Note: Descriptions are shown in the official language in which they were submitted.
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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
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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.
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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
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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.
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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:
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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.
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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;
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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
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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
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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
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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
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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.
