U.S. patent application number 11/462743 was filed with the patent office on 2008-09-04 for method for laterally steering streamer cables.
This patent application is currently assigned to INPUT/OUTPUT, INC.. Invention is credited to Andre W. Olivier.
Application Number | 20080212406 11/462743 |
Document ID | / |
Family ID | 34941439 |
Filed Date | 2008-09-04 |
United States Patent
Application |
20080212406 |
Kind Code |
A1 |
Olivier; Andre W. |
September 4, 2008 |
METHOD FOR LATERALLY STEERING STREAMER CABLES
Abstract
A device and a method for laterally steering a streamer cable
towed underwater behind a seismic survey vessel. The device
includes a cable-steering assembly rotatably attached to a streamer
cable. The assembly includes a body to which one or more wings are
mounted. The wings are arranged to pivot about pivot axes. The
assembly is ballasted so that the pivot axes of the wings are
largely in a vertical plane. A conventional cable-leveling bird is
converted to one version of a cable-steering device by ballasting
to maintain the pivot axes of the bird's wings largely vertical.
With an orientation sensor for sensing the orientation of the
wings, the cable-steering device adjusts the angle of the wings to
provide a sideward component of force to steer the streamer.
Inventors: |
Olivier; Andre W.; (River
Ridge, LA) |
Correspondence
Address: |
LAITRAM, L.L.C.;LEGAL DEPARTMENT
220 LAITRAM LANE
HARAHAN
LA
70123
US
|
Assignee: |
INPUT/OUTPUT, INC.
Stafford
TX
|
Family ID: |
34941439 |
Appl. No.: |
11/462743 |
Filed: |
August 7, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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10709772 |
May 27, 2004 |
7092315 |
|
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11462743 |
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Current U.S.
Class: |
367/17 ;
114/248 |
Current CPC
Class: |
G01V 1/3826
20130101 |
Class at
Publication: |
367/17 ;
114/248 |
International
Class: |
G01V 1/38 20060101
G01V001/38; B63H 25/00 20060101 B63H025/00 |
Claims
1. A method for converting a cable-leveling bird assembly rotatably
attachable to a towed streamer cable into a cable-steering bird
assembly to laterally steer the streamer cable, the cable-leveling
bird assembly being of the type typically operated underwater
suspended below the streamer cable in an orientation wherein two
wings on opposite sides of the cable-leveling bird assembly are
pivotable together about a common pivot axis lying generally in a
horizontal plane, the method comprising: weighting one of the wings
sufficiently to cause the bird assembly to operate laterally offset
from the streamer cable in an orientation wherein the pivot axis of
the wings lies largely in a vertical plane to steer the streamer
cable laterally.
2. (canceled)
3. (canceled)
4. The method of claim 1 comprising: adding a weight inside one of
the wings.
5. The method of claim 1 comprising: forming a void in the interior
of one or more of the wings.
6. The method of claim 1 comprising: adding flotation to the bird
assembly.
7. The method of claim 6 wherein the flotation is added to the bird
assembly at a position on the same side of the cable as the
wings.
8. (canceled)
9. (canceled)
10. (canceled)
11. The method of claim 1 further comprising: operating a second
bird assembly on an opposite side of the streamer cable from the
other bird assembly.
12. (canceled)
13. (canceled)
14. (canceled)
15. The method of claim 18 comprising: forming a void in the
interior of the second wing portion.
16. The method of claim 15 further comprising: filling the void
with a foam material having a specific gravity less than unity.
17. (canceled)
18. A method for converting a cable-leveling bird assembly
rotatably attached to a streamer cable into a cable-steering bird
assembly, the cable-leveling bird assembly being of the type having
a tubular main body offset from the streamer cable with a wing
support section supporting a shaft to which a wing is mounted at
each end on opposite sides of the wing support section, wherein the
cable-leveling bird assembly is typically operated underwater
suspended below the streamer cable wherein the two wings weigh the
same and are pivotable together on the shaft about a common pivot
axis lying generally in a horizontal plane to control the depth of
the streamer cable, the method comprising: substituting a single
wing for the two wings on the shaft, the single wing having a first
wing portion at one end of the single wing and a second wing
portion at the opposite end unitarily formed with the first wing
portion, wherein the first wing portion is sufficiently heavier
than the second wing portion to cause the bird assembly to orient
itself with the pivot axis of the wings disposed generally in a
vertical plane and laterally offset from the streamer cable to
steer the streamer cable laterally through the water.
