WO2014087128A1

WO2014087128A1 - Wireline cable

Info

Publication number: WO2014087128A1
Application number: PCT/GB2013/052928
Authority: WO
Inventors: Carl Wood
Original assignee: National Oilwell Varco UK Ltd
Current assignee: National Oilwell Varco UK Ltd
Priority date: 2012-12-03
Filing date: 2013-11-07
Publication date: 2014-06-12
Anticipated expiration: 2015-06-03

Abstract

A wireline cable (1) comprises inner (10) and outer (20) armour layers formed from wires or strips of armour material wound onto a core (3), with at least one roving (15, 25) disposed between the armour layers (10, 20). The roving (15, 25) typically comprises a bundle of continuous fibres arranged parallel to the strips of armour material, and radially spaced between the armour layers (10, 20). Typically the roving nests in a valley between peaks in each armour layer (10, 20). Typically the roving (15, 25) behaves similarly to the armour layers (10, 20) in respect of elasticity, and heat and pressure resistance.

Description

WIRELINE CABLE

The present invention relates to wireline cable. Wireline is a well known technique for use in oil and gas wells for controlling strings of downhole tools, suspended in a wellbore from a wireline cable. Typical twisted strand wireline cable contains a conductor, such as an electrical conductor, to deliver power to a downhole string, and/or a signal conductor within a core to provide control signals to the string, or to recover data from the string back to the surface, although some more basic wireline cables do not incorporate conductors. Typically the cable extends for many thousands of feet in the well, and is often required to support heavy strings of tools over those long distances, and so typically also has one or more armour layers adapted to protect the core from the axial and compressive loads experienced by the cable in use. Conventional wireline cables typically have a layer of insulation surrounding the conductor, and have an inner armour layer comprising a number of strands wound helically around the insulation. Typically 8 to 10 strands are wound in a helical arrangement around the outer surface of the insulation layer. Typically the outer armour layer comprises a further helical array of 8 to 10 or so strands, which are typically wound on top of the inner armour layer, typically in the opposite helical direction. Winding the inner and outer armour layers in opposite directions provides additional desirable strength characteristics, but results in void spaces being formed between the inner and outer layers of armour. The voids between the armour layers is undesirable, because it forms a leak path along the length of the cable, which increases the risk of the migration of wellbore fluids when the wireline cable is subjected to high pressure differentials, which frequently occurs in use, for example, when the wireline cable is clamped in a sealing arrangement, such as a blow out preventor (BOP) or grease tube. The voids in the cable can be sealed completely as is the case in blocked cable, but blocked cable is extremely expensive to produce and sensitive to rough handling over sheaves, where the bend radius of the inner and outer layers is of course different, and over time this disrupts the blocked seal between the layers.

Another way of controlling this risk is to pack the voids with grease, or with some other high viscosity fluid, which resists the axial migration of the wellbore fluids at high pressure differentials. Even very viscous grease usually undergoes some migration under high pressure differentials, and most methods of dealing with this issue try to achieve a steady and predictable flow of new grease being injected into the cable in the area being sealed, to replace the grease that is gradually migrating away from the sealed area, which maintains the seal while the BOP or other sealing device is closed around the wireline and subjected to a pressure differential. Our previous patent US7611120 discloses a method and apparatus of sealing a wireline cable using solid particles in the grease to flow in the grease and bridge leak paths in the cable, which is a useful improvement.

According to the present invention there is provided a wireline cable comprising first and second armour members and a core, wherein the first and second armour members extend helically around the core, and wherein the cable has at least one roving disposed between the first and second armour members.

Typically the first and second armour members are formed in layers, and typically comprise inner and outer armour layers. Typically the first and second armour members (e.g. the inner and outer armour layers) are radially spaced from one another. Typically the first and second armour members are generally concentric.

Typically the strands forming the inner and outer layers of armour are wound around the core. Typically the inner and outer armour layers are helically wound onto the core in opposite helical orientations. Typically the core can comprise a conductor, e.g. a power conductor. Typically the core can comprise more than one conductor. Typically the core can comprise one or more signal cables. The core can optionally comprise more than one type of inner cable, for example power and signal cables. Optionally the core can comprise an inner strength member to hold axial loads on the cable, e.g. a swabbing line, with or without a conductor and/or signal cable. Typically each of the inner and outer armour layers is formed from a plurality of strands of armour material, such as wire or strips of metal, and typically at least one roving is arranged between circumferentially adjacent strands or strips of armour material in each layer, although not necessarily in precisely the same plane as the components of the armour layers. The armour layers resist axial tension and lateral compression of the cable, and typically comprise the main load -bearing members in the cable.

