Technical field

The present invention relates to cables, and in particular to a cable for use in a well- bore, such as a wireline cable for use in well intervention. In particular embodiments, the cable may supply electrical energy or provide a telemetry line to a weiibore tool attached to the cable in the weiibore.

Background

Cables of various types are used in a wide range of applications to lower or lift equi pment. In the oil and gas exploration and production industry, tools are typically lowered into wellbores using cables. This is usual in a well intervention operation, where during the lifetime of a hydrocarbon production well, there may be a need to perform operations in the weiibore for example to maintain or repair it so that it can continue to produce hydrocarbons. The cables are typically stored on a drum and spooled out as a continuous length into and along the weiibore.

Many wells today have very long weiibore trajectories and may have sections that extend laterally, for example horizontally, over a substantial distance for example several kilometres. The diameter of the weiibore in the farthest reaches may be very small. In the lateral sections, weiibore tractors may be required to pull the cable along with it to position a tool appropriately in the weiibore.

In some cables for well intervention, an electrical conductor is included to allow electrical power to be supplied from the surface through the conductor to the tool, or to allow electrical communication between downhole and surface equipment. The tractors may also be powered by the electrical conductor in the cable.

With reference to Figure 1, a widely used prior art cable 1 is shown. The cable 1 is a 0.79 cm (5/16") diameter mono-conductor cable which may be used in a weiibore in well intervention. The cable 1 has a conductive core 2, an inner armour layer 3, and an outer armour layer 4. The armour layers are designed to give the cable strength and to protect the cable from damage when in use. The inner armour layer 3 is formed of twelve wires 3s, and the outer armour layer 4 has eighteen wires 4s disposed around the long axis (into the page) of the cable. The wires of the armour layers 2, 3 typically comprise steel. An insulation layer 5 is provided around between the inner armour layer and the conductive core 2. An electrical current may then be sup- plied through the conductive core 2, whilst the armour wires 3s, 4s having generally a lesser conductivity than the core 2, provide a current return path. A conductive tape 6 may be provided in contact with the inner armour layer 3 to facilitate the current return. The conductive core 2 typically comprises a copper or copper alloy material.

In a mono-conductor cable such as the cable 1, the conductive core 2 has nineteen small diameter copper wires bundled together. The wires are not insulated and act as a single conducting unit, for supplying electrical power downhole along the cable 1. This is in contrast to a multi-conductor cable, which could have two or more conductors, which are insulated and independent of each other along the cable.

There can be difficulties associated with existing cables. With many of today's designs, the cable may not be strong enough to hold its own weight and/or the weight of equipment attached thereto, particularly when used in deep and far reaches of a well where the length of the cable in the wellbore would be substantial. Intervention operations in deep, far reaching wells using such cables may therefore be u nfeasible. In addition, wellbore fluids typically include corrosive gases such as ca rbon dioxide or hydrogen sulphide. These tend to cause steel armour wires to corrode or deteriorate during use. Typical thinking in corrosive environments is to construct armour wires from stainless steel in order to reduce the corrosion sensitivity and since the strength of stainless steel is generally significantly less than normal-grade steel, a different construction, for example using thicker armour wires or armour layers, is typically proposed in order to provide the equivalent strength performance. However, this in turn can contribute to a significant increase in diameter and weight of the cable. Large-sized and heavy cables can suffer from poor fatigue strength and can make it difficult to access wellbores using tractors. Due to such weight, size and strength issues, existing cables may be not be suitable or may simply not be feasible for use in many wells, in particular where the cable is sought to reach remote locations in the well.

Summary of the invention

According to a first aspect of the invention, there is provided a cable for use in a wellbore, the cable comprising :

- armour;

- a conductive core for conducting electrical energy along the cable; and

- at least one elongate synthetics fibre arranged along the cable in a region between the conductive core and the armour. Preferably, the elongate synthetics fibre comprises at least one para-aramid synthetics fibre, for example Kevlar® or Kevlar®49 fibre. The elongate synthetics fibre may comprise any one or more of: aramid fibre, e.g. Technora® fibre; carbon fibre; ultra- high-molecular-weight polyethylene (UHMWPE, UHMW, high-modulus polyethylene (HMPE), high-performance polyethylene (HPPE)), such as e.g. Spectra® fibre; and carbon nanotube fibre.

