U.S. patent application number 09/121468 was filed with the patent office on 2002-06-20 for optical fiber cable having fiber in metal tube core with outer protective layer..
Invention is credited to BONJA, JEFFREY A., CHESTNUT, CHRISTOPHER J., NORTON, DOUGLAS A., RUBINO, ROBERT A..
Application Number | 20020076177 09/121468 |
Document ID | / |
Family ID | 22396923 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020076177 |
Kind Code |
A1 |
BONJA, JEFFREY A. ; et
al. |
June 20, 2002 |
OPTICAL FIBER CABLE HAVING FIBER IN METAL TUBE CORE WITH OUTER
PROTECTIVE LAYER.
Abstract
A fiber optic cable includes a core and a surrounding protective
layer. The core includes an inner tube having one or more optical
fibers contained therein, and the surrounding protective layer
includes an outer tube received over the inner tube, and a layer of
buffer material positioned between the outer tube and the inner
tube. The buffer material maintains the inner tube generally
centrally located within the outer tube and providing a mechanical
link between the inner tube and the outer tube to prevent relative
movement therebetween. The inner tube may be coated with a low
hydrogen permeability material to minimize the entrance of hydrogen
into the inner tube. The low hydrogen permeability material may be
coated with a protective layer of hard, scratch resistant material
to protect the integrity of the low hydrogen permeability material.
The area in the inner tube not occupied by the optical fibers may
be filled with a filler material, the filler material being
selected to have a sufficient viscosity to resist the shear forces
applied to it as a result of the weight of the optical fibers
within the tube while allowing movement of the optical fibers
within the tube during spooling, deployment and handling of the
cable to thereby prevent damage and microbending of the optical
fibers. The filling material may be impregnated with a hydrogen
absorbing/scavenging material to remove any excess hydrogen within
the inner tube. The optical fibers have an excess length with
respect to the inner tube, and the cable may include an outer
jacket of a high temperature, protective material to protect the
cable during handling and installation.
Inventors: |
BONJA, JEFFREY A.; (AVON,
CT) ; NORTON, DOUGLAS A.; (WINDSOR, CT) ;
CHESTNUT, CHRISTOPHER J.; (ELLINGTON, CT) ; RUBINO,
ROBERT A.; (TOLLAND, CT) |
Correspondence
Address: |
WARE FRESSOLA VAN DER SLUYS &
ADOLPHSON, LLP
BRADFORD GREEN BUILDING 5
755 MAIN STREET, P O BOX 224
MONROE
CT
06468
US
|
Family ID: |
22396923 |
Appl. No.: |
09/121468 |
Filed: |
July 23, 1998 |
Current U.S.
Class: |
385/106 ;
385/126 |
Current CPC
Class: |
G02B 6/4492 20130101;
G02B 6/4484 20130101; E21B 47/135 20200501; G02B 6/4488 20130101;
G02B 6/4427 20130101; E21B 17/00 20130101 |
Class at
Publication: |
385/106 ;
385/126 |
International
Class: |
G02B 006/44; G02B
006/02 |
Claims
We claim:
1. A fiber optic cable, comprising: an inner tube; one or more
optical fibers positioned within said inner tube a layer of buffer
material surrounding said inner tube; and an outer tube surrounding
said buffer material; wherein said buffer material is positioned
between said inner tube and said outer tube and maintains said
inner tube generally centrally located within said outer tube.
2. A fiber optic cable according to claim 1, wherein said buffer
material limits relative movement between said inner tube and said
outer tube.
3. A fiber optic cable according to claim 1, further comprising a
coating on said inner tube, said coating including a low hydrogen
permeability material to minimize the entrance of hydrogen into
said inner tube.
4. A fiber optic cable according to claim 3, wherein said low
hydrogen permeability material is selected from the group
consisting of tin, gold and carbon.
5. A fiber optic cable according to claim 3, further comprising
protective layer on said coating, said protective layer including a
hard, scratch resistant material to protect the integrity of said
coating of low hydrogen permeability material.