Typically the at least one roving occupies at least some of the void spaces within the cable, typically radially between the armour layers.

Typically the first and second armour members are radially spaced, and the at least one roving is provided in a radial space between the first and second armour members. Typically, more than one roving is provided.

Typically the rovings are arranged on opposed faces of the armour layers, typically radial faces (for example inner and outer faces). In certain examples, at least one roving can be arranged on an outer surface of an inner armour layer, and another roving can be arranged on an inner surface of an outer armour layer.

Typically, the surfaces of the inner and outer armour layers are irregular, typically being formed by generally cylindrical strands having circular cross-sections, wherein the strands are parallel to one another in each layer, and extend in opposite helical directions in each layer. This typically forms an irregular or corrugated radially facing surface on each armour layer, typically with peaks and valleys between the individual strands. Typically the rovings are provided in the valleys between the peaks in each layer, and typically have a smaller diameter than the strands or strips forming the armour layers. Typically the adjacent strands in each layer are parallel to one another, and are pressed against each other, leaving little or substantially no space between adjacent strands other than the valleys. Typically the rovings nest in the valleys between the armour strands in each layer, without spacing the armour strands further apart circumferentially or radially.

Typically each roving comprises a bundle of fibres. Typically the fibres are continuous fibres, at least extending axially (typically helically) and typically parallel to the strands or strips forming the armour layers, in an axial direction along the wireline cable. Optionally the rovings are wound separately, or spun, or pulled, or otherwise formed into a bundle before being applied to the cable. Typically the rovings comprise a synthetic fibre material, such as e-glass, nylon, or an aramid, or Kevlar, or similar fibres. The fibres in the roving can be natural or synthetic.

The fibres in the roving can be continuous or non-continuous, although it is optionally advantageous to have at least some continuous fibres in the rovings, and optionally to have both continuous and non-continuous fibres in the roving.

Typically the continuous fibres extend for at least a portion of the axial length of the wireline cable, for example for a number of metres, for example 1, 2, 3, 4 or 5m. Typically the axial length of the continuous fibres is at least as long as a clamping device in which the cable will be used, so that a single continuous fibre extends axially along a sufficient length of the wireline cable to bridge the ends of a BOP or grease tube, or other wireline sealing device in which the wireline cable will be used. Bridging the length of sealing arrangements such as BOPs and grease tubes is useful, because if a single fibre bridges a sufficient axial length of the wireline cable to extend from one end of a grease tube or BOP to the other, then it can be clamped at each end of the BOP etc., and it is less likely for the fibre to migrate from one end of the sealed area to the other, when the sealing is closed around the wireline cable, and a pressure differential is applied.

Typically the rovings extend along the length of the armour layers. The fibres in the roving can be oriented in the same direction, or can be randomly oriented. Optionally the orientation of the fibres in the roving is mixed, with some fibres oriented in the same orientation, parallel to one another, e.g. axially oriented along the roving, and some fibres in the roving having a more random orientation. Typically at least some of the fibres in the rovings are oriented along the sealing axis of the cable, i.e. along the long axis of the cable, or along the long axis of the roving (i.e. helically along the cable). Typically the rovings have a similar elastic modulus to the armour layers, so that axial tension applied to the cable stretches the rovings to the same extent, whereby the rovings do not substantially affect the characteristics of the cable when in tension. Optionally the modulus of the rovings can be manipulated by selecting a material for the fibres of the rovings that has a similar elastic modulus, or alternatively by forming or treating the roving to have a structure that behaves elastically like the armour layer. It is useful if the rovings have similar stretching behaviour to the armour layers once applied, which can be an inherent property of the material from which the rovings are formed, or can be a result of the method of application of the rovings to the cable, or a result of a treatment of the roving.

