`
`
`Ex. PGS 1001
`
`
`
`EX. PGS 1001
`
`
`
`
`
`

`

`111111
`
`1111111111111111111111111111111111111111111111111111111111111
`US007293520B2
`
`c12) United States Patent
`Hillesund et al.
`
`(10) Patent No.:
`(45) Date of Patent:
`
`US 7,293,520 B2
`*Nov. 13, 2007
`
`(54) CONTROL SYSTEM FOR POSITIONING OF
`A MARINE SEISMIC STREAMERS
`
`(75)
`
`Inventors: Oyvind Hillesund, Riston (GB); Simon
`Hastings Bittleston, Bury St Edmunds
`(GB)
`
`(73) Assignee: WesternGeco, L.L.C., Houston, TX
`(US)
`
`( *) Notice:
`
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 102 days.
`
`This patent is subject to a terminal dis(cid:173)
`claimer.
`
`(21) Appl. No.: 111455,042
`
`(22) Filed:
`
`Jun. 16, 2006
`
`3,774,570 A
`3,896,756 A
`3,931,608 A
`3,943,483 A
`3,961,303 A
`4,033,278 A
`4,063,213 A
`4,087,780 A
`4,222,340 A
`4,227,479 A
`4,290,124 A
`
`11/1973 Pearson . . . . . . . . . . . . . . . . . . 114/23 5 B
`7/1975 Pearson eta!. ......... 114/235 B
`111976 Cole ........................... 367/17
`3/1976 Strange .................... 340/7 PC
`6/1976 Paitson ........................ 367/17
`7/1977 Waters ....................... 114/245
`12/1977 Itria et al ...................... 367/17
`5/1978 Itria et al ...................... 367/17
`9/1980 Cole .......................... 114/245
`10/1980 Gertler eta!. .............. 114/312
`9/1981 Cole ........................... 367/18
`(Continued)
`
`FOREIGN PATENT DOCUMENTS
`
`AU
`
`199853305
`
`12/1997
`
`(Continued)
`
`Primary Examiner-Jesus D Sotelo
`(74) Attorney, Agent, or Firm-Liangang (Mark) Ye; Jeffrey
`E. Griffin
`
`(65)
`
`Prior Publication Data
`
`(57)
`
`ABSTRACT
`
`US 2006/0231007 Al
`
`Oct. 19, 2006
`
`(51)
`
`Int. Cl.
`B63B 21166
`(2006.01)
`(2006.01)
`GOJV 1/38
`(52) U.S. Cl. ......................................... 114/244; 367/19
`(58) Field of Classification Search ................ 114/162,
`114/163,242,244,246,253
`See application file for complete search history.
`
`(56)
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,375,800 A
`3,412,705 A
`3,434,446 A
`3,440,992 A
`3,560,912 A
`3,605,674 A
`3,648,642 A
`
`4/1968 Cole eta!. .................. 114/235
`11/1968 Nesson ........................ 115/12
`3/1969 Cole .......................... 114/235
`4/1969 Chance ....................... 114/235
`.. ... .. ... ... ... ... 340/3
`211971 Spink et a!.
`9/1971 Weese .. ... ... .. ... ... ... . 114/235 B
`3/1972 Fetrow eta!. .............. 114/235
`
`A method of controlling a streamer positioning device (18)
`configured to be attached to a marine seismic streamer (12)
`and towed by seismic survey vessel (10) and having a wing
`and a wing motor for changing the orientation of the wing.
`The method includes the steps of: obtaining an estimated
`velocity of the streamer positioning device, calculating a
`desired change in the orientation of the wing using the
`estimated velocity of the streamer positioning device, and
`actuating the wing motor to produce the desired change in
`the orientation of the wing. The invention also involves an
`apparatus for controlling a streamer positioning device
`including means for obtaining an estimated velocity of the
`streamer positioning device, means for calculating a desired
`change in the orientation of the wing using the estimated
`velocity of the streamer positioning device, and means for
`actuating the wing motor to produce the desired change in
`the orientation of the wing.
`
`34 Claims, 3 Drawing Sheets
`
`16
`
`/
`
`Ex. PGS 1001
`
`

