United States Patent 1191
`Anstey et a1.
`
`[54] BROAD LINE SEISMIC PROFILING
`[75] Inventors: Nigel A. Ansley, Sevenoaks, Kent,
`England; M. Turhan Taner,
`Houston, Tex.
`[73] Assignee: Seiscom Delta Inc.
`[22] Filed:
`July 19, 1973
`[21] App]. No.: 380,682
`
`[30]
`
`Foreign Application Priority Data
`July 21, 1972
`United Kingdom ............. .. 34164/72
`
`[52] US. Cl ................. .. 340/155 CP; 340/155 TA;
`340/155 MC; 340/155 F
`[51] Int. Cl ............................................. .. G0lv 1/22
`[58] Field of Search... 340/155 CF, 15.5 TA, 15.5 F,
`340/155 GC, 7 R
`
`[56]
`
`References Cited
`UNITED STATES PATENTS
`
`3,885,225
`[11]
`[451 May 20,1975
`
`3,066,754
`3,284,769
`
`12/1962
`11/1966
`
`Johnson .................... .. 340/155 CD
`Skelton .................. .. 340/155 MC
`
`3,332,511
`
`7/1967
`
`Silverman . . . . . . . . . .
`
`. . . . .. 340/155 TA
`
`3,461,420
`
`8/1969
`
`Silverman .................. .. 340/155 CD
`
`3,671,932
`
`6/1972 Holzman . 1 . . . . . .
`
`. . . . .. 340/155 CD
`
`3,731,270
`3,746,122
`
`5/1973
`7/1973
`
`Penhollow . . . . . .
`. . . .. 340/155 MC
`Davis ........................ .. 340/155 MC
`
`Primary Examiner—Maynard R. Wilbur
`Assistant Examiner—H. A. Birmiel
`Attorney, Agent, or Firm-Pravel & Wilson
`
`[57]
`
`ABSTRACT
`
`A new and improved seismic surveying and pro?ling
`method and apparatus to obtain information concern
`ing the cross-dip components of reflecting subsurface
`interfaces.
`
`2,981,928
`
`4/1961
`
`Crawford et a1. ......... .. 340/155 TA
`
`28 Claims, 5 Drawing Figures
`
`1J7. V/B/Q’A 70/?
`oqatpoooooeeee
`
`1
`l
`
`1
`
`1
`
`Z/VD. WEE/170A’
`
`1
`
`- - — ooooeeeeoooo —
`
`6
`
`3 RD. V/B/Q?fU/Q’
`eeeerbooooooo
`
`¢ = /0 - 22 //z
`
`I = 22 — 34 #2
`
`6= 34 - 46‘ //z
`
`PGS Exhibit 2011, pg. 1
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`PGS Exhibit 2011, pg. 2
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`PGS Exhibit 2011, pg. 3
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`3,885,225
`
`Ill
`
`2
`ally exclusive parts are radiated by the several vibrators
`at any one time. The single recording of the geophone
`output, derived from the several vibrators operating si
`multaneously, may then be separated on the basis of
`frequency to represent recordings from each vibrator
`individually. These separated recordings, after sum~
`ming to provide the full bandwidth of emission from
`each vibrator, may be utilized to provide a measure of
`three-dimensional control.
`It is accordingly an object of the invention to provide
`an improved seismic technique of the pulse
`compression type, yielding a measure of information on
`the dip of re?ecting interfaces, laterally across the line
`of pro?le.
`It is also an object to provide this improvement with
`out a substantial loss of time in the ?eld, or a substan
`tial increase in the cost of the ?eld work, or a sacrifice
`of fold of stack in common-depth-point stacking.
`
`20
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`1
`BROAD LINE SEISMIC PROFILING
`
`BACKGROUND OF THE INVENTION
`
`1. Field of Invention
`The present invention relates to seismic surveying.
`The present invention is a development of the tech
`nique of seismic prospecting by pulse-compression
`methods. It is used to obtain what is known in the art
`as broad-line seismic pro?les.
`2, Description of Prior Art
`The pulse-compression system known in the art by
`the trademark "Vibroseis" has been extensively used in
`seismic surveying. This system is disclosed in US. Pat.