Similar stretching behaviour means that when the cable is wound onto a sheave or drum, and the inner and outer layers of cable are differentially stretched and compressed, the rovings undergo the same degree of resilient stretching, and slide axially very slightly relative to the armour strands when stressed, and recover their original configuration when relaxed. Typically the rovings are stretched and compressed only within their elastic limits of deformation, which are typically similar to those of the armour strands, so that if a high load is applied to the cable sufficient to plastically deform the roving, or cause it to snap or otherwise degenerate, the same kind of damage will likely be sustained by the armour strands, and so the damage to the cable will likely be evident from simple inspection procedures, and the risk of undetectable internal damage will be reduced. Typically the rovings are resistant to high temperatures and pressures, typically encountered in wellbores. Optionally the temperature resistance characteristics of the rovings can be manipulated by selecting a suitable fibre material (typically a natural fibre material) or by treating a fibre material to increase or otherwise modify its temperature resistance characteristics.

Typically the rovings are wound onto the cable as the armour layers are being applied. Typically the rovings are spooled continuously from reels moved helically around the core, in a similar manner to the armour layers. Typically the rovings are applied to the cable between the application of the two armour layers, e.g. they can be wound at the same time, but typically seat onto the cable after the inner armour layer has seated on the cable, and typically before the outer layer has seated on the cable. Typically the rovings are applied parallel to the armour strands, and spaced between them, so that as the adjacent strands draw together into a close packed configuration on the cable to form the armour layers, the rovings are applied between them and nestle in the valleys between the peaks of the armour strands, without interfering with the strand-to-strand contact between adjacent armour strands in each layer. The invention also provides a method of forming a wireline cable, comprising applying first and second armour members around a cable core, and applying rovings between the first and second armour members, typically by winding. The first and second armour members are typically applied in separate layers, typically wound in opposite directions.

Typically the rovings have a smaller diameter than the fibres making up the armour members.

Typically the diameter of the rovings in each layer typically match the valley depth between peaks in each layer, so that the rovings do not protrude from the valleys beyond the height of the peaks. This can be different in each layer, as the outer layer or armour is typically formed by strands of wire that have a larger diameter than the inner layer. Thus, in a relatively small cable, the outer armour layer might be formed from 10-12 wires having a circular cross section and a diameter of 4.5mm. The inner layer might be formed from 8-10 wires having a circular cross section and a diameter of 3.2mm. Thus the valleys between the strands of the outer layer will be deeper than the valleys between the strands of the inner layer. Accordingly the rovings in the inner surface of the outer layer might be of a larger diameter (to fill up the larger void space in the larger outer valleys) than the corresponding rovings in the outer surface of the inner layer. Typically the rovings can be roughly 0.5-0.2x the diameter of the corresponding armour strands, e.g. 0.1-0.12x, but this can be varied in different examples of the invention. For example, in larger cables more strands (15-25) of larger diameter (7-10mm) can form the armour layers, and it is more typical for the strands in the armour layers to be different sizes as the cable diameter increases. The rovings in the two layers need not be the same diameter. Typically the rovings in one layer formed from a consistent diameter of armour strands are all of a similar diameter, typically suitable to nest in the valleys between the peaks of the strands without protruding out of the valley.

Typically the rovings in each of the layers are wound helically in opposite directions to one another.

Typically the rovings are adapted to resist passage of fluids such as grease, by providing an increased surface area to interface with the grease in the cable voids, and thereby reducing flow rates at the interface between the grease and the cable. In certain examples, the rovings increase the resistance to flow of fluids through the voids by increasing the number of boundary condition events in the cable. A boundary condition event occurs when a fluid (e.g. grease or a wellbore fluid) comes in contact with a boundary, and the result of the boundary condition even is that the flow of the fluid at the boundary is zero. The boundary condition events are increased by the increased boundaries formed by the fibres in the rovings. The rovings typically fill the voids between the armour layers, which fills the void and thereby reduces the available area of the axial flow path through the cable which thereby requires a greater pressure differential for the same leakage flow rate, and also provides many thousands of additional boundary condition events where there are effectively "no flow" conditions at the outer surfaces of the fibres in the rovings. In the context of a wireline valve sealing arrangement the grease injected into the sealed area between the rams in the valve tries to flow both upwards and downwards in the void spaces of the cable. When this occurs the fibres in the rovings are subjected to tension and typically this resists migration of the rovings within the void space (e.g. along the cable) so there is less risk that they migrate past the exterior sealing point resulting in a reduced leak risk. The rovings are thus more likely to remain in their original configurations, associated with the armour elements, without being separated from the cable as is often the case with current designs.