`

`US 7,293,520 B2
`Page 2
`
`U.S. PATENT DOCUMENTS
`
`4,313,392 A
`4,323,989 A
`4,404,664 A
`4,463,701 A
`4,484,534 A
`4,694,435 A
`4,709,355 A
`4,711,194 A
`4,723,501 A
`4,729,333 A
`4,745,583 A
`4,766,441 A
`4,767,183 A
`4,843,996 A
`4,890,568 A *
`4,890,569 A
`4,912,684 A
`4,992,990 A
`5,042,413 A
`5,052,814 A
`5,402,745 A
`5,443,027 A
`5,507,243 A
`5,517,202 A
`5,517,463 A
`5,529,011 A
`5,532,975 A
`5,619,474 A
`5,642,330 A
`5,790,472 A
`5,913,280 A *
`5,973,995 A *
`6,011,752 A
`6,011,753 A
`
`211982 Guenther eta!. ........... 1141244
`411982 Huckabee eta!. ............ 367117
`911983 Zachariadis .................. 367119
`811984 Pickett et al ................ 1141245
`1111984 Thillaye du Boullay .... 1141244
`911987 Magneville .................. 367117
`1111987 Woods eta!. ................. 367116
`1211987 Fowler ....................... 1141245
`211988 Hovden et al .......... 1141144 B
`311988 Kirby eta!. ................ 1141244
`511988 Motal .......................... 367118
`811988 Phillips ...................... 343/709
`811988 Martin .................... 350196.23
`711989 Darche ....................... 1141245
`111990 Dolengowski .............. 1141246
`111990 Givens ....................... 1141349
`311990 Fowler ........................ 367/76
`211991 Langeland ................... 367119
`811991 Benoit ........................ 1141244
`1011991 Stubblefield ................. 367115
`411995 Wood ......................... 1141244
`811995 Owsley eta!. .............. 1141244
`411996 Williams eta!. ............ 1141245
`511996 Patel .......................... 343/709
`511996 Hornbostel eta!. ........... 367113
`611996 Williams, Jr ................ 1141245
`711996 Elholm ........................ 367116
`411997 Kuche ......................... 367117
`611997 Santopietro ................. 3671131
`811998 Workman et al .............. 367119
`611999 Nielsen eta!. .............. 1141242
`1011999 Walker et a!.
`................ 367120
`112000 Ambs et al ................... 367117
`112000 Chien .......................... 367121
`
`6,016,286 A
`6,144,342 A
`6,459,653 B1
`6,525,992 B1
`6,549,653 B1
`6,879,542 B2
`6,932,017 B1 *
`
`................ 367 I 17
`112000 Olivier et a!.
`1112000 Bertheas et a!.
`............ 343/709
`1012002 Kuche .. ... ... ... ... .. ... ... ... 367 I 17
`212003 Olivier et a!.
`................ 367 I 17
`412003 Osawa et al ................ 3821162
`412005 Soreau eta!. ................. 367117
`812005 Hillesund et a!. ........... 1141244
`
`FOREIGN PATENT DOCUMENTS
`
`734810 B
`2270719
`69702673 T
`0193215
`0319716
`0321705
`0525391
`0390987
`0613025
`0581441
`0909701
`2093610
`2122562
`2320706
`2331971
`2342081
`992701
`W095131735
`W096121163
`W097111395
`W097130361
`W097145006
`W098128636
`W099104293
`
`AU
`CA
`DE
`EP
`EP
`EP
`EP
`EP
`EP
`EP
`EP
`GB
`GB
`GB
`GB
`GB
`NO
`wo
`wo
`wo
`wo
`wo
`wo
`wo
`* cited by examiner
`
`612001
`1211997
`412001
`111986
`611989
`611989
`211993
`1211993
`811994
`811997
`112003
`911982
`111984
`711998
`611999
`412000
`611999
`1111995
`711996
`311997
`811997
`1211997
`711998
`111999
`
`Ex. PGS 1001
`
`

`

`U.S. Patent
`
`Nov. 13, 2007
`
`Sheet 1 of 3
`
`US 7,293,520 B2
`
`Fig.1.
`Prior Art
`
`20
`
`Ex. PGS 1001
`
`

`

`U.S. Patent
`
`Nov. 13, 2007
`
`Sheet 2 of 3
`
`US 7,293,520 B2
`
`Fig.2.
`
`18
`
`/
`
`Fig.3.
`
`40
`
`_,44
`
`38
`
`Ex. PGS 1001
`
`

