Note: Descriptions are shown in the official language in which they were submitted.
FIBER-OPTIC CABLE
The present invention relates to a fiber-optic cable, for use in a borehole,
also referred
to as the wireline cable.
Definitions: The terms light, optical radiation or optical signal used in the
following refer
to electromagnetic radiation in the optical spectral range, in particular from
XUV to FIR.
Accordingly, within the context of this application, a light waveguide is used
as a
transmission medium for electromagnetic radiation in the optical spectral
range.
In oil and natural gas wells, multi-functional mobile tools ("tractors") are
used for
sensory as well as for maintenance purposes. These are conventionally supplied
with
energy over conventional wireline cable structures. Hitherto, wireline cables
with optical
waveguides integrated in a stainless steel tube are inadequate in practical
use with
distributed fiber-optic sensors because different elongation coefficients of
cables and
tubes during insertion and extraction of the cable, as well as extreme
longitudinal pulling
forces and torsion can occur when driving the tractor. This can cause local
mechanical
deformations and tearing of the tube. An alternative version without a tube
enclosing the
optical waveguide for hermetic protection is also known. The resulting
proposed
structures can indeed allow greater elongation. However, it can be expected
that, for
example, irreversible elongation can occur when the longitudinal tension and
torsional
forces are applied, which cause local stress (locally increased attenuation)
on the
sensor fibers. In addition, by eliminating a tube enclosing the optical
waveguides, the
waveguides are not hermetically protected, which is disadvantageous with
respect to
accelerated aging effects (hydrogen ingression, high temperatures in the
borehole from
200 C to 300 C or higher) in this application.
Both of the above-mentioned variants have the disadvantage that mechanical
forces
(longitudinal tensile forces and torsion) during continuous operation of the
wireline cable
may cause temporary or permanent locally different impairment of the sensory
properties of the optical waveguides as fiber-optic sensors distributed over
various
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locations. This affects the quality of calibration and measurement resolution
of fiber-
optic method for measurement of physical quantities.
Wassink, Sandra, EX-Journal 2011, page 34 - 41, "Wireline - ..." describes the
advantages of wireline technology (from page 38) in land-based oil and natural
gas
production. The application "Wireline" implements technical systems which
allow
measurements within a borehole during ongoing production.
WO 2011/037974 A2 describes the wireline technology with an extension to
additional
maintenance tasks within a borehole. A propulsion unit (tractor) travels along
the
subterranean borehole to perform different tasks (maintenance, measurement),
wherein
power is supplied and data are transferred via the wireline cable.
The tractor and the wireline cable remain permanently in the borehole and, if
necessary,
the tractor can be pulled back with the wireline cable to the starting point
of the
borehole. The optical system (measurement) of physical variables such as
temperature
is simultaneously implemented by using optical fibers within the wireline
cable.
WO 2011/037 974 A2 addresses in this context the requirements for the torsion
properties, the cable weight and the frictional resistance of the wireline
cable. For this
purpose, different design solutions of wireline cables are illustrated in this
document,
which have improved torsion properties (torque balanced) compared to the
existing
wireline cables.
To reduce the frictional resistance, an additional smooth outer jacket is
implemented on
the wireline cable. However, the question remains to which extent smooth
characteristics of a thin plastic jacket can be maintained under adverse
conditions.
Likewise, there is the risk that the jacket can wear off and/or tear.
In U.S. 7,324,730 B2, it is demonstrated that the use of stainless steel tubes
for the
protection of optical fibers in the wireline cable application is not or only
barely suitable.
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Due to high cable elongations of wireline cable in an application, stainless
steel tubes
can be at risk of deformations. In the worst case, the optical fibers within
the steel tubes
are also damaged.
U.S. 7,324,730 B2 discloses novel constructive solutions without metallic
tubes as direct
protection for the optical fibers. These solutions are intended to prevent
damage to the
optical fibers with greater cable elongation.
According to the aforementioned findings, the structures disclosed in WO
2011/037974
A2 do not disclose additional constructive features that would be able to
adequately
protect a stainless steel tube at high elongations of the wireline cable
against
deformation or damage.
