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`PTO/SB/05 (09-04)
`Approved for use through 07/31/2006. OMB 0651-Q032
`U.S. Patent and Trademark Office. U.S. DEPARTMENT OF COMMERCE
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`Attorney Docket No.
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`14.0123-PCT-US-CONT4
`
`(/)
`~r
`
`c
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`\..
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`UTILITY
`PATENT APPLICATION
`TRANSMITTAL
`(Only for new nonprovisional applications under 37 CFR 1.53(b))
`
`First Inventor
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`Oyvind Hillesund
`
`Title
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`~~'S~f'<::o\..(>~ ..
`lrn. ... ~ -
`"""'
`Express Mail Label No. EQ547422835US
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`PTO/SB/17 (12-04)
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`G:JndAr thP. PRoArwnrk RP.dur:tinn Ar:t nf 19!l!i nn nAffiOM ArA rAnuirP.d In rA~nnnd In R miiP.r:linn of infnrrnRiinn uniA~~ it di~niRv~ R VRiitl OMR mnlrnl numhAr
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`'-\'a ;:,I"""
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`Ex. PGS 1047
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`
`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`IN THE UNITED STATES PATENT & TRADEMARK OFFICE
`
`United States Patent Application
`
`For
`
`CONTROL SYSTEM FOR POSITIONING OF MARINE SEISMIC STREAMERS
`
`By: Oyvind Hillesund and Simon Hastings Bittleston
`
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`CONTROL SYSTEM FOR POSITIONING OF MARINE SEISMIC STREAMERS
`
`Cross-reference to Related Applications
`
`[0001]
`
`Applicant claims priority under 35 U.S.C. § 120 from co-pending serial
`
`number 111070,614, filed March 2, 2005, which was a continuation of parent application
`
`5
`
`serial no. 09/787,723, filed July 2, 2001, now Patent 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 September 28, 1999, which in turn claimed priority from Great
`
`Britain patent application number 9821277.3, filed October 1, 1998, from which Applicant
`
`claims foreign priority under 35 U.S.C. § 119, all of which are incorporated herein by
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`10
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`reference. This application is also related to co-pending application serial numbers 111 _
`
`_______ and 1
`
`filed simultaneously herewith, which also are both
`
`incorporated herein by reference.
`
`Background of the Invention
`
`[0002]
`
`This invention relates generally to systems for controlling seismic data
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`15
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`acquisition equipment and particularly to a system for controlling a marine seismic streamer
`
`positioning device.
`
`[0003]
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`A marine seismic streamer is an elongate cable-like structure, typically up
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`to several thousand meters long, which contains arrays of seismic sensors, known as
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`hydrophones, and associated electronic equipment along its length, and which is used in
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`20 marine seismic surveying. In order to perform a 3D marine seismic survey, a plurality of
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`such streamers are towed at about 5 knots behind a seismic survey vessel, which also tows
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`one or more seismic sources, typically air guns. Acoustic signals produced by the seismic
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`sources are directed down through the water into the earth beneath, where they are reflected
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`from the various strata. The reflected signals are received by the hydrophones, and then
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`25
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`digitized and processed to build up a representation of the subsurface geology.
`
`[0004]
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`The horizontal positions of the streamers are typically controlled by a
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`deflector, located at the front end or "head" of the streamer, and a tail buoy, located at the
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`back end or "tail" of the streamer. These devices create tension forces on the streamer which
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`constrain the movement of the streamer and cause it to assume a roughly linear shape. Cross
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`currents and transient forces cause the streamer to bow and undulate, thereby introducing
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`deviations into this desired linear shape.
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`[0005]
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`The streamers are typically towed at a constant depth of approximately
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`5
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`ten meters, in order to facilitate the removal of undesired "ghost" reflections from the
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`surface of the water. To keep the streamers at this constant depth, control devices known as
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`"birds", are typically attached at various points along each streamer between the deflector
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`and the tail buoy, with the spacing between the birds generally varying between 200 and 400
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`meters. The birds have hydrodynamic deflecting surfaces, referred to as wings, that allow
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`10
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`the position of the streamer to be controlled as it is towed through the water. When a bird is
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`used for depth control purposes only, it is possible for the bird to regularly sense its depth
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`using an integrated pressure sensor and for a local controller within the bird to adjust the
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`wing angles to maintain the streamer near the desired depth using only a desired depth value
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`received from a central control system.