The cable may typically comprise a plurality of elongate synthetics fibres arranged along the cable in a region between the conductive core and the armour, e.g. in one or more layers.

The cable may have first and second layers wherein the first layer may comprise a first plurality of elongate synthetics fibres in the region between the conductive core and the armour. The second layer may comprise a second plurality of elongate synthetics fibres, in the region between the conductive core and the armour. The first layer may be arranged adjacent to the second layer, and may be further arranged between the conductive core and the second layer. Synthetics fibres in the first layer are typically in touching contact with fibres in the second layer.

The or each elongate synthetics fibre may comprise a yarn extending the length of the cable, e.g . a yarn of synthetics material.

The cable may further comprise at least one layer in the region between the conductive core and the armour. The cable may comprise strands, e.g. in the layer, in which any one or more of the strands, or each strand respectively, comprises a plurality of elongate synthetics fibres. The strands of the layer are preferably arranged side-by- side, more preferably in contact with one another. More specifically, the strands, at least within a particular layer, are arranged in parallel with each other. The strands may also have a spiral path along the cable, i.e. they may have an oblique lay angle, and may run from one end of the cable to the other. In embod iments with first and second layers, strands in the first layer may be twisted in the same sense as in the second layer, e.g. clockwise or anticlockwise about the long axis of the cable, and may have the same lay angle. The cable may have a diameter of 0.79 cm (5/16") in which case the first layer may comprise thirteen strands. In that case, the second layer may comprise twenty strands. The diameter of the strands in the first layer and the second layer prior to laying may be the same. The elongate synthetics fibres, e.g. the fibres in any one strand, are arranged in para llel with each other, thus the fibres when in parallel with each other and following the trajectory of the strand, may also have a spiral path along the cable, when the strand has a spiral path. The elongate synthetics fibres are preferably bundled together. Any one or more or each of the elongate synthetics fibres in any one or more, or each, plurality (e.g. in any one strand) may comprise any one or more of: para-aramid synthetics fibre, such as Kevlar® or Kevlar®49; aramid fibre such as Technora®; carbon nanotubes; and carbon fibre materials. Any one or more strands, or each strand, for example in either or both of the first and second layers, may comprise a collection of synthetics fibres bundled together, e.g. side-by-side, e.g . in parallel.

The synthetics fibre can provide for a light weight cable compared with the prior art, and can improve the strength-to-weight ratio significantly. Synthetics fibre or fibres, strands and/or layers containing such fibre or fibres have individually or collectively a greater tensile strength to weight ratio than metals such as steel, for example stai nless or normal grade high strength steel. A para-aramid such as Kevlar®49 has for example a 5 times greater tensile strength than steel on equal weight bases, i.e. per unit weight. The use of the synthetics fibre or fibres can provide the cable with a significant tensional strength. For example, the use of para-aramid fibre such as Kevlar®, in preference to for example steel armour wire provides a reduction in weight and an increase in tensile strength.

The cable may further comprise electrical insulation between the elongate synthetics fibre or fibres and the armour, as the armour may carry electrical return energy. The cable may further comprise a conductive return facilitator, e.g. an electrical conductive tape, between the electrical insulation and the armour. The insulation may be provided in at least one layer. The insulation may contact an outer surface of the synthetics fibres in the second, outer layer comprising elongate synthetics fibres. The insulation may in effect keep metal armour wires separate from the synthetics fibre or fibres, on opposite sides of the insulation. The insulation can facilitate preventing infiltration of wellbore fluid through the armour to the synthetics fibre. It may prevent electrical short circuiting of the supply of electrical energy in the conductive core, particularly in saline wells. A typical material for the insulation may be for example polyethylene, ethylene tetrafluoroethylene (ETFE) such as Tefzel®, or polytetrafluoroethylene (PTFE) such as Teflon®. The conductive core may comprise at least one conductor member. Typically, the conductive core comprises a plurality of conductor members, which may be bundled together, and may act together to provide a supply of electrical energy through the core. The conductive core may also provide for data collection and electrical communication between downhole and surface equipment. A material of any one or more, or each conductor member may comprise copper or a copper alloy. Accordingly, any one or more, or each, of the conductor member(s) may comprise metal, which may comprise for example copper, a metal alloy, such as a copper alloy, or, any other electrically conductive metal. The conductive core is preferably arranged centrally in the cable. By way of the conductive core, the cable may be equipped for passing an electrical current through the cable, from one end to another, for example to supply electrical power from a surface power supply to a wellbore tool attached at an end of the cable in the wellbore. The conductor members in the core may be twined spirally along the cable. The conductive core may include an elongate support member, and may further include a plurality of conductor members twined spirally around the elongate support member, e.g. at an oblique lay angle, to provide the conductive core. The support member may extend in parallel with the long axis of the cable, and may be of a non-conductive material, which may for example be a plastics material or the like. The support member may be an optical fibre. The conductive member or members may comprise individual wires intertwined with each other.