Accordingly, no suitable precautions for the safe use of stainless steel tubes
in the
wireline cable application exist in conjunction with the portable use of a
tractor. It is
therefore desirable to permanently enable the distributed fiber-optic
measurement of
physical parameters along the cable line in the above application with a
suitable
construction of a wireline cable in a tube, for example made of stainless
steel, and at
least one integrated optical waveguide and to minimize the aforementioned
disadvantages.
A fiber-optic cable of the type mentioned above is known from U.S.
2006/0120675 Al.
The cable disclosed therein includes a stainless steel tube with an optical
fiber disposed
therein. In addition, a reinforcement layer made of aramide fibers is arranged
outside of
the tube and Teflon layers outside of the reinforcing layer to reduce
friction.
The underlying problem to be solved by the present invention is to provide a
fiber-optic
cable of the aforementioned type, in which the risk of damage of the
integrated tube is
reduced.
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The fiber-optic cable includes separating means which can contribute to or may
cause
mechanical decoupling of individual components of the fiber-optic cable. The
mechanical decoupling of individual components of the cable from one another
reduces
the risk of damage to the integrated tube, particularly when the separating
means can
contribute to or cause mechanical decoupling of the at least one tube from the
at least
one additional layer.
For example, the separating means may be provided in form of at least one foil
arranged radially between the at least one tube and the at least one
additional layer.
The at least one additional layer may be formed as an electrical conductor or
as
reinforcing means. Such reinforcing means can absorb tensile forces and may
include
for example fibers, in particular aramide fibers, or may consist of fibers,
particularly
aramide fibers. Alternatively, the reinforcing means may be formed as a
reinforcement,
especially as ordinary lay.
Especially when the separating means are arranged between the at least one
tube and
the reinforcing means, the resulting mechanical decoupling of the tube from
the
reinforcing means very effectively reduces the risk of damage to the tube.
The separating means may include two foils, between which an additional layer
of the
cable is arranged. For example, the inner of the two foils may here directly
or indirectly
surround the tube, whereas the reinforcing means may be arranged between the
two
foils. In this manner, the tube and the reinforcing means can be mechanically
decoupled
from the layers or parts of the cable arranged outside the outermost of the
two outer
foils.
For example, the outermost of the two outer foils may be surrounded by parts
of a
traction cable, which may preferably be conductive. In this way, on the one
hand, power
can be supplied via the cable, wherein for example a second conductor may be
arranged on the outside of the tube. On the other hand, the outermost of the
two outer
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foils may ensure mechanical decoupling of the inner layers of the cable from
the outer
traction cable, which can also serve to absorb tensile forces.
Further features and advantages of the present invention become apparent from
the
following description of preferred embodiments with reference to the
accompanying
drawings Therein
FIG. 1 shows a schematic cross-section through a first embodiment of a
fiber-optic
cable according to the present invention;
FIG. 2 shows a schematic cross-section through a second embodiment of a
fiber-
optic cable according to the present invention;
FIG. 3 shows a schematic cross-section through a third embodiment of a
fiber-optic
cable according to the present invention;
FIG. 4 shows a schematic cross-section through a fourth embodiment of a
fiber-optic
cable according to the present invention;
FIG. 5 shows a schematic cross-section through a fifth embodiment of a
fiber-optic
cable according to the present invention;
FIG. 6 shows a schematic cross-section through a sixth embodiment of a
fiber-optic
cable according to the present invention;
FIG. 7 shows a schematic cross-section through a seventh embodiment of a
fiber-
optic cable according to the present invention.
In the figures, identical or functionally identical parts or components are
provided with
the same reference numerals.
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Wireline cables according to the prior art suffer from the risk of damage to
the integrated
steel tube as a result of elongations.
The invention is intended to show measures for protecting a metallic tube
(preferably
made of stainless steel, alternatively of nickel alloys, aluminum ...), so
that the
advantages of the hermetically sealed metal tube as an enclosure for optical
fibers can
be realized in the "Down-hole Wire line Cable Application".
