NO337696B1 - Improved cable - Google Patents

Description

IMPROVED CABLE

This invention relates to cable, in particular conductive slickline cable for use in oil wells.

Various cable assemblies have been proposed for carrying out maintenance in a borehole. Ty-whip cable assemblies include wireline and slickline cables.

A wireline cable comprises a central conductive core made up of 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 reinforcing wires. The reinforcing wires in the inner layer are wound around the cable's longitudinal axis in the opposite direction to the reinforcing wires in the outer layer. The arrangement gives the cable mechanical strength and helps prevent the cable from unraveling during use.

Wireline cable can be used to deploy relatively heavy loads in boreholes and can be used to communicate with and deliver power to downhole equipment in real time. In addition, in a cable system with surface readout (SRO - Surface Read Out) it can be used to transmit signals and information from downhole equipment to the surface. However, wireline cable has an uneven surface which can prove challenging when designing a seal at the entry point in the borehole. Maintaining the integrity of the seal around the wireline cable is critical as there is a significant safety issue if the seal leaks; this is particularly difficult under high well pressures and can lead to the possibility of acid gas leaks. Also, SRO wireline is a relatively expensive method due to the number of personnel involved in running the system.

A slickline cable comprises a single strand of alloy or steel wire that is used for mechanical manipulation of various equipment in a borehole. The outer surface of a slickline cable is smooth; the frictional force when pulling up or lowering a slickline cable is thus relatively low. Additionally, the complexity of the pressure control equipment used to deploy slickline cable is significantly less than that required to deploy wireline cable. However, slickline cables cannot be used to transmit electricity and therefore cannot be used to communicate electrically, supply power to downhole equipment, or be used for surface reading applications.

EP1403883A2 describes a cable with an electrically conductive, load-carrying core, an insulating layer surrounding the core and an electrically conductive and load-carrying outer element enclosing the insulating layer. The insulating layer can be made of PEEK.

US5351531A describes a system for running a slickline cable, where the system comprises a length of cable, a coil, a packing box through which the cable is passed on its way into a wellbore, as well as means for controlling the coil when running the cable.

It is an aim of the present invention to remove or reduce 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 pressurized well application, the cable comprising: a matrix material;

at least one electrical conductor embedded in said matrix material; and a plurality of structural elements embedded in said matrix material;

as the cable has an external diameter of less than 4 mm.

The cable according to the present invention can be used for carrying out maintenance in a borehole, and is suitable, for example, to communicate electrically and deliver power to downhole tools in real time. In particular, the cable can be used for applications with reading on the surface. In addition and/or alternatively, the cable can be used to pull up or bring down relatively large loads in a borehole. A diameter of less than 4mm has the advantage of allowing the cable to bend sufficiently to be wound up on traditional slickline spools.

The outer surface of the cable is preferably smooth. A smooth outer surface reduces the friction losses involved when raising and lowering the cable into a well. By smooth is meant smooth enough to be used with standard packing boxes and packing glands for slickline cable to retain pressure or seal externally with oil-filled elastomers.

The electrical conductor is capable of carrying 2 A of electrical current at 500 volts.

There may be a plurality of electrical conductors. Any suitable metal or metal alloy wire can be used as an electrical conductor. Copper wire is most preferably used as the at least one electrical conductor. A plurality of electrical conductors allows the cable to have separate conductors for sending signals to and receiving signals from downhole equipment.

The plurality of structural elements is preferably provided through a plurality of carbon fibers. Alternatively, any suitable high tensile orientable material can be used as the structural elements, for example steel, aramid, glass or graphite fibres.

The matrix material is preferably polyether ether ketone (PEEK). Alternatively, the matrix material is high-density polypropylene. The matrix could be any suitable polymer.

The at least one electrical conductor is preferably coated with an insulating material. The insulating material can be an imide. Most preferably, the imide is Kapton™. Alternatively, the at least one electrical conductor is insulated with a layer of, for example, a plastic material or enamel. Self-made plastic insulators include e.g. EPC, PVC, PEEK, PEK and PTFE.

The cable can further comprise an outer protective covering. The outer protective covering is preferably formed from the matrix material. Most preferably, the outer protective cover is PEEK. The use of PEEK as the matrix material and the outer protective coating provides a cable that is impact and abrasion resistant and can withstand conditions, e.g. pressure and temperature, inside a borehole, and is resistant to damage from well fluids.

The diameter of the cable may be less than 3.5 mm.

The diameter of the cable is preferably less than 3.2 mm.