The cable may further comprise holding means for holding the conductor members in place in the core. For example, a binding tape, which may be a heavy duty tape, may be provided around the conductor members for binding the conductor members together in the core, e.g. as a bundle. The holding means or binding tape is typically arranged between the core and the elongate synthetics fibre. The binding tape is preferably cut resistant, and may be electrically insulative. The tape may comprise a polyamide material, for example a meta-aramid such as Nomex®. The tape may be provided around the conductor members, e.g . by helically winding it, with the tape touching an outer surface of one or more of the conductor members. The tape may be arranged to, in effect, separate the conductor members from the synthetics fibre or fibres, between opposite sides of the tape. The holding means may alternatively or additionally comprise a thin insulation plastics member or layer.

The armour preferably comprises armour wires. Any one or more, or each of the a rmour wires may comprise a metal, such as for example: steel; high-strength steel; or stainless steel. Steel is typically advantageous for carrying higher loads and for high frictional wear resistance, e.g. if the armour wires come into contact and rub against a wall of the wellbore in use. In other variants, any one or more of the armour wires may comprise lighter metals or other metals which can for example enhance electrical conductivity for a current return path. The armour wires may comprise a first armour wire and a second armour wire, and the first armour wire may have greater electrical conductivity than the second armour wire. The first armour wire may for instance be a copper or copper alloy wire, whilst the second armour wire may be steel wire for example high-strength or stainless steel. For example, any one or more or each of the armour wires may comprise: titanium, aluminium, alloys thereof or other metals or metal alloys. The armour wires may typically have a helical path along the cable, i.e. have an oblique lay angle. The armour wires typically run in parallel with each other. The armour may comprise an armour layer on a periphery of the cable. The armour wires are preferably provided side-by-side in the armour layer, preferably with adjacent wires in contact with one another. The armour member, amour layer and/or armour wires, may be configured to be exposed to the environment surrounding the cable, for example the wellbore environment e.g. well fluids etc.

The conductive tape is typically arranged in contact with the armour, or amour wires, for facilitating provision of an electrical return path via the armour wires, for example along cable and back toward the surface in use. The armour wires may typically be twisted in a direction opposite to that of the strands comprising synthetics fibres.

In 0.79 cm (5/16") size of this cable, the armour wires are configured to bear around 35% of the total breaking strength of the cable. The synthetics fibre or fibres, e.g. in the first and second layers, are configured to provide around 65% of the total brea king strength of the cable. In the embodiment with first and second layers comprising elongate synthetics fibres, the first layer when the fibres comprise a para-aramid such as Kevlar®49 may provide around 26% of the breaking strength while the second layer could provide around 39% of the total breaking strength of the cable.

The cable is preferably for use in well intervention operations. The cable may preferably be a wireline cable. In addition, the cable is preferably a mono-conductor cable. The cable is typically configured to be stored on and/or spooled out from or onto a drum in performing a wellbore operation.

According to a second aspect of the invention, there is provided a cable for use in a wellbore, the cable comprising : armour wires;

- a conductive core for conducting electrical energy along the cable; and

- at least one layer of elongate synthetics fibres arranged along the cable in a region between the conductive core and the armour wires.

Any of the armour wires, conductive core, the layer and the synthetics fibres may be as set out in relation to those features in the first aspect of the invention.

According to a third aspect of the invention, there is provided a cable for use in a well- bore, the cable comprising :

armour;

a conductive core for carrying electrical signals along the cable; and

at least one elongate synthetics fibre arranged along the cable in a region between the conductive core and the armour.

