throbber
Q
`Amsterdamt ‘log
`
`Z037
`
`W.H. Dragoset* (WesternGeco), H. Li (WesternGeco). L. Cooper
`(WesternGeco). D. Eke (WesternGeco). J. Kapoor (WesternGeco), I. Moore
`(WesternGeco) & C. Beasley (WesternGeco)
`
`ysummasr
`
`We acquired a small 3D wide-azimuth (WAZ) survey using simultaneous dithered sources in a
`geologcally complex area that had been previously acquired with a standard WAZ configuration. The
`simultaneous—sou:rce data were processed without application of any explicit separation procedure. Various
`results were compared to the results from the standard WAZ data set. Based on these comparisons. we
`concluded the following: 1) Velocity model building (based on angle gather quality) and 3D SRME
`multiple attenuation are possible with non-separated simultaneous-source data. 2) Migrated images for the
`two data sets were essentially identical, except that 3) because of better spatial sampling, the simultaneous
`source image had a better signal-to-noise ratio at depth.
`
`715‘ EAGE Conference 8. Exhibition — Amsterdam, The Netherlands, 8 - 11 June 2009
`
`PGS Exhibit 2020, pg. 1
`WesternGeco V. PGS (IPR20l5-00309, 310, 311)
`
`PGS Exhibit 2020, pg. 1
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`Amsterdam
`
`Introduction
`
`Within the last five years, wide-azimuth (WAZ) 3D marine surveys have become an accepted
`method of improving subsurface illumination and seismic data quality. Although a wide
`variety of such survey designs are possible, they share a common trait: a constraint imposed
`by the relationship between the number of sources, boat speed, shot spacing, and record
`length. Eliminating that constraint would add a degree of freedom to WAZ survey design,
`thereby enabling faster, more efficient surveys, better illumination, and improved data quality.
`Shooting marine sources simultaneously rather than sequentially is a method of relaxing that
`survey design constraint.
`
`An interfering marine source has traditionally been considered to be noise that must be
`removed in processing. However, Beasley et al. (1998) and Bealsey (2008) showed that the
`interfering source could be separated in processing and hence used as signal. This approach
`exploits spatial separation of the sources and geometry-related filters such as DMO and
`prestack migration to accomplish the separation. Another approach to simultaneous impulsive
`sources considered recently by several authors has its roots in efforts to deal with seismic
`crew interference (Lynn et al. 1987; Haldorsen and Farmer 1989). As Lyrm et al. stated
`..
`mis-synchronization of the survey and noise sources gives rise to time misa.-'ignment of the
`crew noise when the data are sorted into common-midpoint {Cll4fP) gathersfor stacking.
`this n'tisaiignrnent is fimdamental to our ability to srqopress the noise.” More recently, others
`have expanded upon these concepts and a number of field tests have been acquired and
`processed (Berlchout et al. 2008: Hampson et al. 2008; Fromyr et al. 2008; Moore et al. 2008).
`
`This paper describes a small 3D WAZ field test that was acquired in 2008 using two pairs of
`simultaneous sources. The test was perfomled in the Gulf of Mexico over an area that had
`been acquired earlier using a standard. four-sequential-source WAZ survey design. This
`allowed a direct comparison of the final simultaneous-source (hereafter abbreviated as
`Simsrc) and sequential-source images. The purpose of the test was to evaluate Simsrc
`technology in a WAZ setting. Specifically, we aimed to answer these questions: 1) How are
`key prestack steps in the data processing flow, such as velocity model building and multiple
`attenuation, affected by applying them to non-separated SimSrc data? 2) Can we achieve
`acceptable images using only a geometric filter (prestack migration hi this case) to untangle
`the interference between the simultaneous sources? 3) How do the signal-to-noise ratios of the
`two final images compare? Following this introduction, we describe the SirnSrc field test,
`examine the data processing results. compare them to the results fiom the sequential-source
`survey, and then discuss the three questions.
`
`Field test description
`
`The field test covered about six OCS blocks that were acquired as an eight-swath extension of
`a WesternGeco WAZ survey, hereafter referred to as WAZ 4 (Figure 1). The acquisition
`sequence was as follows: 1) The seismic crew sailed to the northeast, acquiring a standard
`WAZ swath at the western edge of WAZ 4. 2) At the boundary between WAZ 4 and WAZ 2
`(a survey previously acquired), the crew switched over to simultaneous shooting and recorded
`an additional 25 km. 3) The crew turned around and acquired another SimSrc swath while
`sailing to the southwest. 4) At the boundary between surveys, the crew switched back to
`standard acquisition and continued on. recording a WAZ 4 swath as it sailed southwest.
