Note: Descriptions are shown in the official language in which they were submitted.
CA 02952155 2016-12-16
Fiber optic splice protector for harsh environments
Field of the invention
The invention relates to a device for supporting a spliced optical fiber that
is used
in harsh environments, such as in wells for the exploration or production of
hydrocarbon
fuels. The invention also extends to a method for mounting a spliced optical
fiber to a
splice protector.
Background of the invention
Oil and gas wells are harsh environments because of the presence of chemically
active materials and high temperatures and pressures. Deep wells and
development
stimulation methods that involve injection of pressurized steam have further
raised the
operating well temperatures which places even more stress on in-well
instrumentation.
These harsh conditions create reliability issues for legacy electrical and
electronics
instrumentation. Optical fiber based instrumentation is more robust and
reliable as long
as the optical fiber is sealed for both hermeticity and mechanical protection.
One source of failure of an optical fiber is the weaker mechanical connection
produced when two strands are joined by fusion splicing. These splices are
done by
aligning the strand and melting them locally, usually by an arc effect, to
fuse them. This
method is well known and widely used, but creates a weak mechanical connection
that
usually has no more than 15% of original fiber axial strength. The fused
interphase also
leads to a much weaker performance in bending.
U.S. Patents 4,861,133 to Blume et al. and 5,416, 873 to Huebscher et al.
illustrate a prior art device for protecting a fused optical fiber joint. In
both instances, the
protective device is a V shaped clamp receiving the splice that is closed on
it such as to
prevent it from bending.
Another approach proposed in the U.S. Patent 4,509,820 to Murata et al. is to
place the splice in a heat shrunk tube containing a metal rod intended to
protect the
1
CA 02952155 2016-12-16
splice from excessive bends. A drawback of this splice protector is the
limited
temperature range the splice can tolerate. Heat shrinkable material cannot
tolerate very
high temperatures which limits the applications of the optical fiber. In
addition, the
difference of thermal expansion between the metal rod and the optical fiber
creates an
axial stress on the already mechanically weak joint.
U.S. Patent 5,731,051 to Fahey et al. proposes a sleeve for protecting a
fusion
splice with a support element made of polymer having a coefficient of thermal
expansion which is approximately equal to the coefficient of thermal expansion
of the
optical fiber. In this fashion, as the fusion splice experiences temperature
variations it
will expand or shrink at approximately the same rate as the support element,
avoiding
stresses that would arise otherwise.
U.S. Patent 7,949,289 to Matsuyama et al. proposes a higher temperature
material splice protection tube to expand the thermal operating range of the
optical fiber,
however the range still cannot reach the temperatures encountered in steam
stimulated
wells which typically vary from 150 degrees C to 350 degrees C. Similar
limitations
apply to the splice protector disclosed in the U.S. Patent 5,157,751 to Maas
et al.
An optical fiber designed for operations in oil or gas wells must be sealed
from
chemical contaminants. Typically, this is accomplished by placing the optical
fiber in a
capillary tube that isolates the optical fiber from the environment. The tube
is made from
metallic material such as Inconel or stainless steel. Inconel 825 is a
specific example of
an alloy that can be used for manufacturing the capillary tube. Inconel 825 is
considered to be a high performance alloy that offers excellent resistance to
heat and
corrosion while retaining good mechanical properties such as resistance to
stress-
corrosion cracking, localized pitting and crevice corrosion.
Challenges arise when a fusion splice covered by a heat shrink splice
protector is
placed in a capillary protection tube. The splice protector is of larger
diameter than the
optical fiber and it is heavier, such that it has a tendency to move around in
the capillary
2
CA 02952155 2016-12-16
tube. As such, it is submitted to mechanical vibrations and shocks, thus
creating a
failure point for the optical fiber.
Therefore, there is a need in the industry to provide a splice protector that
is
compatible with a capillary tube used in an oil or gas well that alleviates
the drawbacks
associated with prior art devices.
Summary of the invention
As embodied and broadly described herein the invention provides an optical
fiber
cable for installation in a subterranean formation. The subterranean formation
could be
of the type where the temperature is in excess of 150 degrees C. The optical
fiber cable
has an outer metallic jacket defining an elongated conduit with an internal
elongated
channel that receives an optical fiber. The optical fiber has two strands
joined by a
splice. A splice protector has a body with a passageway receiving the splice.
The body
has an outer region configured to be joined by a fusion weld to the outer
metallic jacket.
Optionally, the body has a heat shield positioned between the passageway and
outer region to prevent heat damage to the optical fiber when the body is
fusion welded
to the metallic jacket. The heat shield is made of metallic material that has
a sufficient
heat capacity to buffer the thermal energy generated during the welding
process and
avoid that the internal area of the splice protector is heated to a point
where damage to
the optical fiber can occur. In a specific example of implementation, the heat
capacity is
of at least 0.1 J/g C. Also, the heat shield has a sufficient thermal
diffusivity such as
the thermal energy input during the welding process migrates rapidly
throughout the
heat shield, avoiding hot spots that can melt or otherwise damage the heat
shield
adjacent the welded area. In a specific example, the heat shield has a thermal
diffusivity
a = k/(pCp) >= 30 mm2/s. The heat shield has a sufficiently high melting point
to
tolerate without melting the welding temperature. A heat shield made of
metallic
material, such as copper has been found satisfactory.
