I
`Ulllted States Patent
`
`[19]
`
`;l
`.1
`
`L
`USOO5717655A
`
`1
`
`1
`1
`
`[11] Patent Number:
`
`5,717,655
`
`
`Beasley
`[45] Date of Patent:
`Feb. 10, 1998
`
`[54] METHOD FOR PROVIDING UNIFORM
`SUBSURFACE COVERAGE IN THE
`PRESENCE OF S1-EEP Dlps
`
`[75]
`
`Inventor; Craig J_ geasley, Houston_ Tex
`
`[73] Assignee: Western Atlas Interllalional, Ina.
`Houston. Tex.
`
`[21] Appl. No.: 829,485
`
`[22] Filed:
`
`Mar. 28, 1997
`
`Related U.S. Application Data
`
`[63] Continuation ofSer. No. 423 731 Apr.18 1995 abandoned.
`'
`’
`'
`Int. Cl.‘ .............................. .. G01V 1/20; G0lV 1/36
`[51]
`[52] U.S. Cl.
`................................. 367/53; 367/21; 367/56;
`.
`364/421
`FlCld Of Search ................................ ..
`21. 53»
`367/563 364/421
`
`[561
`
`Refemnces cited
`U.S_ PATENT DOCUMENTS
`
`3,290,644 12/1966 Hoskins .................................... 367/21
`4,914,636
`4/1990
`4,930,110
`5/1990
`4,970,696
`ll/1990
`5,430,689
`7/1995
`5,450,370
`9/1995
`
`OTHER PUBLICATIONS
`_
`_
`_
`_
`Beasley, Cra1gl.. Quality Assurance of Spatial Sampling for
`DMO. 63rd Annual Meeting of Society of Exploration
`Geophysicists. published in Expanded Abslracts. pp.
`544-547. 1993.
`
`Vermeer. Gijs 1.0.. Seismic Acquisition 3: 3-D Data Acqui-
`sition. 64th Annual Meeting of the Society of Exploration
`Geophysicists. published in Expanded Abstracts. pp.
`906-909. 1994.
`Egan. Mark S.; Dingwall. Ken; and Kapoor. Jerry; Shooting
`direction: A 3-D marine survey design issue. The Leading
`Edge, Nov. 1991. pp. 37-41.
`
`P"”""Y E’“’"“"""N°15°" M°5k°“’i‘Z
`Attomey, Agent, or Fz'rm—William A. Knox
`
`ABSTRACT
`[573
`A method for minimizing non-uniform insonification of
`subsurface fofmafions in thc P1-cscncg of stgcp dips whgn
`advancing a swath of elongated parallel seismic streamer
`cables along a line of survey. A first acoustic source is
`stationed at the leading end of the swath and a second source
`is stationed at the trailing end of the swath. The sources are
`activated in alternate cycles at preselected timed intervals to
`Provide dowmdip and up_diP seismic data Sets_ The data scts
`are processed and merged to eliminate obj eclionable shadow
`zones.
`
`1 Claim, 4 Drawing Sheets
`
`
`
`31~.j'D'g'c‘o5§Ee‘;,
`
`:j'o'a1:’o5EEe‘;.~33
`
`.32
`
`
`
`DOWN—D|P
`PROCESSING
`
`
`UP—D|F’
`
`PROCESSING
`
`
`
`34
`
`WesternGeco V. PGS (IPR2015-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 1
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`U.S. Patent
`
`Feb. 10, 1998
`
`Sheet 1 of 4
`
`5,717,655
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`10
`
`Di-1
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`5
`
`Di+1
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`Di+2
`
`Di+3
`
`Di-n
`
`
`
`WesternGeco V. PGS (IPR2015-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 2
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`AlnCLl3P3U
`
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`
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`
`
`my
`
`PGS Exhibit 2009, pg. 3
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`U.S. Patent
`
`Feb. 10, 1998
`
`Sheet 3 of 4
`
`5,717,655
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`CROSSLINE
`
`CROSSLINE
`
`M6
`
`INLINE
`
`FIG. 5
`
`INLINE
`
`FIG. 6
`
`WesternGeco V. PGS (IPR2015-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 4
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`U.S. Patent
`
`Feb. 10, 1993
`
`Sheet 4 of 4
`
`5,717,655
`
`3 "7"b_E_c:‘o6EEe‘}
`
`\ _ _ _ _ _ _ __
`
`('b_E_<:'o6Er'2‘/T‘ 33
`
`\ _ _ _ _ _ _ __
`
`
`
`FIG. 8
`
`Tf__.L__1_:_5,3nsL
`to
`in
`g 37
`
`WesternGeco V. PGS (IPR2015-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 5
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`1
`METHOD FOR PROVIDING UNIFORM
`SUBSURFACE COVERAGE IN THE
`PRESENCE OF STEEP DIPS
`
`This application is a continuation of application Ser. No.