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`15
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`[0006] While the majority of birds used thus far have only controlled the depth
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`of the streamers, additional benefits can be obtained by using properly controlled
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`horizontally steerable birds, particularly by using the types of horizontally and vertically
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`steerable birds disclosed in our published PCT International Application No. WO 98/28636.
`
`The benefits that can be obtained by using properly controlled horizontally steerable birds
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`20
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`can include reducing horizontal out-of-position conditions that necessitate reacquiring
`I
`seismic data in a particular area (i.e. in-fill shooting), reducing the chance of tangling
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`adjacent streamers, and reducing the time required to tum the seismic acquisition vessel
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`when ending one pass and beginning another pass during a 3D seismic survey.
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`[0007]
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`It is estimated that horizontal out-of-position conditions reduce the
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`25
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`efficiency of current 3D seismic survey operations by between 5 and 10%, depending on
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`weather and current conditions. While incidents oftangling adjacent streamers are relatively
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`rare, when they do occur they invariably result in prolonged vessel downtime. The loss of
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`efficiency associated with turning the seismic survey vessel will depend in large part on the
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`seismic survey layout, but typical estimates range from 5 to 10%. Simulations have
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`concluded that properly controlled horizontally steerable birds can be expected to reduce
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`these types of costs by approximately 30%.
`
`[0008]
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`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
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`5
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`transmit the magnitudes and directions of any required wing angle changes to the birds.
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`While this method greatly simplifies the circuitry needed within the bird itself, it is virtually
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`impossible for this type of system to closely regulate the horizontal positions of the birds
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`because it requires manual input and supervision. This becomes a particularly significant
`
`issue when a substantial number of streamers are deployed simultaneously and the number
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`10
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`of birds that must be controlled goes up accordingly.
`
`[0009]
`
`Another system for controlling a horizontally steerable bird is disclosed
`
`in our published PCT International Application 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
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`15
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`birds to adjust the wing angles. The actual horizontal positions of the birds may be
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`determined every 5 to 1 0 seconds and there may be a 5 second delay between the taking of
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`measurements and the determination of actual streamer positions. While this type of system
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`allows for more automatic adjustment of the bird wing angles, the delay period and the
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`relatively long cycle time between position measurements prevents this type of control
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`20
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`system from rapidly and efficiently controlling the horizontal position of the bird. A more
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`deterministic system for controlling this type of streamer positioning device is therefore
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`desired.
`
`[0010]
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`It is therefore an object of the present invention to provide for an
`
`improved method and apparatus for controlling a streamer positioning device.
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`25
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`[00 11]
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`An advantage of the present invention is that the position of the streamer
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`may be better controlled, thereby reducing the need for in-fill shooting, reducing the chance
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`of streamer tangling, and reducing the time needed to tum the seismic survey vessel.
`
`[0012]
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`Another advantage of the present invention is that noise in marine seismic
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`data associated with streamer position over-correction and streamer positioning errors can be
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`significantly reduced.
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`Summary of the Invention
`
`[0013]
`
`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
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`therealong and each streamer positioning device having a wing and a wing motor for
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`changing the orientation of the wing so as to steer the streamer positioning device laterally,
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`said methods and apparatus involving (a) obtaining an estimated velocity of the streamer
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`positioning devices, (b) for at least some of the streamer positioning devices, calculating
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`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.
`
`[0014]
`
`The invention and its benefits will be better understood with reference to
`
`the detailed description below and the accompanying figures.
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`Brief Description of the Drawings
`
`[0015]
`
`FIG. 1 is a schematic diagram of a seismic survey vessel and associated
`
`seismic data acquisition equipment;
`
`[0016]
`
`FIG. 2 is a schematic horizontal cross-sectional view through a marine
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`seismic streamer and an attached streamer positioning device;
`
`[0017]
`
`FIG. 3 is a schematic vertical cross-sectional view through the streamer
`
`positioning device from FIG. 2; and
`
`[0018]
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`\
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`FIG. 4 is a schematic diagram of the local control system architecture of
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`the streamer positioning device from FIG. 2.
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`Detailed Description of the Invention
`
`[0019]
`
`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 seismic 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
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`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 1 0 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.
`
`[0020]
`
`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 horizontally 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 vertical (depth) and horizontal directions.
