EP3797431A1

EP3797431A1 - Multilayer cables for an offshore environment

Info

Publication number: EP3797431A1
Application number: EP19731322.4A
Authority: EP
Inventors: Jérôme CHAUVEAU; Jérôme RONDIN; Florent ABGRALL
Original assignee: Arkema France SA
Current assignee: Arkema France SA
Priority date: 2018-05-22
Filing date: 2019-05-14
Publication date: 2021-03-31
Also published as: US20210146658A1; FR3081602B1; WO2019224452A1; FR3081602A1

Abstract

The invention relates to the field of cables for an offshore environment (known as "downhole cables"). More particularly, the invention relates to an electrical cable having an insulating multilayer structure based on fluorinated polymers and polyolefins. This structure is made up of multiple layers that are intercohesive and obtained by coextrusion. The invention also relates to the use of said cable as a drilling material for extracting petroleum or natural gas.

Description

MULTILAYER CABLES FOR

OFFSHORE ENVIRONMENT

FIELD OF THE INVENTION

The present invention is in the field of cables for offshore environment (called downhole cables). More particularly, the invention relates to an electrical cable comprising an insulating multilayer structure based on fluorinated polymers and polyolefins. This structure is formed of several cohesive layers between them and obtained by coextrusion. The invention also relates to the use of said cable as drilling equipment for the extraction of oil or natural gas.

TECHNICAL BACKGROUND

The so-called'downhole cables' are cables that allow the power supply of drilling utilities in the context of oil or gas exploitation. These cables or cable structures (consisting of several individual cables) are used in the context of API 17J chemical specifications and in a thermal environment ranging from 130 to 180 ° C.

An electrical cable is generally made of a conductive material coated with one or more layers of polymeric materials acting as a chemical and thermal insulator. During their use, electrical cables are commonly subject to stresses both mechanical, chemical and thermal, detrimental to the integrity of their insulators.

According to API 17J chemical specifications, electrical cables and cable structures are subject to operating conditions including at least the following elements: brackish water (mixture of dirty water, oil, mineral substances and gas),

gas pressure up to 18 MPa,

hydrostatic pressure up to 35 MPa,

exposure temperatures ranging from -40 ° C to 180 ° C,

pH ranging from 5.0 to 8.5, this range can be extended from 3.0 to 9.5 and can, for periods up to 6h, down to pH equal to zero,

presence of aggressive chemical agents such as: H ₂ S (up to 1.25 g / l), C0 ₂ (up to 0.15 g / l), Cl (up to 20 g / l), HC0 ₃ (up to 1 g / l), Ca (up to 2 g / l), Mg (up to 0.13 g / l), Fe (up to 0.032 g / l), Na + K ( up to 8.6 g / l). The purpose of this specification is to prevent any swelling and / or shrinkage and / or cracking of the insulating layers that are in contact with the extraction medium having the characteristics described above. The insulating layers must in particular be subjected to pH values ranging up to 0 and concentrations of hydrochloric acid injected into the well of up to 30% by weight.

Electrical cables insulated with multilayer structures comprising an inner layer of polyethylene and an outer layer of a fluoropolymer (for example polyvinylidene fluoride or PVDF) are known. However, the inner layer and the outer layer can delaminate easily because of the lack of adhesion between the two types of polymers, which have no chemical affinity for each other, resulting in embrittlement of the entire electric cable. It is therefore desirable to be able to improve the adhesion between the layers to improve the properties of the electric cables.

The Applicant has already proposed in WO 2007/006897 to solve this delamination problem by combining a layer based on a polyolefin and / or a functionalized polyolefin and a fluoropolymer layer comprising at least a fluoropolymer on which has been grafted by irradiation at least one unsaturated monomer. This multilayer structure gives very satisfactory results in terms of adhesion between layers; however, the fluoropolymer modified by radiation grafting, used in this structure, alone or as a mixture, has a low degree of grafting which can limit the adhesion and its maintenance over time in severe environments as described above.

There is therefore a need to develop new insulating multilayer structures for electric cables used for the extraction of oil or natural gas, which have sufficient chemical and thermal resistance over the entire duration of use of these cables for durations up to 20 years, while maintaining their functional and structural integrity through improved adhesion between the polyolefin-based (or the layers) and the fluoropolymer-based layer.