3
CA 02952155 2016-12-16
In a specific and non limiting example, the outer region of the body is made
of a
material that is weld compatible with the outer jacket. A materiel of choice
for both the
outer jacket and the outer region is Inconel which is highly resistant to
corrosion and at
the same time it has good mechanical properties. Inconel 825 is an alloy that
has been
found satisfactory for use in high temperature oil and gas applications. In
this example
of implementation, the body has an external jacket of Inconel that is of the
same cross-
sectional dimension than the outer cable jacket, also made of Inconel.
As embodied and broadly described herein, the invention also provides a method
for installing a spliced optical fiber in a splice protector. The method
includes bringing
the splice and the optical fiber to a temperature corresponding to a service
temperature
of the optical fiber and securing the optical fiber to the splice, while both
are at the
service temperature.
Typically, the splice protector and the optical fiber have different
coefficients of
thermal expansion. The above method of installation allows securing the
optical fiber to
the splice and reducing the magnitude of mechanical stresses acting on the
splice when
the service temperature is significantly different from room temperature.
The service temperature is a temperature at which the optical fiber is exposed
during its operation. In many applications, the service temperature is not a
fixed
temperature value; rather it resides in a range of temperatures. For example,
in the oil
and gas industry, an optical fiber inserted in a well, such as a Steam
Assisted Gravity
Drainage (SAGD) well is subjected to a temperature in the range from about
150 degrees C to about 350 degrees C. So, in those applications, the service
temperature varies between the extremes of that operational range.
Advantageously, the service temperature picked at which the optical fiber and
the
splice protector are brought during the installation operation is selected
such that when
the optical fiber and the splice protector are at the highest end of the
operational range,
4
CA 02952155 2016-12-16
the stress acting on the optical fiber is below a level that will damage the
optical fiber
and particularly the splice.
The computation of the temperature at which the installation is performed can
be
done as follows. The first step is to determine the maximal allowable stress
to which
the optical fiber and the splice can be subjected. Once this is determined,
the second
step is to compute on the basis of the thermal expansion coefficient
differential between
the optical fiber and the splice protector, the temperature difference at
which the
maximal stress level will arise. The service temperature picked for the
installation is the
highest end of the operational temperature range minus the computed
temperature
difference.
The method for installing a spliced optical fiber in a splice protector can
also be
performed at room temperature (20 degrees C) by providing the requisite degree
of
Excess Fiber Length (EFL) between the attachment points of the optical fiber
strands to
the splice protector.
As embodied and broadly described herein the invention thus provides an
optical
fiber cable for installation in a subterranean formation. The optical fiber
cable has an
outer metallic jacket defining an internal elongated conduit and an optical
fiber
extending in the internal elongated conduit, the optical fiber having first
and second
strands joined by a splice. A splice protector having a body with a through
bore receives
the splice. The body has an outer region joined by a fusion weld to the outer
metallic
jacket.
As embodied and broadly described herein the invention also provides an
optical
fiber cable for installation in a subterranean formation. The optical fiber
cable has an
outer metallic jacket defining an internal elongated conduit, the outer
metallic jacket
having first and second portions.
CA 02952155 2016-12-16
An optical fiber extends in the internal elongated conduit, the optical fiber
having
first and second strands joined by a splice. A splice protector is provided
including a
body with a through bore receiving the splice, the body having a first
attachment point at
which the first strand is secured and a second attachment point, spaced apart
from the
first attachment point at which the second strand is secured, the splice being
located
between the first and second attachment points, at room temperature an optical
fiber
segment between the first and second attachment points having a non-nil degree
of
Excess Fiber Length (EFL).
As embodied and broadly described herein, the invention further provides a
splice protector for an optical fiber. The splice protector has an elongated
body with a
first end portion and a second end portion, the body further having a
longitudinal
passageway configured for receiving an optical fiber with first and second
strands
connected to each other by a splice. Each end portion of the body is
configured for
insertion in a respective cavity of an optical fiber cable section. First and
second
abutments are associated with the first and second end portions, each abutment
configured for engaging the outer metallic jacket of the optical fiber cable
section when
the optical fiber cable section is mounted to the respective end portion. The
body also
has an outer region between the first and second abutments, the outer region
being
substantially flush with the outer metallic jacket of at least one of the
optical fiber cable
sections.
As embodied and broadly described herein, the invention further provides a
splice protector for an optical fiber. The splice protector has an elongated
body having
a first end portion and a second end portion. The body includes a longitudinal
passageway configured for receiving an optical fiber having first and second
strands
connected to each other by a splice. Each end portion of the body is
configured for
insertion in a cavity of an optical fiber cable section having an outer
metallic jacket.
First and second abutments associated with the first and second end portions
are
provided, each abutment engaging the outer metallic jacket of the optical
fiber cable
section when the optical fiber cable section is mounted to the respective end
portion. An
6
CA 02952155 2016-12-16
outer region extends between the first and second abutments, the outer region
being
made of metallic material capable of being fusion welded to the outer metallic
jackets of
the optical fiber cable sections.