This results in a cable that can resist leaks better than current standard cables or particle-blocked cables, and with greater reliability and repeatability, and at a fraction of the manufacturing cost of fully blocked cables.

The various aspects of the present invention can be practiced alone or in

combination with one or more of the other aspects, as will be appreciated by those skilled in the relevant arts. The various aspects of the invention can optionally be provided in combination with one or more of the optional features of the other aspects of the invention. Also, optional features described in relation to one example can typically be combined alone or together with other features in different examples of the invention.

Various examples and aspects of the invention will now be described in detail with reference to the accompanying figures. Still other aspects, features, and advantages of the present invention are readily apparent from the entire description thereof, including the figures, which illustrates a number of exemplary embodiments and aspects and implementations. The invention is also capable of other and different examples and aspects, and its several details can be modified in various respects, all without departing from the spirit and scope of the present invention. Accordingly, the drawings and descriptions are to be regarded as illustrative in nature, and not as restrictive. Furthermore, the terminology and phraseology used herein is solely used for descriptive purposes and should not be construed as limiting in scope. Language such as "including," "comprising," "having," "containing," or "involving," and variations thereof, is intended to be broad and encompass the subject matter listed thereafter, equivalents, and additional subject matter not recited, and is not intended to exclude other additives, components, integers or steps. Likewise, the term "comprising" is considered synonymous with the terms "including" or

"containing" for applicable legal purposes.

Any discussion of documents, acts, materials, devices, articles and the like is included in the specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention.

In this disclosure, whenever a composition, an element or a group of elements is preceded with the transitional phrase "comprising", it is understood that we also contemplate the same composition, element or group of elements with transitional phrases "consisting essentially of", "consisting", "selected from the group of consisting of", "including", or "is" preceding the recitation of the composition, element or group of elements and vice versa.

All numerical values in this disclosure are understood as being modified by "about". All singular forms of elements, or any other components described herein are understood to include plural forms thereof and vice versa.

In the accompanying drawings,

Fig 1 is a perspective view of a cable showing the different sequential layers peeled back;

Fig 2 is a side view of the fig 1 cable; and

Fig 3 is part section view through fig 2. Referring now to the drawings, a wireline cable 1 typically has an inner conductor 2 surrounded by a layer of insulation 3. The conductor 2 (and optionally the insulation 3) typically forms the core of the cable, and typically carries power and or signals to and from a surface power supply to a string of tools suspended in the wellbore from the cable. The conductor 2 can be an electrical conductor in this example, but in different examples of the invention, the conductor 2 can serve as a conduit for other power sources. In certain examples, the conductor 2 can comprise a signal conduit in addition to or instead of the power conduit. In certain examples of the invention, the core can comprise more than one conductor 2, for example multi-conductor cables can comprise two, three, four, five or more conductors, surrounded by one or more layers of insulation 3. Some examples of the invention can be formed with simple support members (e.g. simple wire) in the core, without any form of power or signal conduit or conductor.

The outer surface of the layer of insulation 3 is typically provided with an inner layer of armour 10 and an outer layer of armour 20. Typically the inner layer 10 and the outer layer 20 of armour each comprise a helical arrangement of multiple strands, typically strands of wire, which typically extend helically in different directions around the cable. Typically the strands of wire forming the inner 10 and outer 20 armour layers are formed from stainless steel, and are typically cold formed, although other methods of forming the strands making up each layer is entirely within the scope of the invention. In the present example, the inner armour layer 10 is formed by 12 strands of e.g. stainless steel cold drawn or cold formed wire having a cylindrical cross-section, as best shown in fig 3. The strands of the inner layer 10 of armour are typically applied to the outer surface of the insulation 3 in a clockwise helix, viewed from the top of the cable 1 (the right-hand end of the cable as shown in figs 1 and 2), typically by winding the separate strands from bobbins or the like helically in a clockwise direction around the core. Typically the outer layer 20 of armour is formed by 18 strands of stainless steel cold drawn wire having a similar cross-sectional diameter to the strands forming the inner armour layer 10. Typically the outer armour 20 strands extend anticlockwise (from the perspective of the upper end of the cable) around the cable. Thus, the strands forming the outer armour layer 20 extend helically in an opposite direction to the strands forming the inner armour layer 10. Accordingly, the strands forming the outer layer 20 extend over the radially outermost surfaces of the strands forming the inner layer 10, creating void spaces between the two layers, as best shown in fig 3. Typically the inner and outer armour layers 10, 20 are applied (e.g. wound) at the same time, from respective bobbin devices, when the cable 1 is being made up.