19. The method of claim 18 further comprising: including an
orientation sensor in the tubular main body of the bird assembly to
provide a signal representative of the orientation of the bird.
20. The method of claim 18, wherein replacing the two wings on the
shaft with a single wing further comprises: enclosing a weight
within the interior of the first wing portion.
Description
BACKGROUND
[0001] The invention relates generally to marine seismic
prospecting and, more specifically, to devices and methods for
controlling the lateral position of streamer cables towed
underwater behind survey vessels.
[0002] In marine seismic exploration, instrumented cables, known as
streamers, are towed underwater by a survey vessel. The streamers
are outfitted with a variety of electronic devices, including
hydrophones that detect seismic signals transmitted into the water
and reflected off geologic structures beneath the sea floor.
[0003] Devices known as cable-leveling birds are attached to a
streamer at intervals along its length to control the streamer's
depth. The birds are equipped with adjustable diving planes,
generally referred to as wings, each having a pitch axis about
which the wings can be pivoted by a motor to generate the lift
needed to maintain the cable at a desired depth. Most commonly, the
birds are rotatably attached to the streamer and weighted to hang
pendulously from the cable with the pitch axis of the wings below
the cable. These birds are effective depth-control devices.
[0004] It is not uncommon for a survey vessel to tow six or eight
or more streamers of lengths up to 12 km. Because the costs of lost
survey time and of replacing a damaged or lost streamer are so
high, it is important that the streamers not become entangled
during their deployment. Entanglement is more likely to occur in
the presence of strong cross currents or while the survey vessel is
turning to make another pass across the survey zone. To help avoid
entanglement in turns, for example, each streamer is often operated
at a different depth. While this technique provides some measure of
entanglement control, it also subjects the cables to potentially
strong shear layers of current that vary considerably with depth,
possibly increasing the risk of entanglement. Generally the most
satisfactory way to avoid entanglement with conventional systems is
to steer the vessel through wide turns and to overspace the
streamers from each other. But these techniques increase cost and
reduce the precision of the seismic image.
[0005] Paravanes and other devices are used to separate the
streamers at their head ends close to the survey vessel. But
lateral streamer control and streamer position predictability
diminish as cable tension lessens down the lengths of streamers.
The wake created by the seismic vessel creates a phenomenon known
as "trouser" effect on the array. The streamers fan out port and
starboard, creating a large void in the seismic coverage directly
aft of the vessel. The streamers assume the shape of trousers.
These voids must be resurveyed on subsequent passes known as
"in-fill." In-fill can increase the cost of seismic surveying by up
to 20%. Lack of repeatability in processes and positional
inaccuracies can reduce the quality of the seismic data and
increase the cost by necessitating in-fill. Thus, there is a need
to provide a technique for lateral streamer positioning to reduce
the cost of operation and to improve the quality of the resultant
seismic image.
[0006] Today's state-of-the-art seismic vessels have the capacity
to deploy, tow, and recover up to 18 streamers. Existing deployment
schemes limit the degree to which streamers can be simultaneously
deployed, which greatly increases the cost of operation. There is a
need to provide for lateral streamer control during the deployment
and recovery phases to support simultaneous streamer operation
without entanglement.
SUMMARY
[0007] Accordingly, a method embodying features of the invention is
provided for laterally steering a streamer. A bird assembly of the
kind typically operated in a depth-controlling orientation in which
one or more wings are pivotable about one or more pivot axes that
lie generally in a horizontal plane is operated in another way. The
bird assembly is operated in an orientation in which the one or
more pivot axes of the one or more wings lie largely in a vertical
plane to steer the streamer laterally.
[0008] In another aspect of the invention, a method for laterally
steering a streamer cable with a cable-leveling bird having a pair
of wings normally operated underwater with the pair of wings
pivotable about horizontal axes comprises converting the
cable-leveling bird, which is rotatably attachable to a streamer
cable, into a cable-steering bird by ballasting the bird so that it
operates underwater in an orientation in which each of the wings
pivots about a pivot axis that lies largely in a vertical plane to
steer the attached underwater cable laterally.