`08l423.78l. filed Apr. 18. 1995. now abandoned.
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Invention
`
`3-D marine seismic surveys entail towing a swath of
`elongated seismic sensor arrays. Subsea formations are
`acoustically illuminated to produce seismic reflection data
`that are detected and processed by the arrays and associated
`ancillary equipment. In the presence of steeply-dipping
`subsea formations. this invention corrects the non-uniform
`illumination of the formations due to the awkward geometry
`caused by the steeply-dipping wavefield trajectories.
`2. Discussion of Related Art
`
`This method may be applied to any form of seismic
`operation. be it on land or on sea. However for convenience.
`by way of example but not by way of limitation.
`this
`disclosure will be explained in terms of a marine seismic
`survey.
`
`In 3-D marine operations. a seismic ship tows a swath
`including a plurality of parallel seismic streamer cables
`along a desired line of survey. the cables being submerged
`by a few meters beneath the water surface. The number of
`cables that make up a swath depends only on the mechanical
`and operational capabilities of the towing ship. There may
`be six or more such cables, spaced about 50 to 100 meters
`apart. The respective cables may be up to 3000 meters long.
`Each streamer cable typically includes about 120. spaced-
`apart seismic detector groups. Each group consists of one or
`more individual interconnected detectors. each of which
`services a single data channel. The group spacing is on the
`order of 25 to 50 meters longitudinally along the cable. The
`seismic detectors are transducers that perceive the mechani-
`cal activity due to reflected acoustic wavefields and convert
`that activity to electrical signals having characteristics rep-
`resentative of the intensity.
`timing and polarity of the
`acoustic activity as is well known to the art. The detectors
`are operatively coupled to data-storage and processing
`devices of any desired type.
`An acoustic source such as an array of air guns. is towed
`in the water by the ship near the leading end of the swath of
`seismic streamer cables. As the ship proceeds along the line
`of survey, the source is fired (activated) at selected spatial
`intervals equal. for example. to a multiple of the seismic
`detector group spacing. to acoustically illuminate (insonify)
`the subsurface formations. Assuming the ship travels at a
`constant velocity such as six knots,
`the source may be
`conveniently fired at selected time intervals such as every
`five seconds. assuming a 50-meter group interval. The
`wavefield emitted by the sorn'ce. travels downwardly to be
`reflected from subsea earth formations whence the wavefield
`is reflected back to the water surface where the reflected
`wavefreld is received by the detectors and converted to
`electrical signals as previously explained. The detected
`electrical signals are transmitted to any well-known signal
`recording and processing means for providing a physical
`model of the subsurface.
`
`20
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`30
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`35
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`45
`
`50
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`
`For a better understanding of a problem to be solved by
`this disclosure. FIG. 1 shows a source. S. at or near the
`surface 10 of the water 12. Detectors Di“. D,-+2. D,-+3 are
`disposed near the water surface above a flat-lying formation
`
`65
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`5,717,655
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`5
`
`2
`F. A wavefield emitted from S follows the indicated ray paths
`to the respective detectors as shown. For example. the ray
`path from S to D,-+3 is reflected from incident point IP on
`formation F. The incident angle ¢,. relative to the perpen-
`dicular to F at IP or zero-offset point Z. must equal the angle
`of reflection 4), as in geometric optics. assuming the earth
`material is isotropic. The stnface expression of the subsur-
`face reflection point. R. the midpoint between S and D,-+3. M
`and the zero offset point Z are coincident. The incident
`points of all of the raypaths are evenly distributed along the
`line as shown.