In contrast to the use of optical fibers for communication purposes, special
requirements
for a mechanically stress-free sensor path exist with the fiber-optic sensor
systems (for
example, DTS - distributed temperature sensing). Additional temporally or
spatially
variable losses due to temporary or local mechanical stress can directly
affect the
measurement of the physical quantity, which may require a recalibration of the
measurement system.
The optical fibers should therefore be suitable for use in sensor systems
(especially
DTS) without being subjected to mechanical stress.
The availability and reliability for using optical fibers is increased and the
failure rate is
likewise reduced. A service interruption caused by the failure of the optical
fibers when
operating the down-hole wells should be avoided.
As a first solution approach (FIGS. 1 to 4), a down-hole wireline cable is to
be
augmented with optical fibers in a protective metal casing (preferably a
stainless steel
tube).
The original mechanical properties of the down-hole wireline cable should
hereby be
preserved.
In contrast to the prior art, where mechanical stresses (particularly
longitudinal
elongation) are problematic when using a metal or stainless steel tube with
integrated
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optical waveguides, suitable constructive measures according to the invention
are
presented which largely decouple the metal or stainless steel tube from the
mechanical
loads introduced on the actual wireline cable.
In another solution approach (FIGS. 5 to 7), the modification represents an
exchange of
the metallic strain relief elements against "low-modulus aramide" fibers.
The longitudinal elongation is sufficiently reduced due to the lower weight
and the
smaller cable modulus of aramide, thereby eliminating the deformation of the
stainless
steel tube under tensile load.
The embodiment shown in FIG. 1 includes a metallic tube 1, which is preferably
made
of stainless steel, or alternatively of nickel alloys or aluminum or aluminum
alloys. The
tube may be formed as a double-layered, a three-layered or a multi-layered
tube. Such
configuration is usually mechanically more stable than standard metal tubes
and is
buckling- and pressure-resistant.
In the illustrated embodiment, two optical waveguides 2 are arranged in the
tube 1. It is
also possible to provide more or fewer than two optical waveguides 2.
Moreover, an
additional filler material, such as a gel, may be provided in the cavity of
the tube 1.
The optical waveguides 2 can be used for fiber-optic sensor systems for
measuring, for
example, temperature and/or pressure and/or vibration. The optical waveguides
2 can
be single-mode or multi-mode fibers and can be provided with a coating, for
example,
acrylic, carbon, or preferably polyimide to increase the mechanical, chemical
and
thermal resistance. The optical waveguides 2 are disposed in the tube 1 with
an excess
length, wherein the excess length is, for example, one-thousandth of the
overall length.
The tube 1 is provided on the outside with a conductor 3, preferably made of
copper,
alternatively aluminum or other alloys or metals with good conductivity. The
conductor 3
is formed as a stranded layer, as a braid or as a foil tape, and serves as an
inner
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conductor for supplying power to the fiber-optic cable. With the configuration
as
stranded layer, fabric or foil tape, an additional bracing effect as
mechanical protection
for the tube 1 is obtained.
Alternatively, an electrically conductive fabric/braid, preferably made of
copper, and in
addition an electrically conductive layer, preferably of copper, may be
provided on the
tube 1.
The first embodiment further includes a foil 4 arranged outside the conductor
3 as
separating means or tape. The foil 4 is preferably made of PTFE. The foil 4
may serve
as separating means or separating layer for mechanical decoupling.
In addition, longitudinal fibers 5, preferably made of aramide, are provided
outside of the
foil 4, which operate as reinforcing means or as strain relief elements for
the tube 1
Instead of the fibers 5, a two-layer or multi-layer stranding with left-hand
and right-hand
lay may be provided.
Another foil 6 is provided outside the fibers 5 or outside the two-layer
stranding with left-
hand and right-hand lay. The other foil 6 can be constructed as tape or be
longitudinal,
and is preferably made of PTFE. The other foil 6 may also serve as separating
means
or separating layer for mechanical decoupling.
An insulation 7, in particular a high voltage insulation, is provided outside
of the foil 6,
which is made in particular from a chemically resistant and temperature-
resistant plastic
material such as for example fluoropolymer, preferably EPR or ETFE.
Optionally, longitudinal fibers 8, preferably made of aramide, which operate
as
reinforcing means or as additional strain relief elements for the isolation 7
are arranged
outside the insulation 7. Alternatively, a two-layer or multi-layer stranding
with left-hand
and right-hand lay may be provided.