`Nos. 2,688,124, 2,808,577, 2,874,795, 2,910,134 and
`3,065,453. A ?eld technique commonly used with this
`system included: the use of several vibrators emitting
`long swept-frequency signals in the seismic frequency
`range, the reception of the emitted signals (after re?ec
`tion and refraction within the earth) by detectors
`spaced along a spread, and the cross-correlation of the
`received signals against the emitted swept-frequency
`signals. These operations yielded a seismic record
`which was then processed into a representation of a
`cross-section of the earth, using techniques well known
`in the art. In the prior practice of the system, the seis
`mic records and the cross-section which were formed
`did not include any information which allowed a dis
`tinction between re?ection paths confined to the verti
`cal plane through the spread and re?ection paths not
`so con?ned; they did not give three~dimensional con—
`trol over the seismic record content.
`Broad-line seismic profiling was one of several meth
`ods for obtaining a measure of three-dimensional con
`trol by associating a single conventional spread of de
`tectors with several lines of seismic sources spaced lat
`erally from the spread. The resulting reflection signals
`could then be processed into a single seismic cross
`section with auxiliary information on the cross~dip
`components of the re?ecting interfaces also available.
`Information on cross-dip components has become of
`major and increasing importance to proper seismic in
`terpretation. First. it represents protection against the
`mis-picking of re?ections which can occur by the fore
`ing of continuity between separated and discontinuous
`re?ectors which are actually on different sides of the
`line of profile. Second, it warns against the calculation
`of interval velocities and layer thicknesses between in
`terfaces which have different cross~dip components,
`and for which such calculations are not valid. Third, it
`warns against violations of the common assumption in
`migration techniques, that cross-dip components are
`negligible; if the information is sufficiently precise, it
`allows a rigorous three-dimensional migration.
`
`30
`
`35
`
`40
`
`FIG. 1 illustrates a common method of operation in
`the prior art, using vibratory sources;
`FIG. 2 illustrates a common method of wide-line pro
`?ling in the prior art;
`FIG. 3 illustrates a ?eld arrangement according to
`the present invention;
`FIG. 4 illustrates one method of making bandwidth
`allocations to three vibrators spaced apart across the
`line of pro?le and radiating simultaneously, so that fre
`quency discrimination may be maintained between
`therebetween; and
`FIG. 5 illustrates a variation on the arrangement of
`FIG. 4 to ensure a better spatial distribution of the sev
`eral frequency bands.
`
`DESCRIPTION OF PREFERRED EMBODIMENT
`Since many types of pulse-compression systems exist,
`the present invention is not generally restricted to any
`one of these. For the purposes of describing a preferred
`embodiment, the system which will be described as ex
`emplary in the present context is that known by the
`trademark: Vibroseis.
`FIG. 1 depicts a common prior art Vibroseis ?eld
`technique. A line of pro?le is illustrated at l. The seis
`mic line of pro?le 1 is divided into intervals typically
`l00m in length by marks 2. A spread of detectors, typi
`cally disposed in 24 arrays each of length 91 meters is
`diagramatically represented by the representative ar
`rays 3. Offset from the nearest detector array 3 by sev
`eral intervals is a source array 4. The source array 3 is
`shown as three vibrators 5, side by side, occupying
`twelve positions 6 along the array dimension (which, in
`this case, is taken as 91m). At each of these positions
`the three vibrators, in unison, emit a controlled swept
`frequency signal exempli?ed as 10—46Hz. In the re
`cording instruments, the signals derived from each
`array 3 for each of the twelve emissions are summed.
`From the arrangement of FIG. la, therefore, the ?nal
`output is a 24~channel recording representing the com
`posite signal produced by 12 sweeps from three vibra
`tors, into 24 arrays.
`The vibrators 5 are sometimes used side-by-side, as
`in FIG. Ia, and sometimes nose-to-tail. When they are
`side-by-side, the lateral separation is maintained fairly
`small so that cross-dipping relfections are not preju
`diced.
`
`55
`
`60
`
`SUMMARY OF INVENTION
`Brie?y, the present invention provides a new and im
`proved method and apparatus for broad-line seismic
`pro?ling. The present invention utilizes a single spread
`of detectors laid in conventional fashion along a line of
`pro?le. Several vibratory sources are spaced apart
`transversely of the line. This spacing is such as to allow
`a measure of three-dimensional control. The vibrators
`emit their signals simultaneously, and the normal fre
`quency bandwidth is emitted by each vibrator. How
`ever, this bandwidth is divided into several parts, and
`these are allocated to individual vibrators, in a se
`quence of separate emissions, in such a way that mutu
`
`PGS Exhibit 2011, pg. 4
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`3,885,225
`
`20
`
`25
`
`3
`When the 12 sweeps are recorded into the arrange
`ment of FIG. la the vibrators reach a position 7. By
`means of a roll-along switch, the active part of the
`spread is now changed to that shown in FIG. 1b. The
`vibrators assume their positions 8 at the start of a new
`source array 9, and again emit 12 identical sweeps, in
`unison, over this array.