As embodied and broadly described herein the invention further provides a
method for installing an optical fiber having first and second sections joined
by a splice
to a splice protector, wherein the splice protector and the optical fiber are
for use at a
location where the temperature is in excess of 150 degrees C. The splice
protector has
an elongated body with a first end portion and a second end portion, the body
having a
coefficient of thermal expansion that exceeds a coefficient of thermal
expansion of the
optical fiber. The method including affixing the optical fiber at a first
location to the body
and to a second location to the body that is remote from the first location,
and providing
in a segment of the optical fiber including the splice between the first and
second
locations has an EFL of at least 0.1 % at room temperature.
As embodied and broadly described herein the invention yet provides an optical
fiber
cable for installation in a subterranean formation. The optical fiber cable
has a first
functional segment, characterized by a first function and a second functional
segment
characterized by a second function that is different from the first function,
one of the first
and second functions including measuring at least one physical parameter of
the
subterranean formation. Each of the first and second functional segments
include an
outer metallic jacket defining an elongated internal conduit and an optical
fiber strand
extending in the elongated internal conduit. The optical fiber strand of the
first functional
segment is connected to the optical fiber strand of the second functional
segment by a
splice and the splice is placed in a splice protector. The splice protector is
affixed to the
outer metallic jacket of the first functional segment and to the outer
metallic jacket of the
second functional segment.
As embodied and broadly described herein, the invention also provides a method
for
producing an optical fiber cable for use in a subterranean formation for
measuring one
or more physical parameters of the subterranean formation. The method
including
providing a plurality of segments for connection to one another to assemble
the optical
7
CA 02952155 2016-12-16
fiber cable, the plurality of segments including a first functional segment
and a second
functional segment, each functional segment including an elongated outer
metallic
jacket defining an elongated internal conduit and an optical fiber strand
extending in the
elongated internal conduit, the first functional segment being characterized
by a first
function and the second functional segment being characterized by a second
function,
the first function being different from the first function, one of said first
and second
functions including measuring at least one physical parameter of the
subterranean
formation. The method also includes connecting the segments to one another to
form
the optical fiber cable that includes connecting the optical fiber strand of
the first
functional segment to the optical fiber strand of the second functional
segment by a
splice, placing a splice in a splice protector and affixing the splice
protector to the outer
metallic jacket of the first functional segment and to the outer metallic
jacket of the
second functional segment.
Yet, as embodied and broadly described herein, the invention provides an
optical fiber
cable for installation in a subterranean formation. The optical fiber cable
has an outer
metallic jacket defining an internal elongated conduit and an optical fiber
extending in
the internal elongated conduit, the optical fiber having first and second
strands joined by
a splice. A portion of the optical fiber cable including the splice
demonstrates no
permanent damage when subjected to a bent test during which the portion of the
optical
fiber cable acquires a radius of curvature that is less than 24 inches.
Brief description of the drawings
Figure 1 is a side elevational view of the splice protector according to a non-
limiting
example of implementation of the invention;
Figure 2 is a cross-sectional view taken along lines A-A in figure 1;
Figure 3 is transverse cross-sectional of the splice protector shown in figure
1;
8
CA 02952155 2016-12-16
Figure 4 is a perspective view of the splice protector according to a variant;
Figure 5 is a side elevational view if the splice protector shown in Figure 4;
Figure 6 is a cross-sectional view taken along lines A-A in Figure 5;
Figure 7 is an enlarged view of area B shown in Figure 6;
Figure 8 is a schematical view showing the splice protector according to the
invention
mounted to the jacket of an optical fiber cable.
Figure 9 is a vertical cross-sectional view of an optical fiber cable; and
Figure 10 is schematical view of an optical fiber cable having different
functional
sections;
Figure 11 illustrates the equipment used for installing an optical fiber cable
in a well;
Figure 12 illustrates an optical fiber cable inserted in a passageway in a
swellable
packer that is placed in a well;
Figures 13 to 18 illustrate a set-up for performing a bend test on the optical
fiber cable.
Detailed description
Figure 1 illustrates an example of a splice protector according to the
invention.
The splice protector is configured to be integrated to the outer protective
jacket of an
optical fiber cable to mechanically protect a splice made in the optical fiber
of the cable.
9
CA 02952155 2016-12-16
Figure 9 shows a longitudinal cross-sectional view of the optical fiber cable
before the splice is made. The cable 10 has an outer protective jacket 12 that
defines
an internal cavity 14 for receiving an optical fiber 16. The optical fiber
carries optical
signals. The signal would typically convey measurement information, such as
pressure,
and temperature, among others.
The jacket 12 is designed to protect the optical fiber from the environment.
When the optical fiber cable 10 is installed in a subterranean formation where
high
temperatures and pressures are prevalent, such as in an oil or gas well, the
jacket 12 is
made of metallic material, such as Inconel 825 that provides mechanical and
thermal
protection.
In a specific example of implementation, the jacket 12 has a circular cross-
sectional shape, however other shapes are possible.
Advantageously, the external diameter of the jacket 12 is as small as possible
such that the optical fiber cable takes as little space as possible in the
oil/gas well
passageway. In addition, a small diameter cable is desirable because it allows
installing
the cable 12 by inserting it through packers that seal the oil/gas well
passageway from
the exterior. In this fashion, the optical fiber cable 12 can be installed
while the oil/gas
well is in operation and without special seals. A large diameter cable would
make such
insertion more difficult, requiring interruption of the operation of the
oil/gas well.
In a specific example of implementation, the optical fiber cable 12 has a
cross-
sectional dimension in the range from about 0.1 inches to about 0.625 inches.