According to a fourth aspect of the invention, there is provided a cable for use in a wellbore, the cable comprising :

armour;

a conductive core for conducting electrical energy along the cable; and at least one layer in a region between the conductive core and the armour, the layer comprising strands which add to the thickness of the cable, the strands being arranged side-by-side and in contact with one another around the core, at least one of the side-by-side strands comprising a collection of elongate synthetics fibres bundled together, the fibres being arranged along the cable in said region .

The synthetics fibres may be configured to provide a greater proportion of the total breaking strength of the cable than the armour. The synthetics fibres may be configured to provide 50% or more of the total breaking strength of the cable. The synthetics fibres may provide in the range of 50% to 80% of the total breaking strength of the cable, for example 60% to 70% of the total breaking strength . The synthetics fibres may be configured to provide any percentage value of the total breaking strength of the cable in those ranges. The armour may be configured to provide 50% or less of the total breaking strength of the cable. The armour may be configured to provide in the range of 20% to 50% of the total breaking strength of the cable, for example 30% to 40% of the total breaking strength. The armour may be configured to provide any percentage value of the total breaking strength in those ranges. The elongate synthetics fibres may comprise para-aramid fibre.

The elongate synthetics fibres may comprise any one or more of: aramid fibre; carbon fibre; ultra-high-molecular-weight polyethylene fibre; and carbon nanotube fibre.

Said layer, or the strand comprising the fibres, thereof may have an equal or greater thickness than the armour.

Filler gel may occupy residual spaces in and around the strands of the layer. The filler gel may occupy interstitial spaces between adjacent strands.

The armour may have a lay angle that is different, e.g. greater, in magnitude than those of the strands of the layer. The lay angles of the armour and/ or the strand(s) comprising the elongate fibres may have lay angles selected to balance torque in the cable. The armour may comprise wires which turn spirally about a longitudinal axis of the cable in an opposite sense to the strands of the layer. That is, the armour may comprise wires which, moving in a reference direction along the longitudinal axis, may turn spirally clockwise about a longitudinal axis of the cable and the strands of the layer may turn spirally anti-clockwise, or vice-versa in an opposite reference direction. The layer may typically have at least one adjacent pair of the side-by-side strands in which the strands in the pair both comprise elongate synthetics fibres bundled together. In other words, the strand comprising elongate synthetics fibrers may have another strand next to it which may also comprise elongate synthetics fibres. The strand comprising the elongate synthetics fibres may have a first strand next to it on one side and a second strand next to it on the other side, the first and second strands both also comprising elongate synthetics fibres.

The strands in the layer of side-by-side strands may be non-circular, e.g. wedge shaped, in cross-section. Upon laying of the strand(s) comprising elongate synthetics fibres, the strand(s) may be pressed together, such that the circumferential width and/or thickness of the strand(s) comprising elongate synthetics fibres may adapt and/or change in shape according to adjacent structure, which structure may include for instance a neighbouring strand and/or a neighbouring layer to which the strand(s) comprising the elongate synthetics fibres is/are applied. The elongate synthetics fibres in the strand, and/or the strand, may complement adjacent structure. For example, the elongate synthetics fibres in the strand, and/or the strand, may adapt to the shape of a neighbouring layer on which it is laid and/or one or more neighbouring strands.

The layer may be a first layer, and the strands may be first strands, and the cable may further comprise a second layer between the armour and the core, wherein the second layer may comprise second strands which add to the thickness of the cable. The second strands may be arranged side-by-side and in contact with one another around the core, and at least one of the side-by-side second strands may comprise a collection of elongate synthetics fibres bundled together.

According to a fifth aspect of the invention there is provided a cable for use in a well- bore, the cable comprising :

armour;

a conductive core for conducting electrical energy along the cable; and elongate synthetics fibres arranged along the cable in a region between the conductive core and the armour.

The cable may further comprise a layer in which at least one strand of the layer contributes to the thickness of the cable, the strand comprising the elongate synthetics fibres.

The elongate synthetics fibres may preferably be bundled together.

The elongate synthetics fibres, e.g. those of one or more strands of a layer comprising side-by-side strands, may be adapted (e.g. due to laying of the strand) in shape to complement adjacent structure, e.g. a neighbouring strand, layer, or other structure. Such a strand comprising synthetics fibres may adapt in shape to obtain a wedge shaped section in the layer once emplaced.