6. A fiber optic cable according to claim 5, further comprising a
filler material received in said inner tube.
7. A fiber optic cable according to claim 6, wherein said filler
material is selected to have a sufficient viscosity to resist the
shear forces applied to said filler material as a result of the
weight of said optical fibers within said inner tube to generally
maintain the position of said optical fibers within said inner tube
and to allow movement of said optical fibers within said inner tube
during movement of the fiber optic cable.
8. A fiber optic cable according to claim 6, wherein said filler
material is impregnated with a hydrogen scavenging material.
9. A fiber optic cable according to claim 8, wherein said hydrogen
scavenging material is selected from the group consisting of
palladium or tantalum
10. A fiber optic cable according to claim 8, wherein said optical
fibers have an excess length with respect to said inner tube.
11. A fiber optic cable according to claim 9, further comprising an
outer jacket of protective material surrounding said outer
tube.
12. A fiber optic cable according to claim 1, further comprising a
filler material received in said inner tube.
13. A fiber optic cable according to claim 12, wherein said filler
material is selected to have a sufficient viscosity to resist the
shear forces applied to said filler material as a result of the
weight of said optical fibers within said inner tube to generally
maintain the position of said optical fibers within said inner tube
and to allow movement of said optical fibers within said inner tube
during movement of the fiber optic cable.
14. A fiber optic cable according to claim 12, wherein said filler
material is impregnated with a hydrogen scavenging material.
15. A fiber optic cable according to claim 14, wherein said
hydrogen scavenging material is selected from the group consisting
of palladium or tantalum
16. A fiber optic cable according to claim 1, wherein said optical
fibers have an excess length with respect to said inner tube.
17. A fiber optic cable according to claim 1, further comprising an
outer jacket of protective material surrounding said outer
tube.
18. A fiber optic cable according to claim
19. A fiber optic cable according to claim 1, wherein said filler
material is selected from the group consisting of
Fluoroethylenepropylene (FEP), Ethylene-chlorotrifluoroethylene
(ECTFE), Polyvinylidene fluoride (PVDF), perfluor alkoxy (PFA),
TEFLON, TEFLON PFA and TETZEL.
Description
TECHNICAL FIELD
[0001] The present invention relates to fiber optic cables, and
more particularly, to fiber optic cables for use in harsh
environments.
BACKGROUND OF INVENTION
[0002] With advancements in the area of fiber optic sensors,
particularly for use in harsh environments, such as in oil and gas
wells, there is an increasing need for fiber optic cables that can
survive harsh environments. For example, the harsh environment
encountered in down-hole fiber optic sensing applications places
demanding requirements on the design of fiber optical cables for
use in the down-hole environment. Such a fiber optic cable may be
used to interconnect a down-hole fiber optic sensor with
instrumentation located at the surface of a well bore.
[0003] Down-hole environmental conditions can include temperatures
in excess of 130.degree. C., hydrostatic pressures in excess of
1000 bar, vibration, corrosive chemistry and the presence of high
partial pressures of hydrogen. Down-hole applications also lead to
the requirement that the fiber optic cable be produced in lengths
of 1000 m and longer. Because of the long cable lengths in such
applications, the fiber optic cable must be designed to support the
optical fiber contained therein from excessive strain associated
with the weight of the long length of optical fiber.
[0004] The deleterious effects of hydrogen on the optical
performance of optical fiber, particularly in sub-sea installations
for the telecommunications industry, have long been documented. To
protect optical fibers from the effects of hydrogen, hermetic
coatings and barriers, such as carbon coatings and the like, have
been used to minimize the effects of hydrogen in such sub-sea
telecommunications applications. However, at the elevated
temperatures experienced in a harsh down-hole environment, such
coatings lose their resistance to permeability by hydrogen.
Additionally, at such high temperatures, the effects of hydrogen on
an optical fiber may be accelerated and enhanced.
[0005] Therefore, there exists the need for a fiber optic cable
that is suitable for use in such harsh environments.