Between the outer surface of the inner layer 10 of armour, and the inner surface of the outer layer 20 of armour, is provided at least one roving 15, 25. Typically, at least 2 layers of rovings 15, 25 are provided in the spaces between the inner and outer layers 10, 20 of armour on the cable 1.

In the present case, the cable has at least two rovings which in this example are arranged in two layers. The first (inner) layer 15 of rovings is associated with the inner layer 10 of armour, and the second (outer) layer of rovings 25 is associated with the outer layer of armour 20. Typically the rovings 15 associated with the inner layer of armour 10 are associated with the outer surface of the inner layer 10. Typically the rovings 25 associated with the outer layer of armour 20 are associated with the inner surface of the outer layer 20. Typically in the case of the cable 1 shown in this example, the layers 10, 20 are concentric and the inner surface of the outer layer 20 faces the outer surface of the inner layer 10. Accordingly, in this example, the two layers of rovings 15, 25 engage each other at an interface between them, but this is not an essential component of the invention.

The rovings 15, 25 are provided on the opposed surfaces of the armour layers 10, 20, which are irregular, as a result of the peaks and valleys extending in opposite helical directions in each layer. The rovings 15, 25 are provided in the valleys between the peaks in each layer 10, 20, and typically have a smaller diameter than the strands or strips forming the armour layers, so that they fill the valleys but do not protrude radially from them.

Typically the rovings 15, 25 comprise bundles of fibres. Typically at least some of the fibres in each roving are continuous fibres, at least extending axially along the rovings for 2, 3, 4, 5 or more meters, so that the continuous length of roving fibres exceeds the axial length of a BOP or other pressure retaining device in which the cable will be clamped. The rovings 15, 25 typically comprise a temperature- resistant synthetic nylon polymeric fibre material. Other good candidates include glass fibres such as e-glass, aramid fibres, or Kevlar, or other synthetic fibres. The fibres in the roving can also be natural such as wool or cotton fibres, which can have enhanced resistance to heat and chemical degradation.

The fibres in each roving 15, 25 are typically a mixture of continuous and non- continuous fibres. Typically the continuous fibres extend for at least a portion of the axial length of the wireline cable, for example for a number of metres, for example 2, 3, 4, or 5m, so that a single continuous fibre typically extends axially along a sufficient length of the wireline cable to bridge the ends of a BOP or grease tube. Bridging the length of sealing arrangements such as BOPs and grease tubes is useful, because if a single fibre bridges a sufficient axial length of the wireline cable to extend from one end of a grease tube or BOP to the other, then it is less likely for that fibre to migrate within the voids when a pressure differential is applied.

The fibres in the rovings 15, 25 typically include at least some fibres that are parallel to one another i.e. oriented in the same direction, axially oriented along the roving, as well as some fibres that are randomly oriented.

Typically the rovings 15, 25 have a similar elastic modulus to the armour layers 10, 20, so that axial tension applied to the cable 1 stretches the rovings 15, 25 to the same extent, whereby the rovings 15, 25 do not substantially affect the

characteristics of the cable 1 when in tension. Optionally the modulus of the rovings 15, 25 can be manipulated by selecting a material for the fibres of the rovings 15, 25 that has a similar elastic modulus, or alternatively by forming the roving 15, 25 to have a structure that behaves elastically in a similar manner as the armour layers 10, 20. Typically the rovings 15, 25 are resistant to high temperatures and pressures, typically encountered in wellbores. Optionally the temperature resistance characteristics of the rovings can be manipulated by selecting a suitable fibre material (typically a natural fibre material) or by treating a fibre material to increase or otherwise modify its temperature resistance characteristics.