According to a sixth aspect of the invention, there is provided a method of using the cable of any of the first to third aspects in a wellbore.

According to a seventh aspect of the invention, there is provided a method of making the cable of any of the first to third aspects of the invention.

Any of the above aspects of the invention may include further features as described in relation to any other aspect, wherever described herein. Features described in one embodiment may be combined in other embodiments. For example, a selected feature from a first embodiment that is compatible with the arrangement in a second embodiment may be employed, e.g . as an additional, alternative or optional feature, e.g. inserted or exchanged for a similar or like feature, in the second embodiment to perform (in the second embodiment) in the same or corresponding manner as it does in the first embodiment.

The cable may be substantially as shown herein in any one of the drawings, or as otherwise described herein. A feature which is not shown or described may be considered not to be present or not required in any given embodiment of the cable. However, it will be appreciated that any such embodiment can still have one or more further features in addition to those shown or described.

Embodiments of the invention can be advantageous in various ways. In particular, synthetics fibres may provide the cable with high strength, may provide relatively low weight, and/or may give enhanced corrosion resistance in a wellbore, compared with prior art. Low weight by use of synthetics fibres in embodiments of the invention may reduce friction against a wellbore wall . With reduced frictional force, susceptibility to wear and/or deterioration of cable may also be reduced, as compared with prior art. In embodiments, use of stainless steel in the outer armour, and the use of synthetics fibres, may provide enhanced resistance against corrosion by sweet/sour gases such as H ₂ S / C0 ₂ e.g. in a corrosive wellbore environment, which may allow the cable to be used in such an environment and/or better withstand deterioration and wear.

Further advantages of embodiments the invention and its features are described and will be apparent from the specification throughout.

Description and drawings

There will now be described, by way of example only, embodiments of the invention with reference to the accompanying drawings, in which :

Figure 1 is a cross-sectional representation of a prior art cable for use in a well intervention operation;

Figure 2 is a side view strip-back representation of a cable according to an embodiment of the invention;

Figure 3 is an expanded cross-sectional representation of the cable of Figure 2 along the line AA; Figure 4 is a side view strip-back representation of a cable according to another embodiment of the invention;

Figure 5 is an expanded cross-sectional representation of the cable of Figure 4 along the line BB;

Figure 6 is a schematic representation showing the cable of Figures 2 or 4 in use in a wellbore; and

Figure 7 is a block diagram representation of a method for making the cable of

Figure 2.

With reference first to Figures 2 and 3, a cable 10 is shown. The cable 10 is a mono- conductor cable and is configured to be used in a wellbore (not shown), as will be explained further below. The cable 10 is elongate and has a central longitudinal axis 13. The cable 10 has a layered structure built up radially about a core. The cable 10, as a result, has several concentric layers about the axis 13, as will be described, and has a 5/16" (0.79 cm) outer diameter.

The core of the cable 10 is in the form of a conductive core 20 for conducting electrical energy along the cable 10. Radially outwardly of the conductive core 20, the cable 10 has, in succession, a binding tape layer 30, a first Kevlar® fibre (synthetics fibre) layer 40, a second Kevlar® fibre (synthetics fibre) layer 50, an insulation layer 60 and an armour layer 80. In this way, the first and second Kevlar® fibre layers 40, 50 are arranged between the conductive core 20 and the armour layer 80. The Kevlar® fibre layers 40, 50 are configured to give strength to the cable 10 to handle high tensile loads, along the longitudinal axis of the cable, whilst being of low weight. In addition, the Kevlar® fibre layers 40, 50 provide high resistance to corrosion in acid conditions in which wellbore fluids containing for example carbon dioxide or hydrogen sulphide may penetrate or infiltrate the cable through the armour layer 80. The a rmour layer 80 is configured to be exposed to the wellbore fluid and wellbore wall in use. Thus, the armour layer 80 is arranged toward the outside of the cable 10 and to make contact with the wall if contact should happen to occur between the cable 10 and the wall in use. It will be appreciated that the wall of the wellbore may be the casing wall. The layer 80 serves to protect the carbon fibre layers 40, 50 and other layers on the inside of the cable 10, whilst also contributing a significant strength bearing capacity. The armour layer 80 also acts to provide an electrical return path. Thus, electrical energy may be supplied to a tool at an end of the cable in the wellbore along the conductive core 20, and electrical returns from the tool may pass through the armour layer 80, where it may leak electrical energy to earth. The construction of the cable 10 and its layered structure is now described in more detail. The conductive core 20 includes in this case nineteen conductors in the form of wires 22 of copper alloy. No insulation is provided between the wires 22. The wires 22 cooperate to supply the necessary electrical energy, for example as required to power a wellbore tool (not shown) attached at an end of the cable. The wires 22 in this case extend along the cable in parallel with the longitudinal axis 13. The wires 22 are bundled together such that there is electrical contact between them. Hence, they are not electrically insulated from one another. In other embodiments, the wires 22 are intertwined and/or may be insulated, and/or may comprise an electrically conductive material other than copper such as for example a copper alloy or the like.