`
`Figure 2 shows the details of the WAZ acquisition configuration. The seismic crew consisted
`of three source-only boats and a cable-plus-source boat. Over the WAZ 4 area, the sources
`fired in the sequence A, B, C. D. Over the WAZ 2 area. the sources tired in the pattern shown
`in the figure. The older WAZ 2 survey was acquired in the same fashion as the standard WAZ
`4 survey. Note that, compared to the WAZ 4 lines, the SimSrc lines had twice as much
`seismic energy entering the subsurface and half the inline source interval. The firing times for
`the second source hr each SimSrc pair were perturbed (dithered) m an incoherent pattern
`
`7'15‘ EAGE Conference & Exhibition — Amsterdam. The Netherlands, 8 - 11 June 2009
`
`PGS Exhibit 2020, pg. 2
`WesternGeco V. PGS (IPR2015-00309, 310, 311)
`
`PGS Exhibit 2020, pg. 2
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`W
`Amsterdam
`within a 300-ms window that was designed for optimal source separability when using the
`separation algorithm of Moore et a1. (2008).
`
`,
`
`the fieid crew was
`test. Prior to the test,
`- shooting WAZ 4 using a standard source
`configuration. The 1mtern—most WAZ 4 lines
`were extended into the WAZ 2 area (outlined
`by thick red (lines) and shot with simultaneous
`sources (see Figure 2). The area covered by
`the test has a typical’ deepwater Gulf ofMexico
`--.- sait geology.
`
`firing sequence
`
`Nominal inline coordinates
`
` "1 Figure 1 Plan for the 3D SimSrc WAZ field
`the top— left of thefigure.
`
`SourceA&£
`Scum aw
`Swmeflc
`Scum am
`Em
`
`tlm
`sum
`75'“
`"25,"
`
`SouroeD
`
`‘E
`
`3*
`
`SouroeB mm
`
`i
`
`1%
`
`_
`_
`_
`_
`.
`Figure 2 SunSrc test acquisitzon
`configuration. The WA_Z 4 lines (see
`Figure I) were acquired with the
`four sources shooting sequentially
`As the crew crossed into the area of
`the test,
`the shooting configuration
`was
`changed
`to
`pairs
`of
`simultaneous
`sources
`using
`the
`firing sequence shown in the table at
`
`Processing results and comparisons
`
`Because of the salt-related steep dips present in the data, the relatively large inline sampling
`interval (75 in per source pair), and the spatial aliasing-related assumptions of Moore et al.’s
`algorithm (2008), good separation for this test was not possible using that method. Instead, we
`chose to process the data as if simultaneous sources were not present, thereby relying on only
`the imaging step to perform the source separation as described in Beasley et al. (1998). The
`migration of the Simsrc data was accomplished as follows: 1) Duplicate the recorded
`simultaneous-source sl1ot records. 2) Put the geometry from one source m the trace headers of
`one copy and the geometry from the other source in the other copy. 3) Apply the dither time
`statics to the copy with the dithered source geometry. 4) Merge the two data sets. 5) Migrate
`the merged data.
`
`Figure 3 shows a comparison of depth-migrated images for the Simsrc test and the WAZ 2
`survey. Both data sets had standard noise attenuation and wavelet processing steps applied,
`but neither had any multiple attenuation applied. They were then migrated with the WAZ 2
`velocity model using identical migration apertures. As expected, the Sin1Src image has a
`better signal-to-noise ratio. Aside from that, the two images are comparable, which suggests
`that the imaging step was successful at directing the energy from the simultaneous sources to
`its proper location.
`
`In a production survey, one usually will not have access to a preexisting velocity model. One
`important question. then, is what impact will non-separated simultaneous sources have on the
`velocity-building procedure. We tested this by comparing angle gathers for both surveys
`(Figure 4). The gathers from the Si;mSrc data are of lesser quality, but nevertheless, they do
`contain clearly pickable events.
`
`7'15‘ EAGE Conference & Exhibition — Amsterdam. The Netherlands, 8 - 11 June 2009
`
`PGS Exhibit 2020, pg. 3
`WesternGeco V. PGS (IPR2015-00309, 310, 311)
`
`PGS Exhibit 2020, pg. 3
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`O
`Amsterdamlb
`
`
`
`Figure 3 Comparison ofKirehhrfi"presrack depth migrations for the standard WAZ survey (A) and the
`3D Sim.S‘rc test (B). Nate the inqrroved signal strength in B, best seen at the lower right.
`
`are pickable.