SUMMARY OF THE INVENTION
[0006] An object of the present invention is to provide a fiber
optic cable for use in a harsh environment.
[0007] A further object of the invention is to provide such a fiber
optic cable that minimizes the exposure of optical fibers to
hydrogen contained in the harsh environment, particularly at high
temperatures.
[0008] A still further object of the invention is to provide such a
fiber optic cable wherein the optical fibers contained in the cable
are not exposed to significant damaging strain over a wide range of
operating temperatures.
[0009] According to the present invention, a fiber optic cable
includes a core and a surrounding protective layer. The core
includes an inner tube having one or more optical fibers contained
therein, and the surrounding protective layer includes an outer
tube received over the inner tube, and a layer of buffer material
positioned between the outer tube and the inner tube, the buffer
material maintaining the inner tube generally centrally located
within the outer tube and providing a mechanical link between the
inner tube and the outer tube to prevent relative movement
therebetween.
[0010] According further to the present invention, the inner tube
may be coated with a low hydrogen permeability material to minimize
the entrance of hydrogen into the inner tube. According still
further to the invention, the low hydrogen permeability material
may be coated with a protective layer of hard, scratch resistant
material to protect the integrity of the low hydrogen permeability
material.
[0011] In still further accord with the invention, the area in the
inner tube may be filled with a filler material, the filler
material being selected to have a sufficient viscosity to resist
the shear forces applied to it as a result of the weight of the
optical fibers within the tube while allowing movement of the
optical fibers within the tube during spooling, deployment and
handling of the cable to thereby prevent damage and microbending of
the optical fibers. According still further to the present
invention, the filling material may be impregnated with a hydrogen
absorbing/scavenging material.
[0012] According further to the invention, the optical fibers have
an excess length with respect to the inner tube. According further
to the invention, the cable may include an outer jacket of a high
temperature, protective material to protect the cable during
handling and installation.
[0013] The fiber optic cable of the present invention provides a
significant advantage over the prior art. The cable provides
significant resistant to the damaging effects of hydrogen on an
optical fiber by minimizing the exposure of the optical fibers to
hydrogen. The inner tube of the cable is coated with a low hydrogen
permeability material to limit the ingress of hydrogen into the
inner tube. Additionally, the filling material within the inner
tube is impregnated with a hydrogen absorbing/scavenging material
to remove any hydrogen that may enter the inner tube. A protective
coating is received over the low hydrogen permeability material to
maintain the integrity of the coating for handing and manufacturing
of the cable. To provide a high strength cable capable of
deployment in a harsh environment, the inner tube is surrounded by
protective layer that includes a buffer material surrounded by an
outer tube.
[0014] The foregoing and other objects, features and advantages of
the present invention will become more apparent in light of the
following detailed description of exemplary embodiments thereof, as
illustrated in the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a cross-sectional view of the fiber optic cable of
the present invention; and
[0016] FIG. 2 is a perspective view of the fiber optic cable of
FIG. 1 within a well bore of an oil and/or gas well.
DETAILED DESCRIPTION OF THE INVENTION
[0017] Referring now to FIG. 1, a fiber optic cable 10 manufactured
in accordance with the present invention includes a fiber in metal
tube (FIMT) core 11 having an inner tube 13 surrounding one or more
optical fibers 16, 17. The inner tube 13 may be a laser welded
tube, e.g., a length-wise laser welded tube, manufacture from a
corrosion resistant material, such as a corrosion resistant metal
alloy. Examples of suitable corrosion resistant metal alloys
include, but are not limited to; Stainless Steel 304; Stainless
Steel 316; Inconel 625; Incoloy 825. The inner tube 13 diameter may
be in the range of 1.1 to 2.6 mm, and in an exemplary embodiment of
the invention is 2.4 mm. Although the inner tube is described as
being 1.1 to 2.6 mm in diameter, the diameter of the inner tube may
vary over a large range, depending upon the materials used and the
number of optical fibers to be placed in the inner tube. The inner
tube 13 wall thickness is selected to be sufficient for the laser
welding process. For example, the inner tube 13 wall thickness for
a Stainless Steel 304 tube may be 0.2 mm.