`

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`tii
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`76
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`36
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`58
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`A/0
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`110
`
`I
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`Processor
`Unit
`M
`
`24
`
`Fig.4.
`r-
`
`-
`l
`Ace
`Horizontal
`_J
`
`I
`I 6a
`-
`
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`.... Driver
`Motor
`62
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`t
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`Sensor
`12
`
`J
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`
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`Motor
`_.._ Left Wing
`M _J
`I
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`
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`I
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`J.4
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`--
`Indicator
`61
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`~
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`Indicator
`!24
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`.....J Driver
`62
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`Sensor
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`z 0
`~ ....
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`.....
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`
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`
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`
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`
`Ex. PGS 1001
`
`

`

`US 7,293,520 B2
`
`1
`CONTROL SYSTEM FOR POSITIONING OF
`A MARINE SEISMIC STREAMERS
`
`CROSS-REFERENCE TO RELATED
`APPLICATIONS
`
`2
`be obtained by using properly controlled horizontally steer(cid:173)
`able birds, particularly by using the types of horizontally and
`vertically steerable birds disclosed in our published PCT
`International Application No. WO 98/28636. The benefits
`that can be obtained by using properly controlled horizon(cid:173)
`tally steerable birds can include reducing horizontal out-of(cid:173)
`position conditions that necessitate reacquiring seismic data
`in a particular area (i.e. in-fill shooting), reducing the chance
`of tangling adjacent streamers, and reducing the time
`10 required to tum the seismic acquisition vessel when ending
`one pass and beginning another pass during a 3D seismic
`survey.
`It is estimated that horizontal out-of-position conditions
`reduce the efficiency of current 3D seismic survey opera(cid:173)
`tions by between 5 and 10%, depending on weather and
`current conditions. While incidents of tangling adjacent
`streamers are relatively rare, when they do occur they
`invariably result in prolonged vessel downtime. The loss of
`20 efficiency associated with turning the seismic survey vessel
`will depend in large part on the seismic survey layout, but
`typical estimates range from 5 to 10%. Simulations have
`concluded that properly controlled horizontally steerable
`birds can be expected to reduce these types of costs by
`25 approximately 30%.
`One system for controlling a horizontally steerable bird,
`as disclosed in UK Patent GB 2093610 B, is to utilize a
`manually-operated central control system to transmit the
`magnitudes and directions of any required wing angle
`30 changes to the birds. While this method greatly simplifies
`the circuitry needed within the bird itself, it is virtually
`impossible for this type of system to closely regulate the
`horizontal positions of the birds because it requires manual
`input and supervision. This becomes a particularly signifi-
`35 cant issue when a substantial number of streamers are
`deployed simultaneously and the number of birds that must
`be controlled goes up accordingly.
`Another system for controlling a horizontally steerable
`bird is disclosed in our published PCT International Appli(cid:173)
`cation No. WO 98/28636. Using this type of control system,
`the desired horizontal positions and the actual horizontal
`positions are received from a remote control system and are
`then used by a local control system within the birds to adjust
`the wing angles. The actual horizontal positions of the birds
`may be determined every 5 to 10 seconds and there may be
`a 5 second delay between the taking of measurements and
`the determination of actual streamer positions. While this