Advantageously, the cross-sectional dimension is less than about 0.35 inches,
and
preferably of 0.25 inches or less. When the jacket 12 is of a circular cross-
sectional
configuration, the cross-sectional dimension corresponds to its diameter.
The optical fiber cable 10 is spoolable. This means that it is sufficiently
small and
flexible to be wound on a spool and transported in a wound configuration
between the
CA 02952155 2016-12-16
manufacturing facility and the installation site. At the installation site,
the optical fiber
cable 10 is unwound from the spool as it is inserted into the oil/gas well.
In addition, a spoolable optical fiber cable 10 implies that the cable will
not be
damaged when wound on the spool for transportation or threaded through a shear
during the placement of the optical fiber cable 10 in the subterranean
formation. By not
damaged is meant that the optical fiber cable 10 will not kink, bend or fold
in a way that
its structural integrity and functional integrity will be impaired.
The length of the optical fiber cable 10 can vary depending on the
installation.
The range of lengths can be between several hundredth meters to several
kilometers.
With such lengths the ability to spool the cable is an important consideration
because
otherwise transportation of the cable 10 will be difficult.
While custom optical fiber cable lengths can be manufactured for different
installations, it is not always possible to determine before hand the exact
length that will
actually be required. Accordingly, there is an advantage to be able to splice
cable
sections together to build up the length that the installation needs.
Also, splicing makes it possible to produce long spans of optical fiber cable
from
shorter prefabricated sections. Instead of custom making each cable, the
factory can
produce prefabricated sections that are kept in inventory. When a cable of a
certain
length is to be produced, the required number of prefabricated sections are
spliced
together. This provides more flexibility as optical fiber cables of varying
lengths can be
assembled at locations that are remote from the manufacturing site, simply by
keeping
on hand prefabricated sections and a splicing station.
In addition, splicing allows making an optical fiber cable having different
sensor
arrangements over selected lengths. The inventory of prefabricated sections
can be
provided with sections having sensors for different parameters, such as
temperature
and/or pressure. A custom optical fiber cable is built by splicing sensor
array sections
11
CA 02952155 2016-12-16
with plain sections that have no sensing capability. This approach allows
producing
optical fiber cables having the desired sensing capability, at the desired
location on the
cable (the desired position between the cable ends) and over the desired
length.
With specific reference to Figure 1, the splice protector 11 is designed to
receive
an optical fiber section that has a splice into it. The splice protector 11
engages the
protective jacket of the optical fiber cable on both sides of the splice to
provide stable
support for the splice. The splice protector 11 has an optical fiber carrier
13 designed to
receive the optical fiber strands with the splice. The optical fiber carrier
13 has a
longitudinal passageway, such as a through bore 15 through which the optical
fiber (not
shown) can be threaded. The through bore generally extends along the
longitudinal
axis of the splice protector 11.
The length of the optical fiber carrier 13 can vary depending on the
application.
For example, the optical fiber carrier 13 can be 5 inches in length for
applications in
which the diameter of the optical fiber cable is of about 0.25 inches.
At each end of the optical fiber carrier 13 is provided an attachment point
17, 18
at which the optical fiber strands are secured to the optical fiber carrier
13. Different
attachment methods are possible.
Epoxy based adhesive can be used for
comparatively low temperature applications. For service temperatures that are
above
150 degrees Celsius, a polyamide based adhesive can be used.
Note that the attachment points 17, 18 include a window 20 that exposes the
optical fiber strand and allows the adhesive to be deposited on the optical
fiber carrier
13 such as to create a bond surface over a sufficient length for good
adhesion.
In a specific example of implementation the optical fiber carrier 13 is made
of
metallic material.
12
CA 02952155 2016-12-16
The optical fiber carrier is surrounded by a cylindrical heat shield 22. The
heat
shield 22 is a thermal buffer to absorb and dissipate heat generated when the
splice
protector 11 is fusion welded to the protective jacket of the optical fiber
cable. The heat
shield is concentric with the optical fiber carrier 13. The ability of the
heat shield to
buffer thermal energy during the welding operation can be expressed in terms
of heat
diffusivity. A material that is highly thermally conductive distributes
thermal energy
rapidly throughout the body of the material, thus avoiding creating a large
temperature
gradient. This factor is important in the context of fusion welding where a
significant
amount of heat is locally generated to melt the material of the outer jacket.
Copper,
silver, gold and alloys of high content of these materials work well. Also it
is possible to
provide the heat shield with a geometrical design having a high surface/volume
ratio,
such as radiating fins.
Preferably, the thermal diffusivity of the heat shield should be higher or
equal to
30, but generally the higher the value the better. Specific examples of
thermal diffusivity
values for specific materials are: silver = 165, gold = 127, copper = 111, Al
= 84, but
A1203 = 12 mm2/s, making Al a questionable long term choice since it can
convert to
aluminum oxide which reduces the thermal diffusivity significantly.
Yet, another characteristic of the heat shield 22 is its high melting
temperature to
avoid liquefying during the fusion weld.