`
`Figure 4 Kirchhafiprestack dept}:
`migration angle gathers. A) WAZ
`2 survey. B) SimSrc survey. The
`gathers from the WAZ 2 survey
`are less
`nevertheless,
`the
`gathers from the Sz'm'.S‘rc survey
`
`Another question is how well multiple attenuation will perform on non-separated SimSrc
`data. We tested this by applying a version of 3D SRME (Moore and Dragoset 2008) to the
`non-separated data using the same steps as those used for the migration, except that step 5
`was to predict and subtract the multiples. We expected the massive stack involved in 3D
`SRME multiple prediction to remove the contribution of the source incoherencies to predicted
`multiples. Figure 5 shows the SimSrc result and that of applying the same 3D SRME
`algorithm to a similar line fi'om the WAZ 2 survey. The two results are of comparable quality.
`
`Conclusion
`
`We acquired a small 3D WAZ survey using simultaneous dithered sources in a geologically
`complex area that had been acquired previously with a standard WAZ configuration. The
`SimSrc data were processed without application of any explicit separation procedure. Various
`results were compared to the results from the standard WAZ data set. Based on these
`comparisons, our answers to the questions posed in the introduction are: 1) Velocity model
`building (based on angle gather quality) and 3D SRME are possible with non-separated
`SimSrc data. Angle gather quality (and the quality of results of other prestaek processes),
`however, might be a concern in other survey areas. 2) Migrated images for the two data sets
`were essentially identical, except that 3) because of better spatial sampling, the SimSrc image
`had a better signal-to-noise ratio at depth We believe that our test is highly encouraging for
`Sin1Src technology, especially because We expect that future advances in the acquisition of
`SimSrc data and explicit separation procedures will improve upon the results shown here.
`
`'71“ EAGE Oonference & Exhibition —Amsterdam_. The Netherlands, 8 - 11 June 2009
`
`PGS Exhibit 2020, pg. 4
`WesternGeco V. PGS (IPR2015-00309, 310, 311)
`
`PGS Exhibit 2020, pg. 4
`WesternGeco v. PGS (IPR2015-00309, 310, 311)
`
`

`
`0
`Amsterdaml’o9
`
`Figure 5 Unungrared stacks befiare and afier 3D SRME. Arrows iridicate the waterbotrom mnitipvle.
`Because the two lines were recorded at d1_'fi"erem‘ times, they are near each other, bu! are not identical.
`A) WAZ 2 before SRME. 3) SimSrc before SRME. C) WAZ 2 afler SRME. D) SimS?*c afier SRME.
`
`Acknowledgments
`
`We acknowledge David Wilson, Tor Ornmundsen, Morten Svendsen, and the crews of line
`Neptune, Kylie Williams, Odyssey, and Snapper for their contributions to the SiI[ISIc field
`test. We also thank WesternGeco management for their support and for permission to publish.
`
`References
`
`Beasley, C., Chambers, R. aid Jiang, Z. [1998] A new look at simultaneous sources. 68th SEG
`Interwafionaf Exposition andMeefing, Expanded Abstracts, 133-135.
`Beasley, C.J. [2008] A new look at marine simultaneous sources, Ilie Leading Edge, 27, No. 7, 914-
`917.
`
`Berkhout, A.I., Blacquiere, G. and Verschuur, E. [2008] From simultaneous shooting to blended
`acquisition. 78th S_{EG1in‘emotionaf Expasifion andilafeeting, Expanded Abstracts, 2831-2838.
`Fromyr, E., Cambois, G., Loyd, R. and Kinkeasd, J. [2008] Flam — A Simultaneous Source Wide
`Azimuth Test. 78th SEG Imernafional Exposition and Meetmg, Expanded Abstracts, 2821-2825.
`Haldorsen, J. and Farmer, P. [1989] Suppression of high-energy noise using an alternative stacking
`procedure. Geophysics, 54, No.2, 181-190.
`Hampson, G., Stefani, J. and Herkenhoff, F. [2008] Acquisition using simultaneous sources. The
`Leading Edge, 27, No. 7, 913-923.
`Lynn, W., Doyle, M., Larner, K. And Marsehall, R. [1987] Experimental investigation of interference
`fi'om other seismic crews. Geophysics, 52, No. 11, 1501-1524.
`Moore, 1. and Dragoset, B. [2008] General surfice multiple prediction: a flexible 3D SRME algorithm.
`Fi?'S1‘Break, 26, September, 89-100.
`Moore, I., Dragoset, B., Ommundsen, T., Wilsm1, D., Ward, C. and Eke, D. [2008] Simultaneous
`source Separation using dithered sources.
`78?}: SEG International
`and Meefing,
`Expanded Abstracts, 2806-2810.
`
`71“ EAGE Oonference & Exhibition —Amsterdam, The Netherlands, 8 - 11 June 2009
`
`PGS Exhibit 2020, pg. 5
`WesternGeco V. PGS (IPR2015-00309, 310, 311)
`
`PGS Exhibit 2020, pg. 5
`WesternGeco v. PGS (IPR2015-00309, 310, 311)

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