Note: Descriptions are shown in the official language in which they were submitted.
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COMBINATION FIBER OPTIC/ELECTRICAL WELL LOGGING CABLE
BACKGROUND OF THE INVENTION
Field of the Invention
The invention is related to the field of armored electrical cables used in well
logging. More specifically, the invention is related to well logging cables which include
one or more optical fibers for con~llullicating data and/or control signals between the
earth's surface and well logging instruments attached to one end of the logging cable.
Description of the Related Art
Electrical well logging cables typically include one or more in~ul~tç~l electrical
conductors ~ulloullded by a plurality of steel armor wires which provide the cable with
tensile strength and abrasion resistance. The electrical conductors transmit electrical
power to well logging instruments attached to one end of the cable, and transmit data
and/or control signals between equipment located at the earth's surface and the well
logging ilL~llulllents.
Some well logging instruments ~lallsll~i~ signal data at such high rates that using
electrical conductors for such data tr~n~mi~.sion is ~liffirlllt When using such well logging
instruments it is desirable to use optical fibers to carry optical data telemetry because
optical telemetry typically has much greater data tr~n~mi~sion rate capability than does
electrical telemetry. The well logging i~lUlll~llL~ using optical data telemetry preferably
should receive electrical power from the earth's surface over the logging cable just as do
electrical telemetry logging il~lulllellL~, so a logging cable including a combination of
electrical conductors and optical fibers is desirable. Several types of combination fiber
optic/electrical cable are known in the art. A sales brochure entitled "Electro-Optical
Mechanical Umbilicals" published by Vector Cable Colllpally, Sugar Land, Tex.
(publication date unknown) shows several configurations for an electrical cable including
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both optical fibers and electrical conductors ~u~ ullded by steel armor wires. The cables
disclosed in the Vector Cable Colllpally brochure, however, are typically 2/3 of an inch
or more in external (li~m~ter, making them impracticable for use as a well logging cable.
Typical well logging cables do not exceed about 17/32 inch external diameter. This is
mainly because of space limitations on the typical well logging surface instrumentation
system, and as known in the art is also related to the use of certain wireline wellbore
pressure control equipment the use of which is made more difficult to use as the ~ er
of the logging cable is increased.
Another type of combination optical fiber/electrical cable is disclosed in U. S.patent no. 4,697,875 issued to Priaroggia. The cable disclosed in the Priaroggia '875
patent is entirely unsuitable for use as a well logging cable because the electrical
conductors are disposed externally to a wire rope strength member, and are covered
externally with a plastic jacket. As is well known in the art of well logging, the typical
well logging cable should have an abrasion resistant material such as steel on the outside.
Other colllbh~lion fiber optic/electrical well logging cables are disclosed in U. S.
patent no. 4,696,542 issued to Thompson and U. S. patent no. 4,522,464 issued toThompson et al. The cables disclosed in these patents have limitations to their use as well
logging cables which are well documented in U. S. patent no. 5,495,547 issued to Rafie
et al and assigned to the assignee of this invention. More specifically, the cables disclosed
in the Thompson '542 and Thompson et al '464 patents do not have, to the greatest extent
possible, the electrical and mechanical characteristics of well logging cables which have
only electrical conductors. Having such electrical and mech~nir~l properties is desirable
in a well logging cable to enable use of such logging cables in situations where the logging
instruments attached to the cable only include electrical telemetry, thus avoiding the need
to have different types of cable available for each type of instrument telemetry system.
The Rafie et al '547 patent discloses several configurations for a combination fiber
optic/electrical well logging cable which retain the pler~ d electrical and mechanical
characteristics of conventional well logging cables which have only electrical conductors.
The cables disclosed by Rafie et al '547 however, require expensive and difficult to use
connection devices to make the electrical and optical connections to the well logging
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instruments attached to the end of the cable. What is needed is a combination fiber
optic/electrical well logging cable which retains the electrical and mechanical
characteristics of a conventional electrical well logging cable having only electrical
conductors, and includes the capability of electrical and m~ch~ni~l connection to the well
logging instruments using conventional electrical/mechanical connection techniques.
SUMMARY OF THE INVENTION
The invention is a combination fiber optic/electrical well logging cable. The cable
includes at least one insulated electrical conductor and a plurality of armor wires
surrounding the electrical conductor. In one embodiment of the invention, the cable
includes seven insulated electrical conductors arranged in a regular hexagonal pattern.
The armor wires include at least one tube having an optical fiber disposed inside the tube.
In a prefelled embodiment of the invention, the armor wires are disposed in two
concentric layers circumscribing the electrical conductors. One or more of the armor
wires in the inner layer of armor wires includes the tube having the optical fiber disposed
therein.
The tube has an external ~i~m~ter which is substantially the same as the armor
wires in the layer in which the tube is located. The inner ~ m~ter of the tube is selected
to provide just enough room for the optical fiber to move about freely, but to retain
enough crush strength for the tensile and side loads expected to be applied to the cable.