Instead of using metallic materials, the heat shield 22 can be made from a
ceramic-based material which has a high temperature resistance, in other words
it can
withstand temperatures in the order of magnitude of those generated during the
fusion
weld without structural degradation. The ceramic material that can be used can
be
selected to have comparatively high thermal diffusivity or a comparatively low
thermal
diffusivity. A high thermal diffusivity material will transmit easily heat
throughout the
body of the heat shield 22, while a low thermal diffusivity material will
transmit heat
poorly. In the latter case, when the fusion weld is performed, the parts of
the heat
shield 22 that are adjacent the welding arc will be heated to a temperature
that is close
13
CA 02952155 2016-12-16
to the melting temperature of the outer jacket, however owing to the
temperature
resistance of the ceramic, the material will not be damaged. Due to the lower
thermal
diffusivity, the high temperature zone will remain localized and will not
propagate
throughout the entire body of the heat shield. In this fashion, the optical
fiber
carrier 13 and the optical fiber mounted to it will be thermally protected.
A heat shield made of ceramic based material that has high thermal diffusivity
works similarly to a heat shield made of metal, in the sense that it uses the
volume of
the entire heat shield to buffer the heat injection during the welding
operation.
In terms of dimensions, the heat shield 22 has a transverse dimension that is
less than the transverse dimension of the optical fiber cavity, such as to
allow the heat
shield to fit therein. In this fashion, the heat shield 22 has end portions
24, 26 that fit
within the sections of the optical fiber cable that are on either side of the
splice
protector 11. At the same time the longitudinal extent of the heat shield 22
should be
less than the longitudinal extent of the optical fiber carrier 13, to leave
the
windows 20 exposed to allow the installation of the optical fiber in the
optical fiber
carrier 13.
When the optical fiber carrier 13 and the heat shield are made of metallic
material, they can be secured to one another during the manufacturing of the
splice
protector 11 by brazing, as shown at 28 in Figure 2.
The splice protector also has an outer cover 30 that is concentric with the
heat
shield 22 and with the optical fiber carrier 13. As better shown in Figure 2,
the outer
cover 30 has a central portion 32 and side portions 34, 36. The side portions
snugly
cover the end portions 24, 26 of the heat shield 22. The difference in
thickness
between the central portion 32 and the side portions 34, 36 constitute radial
shoulders
against which abut the outer jackets of the optical fiber cable sections on
either side of
the splice protector 11.
14
CA 02952155 2016-12-16
The outer cover 30 is made of material that is compatible with the material of
the
outer jacket of the optical fiber cable and that can be fusion welded with it.
For
instance, the outer cover 30 can be made from the same material as the outer
jacket.
The process for installing the splice protector 11 will now be described in
connection with Figures 8 and 9.
Figure 8 shows two section of optical fiber cable 40, 42 shown in dotted lines
on
either side of the splice protector 10. This is the position in which the
sections 40 and
42 are ready to be fusion welded to the splice protector 10.
The sections 40, 42 may be prefabricated sections to be joined to one another
to
form a longer length of optical fiber cable. Each section 40, 42 has a free
end from
which a fiber pigtail projects. The pigtail from one of the sections 40, 42 is
inserted
through the through bore 15 of the optical fiber carrier 13 until the pigtail
exits the
opposite side of the through bore 15. The pigtails are then connected to one
another by
any appropriate method to create a connection allowing signal transmission. At
that
point, the connection can be tested for structural resistance and functional
requirements. If the tests are satisfactory, the optical fiber strand with the
splice is
pulled back until the optical fiber splice resides somewhere at mid point in
the optical
fiber carrier 13.
Next, the optical fiber strand that runs through the optical fiber carrier 13
is
affixed to the carrier 13. This is performed by heating the splice protector
10 to bring it
to its service temperature. The service temperature is the temperature at
which the
optical fiber is exposed during its operation.
In many applications, the service
temperature may not be a fixed temperature value; rather it resides in a range
of
temperatures. For example, in the oil and gas industry, an optical fiber in a
well, such
as Steam Assisted Gravity Drainage (SAGD) well, is subjected to a temperature
that
varies in the range from about 150 degrees C to about 350 degrees C. So, in
those
CA 02952155 2016-12-16
applications, the service temperature is any temperature between the extremes
of that
operational range.
Advantageously, the service temperature picked at which the optical fiber and
the
splice protector are brought during the installation operation is selected
such that when
the optical fiber and the splice protector are at the highest end of the
operational range,
the stress acting on the optical fiber is below a level that will damage the
optical fiber
and particularly the splice.
The computation of the service temperature picked at which the installation is
performed can be done as follows. The first step is to determine the maximal
allowable
stress to which the optical fiber and the splice can be subjected. Usually,
this is a fixed
parameter that is well known and depends on the optical fiber used and the
method of
splicing used. Once this is determined, the second step is to compute on the
basis of
the thermal expansion coefficient differential between the optical fiber and
the splice
protector, the temperature difference at which the maximal stress level will
be produced.
The service temperature picked for the installation is the highest end of the
operational
temperature range minus the temperature difference.
The splice protector 10 can be heated to the service temperature by using hot
air. Once the splice protector 10 and the optical fiber segment with the
splice residing in
the optical fiber carrier 13 are brought to the desired temperature, the
optical fiber
strands on either side of the splice are affixed to the attachment points 17,
18 by using
adhesive material or a suitable mechanical fastener. In the case of adhesive,
the
material selected should be able to withstand the service temperature without
degrading
over time. Polyamide based adhesives are suitable for a service temperature in
the
range of about 150 degrees Celsius to about 300 degrees Celsius.