Most preferably, the diameter of the cable is essentially the same as that of slickline cable. A slickline cable's diameter is 3.175mm or 1/8". A diameter of this size allows the cable to easily wind up on traditional slickline spools and can be used with a slickline unit and slickline lubricators. Being able to use traditional slickline -equipment instead of wireline cable systems is a significant advantage because the physical size of the equipment is reduced, the needs of operational crew are less and grease injection is not required.Also, slickline seal is able to withstand high pressure and sour gas without leakage .

The cable is preferably load-bearing. The cable may be able to withstand loads of 1,150 kg (2,500 lb).

Where there is a plurality of electrical conductors to communicate with a downhole tool, there may be at least one transmit line and at least one receive line. The majority of leaders can be a twisted pair.

The cable can further include one or more fiber optic cables.

The cable can preferably work at temperatures of up to 180 °C.

The weight of the cable is preferably less than 15 kg/km. This is less than half the weight of a traditional steel slickline cable.

The cable's weight can be less than 10 kg/km.

Most preferably, the weight of the slickline cable is 8.5 kg/km.

The safe working pressure of the cable is preferably 1000 bar (15,000 psi).

According to another aspect of the present invention, there is provided a system for running cable into a borehole, which system comprises: a length of cable;

coiling means for storing the cable length;

a packing box through which the cable accesses the borehole; and

control means for controlling the coiling means to allow feeding of the length of cable into the borehole and to allow withdrawal of the cable from the borehole, through the packing box, said cable comprising: a matrix material, at least one electrical conductor embedded in the matrix material, and a plurality of structural elements embedded in the matrix material;

as the cable has an external diameter of less than 4 mm.

The control means is preferably adapted to send signals to and receive signals from downhole equipment.

The coil means and packing box are preferably adapted to be used with slickline cables.

According to a third aspect of the present invention, there is provided a method for manufacturing a cable, which method comprises the steps of: applying an insulating coating to at least one electrical conductor to form at least one insulated conductor;

combining the at least one insulated conductor and a yarn comprising a structural element and a matrix material to form at least one preconsolidation conductor;

consolidating the at least one preconsolidation conductor to melt and compress the at least one preconsolidation conductor to form the at least one consolidated conductor; and

preheating and passing the at least one consolidated conductor through an extrusion coating machine to apply to the at least one consolidated electrical conductor a coating of the matrix material to form a cable having a diameter of less than 4 mm.

The at least one insulated conductor and the yarn are preferably combined by respinning.

Where the at least one insulated conductor and the yarn are combined by respinning, the method preferably includes the additional step of winding the at least one wrapped conductor onto a winding spool.

The consolidation takes place preferably by heat pultrusion.

Alternatively or in addition, the consolidation can take place by roller profile drawing.

By virtue of the present invention, a cable is provided that can be used with traditional slickline equipment and can also carry and communicate with downhole equipment.

The present invention will now be described by way of example, referring to the accompanying drawings, where: Fig. 1 shows a cross-section of a cable according to a preferred embodiment of the present invention; Fig. 2 is a schematic representation of a system for running the cable of fig. 1 into a borehole; Fig. 3 shows a cross-section of a cable in accordance with an alternative embodiment of the present invention; Fig. 4 shows a cross-section of a cable according to a further embodiment of the present invention; Fig. 5 shows a cross-section of a cable according to an even further embodiment of the present invention; Fig. 6 shows a cross-section of a cable according to an even further embodiment of the present invention; Fig. 7 shows a cross-section of a cable according to an even further embodiment of the present invention; Fig. 8 is a schematic representation of a system for producing the cable of fig. 1; Figures 9A and 9B are schematic representations of an alternative system for manufacturing the cable of Figure.

1; and

Fig. 10 is a schematic representation of a further alternative system for producing the cable of fig. 1.

Reference is first made to fig. 1, where a cross-section of a cable is shown, generally indicated by the reference number 10, according to a preferred embodiment of the present invention. The cable 10 includes an electrical conductor 12 of silver-plated copper with a diameter of 0.6 mm, which is coated with a 0.2 mm thick layer of insulating material 14. In this case, the insulating material 14 is an imide marketed under the name Kapton™. The insulated conductor 12 has an external diameter of 1 mm.

The insulated conductor 12 is surrounded by a polyetheretherketone (PEEK) matrix 16, in which are embedded carbon fiber structural elements 20 (only one area of carbon fiber structural elements 20 is indicated in Fig. 1 for clarity; however, it should be understood that these are dispersed throughout the entire matrix 16). The matrix layer 16 is formed of two separate layers, which are not visible in the finished cable 10, where the first layer is a carbon-PEEK wrap with 16 strands of 1 mm silver on cups, and the second layer is carbon-PEEK wrap . This structure is explained in more detail with reference to fig. 8. The matrix layer 16 is 0.95 mm thick, whereby an external diameter of the matrix-coated conductor is 2.9 mm.