SUMMARY OF THE INVENTION

The invention relates first of all to an electric cable comprising a conductive core surrounded by a multilayer structure intended to protect said core from chemical and thermal aggressions. This multilayer structure is obtained by coextrusion then crosslinked by irradiation of electron beam. Different multilayer structures are covered by the invention, they comprise the following layers, from the inside to the outside:

a first inner layer and predominant polyolefin, playing the role of insulating layer; optionally, a cl 'layer acting as a binder consisting of a polyolefin different from that of the c2 layer and having reactive functions obtained by copolymerization or grafting;

a second layer C2 acting as a binder, chemically compatible with the polyolefin inner layer and having reactive functions obtained by copolymerization or grafting;

a third layer c3 comprising a second binder that can react chemically with the second layer c2. This layer is fluorinated and already provides resistance to external chemical attack;

a fourth protective layer 4 comprising a fluoropolymer based on vinylidene fluoride for providing chemical and thermal resistance.

Each of the layers described above may, independently, comprise a crosslinking agent. According to one embodiment, the cl and c4 layers each contain a crosslinking agent whose mass content varies, independently of one layer to another, from 0.5 to 5%, preferably from 2 to 4%.

According to one embodiment, the layers c2 and / or c3 do not contain a crosslinking agent.

According to another embodiment, the layers c2 and / or c3 contain a crosslinking agent at a level ranging from 0.5 to 5%, preferably between 2 and 4%.

The multilayer structures are obtained by coextrusion and then crosslinked by irradiation.

The invention also relates to cable structures formed of several individual cables having the structure described above, wrapped in a protective layer.

The invention also relates to a method of manufacturing the multilayer structure by coextrusion followed by radiation crosslinking.

The invention also relates to the use of such an electric cable as drilling equipment for the extraction of oil or natural gas or for geothermal drilling.

Advantageously, the use of an electric cable comprising this structure, in the oil or natural gas drilling medium, makes it possible to avoid severe damage to the electrical insulation layers of each cable constituting the cable structure, which generates a complete malfunction of the line. The present invention overcomes the disadvantages of the state of the art. It more particularly provides a cable having a combination of properties, namely:

a better adhesion to the interfaces of the layers enveloping the metallic core of the cable thanks to the use of coextrusion binders (c2 and c3),

an improved thermal resistance due to the crosslinking of all the layers, for temperatures up to 180 ° C.,

a dimensional stability under improved temperature due to the crosslinking of all the layers,

- better barrier properties to oils and solvents thanks to the use of a fluorinated external protection layer (see above),

- Better resistance to abrasion, by the crosslinking of the outer layer in contact with the other cables and the inner layer in contact with the core of the cable.

The improvements described above relate to cables known to those skilled in the art, in particular:

cables comprising only an insulating layer of crosslinked polyolefin, and cables comprising a polyolefin insulating layer and a fluorinated barrier layer, all crosslinked.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The invention is now described in more detail and without limitation in the description which follows.

The invention proposes to provide an electric cable capable of withstanding in an off-shore environment. For this purpose, it relates in a first aspect to a cable comprising a conductive core surrounded by a multilayer structure for protecting said core from chemical and thermal attack.

The various constituent parts of the cable according to the invention are described below.

According to various embodiments, said cable comprises the following characters, if necessary combined.

Conducting heart

The core of the cable is a current conducting material selected from copper, copper-nickel alloys, aluminum and composite electrical materials. Multilayer structure

Different multilayer structures are covered by the invention, they comprise the following layers, from the inside to the outside:

a first and predominant polyolefin inner layer acting as an insulating layer;

- Optionally, a layer cl 'acting as a binder, consisting of a polyolefin different from that of the layer c2 and having reactive functions obtained by copolymerization or grafting;

a second layer C2 acting as a binder, chemically compatible with the polyolefin inner layer (cl or cl '), consisting of a polyolefin and having reactive functions obtained by copolymerization or grafting;

a third layer c3 acting as a binder and based on a mixture of fluoropolymer and functionalized acrylic polymer, which can react chemically with the second layer c2; and

a fourth protective layer 4 comprising a fluoropolymer based on vinylidene fluoride which makes it possible to provide the chemical and thermal resistance.

Internal layer cl

The insulating layer is predominantly composed of polyolefin. This term denotes a polymer comprising predominantly ethylene and / or propylene units.