`type of system allows for more automatic adjustment of the
`bird wing angles, the delay period and the relatively long
`50 cycle time between position measurements prevents this
`type of control system from rapidly and efficiently control(cid:173)
`ling the horizontal position of the bird. A more deterministic
`system for controlling this type of streamer positioning
`device is therefore desired.
`It is therefore an object of the present invention to provide
`for an improved method and apparatus for controlling a
`streamer positioning device.
`An advantage of the present invention is that the position
`of the streamer may be better controlled, thereby reducing
`the need for in-fill shooting, reducing the chance of streamer
`tangling, and reducing the time needed to turn the seismic
`survey vessel.
`Another advantage of the present invention is that noise in
`marine seismic data associated with streamer position over(cid:173)
`correction and streamer positioning errors can be signifi(cid:173)
`cantly reduced.
`
`Applicant claims priority under 35 U.S.C. § 120 from Ser.
`No. 11/070,614, filed Mar. 2, 2005, now U.S. Pat. No.
`7,080,607, which was a continuation of parent application
`Ser. No. 09/787,723, filed Jul. 2, 2001, now U.S. Pat. No.
`6,932,017, which was a 35 U.S.C. § 371 national stage filing
`from Patent Cooperation Treaty application number PCT/
`IB99/01590, filed Sep. 28, 1999, which in turn claimed
`priority from Great Britain patent application number
`9821277.3, filed Oct. 1, 1998, from which Applicant claims 15
`foreign priority under 35 U.S.C. § 119, all of which are
`incorporated herein by reference. This application is also
`related to co-pending application Ser. Nos. 11/454,352 and
`11/454,349, filed simultaneously herewith, which also are
`both incorporated herein by reference.
`
`BACKGROUND OF THE INVENTION
`
`This invention relates generally to systems for controlling
`seismic data acquisition equipment and particularly to a
`system for controlling a marine seismic streamer positioning
`device.
`A marine seismic streamer is an elongate cable-like
`structure, typically up to several thousand meters long,
`which contains arrays of seismic sensors, known as hydro(cid:173)
`phones, and associated electronic equipment along its
`length, and which is used in marine seismic surveying. In
`order to perform a 3D marine seismic survey, a plurality of
`such streamers are towed at about 5 knots behind a seismic
`survey vessel, which also tows one or more seismic sources,
`typically air guns. Acoustic signals produced by the seismic
`sources are directed down through the water into the earth
`beneath, where they are reflected from the various strata.
`The reflected signals are received by the hydrophones, and
`then digitized and processed to build up a representation of 40
`the subsurface geology.
`The horizontal positions of the streamers are typically
`controlled by a deflector, located at the front end or "head"
`of the streamer, and a tail buoy, located at the back end or
`"tail" of the streamer. These devices create tension forces on 45
`the streamer which constrain the movement of the streamer
`and cause it to assume a roughly linear shape. Cross currents
`and transient forces cause the streamer to bow and undulate,
`thereby introducing deviations into this desired linear shape.
`The streamers are typically towed at a constant depth of
`approximately ten meters, in order to facilitate the removal
`of undesired "ghost" reflections from the surface of the
`water. To keep the streamers at this constant depth, control
`devices known as "birds", are typically attached at various
`points along each streamer between the deflector and the tail 55
`buoy, with the spacing between the birds generally varying
`between 200 and 400 meters. The birds have hydrodynamic
`deflecting surfaces, referred to as wings, that allow the
`position of the streamer to be controlled as it is towed
`through the water. When a bird is used for depth control 60
`purposes only, it is possible for the bird to regularly sense its
`depth using an integrated pressure sensor and for a local
`controller within the bird to adjust the wing angles to
`maintain the streamer near the desired depth using only a
`desired depth value received from a central control system. 65
`While the majority of birds used thus far have only
`controlled the depth of the streamers, additional benefits can
`
`Ex. PGS 1001
`
`

