IMPROVED CABLE
This invention relates to cable, particularly to conductive slickline cable for use in oil wells.
Various cable assemblies have been proposed for the deployment of services in a well bore. Typical cable assemblies include wireline and slickline cables.
A wireline cable comprises a central conductive core formed from a number of electrical conductors. The core is surrounded by a layer of insulating material, which in turn, is surrounded by an inner layer and an outer layer of armour wires. The armour wires of the inner layer are wrapped around the longitudinal axis of the cable in the opposite direction to the armour wires of the outer layer.
The arrangement provides the cable with mechanical strength and helps to prevent the cable from unravelling during use.
Wireline cable may be used to deploy relatively large loads in wellbores and may be used to communicate with and power downhole equipment in real-time.
Furthermore, in a surface read out (SRO) wireline system it can be used to transmit signals and information from downhole equipment to surface. However, wireline has an uneven surface which can prove challenging to form a seal at the point of entry into the wellbore. Maintaining the integrity of the seal around the wireline is crucial as there is a considerable safety issue if the seal leaks, this is particularly difficult under high well pressures and can lead to the possibility of sour gas leaks.
Furthermore SRO wireline is a relatively expensive process becau8e of the number of crew involved in running the system.
A slickline cable comprises a single strand of alloy or steel wire used for the mechanical manipulation of various equipments in a wellbore. The outside surface of a slickline cable is smooth; thus, the frictional force in raising or lowering a slickline cable is relatively low. In addition, the complexity of pressure control equipment used to deploy slickline cable is considerably less than that which is necessary to deploy a wireline cable. Slickline cables, however, cannot be used to transmit electricity and, accordingly, cannot be used to communicate electrically, power downhole equipment or be used for surface read out applications.
It is an object of the present invention to obviate or mitigate at least one of the aforementioned disadvantages.
According to a first aspect of the present invention there is provided a cable for use in a pressurised well application, the cable comprising:
a matrix material;
at least one electrical conductor embedded in said matrix material; and a plurality structural members embedded in said matrix material;
the cable having an external diameter of less than 4mm.
The cable of the present invention may be used for the deployment of services in a wellbore, and is suitable, for example, for communicating electrically and for powering downhole tools in real time. Particularly the cable can be used for surface read out applications.
Additionally and/or alternatively, the cable may be used to raise or lower relatively large loads in a wellbore.
A diameter of less than 4mm has the advantage of permitting the cable to flex sufficiently to be wound onto conventional slickline reels.
Preferably, the external surface of the cable is smooth. A smooth external surface reduces the frictional losses involved in raising and lowering the cable into a well. By smooth it is meant smooth enough to use with standard slickline cable stuffing boxes and packing glands to contain well pressures or seal externally with oil filled elastomers.
The electrical conductor is able to carry 2 amps of electrical current at 500 volts.
There may be a plurality of electrical conductors.
Any suitable metal or metal alloy wire may be used as an electrical conductor. Most preferably, copper wire is used as the at least one electrical conductor. A
plurality of electrical conductors permits the cable to have separate conductors for sending signals to, and receiving signals from, downhole equipment.
Preferably, the plurality of structural members is provided by a plurality of carbon fibres. Alternatively, any suitable orientable, high tensile strength material may be used as the structural members, for example steel, aramid, glass or graphite fibres.
Preferably, the matrix material is polyetheretherketone (PEEK). Alternatively, the matrix material is high density polypropylene. The matrix could be any suitable polymer.
Preferably, the at least one electrical conductor is coated with an insulating material. The insulating material may be an imide. Most preferably the imide is KaptonTM. Alternatively, the at least one electrical conductor is insulated by a layer of, for example, a plastics material or enamel. Suitable plastics insulators include, for example, EPC, PVC, PEEK, PEK and PTFE.
The cable may further comprise an outer protective coating. Preferably, the outer protective coating is formed from the matrix material. Most preferably, the outer protective coating is PEEK. The use of PEEK as the matrix material and the outer protective coating provides a cable which is impact and abrasion resistant, and can withstand conditions, for example, of pressure and temperature within a well bore, and is resistant to damage by well fluids.
The diameter of the cable may be less than 3.5 mm.
Preferably, the diameter of the cable is less than 3.2mm.
Most preferably, the diameter of the cable is substantially the same as slickline cable. The diameter of slickline cable is 3.175mm or 14". A diameter of this magnitude permits the cable to be readily wound onto conventional slickline reels and be used with a slickline unit and slickline lubricator. Being able to use conventional slickline equipment instead of wireline cable systems is a considerable advantage because the physical size of the equipment is reduced, the operational manpower requirements are less and grease injection is not required. Furthermore, slickline pack off is capable of taking high pressure and sour gas without leakage.
Preferably, the cable is load bearing. The cable may be capable of withstanding loads of 1,150 kg (2,500 lbs).
Where there is a plurality of electrical conductors for communicating with a downhole tool, there may be at least one transmit line and at least one receive line.
The plurality of conductors maybe a twisted pair.