In a particular embodiment of the invention, the tube includes an inner layer
consisting of a thin walled tube, a metal foil layer wrapped around the outside of the inner
layer, and an outer layer consisting of another thin walled tube on the outside of the foil
layer. The metal foil layer substantially fills the annular space between the inner layer and
the outer layer so that the tube behaves mech~ni~lly similarly to a solid tube having the
same internal and external tii~mPterS.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a cross-section through a well logging cable according to the invention.
Figure 2 shows steel tubes having optical fibers therein used in substitution of one
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or more of the inner and/or outer armor wires of the logging cable shown in Figure 1.
Figure 3 shows an alternative design for the steel tubes shown in Figure 2 wherein
the tube consists of an inner layer, a foil layer and an outer layer.
DESCRIPTION OF THE PREFERRED EMBODIMENT
A cross-section of a colllbhlalion fiber optic/electrical well logging cable according
to the invention is shown at 10 in Figure 1. The logging cable 10 includes a central
conductor bundle 2. The central bundle 2 for the cable 10 shown in Figure 1 includes
seven insulated electrical conductors 9 arranged in a regular hexagonal pattern. Each one
of the electrical conductors 9 can be formed from stranded copper wires 12 ~ulloul1ded
by an in~ ting sheath 8 made of plastic or other suitable electrically in~ ting, flexible
material. Typical (lim~n~ions for the conductors 9 are disclosed, for example, in a product
catalog published by Camesa, Inc., Rosenberg, Tex., listing the construction of each of
the conductors 9 as including seven stranded copper wires each one 0.0128 inch diameter,
~ullounded by a 0.084 inch insulating sheath made from polypropylene or " lL~LL"(trade name of a copolymer made by E. I. DuPont de Nemours & Co.). Void spaces 14
between the conductors 9 within the hexagonal pattern can be filled with a suitable plastic
insulating material well known in the art.
It is to be clearly understood that the configuration of the central bundle 2 shown
in Figure 1 is only an example and is not meant to limit the invention to seven in~ ted
conductors 9. Other acceptable configurations for the central bundle 2 are well known in
the art and can include a diffelclll number of, or different sizes of electrical conductors.
For example, certain smaller diameter well logging cables well known in the art include
a central bundle consisting of only one in~ tccl eleckical conductor. Other well logging
cables include three or four in.~ tecl electrical conductors in the central bundle 2.
An alternative design to the stranded copper conductors shown in the Camesa, Inc.
catalog is disclosed, for example, in U. S. patent no. 5,495,547 issued to Rafie et al. The
alLelllative electrical conductor 9 can include a copper covered steel wire about 0.027
inches in di~m~t~r surrounded by nine copper wires each about 0.0128 inches in di~m~t~r,
these all being surrounded by an insulating jacket of about 0.084 inches in (li~m~ ter. This
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configuration for the alternative electrical conductor is shown at Figure 3 in the Rafie et
al '547 patent.
Either type of electrical conductor 9 as just described herein can be electrically
conn~cted to well logging instruments (not shown) by using sealed electrical connectors
5 well known in the art.
Once again lere~ g to Figure 1, the central bundle 2 is typically surrounded by
two concentric layers of steel armor wires. The armor wires 4, 6 can also be formed from
corrosion-resistant alloy such as one known by trade designation MP-35N where the
logging cable is intended to be used in wellbores having corrosive fluids therein. The
armor wires include inner armor wires shown at 4 ~lll~ing the innermost concentric layer.
For the cable 10 shown in Figure 1, the inner armor wires 4 can include eighteen steel
wires each having an external di~m~ter of about 0.047 inches. The inner armor wires 4
are themselves typically ~ull~ullded by an outer layer of armor wires 6. For the cable
shown in Figure 1, the outer armor wires 6 can include eighteen steel wires each having
an external diameter of about 0.066 inches. It is to be clearly understood that other
numbers of, diameters of, and number of layers of armor wires can be used with this
invention consistent with ~ g the external ~i~mPter of the cable 10 and at the same
time providing commercially acceptable breaking strength of the cable 10. The numbers,
m~ters of and numbers of layers of the armor wires shown in Figure 1 are meant only
to serve as an example of a suitable configuration and are not meant to limit the invention.
In the invention, one or more of the inner armor wires 4, such as the one shown
at 4A, can consist of a steel tube having an optical fiber disposed therein, as will be
further explained. Alternatively, or in addition to the tube shown at 4A, one or more of
the outer armor wires 6, such as the one shown at 6A, can consist of a steel tube having
an optical fiber disposed therein, as will be further explained. If the armor wires 4, 6 are
formed from a corrosion resistant alloy, such as the previously described MP-35N, then
the tubes, 4A, 6A should be formed from the same or similar material to provide the
desired corrosion resistance.
The tube 4A which sub~lilu~es for one of the inner armor wires 4 is shown in more
detail in Figure 2. This tube 4A should have an external ~ m~ter substantially the same
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as the external (ii~m~ter of the inner armor wires 4 so that symmetry of the layer of armor
wires is m~int~inPd. In this example, the outer ~ m~ter of the tube 4A can therefore be
about 0.047 inches. An optical fiber 16 disposed inside the tube 4A can be of types
known in the art. The fiber 16 shown in this example has an external diameter of about
0.007 inches. The internal di~m~ter of the tube 4A in this example is about 0.023 inches.