According to one embodiment, the polyolefin is a polyethylene (PE), homo- or copolymer, the comonomer being chosen from propylene, butene, hexene or octene. It may also be a polypropylene (PP), homo- or copolymer, the comonomer being chosen from ethylene, butene, hexene or octene. Polypropylene is iso- or syndiotactic polypropylene.

According to one embodiment, the polyethylene is selected from high density polyethylene (HDPE), low density (LDPE), medium density (MDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE). The polyethylene can be obtained using a Ziegler-Natta, Phillips or metallocene catalyst or by the high pressure process.

According to one embodiment, the polyolefin is a copolymer of ethylene and propylene (known as EPM) or a copolymer of ethylene, propylene and a diene (such as 4-hexadiene, ethylidene norbornene or butadiene), known as EPDM. According to one embodiment, said copolymer of ethylene and propylene is a block copolymer.

According to one embodiment, the polyolefin constituting the clayer is a crosslinked polyethylene (abbreviated PEX). PEX has better non-crosslinked PE than mechanical properties (especially crack resistance) and better chemical resistance. The crosslinked polyethylene may be, for example, a polyethylene comprising hydrolysable silane groups (as described in documents WO 01/53367 or US20040127641) which has then been crosslinked after reaction between them silane groups. The reaction of silane groups Si-OR between them leads to Si-O-Si bonds which connect the polyethylene chains to each other. The content of hydrolysable silane groups may be at least 0.1 hydrolysable silane groups per 100 units -CH ₂ - (determined by infrared spectrometry).

According to one embodiment, the polyethylene is crosslinked using radiation, for example gamma radiation. It may also be a polyethylene crosslinked using a radical initiator of the peroxide type. It is therefore possible to use a PEX of type A (crosslinking using a radical initiator), type B (crosslinking with silane groups) or type C (crosslinking by irradiation).

Layers acting as binder

The multilayer structure surrounding the conductive core of the cable according to the invention comprises two or three layers acting as a binder between the insulating clayer and the protective layer c4.

Optional binder layer

According to one embodiment, the multilayer structure which surrounds the conductive core of the cable according to the invention comprises a functionalized polyolefin binder layer, designated by cl '. This is particularly the case when the clayer is made of polypropylene. This layer is placed between the cl layer and the c2 layer.

The layer cl 'comprises a functionalized olefinic polymer having a different structure from that of the functionalized polyolefin constituting the layer c2. This ensures better cohesion between these binder layers, the functional groups of the polyolefin of the layer c 'being able to interact with the functional groups of the polyolefin constituting the layer c2. The functional groups of the functionalized polyolefin of the layer c1 'are chosen from unsaturated carboxylic acids, unsaturated dicarboxylic acids having 4 to 10 carbon atoms and their anhydride derivatives.

The functionalized polyolefin is chosen from polymers obtained by grafting at least one unsaturated polar monomer having a functional group as described above on at least one propylene homopolymer or a copolymer of propylene and of an unsaturated polar monomer chosen from C1-C8 alkyl esters or glycidyl esters of unsaturated carboxylic acids, or unsaturated carboxylic acid salts or mixtures thereof. Preferably, the functionalized polyolefin of the clayer is a polypropylene grafted with maleic anhydride.

Advantageously, the polymer comprises en masse an amount of said grafting monomer equal to or less than 5%.

Layer c2

The binder layer c2 is chemically compatible with the insulating inner layer c1 or the clayer, if present. It consists of a functionalized polyolefin which has reactive functions obtained by copolymerization or grafting.

According to one embodiment, the functionalized polyolefin is a copolymer of ethylene and / or propylene and at least one unsaturated polar monomer chosen from:

(C 1 -C 5) alkyl (meth) acrylates, especially methyl, ethyl, propyl, butyl, 2-ethylhexyl, isobutyl or cyclohexyl (meth) acrylate;

unsaturated carboxylic acids, their salts and anhydrides, especially acrylic acid, methacrylic acid, maleic anhydride, itaconic anhydride, citraconic anhydride;

unsaturated epoxides, especially aliphatic glycidyl esters and ethers such as glycidyl allyl glycidyl ether, vinyl glycidyl ether, maleate and itaconate, glycidyl acrylate and methacrylate, as well as alicyclic glycidyl esters and ethers;

vinyl esters of saturated carboxylic acids, especially vinyl acetate, vinyl propionate or vinyl butyrate.

