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`Coiled Tubing
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`4-D Seismic
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`PGS Exhibit 1087, pg. 1
`PGS v. WesternGeco (IPR2014-00688)
`
`

`
`MARCH 2OI I EEP
`'It's all acquisition's fault'
`
`AS SEEN IN
`
`Advonced fime-lopse seismic ocquisition improves quolifi ond delivers results more quickly.
`
`Poddy Smith, Wester nGeco
`
`I nragine a world where tirne-lapse seismic surveys were
`I acquired identically frour ¡,e2¡ to year, ancl the acquisi-
`tion environment clicl not charìge. The tirne-lapse seis-
`mic dat.a processor'sjob wouìd be easy- design a sirnple
`a¡rd ¡'ol-¡ust plot--essing llow that iruages tlre seismic clata
`consistently from one sLlrvey to the next.
`Unfortunatel¡ the processor's job is anything but sim-
`ple. Many things, notably the environment, change from
`sllrvey to suuvev. These changes introdr"rce clata perturba-
`tions that ruust be conrpensated for. Compensatiol
`processes olten rely on measurernents made fi'<>m the
`seismic data themselves, and it can be a delicate and
`time<onsuuring business to do this lvithout modi$,ing
`the changes related to hydrocarbon prodnction tcr
`resolve.
`Sc¡, irr a scrrsc, lhc lorrg clclay that frcc¡uently occuls
`l¡etween end of acquisition and start of interp¡'etation is
`due to acquisition rather than processing.
`
`Conlrol whol you con,
`meqsure whol you connol
`Onc approach to rcsolving this problcm is to control thc
`variability oÊ the acqnisition. For exanrple, one might
`place a permanent seismic monitoring systenì over a
`producing field so the locations ¿ncl characteristics of
`the receivers ancl instruments are fixed. This can be a
`gçoocl solution, bnt in many cases the flexibility ancl cost-
`effectiveness of marine streamer acquisition make it a
`preferrecl technology.
`to control
`WesternGeco ha.s developed a technôlo€ry
`the variability of m¿rine s[earìr.er acquisition, first by
`introducing a steerable strearner that records the output
`of individually calibratecl hydrophones and then by
`cleploying a frrlly integrated svstem called Dynamic
`Spread Control (DSC). ï'his sptem rnonitors the envi-
`ronment and automatically steers the vessel, sources,
`and streamers to acquire the desi¡'ed shot and receiver
`locations. The first ¡çeneration of DSC could steer the
`streanìers up to about three clegrees against prevailing
`currents, controlling cross-flow noise tning digital noise
`suppression algorithms applied to the point receiver
`data. A new generation ofsteering devices, which can
`
`EPmg.corÌr. I March 20ll
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`Survey.qveÌqged CMS slgnolure8 ore 3hown lor o pcl¡ ol llme.
`lopso survoyi ocqulrod t¡3lng ldonllcol sourc€ colrflgulullons
`qnd porumclcl!. thc mlddlc poncl lo lhc rlghl .hows lho +D
`dlllêrêncê lhdl rêaull3 when lhê zêro,Þhoslng oÞ€rolor co!ìì
`puled lor lño ll13l 3urvoy 13 qpplþd to bolh dolosob. low.lre-
`q$ncy þ3lduol ono€V b mdrkod by orrow3. (lmqge! aourle¡y
`ot W€slornooco; ddlo cor¡rtê3y ol Stololl)
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`achieve a feather differential up to six clegrees, was
`introduced in 2010.
`However, seismic acquisition conpanies cannot con-
`trol the waves. The acquisition environment changes
`during ancl between surveys. The \4'esternGeco
`apprnach is to nteasure these changes to enahle cleter-
`ministic compensation rather than derive corrections
`I'rom the seismic clata themselves. The result is more
`accurate and is unaffected by surve,v-tô-survey changes
`caused by hydrocarbon prochrction.
`A wicle range of information is measurecl. For every
`shot. the Calibrated Marine Source (CMS) systern nreas-
`ures the output ofeach airgun in the source array.
`These are combined to create an individual fàrfìeld sig-
`
`wG-PGS00036599
`
`PGS Exhibit 1087, pg. 2
`PGS v. WesternGeco (IPR2014-00688)
`
`

