U.S. patent application number 09/873894 was filed with the patent office on 2002-12-05 for bird communications system in a marine seismic cable.
Invention is credited to Hepp, John, Maples, Mike, Spackman, James.
Application Number | 20020181327 09/873894 |
Document ID | / |
Family ID | 25362543 |
Filed Date | 2002-12-05 |
United States Patent
Application |
20020181327 |
Kind Code |
A1 |
Spackman, James ; et
al. |
December 5, 2002 |
BIRD COMMUNICATIONS SYSTEM IN A MARINE SEISMIC CABLE
Abstract
A communication housing for devices external to a solid marine
seismic cable, especially for level control devices, comprises an
upper housing half and a lower housing half, coupled together
around the cable. The upper housing half includes a plurality of
wells, for example three wells, each adapted to receive a
communication coil. The lower housing half has no such wells. The
communication coils are wound in series to reinforce the signal
strength of the communication signal. The communication coils are
preferably formed to two segments, joined together at a flexible
joint to reduce the likelihood of breakage of the coil core as the
cable is wound onto a takeup reel aboard the exploration
vessel.
Inventors: |
Spackman, James; (Buchanan
Dam, TX) ; Maples, Mike; (Houston, TX) ; Hepp,
John; (Irving, TX) |
Correspondence
Address: |
Tim Cook
Bracewell & Patterson, L.L.P.
P.O.Box 61389
Houston
TX
77208-1389
US
|
Family ID: |
25362543 |
Appl. No.: |
09/873894 |
Filed: |
June 4, 2001 |
Current U.S.
Class: |
367/19 |
Current CPC
Class: |
G01V 1/201 20130101;
G01V 1/3808 20130101 |
Class at
Publication: |
367/19 |
International
Class: |
G01V 001/38 |
Claims
We claim:
1. A marine seismic cable assembly comprising: a. a cable having an
axis; and b. a communication coil housing which clamps around the
cable, the housing containing a plurality of communication coils
adapted for communicating with an external device, wherein any two
adjacent communication coils, are radially offset from each other
by no more than about 44.degree. from each other.
2. The assembly of claim 1, wherein the housing comprises an upper
housing half and a lower housing half, and wherein the
communication coils are contained within the upper housing half,
and wherein the lower housing half contains no communication coils,
and wherein there is no interconnect wiring between the halves.
3. The assembly of claim 2, further comprising a plurality of wells
formed in the upper housing, and wherein each of the plurality of
communication coils is mounted in its respective well.
4. The assembly of claim 3, further comprising a magnetically
permeable potting material sealing each of the plurality of
communication coils in its respective well.
5. The assembly of claim 1, wherein each of the plurality of
communication coils comprises a pair of coil segments and a
flexible joint between the coil segments.
6. The assembly of claim 5, wherein the segments are coupled
together electrically in series.
Description
FIELD OF THE INVENTION
[0001] The present invention relates generally to the field of
marine seismic cables, and, more particularly, to a structure and
method of communicating with a level control device coupled to the
cable, known in the art as a "bird".
BACKGROUND OF THE INVENTION
[0002] Solid and semi-solid seismic exploration cables for the
marine seismic exploration industry have been in development for
some time. Marine seismic cables are central to the acquisition of
data for seismic exploration at sea and the development of solid or
semi-solid cables has been directed to eliminating the well-known
and documented problems associated with fluid filled cables. For
example, the fluid in a fluid-filled cable effects the buoyancy of
the cable, which is also affected by the temperature and salinity
of the water in which the cable towed. Further, oil-filled cables
may leak. The outer jacket of a seismic cable of the prior art is
prone to rupture or tearing. This is particularly undesirable
because this exposes the internal electrical components to
seawater, and disrupts the buoyancy of the cable. Thus, a totally
solid seismic cable would eliminate such drawbacks of fluid-filled
cables.
[0003] Depth control devices on the cable, commonly known as birds,
are attached to the cable at intervals in order to maintain the
cable at a predetermined depth. Such birds are typically attached
to the cable through a collar arrangement firmly mounted to the
cable. In such systems, communication is coupled through magnetic
induction coupling between a communication coil within the fluid in
the cable and secondary coils in the bird. However, streamer
communications coils are typically constructed with the wiring
wound around single ferrite core. Such bulky and fragile devices
are not suitable for installation into a solid streamer cable.
[0004] Other external devices such as acoustic location modules,
compasses, and depth transducers may also use the communication
coil for telemetry. This wireless communication system, commonly
known in the art, eliminates the need for a physical connection
between the communication coil inside the cable and the external
device, thus better ensuring water-tight enclosure of the cable.
The prior art wireless communication system used with a
kerosene-filled cable, or non-solid cable, includes a single coil
that is attached with plastic "ties" to the bundles of wires which
make up a center core of such a cable.