`
`In regions of steep dip. the symmetrical picture of FIG. 1
`is distorted as shown in the 2-D illustration of FIG. 2. Here.
`with a dip of 45°. while the angles of incidence and
`reflection ti), and (3),, are equal. the zero-ofliset point Z. is
`up-dip of the midpoint M. The surface expression R. of the
`reflection point (incident point IP) lies not between the
`source and detector as in FIG. 1. but up-dip of the source S.
`FIG. 3 traces a number of raypaths from a source S to
`detectors DH. Di“. DM. DH3. Di“, for a 45°-dipping bed
`F. The important point to observe in this Figure is the
`non-uniform spacing of the incident points. Because reci-
`procity holds. assuming that the earth materials are isotropic.
`the source and detectors can be interchanged. It is thus
`evident that when shooting down-dip. the incident points
`tend to bunch up. Shooting up-dip results in a spreading-
`apart of the incident points. Because of the complex non-
`uniform subsurface illumination. significant undesirable
`shadow zones are formed. The problem becomes particu-
`larly troublesome where multiple cables are used in a 3-D
`swath. due to the additional awkward lateral geometry.
`One method for minimizing shadow zones is taught by C.
`Beasley in U.S. patent application Ser. No. 08/069565 filed
`May 28. 1993. entitled Quality Assurance for Spatial Sam-
`pling for DMO. assigned to the assignee of this invention.
`the application now having issued Sep. 12. 1995 as U.S. Pat.
`No. 5.450.370 to Craig J. Beasley et at. That patent is the
`basis for a paper delivered in 1993 at the 63rd Annual
`meeting of the Society of Exploration Geophysicists and
`published in Expanded Abstracts. pp 544-547. That inven-
`tion provided a method for examining the geometry of the
`disposition of a plurality of sources and receivers over an
`area to be surveyed with a view to optimizing the array to
`avoid shadow zones in the data and to optimize the resulting
`seismic image. The method depends upon studying the
`statistical distribution of dip polarity in dip bins along
`selected CMP azimuths. The method was implemented by
`rearranging the geometrical disposition of the sources and
`receivers. It was not directed to the per se problem of
`non-uniform subsurface coverage and shadow zones in the
`presence of steep dips.
`Another discussion directed to symmetric sampling is
`found in a paper entitled 3-D Symmetric Sampling by G.
`Vermeer and delivered 1994 in a paper at the 64th Annual
`Meeting of the Society of Exploration Geophysicists.
`Expanded Abstracts. pp 906-909. Here. the authors review
`the various different shooting geometries involved in land
`and marine surveys including 2-D. 3-D and 5-D configura-
`tions. The presence of non-uniform subsurface insonifica-
`tion is recognized and the need for symmetric sampling to
`prevent aliasing is emphasized.
`M. S. Egan et al.. in a paper entitled Shooting Direction:
`21 3-D Marine Survey Design Issue. published in The Lead-
`ing Edge. November. 1991. pp 37-41 insist that it is impor-
`tant to maintain consistent source-to-receiver trajectory azi-
`muths to minimize shadow zones. imaging artifacts and
`
`WesternGeco V. PGS (IPR20l5-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 6
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`5,717,655
`
`3
`aliasing in regions of steep dips. They are particularly
`concerned about 3-D marine surveys in areas where the
`proposed seismic lines are obstructed by shipping. offshore
`structures and other cultural obstacles.
`
`There is a need for equalizing the density of the subsur-
`face coverage provided by wide. towed swaths of seismic
`streamer arrays in the presence of steeply-dipping earth
`fonnations in the circumstance where the acoustic source is
`located at an end of the swath.