If the splice protector 10 is left to cool to room temperature, the splice
protector
will contract more than the optical fiber due to the difference between the
respective
expansion coefficients. Accordingly, the optical fiber segment will develop a
degree of
16
CA 02952155 2016-12-16
Excess Fiber Length (EFL) between the attachment points 17, 18. That degree of
EFL
will dissipate when the optical fiber cable is brought into service as a
result of the
expansion of the splice protector 10.
Alternatively, the installation of the optical fiber segment into the optical
fiber
carrier 13 can be done at room temperature without heating the splice
protector 10.
The optical fiber segment is affixed to the attachment points 17, 18, but with
a degree of
EFL between them such that when the splice protector 10 is in service, the
degree of
EFL will compensate for the greater thermal expansion of the splice protector
10.
The degree of EFL can be determined on the basis of the differential between
the
coefficients of thermal expansion of the splice protector and the optical
fiber and the
service temperature. The EFL is usually expressed as a percentage of length of
the
optical fiber. The specific EFL length value can be computed based on the
percentage
and the distance between the attachment points 17, 18. For example, for a 10%
EFL
and an inter-attachment point distance of 5 inches, the fiber length that is
to be threaded
in the bore 15 at room temperature is of 5.5 inches.
In a specific example of implementation, the ELF is of at least 0.1%.
Advantageously, the EFL is of at least about 0.15%, more advantageously of at
least
about 0.2% and preferably of about 0.25%.
Specifically, when the EFL for a certain installation has been determined, two
reference marks are made on the optical fiber indicating to the technician the
locations
on the optical fiber to affix to the attachment points 17, 18. The distance
between the
reference marks is the distance between the attachment points plus the EFL
length.
For the installation, the technician places one reference mark in alignment
with the first
attachment point and affixes it there such that it is firmly attached. Then
the technician
places the second reference mark in alignment with the other attachment point
and
affixes it at that location as well. It will be understood that the portion of
the optical fiber
17
CA 02952155 2016-12-16
strand between the attachment points 17, 18 is left free and unattached to the
splice
protector 10.
Once the optical fiber has been secured to the optical fiber carrier 13, the
open
ends of the sections 40, 42 are inserted over the end portions 24, 26. The
diameter of
the side portions 34, 36 matches the internal diameter of the outer jacket
such that there
is no free play and the sliding fit is snug. In this fashion, the central
portion 32 will be
flush with the outer jacket. A weld 44 is made at both junctions to create a
fusion weld
joining the central portion 32 to the outer jacket of sections 40, 42. An
orbital welding
process can be used for this purpose.
The welding process used can be a two-step process. A first weld is made at
one end of the central portion 32 to join the central portion 32 to section
40. The weld
just created becomes a heat dissipation path allowing thermal energy in the
heat shield
52 to migrate into the outer jacket of section 40. During the second welding
step, which
connects the central portion 32 to section 42, the thermal absorption capacity
of the
heat shield 52 is effectively augmented since there is now an additional heat
dissipation
channel available.
Note that the ability of the heat shield 52 to channel thermal energy into the
outer
jacket at both ends exists even before the welds are made. As long as there is
some
degree of physical contact between the side portions 34, 36 and the internal
surface of
the outer jacket, heat will be channeled away from the heat shield 52. Making
the
physical connection between the side portions 34, 36 and the internal surface
of the
outer jacket tighter will improve the thermal transfer ability of the heat
shield 52. The
need for a tighter fit to improve the thermal transfer needs to be balanced
against the
ability of the side portions 34, 36 to be inserted within the outer jacket
during the
assembly without the need of special tools or excessive force.
Once the welding process is completed, the welds can be inspected for sealing
integrity and structural integrity. The optical fiber cable can be subjected
to pressure
18
CA 02952155 2016-12-16
testing to ensure that the welds create a hermetic seal. X-ray can be used to
ensure
proper weld penetration. Suitable mechanical tests such as one subjecting the
welds to
a twisting stress can be used to verify the structural integrity.
The resulting structure provides a constant cross-sectional dimension without
any major variations. Major variations would make it difficult for the optical
fiber cable to
be inserted in the well.
Figures 4 to 7 illustrate a variant. The splice protector 46 has a longer
optical
fiber carrier 48 to further isolate the optical fiber attachment from the heat
generated
during the welding operation. In the example shown, the optical fiber carrier
48 is
longer on one side. This arrangement is used in instances where one attachment
point
is more heat sensitive than the other.
Figure 7, which is an enlarged cross-sectional view of detail B shown in
Figure 6.
The optical fiber carrier 48 is secured with a brazing joint 50 to the heat
shield 52.
In a possible variant, the splice protector can be used to make the junction
between optical fiber cable sections that have different diameters. In such
case, the
central portion of the outer cover 32 is flared, expanding from the smaller
diameter
section to the larger one.
Figure 10 is an example of a modular construction optical fiber cable 54 that
uses
the splice protector according to the invention. The optical fiber cable 54 is
an
assembly of different sections that have different functional attributes. The
section 56 is
a plain cable section which is used for signal transport only. It has an outer
jacket
housing an optical fiber which conveys optical signals. The plain cable
section 56 does
not provide any sensing capability. Its function is only to transport the
optical signal.