`
`4-D SEISMIC
`
`Source positioni ng d itference
`?tl03 - ?006 ?006 - iln8
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`Source t receiver positioning difference
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`lhe loll pqnol oompqrê3 3or¡nlo Þo¡lllonlng dllloroncôa for turvoy3 ccqulrðd In 2003, 2ooó, qnd 2oo8 wllh ldónllêdl oêqul¡lllon conflgu.
`rollon3. DgC Þduccr lhc tourEc snd þccly.r porlllqrlng cror3 lo woll bclow ló¡l tt (50 m) tor moll ot thc aurvcy. (Dqlc coudaay ol
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`nature for each shot, enabling compensation of shot
`toshot and surve¡to{urvey variations in source output.
`GPS-Lrascd rneasurcnrerrts of actual ticle hcighs ate
`made and can be significantþ more accurate than those
`predicted from tide tables. In addition, the 4D CALM
`system measures the effect ofsea*urface waves on seis-
`mic data. The seismic sources, being suspended from
`floats, tend to move up and down with the wares.
`This movcmcnt is r¡casurcd by GPS and cnablcs com-
`pensation of the effects of wave motion on the source
`datum. The streamers, on the other hand, tend to stay
`at the same level within the rvater column, and the waves
`nìove up and down above them as the seismic shot is
`recordecl. This causes the streamer ghost component
`of the seismic wavelet io vary with acquisition record
`time and offset along the streamer. The QMarine
`point-receiver marine seismic s¡ntem digitally records
`the output of each individually calibrated þdrophone
`as a continuous full-bandwidth streanr of data, enabling
`the very low-frequency pressure information associated
`with the wave motir.¡n to be captured and inverted fnr
`wave heights. These are used to compute time- and oÊ
`set-variant filters that remove the effects of wave motion
`o¡r the streamer ghost.
`Another technique acquires velocity information in
`the water column. The rystem continuously records a
`depth- and space-variant water column seismic velocity
`profile as each line is being acquired. This enables
`deterministic compensation of the effects of line-toline
`
`and survey-to-survey changes in water column velocity.
`This is the most recently introduced component and
`represerrts tl¡e last piece irr the lirncJapse seisruic acqr"ri-
`sition puzzle. All corrections that are routinely applied
`in time-lapse seismic processing now are handlecl by the
`acquisition s)6tem.
`In 2006 and 2008, survey-averaged CMS signatures for
`a pair of timeJapse surveys were acquired using identical
`sourcc configurations and paramctcrs. Thcsc wavclcts
`are the desirecl outpìrt of the shot-by+hot CMS signature
`deconvolution procedure. The averagecl signatures are
`used to compute combined zero-phasing and debub
`blin¡ç operators that are applied to the seismic data.
`A 4D difference resulted when the zero-phasing opera-
`tor computed for the 2006 survey was applied to both the
`2006 ancl 2008 datasets, as would be the case when pro-
`cessing conventional 4D seismic data. Lonr-frequency
`residual energy can be seen on the survey. Ifeach survey
`is zero-phased using an opelator derived from the appro-
`priate signatu'e for that survcy, the low-frequency erìerg'y
`is no longer present. The minc¡r differences in resiclual
`br"rbble train between the two sþatures are genuine. At
`first glance, this could appear to be a minor issue, but it
`can si¡¡nificantþ hamper 4D seismic inversion.
`Source positioning differences were compared for sur-
`veys acquired in 2003, 2006, and 2008 with identical
`acquisition configurations. The 2006 survey did not
`attempt to duplicate the 2003 sollrce and receiver loca-
`tions, and the source positioning differences âre, as a
`
`M¡¡ch 20ll I EPrneg.corn
`
`wG-PGS00036600
`
`PGS Exhibit 1087, pg. 3
`PGS v. WesternGeco (IPR2014-00688)
`
`

`
`result, large. The 2008 survey used DSC to duplicate the
`2006 source locations, resulting n95% ofsource loca-
`tions being repeated to within 8.2 ft (2.5 m). The source
`and receiver positioning difference maps can be seen
`for the same comparisons, computed at an offset of
`6,400 ft (1,950 m). DSC reduced soLlrce and receiver
`positioning errors to well below 164 ft (50 rn) for most
`of the survey.
`This has a direct impact on 4'D data quality. The use
`of DSC reduces the gerreral normalized root-mean
`squared difference levels to 8% ta 12%.
`
`flimplified timelopse s€bm¡c dolo procerCng
`The Q-Marine acquisition systen now can deliver accu-
`rately repeated timeJapse seismic data with all necessary
`environmental corrections applied. The data processor's
`job is confined to removing noise and multiples in a
`
`¡'obust manner and regularizing and imaging the time-
`lapse seismic datasets. Each new survey can be processed
`independently of the previous one, minimizing the like-
`lihood that the timeJapse processing flow will rnodi$
`the time-lapse seismic signal.
`In the past, WesternGeco has routinely delivered time-
`lapse seismic datasets using predefined processing flows
`with turnarounds between one and eight weeks. Turn-
`arounds are expected to reduce further when rnultiple
`vintages acquirecl with all of the components become
`available.
`Advanced timelapse acquisition technology can accu-
`lately represe nt changes in the suL¡sur-face and deliver
`results within tirne fiames previor-rsly associated with
`"quick-look" volumes. This accuracy and efficient deliv-
`ery directly benefits reservoir engineem who use the
`data to rnonitor thei¡'rese¡voirs. F
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`2003 - 2006
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`2û06 - 2008
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`@ HnnTENERGY I lólós,voss,sTE, t000,HousIoN.TX77057usA | +l 7132ó0ó400 | FAX+r7t38408585
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`wG-PGS00036601
`
`PGS Exhibit 1087, pg. 4
`PGS v. WesternGeco (IPR2014-00688)