`Thus, a second 24-channel recording is obtained,
`representing a sample of the subsurface structure of the
`earth shifted IOOm horizontally along the pro?le, rela
`tive to that of FIG. la.
`As is well known in the art, these recordings may
`then be processed to give a 12-fold common-depth
`point stack and a ?nal cross-section which purports to
`display the re?ections occurring vertically below the
`line of pro?le 1. In fact, the presence of cross-dip in the
`subsurface structure means that reflection points indi
`cated in the seismic cross-section are displaced to one
`side or other of this vertical plane.
`FIG. 2 illustrates one of several known approaches to
`solve the cross-dip problem, as an example of wide-line
`profiling. FIG. 2a depicts the arrangement which yields
`an equivalent record to the ?rst of the records de
`scribed above in connection with FIG. 1. However, the
`seismic source, instead of occupying a position or a
`suite of positions on (or substantially on) the line of
`profile 1 as in FIG. 1, is offset laterally from the line of
`pro?le l by a distance 10. The effective source position
`is therefore at 11. In the case of explosive seismic ex
`ploration work with deep drilled holes, the source posi
`tion 11 represents the location of the shot-point. In the
`case of work using surface sources or shallow holes, the
`source position 11 represents the center of some array
`(which may be similar or identical to the array shown
`at 4 in FIG. la).
`FIG. 2b shows the next recording arrangement.
`Again, the source and the detector spread are moved
`one interval to the right (as in FIG. lb). However, the
`effective source position is now at (or centered on)
`point 12, which is on the line of profile 1.
`FIG. 2c shows the next recording arrangement. Again
`the source and the detector spread are moved one in
`terval to the right, but the effective source position is
`now at 13, offset a distance 10 on the other side of the
`line of pro?le 1 from the source position 11. Subse
`quent recording arrangements repeat the pattern repre
`sented by FIGS. 2a-c.
`Processing of the output data from the source and de
`tector arrangement of FIGS. 20, 2b, and 20 yields three
`cross-sections, each representing 4-fold common
`depth—point stack. In the absence of cross-dips, the ?rst
`stack represents reflections originating in the vertical
`plane through a line 14 in FIG. 2a, the second stack
`represents those re?ections originating under the line
`of pro?le in FIG. 2b, and the third stack indicates those
`re?ections originating under the line 15 in FIG. 2c. The
`stacked cross-sections may then be scanned laterally by
`an analyst, to enhance events within a prescribed range
`of cross-dips, and to measure these cross-dips. The dis
`tance 10 is selected to provide the best compromise be
`tween the accuracy of the dip measurement and the
`ambiguity represented by the well-known alias effect.
`Co-pending US. applications Ser. Nos. 300,672 and
`300,718, ?led Oct. 25, 1972, describes a method by
`which the ?nal output from this process may be a single
`cross-section depicting the line of pro?le, and in which
`the reflections exhibit (by display bias or by color)
`
`4
`characteristics showing whether they are in front of or
`behind this line of pro?le.
`FIG. 3 illustrates the method of the present inven
`tion. As in FIG. 1a, FIG. 3a depicts three vibrators 5
`s occupying 12 positions 6 over the length of a 91m
`source array. The detector spread 3 is identical to that
`of FIG. 1a.
`The change of position between the first recording
`arrangement in FIG. 3a and the second recording ar
`rangement illustrated in FIG. 3b is analogous to that be
`tween FIG. la and FIG. 1b; after each vibrator sweeps
`the last position of its first source array, it is moved
`foreward to the ?rst position of its second source array,
`and continues thus. A distinction between FIG. 1 and
`FIG. 3 is that the vibrators are spaced apart laterally by
`a significant distance 10, equivalent to that used for the
`wide-line effect in FIG. 2. A second distinction is that
`the three vibrators do not radiate the same signal in
`unison, and do not radiate the same signal at the twelve
`source positions 6.
