EP0907188A1

EP0907188A1 - Multiconductor electrical cable

Info

Publication number: EP0907188A1
Application number: EP98301359A
Authority: EP
Inventors: Timothy B. Bruewer
Original assignee: Camco International Inc
Current assignee: Camco International Inc
Priority date: 1997-10-02
Filing date: 1998-02-25
Publication date: 1999-04-07
Also published as: NO984426L; CA2249135A1; NO984426D0

Abstract

A multiconductor electrical cable (28) for use in a subterranean wellbore includes at least one electrical conductor (30) surrounded by one or more layers (32) of insulating material. At least one layer of the insulating material includes ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM) and/or polyolefin elastomer formed using a stereoregular polymerization catalyst (POE). This insulating material has a higher degree of crystallinity than previous insulation materials, with a higher tear retention and a higher tensile retention and less elongation loss over previous insulation materials, both before and after exposure to hydrocarbons in a subterranean wellbore environment.

Description

The present invention relates to multiconductor electrical cables and, more particularly, to multiconductor electrical cables for use in subterranean wellbores.
Multiconductor electrical cables that are used to power wellbore equipment, such as electrical submergible pumping systems, must be capable of withstanding the high temperatures, high pressures and/or corrosive fluids often encountered within subterranean wellbores. As used herein, the term "high temperature" means temperatures of greater than about 180 F and as high as about 500 F. The term "high pressure" means pressures as high as about 5,000 psi. Further, the term "corrosive fluids" means liquids and gases which can cause degradation to cable insulating materials and/or corrosion to the electrical conductors, such as liquids and/or gases containing hydrogen sulfide, carbon dioxide, brine, and the like.
Subterranean wellbore cables include several layers of different materials to either protect the copper conductors from mechanical damage and/or from damage from corrosive fluids. Usually, the copper conductors are sheathed in one or more layers of insulating materials, such as ethylene propylene diene methylene terpolymer ("EPDM"), and a thin sheath of extruded lead to act as a fluid barrier. Often, a jacket of EPDM or nitrile rubber is then applied around the conductors. As a final protection, a metal armour is applied over the electrical conductors.
While EPDM and other similar compounded materials provide excellent electrical and temperature stability in most wellbore applications, there is a major problem in their long term use in a wellbore. This problem is that the EPDM absorbs oil and then swells, thereby directly leading to structural and electrical failures of the cable. Common methods to minimize the effects of the oil upon the EPDM insulation have been to use compounds which have a relatively high degree of physical strength, as measured by resistance to elongation, and a relatively high tensile strength of the EPDM insulation. These compounds use relatively high degrees of cross-link density and/or fine particle size filler materials. However, these compounds show a loss of resistance to mechanical damage, especially in wellbore environments where the insulation is subjected to torsional stress.
The present invention has been contemplated to overcome the foregoing deficiencies and meet the above described needs. Specifically, the present invention is a multiconductor electrical cable for use in a subterranean wellbore that includes at least one electrical conductor surrounded by one or more layers of insulating material. At least one layer of the insulating material includes ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM) and/or polyolefin elastomer formed using a stereoregular polymerization catalyst (POE). This insulating material has a higher degree of crystallinity than previous insulation materials, with a higher tear retention and a higher tensile retention and less elongation loss over previous insulation materials, both before and after exposure to hydrocarbons in a subterranean wellbore environment.

Brief description of the drawings:

