deleterious well fluids. Combinations of materials and structures, e.g. combinations of extruded and taped layers, also may be used to construct barrier layer 60.

[0033] The previously described layers are illustrated as located around each individual conductor 56. The external layer 62, e.g. the outer jacket layer, may be located around individual connectors 56, but the external layer 62 also may be formed around a plurality of conductors collectively as illustrated in Figures 2 and 3. During construction of power cable 24, the external layer 62 may be continually extruded to prevent the formation of gaps or voids in the external layer that could otherwise allow for ingress of fluids. The material used to form external layer 62 combines excellent fluid and gas resistance, low surface energy to prevent adhesion of fluids during running out of hole, good mechanical properties, low cost, and good processability. For example, the external layer 62 may be an extruded layer comprising a high temperature resin (i.e. a resin suitable for use in high temperature environments) combined with a size disparate copolymer which creates amorphous regions 76 in the extruded layer 62 to, for example, resist crack propagation.

[0034] An example of the high temperature resin comprises a copolymer of polyvinylidene fluoride (PVDF). A diagrammatic representation of an example of the PVDF monomer is illustrated in Figure 5. An embodiment of the size disparate copolymer comprises hexafluoropropylene (HFP). A diagrammatic representation of an example of HFP monomer is illustrated in Figure 6. The high crystallinity of the PVDF component provides high strength and stiffness, while incorporation of the size disparate copolymer, e.g. HFP, disrupts the crystallinity to create amorphous regions 76 that limit or prevent crack propagation. In the case of HFP, HFP is 100% fluorinated and thus also improves fluid resistance while reducing the likelihood of crack propagation.

[0035] For some applications, an optimized copolymer with predominantly PVDF in combination with a small proportion of HFP can be used to create a material with a high tensile strength and modulus while retaining excellent toughness and resistance to environmental stress cracking. Examples of such materials are Kynar Flex grades of PVDF copolymer resin available from Arkema corporation based in Paris, France.

[0036] However, other materials may be used to form external layer 62.

Examples of other high temperature, high-strength resins include ethylene

tetrafluoroethylene (ETFE) or polyetheretherketone (PEEK). Additionally, various fillers may be incorporated into the thermoplastic jacket material used to form external layer 62. The fillers may be designed to improve or manipulate properties such as tensile strength, abrasion resistance, thermal conductivity, and/or other properties of the material used to form external layer 62.

[0037] External layer 62 also may be extruded in a manner which reduces or eliminates voids between the external layer 62 and the adjacent layer, e.g. barrier layer 60. It should be noted that in some applications the external layer 62 may be formed against a layer comprising a lead material. The potential voids may be reduced or eliminated by, for example, extruding external layer 62 via compression extrusion techniques. By way of further example, the extruded external layer 62 may be bonded to the adjacent layer by using surface treatments, adhesives, tie-layer compounds, and/or other bonding techniques.

[0038] In some applications, the external layer 62 may be formed of a plurality of co-extruded layers. In some embodiments of this latter example, the outer layer of external layer 62 may comprise ETFE, PVDF, PEEK, and/or other suitable materials while an inner layer of external layer 62 may be formed of a lower-cost, high temperature polymer such as nylon 12 or aliphatic polyetherketone. Additionally, the co-extruded layers of external layer 62 may be bonded together via the co-extrusion process. The co- extrusion process applied to external layer 62 facilitates construction of a low-cost layer 62 while maintaining performance of the layer as a fluid barrier.

[0039] Depending on the application, the electrical power cable 24 may have a variety of configurations with other and/or additional components. For example, additional or other layers may be incorporated into the power cable 24 beneath the external layer 62. Various tapes, extrusions, or other structures and techniques may be used in forming the various layers of the power cable 24. The power cable 24 also may have an individual conductor or a plurality of conductors, e.g. three conductors, depending on the desired power cable application. The external layer 62 may be formed of various types, ratios and combinations of high temperature resin and size disparate copolymer. Additionally, fillers and other types of materials may be mixed into the external layer to provide the external layer with desired properties for a given application.

[0040] 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. An electrical power cable, comprising: an electrical conductor;

an insulation layer located around the electrical conductor; a barrier layer located around the insulation layer; and

an external layer having an exterior surface exposed to a surrounding environment, the external layer being an extruded layer comprising a high temperature resin combined with a size disparate copolymer which creates amorphous regions in the extruded layer to resist crack propagation.

2. The electrical power cable as recited in claim 1, wherein the high temperature resin comprises polyvinylidene fluoride (PVDF).

3. The electrical power cable as recited in claim 1, wherein the high temperature resin comprises ethylene tetrafluoroethylene (ETFE).

4. The electrical power cable as recited in claim 1, wherein the high temperature resin comprises polyetheretherketone (PEEK).

5. The electrical power cable as recited in claim 1, wherein the size disparate

copolymer comprises hexafluoropropylene (HFP).

6. The electrical power cable as recited in claim 1, wherein the high temperature resin comprises polyvinylidene fluoride (PVDF) and the size disparate copolymer comprises hexafluoropropylene (HFP).

7. The electrical power cable as recited in claim 1 , further comprising a conductor shield having a semiconductive layer disposed between the electrical conductor and the insulation layer.

8. The electrical power cable as recited in claim 1, further comprising an insulation shield having a semiconductive layer applied over the insulation layer to minimize electrical stresses in the electrical power cable.

9. The electrical power cable as recited in claim 8, further comprising a conductive layer arranged to serve as a ground plane.

10. The electrical power cable as recited in claim 1, wherein the electrical conductor comprises a plurality of electrical conductors.

11. The electrical power cable as recited in claim 1 , wherein the electrical conductor comprises three electrical conductors surrounded collectively by the external layer.

12. A method, comprising: locating an insulation layer around an electrical conductor; positioning the insulation layer and the electrical conductor within an external layer to construct a power cable, the external layer having an exterior surface exposed to a surrounding environment, the external layer being an extruded layer comprising a high temperature resin combined with a size disparate copolymer which creates amorphous regions in the extruded layer; and connecting the power cable to an electric submersible pumping system.

13. The method as recited in claim 12, further comprising forming the high

temperature resin with polyvinylidene fluoride (PVDF).

14. The method as recited in claim 12, further comprising forming the high temperature resin with ethylene tetrafluoroethylene (ETFE).

15. The method as recited in claim 12, further comprising forming the high

temperature resin with polyetheretherketone (PEEK).

16. The method as recited in claim 12, further comprising forming the size disparate copolymer with hexafluoropropylene (HFP).

17. The method as recited in claim 12, further comprising forming the high

temperature resin with polyvinylidene fluoride (PVDF) and the size disparate copolymer with hexafluoropropylene (HFP).

18. A system, comprising : an electrically powered system deployed in a well; and

an electrical power cable coupled to the electrically powered system, the electrical power cable comprising:

a plurality of conductors with each conductor being surrounded by a conductor shield, an insulation layer, an insulation shield, and a barrier layer; and

an external layer surrounding the plurality of conductors collectively, the external layer being an extruded layer comprising a high temperature resin combined with a size disparate copolymer which creates amorphous regions in the extruded layer to resist crack propagation .

19. The system as recited in claim 18, wherein the electrical power cable further comprises a ground plane in the form of a conductive layer positioned externally of each conductor. The system as recited in claim 18, wherein the conductors of the plurality of conductors are arranged in a generally flat configuration.