Typically the rovings 15, 25 are wound onto the cable 1 as the armour layers 10, 20 are being applied. Typically the rovings 15, 25 are spooled continuously from reels moved helically around the core during the winding process, in a similar manner to the armour layers 10, 20. Typically the rovings 15, 25 are applied to the cable 1 between the application of the two armour layers, e.g. all four bobbins are spooled at the same time, winding the inner and outer armour layers 10, 20 and the inner and outer rovings 15, 25 at the same time, but the order in which the respective windings engage with the cable is different, and the sequence of engagement is typically inner armour, inner roving, outer roving, then outer armour. Thus although all the rovings are typically wound continuously at the same time as the armour layers, the inner roving 15 typically contacts and seats on the cable 1 after the inner armour layer 10 has seated on the cable, and the outer roving is typically laid fractionally before the outer armour layer 20 has seated on the cable. Typically the rovings 15, 25 are applied parallel to their respective armour strands, and spaced between them, so that as the adjacent strands draw together into a close packed helical configuration on the cable 1 to form the armour layers 10, 20, the rovings 15, 25 are applied between them and nest in the valleys between the peaks of the armour strands in each layer, without spacing the armour strands further apart circumferentially or radially, and without interfering with strand-to-strand contact between adjacent armour strands in each layer 10, 20. Typically the rovings 15 in the inner armour layer match the valley depth between peaks in the inner armour layer 10, so that the rovings 15 do not protrude from the valleys beyond the height of the peaks in the inner armour layer 10. The rovings 15, 25 are typically applied to the cable 1 in the same manner as the armour strands in the inner and outer layers 10, 20, and the inner armour rovings 15 typically follow the same helical path of the inner armour strands, extending in a clockwise direction around the outer surface of the inner armour layer 10, and typically nesting in the valleys between the peaks formed by adjacent armour strands in the inner layer 10. Therefore, as can be best seen in cross-section in figure 3, the inner armour rovings 15 substantially fill the voids between the outer circumference of the inner layer 10 and the valleys between adjacent inner armour strands. The inner armour rovings 15 are typically formed from continuous fibres, or at least comprise at least some continuous fibres, extending axially along the length of each roving 15, and therefore extending helically around the cable 1 for a substantial length of the cable 1. A typical length of a single continuous fibre in the roving 15 can typically be of the order of 1 to 4 m, although longer or shorter continuous fibres can optionally be used in different examples. Typically more than one continuous fibre is used in each roving 15, so that each roving 15 that is nested between adjacent strands of the inner armour layer 10 comprises a bundle of continuous fibres which are generally arranged in the same axial orientation along the roving 15. The inner rovings 15 can typically also incorporate non-continuous fibres, having shorter lengths than the continuous fibres, and being bundled together with the continuous fibres in a less organised arrangement. The orientation of the non-continuous fibres is unimportant, and it can be advantageous, in certain examples of the invention, that then non-contiguous fibres making up at least a part of each roving 15 are somewhat randomly oriented within the roving 15, particularly on the outer surface of the roving 15, so that the surface area of each roving 15 is larger than would be the case if all of the fibres in the roving 15 were oriented in the same direction. Typically the rovings 15 match the valley depth between peaks in the inner layer of armour 10, so that the rovings 15 do not protrude from the valleys beyond the height of the peaks. In the present example, the armour strands can optionally have a similar diameter, e.g. 4-5mm, and the rovings can optionally have a smaller diameter, so as to nest more effectively in the valleys without protrusion beyond the peaks, thereby filling as much of the voids between the strands in one layer as possible, without increasing the distance between the layers and thereby increasing the void space. A typical diameter of the rovings in this example might be 0.4-.05mm. The structure and arrangement of the outer layer of rovings 25 is generally similar to that of the inner layer of rovings 15. The outer armour rovings 25 also typically comprise continuous fibres with the same characteristics as those described for the inner armour rovings 15, but has indicated above, the outer armour rovings 25 differ from the inner armour rovings 15 in that they follow the helical path taken by the strands of the outer armour layer 20 which extends in an anticlockwise direction, opposite to that of the inner armour layer 10 and the inner armour rovings 15. Like the inner armour rovings 15, the outer armour rovings 25 are nested between adjacent strands of the outer armour layer 20, and typically also comprise continuous fibres that can be axially oriented along the roving 25. Non- continuous fibres can typically be incorporated within the outer rovings 25 to increase the surface area of the roving 25 that is available for contact with fluids in the interstitial spaces between the inner and outer layers of armour 10, 20. Thus, the voids between the inner circumference of the outer layer and the strands of the outer layer 20, which are formed between the peaks of the respective strands in the outer layer 20, are typically substantially filled by the outer rovings 25. As can be best seen in figures 1 and 2, the outer rovings 25 overlie the inner rovings 15, riding across them in the opposite helical direction.