Figure 1 is a cross-sectional, elevational view of an electric submergible pumping system (ESP) suspended within a subterranean wellbore.
Figure 2 is a cross-sectional, perspective view of one preferred embodiment of a multiconductor electrical cable of the present invention.
As described above, the present invention comprises a multiconductor electrical cable for use in a subterranean wellbore. While the cable of the present invention can be used in many differing electrical power transmission environments, for the purposes of the present discussion it will be assumed that the cable is used to supply electricity to an electric submergible pumping system ("ESP"). As is well known to those skilled in the art, the ESP is set within a casing that is cemented within a subterranean wellbore that penetrates one or more subterranean earthen formations. Typical ESP's comprises an elongated electric motor, an oil-filled motor protector, and a multistage pump connected to a production tubing. The electrical cable extends from a surface power source downwardly within the casing and is operatively connected to the electric motor.
The electrical cable of the present invention is made to withstand relatively high temperatures, high pressures and corrosive fluids encountered within subterranean wellbores; however, it should be understood that the electrical cable of the present invention can also be used in less difficult applications, such as surface power transmission, under water uses, and the like. As used herein, the term "high temperature" means temperatures of greater than about 180 F and as high as about 500 F. The term "high pressure" means pressures as high as about 5,000 psi. Further, the term "corrosive fluids" means liquids and gases which can cause degradation to insulating materials and/or corrosion to the electrical conductors, such as liquids and/or gases containing hydrogen sulfide, carbon dioxide, brine, and the like.
To better understand the present invention, reference will be made to the accompanying drawings. Figure 1 shows a wellbore 10, used for recovering fluids such as water and/or hydrocarbons, that penetrates one or more subterranean earthen formations 12. The wellbore 10 includes a wellhead 14 removably connected to an upper portion of a production tubing and/or casing string 16, as is well known to those skilled in the art. If the casing string 16 extends across a fluid producing subterranean formation 12, then the casing string 16 can include at least one opening or perforations 18 for permitting fluids to enter the interior thereof An electric submergible pumping system ("ESP") 20 is shown suspended within the casing string 16, and generally includes an electric motor 22, an oil-filled motor protector 24, and a pump 26. The ESP 20 is shown in Figure 1 as deployed in a "conventional" configuration, with the motor 22 below the pump 26; however, it should be understood that the present invention can be used when the ESP 20 is in an "upside down" configuration, commonly known as a "bottom intake system."
A multiconductor cable 28 extends from a source of electrical power (not shown) at the earth's surface, through the casing 16, and is operatively connected to the motor 22. The cable 28 is preferably banded or strapped at intervals to a production tubing string 29, which is used to convey fluids from the pump 26 to the wellhead 14 at the earth's surface.
For the purposes of this discussion, the terms "upper" and "lower", "above" and "below", "uphole" and "downhole", and "upwardly" and "downwardly" are relative terms to indicate position and direction of movement in easily recognized terms. Usually, these terms are relative to a line drawn from an upmost position at the surface of the earth to a point at the center of the earth, and would be appropriate for use in relatively straight, vertical wellbores. However, when the wellbore is highly deviated, such as from about 60 degrees from vertical, or horizontal, these terms do not make sense and therefore should not be taken as limitations. These terms are only used for ease of understanding as an indication of what the position or movement would be if taken within a vertical wellbore.
Figure 2 shows one preferred embodiment of an electrical cable 28 of the present invention with three electrical conductors 30 in a round configuration. The cable 28 also can be formed to have a relatively flat configuration, with the electrical conductors 30 in parallel and side-by-side relationship. Each of the electrical conductors 30 are single drawn wires of copper or copper alloys, or are formed from a twist of several wires. For typical wellbore applications, the conductors 30 are single drawn wires having a diameter or gauge thickness of from about 0.160" (6 AWG) to about 0.414" (2/0 AWG). If the cable 28 is to be used in extremely corrosive environments, each of the conductors 30 can have a relatively thin coating (not shown) of lead, tin or alloys thereof, hot dipped, heat extruded, or electroplated thereon. One or more ground wires (not shown) may be included, as well as other wires, conductors, conduits, fibre optics, and the like, as may be used to transmit fluids and/or information and command signals through the power cable 28.
At least one of the electrical conductors 30, and preferably all of the conductors 30, is sheathed in at least one layer of an insulating material 32, selected from the group consisting of polyolefin elastomers, ethylene propylene diene methylene, ethylene propylene rubber, polychloroprene, polyimide, fluroelastomers, polypropylene, polyethylene, polyether, and copolymers, mixtures, blends and alloys thereof. If a polyether insulating material is selected, then preferred materials are selected from the group consisting of polyetherketone (PEK), polyetheretherketone (PEEK), polyetherketoneketone (PEKK), polyetherketoneetherketoneketone (PEKEKK), and mixtures, blends and alloys thereof.
The insulating material 32 is applied to the conductor 30 by spiral or longitudinal wrapping, or preferably by heat extrusion, as is well known to those skilled in the art. In addition, to protect the conductors 30 and the insulation material 32 from damage caused by corrosive fluids, a fluid barrier (not shown) may be applied to the outer surface of the insulating material 32. The fluid barrier can be spirally wrapped or extruded non-metallic materials, such as polyvinyl fluoride, polyvinylidene fluoride, fluorinated ethylene propylene, or blends, mixtures or alloys thereof The fluid barrier is preferably one or more extruded layers of a metal, such as lead, tin, and/or alloys thereof.
A jacket 34 of elastomeric material surrounds the plurality of electrical conductors 28 and is selected from the group consisting of nitrile rubber, ethylene propylene, ethylene propylene diene methylene terpolymer, polychloroprene, polyolefin elastomer, polyethylene, polypropylene, polyethylene, polyether, and copolymers, mixtures, blends and alloys thereof. An outer metal armour 36 covers the jacket of elastomeric material 34, as is well known to those skilled in the art.
As stated above, the cable of the present invention uses a new type of insulating material 32 that has improved properties over prior insulations. This new type of insulating material 32 has several preferred compound formulas. One preferred embodiment of the insulating material 32 has as a major constituent ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM). This SEPDM process is fully disclosed in U.S. Patents 5,272,236 and 5,278,272, which is herein incorporated by reference. The SEPDM is commercially available from DuPont Dow Elastomers, LLC under the "NORDEL IP" trademark.
A second preferred embodiment of the insulating material 32 comprises a blend of ethylene propylene diene methylene rubber (EPDM) of prior formulations and a polyolefin elastomer formed using a stereoregular polymerization catalyst (POE). This POE process is fully disclosed in the same two U.S. Patents above. The POE is commercially available from DuPont Dow Elastomers, LLC under the "ENGAGE" trademark.
A third preferred embodiment of the insulating material 32 comprises a blend of ethylene propylene copolymer (EPC) of commercially available formulation and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE). The EPC is commercially available from various sources, such as DSM CoPolymer under the "KELTAN" trademark, Exxon Chemical under the "VISTALON" trademark, and Uniroyal Chemical under the "TRILENE" trademark.
A fourth preferred embodiment of the insulating material 32 comprises a blend of ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE).
The preferred formulations of the above mentioned preferred embodiments are expressed hereafter using a well known elastomer standard of parts per hundred parts of rubber or "phr". Specifically, the formulations comprise about 80 - 100 phr of SEPDM; about 80 - 0 phr of EPDM, and about 20 - 100 phr of POE; about 80 - 0 phr of EPC, and about 20 - 100 phr of POE; and about 80 - 0 phr of SEPDM, and about 20 - 100 phr of POE.