`The signal to be radiated by a particular vibrator at
`a particular source position is selected on the basis of
`its frequency band. The selection is such that the full
`bandwidth of lO-46 Hz (in the illustrative case) is radi
`ated from each source array, but that at any one triplet
`grouping of three source positions 6 the three vibrators
`S sending signals are occupying different and distin
`guishable frequency bands in their output frequency
`spectrum.
`An illustration of this is obtained by dividing the fre
`quency range or spectrum lO-46 Hz into three equal
`ranges or bands 10-22, 22-34 and 34-46 Hz. Then, as
`shown in FIG. 4, the first vibrator 5 in the triplet group
`ing emits a signal in the band lO-22 Hz on the first four
`of its 12 source positions 6, a signal in the band 22-34
`Hz on the second four source positions 6, and a signal
`in the band 34-46 Hz on the third four source positions
`6. The second vibrator 5 emits a signal in the band
`22-34 Hz on the ?rst four of its 12 source positions 6,
`a signal in the band 34-46 Hz on the second four
`source positions 6, and a signal in the band 10-22 Hz
`on the third four source positions 6. The third vibrator
`5 emits a signal in the band 34-46 Hz on the ?rst four
`of its 12 source positions 6, a signal in the band lO-22
`Hz on the second four source positions 6, and a signal
`in the band 22-34 Hz on the third four source positions
`6.
`At the ?rst source position 6, therefore, the ?rst vi
`brator 5 is radiating the frequency band 10-22 Hz, the
`second vibrator 5 is radiating the 22-34 Hz, and the
`third vibrator 5 is radiating the frequency band 34-46
`Hz. A standard 24-channel recording is made of the de
`tector signals received at the detector array 3 resulting
`from the response of the subsurface structure, and then
`signals from the second, thrid and fourth source posi
`tions are sent, received and recorded in the same man
`ner. These four recordings are then summed, either in
`the ?eld or elsewhere, to give a single 24-channel re
`cording representing the detector signals received and
`recorded for the first four source positions in the
`source array. Similarly, single 24-channel recordings
`are obtained for the second four positions and the third
`four positions. The three 24-channel recordings corre
`spond to three vertical slices through FIG. 4.
`Each of the three 24-channel recordings is then cor
`related against the three separate and distinct emitted
`signals which gave rise to it. This process effectively
`
`35
`
`45
`
`60
`
`PGS Exhibit 2011, pg. 5
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`3,885,225
`
`15
`
`30
`
`35
`
`5
`separates the part of the recorded signal which is due
`to each emission from the remaining portions of the sig
`nal. Thus, by correlating the ?rst recording against the
`signal in the band 10-22 Hz emitted by the ?rst vibra
`tor, a re?ection record is obtained representing the re
`?ection paths from the ?rst vibrator to the spread,
`within the stated bandwidth.
`The correlation process, effected in this manner on
`the three 24-channel recordings, yields a total of nine
`24-channel records. The three of these records due to
`the ?rst vibrator are then summed. This gives a hori
`zontal slice across FIG. 4: a 24-channel record having
`the full bandwidth lO—46 Hz, and substantially as it
`would have been if the ?rst vibrator alone had been
`used.
`Similarly, the three 24-channel records due to the
`second vibrator are summed, and those due to the
`third. The result is three new records, whose re?ection
`content differs only to the degree that cross-dips are
`present in the subsurface structure.
`Repetition of the above procedure for each detector
`array yields three 24-channel records per interval, and
`thus three cross-sections each representing 12-fold
`stack. The three cross-sections so formed represent re
`?ection points which, in the absence of cross-dips, are
`respectively in front of, in the plane of, and behind the
`vertical through the line of pro?le. Each cross-section
`incorporates full 12-fold stack, though it has the signal»
`to-noise ratio associated with one vibrator only.
`Subsequent processing is as described in the above
`discussion of the prior art. The single cross-section ob—
`tained by cross-scanning has the full signal-to-noise
`ratio associated with three vibrators. and full 12-fold
`stack. The present invention does not affect the speed
`of the ?eld work, and involves only minor increase in
`the cost of field equipment (for automatic selection or
`control of the emitted signals). The ?eld work appears
`the same, except that the vibrators are spaced apart lat
`erally; the final seismic cross-section appears the same,
`except that it now includes auxiliary information on the
`cross-dips,
`This illustrative embodiment of the method of the in~
`vention is not intended to limit the invention to a par
`ticular number of vibrators, detectors, source positions,
`fold of stack, or cross-sections, nor to limit the type or
`bandwidth of the radiated signal or the subdivisions
`thereof. The ?gures quoted, and the particulars of the
`arrangements shown in the drawings, are solely for pur
`poses of illustration.