[0018] The inner tube 13 is coated or plated with a low hydrogen
permeability material coating 19, such as tin, gold, carbon, or
other suitable low hydrogen permeability material. The thickness of
the coating 19 is selected to provide a barrier to a high partial
pressure hydrogen environment. Depending upon the selection of
material, the coating thickness may be in the range of 0.1 to 15
microns. For example, a carbon coating may have a thickness as thin
as 0.1 microns, while a tin coating may be approximately 1.3
microns in thickness. The coating 19 may be over coated 21 with a
protective layer of hard, scratch resistant material, such as
nickel or a polymer such a polyamide. The over coating 21 may have
a thickness in the range of 2 to 15 microns, depending on the
material.
[0019] The inner tube 13 may be filled with a filler material 22,
to generally fill the void spaces within the inner tube 13 not
occupied by the optical fibers 16, 17. The filler material 22
supports the optical fibers 16, 17 within the inner tube 13. The
filler material 22 is selected to have sufficient viscosity so as
to resist the shear forces applied to it as a result of the weight
of the fiber in a vertical well installation to thereby provide the
desired support for the optical fibers 16, 17 over the entire
operating temperature range of the cable 10, including temperatures
typically in the range of 10.degree. C. to 200.degree. C., however,
the cable may be used over a wider temperature range, depending on
the selection of materials, primarily related to the buffer
material 35 and coatings on the optical fibers 16, 17.
Additionally, the filler material 22 must allow the optical fibers
16, 17 to relax and straighten with respect to the inner tube 13
due to differences in the coefficients of thermal expansion between
the optical fiber 16, 17 and the inner tube 13 and during spooling
and deployment of the cable 10. The viscosity of the filler
material may widely vary, depending on the specific cable design,
including the diameter of the inner tube and the number of fibers
in the inner tube. The filler material 22 also provides additional
benefits of preventing chaffing of the coatings on the optical
fibers 16, 17 as a result of bending action during installation and
vibration of the cable 10. Another advantage is that the filler
material 22 serves as an integrator of inner tube surface roughness
to avoid microbend losses in the optical fibers 16, 17. Suitable
filler materials include standard thixotropic gel or grease
compounds commonly used in the fiber optic cable industry for water
blocking, filling and lubrication of optical fiber cables.
[0020] To further reduce the effects of hydrogen on the optical
fibers 16, 17, the filler material 22 may be impregnated with a
hydrogen absorbing/scavenging material 23, such as palladium or
tantalum. Alternatively, the inner surface 24 of the inner tube 13
may be coated with the hydrogen absorbing/scavenging material, or
such material may be impregnated into the tube material.
[0021] Referring also to FIG. 2, the cable 10 of the invention may
be used in the wellbore 27 of and oil and/or gas well. The optical
fibers 16, 17 are selected to provide reliable transmission of
optical signals between the ends 25, 26 of the cable 10, such as
between a fiber optic sensor 28 positioned within the wellbore 27
and optical signal processing equipment 30. Suitable optical fibers
include low defect, pure silica core/depressed clad fiber.
Alternatively, suitable fibers include germanium doped single mode
fiber or other optical fiber suitable for use in a high temperature
environment. Both fibers 16, 17 may be of the same type or of
different types. Although the invention is described herein as
using two optical fiber 16, 17 within the inner tube 13, it will be
understood by those skilled in the art that one or more fibers may
be used. The total number of fibers within the inner tube 13 is
limited by the diameter of the inner tube such that sufficient
space is provided within the inner tube to prevent microbending of
the optical fibers 16, 17 during handing and deployment of the
cable 10.