`
`SUNIMARY OF THE INVENTION
`
`In an aspect of this invention. there is provided a method
`for providing a more uniform insonification of subsurface
`earth formations for the purpose of minimizing shadow
`zones. To that end. a swath of parallel. elongated seismic
`cables. each including a plurality of spaced-apart seismic
`detectors. are advanced along a line of survey. A first
`acoustic source is positioned near the leading end of the
`swath and a second acoustic source is located near the
`trailing end of the swath. At alternate timed intervals. the
`sources launch a wavefield that is reflected from the sub-
`
`surface earth formations to provide first and second seismic-
`signal data sets. Means. operatively coupled to the detectors.
`process and merge the first and second data sets to provide
`a uniformly-insonified model of the subsurface earth forma-
`tions substantially free of shadow zones.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`The novel features which are believed to be characteristic
`of the invention. both as to organization and methods of
`operation. together with the objects and advantages thereof.
`will be better understood from the following detailed
`description and the drawings wherein the invention is illus-
`trated by way of example for the purpose of illustration and
`description only and are not intended as a definition of the
`limits of the invention:
`
`FIG. 1 shows acoustic raypaths in the presence of zero
`dip;
`FIG. 2 provides definitions for certain data-processing
`terms;
`FIG. 3 demonstrates the non-unifonn insonification of the
`subsurface in the presence of steep dips;
`FIG. 4 is a plan view of the configuration of a typical
`swath of cables and associated acoustic sources such as may
`be used in 3-D marine seismic surveying;
`FIG. 5 shows the surface expression of subsurface reflec-
`tion points and the shadow zones associated with steep dips
`with respect to a swath where the source is positioned near
`the leading end of the swath;
`FIG. 6 shows the surface expression of subsurface reflec-
`tion points and the shadow zones associated with steep clips
`with respect to a swath wherein the source is located near the
`trailing end of the swath;
`FIG. 7 is a schematic flow diagram of the data processing
`method; and
`FIG. 8 is a timing diagram for controlling the activation
`sequence of the acoustic sources.
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODJMENT
`
`20
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`
`Please refer now to FIGS. 3 and 4. FIG. 4 is a plan view
`of a 3-D swath 13 of six parallel seismic cable arrays A1—A6
`which are being towed through a body of water by a ship 14.
`(It should be understood that. if land operations are under
`
`65
`
`4
`consideration. the cables could be towed by one or more
`trucks or could be laid out by cable trucks using roll-along
`techniques in a manner well-known to the seismic industry).
`Signals from the respective cable arrays AI—A6 are fed over
`a data-signal manifold 20 to a processing means 22 of any
`well-lcnown type.
`installed on ship 14 and operatively
`coupled to means 22 by electrical lead-ins 16 and 18. A
`discrete acoustic source SL is towed by ship 14 near the
`leading end of swath 13. substantially at the center of the
`swath. More than one discrete source such as SL' and SL".
`oifset from the center line may be used if desired.
`Dashed line M3 is a line of midpoints that might be
`associated with seismic cable A3 positioned towards the
`center of the swath such as suggested by FIG. 3 for a 2-D
`slice of the earth where it was shown that the subsurface
`reflection points tend to converge when shooting down—dip.
`In the case of a 3-D operation. employing the swath of FIG.
`4. the laterally~distributed. crossline lines of midpoints cor-
`responding to detector cables A2 and A1 are shown as
`dashed lines M2 and M1. Similar lines (not shown) may be
`drawn for cables A4—A6.
`
`FIG. 5 shows. as small rectangles. the surface expression
`of steeply-dipping subsurface reflection points for every
`12th detector of a 120-detector swath of six cables repre-
`sented as straight. evenly-spaced. horizontal lines A1—A6.
`With the cables spaced 100 meters apart. the solid lines
`represent the lines of midpoints for the respective cables and
`are 50 meters apart. each cable being 3000 meters long. The
`source SL is at the leading or left hand end of the swath;
`up-dip and direction of advance of the ship are to the left. As
`would be expected from FIG. 3. the reflection points tend to
`converge down-dip along the inline direction. Crossline. the
`subsurface reflecfion points do not stray far from the inner
`central-cable midpoint lines M3 and M4. But the subsurface
`reflection points for the outer midpoint lines M1. M2. M5
`and M6. corresponding to cable A1. A2.AS and A6 converge
`towards the center line of the swath 13 by 25 to 30 meters,
`creating down-dip crossline shadow zones marked by the
`arrows 27 and 29 at the right hand end of the swath 13.