`Several variations and improvements on the method
`described above are also within the scope of the inven‘
`tion. A ?rst variation provides a modification of the
`source array illustrated by FIG. 4. It is clear from the
`?gure that it may not be desirable to radiate the low
`frequencies from one end of the source array 6, the
`middle frequencies from the middle of the array 6. and
`the high frequencies from the other end of the array 6.
`This is easily taken into account by the arrangement of
`FIG. 5, in which the three subdivisions of the total
`bandwidth are radiated in turn across the whole array.
`Increased field storage is required for this, since the
`?rst ?eld sum is of emissions numbers I, 4, 7 and 10
`(instead of emission 14), the second field sum is of
`emissions numbers 2, 5, 8 and 11 (instead of 5—8), and
`the third ?eld sum is of emissions numbers 3, 6, 9 and
`12 (instead of 9-12).
`
`6
`A second variation is appropriate if the radiated
`waveforms are short swept-frequency signals or band
`limited random signals. in these cases it is undesirable
`to have simultaneous radiation in adjacent frequency
`bands. The solution, illustrated by reference to the prev
`vious example, is to divide the total bandwidth into six
`divisions instead of three, and to radiate the odd and
`even divisions in alternate emission periods. This re
`moves any risk that the correlation process will not be
`able to separate the signals due to the three vibrators,
`This precaution is not necessary if the emissions take
`the form of swept-frequency signals of duration long
`compared to the maximum re?ection time of interest.
`other variations are appropriate if considerable har
`monic distortion occurs in the vibrators or in their cou
`pling with the ground. This is important because the
`distortion products of the emission at it) Hz cannot be
`distinguished from genuine emissions at 20 Hz, 30l-lz
`and other integer multiple frequencies of IOHZ.
`lf distortion is serious, therefore, the capacity of the
`correlation process to separate the signals from differ~
`ent vibrators is impaired.
`One solution to this is to resonate the vibrators. The
`present invention represents a general improvement
`over the prior art in this respect; the restriction of the
`bandwidth required from a vibrator on any one emis
`sion means that is becomes feasible to obtain signifi
`cant resonance advantage over this narrow band. With
`some types of vibrator, the internal drive system may
`also be better optimized if the required bandwidth is
`decreased. The control of resonance may be made by
`variation of the effective mass and/or the effective
`compliance of the vibrator and its coupling to the
`ground, and may be linked automatically to the control
`de?ning the frequency band of the signal to be emitted.
`A second solution to the distortion problem is pro
`vided by reducing the bandwidth of the emissions, and
`by choosing the resulting narrow bands to ensure that
`the frequency content of the distortion products of one
`emission is not common to any other emission being re
`corded at the same time. This may be illustrated by di»
`viding the previous bandwidth of llle-4o H2 into twelve
`subdivisions instead of three, while still maintaining
`twelve emissions across the source array, clearly this
`means that each signal has a bandwidth of only 3 Hz
`and is radiated only once from each source array. The
`following table lists a suitable arrangement of band
`widths for each of the i2 emissions from each of the
`three vibrators; this arrangement not only ensures that
`second and third harmonics cause no ambiguity in the
`correlations, but also that adjacent bands are not radiv
`ated simultaneouslyv
`
`45
`
`50
`
`55
`
`65
`
`Emission
`No.
`
`First
`vibrator, H7
`
`Second
`vibrator, Hz
`
`Third
`vibrator, H7
`
`l
`2
`3
`4
`5
`6
`7
`8
`9
`I0
`l l
`I2
`
`[0»l3
`lhwli)
`43AM»
`l3-l6
`i942
`3337
`21-25
`28-31
`404?
`2528
`3PM
`37*“)
`
`lb—lq
`~13~4b
`i043
`i9~22
`3447'
`1346
`28-31
`4U~43
`22-25
`3| 3-4
`37~~lll
`25~28
`
`43—46
`[(Pl 3
`lfnt‘)
`34-37
`ll~l t:
`“#12
`40 a1 .1.