The functionalized polyolefin may be obtained by copolymerization of ethylene and / or propylene and at least one unsaturated polar monomer selected from the above list. The copolymerization is carried out at high pressures greater than 1000 bar according to the so-called high-pressure process, described for example in the documents FR 2498609, EP 0 174 244 or EP 0 177 378. According to one embodiment, the functionalized polyolefin obtained by copolymerization comprises, by weight, from 50 to 99.9% of ethylene, preferably from 60 to 99.9%, even more preferably from 65 to 99% and from 0.1 to 50%, preferably from 0.1 to 40%, more preferably from 1 to 35% of at least one polar monomer from the above list.

According to one embodiment, the functionalized polyolefin is a copolymer of ethylene and an unsaturated epoxide, preferably glycidyl (meth) acrylate, and optionally a (C 1 -C 10) alkyl (meth) acrylate or of a vinyl ester of saturated carboxylic acid. The content of unsaturated epoxide, especially glycidyl (meth) acrylate, is between 0.1 and 50%, advantageously between 0.1 and 40%, preferably between 1 and 35% and even more preferably between 1 and 20%. .

According to one embodiment, the functionalized polyolefin is a copolymer of ethylene and an unsaturated acid anhydride, preferably maleic anhydride, and optionally a C 1 -C 10 alkyl (meth) acrylate or of a vinyl ester of saturated carboxylic acid. The content of unsaturated acid anhydride, in particular maleic anhydride, is between 0.1 and 50%, advantageously between 0.1 and 40%, preferably between 1 and 35% and even more preferably between 1 and 10%.

According to one embodiment, the functionalized polyolefin forming the layer c2 is obtained by free radical grafting of an unsaturated polar monomer such as those mentioned above, on a polyolefin. The grafting takes place in an extruder or in solution in the presence of a radical initiator. As examples of radical initiators, t-butyl hydroperoxide, cumene hydroperoxide, di-isopropylbenzene hydroperoxide, di-tert-butylperoxide, t-butyl- cumyl peroxide, dicumyl peroxide, 1,3-bis (t-butylperoxyisopropyl) benzene, benzoyl peroxide, iso-butyrylperoxide, bis-3,5,5-trimethylhexanoyl peroxide or methyl ethyl ketone peroxide.

The grafting of an unsaturated polar monomer on a polyolefin is known to a person skilled in the art. For more details, reference may be made for example to documents EP 0 689 505 or US Pat. No. 5,235,149. The polyolefin on which the polar monomer is grafted unsaturated can be a polyethylene, especially high density polyethylene (HDPE) or low density (LDPE), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE). The polyethylene can be obtained using a Ziegler-Natta, Phillips or metallocene catalyst or by the high-pressure process. The polyolefin may also be a polypropylene, especially an iso- or syndiotactic polypropylene. According to one embodiment, the polymer on which the unsaturated polar monomer is grafted is a copolymer of ethylene and at least one unsaturated polar monomer chosen from:

vinyl esters of saturated carboxylic acids, especially vinyl acetate or vinyl propionate.

The layer c2 may comprise a single functionalized polyolefin or a mixture of several functionalized polyolefins, optionally mixed with a non-functionalized polyolefin. It can be for example a mixture:

a copolymer of ethylene and a C 1 -C 5 alkyl (meth) acrylate or a saturated carboxylic acid vinyl ester,

with a copolymer of ethylene and an unsaturated epoxide, preferably glycidyl (meth) acrylate, and optionally a (C 1 -C 5) alkyl (meth) acrylate or a vinyl carboxylic acid ester saturated.

Another example of mixing is that:

a copolymer of ethylene and a C 1 -C 5 alkyl (meth) acrylate or a saturated carboxylic acid vinyl ester

with a copolymer of ethylene and an unsaturated acid anhydride, preferably maleic anhydride, and optionally a (C 1 -C 5) alkyl (meth) acrylate or a vinyl carboxylic acid ester saturated.

According to a preferred embodiment, the layer c2 is formed of a copolymer of ethylene and glycidyl methacrylate.