`
`[0021]
`
`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 vessel 10 and a local control system located within or near the birds 18. The
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`global control system 22 is typically connected to the seismic survey vessel's navigation
`
`system 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.
`
`[0022]
`
`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
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`separation 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 magnitude of the side control required to
`
`property position the streamers. To compensate for these localized current fluctuations, the
`
`inventive control system utilizes a distributed processing control architecture and behavior(cid:173)
`
`predictive model-based control logic to properly control the streamer positioning devices.
`
`[0023]
`
`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 programmed 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(cid:173)
`
`based global 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.
`
`[0024]
`
`The global control system 22 preferably maintains a 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
`
`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
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`streamer skin itself), it is important that the streamer movements be restrained and kept to
`
`the minimum correction required to properly position the streamers. Any streamer
`
`positioning device control system that consistently overestimates 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 current systems, this type of over(cid:173)
`
`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.
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`[0025]
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`The global control system 22 preferably calculates the desired vertical
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`and horizontal forces based on the behavior of each streamer and also takes into account the
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`behavior of the complete streamer array. Due to the relatively low sample rate and time
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`delay associated with the horizontal position determination system, the global control
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`system 22 runs position predictor software to estimate the actual locations of each of the
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`birds 18. The global control system 22 also checks the data received from the vessel's
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`navigation system and the data will be filled in if it is missing. The interface between the
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`global control system 22 and the local control system will typically operate with a sampling
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`frequency of at least 0.1 Hz. The global control system 22 will typically acquire the
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`following parameters from the vessel's navigation system: vessel speed (m/s), vessel heading
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`(degrees), current speed (m/s), current heading (degrees), and the location of each of the.
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`birds in the horizontal plane in a vessel fixed coordinate system. Current speed and heading
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`can also be estimated based on the average forces acting on the streamers 12 by the birds 18.
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`The global control system 22 will preferably send the following values to the local bird
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`controller: demanded vertical force, demanded horizontal force, towing velocity, and
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`crosscurrent velocity.
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`[0026]
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`The towing velocity and crosscurrent velocity are preferably "water-
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`referenced" values that are calculated from the vessel speed and heading values and the
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`current speed and heading values, as well as any relative movement between the seismic
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`survey vessel 10 and the bird 18 (such as while the vessel is turning), to produce relative
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`velocities of the bird 18 with respect to the water in both the "in-line" and the "cross-line"
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`directions. Alternatively, the global control system 22 could provide the local control system
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`with the horizontal velocity and water in-flow angle. The force and velocity values are
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`delivered by the global control system 22 as separate values for each bird 18 on each
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`streamer 12 continuously during operation ofthe control system.
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`[0027]
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`The "water-referenced" towing velocity and crosscurrent velocity could
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`alternatively be determined using flowmeters or other types of water velocity sensors
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`attached directly to the birds 18. Although these types of sensors are typically quite
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`expensive, one advantage of this type of velocity determination system is that the sensed in(cid:173)
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`line and cross-line velocities will be inherently compensated for the speed and heading of
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`10
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`Ex. PGS 1047
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`marine currents acting on said streamer positioning device and for relative movements
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`between the vessel 1 0 and the bird 18.
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`[0028]
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`FIG. 2 shows a type of bird 18 that is capable of controlling the position
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`of seismic streamers 12 in both the vertical and horizontal directions. A bird 18 of this type
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`is also disclosed in our PCT International Application No. WO 98/28636. While a number
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`of alternative designs for the vertically and horizontally steerable birds 18 are possible,
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`including those utilizing one full-moving wing with ailerons, three full-moving wings, and
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`four full-moving wings, the independent two-wing principal is, conceptually, the simplest
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`and most robust design.
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`[0029]
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`In FIG. 2, a portion of the seismic streamer 12 is shown with an attached
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`bird 18. A communication line 24, which may consist of a bundle of fiber optic data
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`transmission cables and power transmission wires, passes along the length of the seismic
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`streamer 12 and is connected to the seismic sensors, hydrophones 26, that are distributed
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`along the length of the streamer, and to the bird 18. The bird 18 preferably has a pair of
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`independently moveable wings 28 that are connected to rotatable shafts 32 that are rotated
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`by wing motors 34 and that allow the orientation of the wings 28 with respect to the bird
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`body 30 to be changed. When the shafts 32 of the bird 18 are not horizontal, this rotation
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`causes the horizontal orientation of the wings 28 to change and thereby changes the
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`horizontal forces that are applied to the streamer 12 by the bird.