A splice protector 58 joints the optical cable section 56 to another
functional
section 60. The section 60 has sensing capability and it can measure a
physical
19
CA 02952155 2016-12-16
parameter in the subterranean formation in which the optical fiber cable 54 is
installed.
For example, the physical parameter that is measured is pressure and/or
temperature.
An example of an optical fiber cable that can be used for pressure and
temperature
sensing is described in Canadian Patent Application 2, 744, 734. Note that
technically,
the section 60 has, in addition to the sensing function, a signal transport
function as well
since the optical signal also travels through section 60.
A splice protector 62 joins the functional section 60 to another functional
section
64. The section 64 can provide a sensing function that measures the same or
different
physical parameter(s) or it can provide a signal transport function as the
cable section
56.
It will become apparent that the splice protector can be used to assemble
optical
fiber cables that have sections of different properties at selected locations
of the cable
such as to provide sensing capabilities of the type required and at the
location required.
The cable assembly operation can be carried out in the field or close to the
installation
site.
If the assembly operation is performed remotely from the installation site,
the
assembled optical cable can be wound on a spool to facilitate transport. The
spooled
cable is transported to the installation site and threaded into the well by
using traditional
capillary lines installation methods, while it is simultaneously being unwound
from the
spool. In many instances, this approach allows performing the installation
without
interfering with the well operation and without the need to install any
special seals since
the optical fiber cable is sufficiently small to pass through existing seals
without
compromising their sealing function.
Figure 11 illustrates equipment that is used for installing an optical fiber
cable 10 in a
well. The equipment includes a rig 70 that supports a sheave 72 on which the
optical
fiber cable 10 is held. The optical fiber cable 10 arrives at the installation
site wound on
a spool 74. The optical fiber cable 10 is threaded from the spool 74 through
the sheave
CA 02952155 2016-12-16
72 that is located at a higher elevation than the spool 74. The outgoing run
of the
optical fiber 10 that leaves the sheave 72 is inserted in the well. The
optical fiber cable
is unwound from the spool 74 and progressively inserted in the well until it
reaches
the desired installation depth.
The insertion of the optical fiber cable 10 in the well is thus a continuous
process.
When the optical fiber cable 10 has been completely assembled at the
manufacturing
site, there is no need to make any cable splices at the installation site and
the optical
fiber cable is put in place by unrolling it from the spool 74 and pushing it
in the well bore
until in reaches the intended installation depth.
The optical fiber 10 has a structure allowing the cable to bend without being
damaged.
The optical fiber cable 10 is mostly subjected to bends during the
manufacturing and
installation process and resists those bending stresses without damage that
would
otherwise undermine its long-term reliability.
The optical fiber cable 10 can also be subjected to bends when it is threaded
in a well
bore that has elbows, such as wells having a vertical section that turns
horizontally at a
certain depth. Note that the bends to which the optical fiber cable is
subjected when
installed in the well, typically are not as severe as those arising during
manufacturing or
the threading of the optical fiber cable through the installation sheave,
because of the
large radius of curvature of the elbow.
The bend stresses to which the optical fiber cable is subjected during
manufacturing
occur when the optical fiber cable 10 is wound on the spool 74. Another bend
stress
arises during the installation of the optical fiber cable 10 when the cable is
unwound. In
other words, the optical fiber cable 10, which has taken a set when wound on
the spool
74, is bent again, but in the reverse direction to be straightened out.
The most severe bending stress arises when the optical fiber cable 10 passes
over the
sheave 72 because the sheave 72 has a radius of curvature that is smaller than
the
21
CA 02952155 2016-12-16
radius of the spool 74 and the elbow radius in the well. Again, the bend
stress is a dual
one. There is a first bend when the optical fiber cable 10 enters the sheave
72 and
curves around it, and a second bent when the optical fiber cable 10 exits the
sheave 72
and straightens out to enter the well.
Since the installation of the optical fiber cable 10 is a continuous
operation, the optical
fiber 10 is subjected on its entirety to a bend stress over the sheave 72
during the
installation process, as the cable is threaded over that sheave. This means
that for the
optical fiber cable 10 to remain operational, it should be able to withstand
the bend
stress without permanent damage. A permanent damage resulting from bent stress
is
defined in this specification as:
1.
A buckled outer metallic jacket in the area of the bend that is subjected to
compressive stress. A buckle is a permanent deformation in the outer
metallic jacket, which will not go away as the optical fiber cable 10
straightens, such as when it exits the sheave 72. If the buckling is
severe enough it could constrict the internal elongated conduit and
interfere with the optical fiber. For instance, in extreme cases the
buckling can pinch the optical fiber and sever it. Even if the buckling
does not sever the optical fiber, it will create an internal deformation in
the otherwise smooth walls that will prevent or interfere with the relative
movement between the optical fiber and the outer jacket resulting from
a different coefficient of thermal expansion. Such relative movement
arises when the optical fiber cable 10 is subjected to its service
temperature in the well. An interference with the relative motion will
create elongation stress in the optical fiber. Such elongation stress, if
sufficiently severe could break the optical fiber. Even if the stress is not
high enough to break the optical fiber, the added stress in the optical
fiber could induce artifacts in the temperature or pressure
measurements.
22
CA 02952155 2016-12-16
2.