`

`US 7,293,520 B2
`
`3
`SUMMARY OF THE INVENTION
`
`The present invention provides methods and apparatus for
`controlling the positions of marine seismic streamers in an
`array of such streamers being towed by a seismic survey
`vessel, the streamers having respective streamer positioning
`devices disposed therealong and each streamer positioning
`device having a wing and a wing motor for changing the
`orientation of the wing so as to steer the streamer positioning
`device laterally, said methods and apparatus involving (a)
`obtaining an estimated velocity of the streamer positioning
`devices, (b) for at least some of the streamer positioning
`devices, calculating desired changes in the orientation of
`their wings using said estimated velocity, and (c) actuating
`the wing motors to produce said desired changes in wing
`orientation.
`The invention and its benefits will be better understood
`with reference to the detailed description below and the
`accompanying figures.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`4
`and obtains estimates of system wide parameters, such as the
`vessel's towing direction and velocity and current direction
`and velocity, from the vessel's navigation system.
`The most important requirement for the control system is
`to prevent the streamers 12 from tangling. This requirement
`becomes more and more important as the complexity and the
`total value of the towed equipment increases. The trend in
`the industry is to put more streamers 12 on each seismic
`survey vessel 10 and to decrease the horizontal separation
`10 between them. To get better control of the streamers 12,
`horizontal steering becomes necessary. If the birds 18 are not
`properly controlled, horizontal steering can increase, rather
`than decrease, the likelihood of tangling adjacent streamers.
`Localized current fluctuations can dramatically influence the
`15 magnitude of the side control required to properly position
`the streamers. To compensate for these localized current
`fluctuations, the inventive control system utilizes a distrib(cid:173)
`uted processing control architecture and behavior-predictive
`model-based control logic to properly control the streamer
`20 positioning devices.
`In the preferred embodiment of the present invention, the
`global control system 22 monitors the actual positions of
`each of the birds 18 and is progrmed with the desired
`positions of or the desired minimum separations between the
`seismic streamers 12. The horizontal positions of the birds
`18 can be derived, for instance, using the types of acoustic
`positioning systems described in our U.S. Pat. No. 4,992,990
`or in our PCT International Patent Application No. WO
`98/21163. Alternatively, or additionally, satellite-based glo-
`30 bal positioning system equipment can be used to determine
`the positions of the equipment. The vertical positions of the
`birds 18 are typically monitored using pressure sensors
`attached to the birds, as discussed below.
`The global control system 22 preferably maintains a
`35 dynamic model of each of the seismic streamers 12 and
`utilizes the desired and actual positions of the birds 18 to
`regularly calculate updated desired vertical and horizontal
`forces the birds should impart on the seismic streamers 12 to
`move them from their actual positions to their desired
`40 positions. Because the movement of the seismic streamer 12
`causes acoustic noise (both from seawater flow past the bird
`wing structures as well as cross current flow across the
`streamer skin itself), it is important that the streamer move(cid:173)
`ments be restrained and kept to the minimum correction
`45 required to properly position the streamers. Any streamer
`positioning device control system that consistently overes(cid:173)
`timates the type of correction required and causes the bird to
`overshoot its intended position introduces undesirable noise
`into the seismic data being acquired by the streamer. In
`50 current systems, this type of over-correction noise is often
`balanced against the "noise" or "smearing" caused when the
`seismic sensors in the streamers 12 are displaced from their
`desired positions.
`The global control system 22 preferably calculates the
`55 desired vertical and horizontal forces based on the behavior
`of each streamer and also takes into account the behavior of
`the complete streamer array. Due to the relatively low
`sample rate and time delay associated with the horizontal
`position determination system, the global control system 22
`runs position predictor software to estimate the actual loca(cid:173)
`tions of each of the birds 18. The global control system 22
`also checks the data received from the vessel's navigation
`system and the data will be filled in if it is missing. The
`interface between the global control system 22 and the local
`control system will typically operate with a sampling fre(cid:173)
`quency of at least 0.1 Hz. The global control system 22 will
`typically acquire the following parameters from the vessel's
`
`FIG. 1 is a schematic diagram of a seismic survey vessel
`and associated seismic data acquisition equipment;
`FIG. 2 is a schematic horizontal cross-sectional view 25
`through a marine seismic streamer and an attached streamer
`positioning device;
`FIG. 3 is a schematic vertical cross-sectional view
`through the streamer positioning device from FIG. 2; and
`FIG. 4 is a schematic diagram of the local control system
`architecture of the streamer positioning device from FIG. 2.
`
`DETAILED DESCRIPTION OF THE
`INVENTION
`
`In FIG. 1, a seismic survey vessel 10 is shown towing
`eight marine seismic streamers 12 that may, for instance,
`each be 3000 meters in length. The outermost streamers 12
`in the array could be 700 meters apart, resulting in a
`horizontal separation between the streamers of 100 meters in
`the regular horizontal spacing configuration shown. A seis(cid:173)
`mic source 14, typically an airgun or an array of airguns, is
`also shown being towed by the seismic survey vessel10. At
`the front of each streamer 12 is shown a deflector 16 and at
`the rear of every streamer is shown a tail buoy 20. The
`deflector 16 is used to horizontally position the end of the
`streamer nearest the seismic survey vessel 10 and the tail
`buoy 20 creates drag at the end of the streamer farthest from
`the seismic survey vessel 10. The tension created on the
`seismic streamer by the deflector 16 and the tail buoy 20
`results in the roughly linear shape of the seismic streamer 12
`shown in FIG. 1.
`Located between the deflector 16 and the tail buoy 20 are
`a plurality of streamer positioning devices known as birds
`18. Preferably the birds 18 are both vertically and horizon(cid:173)
`tally steerable. These birds 18 may, for instance, be located
`at regular intervals along the streamer, such as every 200 to
`400 meters. The vertically and horizontally steerable birds
`18 can be used to constrain the shape of the seismic streamer
`12 between the deflector 16 and the tail buoy 20 in both the 60
`vertical (depth) and horizontal directions.
`In the preferred embodiment of the present invention, the
`control system for the birds 18 is distributed between a
`global control system 22 located on or near the seismic
`survey vessel10 and a local control system located within or 65
`near the birds 18. The global control system 22 is typically
`connected to the seismic survey vessel's navigation system
`
`Ex. PGS 1001
`
`