`22-25
`Zl‘l—3l
`3740
`I5~Zii
`3lw34
`
`PGS Exhibit 2011, pg. 6
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`3,885,225
`
`25
`
`45
`
`7
`Additional help with the distortion problem may be
`obtained, where the radiated signal is of swept
`frequency type, by judicious alternation of upsweeps
`and downsweeps; by this means the time at which cor
`relation ambiguities occur may be manipulated to be
`outside the range of relfection times considered.
`Various modi?cations of the system described may be
`implemented to improve the accuracy of the cross-dip
`measurement. For example, a larger number of vibra
`tors may be used, occupying a greater distance trans
`verse to the spread; in this case, appropriate reductions
`may be made in the bandwidth of each individual emis~
`sion. Alternatively, two passes may be made by three
`vibrators, one pass each side of the line of pro?le; thus
`six lines of source arrays may be generated. The display
`method of the aforementioned application by which
`cross-dips compiled at each depth-point may be dis~
`played individually in color provides the maximum pos
`,sible statistics for the cross-dip determination, and
`presents these in a form readily assimilated by the eye,
`so that the ?eld effort required to obtain satisfactory
`cross-dip indications is minimized if this display tech~
`nique is used.
`The foregoing disclosure and description of the in
`vention are illustrative and explanatory thereof, and
`various changes in the size, shape, and materials as well
`as in the details of the illustrated construction may be
`made without departing from the spirit of the inven~
`tion.
`We claim:
`1. A method of obtaining cross-dip information in
`seismic reflection pro?ling by the simultaneous radia
`tion, from a plurality of points spaced at different dis
`tances from the line of pro?le, of swept frequency seis
`mic signals from each of the spaced points differing in
`frequency from the seismic signals of the other spaced
`points so that the signals, after transmission and recep
`tion along different laterally spaced travel paths, may
`be identified as to their particular sources and travel
`paths on the basis of a frequency discrimination so that
`the signals can be processed to obtain cross dip infor
`mation.
`2. In the techniques of obtaining three dimensional
`seismic control by broad-line pro?ling using vibratory
`sources, the method represented by the following steps:
`a. dividing the bandwidth to be radiated into a plural
`ity of frequency bandwidth parts;
`b. establishing a spread of detectors along a pre
`scribed line of profile;
`c. disposing a plurality of vibratory sources in a
`spaced-apart relationship generally transverse to
`the said line of profile;
`d. radiating from each such source along a distinct
`laterally spaced travel path a signal constrained to
`one of the frequency bandwidth parts, the radia~
`tions from a plurality of sources overlapping in
`time;
`e. deriving from the spread of detectors signals repre
`senting the composite ground vibration induced by
`the plurality of sources in combinations;
`separating the individual contributions of the plu
`rality of sources to the composite vibration signal
`on the basis of a frequency discrimination to indi
`cate the particular sources and their signal travel
`paths; and
`
`20
`
`8
`g. utilizing the separate vibration information to give
`a measure of the three-dimensional disposition of
`relfectors within the earth.
`3. The method according to claim 2, and including
`5 the following further steps:
`a. making a plurality of emissions from each source,
`each of which emissions represents one of the plu
`rality of frequency bandwidth parts, so that the
`complete bandwidth to be radiated is radiated from
`each source but so than no two bandwidth parts are
`radiated simultaneously; and
`b. after said step of separating the individual contri
`butions of the sources, summing the emissions as
`cribed to each source and thereby deriving signals
`of full bandwidth from each source.
`4. The method according to claim 3, in which the plu
`rality of source emissions are disposed over a distance
`representing a desired source-array dimension.
`5. The method according to claim 3, in which distor
`tion problems are minimized by the selection of the
`simultaneously-radiated bandwidth parts in such man
`ner that they do not include any harmonically-related
`frequencies.
`6. The method according to claim 2, which also in
`cludes the step of correlating the detected signals
`against the emitted signals.
`7. The method according to claim 2, in which said
`step of separating the individual contributions of the
`plurality of the sources on the basis of a frequency dis
`30 crimination is performed by correlating the detected
`signals against the emitted signals.
`8. The method according to claim 2, in which advan
`tage is taken of the narrow bandwidth of each of said
`parts to resonate the vibratory source over that band
`35 width.
