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OilfieldTechnology
February
2014
The IsoMetrixsystemcomputesthepressurewavefieldatanyposition
withinthestreamerspreadusingthedenselysampled6.25mx6.25m
surface IsoGrid.Forcomparisontoanearlier, legacydataset,asetof
‘virtual’streamerscanbeproducedtomatchthepositionsoftheprevious
survey.Thiscansignificantly improverepeatability in4Dtime‑lapse
projects.
Improvedproductivity
Theswell fromoceanwavescreatesnoise inseismicmeasurements,
particularlywhenstreamersare towedclose to theseasurface.
Conventional seismicsurveysareprone tosignificantnon‑productive
time (NPT)asadirect resultof theseconditionswhilecrews
awaitbetterconditions tobeginor resumeasurvey.The full3D
deghostingcapabilityof the IsoMetrix technologymeans that its
multi‑measurementstreamersystemscanbe toweddeeper than
normal,allowingextensionof theseismicacquisitionwindowby
reducing the impactofadverseweatherconditions.
Thereareoftenhigh levelsofseismicactivity indevelopedoilfield
areas,particularlywhentheacquisition ‘window’ isgovernedby
seasonalweatherconditions. It iscommon foraseismicvessel to
havetostand idlewhileanothersurvey isbeingacquirednearby; this
isknownastime‑sharingand isanothercauseofNPT.Withthenew
technology,adequatesamplingofcoherentnoise fromexternalsources
suchasrigsorotherseismicvessels– inboth inlineandcrossline
directions–enablesthis interferencetoberemovedduringprocessing
when, inconventionalsurveys, thedatamightneedtobereshot.
Duringearlyseatrialsof the IsoMetrixtechnology,anothersurvey
wasbeingconducted incloseproximity.Thisgeneratedsignificant
seismic interferenceontheresultingseismicdata.Themeasured
interferencecame fromadirectionalmostorthogonal tothe
multimeasurementstreamers.The interferenceappearedasaseries
ofstrongandcompactevents,havingveryhighapparentvelocity
alongthe inlinedirectionofeachstreamer.Thistypeofnoisewould
traditionallybeverydifficulttosafelyremovewithout impactingthe
underlyingseismicsignal.GMPprocessingenabledthedata, including
the interference, tobeproperlysampled inthecrosslinedirection.This
allowedappropriate filterstobeappliedtoremovethe interference
whilemaintainingtheseismicsignal.
Improvingimagingqualityaroundtheworld
Since its launch inJune2012, IsoMetrixtechnologyhasbeen
deployedoff fourcontinents.Acquisitionof the firstcommercial
projectwascompleted intheNorthSeaduringAugust2012,and
was followedbysurveys inthearea fortwoadditionaloperators.
Preliminaryresults fromtheNorthSeaBruceFieldareawerepresented
attheSEG InternationalExpositionand83
rd
AnnualMeeting in
September2013.Theseshowedthat,comparedtoaconventional
3Dsurvey, thistechnologydelivered fresh interpretational insights
ranging frombetterclarity inshallowhazard identificationto improved
reservoircharacterisation.Thenew isometricseismicdataset
providesanopportunitytorevise fault interpretation,andreservoir
compartmentalisationunderstanding, inacomplexstructuralsetting.
Figure2showsthe improved imageclarity in fine‑scale faulting
andshallowchanneldefinition,alsosuggestingsubtle lithological
variations inchannel fill,comparedtotheconventional (broadband
hydrophone‑only)equivalent.
InFebruary2013,acquisitionofan isometric3Dsurveywas
completed forThomboPetroleumLtd.overtheA‑J1grabenofBlock2B,
offthewestcoastofSouthAfrica.ThisgrabencontainstheA‑J1oil
discoverydrilledandtestedbySoekor in1988.Thenewdatawillallow
Thomboand itspartnerAfrenplctoevaluate indetail theextentof the
A‑J1oildiscovery,andtheotherprospectsand leads intheareathathad
previouslybeen identified fromexisting2Dseismicdata.
April2013sawthestartofacquisition,onamulticlientbasis,ofa
survey locatedtothenorthof theWesternGecoBjørnøya IceBearand
WestLoppa3Dseismicsurveyareas inthewesternBarentsSea.Asurvey
offshoreCanadacommenced inJune, followedbyacontinuation in
theprogrammeofcommercialprojectsaroundtheworld. InJanuary
2014, thetechnologymade itsdebut inAustralia,working forWoodside
onthe4000km
2
Fortunasurvey, the largestseismicsurveyevertobe
conductedovertheNorthWestShelfprojectacreage.
Integratedacquisitionandprocessingsystemshavebeenbuiltto
handlethe largevolumesofdatadeliveredby IsoMetrixtechnology.The
computepower installedontheseismicvessel
WGVespucci
made it
the fourth largestSchlumbergerdataprocessingcentreworldwide,and
enableskeyelementsof theprocessingtobeperformedonboard,along
with fast‑trackproducts for initialgeological interpretation.Thedataare
thensentashore for furtherprocessing, leveragingtheabilitiesofhighly
experiencedpetrotechnicalexpertstoextractmaximumvalue.
Newgeologicalinsights
Thenewacquisitiontechnology,combinedwithadvancedprocessing
algorithms,providesbroadbanddata inallthreedimensions. It is
deliveringnew insights intothegeologyofthesubsurface,withfine‑scale
isometricsamplingforoptimised imagingand interpretation.The
technologyalsopromotescost‑effectiveexplorationtechniques,allowing
wideranddeeperstreamertowingwithoutcompromisingsamplingor
bandwidth.
Figure2.
Improved imageclarityofshallowgeologicalfeatures is
demonstrated inthisexampledepthslicefroma3D interpretation
attributevolumefromanareaoftheNorthSea.The IsoMetrix image
(bottom)showshigherresolutionofchanneledges, lithological
variationsandfaultingcomparedtotheconventional(broadband
hydrophone-only)equivalent(top). ImagecourtestyofWesternGeco.