Each of the above formulations can include one or more of the following additional materials: about 75 - 200 phr of a reinforcing agent, such as kaolin clay; about 10 - 0 phr of an electrical stabilizer, such as lead oxide; an antioxidant; a cure accelerator; a process aid agent, such as microcrystalline wax; and a curing agent. For example, one preferred embodiment of the insulating material 32 of the present invention has the following material formulation:

80.0 - 0.0 phr	SEPDM
20.0 - 100.0 phr	Polyolefin elastomer (POE)
1.0 - 3.0 phr	Polymerized 1,2-dihydro-2,2,4-trimethylquinoline
5.0 - 15.0 phr	High vinyl polybutadiene
75.0 - 200.0 phr	Kaolin clay
5.0 phr	Lead oxide
5.0 phr	Microcrystalline wax
1.5 phr	alpha, alpha prime - bis(t-butylperoxy)-diisopropylbenzene.

To prove the efficacy of the present invention, tests were conducted to find out the physical properties of two of the preferred embodiments in comparison to the physical properties of a prior EPDM insulation. The formulations and the results are contained in Table 1. The results show that in comparison to the standard prior EPDM insulation, the new materials have significant increases in tensile strength, elongation, and tear resistance, even after being immersed in water and hydrocarbon fluids.
Whereas the present invention has been described in particular relation to the drawings attached hereto, it should be understood that other and further modifications, apart from those shown or suggested herein, may be made within the scope of the present invention as defined in the claims.

Claims

A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM); and an outer protective armour surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene diene methylene rubber (EPDM) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and an outer protective armour surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene copolymer (EPC) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and an outer protective armour surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and an outer protective armour surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM); and a jacket of elastomeric material surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising : a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene diene methylene rubber (EPDM) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and a jacket of elastomeric material surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene copolymer (EPC) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and a jacket of elastomeric material surrounding the plurality of electrical conductors.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM) and polyolefin elastomer formed using a stereoregular polymerization catalyst (POE); and a jacket of elastomeric material surrounding the plurality of electrical conductors.
A multiconductor electrical cable of Claim 6 and further comprising about 80 - 0 phr of EPDM, and about 20 - 100 phr of POE.
A multiconductor electrical cable of Claim 7 and further comprising about 80 - 0 phr of EPC, and about 20 - 100 phr of POE.
A multiconductor electrical cable of Claim 8 and further comprising about 80 - 0 phr of SEPDM, and about 20 - 100 phr of POE.
A multiconductor electrical cable of Claim 11 and further comprising about 75 - 200 phr of a reinforcing agent.
A multiconductor electrical cable of Claim 12, wherein the reinforcing agent comprises kaolin clay.
A multiconductor electrical cable of Claim 1 and further comprising about 10 - 0 phr of an electrical stabilizer.
A multiconductor electrical cable of Claim 14 wherein the electrical stabilizer comprises lead oxide.
A multiconductor electrical cable for use in a subterranean wellbore, comprising: a plurality of electrical conductors; at least one layer of insulating material surrounding at least one of the electrical conductors; the insulating material comprising a blend of about 80 - 0 phr of ethylene propylene diene methylene rubber formed using a stereoregular polymerization catalyst (SEPDM), about 20 - 100 phr of polyolefin elastomer formed using a stereoregular polymerization catalyst (POE), about 75 - 200 phr of a reinforcing agent, and about 10 - 0 phr of an electrical stabilizer; and a jacket of elastomeric material surrounding the plurality of electrical conductors.
A multiconductor electrical cable of Claim 16, wherein the jacket of elastomeric material is selected from the group consisting of nitrile rubber, ethylene propylene, ethylene propylene diene methylene terpolymer, polychloroprene, polyolefin elastomer, polyethylene, polypropylene, polyethylene, polyether, and copolymers, mixtures, blends and alloys thereof.