The binding tape layer 30 which surrounds the core 20 facilitates bundling of the copper wires 22. The layer 30 is provided by way of an elongate tape strip which is wound continuously around the wires 22 of the conductive core 20 along the cable 10, so as to cover the wires 22. The tape strip is formed of synthetics material and results in a layer 30 which is resistant to abrasion and cutting, helping to keep the cable 10 together should it be subjected to abrasion or cuts damage. The tape strip also functions to bind together the wires 22, as a tight bundle, providing a relatively smooth and solid base for laying further layers around it.

The first and second Kevlar® fibre layers 40, 50 are provided around the binding tape layer 30. In this case, the first fibre layer 40 has thirteen strands 42 arranged side- by-side around the conductive core 20, against the outside of the bind ing tape layer 30. The strands 42 are laid helically about the longitudinal axis 13 in a gentle spiral with successive spiral turns about the axis 13 along the length of the cable. However, the strands 42 themselves run in parallel to each other. Therefore, a cross-sectional configuration of the cable 10 in the plane perpendicular to the axis 13 as shown in Figure 3 does not change along the length of the cable 10, apart from the placement rotationally of the individual strands 42 about the axis 13 (or of any other similarly helically provided strands or members in other layers, such as in the second fibre layer 50 or the armour layer 80).

Each of the strands 42 contains a collection of Kevlar® yarns, and each yarn is typically formed of many long spun Kevlar® fibres which are combined together. An individual yarn has a length which runs the full length of the cable 10. The yarns run in parallel with each other along the strands 42 in which they are contained. The yarns are tightly packed together in the strands 42 in the layer 40, with adjacent yarns in contact with each other. The Kevlar® yarns are in this way held securely in their intended configuration. Likewise, the strands 42 themselves are tightly packed and in contact with each other in their side-by-side arrangement. The strands 42 are highly fibrous consisting of thin side-by-side yarns, for example many 10's or 100's of yarns, and can be fairly soft and deformable in shape. The fibres or yarns in this embodiment are not embedded in any resin or adhesive. As can be seen in Figure 3, the strands 42 are not circular in section but when laid in the cable 10 are deformed somewhat in the shape of a tapering wedge to fill space in and around the strands 42 and comply with the diameter and layering of the cable 10, providing thereby a layer 40 that is highly dense in Kevlar® fibres. In particular, it can be seen that the region of contact of each strand 42 against the binding tape layer 30 toward the inside of the cable 10 is smaller than the region of contact that it makes against the second Kevlar® fibre layer 50 toward the outside.

Whilst the deformability of the strands is good, some residual spaces may form in and around the strands 42, and a conventional cable filler gel is applied to the layer 40 during construction to occupy any such residual spaces.

Each strand is made by twisting the yarns slightly and opposite to the helix angle of the strand and by applying finishing oil to generate a fibre strand with a ci rcular cross- section which eventually will deform, e.g. upon manufacture when laying the strands, to make the strand 42 shaped as shown in the Figure 3.

The second Kevlar® fibre layer 50 is constructed similarly to the first Kevlar® fibre layer 40, but in this case comprises twenty strands 52 arranged side-by-side against the outside of the first Kevlar® fibre layer 40. The strands 52 lie in contact against the insulation layer 60 toward the outside, and against the first Kevlar® fibre layer 40 toward the inside of the cable.