C3 fluorinated binder layer

This binder layer comprises a mixture of at least one fluorinated polymer and a functionalized acrylic copolymer. It is able to react chemically with the layer c2 increasing the cohesion of the multilayer structure. This layer is fluorinated and thus contributes to the resistance to external chemical attack of the cable.

The fluoropolymer of the layer c3 is chosen from homopolymers of vinylidene fluoride (PVDF) and copolymers of vinylidene fluoride and at least one other comonomer. According to one embodiment, the VDF comonomer is chosen from vinyl fluoride, trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro (alkyl vinyl) ethers such as perfluoro (methylvinyl) ether (PMVE), perfluoro (ethylvinyl) ether (PEYE), perfluoro (propylvinyl) ether (PPVE), perfluoro (1,3-dioxozole); perfluoro (2,2-dimethyl-1,3-dioxol) (PDD), the product of formula CF2 = CFOCF2CF (CF3) OCF2CF ₂ X wherein X is SO ₂ F, CO ₂ H, CH ₂ OH; CH ₂ OCN or CH ₂ OPO ₃ H, the product of formula CF 2 = CFOCF ₂ CF ₂ SO ₂ F; the product of formula F (CF ₂ ) nCH ₂ OCF = CF ₂ in which n is 1,2, 3, 4 or 5, the product of formula RiCH ₂ OCF = CF ₂ in which R 1 is hydrogen or F (CF ₂ ) _Z and z is 1, 2, 3, or 4; the product of formula R ₃ 0CF = CH ₂ in which R 3 is F (CF ₂ ) _Z and z is 1, 2, 3, or 4 or alternatively perfluorobutylethylene (PFBE), fluoroethylenepropylene (FEP), 3.3, 3-trifluoropropene, trifhioromethyl-3,3,3-trifhioro-1-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, E-

1.3.3.3-tetrafluoropropene or HFO-1234zeE, ZI, 3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, lel, 2,3,3-tetrafluoropropene or HFO-1234ye, the

1.1.3.3-tetrafluoropropene or HFO-1234zc, chlorotetrafluoropropene or HCFO-1224, chlorotrifluoropropenes (especially 2-chloro-3,3,3-trifluoropropene), 1-chloro-2-fluoroethylene, trifluoropropenes (especially 3 3,3-trifluoropropene), pentafluoropropenes (especially 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene), 1-chloro-2,2-difluoroethylene, 1-bromo-2,2-difluoroethylene, and bromotrifluoroethylene. Fe copolymer may also include non-fluorinated monomers such as ethylene.

According to one embodiment, the fluorinated copolymer that can be used for the c3 layer is a copolymer of VDF and HFP.

According to one embodiment, the level of HFP in this VDF-HFP copolymer is greater than 15% by weight and has a melting point greater than 165 ° C.

Functionalized acrylic copolymer contained in the layer c3 denotes a copolymer comprising:

- reasons of the type:

in which R 1 and R ₂ represent a hydrogen atom or a linear or branched alkyl having from 1 to 20 carbon atoms; R1 and R2 may be the same or different; - and patterns of the type:

wherein R ₃ is a hydrogen atom or a linear or branched alkyl containing one to twenty carbon atoms.

This last unit may be in its acid form, but also under its anhydride derivatives or a mixture thereof. When in the form of anhydride, this unit may be represented by the formula:

wherein R ₄ and R ₅ represent a hydrogen atom or a linear or branched alkyl having from 1 to 20 carbon atoms; R ₄ and Rs may be the same or different.

According to one embodiment, the acrylic copolymer comprises up to 50% by weight of the unit in acid form or its anhydride derivative or a mixture of both. Advantageously, the acrylic copolymer comprises up to 25% by weight of the unit in acid form or its anhydride derivative or a mixture of these.

According to another embodiment, R 1 and R ₂ represent the methyl radical.

According to another embodiment, R ₃ represents the hydrogen or methyl radical in the case where the unit carrying it is in acid form, and R ₄ and Rs represent the hydrogen or methyl radical in the case where the unit is in the form of anhydride.

According to one embodiment, the acrylic copolymer is a copolymer of methyl methacrylate and glutaric anhydride.

According to one embodiment, the acrylic copolymer is a copolymer of methyl methacrylate and methacrylic acid.