The outermost layer in the cable 10 is a protective covering 18 which is made entirely of PEEK. With the protective covering, the final outer diameter of the cable 10 is 3.175 mm, which is the same diameter as traditional slickline cable. The outer surface of the outer protective layer 18 is smooth and allows the cable 10 to be used with slickline cable gland boxes to contain well pressure or seal externally with oil-filled elastomers.

Reference is now made to fig. 2, where a schematic representation of a system 21 for running the cable 10 in fig. 1 into a borehole. The cable 10 is initially wound up on a drum 22 which is connected to a control unit 24. The control unit 24 regulates the feeding of the cable 10 into a drill hole 26 and can receive signals from a tool string 28 regarding the location of the tool string 28 and data regarding the environment down the hole.

The system 21 also includes a first pulley 30 which feeds the cable 10 to the packing box 32 via a second pulley 31 which is mounted at the top of a riser (not shown).

Reference is now made to fig. 3 to 7, where cross-sections of cables according to alternative embodiments of the present invention are shown. Fig. 3 shows a cable 70 having a conductive core 40 coated with a Kapton™ insulating layer 42 which is in turn surrounded by a PEEK matrix 46. Embedded in the PEEK matrix 46 are carbon fiber structural elements (not shown for clarity) and eight electrical return lines 44. The cable 10 is terminated by an outer protective PEEK cover 48. Fig. 4 shows a cable 72 where the core 40 consists of seven core wires 50, while the rest of the construction is the same as in the cable 70 in fig. 3.

The cable 74 in fig. 5 has an insulated supply line 52 and an insulated return line 54 embedded in the PEEK-carbon fiber matrix 46. Again, an outer covering 48 of pure PEEK is applied.

In fig. 6, the PEEK-carbon fiber matrix 46 forms the center of a cable 76. This is surrounded by a first layer of PEEK 56, in which are inserted eight feed lines 58. This first layer 56 is coated with insulating Kapton™ 60, and there is applied a second layer PEEK 62, in which eight return lines 64 are inserted, offset in relation to the supply lines 58. A final, outer protective cover 48 of PEEK is then applied.

A cable 78 shown in fig. 7 has an insulated supply line 52 and an insulated return line 54 which is offset from the center 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 fiber matrix 46.

A number of alternative methods of manufacturing the cable of fig. 1 is shown in fig. 8, 9A, 9B and 10.

Reference is first made to fig. 8 which is a schematic representation of a system 101 for producing the cable 10 in fig. 1, where the system comprises a coil 100 around which is wound insulated electrical conductor 12 coated with Kapton™ insulating material 14 which is then covered by a braid of eight strands of 0.15 mm silver coated copper wire. The electrical conductor 12 passes into a respinning machine 102 which respins the electrical conductor 12 with a number of yarn threads 104,105 of carbon fiber and PEEK from yarn spools 106,107. The resulting wound electrical conductor 108 then passes to a consolidator 110 which consolidates the wound electrical conductor 108 to form consolidated wire 112 through a heat pultrusion process. The consolidated wire 112 then passes through a final overcoating machine 114 which applies to the consolidated wire 112 a protective outer layer 18 of pure PEEK to form the cable 10. The overcoating machine 114 ensures a uniform, smooth and durable finish by preheating the consolidated wire and applying pressure to apply the outer protective covering 18. The cable 10 is then collected on a winding spool 116.

An alternative system 117 for producing cable 10 is shown in fig. 9A and 9B. The system 117 is a

two-stage system. In fig. 9A showing a schematic representation of the first step, the wound electrical conductor 108 is wound onto a preliminary winding coil 118. The preliminary winding coil 118 is moved to the second step, as shown in FIG. 9B, a schematic representation of the second step, where the winding coil 118 becomes the supply coil 118. The wound electrical conductor 108 is then passed through a roll profit drawing consolidation system 120 which consolidates the wound electrical conductor 108 to form consolidated wire 112 through a heat pultrusion process. 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 the cable 10. The cable 10 is then collected on a take-up spool 116. Although this system is shown as two-stage system, it should be understood that it could be a one-stage process.

Fig. 10 shows a schematic representation of a further, alternative system 121 for the production of the cable 10 using unidirectional pultrusion. 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 coating to the consolidated conductor 112 layer 18 of pure PEEK for designing the cable 10.

Various modifications and improvements can be made to the designs described above, without going beyond the scope of the invention. For example, it should be understood that any suitable arrangement of the construction elements, at least one conductor and matrix, could be chosen within the framework of the broadest aspect of the invention.