[0005] A possible solution to the problem of communication between
a device external to a marine seismic cable and the cable was
suggested in U.S. Pat. No. 5,923,616 to Badger et al. A system was
suggested including a solid marine seismic cable assembly including
communication coil housings which clamp around a cable in a
spaced-apart relationship. Each housing contains at least two
communication coils adapted for communicating with an adjacent
external device. Two of the communication coils, whether or not
adjacent to one another, are offset at least 90 .degree.from each
other about the axis of the cable. Each external device has a unit
which communicates with the communication coil via magnetic
induction signals.
[0006] A major deficiency of this type of construction is that it
requires the coils in each housing to be wired together. This
increases the complexity of manufacture and compromises reliability
in the system as a whole.
[0007] The coils of the communication system are offset at least
90.degree. from each other so that, as the external device revolves
around the housing, magnetic coupling is maintained. However, the
single coil arrangement often results in low signal strength with
poor coupling. Further, having only a single coil in communication
at one time necessarily means that one coil is superfluous. Thus,
there remains a need for a system which provides greater signal
strength with all communication coils effectively employed. Such a
system should provide for radial alignment, despite the movement of
the cable and the external devices.
SUMMARY OF THE INVENTION
[0008] The present invention addresses these and other needs in the
art by providing a communication housing, especially for level
control devices, comprising an upper housing half and a lower
housing half, coupled together around the cable. The upper housing
half includes a plurality of wells, for example three wells, each
adapted to receive a communication coil. The lower housing half has
no such wells, and there is no interconnect wiring between the
halves.
[0009] The communication coils are wound in series to reinforce the
strength of the communication signal. Each of the individual
communication coils is preferably formed in two segments, joined
together at a flexible joint to reduce the likelihood of breakage
of the coil core as the cable is subjected to bending under load as
it is wound onto a takeup reel aboard the exploration vessel.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] These and other features of the invention will be apparent
to those of skill in the art from a review of the following
detailed description along with the accompanying drawings.
[0011] FIG. 1 is an overall schematic of a marine seismic
system.
[0012] FIG. 2 is a partial cutaway view of a streamer cable showing
the exterior of a communications housing of the invention.
[0013] FIG. 3 is a perspective view of the communications housing
of the present invention.
[0014] FIG. 4 is an end section view of the housing portions of the
invention.
[0015] FIG. 5 is an electrical schematic diagram of the wiring of
the communication coils of the invention.
DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT
[0016] FIG. 1 depicts a schematic of a basic marine seismic cable
system including a vessel 10 towing a cable 12. The cable has a
number of pieces of auxiliary equipment, such as depth control
devices, associated with it that are not shown in order to simplify
FIG. 1. The cable 12 also includes a number of spaced-apart
locations 14 along the streamer where such level control devices
(birds) are to be coupled to the cable. Communications housings 18
are placed at the spaced-apart locations 14, covered by a foam 22
and sealed with a jacket 16, preferably made of polyurethane, to
present a smooth profile with an interior solid cable 19 to
minimize flow noise. The cable is preferably a solid cable, with
none of the fluid of well-known cables for providing buoyancy. It
is in the communications housing 18 wherein the present invention
resides.
[0017] FIGS. 3 and 4 depict a communications coil housing 30 of the
present invention. The housing 30 comprises an upper housing half
32 and a lower housing half 34. The upper housing half 32 is
provided with wells 36, such as for example three such wells 36 as
shown in FIGS. 3 and 4. In contrast, no such wells are provided in
the lower housing half 34. The upper and lower housing halves are
firmly coupled together with screws or bolts 38 or other
appropriate means around the interior solid cable 19, and are
formed of a material which will not interfere with communication
signals. The cable 16 and the housing 30 are co-axial along an axis
39.
[0018] Positioned in the wells 36 are communications coils 40 and
as shown in FIGS. 3, 4, and 5 there are preferably three such coils
40. The coils 40 are wound in such a manner as to reinforce the
signal strength of the communication signal that they carry. The
coils 40 are preferably potted into the wells 36 with a
magnetically transparent potting material. Further, the wells, and
therefore the coils, are positioned at 44.degree. between adjacent
coils, or no more than 88.degree. between the outside coils.
[0019] FIG. 5 shows how the communication coils 40 are wired
together with signal wire 42. The three communication coils 40 are
each comprised of a pair of coil segments 44, wire together in
series. In between the pair of coil segments 44 is a flexible joint
46, such as for example a soft rubber joint. The flexible joint has
been found desirable because the cores of the segments 44 are
somewhat brittle, in order to provide adequate magnetic
permeability. For example, the core of the coil is typically made
of a ferrite rod, which is wound with insulated copper wire to form
the communication coil. The flexible joints 46 reduce the
likelihood of the communication coils 40 breaking when the cable is
reeled onto the cable reel aboard the vessel.
[0020] The principles, preferred embodiment, and mode of operation
of the present invention have been described in the foregoing
specification. This invention is not to be construed as limited to
the particular forms disclosed, since these are regarded as
illustrative rather than restrictive. Moreover, variations and
changes may be made by those skilled in the art without departing
from the spirit of the invention.
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