Loss of hermeticity in the outer metallic jacket. Loss of hermeticity is
defined as the occurrence of leakage pathways in the outer metallic
jacket allowing a fluid outside the outer metallic jacket to penetrate the
internal cavity. The fluid, which can be a gas or a liquid, would thus
enter the internal cavity and attack the fragile optical fiber.
To determine if the optical fiber cable 10 can withstand bending stresses
arising during
manufacturing, transportation and installation, the optical fiber cable 10 is
subjected to a
bending stress test. The test procedure is described below in conjunction with
Figures
13 and 18.
During the test procedure the optical fiber cable 10 is subjected to a bend
and then it is
straightened out. The outer jacket of the optical fiber cable 10 is visually
inspected for
buckling. A hermeticity test is performed to check for leakage pathways. If no
bucking
is visually observed and no leakage detected, the optical fiber cable 10
passes the test.
As shown in Figure 13, a section of optical fiber cable 10 to be tested is
placed adjacent
a circular body 80, which has a radius of curvature R. As shown next in Figure
14, the
section of optical fiber cable 10 is bent around the body 80 such that the two
legs 82
and 84 are generally parallel to one another. In this configuration, a bend of
180
degrees has been achieved. Note that due to the springiness in the optical
fiber cable
10, it will likely be necessary to bend the optical fiber cable 10 over an
angle slightly
more than 180 degrees such that upon removal of the bending force acting on
the
optical fiber cable 10 the legs 82 and 84 remain substantially parallel.
The bending of the optical fiber cable 10 around the body 80 can be made by
hand or
by automated equipment.
As shown next at Figure 15, a reverse bend is performed. The legs 82 and 84
are
spread apart in an effort to straighten the optical fiber cable 10. The
spreading is
performed until the legs 82 and 84 are generally collinear when the reverse
bending
23
CA 02952155 2016-12-16
force is removed. Note that a slightly curved section 86 in the optical fiber
cable 10 is
likely to remain between the legs 82 and 84.
The section of optical fiber cable 10 is now visually inspected to determine
if any
buckling has occurred. If any buckling is present it will be on the side of
the optical fiber
cable 10 which faces the round body 80 and which is subjected to compressive
stress
during the bend. Any buckling will produce locally a marked change in the
cross-
sectional shape of the optical fiber cable 10. The cross-sectional shape will
no longer
be circular or oval. Rather it will show an inward deformation in the outer
metallic
jacket.
If no buckling is observed, the optical fiber cable 10 is subjected to a
hermeticity test
procedure. The purpose of the hermeticity test procedure is to detect the
presence of
leakage pathways that may have been created in the outer metallic jacket as a
result of
the bending stresses. The hermeticity test procedure is performed by
subjecting the
outer metallic jacket to a pressure differential between the inside and the
outside and
testing for leaks. Gas, such as air is pumped in the outer metallic jacket and
an internal
pressure of 1000 pounds per square inch (psi) is established with relation the
exterior.
The pressurized section of optical fiber cable is tested for leaks. This can
be done in a
number of ways. A simple procedure is to dip the pressurized cable section in
water
and visually look for air bubbles. The optical fiber cable section fails the
test if any air
bubbles are present, indicating the existence of fissures in the outer
metallic jacket.
As a practical matter, the presence of the optical fiber in the outer metallic
jacket does
not influence the outcome of the bending stress test and can be removed. In
other
words, the test can be satisfactorily performed on the outer metallic jacket
alone.
The same procedure is followed when testing a section including a splice
protector. The
procedure is illustrated in Figures 16 to 18. As shown in Figure 16, a section
of optical
fiber cable 10 is placed adjacent the round body 80, such that the splice
protector 88
would be in the center of the bend. As shown in Figure 17, the optical cable
10 is bent
24
CA 02952155 2016-12-16
at 180 degrees and then straightened out, as Figure 18 indicates. The optical
fiber
cable 10 is then inspected visually for buckling and pressure tested for
hermeticity.
Usually, the critical part where leakage pathways may develop is at the welds
90 and 92
between the splice protector 88 and the adjoining segments of the outer
metallic jacket.
The optical fiber cable 10 has a construction such that it can successfully
pass the
bending stess test when the round body 80 has a radius R that is less than 24
inches,
preferably less than 18 inches, more preferably less than 12 inches and even
more
preferably of less than 6 inches.
Figure 12 illustrates the installation of the optical fiber 10 in the well
bore. The well bore
is shown at 100. The optical fiber cable 10 is run along most of the well bore
length and
passes through swellable packers that are installed at spaced apart locations
in the well
bore to isolate different well bore sections from one another. The swellable
packers
can be inflated hydraulically or pneumatically to create a fluid-tight seal
preventing the
passage of fluid between well bore sections on either side of a packer. The
reference
numeral 102 in Figure 12 identifies a swellable packer that is in the process
of being
inserted in the well bore 100. Once in place, the swellable packer 102 can
radially
expand when pumped with fluid to create a fluid tight seal.
Since the cross-sectional dimension of the optical fiber cable 10 is small, it
can be
placed in a slit 104 that extends lengthwise from one end of the swellable
packer 102 to
the other. This approach allows to place the optic fiber cable 10 within the
swellable
packer 102 and avoids that the optical fiber cable 10 is pinched between the
outer
periphery of the swellable packer 102 and the well bore. It the latter
scenario, the
optical fiber cable 10 may prevent the swellable packer to create an adequate
seal.