The internal di~mPter of the tube 4A should be selected to provide enough space for the
optical fiber 16 to move about freely inside the tube 4A, but should also be no more than
that which is reasonably needed for the optical fiber 16, so that the tube 4A will have
sufficient strength to resist crushing under tensile and side loading which is likely to be
applied to the cable (10 in Figure 1). Methods for calculating a maximum internal
diameter of the tube 4A which will allow for the m~ximllm expected tensile and side
loading on the logging cable 10 are known in the art, including finite element analysis as
can be perfo~med using a co~ u~er program sold under the trade name "ANSYS" by
Southpoint, 275 Technology Dr., Canonsburg, PA.
As previously explained, one or more of the outer armor wires (6 in Figure 1) may
also consist of a steel tube 6A (or corrosion resistant alloy tube as previously explained)
inside which is disposed an optical fiber 18. In the example in Figure 2, the tube 6A can
have an external ~ m~ter of 0.066 inches and an internal diameter of about 0.023 inches
to accommodate the optical fiber 18. The external and internal diameters of the tube 6A
should be selected to satisfy substantially the same mechanical criteria as the tube 4A
substituting one of the inner armor wires (4 in Figure 1). It should be noted that
substitution of one or more of the outer armor wires (6 in Figure 1) by the tube 6A may
be less desirable than subslilulillg one or more of the inner armor wires (4 in Figure 1)
with the tube 4A, from the standpoint of possibility of failure of the tube 6A due to wear
in its outer surface by abrasion with continued use. The example of the tube 6A is
intended primarily to show that the invention is not to be limited in scope to substitution
of inner armor wires 4 by the tube 4A.
DESCRIPTION OF A SPECIFIC EMBODIMENT
Figure 3 shows a different design for the tube 4B which is intended to facilitate
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splicing of the well logging cable at any intermP~ te position along its length, while
m~int~ining the hydraulic integrity of the tube 4B so that fluid under very high pressure,
as is typically present in a wellbore, may be excluded from the inside of the tube 4B.
The tube 4B consists of an outer layer 20, a metal foil layer 22 and an inner layer
24. The optical fiber 16 is disposed within the inside of the inner layer 24 just as it is in
the first embodiment of this invention.
The outer layer 20 can be a thin walled tube, which in this example can have an
external ~ m~ter of about 0.047 inches and an internal diameter of about 0.037 inches.
The external ~ m~ter of the outer layer 20 is selected in this example for the case where
the tube 4B will be included within the inner layer of armor wires on the cable (shown in
Figure 1- at 10). The outer layer 20 could also have an external diameter about the same
as that of the armor wires in the outer layer of armor (6 in Figure 1) if that is where the
tube is to be located. The outer layer 20 can be made from steel or the corrosion resistant
alloy such as MP-35N used for any of the other armor wires (4 in Figure 1) in the cable.
The inner layer 24 can also be formed from thin walled tube. In this example, the
inner layer 24 has an internal ~ mPter of about 0.020 inches and an external diameter of
about 0.028 inches. The internal ~ m~ter of the inner layer 24 should be large enough
to enable the fiber 16 to move about freely, but be no larger than that needed to m~int~in
sufficient crush resistance and tensile strength of the tube 4B, just as is the case for the
first embodiment of the tube (4A in Figure 2) in this invention. The inner layer 24 can
be made from the same material as the outer layer 20, but this is not necessary to
construction of the tube 4B.
The annular space between the inner layer 24 and the outer layer 20 can be filled
with a metal foil 22 wrapped in a helical pattern around the outside of the inner layer 24.
The thickness of the metal foil 22 should be about the same as the width of the annular
space between the inner layer 24 and the outer layer 20. Since the annular space between
the outer layer 20 and the inner layer 24 is substantially filled by the metal foil 22, the
tube 4B will have nearly the same crush strength as that of the solid-construction tube (4A
in Figure 2) in the first embodiment of the invention.
It is contemplated that where the logging cable (10 in Figure 1) must be spliced,
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the fiber 16 may be coupled using techniques known in the art. The inner layer 24 may
be coupled using a thin walled steel sleeve (not shown) which fits over the outside of the
inner layer 24 and can be welded or otherwise coupled to exclude entry of fluid under high
pressure from entering the inside of the inner layer. The metal foil 22 may be substituted
by compressible material such as plastic, or can be omitted, over the interval in which the
sleeve (not shown) is located. Then the outer layer 20 may be joined by butt welding or
similar to provide mechanical coupling between the joined ends across the splice.
The tube 4B in Figure 3 has about the same internal and external (li~m~ter as the
solid-construction tube (4A in Figure 2) and retains substantially the same mechanical
properties of the solid-construction tube (4A in Figure 2), but is better adapted to m:~int~in
hydraulic integrity across a splice than is the solid-construction tube (4A in Figure 2).
Those skilled in the art will devise other embodiments of this invention which do
not depart from the spirit of the invention as disclosed herein. Accordingly, the invention
is to be limited in scope only by the attached claims.
What is claimed is:
