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`Y
`
`WesternGeco Ex. 1023, pg. 1
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
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`WesternGeco Ex. 1023, pg. 2
`WesternGeco v. PGS
`IPR2015-00309
`
`

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`WesternGeco Ex. 1023, pg. 3
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`APPROVED FOR LICEiISE
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`WesternGeco v. PGS
`IPR2015-00309
`
`

`
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`J ................................. Rejected
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`- (Through numberal) Cancoled
`+ ................................. Resiricled
`N ................................. Non-elected
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`(LEFT TNSTDE)
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`24
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`32
`33
`34
`35
`36
`37
`38
`39
`40
`41
`42
`43
`44
`45
`46
`47
`48
`49
`50
`
`WesternGeco Ex. 1023, pg. 5
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`Staple lssue Slip Here
`
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`
`DATE
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`
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`
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`
`CLASSIFIER
`
`EXAMINER
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`SPEC, HAND
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`DRAFTING
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`
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`0 ................................. 0bloctod
`
`(LEFT TNSTDE)
`
`WesternGeco Ex. 1023, pg. 6
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`REFEHENCE(S}
`
`ftqretr NUMBEn
`
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`
`IF REISSUE, ORIGINAL PNTCIW NUTVTEE;
`
`PTO 270
`(REV.5-91)
`
`ISSUE CLASSIFICATION SLIP
`
`U,S. DEPARTMENT OF
`PATENT ANo TRAD€rr,lmx Orifi
`
`WesternGeco Ex. 1023, pg. 7
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`\
`
`t
`\
`
`SEARCHED
`
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`
`-4*_2
`
`"r
`
`SEARCH NOTES
`
`INTERFERENCE SEARCHED
`Class
`Sub.
`Date
`Exmr.
`
`(RTGHT OUTSTDE)
`
`WesternGeco Ex. 1023, pg. 8
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`SEARCHED
`
`Class
`
`Sub.
`
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`
`WesternGeco Ex. 1023, pg. 9
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`&
`
`PATENT APPLICATION SERIAL NO.
`
`; 423?81
`
`U.S. DEPARTMENT OF COI'EIERCE
`PATENT AND TRAdEMARK OFFICE
`FEE RECORD SHEET
`
`0?0 AA 04/2&/q5 0g4t3?81
`
`1 101 730'00 cN hlG*95-02
`
`PTO-1 5 56
`G/87)
`
`N,
`
`WesternGeco Ex. 1023, pg. 10
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`The Commissioner of Patents and Trademarks
`
`UU
`
`aPU . s;*
`123?81
`ilB
`Docket No. WG-95-02
`
`for filing is the patent application of CRAIG J. BEASLEY
`R PROVIDING
`UNIFORM SUBSURFACE COVERAGE
`PRESENCE OF STEEP DIPS.
`
`for
`IN
`
`A
`THE
`
`Enclosed are:
`lxl
`A specification consisting of a title page, an 11 page disclosure,
`3 pages of claims, and a 1 page abstract of the disclosure.
`lxl
`One set of informaldrawings consisting of 4 sheets.
`tXI A PreliminaryAmendmentconsisting of 1 page plus an attachment.
`lxl
`An assignment of the invention to western Atlas lnternational,lnc.
`tX] A combined Power of Attorney and Declaration executed by all of the lnventors.
`I I
`A Power of Attorney executed by the lnvento(s)/Assignee.
`tXI AnlnformationDisclosurestatement.
`I I
`Declaration executed by the lnventor(s),
`CLAIMSAS FILED
`
`OTHERTHAN SMALLENTITY
`X
`X
`
`TotalClaims
`Independent Claims
`Basic Fee
`
`TOTAL FILING FEE
`
`8-20 =
`3-3 =
`
`0
`0
`
`$22.00 =
`$0,00 =
`
`$ 0.00
`$ 0.00
`$730.00
`
`$rca-aa.
`
`Check number H10302 is enclosed. However, if the check is missing or the amount is incorrect,
`the Commissioner is hereby authorized to charge any additional fees which may be required, or credit any
`overpayment, to Account No. 23-1205. Iwgjluplig& copies of this sheet are enctosed.
`
`Please address all correspondence in connection with this application to:
`
`WilliamA. Knox
`8310 Ashcroft Drive
`Houston, Texas 77096
`Phone: 7131774-5414
`
`Respectfully submitted,
`
`Date: April 18, 1995
`
`26,636
`
`D(PRESS MAIL CERTIFICATE
`
`MAIL" LABEL NO. :EH01 1 102629Us
`Date of Deposil April 18, 1995
`'I hereby cerlily that this paper and/or fee is being deposited with the United States Postal Service "Express Mail post Office
`to Addresseel service under 37 CFR 1 . l0 on the date indicag4rabove and is addlessejb to the Cogrmissioner of patents and Trademarks.
`Washington D.C. 20231
`
`'EXPRESS
`
`WesternGeco Ex. 1023, pg. 11
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`The Commissioner of Patents and Trademarks
`D.C. 20231
`
`I
`
`t
`
`'^08",q23?81
`Docket No.1ilG-96-02
`
`NEI{ PATENT APPLICATION TRANS!,TITTAL LETTER
`
`ffi$%e 1995 s'l
`
`th for filing is the patent application of CRAIG J.
`METIffE}YFOR PROVIDING UNIFORM SUBSURFACE
`PRESENCE OF STEEP DIPS,
`
`BEASLEY
`COVERAGE
`
`for A
`IN THE
`
`Enclosed are:
`IXI A specification consisting of a title page, an 11 page disclosure,
`3 pages of claims, and a 1 page abstract of the disclosure.
`Xl
`One set of informaldrawings consisting of 4 sheets.
`lxl
`A PreliminaryAmendmentconsisting of 1 page plus an attachment.
`lx]
`An assignment of the invention to western Atlas lnternational,lnc,
`lX] A combined Power of Attorney and Declaration executed by all of the lnventors.
`I I
`A Power of Attorney executed by the lnventor(s)/Assignee.
`tX] AnlnformationDisclosurestatement.
`t ]
`Declaration executed by the tnventor(s).
`CLAIMSAS FILED
`
`TotalClaims
`lndependent Claims
`Basic Fee
`
`TOTAL FILING FEE
`
`8 -20 =
`3-g =
`
`0
`0
`
`$22.00 =
`$0.00 =
`
`$ 0.00
`$ 0.00
`$730.00
`
`u30.00-
`
`OTHERTHAN SMALLENTITY
`X
`X
`
`Check number H10302 is enclosed, However, if the check is missing or the amount is incorrect,
`the Commissioner is hereby authorized to charge any additional fees which miy be required, or credit any
`overpayment, to Account No. 23-1205. Two duplicate copies of this sheet are enclosed.
`
`Please address all correspondence in connection with this application to:
`
`WilliamA. Knox
`8310 Ashcroft Drive
`Houston, Texas 77096
`Phone: 7131774-5414
`
`/
`Date: April 18, 1995
`
`submitted,
`
`No. 26,636
`
`'EXPRESS MAIL" LABEL NO.:EH0I I 102629Us
`Date of Deposit: April 18, 1995
`I hereby certify that this paper and/or fee is being deposited with the United States postal Service 'Express Mail Post Office
`to Addressee' sbrvice under 37 CFR l.l0 on the date indicated
`and is addressed
`ipner ofPatents and Trademarks,
`Washington D.C, 20231.
`
`WesternGeco Ex. 1023, pg. 12
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`1
`
`ilfi 423?E1
`
`wG-95-02
`
`April lS;1995
`
`lo 1qe, fggs
`
`Q-*^rr*S
`
`APPLICATION FOR T.'NTIED STATES PATENT
`
`for
`
`IUETHOD FOR PROVIDING T'NIFORM SUBSURFACE
`
`INVENTOR:
`CRAIG J. BEASLEY
`
`EXPRESS MAIL CERTIFICATE
`
`r.,
`
`'EXPRESS MAIL" LABEL NO. EH01ll02629US
`Date of Deposit April 18, 1995
`I hereby certify that this paper and/or fee is being deposited with the United States Postal Service "Express Mail post Office
`to Addressee' service under 37 CFR I . l0 on the date indicated above and
`to the Commissioner
`Washinglon D,C, 20231.
`
`Signaturel LINDA LOU SOWELL
`Date of Signature: April 18, 1995
`
`WesternGeco Ex. 1023, pg. 13
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`+
`
`PATENT APPLI
`
`'.130 tD \
`*
`00 /i23?81
`wG-9 5-02
`
`METHOD FOR PROVIDING UNIFORM SUBSURFACE COVERAGE
`.
`IN THE PRESENCE 9F STEEP DIPS
`
`BAcKGRouND E rHE rNvENrroN
`
`/Wr\
`,k*
`the rnvention
`3-D marine seismic surveys entail towing a swath of
`elongated seismic sensor arrays' Subsea formations are
`acousticallyitluminatedtoproduceseismicreflectiondata
`thataredetectedandprocessedbythearraysandassociated
`ancil}aryequipment.Inthepresenceofsteeply-dipping
`subseaformations,thisinventioncorrectsthenon-uniform
`itluminationoftheformationsdueto.theawkwardgeometry
`caused by the steeply-dipping wavefield trajectories '
`Discussion o:E Related Art
`This method may be applied to any form of seismic
`operation,be"itonlandoronsea'Howeverforconvenience'
`this
`by way of example but not by way of limitation'
`disclosurewillbeexplainedintermsofamarineseismic
`survey.
`In 3-D marine operations' a seismic ship tows a swath
`includingapluralityofparallelseismicstreamercables
`alongadesiredlineofsurvey,thecabtesbeingsubmerged
`byafewmetersbeneaththewatersurface.Thenumberof
`cables that make up a swath depends ontV.^0*t the mechanical
`and operational capabilit,ies of the towing ship. There may
`be six or more such cabres, spaced about 50 to 100 meters
`apart. The respective cables may be up to 3000 meters long'
`Each streamer cable typicalty includes about 120 '
`spaced-apart seismic detector groups. Each group consists of
`oneormoreindividua}interconnecteddetectors,eachof
`
`10
`
`15
`
`20
`
`25
`
`a.
`
`30
`
`35
`
`1L
`
`/'
`
`WesternGeco Ex. 1023, pg. 14
`WesternGeco v. PGS
`IPR2015-00309
`
`

`
`which services a single data channel' The group spacing i's
`ontheorderof25to50meterslongitudinallyalongthe
`cable. The seismic debectors are transducers that perceive
`the mechanical activity due to reflected acoustic wavefields
`to erectrical signars having
`and convert th-at activity
`characteristics representative of the intensity, timing and
`the acoustic activity as is well known to the
`polarity'of
`art.. The detectors are operativery coupred 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 reading end of t'he
`swathofseismicstreamercables.Astheshipproceedsalong
`thelineofsurvey,thesourceisfired(activated)at
`serected spatial intervars equat, for exampre, to a murtipre
`of t,he seismic detector group spacing' Lo acoustically
`illuminate (insonify) the subsurface formations' Assuming
`theshiptravelsataconstantvetocitysuchassixknots,
`the source may be conveniently fired at selected time
`intervalssuchaseveryfiveseconds,assumingaSo-meter
`groupinterval.Thewavefieldemittedbythesource,t,ravels
`downwardly to be reflected from subsea earth formations
`whencethewavefieldisreflectedbacktothewatersurface
`wherethereflectedwavefieldisreceivedbythedetectors
`and converted to eLectrical signals as previously explained'
`The detected electrical signals are transmitted to any well-
`knownsigna}recordingandprocessingmeansforprovidinga
`physical model of the subsurface'
`Forabetterunderstandingofaproblemtobesolvedby
`this discrosure, Figure 1 shows a source, s, at or near the
`surface 10 of the water 12 ' Detectors Di*l' D'*2' Di*3 Ere
`formation
`disposed near the water surface above a frat-tying
`F.AwavefieldemittedfromSfollowstheindicatedray
`pathstotherespectivedetectorsasshown.Forexample,the
`raypathfromstoD.,*.isreflectedfromincidentpointlP
`on formation F. The incident angle Q. ' relative to the
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`perpendicular to F at rp or zero-offset point z, must eguar
`the angle of refrection 0" as in geometric optics, assuming
`the earth materiar "is isotropic. The surface expression of
`the subsurface refrection point, R, the midpoint between s
`and D,*3, M and the zero offset point z are coincident. The
`incident points of aII of the raypaths are evenly
`distrib'uted along the line as shown.
`rn regions of steep dip, the symmetricar picture of
`Figure 1 is distorted as shown in the 2-D illustration of
`Figure 2- Here, with a dip of 4so, while the angres of
`incidence and reflection $, and Q" are egual, the zero_
`offset point 2,, is up-dip of the midpoint M. The surface
`expression R, of the reflection point (incident point rp)
`lies not between the source and detector as in Figure 1, but
`up-dip of the source S.
`Figure 3 traces a number of raypaths from a source s to
`detectors D,_r, Dr*l , D1*2, Dr*3, Dr*n for.a 45o-dipping bed F.
`The important point to observe in this Figure is the non_
`uniform spacing of the incident points. Because reciprocity
`hords, assuming that the earth materiars are isotropic, the
`source and detectors can be interchanged. rt,is
`thus evident
`that when shooting down-dip, the incident points tend to
`bunch up. shooting up-dip resurts in a spreading-apart of
`the incident points. Because of the complex non-uniform
`subsurface irrumination, significant undesirable shadow
`zones are formed. The problem becomes particularly
`troublesome where multipre cabres 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 US patent application SN Og/069565 filed
`05/28/93, entitred euarity Assurance for spatial Sampling
`for DMo, assigned to the assignee of this invention, the
`as Uq naLent
`.,
`hat patent is
`the basis
`paper delivered in 1 993 at
`Ehe 63rd Annual
`meeting
`Society of Exploration
`
`for a
`of the
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`Geophysicists and published in Expanded Abstractsr pp s44-
`547. That invention provided a method for examining the
`geometry of the disposition of a plurarity 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 resurting seismic image. The method depends
`upon studying the statistical distribution of dip polarity
`in dip bins along serected cMp azimuths. The method was
`implemented by rearranging the geometricar disposition of
`the sources and receivers. ,rt was not directed to t.he 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 paiper entitled 3-D Symmetric Sampling by G.
`Vermeer 2nd detivered 1gg4 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 incruding 2-D, 3-D and 5-D configurations.
`The presence of non-uniform subsurface insonification is
`recognized and the need for symmetric sampling to prevent
`aliasing is.--er+p\sized .
`M. S.lU ES-an ,e*! aI., in a paper entitled Shooting
`Direction: a 3-D Marine Survey Design Issue, published in
`The Leading Edge, November, 1991, pp 37-41 j_nsist that it is
`important to maintain consistent source-to-receiver
`trajectory azimuths to minimize shadow zones, imaging
`artifacts and aliasing in regions of steep dips. They are
`particurarly concerned about 3-D marine surveys in areas
`where the proposed seismic rines are obstructed by shipping,
`offshore structures and other cultural obstacles.
`There is a need for equalizing the density of the
`subsurface coverage provided by wide, towed swaths of
`seismic streamer arrays in t,he presence of steeply-dipping
`earth formations in the circumstance where the acoustic
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`source is located at an end of the swath.
`
`SUMMARY OF THE INVENTION
`rn an aspect of tfri" J-nvention, 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 paralrer, erongated
`seismic cabres, each including a prurality of spaced-apart
`seismic detectors, are advanced arong a rine of survey. A
`first acoustic source is positioned near the leading end of
`the swath and a second acoustic source is rocated near the
`trailing end of the swath. At arternate timed intervals, the
`sources launch a wavefield that is refrected from the
`subsurface earth formations to provide first and second
`seismic-signar data sets. Means, operatively coupred to the
`detectors, process and merge the first and second data sets
`to provide a,uniformly-insonified model of the subsurface
`earth formations substantially free gf 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
`forlowing detailed description and the drawings wherein the
`invention is illustrated by way of example for the purpose
`of irrustration and description only and are not intended as
`a definition of- the limits of the invention:
`FIGURE l/rno*" acoustic raypaths in the presence of
`zero dip;
`-/
`FIGURE 2/provides definitions for certain data-
`processing Ler2B,
`FTGURE 3'demonstrates the non-uniform insonification of
`the subsurface y'
`the presence of steep dips;
`FIGURE 4 4s a plan view of the configuration of a
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`typical swath of cables and associated acoustic sources such
`as may be used in 3-D marine seismic surveying;
`FIGURE S 6o*s the surface expression of subsurface
`refrection points and the shadow zones associated with steep
`dips with respect to a swath where the source is positioned
`near the leadL2dend of the swath;
`FIGURE 6'shows the surface expression of subsurface
`refrection points and the shadow zones associated with steep
`dips with respect to a swath wherein the source is located
`near the LraiL2Kg end of t,he swath;
`FfGURE 7 is a schematic flow diagram of the data
`processing meL\a{ and.
`FIGURE 8'is a timing diagram for controlling the
`activation sequence of the acoustic sources.
`
`DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
`Please refer now to Figures 3 and 4. Figure 4 is a plan
`view of a 3-D swath 1 3 of six parallel seismic cable arrays
`A1-A6 which are being towed through a body of water by a
`ship 14. (ft should be understood that, Lf land operations
`are under consideration, the cables could be towed by one or
`more trucks or could be laid out by cable trucks using
`roll-along technigues in a manner well-known to the seismic
`industry). Signals from the respective cable arrays A1-A6
`are fed over a data-signal manifold 20 to a processing means
`22 of any well-known type, installed on ship 14 and
`operatively coupled to means 22 by electrical
`lead-ins 1 6
`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
`SLr and SL", offset from the center line may be used if
`desired.
`Dashed line M. is a line of midpoints that might be
`associated with seismic cable A3 positioned towards the
`center of the swath such as suggested by Figure 3 for a 2-D
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`slice of the earth where it was shown that the subsurface
`refrection points tend to converge when shooting down-d.ip.
`In the case of a 3-D operation, employing the swath of
`Figure 4, the laterally-distributed,
`crossline trines of
`midpoints corresponding to detector cabres A2 and A1 are
`shown as dashed lines M, and M1. simirar rines (not shown)
`may be drawn for cables A4-A6.
`Figure 5 showsr ds small rectangles, the surface
`expression of steepry-dipping subsurface reflection points
`for every 1 2th detector of a 1 20-detector swath of six
`cables represented as straight, evenly-spaced, horizontal
`Iines 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 cabre being
`3000 meters Iong. 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 Figure
`3, the reflection points tend to converge down-dip along the
`inline direction. Crossline, the subsurface reflection
`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, A5 and A6 converge towards
`the center rine of the swath 13 by 25 to 30 meters, creating
`down-dip crossrine shadow zones marked by the arrows 27 and
`29 at the right hand end of the swath 13.
`Under conventional practice, to fill
`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 uneconomical.
`Please refer now to Figures 4 and 6. A second ship 24,
`towing an acoustic source sr raunches a wavefierd from the
`trairing end of swath 13. Her.e, also, more than one discrete
`source such as ST' and STr t may be used. Figure G shows the
`subsurface reflecting points (smalI rectangles as for Figure
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`5) associated with every 12th detector for swath 13 when
`source ST is actuat.ed. 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-Iine 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, Ieaving a non-
`uniformly insonified up-dip zone as indicated by arrows 31
`and 33.
`Comparison of Figures 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 Figure 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 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
`in completely, as may
`results, with the shadow zones filled
`be seen readily by superimposing (merging) Figure 5 over
`Figure 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 1 3 such
`that. a single activation of a source would produce both an
`up-dip and a down-dip component such as provided by a
`conventional split,-spread. That process is useful with
`single cables or widely-spaced dual cables. But for large-
`scale 3-D swaths or patches that use many closely-spaced
`cables, that procedure is impractical. The physical
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`configuration of the cables cannot be accuratety controlred
`within the reguired 'torerance in actual operation nor could
`a ship, which itself may be 20 meters wide, be safely
`stationed in the middre of the swath without causing cable
`damage.
`rn the presentry-contemprated best mode of operation,
`the swath 1 3 of paraIleI elongated seismic cables is
`effectivery advanced arong a desired rine of survey either
`physicarly as by towing or by use of well-known rorr-arong
`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 trailing end of swath
`1 3. The first and second sources are activated at timed
`intervars in arternate cycres to provide first and second
`reflected war{efields. The reflected wavefields are detected
`and converted to first and second data sets of reflected
`signals. The first and second data sets of electrical
`signars are processed and merged as indicated in the frow
`diagram of Figure 7, to be described later, to provide
`uniformly-insonified subsurface refrection points arong the
`line of survey. Preferably, the swath is advanced along the
`rine of survey at a constant verocity. The rengths of the
`first and second timed interval-s are substantialry constant
`and designed to arrow the swath to advance spatiarly, dt the
`selected verocity of advance, by some desired murtiple of
`the spacing between detector groups in the seismic cabres.
`rn the event that several discrete acoustic sources are
`used at each end of the swath, such as SL, SL', SLil and ST,
`STt, ST'r, the sources may be activated in some desired
`alternating seguence such as SL-ST, SLt-STt, SL'r-ST",
`etc., thereby to provide denser subsurface coverage using
`the same swath of cables.
`Thus far, it has been contempJ-at,ed that the sources are
`activated sequentially and the reflected wavefi.elds are
`recorded is a similar sequence. rf desired, the leading and
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`trairing sources may be arranged to emit encoded wavefields
`using any desired type of coding. The respective sources are
`then programmed to be activated concurrentry 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 commonarity since there is no time shift and
`therefore no spatial refrection-point smearing between
`successive leading and trailing source activations.
`Figure 7 is a schematic flow diagram of the data
`acguisition and processing routine which is implemented by
`processing means 22 on ship 14. A timer 26 controls the
`firing rate of sources sL and sr at first and second timed
`intervals commensurate with the ship's velocity, v, which is
`input to timer 26 from a verocimeter 28 of any desired type
`which may be"a portion of a saterlite navigation system.
`Timer 26 causes sources sL and gr to raunch a first and
`a second acoustic wavefield in alternate cycles in
`accordance with the timing diagram shown in Figure B.
`Assuming that source sL is first activated at time To and
`thereafter repeatedry activated at timed intervars untir
`time Tnr source ST is activated at time to after a time
`shift through delay line 29 of half an interval and
`thereafter repeatedry activated untir time intervar tn.
`Timer 28 is preferably installed on ship 1 4 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 1 3 which is insonified in alternate
`cycres by the sources sL and sr. The electrical data sets
`that are derived from down-dip insonification are detectedr -
`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
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`5
`
`number of well-known processing routines such as application
`of NMo, DMo and migration. rf the recorded refrected
`acoustic wavefierds were encoded, of course optionar
`decoders 31 and 33 (dashed outlines labeled DEC) would be
`inserted between the collect,ive-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 wiII devise obvious
`variations to the examples given herein but which will
`faII
`1 5 within the scope and spirit of this invention which is
`limited only'by the appended claims. rn particurar. this
`invention has been described with particular reference to
`marine seismic exproration at sea but the principles
`involved may be applied equarry welr to rand or shallow
`20 water surveying after suitable obvious modifications to the
`claimed method and system to fit
`the particular environment.
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`WHAT TS CLAIMED IS:
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`CLAIMS
`1. A method of seismic exploration, comprising:
`advancing a swath of paralle1 elongated seismic
`along a line of survey, each said cable including a
`plurality of longitudinally spaced-apart detectors
`detecting acoustic wavefields;
`Iaunching a first acoustic wavefield from the leading
`end of said swath;
`detecting and storing said first acous
`c wavefield,
`following reflection thereof from subsurf e earth
`formations, as a first
`reflected seismic
`ignal recording;
`launching a second acoustic wavefi d from the trailing
`end of said swath;
`detecting and storing said s
`following reflection thereof
`formations, as a second ref
`processing said first
`signal recordingsl and
`forming a substant
`model of dipping subsur
`processed first and se
`recordings.
`
`acoustic wavefield,
`d subsurface earth
`smic signal recording;
`second reflected seismic
`
`zone-free
`th formations
`lected seismic
`
`structural
`by merging the
`sign