According to one embodiment, the functionalized acrylic copolymer is a mixture of these two copolymers. Advantageously, the acrylic copolymer of said layer c3 comprises, by weight, from 1% to 50%, preferably between 1% and 25%, inclusive, of functionalized monomers.

Protection layer c4

The multilayer structure surrounding the core of the cable comprises a fourth layer c4 whose role is to provide more chemical and thermal resistance necessary for the use of the cable in a drilling medium.

This layer is formed of a fluoropolymer as described above for layer c3.

According to one embodiment, said fluoropolymer is a homopolymer of vinylidene fluoride.

According to one embodiment, said fluoropolymer is VDF-HFP copolymer.

The fluoropolymers used in the composition of the layers c3 and c4 may be identical in both layers or not. The layers may also comprise a mixture of at least two fluorinated polymers, this mixture being identical or not in the layers c3 and c4.

According to one embodiment, the cable according to the invention consists of a conductive core surrounded by a coextruded and crosslinked multilayer structure consisting of four layers: layer cl, layer c2, layer c3 and layer c4 as described above .

According to one embodiment, the cable according to the invention consists of a conductive core surrounded by a coextruded and crosslinked multilayer structure consisting of 5 layers: cl layer, cl layer, c2 layer, c3 layer and c4 layer such that described above.

Each of the layers described above, and independently, may comprise a crosslinking agent, preferably triallyl isocyanurate (TAIC). Other examples of crosslinking agents: triallyl cyanurate (TAC), trimethylol propane triacrylate (TMPTA), trimethylol propane trimethacrylate (TMPTMA).

Other additives may be added in one or more layers, namely zinc oxide (ZnO) and / or phosphite type thermal stabilizers.

The multilayer structures described above are obtained by coextrusion and then crosslinked by irradiation. Among the most commonly used radiation are UV rays, infrared rays, X-rays and electron beams (e-beam). Preferably, the electron beams are used because of their excellent penetration power, high achievable dose and industrial availability. Preferably, the irradiation dose used for the crosslinking of these structures is 100 kGy. The multilayer structures described above have an outer diameter ranging from 8 to 14 mm and a total thickness ranging from 2 to 3 mm.

Another object of the invention is the use of an electrical cable having one of the abovementioned structures as drilling equipment for the extraction of oil or natural gas or for geothermal drilling.

Advantageously, these are cable structures formed of several individual cables having the structure described above, wrapped in a protective layer which are used because of their greater strength, especially mechanical.

According to one embodiment, the cable structure consists of three individual cables according to the invention, each containing a copper wire, these copper wires being assembled in parallel.

The three cables are then covered and held together:

either by a polymer sheath (PE, PP or PVDF),

- Or by a fiberglass fabric cladding or wrapped polyolefin fiber fabric ("wrapping").

The three cables and the cladding are then covered:

or by a PET or polyolefin film, and a dry laid nonwoven made of PET or polyolefin,

- either by a non-woven type "dry ugly" PET or wound polyolefin,

all protected by flexible metal armor.

EXAMPLES

The following examples illustrate the invention without limiting it.

Structure 1 (4 layers)

- insulation layer cl: HDPE, thickness 2.1 mm

binder layer c2: copolymer of ethylene and glycidyl methacrylate, thickness 0.1 mm

binder layer c3: mixture of VDF-HFP fluoropolymer and copolymer of methyl methacrylate and glutaric anhydride, 0.1 mm thick

c4 protective layer: VDF-HFP copolymer, 0.4 mm thick. Structure 2 (4 layers)

- insulation layer cl: HDPE, thickness 2.1 mm

c4 protective layer: VDF-HFP copolymer, 0.4 mm thick

The multilayer structure obtained by coextrusion is irradiated with an electron beam (dose: 100 kGy)

Structure 3 (4 layers)

- insulation layer cl: HDPE + 3% TAIC, thickness 2.1 mm

c4 protective layer: VDF-HFP + 3% TAIC copolymer, thickness 0.4 mm

Structure 4 (1 layer): Counterexample

Monolayer structure in HDPE + 3% TAIC (total thickness = 2.7mm) irradiated with electron beam (dose: 100 kGy).

Structure 5 (5 layers)

insulation layer cl: copolymer of PP, thickness 2.1 mm

binder layer cl: maleic anhydride grafted polypropylene, thickness 0.1 mm

c4 protective layer: VDF-HFP copolymer, 0.4 mm thick.