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Also optionally, a tape 9, preferably made of a metal foil, may be disposed
outside the
longitudinal fibers 8 for protecting the insulation from the inner layer of
the traction cable
which will be described below.
The traction cable 10 is provided farther on the outside as two-layer
reinforcement
having in particular has a lay with portions 10a, 10b having a left-hand and a
right-hand
lay. Alternatively, a multi-layer structure may be provided in the lay of the
traction cable
10. A metallic material, preferably G-GIPS OR GHS-GEIPS, may be used as
material
for the traction cable 10. When using a metallic material, the traction cable
10 can be
used as a return conductor.
In the embodiment shown in FIG. 2, an outer jacket 11 having a smooth surface
and
made of chemically resistant and temperature-resistant plastic, for example
fluoropolymer, preferably PEEK or ETFE, is likewise arranged outside the
traction cable
10.
An outer jacket can additionally be extruded, provided that the requirements
for the
pressure within down-hole bore and the outer diameter of the wireline cable
are
satisfied.
The inner members are mechanically decoupled by way of the foils 4, 6, thereby
facilitating "slip" of the inner elements under bending and tensile loads.
Assuming that the mechanical loading of the single-layer, double-layer or
multi-layer
metal tube are in the elastic range, the functionality of the optical fiber 2
can be
expected to have no further limitations.
FIG. 3 shows an embodiment with a metallic tube 1, with optical waveguides 2
arranged
in their interior, as in the first and second exemplary embodiment. In
contrast to these
first embodiments, longitudinally extending fibers 5 made preferably of
aramide and
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operating as reinforcing means are arranged on the outside of the tube 1,
performing
the function of strain relief elements for the tube 1.
Alternatively, a two-or multi-layer stranding with a left-hand lay and a right-
hand lay may
here also be provided.
In the exemplary embodiment of FIG. 3, a foil 4 serving as separating means or
separating layer for mechanical decoupling is disposed on the outside of the
fibers 5.
The foil 4 is surrounded by the conductor 3, which in particular has the same
properties
as the conductor 3 described in connection with FIG. 1.
In the exemplary embodiment according to FIG. 3, an additional foil 6 is
disposed
outside the conductor 3, which like the foil 6 of the first exemplary
embodiment can also
serve as separating means or separating layer for mechanical decoupling.
Furthermore, in the exemplary embodiment of FIG 3, the insulation 7 is
disposed
outside the foil 6. Optionally, as in the first exemplary embodiment, the
longitudinal
fibers 8 operating as reinforcing means and the tape 9 are provided outside
the
insulation 7. However, in the exemplary embodiment according to FIG. 3,
comparable
longitudinal fibers 8 serving as a reinforcing means may also be provided, as
an
alternative or in addition, on the inside of the insulation 7.
Like in the first exemplary embodiment, the traction cable 10 continuous on
the outside
of the tape 9.
An outer jacket 11 is provided in the embodiment shown in FIG. 4, as the
embodiment
of FIG. 2.
Provided that the requirements for the pressure within down-hole bore and the
outer
diameter of the wireline cable can be met, this outer jacket 11 may also be
extruded.
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The elements of the core are mechanically decoupled by way of the structural
design of
the parts 1 and 3 to 6, thus facilitating "slip" of the core elements against
each other
under bending and tensile loading.
Provided that the mechanical stresses of the tube, in particular the two-layer
tube, are in
the plastic range, functionality of the optical waveguide 2 without additional
limitations
can be expected.
FIG. 5 shows an embodiment with a metallic tube 1 with optical fibers 2
arranged in the
interior thereof, as in the first to fourth exemplary embodiment. As in the
first exemplary
embodiment, a conductor 3 which may correspond to the conductor of the first
exemplary embodiment is provided on the outside of the tube 1.
Unlike the first exemplary embodiment, in the embodiment of FIG 5 an
insulation 7
which may correspond to the insulation 7 of the first exemplary embodiment is
disposed
on the outside of the conductor 3.