The cable may further include one or more fibre optic lines.
Preferably, the cable can operate in temperatures of up to 180 C.
Preferably, the weight of the cable is less than 15 kg/km. This is less than half the weight of conventional steel slickline.
The weight of the cable may be less than 10kg/km.
5 Most preferably, the weight of the slickline is 8.5kg/km.
Preferably, the safe working pressure of the cable is 15,000 psi (1000 bar).
According to a second aspect of the present invention there is provided a system for running cable into a wellbore, the system comprising:
a length of cable;
reel means for storing the length of cable;
a stuffing box through which the cable accesses the wellbore, and control means for controlling the reel means to permit feeding of the length of cable into the wellbore, and to permit withdrawing of the cable from the wellbore, through the stuffing box, said cable comprises:
a matrix material, at least one electrical conductor embedded in the matrix material, and a plurality of structural members embedded in the matrix material;
the cable having an external diameter of less than 4mm.
Preferably, the control means is adapted to send signals to and receive signals from downhole equipment.
Preferably, the reel means and the stuffing box are adapted to be used with slickline cables.
According to a third aspect of the present invention there is provided a method of controlling a device located in a wellbore, the method comprising the steps of:
running a device into a wellbore, the device suspended on a cable having a diameter of less than 4mm, and sending control signals to the device via an electrical conductor portion of the cable.
Preferably, the method comprises the additional step of receiving feedback signals from the device via an electrical conductor portion of the cable.
According to a fourth aspect of the present invention there is provided a method of manufacturing a cable, the method comprising the steps of:
applying an insulation coating to an at least one electrical conductor to form an at least one insulated conductor;
combining the at least one insulated conductor and a yarn comprising a structural member and a matrix material to form an at least one pre-consolidation conductor;
consolidating the at least one pre-consolidation conductor to melt and compress the at least one pre-consolidation conductor to form an at least one consolidated conductor; and pre-heating and passing the at least one consolidated conductor through an extruded coating machine to applying a coating of the matrix material to the at least one consolidated electrical conductor to form a cable having a diameter of less than 4mm.
Preferably, the at least one insulated conductor and the yarn are combined by braiding.
Preferably, where the at least one insulated conductor and the yarn are combined by braiding, the method includes the additional step of spooling the at least one braided conductor onto a take-up spool.
Preferably, the consolidation is by heat pulltrusion.
Alternatively, the consolidation is by roller-trusion.
By virtue of the present invention a cable is provided which can be used with conventional slickline equipment and can also support and communicate with downhole equipment.
The present invention will now be described, by way of example, with reference to the accompanying figures in which:
Figure 1 is a cross-sectional view of a cable according to a preferred embodiment of the present invention;
Figure 2 is schematic of a system for running the cable of Figure 1 into a wellbore;
Figure 3 is cross-sectional view of a cable according to an alternative embodiment of the present invention;
Figure 4 is cross-sectional view of a cable according to a further embodiment of the present invention;
Figure 5 is cross-sectional view of a cable according to a yet further embodiment of the present invention;
Figure 6 is cross-sectional view of a cable according to a yet further embodiment of the present invention;
Figure 7 is cross-sectional view of a cable according to a yet further embodiment of the present invention;
Figure 8 is a schematic representation of a system for manufacturing the cable of Figure 1;
Figures 9a and 9b are schematic representations of an alternative system for manufacturing the cable of Figure 1; and Figure 10 is a schematic representation of a further alternative system for manufacturing the cable of Figure 1.
Referring firstly to Figure 1 there is shown a cross-sectional view of a cable, generally indicated by reference numeral 10 according to a preferred embodiment of the present invention. The cable 10 includes a silver plated copper electrical conductor 12 of diameter 0.6mm, which is coated in a 0.2mm thick layer of insulating material 14, in this case the insulating material 14 is an imide marketed under the name of KaptonTM. The insulated conductor 12 has an outside diameter of 1mm.
The insulated conductor 12 is surrounded by a polyetheretherketone (PEEK) matrix 16 in which is embedded carbon fibre structural members 20 (only one region of carbon fibres structural members 20 are indicated on Figure 1 for clarity, however it will be understood that these are spread throughout the matrix 16). The matrix layer 16 is formed from two distinct layers, which are not visible in the finished cable 10, the first layers is a carbon/PEEK braid with 16 ends of lmm silver on copper, and the second layer is carbon/PEEK
braid. This construction is discussed further with reference to Figure 8. The matrix layer 16 is 0.95mm thick, with an outside diameter of the matrix covered conductor being 2.9mm.
The outermost layer of the cable 10 is a protective coating 18 formed entirely PEEK. With the protective coating, the final outside diameter of the cable 10 is 3.175mm which is the same diameter as conventional slickline cable. The outer surface of the outer protective layer 18 is smooth and permits the cable 10 to be used with slickline cable stuffing boxes to contain well pressures or seal externally with oil filled elastomers.