Each of the strands 52 is otherwise configured in the same way as the strands 42 described above in relation to the first layer 40. The strands 52 are laid helically about the longitudinal axis 13 in a gentle spiral with successive spiral turns about the axis 13 along the length of the cable. The provision of the second Kevlar® fibre layer 50 improves the strength-bearing ability of the cable further. In addition, providing the Kevlar® fibres in strands in the two layers 40, 50 facilitate good compaction and distribution of Kevlar® fibres in the cable.

The configuration of the cable 10 and tight packing of fibres in the layers 40, 50 can also resist radial compression or deformation of the cable, for example upon winding the cable on a drum.

In other variants, synthetics fibre layers of different kinds to the layers 40, 50 can be provided where any number of the synthetics fibres or yarns is of some other material. For example, the synthetics fibres or yarns could comprise Technora®, carbon fibres, carbon nanotubes or other high-strength and low-weight synthetics fibres with suitable thermal and chemical properties, so as to withstand temperature and/or chemical conditions in the wellbore (e.g. do not deteriorate substantially) during an operation. Furthermore, the number of strands may be different in other cables, to obtain different strength performances, or for example to accommodate different cable diameters or provide different layer thicknesses.

The insulation layer 60 surrounds the second Kevlar® fibre layer 50 and comprises an insulation material which ensures good electrical insulation between the conductive core 20 and the armour layer 80. The material also separates the armour layer 80 from the Kevlar® fibres, so as to protect the fibre layers 40, 50 from any adverse abrasion by the armour layer 80.

The armour layer 80 has multiple armour members in the form of steel wires 82 disposed side-by-side in the layer 80, around the insulation layer 60. The individual steel wires 82 take a helical path along the cable 10 turning in a succession of spiral turns about the longitudinal axis 13 along the length of the cable 10. The lay angle of the spirals steel wires 82 is greater than that of the strands 42, 52 of the first and second Kevlar® fibre layers 40, 50. In addition, the steel wires 82 are arranged to turn or "twist" in the opposite sense to the turns of the fibre layers 40, 50 in order to balance the torque which tends to be imparted to the cable 10 by virtue of the twisted, spiral configuration of the layers 40, 50.

The steel wires 82 are of a high-strength steel to enhance their strength bearing ability. Turning now to Figures 4 and 5, a cable 110 is shown. The cable 110 is similar to the cable 10. Corresponding features in the cable 110 are denoted with the same reference numerals as those in cable 10 but are incremented by one hundred .

Like the cable 10, the core of the cable 110 is in the form of a conductive core 120 for conducting electrical energy along the cable 110. Radially outwardly of the conductive core 120, the cable 110 has, in succession, a binding tape layer 130, a first Kevlar® fibre (synthetics fibre) layer 140, a second Kevlar® fibre (synthetics fibre) layer 150, and an insulation layer 160. These layers have the same structure as their counterparts in the cable 10, as described above, and their detailed structure is therefore not described further.

However, the cable 110 differs from the cable 10 in that the insulation layer 160 is followed radially outwardly with a conductive tape layer 170 and then by an armour layer 180.