An additional conductor 12 is arranged on the outside of this isolation 7,
which is
preferably also made of copper, or alternatively of aluminum or other highly
conductive
alloys or metals. The conductor 12 is formed as a stranded layer, as a fabric
or as a foil
tape and serves as a return conductor for the power supply of the fiber-optic
cable.
Furthermore, longitudinal fibers 5, preferably made of arannide, which serve
as
reinforcing means or stress relief elements, are arranged outside of the
additional
conductor 12.
A foil 6 which is preferably made of PETP and serves as stranding is arranged
outside
the fibers 5. The foil 6 can serve as separating means or separating layer for
mechanical decoupling.
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The embodiment of FIG. 5 further includes an outer jacket 11 arranged outside
the foil 6
and made of chemically resistant and temperature-resistant plastic, for
example
fluoropolymer, preferably PEEK or ETFE, with a smooth surface.
The embodiment of FIG. 6 includes a metallic tube 1, which may be formed like
the tube
of the first embodiment and also include one or more optical fibers 2 in its
interior.
Moreover, an additional filler material such as a gel may be provided in the
cavity of the
tube 1.
Two conductors 13 having conductor insulation and serving as electrical supply
and
return conductors, preferably made of copper, may be arranged in parallel with
the tube
1. The conductor insulation may be made of a chemically resistant and
temperature-
resistant plastic, for example a fluoropolymer, preferably EPR or ETFE.
Also provided is stranded layer 14 surrounding the tube 1 and the two
electrical
conductors 13. Moreover, longitudinal fibers 5, preferably made of aramide and
serving
as reinforcing means and/or as strain relief elements, are provided outside
the stranded
layer 14.
Instead of the fibers 5, a two-layer or multi-layer stranded layer 5 with a
left-hand and a
right-hand lay may be provided.
A foil 6, which is preferably made of PETP and serves as stranding, is
arranged outside
the fibers 5. The foil 6 can serve as separating means or separating layer for
mechanical decoupling.
The embodiment of FIG. 6 also includes an outer jacket 11 arranged outside the
foil 6
and made of chemically resistant and temperature-resistant plastic, for
example from
fluoropolymer, preferably PEEK or ETFE, with a smooth surface.
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The embodiment shown in FIG. 7 includes a metallic tube 1, which can be
constructed
like the tube of the first embodiment and which can also have one or two more
optical
waveguides in its interior. Moreover, an additional filler material such as a
gel can be
provided in the cavity of the tube 1.
Two conductors 13 operating as electrical supply and return conductors and
preferably
made of copper are arranged in parallel with the tube 1. The conductor
insulation may
be made of a chemically resistant and temperature-resistant plastic, for
example a
fluoropolymer, preferably EPR or ETFE.
Furthermore, stress relief elements 15, preferably made of GFK and extending
in
parallel with the tubes 1 and the conductors 13, are provided. A fill material
may be
provided in the intermediate spaces between the tube 1, the conductors 13 and
the
stress relief elements 15.
Also provided are a stranded layer 14 surrounding the tube 1, the two
electrical
conductors 13 and the stress relief elements 15.
The seventh embodiment further includes a foil 4 arranged outside the stranded
layer
14 for supporting the stranded layer. The foil 4 is preferably made of FIFE.
The foil 4
can also be used as separating means or separating layer for mechanical
decoupling.
In addition, longitudinal fibers 5, preferably made of aramide, are provided
outside the
foil 4, which serve as reinforcing means and/or as strain relief elements for
the tube 1.
Instead of the fibers 5, a two-layer or multi-layer stranded layer may be
provided with a
left-hand and a right-hand lay.
Another foil 6 is provided outside the fibers 5 or outside two-layer stranded
layer having
the left-hand and a right-hand lay. The additional foil 6 can be configured as
tape or
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have a longitudinal extent, and may preferably be made of PTFE. The additional
foil 6
may also serve as separating means or separating layer for mechanical
decoupling
The embodiment according to FIG. 7 further includes an outer jacket 11
arranged
outside the foil 6 and made of a chemically resistant and temperature-
resistant plastic,
for example, of fluoropolymer, preferably PEEK or ETFE, having a smooth
surface.
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