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`[0030]
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`The motors 34 can consist of any type of device that is capable of
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`changing the orientation of the wings 28, and they are preferably either electric motors or
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`hydraulic actuators. The local control system 36 controls the movement of the wings 28 by
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`calculating a desired change in the angle of the wings and then selectively driving the
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`motors 34 to effectuate this change. While the preferred embodiment depicted utilizes a
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`separate motor 34 for each wing 28, it would be also be possible to independently move the
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`wings 28 using a single motor 34 and a selectively actuatable transmission mechanism.
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`[0031] When the bird 18 uses two wings 28 to produce the horizontal and
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`vertical forces on the streamer 12, the required outputs of the local control system 36 are
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`relatively simple, the directions and magnitudes of the wing movements required for each of
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`the wings 28, or equivalently the magnitude and direction the motors 34 need to be driven to
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`11
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`Ex. PGS 1047
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`produce this wing movement. While the required outputs of the local control system 36 for
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`such a two full moving wing design is quite simple, the structure and operation of the overall
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`system required to coordinate control of the device is relatively complicated.
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`[0032]
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`FIG. 3 shows a schematic vertical cross-sectional view through the
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`streamer positioning device shown in FIG. 2 that will allow the operation of the inventive
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`control system to be described in more detail. The components of the bird 18 shown in FIG.
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`3 include the wings 28 and the body 30. Also shown in FIG. 3 are a horizontal coordinate
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`axis 38 and a vertical coordinate axis 40. During operation of the streamer positioning
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`control system, the global control system 22 preferably transmits, at regular intervals (such
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`as every five seconds) a desired horizontal force 42 and a desired vertical force 44 to the
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`local control system 36.
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`[0033]
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`The desired horizontal force 42 and the desired vertical force 44 are
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`combined within the local control system 36 to calculate the magnitude and direction of the
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`desired total force 46 that the global control system 22 has instructed the local control
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`system to apply to the streamer 12. The global control system 22 could alternatively provide
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`the magnitude and direction of the desired total force 46 to the local control system 36
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`instead of the desired horizontal force 42 and the desired vertical force 44.
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`[0034] While the desired horizontal force 42 and the desired vertical force 44 are
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`preferably calculated by the global control system 22, it is also possible for the local control
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`system 36 in the inventive control system to calculate one or both of these forces using a
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`localized displacement/force conversion program. This type of localized conversion
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`program may, for instance, use a look-up table or conversion routine that associates certain
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`magnitudes and directions of vertical or horizontal displacements with certain magnitudes
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`and directions of changes in the vertical or horizontal forces required. Using this type of
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`embodiment, the global control system 22 can transmit location information to the local
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`control system 36 instead of force information. Instead of the desired vertical force 44, the
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`global control system 22 can transmit a desired vertical depth and the local control system
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`36 can calculate the magnitude and direction of the deviation between the desired depth and
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`the actual depth. Similarly, instead of transmitting a desired horizontal force 42, the global
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`control system 22 can transmit the magnitude and direction of the displacement between the
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`12
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`Ex. PGS 1047
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`Attorney Docket No.: 14.0123-PCT-US-CONT4
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`actual horizontal position and the desired horizontal position of the bird 18. One advantage
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`to this alternative type of system is that the required vertical force can be rapidly updated as
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`the local control system receives updated depth information from the integrated pressure
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`sensor. Other advantages of this type of alternative system include reducing communication
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`traffic on the communication line 24 and simplifying the programming needed to convert the
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`measured vertical and/or horizontal displacements into corresponding forces to be applied
`
`by the birds 18.
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`[0035] When the local control system 36 has a new desired horizontal force 42
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`and desired vertical force 44 to be applied, the wings 28 will typically not be in the proper
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`orientation to provide the direction of the desired total force 46 required. As can be seen in
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`FIG. 3, the wings 28 introduce a force into the streamer 12 along an axis perpendicular to
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`the rotational axis of the wings 28 and perpendicular to the streamer. This force axis 48 is
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`typically not properly aligned with the desired total force 46 when new desired horizontal
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`and verti