[0022] The core 11 is surrounded by an outer protective layer 33
that includes a buffer material 35 and an outer tube 38. The buffer
material 35 provides a mechanical link between the inner tube 13
and the outer tube 38 to prevent the inner tube 13 from sliding
under its own weight within the outer tube 38. Additionally, the
buffer material 35 keeps the inner tube 13 generally centered
within the outer tube 38 and protects the inner tube and coating
from damage due to vibration. Suitable buffer materials include
high temperature polymers, such as Fluoroethylenepropylene (FEP),
Ethylene-chlorotrifluoroethylene (ECTFE), Polyvinylidene fluoride
(PVDF), perfluor alkoxy (PFA), TEFLON, TEFLON PFA, TETZEL, or other
suitable materials. The buffer material 35 is first applied over
the inner tube 13 after laser welding and coating/plating, and then
the outer tube 38 is welded over the buffer material and is either
drawn down onto a compressible buffer material 35, or the buffer
material is expanded during a post laser weld thermal process. The
outer tube 38 may be TIG welded, laser welded, or any other
suitable process for joining the outer tube 38 over the buffer
material 35 may be used. In the case of a compressible buffer
material received between a 2.4 mm diameter inner tube and a 0.25
inch (6.345mm) outer tube as illustrated in the exemplary
embodiment of FIG. 1, the buffer material should have a thickness
in the range of 0.183 inches (4.65 mm) and 0.195 inches (4.95 mm),
and preferably 0.189 inches (4.80 mm). Although a range of buffer
material thickness is described with respect to the exemplary
embodiment of FIG. 1, any suitable thickness of buffer material may
be used, depending of the dimensions of the inner tube and outer
tube, to provide the desired mechanical protection of the inner
tube and/or to provide the mechanical linkage between the inner
tube and the outer tube to prevent relative movement
therebetween.
[0023] The outer tube 38 is manufactured of a corrosion resistant
material that easily diffuses hydrogen. For example, the outer tube
is manufactured of the same material of the inner tube 13, without
the low hydrogen permeability coating or hydrogen scavenging
material. The outer tube 38 is provided in a standard diameter
(after draw down if applicable), such as quarter-inch tubing (6.345
mm), and may have a diameter in the range of 4 to 10 mm. The outer
tube 38 may have a wall thickness in the range of 0.7 to 1.2
mm.
[0024] The fiber optic cable 10 must be capable of operation over a
wide range of temperatures, for example between 10.degree. C. and
200.degree. C. In particular, the cable must account for the
differential thermal coefficient of expansion (TCE) represented by
the optical fibers 16, 17 and the inner tube 13. Without accounting
for the differential TCE, long term stress of greater than 0.2% may
be applied to the optical fibers 16, 17 over the operating
temperature range of the cable. Such stress can lead to premature
mechanical failure because of stress corrosion of the fibers 16,
17. To reduce the long-term stress applied to the optical fibers
16, 17 as a result of installation into a high temperature
environment, the inner tube diameter is selected to be large enough
to support an excess length or "serpentine over-stuff" of optical
fiber within the inner tube 13. This excess length may be achieved
by controlling the temperature rise of the inner tube material
during laser welding of the inner tube 13. The temperature is
controlled such that it approximates the anticipated maximum or
normal operating temperature of the final installation. This
process will lead to an excess length of fiber within the inner
tube upon cooling of the inner tube. An excess length of up to 2.0%
has been achieved using such method.
[0025] To further protect the cable 10 during handling and
installation, a protective jacket 40 of a high strength, protective
material may be applied over the outer tube 38. For example, a
jacket of Ethylene-chlorotrifluoroethylene (ECTFE) may be applied
over the outer tube 38 in a generally rectangular configuration to
aid in the handling and deployment of the cable 10. Other
materials, such as Fluoroethylenepropylene (FEP), Polyvinylidene
fluoride (PVDF), Polyvinylchloride (PVC), HALAR, TEFLON PFA, or
other suitable materials may be used as the protective jacket
40.
[0026] Although the invention has been described and illustrated
with respect to exemplary embodiments thereof, the foregoing and
various other additions and omissions may be made therein and
thereto without departing from the spirit and scope of the present
invention.
* * * * *