Rovings 15, 25 therefore occupy the valleys between adjacent strands in the inner and outer layers 10, 20 of the armour, occupying or filling the voids between the two layers 10, 20. This reduces the available area of the axial flow path along the cable 1. Accordingly, any fluid passing along the axial flow path formed by the voids will flow more slowly because of the restricted cross-sectional area available for fluid flow, and/or will require a greater pressure differential to exist along the axial flow path to achieve flow. Also, the increased surface area within the voids that is provided as a result of the surface area of the fibres in each of the rovings increases the boundary surface area that is in contact with the fluid by a significant factor. This effect is especially significant where the rovings 15, 25 comprise non- continuous fibres, particularly those arranged in a random orientation, because the effective surface area in contact with leaking fluid is significantly increased. This creates additional sites for boundary condition events that arise between the leaking grease and the rovings, and further reduces the flow rate of grease through the axial flow path of the cable 1, because as the flowing grease comes into contact with a boundary formed on the roving, for example on a randomly oriented fibre in the roving, the tendency of the grease to flow at that boundary is dramatically reduced, as a result of the boundary condition event.

In use, when the wireline cable 1 is being sealed in a wireline valve or other sealing arrangement such as a BOP or a grease tube, common in wireline intervention procedures, the outer surface of the outer armour layer (or its outer sheath) is clamped, typically by rams that exert significant lateral forces on the outer surface of the cable 1 to clamp it against axial movement through the wireline valve. Most wireline sealing arrangements like BOPs have grease injection facilities to inject grease into the sealed area between rams that are spaced apart along the axis of the wireline cable. As grease is injected in between the rams, it tends to flow into the void between the inner and the outer layers of armour 10, 20, and thereby encounters the rovings 15, 25 disposed in the valleys between adjacent strands of armour. In addition to the boundary condition events that tend to slow the flow rate of grease through the sealed area, and thereby reduce the risks of uncontrolled leaking, the gradual movement of the grease as it migrates axially along the cable tends to exert tension on the rovings 15, 25, which tends to urge the rovings 15, 25 axially along the cable 1, away from the grease injection site. In examples of the invention where continuous fibres are used that span an axial length of cable of a few metres or so, this typically results in a single fibre in each roving extending beyond the clamped and sealed areas of the wireline valve. Accordingly, when the rovings 15, 25 are subjected to tension resulting from the injection of grease into the wireline valve as described above, the individual fibres within each of the rovings are typically long enough to extend outside the sealed area, and underneath the clamped rams, and so are less susceptible to axial movement as a result of the tension caused by the migrating grease. One effect of this is that even when subjected to tension as a result of grease injection and migration in axial directions through the void spaces, the rovings and the fibres therein typically maintain their structural integrity, and resist "bunching up' axially within the voids, leading to a more consistent control of fluid migration through the void spaces in the cable, more consistent flow characteristics of the grease, easier management of grease injection rates, and less chance of disruption and degradation of the rovings over time as a result of continued tension applied by grease migration. Therefore, over the longer term, cables that incorporate rovings according to the invention are typically more robust and less susceptible to degradation as a result of continuous use in high pressure differential conditions.

Claims

1 A wireline cable comprising first and second armour members and a core, wherein the first and second armour members extend helically around the core, and wherein the cable has at least one roving disposed between the first and second armour members.

2 A wireline cable as claimed in claim 1, wherein the first and second armour members are radially spaced from one another with respect to the axis of the core, and respectively comprise inner and outer armour layers each layer being formed from a plurality of strands of armour material.

3 A wireline cable as claimed in claim 2, wherein the plurality of strands of armour material in the outer armour layer are parallel to one another, wherein the plurality of strands of armour material in the inner armour layer are parallel to one another, and wherein the strands of armour material in the inner and outer armour layers extend helically in different directions with respect to an axis of the core.