[0009] In yet another aspect of the invention, an underwater
cable-steering device comprises a connector attachable around the
periphery of an underwater cable section and rotatable about the
cable. A control device includes a body connected to the connector
external of the cable. The control device includes a first wing at
one side of the body and a second wing at an opposite side of the
body. The first wing pivots about a first axis, and the second wing
pivots about a second axis. The two axes may coincide, but do not
intersect the cable. The control device also includes means for
pivoting the wings about their pivot axes. Ballast means is
provided to help ballast the steering device to maintain the pivot
axes largely vertical.
[0010] In another aspect of the invention, an underwater
cable-steering device comprises a connector attachable around the
periphery of an underwater cable section and rotatable about the
cable. A control device includes a body connected to the connector
external of the cable. The control device includes a shaft
extending through the body and defining a pivot axis. A first wing
portion is connected to one end of the shaft at one side of the
body, and a second wing portion is connected to the other end of
the shaft at an opposite side of the body. The two wing portions
may be unitarily formed as a single wing. The pivot axis does not
intersect the cable. Ballast means is provided to help ballast the
steering device to maintain the pivot axis largely vertical.
[0011] In still another aspect of the invention, an underwater
cable-steering device comprises a connector attachable around the
periphery of an underwater cable section and rotatable about the
cable. A control device includes a body connected to the connector
external of the cable. A first shaft extends from a first side of
the body. A first wing attached at an end of the first shaft can
pivot about a first axis defined by the axial rotation of the first
shaft. The first axis does not intersect the cable. The control
device also includes means for pivoting the wings about their pivot
axes. Ballast means is provided to help ballast the steering device
to maintain the first axis largely vertical.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] These features and aspects of the invention, as well as its
advantages, are better understood by reference to the following
description, appended claims, and accompanying drawings, in
which:
[0013] FIG. 1 is an isometric view, partly cutaway, of a
cable-steering device embodying features of the invention on a
section of streamer cable;
[0014] FIG. 2 is a top view of the cable-steering device of FIG.
1;
[0015] FIG. 3 is a cross section of the cable-steering device of
FIG. 1 taken along lines 3-3;
[0016] FIGS. 4A-4C are schematics representing various ways of
ballasting a cable-steering device as in FIG. 1;
[0017] FIG. 5 is a front elevation view of a cable-steering device
as in FIG. 1 with buoyant tank ballast;
[0018] FIG. 6 is a front elevation view as in FIG. 4, but with an
aileron control;
[0019] FIG. 7 is a front elevation view, partly in cross section,
of another version of cable-steering device embodying features of
the invention including wing tip tanks;
[0020] FIG. 8 is a schematic block diagram of the cable-steering
devices of FIG. 1 and FIG. 7;
[0021] FIG. 9 is an isometric view of a dual cable-steering
arrangement using two cable-steering devices as in FIG. 1; and
[0022] FIG. 10 is an isometric view of another version of
cable-steering device embodying features of the invention including
a single wing.
DETAILED DESCRIPTION
[0023] A device, embodying features of the invention, for laterally
steering a streamer cable is shown in FIGS. 1-3. The cable-steering
assembly includes two connectors or cuffs 20 rotatably attached to
collars 22, 23 affixed about the periphery of a streamer 24. Races
are formed on the collars to receive the connectors and allow them
to rotate freely about the streamer. An oversized stop 25 at the
rear of the rear collar 23 keeps the cuffs in position as the cable
is towed in the towing direction 27. Instead of rotating about
collars encircling the streamer, the connectors could rotate about
insert sections placed in-line between two streamer sections. The
insert sections would themselves rotatably receive the connectors.
The cuffs shown in FIGS. 1-3 could be realized as Quick Cuff.TM.
connectors manufactured and sold by Input/Output, Inc. of Stafford,
Tex., USA, and described in detail in U.S. Pat. No. 6,263,823,
which is incorporated by reference. Alternatively, the connectors
could be Quick Latch.TM. connectors, also manufactured and sold by
Input/Output, Inc., and described in U.S. Pat. No. 5,507,243,
incorporated by reference.
[0024] A streamer control device 26 has front and rear pylons 28,
29 that include latching hardware to releasably connect the control
device to the connectors. The pylons extend from a main body 30, in
the form of a hollow tube that houses electronic communication and
control circuits 31, a battery 37, and a drive mechanism 38,
including a motor. Wings 32, 33 extend from opposite sides of a
wing support section 34 of the module body between the two pylons.