`Under conventional practice. to till in the shadow zones.
`the operator would be obliged to resurvey the region by
`making a second pass over the region. That process is
`decidedly uneconornical.
`Please refer now to FIGS. 4 and 6. A second ship 24.
`towing an acoustic source ST launches a wavefield from the
`trailing end of swath 13. Hme, also. more than one discrete
`source such as ST’ and ST" may be used. FIG. 6 shows the
`subsurface reflecting points (small rectangles as for FIG. 5)
`associated with every 12th detector for swath 13 when
`source ST is actuated. As before. the straight horizontal lines
`M1—M6 represent the midpoint lines that make up swath 13.
`Here again. the subsurface reflection points for the two
`middle lines M3 and M4 are nearly coincident with the
`midpoint
`lines although significant up-dip in-line and
`crossline divergence is present. Crossline. the subsurface
`reflection points diverge well outside the lateral limits of the
`swath as demarcated by lines 23 and 25, leaving a non-
`uniformly insonified up-dip zone as indicated by arrows 31
`and 33.
`
`Comparison of FIGS. 5 and 6 show that the crossline
`subsurface coverage provided by the innermost cables A3
`and A4 does not depart very much from the line of midpoints
`regardless of the source location with respect to the leading
`or trailing end of the swath. But FIG. 5 and 6 suggest that
`by insonifying the swath from both ends in alternate cycles.
`the gaps due to non-uniform insonification at the outer
`
`WesternGeco V. PGS (IPR20l5-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 7
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`5,717,655
`
`5
`crossline swath limits, created by single-ended source
`activation. can be virtually eliminated when the resulting
`data are properly processed and merged. By this teaching. a
`model of the subsurface earth formations results. with the
`shadow zones filled in completely. as may be seen readily by
`superimposing (merging) FIG. 5 over FIG. 6. The proposed
`method is therefore an economic alternative to a resurvey
`operation that was previously required.
`It might be suggested that a single acoustic source could
`be positioned at the geometric center of swath 13 such that
`a single activation of a source would produce both an up-dip
`and a down-dip component such as provided by a conven-
`tional split-spread. That process is useful with single cables
`or wide1y—spaced dual cables. But for large-scale 3-D swaths
`or patches that use many closely-spaced cables, that proce-
`dure is impractical. The physical configuration of the cables
`cannot be accurately controlled within the required tolerance
`in actual operation nor could a ship. which itself may be 20
`meters wide. be safely stationed in the middle of the swath
`without causing cable damage.
`In the presently-contemplated best mode of operation. the
`swath 13 of parallel elongated seismic cables is effectively
`advanced along a desired line of survey either physically as
`by towing or by use of well-known roll-along methods. A
`first acoustic source (or sources). SL is located near the
`leading end of the swath. A second acoustic source (or
`sources) ST is positioned near the tra.iling end of swath 13.
`The first and second sources are activated at timed intervals
`in alternate cycles to provide first and second reflected
`waveflelds. The reflected wavefields are detected and con-
`verted to first and second data sets of reflected signals. The
`first and second data sets of electrical signals are processed
`and merged as indicated in the flow diagram of FIG. 7. to be
`described later. to provide uniformly-insonified subsurface
`reflection points along the line of survey. Preferably. the
`swath is advanced along the line of survey at a constant
`velocity. The lengths of the first and second timed intervals
`are substantially constant and designed to allow the swath to
`advance spatially. at the selected velocity of advance. by
`some desired multiple of the spacing between detector
`groups in the seismic cables.
`In the event that several discrete acoustic sources are used
`at each end of the swath, such as SL. SL'. SL" and ST. ST’.
`ST". the sources may be activated in some desired alternat-
`ing sequence such as SL-SI‘. SL'-ST‘. SL"-ST". etc.. thereby
`to provide denser subsurface coverage using the same swath
`of cables.