4 A wireline cable as claimed in claim 2 or claim 3, wherein at least one roving is arranged between circumferentially adjacent strands or strips of armour material in at least one of the inner and outer armour layers.

5 A wireline cable as claimed in any one of claims 2-4, wherein a plurality of rovings are arranged on radially opposed faces of the armour layers.

6 A wireline cable as claimed in any one of claims 1-5, wherein the first and second armour members have opposing surfaces with peaks and valleys, and wherein at least one roving are provided in at least one valley between two peaks. 7 A wireline cable as claimed in claim 6, wherein the roving is dimensioned to nest within the valley without protruding beyond the peaks. 8 A wireline cable as claimed in any preceding claim, wherein the first and second armour members are radially spaced from one another with respect to the axis of the core, and wherein the roving is disposed in a radial space between the first and second armour members.

9 A wireline cable as claimed in any one of claims 1-8, wherein the roving extends helically around the cable, and is parallel to the components of at least one of the armour members. 10 A wireline cable as claimed in any one of claims 1-9, wherein each of the first and second armour members have a plurality of helically extended rovings which extend parallel to the components of each respective armour member.

11 A wireline cable as claimed in any one of claims 1-10, wherein the roving comprises a bundle of fibres.

12 A wireline cable as claimed in claim 11, wherein the fibres of the roving comprise continuous fibres, at least extending between axially spaced positions along the roving.

13 A wireline cable as claimed in any one of claims 11-12, wherein the fibres of the roving are wound, spun, pulled, or otherwise formed into a bundle before being applied to the cable. 14 A wireline cable as claimed in any one of claims 1-13, wherein the roving comprises a synthetic fibre material.

15 A wireline cable as claimed in any one of claims 1-14, wherein the axial length of the cable clamped and exposed to a pressure differential comprises at least some continuous fibres extending between axially spaced clamped portions of the cable. 16 A wireline cable as claimed in any one of claims 1-15, wherein the roving comprises different lengths of fibres.

17 A wireline cable as claimed in any one of claims 1-16, wherein the roving comprises at least some continuous fibres having a minimum length of l-5m.

18 A wireline cable as claimed in any one of claims 1-17, wherein at least some of the fibres in the roving are oriented in different directions.

19 A wireline cable as claimed in any one of claims 1-18, wherein the roving has a similar elastic modulus to at least one of the first and second armour members.

20 A wireline cable as claimed in any one of claims 1-19, wherein the roving and at least one of the first and second armour members have similar resistance to extremes of temperatures and pressures.

21 A method of making a wireline cable, comprising applying first and second armour members to a cable core, and applying at least one roving between the first and second armour members.

22 A method as claimed in claim 21, wherein the armour members and the roving are wound onto the core.

23 A method as claimed in claim 21 or claim 22, wherein the first and second armour members are applied to the core in separate layers, each having a respective roving wound onto the cable parallel to the respective armour member.

24 A method as claimed in claim 23, wherein the roving is applied to the cable between the two armour layers.

25 A method as claimed in any one of claims 21-24, wherein the first and second armour members are radially spaced from one another with respect to an axis of the core, and wherein the roving is applied in a radial space between the armour members.

26 A method as claimed any one of claims 21-25 wherein the roving and the armour members are wound onto the core at the same time, but wherein the roving seats onto the cable after the first armour member has seated on the cable, and before the second layer has seated on the cable.

27 A method as claimed in any one of claims 21-26, wherein the rovings are wound onto the cable as the armour members are being applied.

28 A method as claimed in any one of claims 21-27, wherein the roving and the armour members comprise elongate members spooled from reels moved helically around the core during the winding.

29 A method as claimed in any one of claims 21-28, wherein strands of the roving are applied to the cable along a parallel path to strands of one of the armour members, and wherein the adjacent strands of roving and armour member draw together to nest the rovings in valleys between peaks of the armour strands, without interfering with the strand-to-strand contact between adjacent armour strands in each layer of armour.

30 A method as claimed in any one of claims 21-29, wherein the roving includes a continuous axial fibre extending for more than 1 metre between axially spaced locations on the cable.

31 A method as claimed in any one of claims 21-30, wherein the rovings are wound helically onto the cable, and wherein the rovings associated with one of the armour members are wound helically onto the cable in an opposite direction to the rovings associated with the other of the armour members.