Table 1 shows the advantage of using multilayer structures 1, 2 and 3 in the field of cables for power supply of drilling utilities for oil or gas exploitation. Fa structure 3 allows in particular to significantly increase the temperature of use of the cable. The term "Pass" means that despite exposure to the indicated temperature in oil and brackish water, the structure retains its physical integrity and sufficient mechanical properties, which allows long-term electrical insulation of the cable.

The term "Fails" means that the cable exposed to the indicated temperature in the oil and brackish water experiences a significant loss of mechanical properties and physical integrity, which leads to a short circuit at current flow, and therefore the loss of electrical insulation of the cable.

Membership measurement:

The inter-layer adhesion is measured by a peel test according to the so-called "forced peel" method at a temperature of 23 ° C and a drawing speed of 50mm / min. Strips about 7 mm wide are cut into the tubes. These strips were primed using pliers and a cutter. Once primed, one of the strips is placed in a fitting adapted for small diameter tubes.

The lever arm is composed of layers c4 and c3 and has a total thickness of 500pm. The interface sought is thus that between the layers c3 and c2. The adhesion measurement is carried out 24 hours after the completion of the multilayer structure. Adhesion measurements following the same protocol are also performed after the multilayer structure has been crosslinked by electron beam irradiation.

Aging in

The cables considered are immersed in oil and brackish water for 1200 hours in an oven set at the desired temperature (130, 150 or 170 ° C). After exposure to the indicated temperature, the integrity of the cable is characterized by visual inspection and a measure of electrical continuity is performed using a multimeter.

Table 1

Claims

An electric cable comprising a conductive core surrounded by a coextruded and crosslinked multilayer structure comprising, from the inside towards the outside:

an inner layer and polyolefin;

optionally, a binder layer of functionalized polyolefin binder; a c2 layer of binder, chemically compatible with the cl layer or the cl 'layer and having reactive functions obtained by copolymerization or grafting; a binder layer c3 comprising a mixture of at least one fluorinated polymer and a functionalized acrylic copolymer;

a protective layer c4 comprising a fluoropolymer based on vinylidene fluoride.

2. Cable according to claim 1 wherein said core is a current conducting material selected from copper, copper-nickel alloys, aluminum and composite electrical materials.

3. Cable according to one of claims 1 or 2 wherein said cl layer is composed of polyolefin selected from:

polyethylene homopolymer selected from high density polyethylene (HDPE), low density (LDPE), medium density (LMAP), linear low density polyethylene (LLDPE), very low density polyethylene (VLDPE);

copolymers of ethylene and a comonomer selected from propylene, butene, hexene or octene;

polypropylene homo- or copolymer, the comonomer being selected from ethylene, butene, hexene or octene;

copolymers of ethylene and propylene, including block copolymer, or copolymers of ethylene, propylene and a diene such as 1,4-hexadiene, ethylidene norbornene or butadiene;

the crosslinked polyethylene chosen from a polyethylene comprising hydrolysable silane groups which has then been crosslinked after reaction between them silane groups, and the crosslinked polyethylene using radiation.

4. Cable according to one of claims 1 to 3 wherein said layer c2 consists of a functionalized polyolefin which has reactive functions obtained by copolymerization or grafting.

The cable of claim 4 wherein said functionalized polyolefin is a copolymer of ethylene and / or propylene and at least one unsaturated polar monomer selected from:

The cable of claim 4 wherein said functionalized polyolefin is a copolymer of ethylene and an unsaturated epoxide, preferably glycidyl (meth) acrylate, and optionally a (C 1 -C) alkyl (meth) acrylate. -Cs or a vinyl ester of saturated carboxylic acid.

The cable of claim 4 wherein said functionalized polyolefin is a copolymer of ethylene and an unsaturated acid anhydride, preferably maleic anhydride, and optionally a C1-alkyl (meth) acrylate. -Cs or a vinyl ester of saturated carboxylic acid.

8. Cable according to claim 4 wherein said functionalized polyolefin is obtained by radical grafting of an unsaturated polar monomer on a polyolefin.