`

`US 7,293,520 B2
`
`5
`6
`also be possible to independently move the wings 28 using
`navigation system: vessel speed (m/s), vessel heading (de(cid:173)
`a single motor 34 and a selectively actuatable transmission
`grees), current speed (m/s), current heading (degrees), and
`mechanism.
`the location of each of the birds in the horizontal plane in a
`When the bird 18 uses two wings 28 to produce the
`vessel fixed coordinate system. Current speed and heading
`horizontal and vertical forces on the streamer 12, the
`can also be estimated based on the average forces acting on
`required outputs of the local control system 36 are relatively
`the streamers 12 by the birds 18. The global control system
`simple, the directions and magnitudes of the wing move(cid:173)
`22 will preferably send the following values to the local bird
`ments required for each of the wings 28, or equivalently the
`controller: demanded vertical force, demanded horizontal
`magnitude and direction the motors 34 need to be driven to
`force, towing velocity, and crosscurrent velocity.
`10 produce this wing movement. While the required outputs of
`The towing velocity and crosscurrent velocity are prefer(cid:173)
`the local control system 36 for such a two full moving wing
`ably "water-referenced" values that are calculated from the
`design is quite simple, the structure and operation of the
`vessel speed and heading values and the current speed and
`overall system required to coordinate control of the device
`heading values, as well as any relative movement between
`is relatively complicated.
`the seismic survey vessel10 and the bird 18 (such as while 15
`FIG. 3 shows a schematic vertical cross-sectional view
`the vessel is turning), to produce relative velocities of the
`through the streamer positioning device shown in FIG. 2 that
`bird 18 with respect to the water in both the "in-line" and the
`will allow the operation of the inventive control system to be
`"cross-line" directions. Alternatively, the global control sys(cid:173)
`described in more detail. The components of the bird 18
`shown in FIG. 3 include the wings 28 and the body 30. Also
`tem 22 could provide the local control system with the
`20 shown in FIG. 3 are a horizontal coordinate axis 38 and a
`horizontal velocity and water in-flow angle. The force and
`vertical coordinate axis 40. During operation of the streamer
`velocity values are delivered by the global control system 22
`positioning control system, the global control system 22
`as separate values for each bird 18 on each streamer 12
`preferably transmits, at regular intervals (such as every five
`continuously during operation of the control system.
`seconds) a desired horizontal force 42 and a desired vertical
`The "water-referenced" towing velocity and crosscurrent
`velocity could alternatively be determined using flowmeters 25 force 44 to the local control system 36.
`The desired horizontal force 42 and the desired vertical
`or other types of water velocity sensors attached directly to
`force 44 are combined within the local control system 36 to
`the birds 18. Although these types of sensors are typically
`calculate the magnitude and direction of the desired total
`quite expensive, one advantage of this type of velocity
`force 46 that the global control system 22 has instructed the
`determination system is that the sensed in-line and cross-line
`local control system to apply to the streamer 12. The global
`velocities will be inherently compensated for the speed and 30
`control system 22 could alternatively provide the magnitude
`heading of marine currents acting on said streamer position(cid:173)
`and direction of the desired total force 46 to the local control
`ing device and for relative movements between the vessel1 0
`system 36 instead of the desired horizontal force 42 and the
`and the bird 18.
`desired vertical force 44.
`FIG. 2 shows a type of bird 18 that is capable of 35
`While the desired horizontal force 42 and the desired
`controlling the position of seismic streamers 12 in both the
`vertical force 44 are preferably calculated by the global
`vertical and horizontal directions. A bird 18 of this type is
`control system 22, it is also possible for the local control
`also disclosed in our PCT International Application No. WO
`system 36 in the inventive control system to calculate one or
`98/28636. While a number of alternative designs for the
`both of these forces using a localized displacement/force
`vertically and horizontally steerable birds 18 are possible, 40
`conversion program. This type of localized conversion pro(cid:173)
`including those utilizing one full-moving wing with aile(cid:173)
`gram may, for instance, use a look-up table or conversion
`rons, three full-moving wings, and four full-moving wings,
`routine that associates certain magnitudes and directions of
`the independent two-wing principal is, conceptually, the
`vertical or horizontal displacements with certain magnitudes
`simplest and most robust design.
`and directions of changes in the vertical or horizontal forces
`In FIG. 2, a portion of the seismic streamer 12 is shown
`45 required. Using this type of embodiment, the global control
`with an attached bird 18. A communication line 24, which
`system 22 can transmit location information to the local
`may consist of a bundle of fiber optic data transmission
`control system 36 instead of force information. Instead of
`cables and power transmission wires, passes along the
`the desired vertical force 44, the global control system 22
`length of the seismic streamer 12 and is connected to the
`can transmit a desired vertical depth and the local control
`seismic sensors, hydrophones 26, that are distributed along
`so system 36 can calculate the magnitude and direction of the
`the length of the streamer, and to the bird 18. The bird 18
`deviation between the desired depth and the actual depth.
`preferably has a pair of independently moveable wings 28
`Similarly, instead of transmitting a desired horizontal force
`that are connected to rotatable shafts 32 that are rotated by
`42, the global control system 22 can transmit the magnitude
`wing motors 34 and that allow the orientation of the wings
`and direction of the displacement between the actual hori-
`28 with respect to the bird body 30 to be changed. When the
`55 zontal position and the desired horizontal position of the bird
`shafts 32 of the bird 18 are not horizontal, this rotation
`18. One advantage to this alternative type of system is that
`causes the horizontal orientation of the wings 28 to change
`the required vertical force can be rapidly updated as the local
`and thereby changes the horizontal forces that are applied to
`control system receives updated depth information from the
`the streamer 12 by the bird.
`integrated pressure sensor. Other advantages of this type of
`The motors 34 can consist of any type of device that is
`60 alternative system include reducing communication traffic
`on the communication line 24 and simplifYing the program(cid:173)
`capable of changing the orientation of the wings 28, and they
`are preferably either electric motors or hydraulic actuators.
`ming needed to convert the measured vertical and/or hori(cid:173)
`The local control system 36 controls the movement of the
`zontal displacements into corresponding forces to be applied
`wings 28 by calculating a desired change in the angle of the
`by the birds 18.
`wings and then selectively driving the motors 34 to effec- 65
`When the local control system 36 has a new desired
`tuate this change. While the preferred embodiment depicted
`horizontal force 42 and desired vertical force 44 to be
`utilizes a separate motor 34 for each wing 28, it would be
`applied, the wings 28 will typically not be in the proper
`
`Ex. PGS 1001
`
`