Each wing is mounted on opposite ends 35', 35'' of a single shaft
or on the ends of separate shafts. A drive mechanism inside the
body rotates the single shaft (or the separate shafts) to pivot
each wing about pivot axes 36, 37 defined by the shafts, which are
offset from the cable and do not intersect its long axis.
[0025] Thus far, the description of the cable-steering device
essentially is the same as that for a cable-leveling bird, such as
the DIGICOURSE.RTM. 5010 DIGIBIRD.TM. brand manufactured and sold
by Input/Output, Inc. The purpose of the cable-leveling bird is to
work in conjunction with other such birds attached along a
streamer. To maintain the streamer at a desired depth, pivot axes
of the wings remain generally in a horizontal plane. In this way,
the bird pivots the wings in pitch about the pivot axis. As the
pitch angle of the wings changes, lift is adjusted and,
consequently, the depth of the cable can be controlled. The weight
distribution and specific gravity of the cable-leveling
bird/connector system is such that it remains suspended beneath the
cable with the pivot axes of its wings generally in a horizontal
plane.
[0026] The cable-steering bird of the invention, however, is
ballasted so that the pivot axes of its wings remain largely
vertical (V), as shown in FIGS. 1-3. In this way, changing the
angle a of the wings steers the cable horizontally (H). To maintain
the pivot axes 36, 37 generally vertical, the cable-steering bird
26, the connectors 20, and anything attached to them to rotate
about the cable with them is ballasted to keep specific gravity
about the same as that of the cable itself. One way to achieve this
is to make one of the wings 33 heavier than the other 32. This can
be done, for example, by making the lower wing out of a denser
material or installing a weight 40, such as a lead or tungsten
weight, in a void 42 within the wing. (The wings of cable-leveling
birds are typically solid and molded out of polyurethane.) The
interior of one or both wings can be hollow with a void that is
empty or filled with a foam material 44, such as
glass-sphere-filled polyurethane or glass-sphere-filled epoxy, to
keep them lightweight without affecting their designed shape.
Properly ballasted in this way, the bird is capable of steering the
cable to which it is attached. Even as the cable 24 rotates within
the connector 20 under tow, as shown in FIG. 3, the pivot axes 36,
37 of the wings remain largely in a vertical plane. Even if the
pivot axes of the wings are not perfectly vertical, as long as some
component of the axes lies in a vertical plane, some amount of
steering is possible. For example, if the cable-steering assembly
is insufficiently balanced and the pivot axes are at an angle of
45.degree. relative to both horizontal and vertical, the wings can
still provide a horizontal component of force to steer the
streamer.
[0027] As illustrated in FIGS. 4A-4C, some ways to properly ballast
the cable steering device include: a) making the upper wing light,
the lower wing heavy, e.g., weighted at the lower end, and leaving
the bird body as is (FIG. 4A); b) making the upper wing light, the
lower wing light, and the bird body weighted enough to achieve
neutral buoyancy (FIG. 4B); and c) making the upper wing heavy at
the wing tip, the lower wing heavy at the wing tip, and the bird
body light (FIG. 4C). Thus, the ballast may be apportioned among
the wings and the bird body in a variety of ways to maintain the
wings generally in a vertical plane.
[0028] Other ways of maintaining the pivot axes 36, 37 of the wings
32, 33 largely vertical are shown in FIGS. 5 and 6. In FIG. 5, a
buoyant tank 46, or float, is attached to the bird body 26 as an
appendage. The tank lowers the specific gravity of the bird
assembly. Adjusting the volume of the tank or the length of its
connecting arm 48 adjusts the specific gravity of the
cable-steering assembly to maintain the pivot axes vertical. Adding
flotation in this way can be used alone or in conjunction with
adjusting the absolute and relative weights of the wings. Both
these means for ballasting are effective in properly orienting the
wings. Optionally, a weight 50, negatively buoyant, can be attached
to the connector at a position on the opposite side of the cable to
right the pivot axes of the bird assembly. These ballasting means
may be used to preadjust the cable-steering assembly before
deployment underwater. They are also hydrostatic in that they do
not depend on the speed of the tow to be effective.
[0029] Another way to maintain the pivot axis of the wings vertical
is shown in FIG. 6. In this version, an aileron 52 is controlled by
an aileron controller 54 attached to the connector 20 on the
opposite side of the streamer from the cable-steering device 26.