9. Cable according to one of claims 1 to 8 wherein said cl 'layer consists of at least one functionalized polyolefin, obtained by grafting at least one unsaturated polar monomer having as functional group an unsaturated carboxylic acid, a unsaturated dicarboxylic acid having 4 to 10 carbon atoms and their anhydride derivatives, on a propylene homopolymer or a copolymer of propylene and an unsaturated polar monomer selected from C1-C8 alkyl esters or glycidyl esters of carboxylic acids unsaturated, or unsaturated carboxylic acid salts or mixtures thereof.

10. Cable according to one of claims 1 to 9 wherein said layer c3 comprises a mixture of at least one fluorinated polymer and a functionalized acrylic copolymer.

11. Cable according to claim 10 wherein said fluoropolymer is chosen from homopolymers of vinylidene fluoride (PVDF) and copolymers of vinylidene fluoride and at least one other comonomer, the latter being chosen from vinyl fluoride, trifluoroethylene (VF3), chlorotrifluoroethylene (CTFE), 1,2-difluoroethylene, tetrafluoroethylene (TFE), hexafluoropropylene (HFP), perfluoro (alkyl vinyl) ethers such as perfhioro (methylvinyl) ether (PMVE), perfluoro (ethylvinyl) ether (PEVE), perfluoro (propylvinyl) ether (PPVE), perfluoro (1,3-dioxozole); perfluoro (2,2-dimethyl-1,3-dioxol) (PDD), the product of formula CF ₂ = CFOCF ₂ CF (CF ₃ ) OCF ₂ CF ₂ X wherein X is SO ₂ F, CO ₂ H, CH ₂ OH; CH ₂ OCN or CH ₂ OPO ₃ H, the product of formula CF ₂ = CFOCF ₂ CF ₂ SO ₂ F; the product of formula F (CF ₂ ) nCH ₂ 0CF = CF ₂ in which n is 1,2, 3, 4 or 5, the product of formula R _I CH ₂ 0CF = CF ₂ in which R 1 is hydrogen or F (CF ₂ ) _Z and z is 1, 2, 3, or 4; the product of formula R ₃ 0CF = CH ₂ in which R ₃ is F (CF ₂ ) _Z and z is 1, 2, 3, or 4 or else perfluorobutylethylene (PFBE), fluoroethylenepropylene (FEP), 3.3 3-trifluoropropene, trifhioromethyl-3,3,3-trifhioro-1-propene, 2,3,3,3-tetrafluoropropene or HFO-1234yf, EI, 3,3,3-tetrafluoropropene or HFO-1234zeE , Zl, 3,3,3-tetrafluoropropene or HFO-1234zeZ, 1,1,2,3-tetrafluoropropene or HFO-1234yc, lel, 2,3,3-tetrafluoropropene or HFO-1234ye, l, l, 3,3-tetrafluoropropene or HFO-1234zc, chlorotetrafluoropropene or HCFO-1224, chlorotrifluoropropenes (especially 2-chloro-3,3,3-trifluoropropene), 1-chloro-2-fluoroethylene, trifluoropropenes (especially 3 3,3-trifluoropropene), pentafluoropropenes (especially 1,1,3,3,3-pentafluoropropene or 1,2,3,3,3-pentafluoropropene), 1-chloro-2,2-difluoroethylene, 1-bromo-2,2-difluoroethylene, and bromo trifluoroethylene.

12. Cable according to one of claims 10 and 11 wherein said fluoropolymer is a copolymer of vinylidene fluoride and hexafluoropropylene.

13. Cable according to one of claims 10 to 12 wherein said acrylic copolymer is a copolymer of methyl methacrylate and glutaric anhydride, or a copolymer of methyl methacrylate and methacrylic acid, or a mixture of these two copolymers .

14. Cable according to one of claims 1 to 13 wherein said layer c4 is a homopolymer of vinylidene fluoride or a copolymer of vinylidene fluoride and hexafluoropropylene.

15. Cable according to one of the preceding claims wherein the cl and c4 layers each contain from 0.5 to 5% by weight of a crosslinking agent.

16. Use of an electric cable according to one of claims 1 to 15 as drilling equipment for the extraction of oil or natural gas or for geothermal drilling.

17. A method of manufacturing an electrical cable according to one of claims 1 to 15 comprising a conductive core surrounded by a multilayer structure, wherein said multilayer structure is obtained by coextrusion, then crosslinked by irradiation of electron beam.