`9. A method of seismic pro?ling with seismic signals
`in a de?ned frequency spectrum to obtain cross~dip in
`formation regarding subsurface structure, comprising
`the steps of:
`a. sending a ?rst seismic signal having a frequency
`range within a ?rst band in the defined frequency
`spectrum from a ?rst source along a ?rst travel
`path through the subsurface structure;
`b. sending a second seismic signal having a frequency
`range within a second band distinct from the ?rst
`band in the de?ned frequency spectrum from a sec
`ond source along a second travel path different
`from the ?rst travel path through the subsurface
`structure;
`c. recording the response re?ected by the subsurface
`structure during travel of the ?rst and second seis
`mic signals along the ?rst and second travel paths
`therethrough; and
`d. processing the recorded response to separate the
`response of the subsurface structure to the first
`seismic signal and the second seismic signal from
`each other. so that cross-dip present in the subsur
`face structure is indicated by differences in the sep
`arated responses.
`10. The method of claim 9, wherein said step of pro
`cessing comprises the steps of:
`a. correlating the recorded response with the ?rst
`seismic signal to determine the response of the sub
`surface structure thereto; and
`b. correlating the recorded response with the second
`seismic signal to determine the response of the sub
`surface structure thereto.
`
`55
`
`65
`
`PGS Exhibit 2011, pg. 7
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`9
`11. The method of claim 9, wherein said step of pro
`cessing includes the step of:
`summing the separated responses of the subsurface
`structure.
`12. The method of claim 9 further including the step
`of:
`sensing the response re?ected by the subsurface
`structure with a spread of detectors laid along a
`line of seismic profile.
`13. The method of claim 12, wherein:
`said step of sending from a ?rst source comprises
`sending a ?rst Seismic signal from a shot-point
`spaced apart transversely from the line of seismic
`profile.
`14. The method of claim 12, wherein:
`said step of sending from a second source comprises
`sending a second seismic signal from a shot-point
`spaced apart transversely from the line of seismic
`profile.
`15. The method of claim 9, wherein:
`said step of sending from a second source comprises
`sending the second seismic signal simultaneously
`with the ?rst seismic signal.
`16. The method of claim 9, further including the step
`of:
`sending a third seismic signal, having a frequency
`range within a third band distinct from the ?rst
`band and second hand within the de?ned fre
`quency spectrum from a third source along a third
`travel path different from the ?rst and second
`travel paths.
`17. The method of claim 16, wherein said step of re
`cording comprises recording the response of the sub
`surface structure to the first, second and third seismic
`signals and further including the step of:
`sensing the response reflected by the subsurface
`structure with a spread of detectors laid along a
`line of seismic profile.
`18. The method of claim 17 wherein:
`said step of sending from a third source comprises
`sending a third seismic signal from a shot-point
`spaced apart transversely from the line of seismic
`profile.
`19. The method of claim 9, wherein the ?rst and sec
`ond sources are each moved to new shotpoints subse
`quent to said steps of sending, and further including the
`steps of:
`a. sending the first seismic signal from the ?rst source
`at its new shot-point; and
`b. sending the second seismic signal from the second
`source at its new shot-point.
`20. The method of claim 9, wherein the ?rst and sec
`ond sources are each moved to new shot-points subse
`quent to said steps of sending, and further including the
`steps of:
`a. sending a seismic signal of like frequency band to
`the second seismic signal from the ?rst source at its
`new shot-point; and
`b. sending a seismic signal of like frequency band to
`the first seismic signal from the second source at its
`new shot-point.
`21. An apparatus for seismic pro?ling of subsurface
`
`10
`geological structures with seismic signals in a defined
`frequency spectrum to obtain cross-dip information re
`garding subsurface structure, comprising:
`a. ?rst source means for sending a ?rst seismic signal
`having a frequency range within a first band in the
`de?ned frequency spectrum along a ?rst travel
`path through the subsurface structure;
`b. second source means spaced from said ?rst source
`means for sending a second seismic signal having a
`frequency range within a second band distinct from
`the ?rst band in the de?ned frequency spectrum
`along a second travel path through the subsurface
`structure different from the ?rst travel path;
`c. means for recording the response reflected by the
`subsurface structure during travel of the ?rst and
`second seismic signals along the first and second
`travel paths therethrough; and
`d. means for processing the recorded response to sep
`arate the response of the subsurface structure to
`the ?rst seismic signal and the second seismic sig
`nal from each other, so that cross-dip present in the
`subsurface structure is indicated by