Referring now to Figure 2, there is shown a schematic of a system 21 for running the cable 10 of Figure 1 into a wellbore. The cable 10 is initially wound onto a drum 22 which is connected to a control unit 24. The control unit 24 controls the feed of the cable 10 into a wellbore 26 and can receive signals from a tool string 28 regarding the location of the tool string 28 and data relating to the downhole environment.
The system 21 also includes a first pulley 30 which feeds the cable 10 to the stuffing box 32 via a second pulley 31 which is mounted at the top of a riser (not shown ) .
Referring now to Figures 3 to 7 there are cross sectional views of cables according to alternative embodiments of the present invention.
Figure 3 shows a cable 70 having a conducting core 40 coated with a KaptonTM insulating layer 42 which in turn is surrounded by a PEEK matrix 46. Embedded in the PEEK matrix 46 are carbon fibre structural members (not shown for clarity) and eight electrical return lines 44.
The cable 10 is finished with an outer protective coating of PEEK 48.
Figure 4 shows a cable 72 in which the core 40 is made up of seven core wires 50, the remaining structure being the same as the cable 70 of Figure 3.
The cable 74 of Figure 5 has an insulated feed wire 52 and an insulated return wire 54 embedded in the PEEK/carbon fibre matrix 46. Again an external coating 48 of pure PEEK is applied.
In Figure 6 the PEEK/carbon fibre matrix 46 forms the centre of a cable 76. This is surrounded by a first 5 layer of PEEK 56 in which are embedded eight feed lines 58. This first layer 56 is coated with insulating KaptonTM 60 and second layer of PEEK 62 is applied in which are embedded eight return lines 64 offset from feed lines 58. A final outer protective coating 48 of PEEK is 10 then applied.
The cable 78 shown in Figure 7 has an insulated feed line 52 and an insulated return line 54 are offset from the centre of the cable 78 and embedded in the outer protective layer 48 of pure PEEK. The core of the cable 10 is the PEEK/carbon fibre matrix 46.
A number of alternative methods of manufacturing the cable of Figure 1 is shown in Figures 8, 9a, 9b and 10.
Referring firstly to Figure 8 a schematic representation of a system 101 of manufacturing the cable 10 of Figure 1, the system comprises a spool 100 around which is wound insulated electrical conductor 12 coated with KaptonTM insulating material 14, which is then covered by a braid of eight ends of 0.15mm silver coated copper wire. The electrical conductor 12 passes into a braiding machine 102 which braids the electrical conductor 12 with a number of yarns 104,105 of carbon fibre and PEEK from yarn spools 102,106. The resulting braided electrical conductor 108 then passes to a consolidator 110 which consolidates the braided electrical conductor 108 to form consolidated wire 112 by an action of heat pulltrusion. The consolidated wire 112 then passes through a final coating machine 114 which applies a protective outer layer 18 of pure PEEK to the consolidated wire 112 to form cable 10. The coating machine 114 ensures a consistent smooth and resistant finish by preheating the consolidated wire and using pressure to apply the outer protective coating 18. The cable 10 is then gathered on a take-up spool 116.
An alternative system 117 for manufacturing cable 10 is shown in Figure 9a and 9b. The system 117 is a two-stage system. In Figure 9a which shows a schematic representation of the first stage, the braided electrical conductor 108 is spooled onto an interim take-up spool 118. The interim take-up spool 118 is moved to the second stage, as shown in Figure 9b, a schematic representation of the second stage, where the take-up spool 118 becomes the feed spool 118. The braided electrical conductor 108 is then passed through a roller-trusion consolidation system 120 which consolidates the braided electrical conductor 108 to form consolidated wire 112 by an action of heat pulltrusion. The consolidated wire 112 then passes through a final coating machine 114 which applies a protective outer layer 18 of pure PEEK to the consolidated wire 112 to form cable 10.
The cable 10 is then gathered on a take-up spool 116.
Although this system is shown as two-stage system, it will be understood that it could be a single stage process.
Figure 10 shows a schematic representation of a further alternative system 121 for manufacturing the cable 10 using unidirectional pulltrusion. The electrical conductor 12 and PEEK yarn 104 are unwound from their respective spools 100, 106. The conductor 12 and yarn 104 are fed into a hot melt consolidation system 122 where they are combined with carbon and consolidated to form a consolidated electrical conductor 124. The consolidated electrical conductor 124 passes through a coating machine 114 which applies a protective outer layer 18 of pure PEEK to the consolidated wire 112 to form cable 10.
Various modifications and improvements may be made to the embodiments hereinbefore described without departing from the scope of the invention. For example, it will be understood that any suitable arrangement of the structural members, at least one conductor and matrix could be chosen within the scope of the broadest aspect of the invention.
Furthermore, in the system described in Figure 10, the carbon could be added earlier in the process, for example by being introduced as part of a carbon/PEEK
yarn, prior to a consolidation stage 122.
Those of skill in the art will also recognise that the above described embodiment of the invention provides a cable which has the advantage of being able to be used with conventional slickline equipment and which can support and communicate with downhole equipment.