`
`Thus far. it has been contemplated that the sources are
`activated sequentially and the reflected wavefields are
`recorded is a similar sequence. If desired. the leading and
`trailing sources may be arranged to emit encoded wavefields
`using any desired type of coding. The respective sources are
`then programmed to be activated concurrently instead of
`sequentially. The combined reflected wavefields as recorded
`are then decoded prior to processing. The advantage to that
`technique is that
`the subsurface incident points have
`improved commonality since there is no time shift and
`therefore no spatial reflection—point smearing between suc-
`cessive leading and trailing source activations.
`FIG. 7 is a schematic flow diagram of the data acquisition
`and processing routine which is implemented by processing
`means 22 on ship 14. A timer 26 controls the firing rate of
`sources SL and ST at first and second timed intervals
`commensurate with the ship’s velocity. V. which is input to
`timer 26 from a velocimeter 28 of any desired type which
`may be a portion of a satellite navigation system.
`Timer 26 causes sources SL and S1‘ to launch a first and
`a second acoustic wavefield in alternate cycles in accordance
`
`6
`with the timing diagram shown in FIG. 8. Assuming that
`source SL is first activated at time To and thereafter repeat-
`edly activated at timed intervals until time T,,. source S1‘ is
`activated at time to after a time shift through delay line 29
`of half an interval and thereafter repeatedly activated until
`time interval tn. Timer 28 is preferably installed on ship 14
`but sends source-activation commands to source ST on ship
`24 by any convenient synchronizing means such as by radio.
`Item 30 symbolizes the mass of detectors included by
`seismic cable swath 13 which is insonifred in alternate
`cycles by the sources SL and ST. The electrical data sets that
`are derived from down-dip insonification are detected,
`stored as a first recording and then processed in device 32.
`Similarly. up-dip data sets are detected. stored as a second
`recording and processed in device 34. Devices 32 and 34
`may be portions of a suitably—programmed computer using
`any of a number of well-known processing routines such as
`application of NMO. DMO and migration. If the recorded
`reflected acoustic wavefields were encoded. of course
`optional decoders 31 and 33 (dashed outlines labeled DEC)
`would be inserted between the collective—detector symbol 30
`and processors 32 and 34.
`Following processing. the processed down-dip and up-dip
`data sets are merged at 36 to provide a filled-in model of the
`subsurface such as may be produced by a display device 38
`of any desired type.
`This invention has been described with a certain degree of
`specificity by way of example but not by way of limitation.
`Those skilled in the art will devise obvious variations to the
`examples given herein but which will fall within the scope
`and spirit of this invention which is limited only by the
`appended claims. In particular.
`this invention has been
`described with particular reference to marine seismic explo-
`ration at sea but the principles involved may be applied
`equally well to land or shallow water surveying after suit-
`able obvious modifications to the claimed method and
`system to fit the parficnlar enviromnent.
`What is claimed is:
`1. A method of 3-dimensional seismic exploration for
`substantially uniformly insonifying steeply-dipping subsur-
`face earth formations including the steps of advancing a
`swath of laterally spaced—apart parallel elongated seismic
`cables over a area of survey, each said cable including a
`plurality of spaced-apart seismic transducers. the method
`comprising;
`at predetermined time intervals, substantially simulta-
`neously launching a first acoustic wavefield from a
`point substantially centered ahead of the leading end of
`the swath. the first wavefield being characterized by a
`first unique code and launching a second acoustic
`wavefield from a point substantially centered behind
`the trailing end of the swath. the second acoustic
`wavefield being characterized by a second unique code;
`detecting and recording the combined first and second
`encoded acoustic wavefields, following reflection
`thereof from subsurface earth formations;
`
`decoding the combined recorded reflected wavefields to
`separate the first and second reflected acoustic wave-
`fields;
`
`separately processing each of the decoded first and second
`recorded reflected wavefields;
`
`generating a substantially uniformly-insonified model of
`dipping subsurface earth formations by merging the
`first and second processed reflected waveflelds.
`*
`*
`*
`*
`*
`
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`65
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`WesternGeco V. PGS (IPR20l5-00309, 31
`
`PGS Exhibit 2009
`
`PGS Exhibit 2009, pg. 8
`WesternGeco v. PGS (IPR2015-00309, 310, 311)