Alternatively, the aileron 52' could extend from the cable-steering
device directly. The aileron rotates about a generally horizontal
axis 56 similar to the wings of a cable-leveling bird and provides
more or less lift to the cable-steering assembly as a function of
its pitch angle of attack. But, in this version, the amount of lift
depends on the speed of the streamer through the water. The aileron
controller may include an orientation sensor to determine its
orientation relative to vertical.
[0030] Another version of cable-steering device is shown in FIG. 7.
In this version, the wings 90, 91 are tipped with bulbous portions,
or tanks 92, 93, which provide more volume for ballast control. In
the example, the upper wing includes a greater volume of
low-density material than the upper wing of FIG. 1. The lower end
of the lower wing may include a denser molded or fill material 94
or a weight 95 in the lower wing-tip tank.
[0031] The wing control portion of the cable-steering bird is shown
in FIG. 8. A controller 59, preferably including a microprocessor,
receives signals 60, 61 representing the orientation of the bird
body relative to vertical as defined by the gravity vector.
Orientation sensors, such as an inclinometer 62 or an accelerometer
63, are used to determine the orientation. In some cases, an
inclinometer alone may be sufficient. In other cases, in which
cable accelerations are frequent and significant, multiple-axis
accelerometers may be necessary. From the orientation sensor
signals, the controller can determine the orientation of the wings.
The cable is steered by adjusting the angle of attack of the wings
32, 33. A shipboard controller keeping track of all the streamers
being towed determines what action each cable-steering device
should take. The shipboard controller communicates that action to
the controller in the cable-steering device, which adjusts the
wings accordingly. A signal 64 representing a change in the wing
angles and determined by the controller from its computation of the
orientation of the device and from the steering command is sent to
the wing drive mechanism 38, which includes one or more wing
actuators 64. The wing actuators rotate the shaft or shafts 35,
changing the angles of attack of the wings to change and,
consequently, the lateral force on the streamer. The wings can be
controlled independently by separate actuators and shafts or in
unison by a single actuator and a single shaft.
[0032] As shown in FIG. 9, it is also possible to attach a pair of
cable-steering devices 26, 26' to a streamer 24 with a connector
20. Each device is connected to the connector circumferentially
spaced 180.degree. to be positioned on opposite sides of the
streamer. This arrangement would provide more wing surface area to
exert greater lateral forces for steering the streamer. Each
cable-steering device is ballasted, for example, by a weight in the
lower wing, to maintain the wings in a generally vertical
plane.
[0033] A single-wing version of cable-steering bird embodying
features of the invention is shown in FIG. 10. While multi-wing
versions make independent wing angle control for roll compensation
possible, a single wing version provides dedicated lateral
steering. This version is controllable by a controller as in FIG.
8. As in FIG. 1, a main body 66 attaches to a connector 20 that
allows the body to be rotatable about a streamer cable. Like the
body 30 in FIG. 1, the body 66 houses electronic communication and
control circuits, a battery, and a drive mechanism, including a
motor. Opposite ends 68, 69 of a shaft 70 extend from opposite
sides of the body. A wing 71 includes a first wing portion 72 and
an opposite second wing portion 73. The wing is formed of a
polyurethane outer skin and an internal filler of
glass-sphere-filled epoxy, for example, for lower density. Each
wing portion is connected to an end of the shaft at attachment arms
74, 75. The shaft defines a pivot axis 78 about which the wing
pivots. The two wing portions are preferably formed unitarily. The
wing is ballasted so that the pivot axis lies largely in a vertical
plane for laterally steering a streamer cable. The first wing
portion, for example, can be ballasted with a material whose
density is greater than that of water to urge it to ride below the
streamer. The second wing portion, for example, can be ballasted
with one or more voids that may be filled with a material less
dense than water to urge it to ride above the streamer. With these
and the other ballasting techniques already described, the single
wing can be made to ride through the water with vertical
stability.
[0034] Although the invention has been described with respect to a
few preferred versions, other versions are possible. For example,
the angles of each wing could be changed relative to each other to
help maintain the wing pivot axes vertical. As another example,
floats can be added to ballast the cable-steering assembly at
various positions around the periphery of the connectors, to the
body of the assembly at various positions, or internal to the body
itself. So, as these few examples suggest, the scope of the
invention is not meant to be limited to the preferred versions
described in detail.
* * * * *