The conductive tape layer 170 is provided by way of an elongate conductive tape strip which is wound continuously around the insulation layer 160 along the length of the cable 160 so that it covers the insulation layer 160. The armour layer 180 has a rmour wires 182 which lie in contact against the outside of the conductive tape layer 170. The conductive tape in layer 170 facilitates the return of electrical current on the outside of the insulation. In this example, the armour wires 182 are of stainless steel. By way of the stainless steel, the armour wires 182 are less susceptible to corrosion from corrosive fluids in the wellbore. However, the stainless steel is less conductive than the normal high strength grade steel as used in the armour of the cable 10, and therefore the conductive tape strip is applied to enhance the conductive properties in the layering outside the insulation layer 160. The high strength steel contains small amounts of other elements, additional to carbon, in the alloy with iron, whilst the stainless steel alloy includes significant amounts of such other elements such as Cr, Ni, Mo, and the like, causing reduced electrical conductivity (but better corrosion resistance). It will be noted that there is electrical contact between the armour wires 182 and tape strips in the conductive tape layer 170, and that electrical energy may be returned both in the wires 182 of the armour layer 180 and the conductive tape layer 170. The conductive tape may comprise a copper material or other conductive material preferably with greater conductivity than the stainless steel of the wires 182. In Figure 6, the cable 10, 110 is shown in use in a wellbore 200 in the subsurface 201 for performing a well intervention operation. The wellbore 200 contains fluid including hydrogen sulphides or carbon dioxide. In order to deploy the cable 10, 110, the cable 10, 110 is stored in coiled configuration on a winch drum 202 at the surface 203, and a first end 111 of the cable 10, 110 is provided with an intervention tool 204. The cable 10, 110 is then spooled out from the drum 202 into the wellbore 200 so that the first end 111 of the cable 10, 110, and the tool 204 attached thereto, is translated along the wellbore 200 to position the intervention tool 204 in the desired location. A second end 112 of the cable 10, 110 is held on the winch drum 202 at the surface 203. In practice, a first length of the cable 10, 110 will remain coiled on the drum 202, whilst a second length of the cable 10, 110 will be disposed in the wellbore 200, as seen in Figure 6. Electrical energy can be supplied from a power supply (not shown) at the surface 203 through the conductive core 120 along the cable 10, 110 to the tool 204. The electrical energy may comprise electrical signals and/or power for the tool. The tool 204 is retrieved by spooling the cable 10, 110 back in and onto the drum 202.

In Figure 7, a method 500 of making the cable 10 is shown with the following steps SI to S5 (correspondingly referenced in Figure 7) :

In SI, the conductors 22 are bound together, for example with the assistance of the binding tape strip, for providing the conductive core 20 for use in supplying electrical energy through the cable 10.

In S2 and S3, the synthetics, e.g. Kevlar®, fibres are bundled together in strands 42, 52, and the strands 42, 52 are then laid around the conductive core 20 from SI, with a gentle spiral trajectory along the cable 10 turning successively about the long axis of the cable 10. A first set of strands 42 is wound onto the bound core to provide a first synthetics fibre layer 40, and a second set of strands 52 is wound onto the first synthetics fibre layer to provide a second synthetics fibre layer 50 around the core 20. The strands are initially cylindrical in shape but deform upon laying, to provide tight packing of fibres in the two layers 40, 50, such that each of the deformed strands have a wedge-shaped section, tapering inwardly toward the conductive core.

In S4, electrical insulation is applied on the outside of second synthetics fibre layer to provide the layer 60, and in S5, the armour layer 80 is provided by winding steel wires 82 around the insulation layer 60. The method 500 is typically performed in a continuous process. As such, it will be appreciated that the steps SI to S5 in practice may take place simultaneously during manufacture, albeit at different points along the cable 10. In making the cable 110, a method the same as the method 500 can be employed, except additionally having a step for applying a conductive strip tape to provide the conductive tape layer 170 around the insulation, before then applying the armour wires 182 onto the conductive tape layer 170.

From the above, it can in particular be observed that the cable of the invention can have a number of features or properties as set out by the following dashed paragraphs:

- The armour is spaced from the core by the first and second fibre layers. The cable may have at least one layer or at least two layers which each comprise elongate synthetics fibres, and which space apart the armour from the core.

- The first and second fibre layers are spaced from the armour layer, e.g. by insulation and/or the conductive tape layer.

- The thickness of the first and second fibre layers together, is greater than that of the armour.

- The strands in the first fibre layer are all of substantially equal thickness. The strands in the second fibre layer are all of substantially equal thickness.

- The space occupied by the synthetics fibres is annular about the core.

- The magnitude of the lay angle of first or second fibre layers is different to that of the armour.

- The strands in the first and second fibre layers are laid with the same orientation of helical twist about the longitudinal axis, e.g. both have a positive lay angle.

- The wires in the armour are laid with an orientation of helical twist about the axis that opposes the orientation of twist of the first and second fibre layers, e.g. the ar- mour wires have a negative lay angle. It can be appreciated that the lay angles of the armour and/or strands are oblique to the longitudinal axis of the cable.

- A single armour layer is used.

- The thickness of the cable is dependent upon the thickness of the fibres.

- The fibre layer(s) or fibres therein, contribute a greater proportion of the strength to the cable than the armour.

- The strands in the first and second fibre layers are arranged circumferentially side- by-side and in contact with one another around the core.

Various modifications and improvements may be made without departing from the scope of the invention described herein.