`

`US 7,293,520 B2
`
`7
`orientation to provide the direction of the desired total force
`46 required. As can be seen in FIG. 3, the wings 28 introduce
`a force into the streamer 12 along an axis perpendicular to
`the rotational axis of the wings 28 and perpendicular to the
`streamer. This force axis 48 is typically not properly aligned
`with the desired total force 46 when new desired horizontal
`and vertical force values are received from the global control
`system 22 or determined by the local control system 36 and
`some rotation of the bird 18 is required before the bird can
`produce this desired total force 46. As can be seen, the force
`axis 48 is directly related to the bird roll angle, designated
`in FIG. 3 as <jl.
`The local control system 36 optimizes the control process
`by projecting the desired total force 46 onto the force axis 48
`(i.e. multiplying the magnitude of the desired total force by
`the cosine of the deviation angle 50) to produce an inter(cid:173)
`mediate desired force 52 and then adjusting the wing com(cid:173)
`mon angle a (the angle of the wings with respect to the bird
`body 30, or the average angle if there is a non-zero splay
`angle) to produce this magnitude of force along the force
`axis. The calculated desired common wing angle is com(cid:173)
`pared to the current common wing angle to calculate a
`desired change in the common wing angle and the wing
`motors 34 are actuated to produce this desired change in the
`orientation of the wings.
`A splay angle is then introduced into the wings 28 to
`produce a rotational movement in the bird body 30 (i.e. to
`rotate the force axis 48 to be aligned with the desired total
`force 46). The splay angle is the difference between the
`angles of the wings 28 with respect to the bird body 30. As 30
`the bird body 30 rotates and the force axis 48 becomes more
`closely aligned with the desired total force 46, the bird roll
`angle and the bird roll angular velocity are monitored, the
`splay angle is incrementally reduced, and the common angle
`is incrementally increased until the intermediate desired 35
`force 52 is in the same direction and of the same magnitude
`as the desired total force. The local control system 36
`carefully regulates the splay angle to ensure that the
`streamer is stable in roll degree of freedom. The calculated
`common wing angle and the splay angle are also regulated 40
`by the local control system 36 to prevent the wings 28 from
`stalling and to ensure that the spl