Moreover, the carbon in the system described in fig. 10 is added earlier in the process, for example by being introduced as part of a carbon-PEEK yarn before a consolidation step 122.

Those skilled in the art will also recognize that the above-described embodiment of the invention provides a cable that has the advantage of being usable with traditional slickline equipment and capable of carrying and communicating with downhole equipment.

Claims (31)

1. Cable for use in pressurized well applications, where the cable comprises a matrix material; at least one electrical conductor embedded in said matrix material; as the cable has an external diameter of less than 4 mm, characterized by a plurality of structural elements are embedded in said matrix material. 2. Cable as specified in claim 1, characterized in that the outer surface of the cable is smooth. 3. Cable as specified in claim 1 or 2, characterized in that the cable comprises a plurality of electrical conductors. 4. Cable as set forth in any preceding claim, characterized in that the plurality of structural elements is provided through a plurality of carbon fibers. 5. Cable as stated in any one of claims 1 to 3, characterized in that an orientable material with high tensile strength is used as structural elements. 6. Cable as set forth in any preceding claim, characterized in that the matrix material is polyetheretherketone (PEEK). 7. Cable as stated in any one of claims 1 to 5, characterized in that the matrix material is high density polypropylene. 8. Cable as stated in any preceding claim, characterized in that the at least one electrical conductor is coated with an insulating material. 9. Cable as stated in claim 8, characterized by the insulation material being imid. 10. Cable as stated in claim 8, characterized by atimide Kapton™. 11. Cable as stated in any one of claims 1 to 8, characterized in that the at least one electrical conductor is insulated with a layer of plastic material or enamel. 12. Cable as stated in any preceding claim, characterized in that the cable further comprises an outer protective covering. 13. Cable as specified in claim 12, characterized in that the outer protective covering is formed from the matrix material. 14. Cable as specified in claim 13, characterized in that the outer protective covering is PEEK. 15. Cable as set forth in any preceding claim, characterized in that the diameter of the cable is less than 3.5 mm. 16. Cable as specified in claim 15, characterized in that the diameter of the cable is less than 3.2 mm. 17. Cable as set forth in any preceding claim, characterized in that the diameter of the cable is essentially the same as that of a slickline cable. 18. Cable as specified in any preceding claim, characterized in that the cable is load-bearing. 19. Cable as stated in any one of claims 3 to 18, characterized in that there is at least one transmission line and at least one reception line. 20. Cable as stated in claim 19, characterized in that the plurality of conductors is a twisted pair. 21. Cable as stated in any preceding claim, characterized in that the cable further includes one or more fiber optic cables. 22. Cable as specified in any preceding claim, characterized in that the weight of the cable is less than 15 kg/km. 23. Cable as stated in claim 22, characterized in that the cable's weight is 8.5 kg/km. 24. System for running a cable into a borehole, characterized in that the system comprises: a length of cable; coiling means for storing the cable length; a packing box through which the cable accesses the borehole; and control means for controlling the coil means to allow feeding of the cable length into the borehole, and to allow withdrawal of the cable from the borehole, through the packing box, said cable comprising: a matrix material, at least one electrical conductor embedded in the matrix material, and a plurality of structural elements embedded in the matrix material; as the cable has an external diameter of less than 4 mm. 25. System as stated in claim 24, characterized in that the control means is adapted to send signals to and receive signals from downhole equipment. 26. System as stated in claim 24 or 25, characterized in that the coil means and the packing box are adapted for use together with slickline cables. 27. Method for manufacturing a cable, characterized in that the method comprises the steps: applying an insulating coating to at least one electrical conductor to form at least one insulated conductor; combining the at least one insulated conductor and a yarn comprising a structural element and a matrix material to form at least one preconsolidation conductor; consolidating the at least one preconsolidation conductor to melt and compress the at least one preconsolidation conductor to form the at least one consolidated conductor; and preheating and passing the at least one consolidated conductor through an extrusion coating machine to apply a coating of the matrix material to the at least one consolidated electrical conductor to form a cable having a diameter of less than 4 mm. 28. Method as stated in claim 27, characterized in that the at least one insulated conductor and the yarn are combined by respinning. 29. Method as stated in claim 28, characterized in that the at least one insulated conductor and the yarn are combined by respinning. wherein the method includes the additional step of winding the at least one wrapped conductor onto a winding coil. 30. Method as stated in any of claims 27 to 29, characterized in that the consolidation takes place by heat pultrusion. 31. Method as stated in any one of claims 27 to 29, characterized in that the consolidation takes place by roller profile drawing.