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SPE-1009-0047-JPT

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SPE 1009 0047 JPT
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Duringthepastdecade,multipletransversefracturinginhorizontalwellshasbeenappliedsuccessfullyinonshorelow-permeabilityreservoirs.Thereasonsforthesuccessofthistechniquearerelatedtotheeffec-tivenessofhydraulicfracturingforproductionenhancementandtotherelativelylowcostofpumpingservicesonshore.Offshore,highdirectandindirectcostsandtherisksassociatedwithoperationshavelimitedtheuseofthistechnology.Thisstudydocumentsthesuccessfuleffortoftakingthesetechniquesoffshore.Transversefrac-turingwithmultistagecompletion—withproperlyengineereddesignofthewelltrajectory—canprovideeco-nomicsuccessoffielddevelopmentoflow-permeabilityreservoirs.IntroductionTheFoukandamarinefieldis20kmnorthoftheKitinaplatformand52kmwestofthecityofPointeNoire,Congo.Averagewaterdepthis100m.Thefieldwasdiscoveredin1998,withinitialproductioninJune2001.Thatyear,onewellwasdrilledintheDreservoir,butithadverypoorreservoircharacteristics,andthislevelwasabandoned.Thewellwasrecom-pletedintheshallowerB4reservoir.Thelow-permeabilityDreservoir(lessthan10md)wasabandoned.SuccessfulfracturetreatmentsintheKitinafieldinMay2007provedthepossibilityofobtainingeconomicalratesfromamarginalreservoir.Itwasdecidedtotestthemultistagehydrau-lic-fracturingtechnologyontheprevi-ouslyabandonedDreservoirintheFoukandafield.Synergyfromearlycooperationamongdrilling,reservoir,andproduc-tion-enhancementengineersprovedkeyfortheoperation.Anoptimumprocesspathwasfollowed:reser-voirassessment,selectingoptimumfracture(s)configuration,providinginputforthedrillingplan,select-ingthepropercompletiontoallowoptimumfracture(s)placement,and,finally,planexecution.TheoriginalplanonFoukandawastodrillanewverticalordeviatedwellwithoneortwofractures.Fracturingengineerssuggestedchangingthisplananddrillingahorizontalwellandcompletingitwithmultipletransversefractures.Thedeviatedwellwasdis-cardedbecauseofcomplexfracture-growingissues,which,inthebestcase,couldhavetransversefracturesthatarenotproperlyspaced,resultinginfracture/productioninterference.Theadvantageofhavingtransversefrac-turesinahorizontalwellisthepos-sibilityofproperspacinganddecidingtheoptimumnumberoffracturesthatarerequired.PhysicalLimitationsofFracturingOffshoreTherearemanylimitationstofractur-ingoffshorethatmaynotbeanissueonland.Itwasdecidedtoplacefrac-turingskidsonthedeckareaofthelargeplatform-tender/rig-supportbarge,Barracuda.The1200-m2open-deckspaceallowedriggingupfourhigh-pressurefracturingpumpsandblend-ingandbulkequipment,aswellasuseofbelow-deckfluidstorage(240m3)ofbatch-mixedgelledfluids.Afracturedesignandsequenceofoperationswasbuiltaroundthegivensetofequipment,capabilities,andavailablecrew.ReservoirSimulationDeterminingtheprofitabilityofhydrau-licfracturinginanoffshorelow-perme-abilityreservoiriscritical.ThedesignphaseofthenewFoukandawellwassupportedbyanumericalsimulatorthatassessestheproductivityincreaseresult-ingfromvariousfracturegeometriesandwellboreconfigurationsandthatdefinesprojecteconomicsproperly.Planningoptimumfracturespacing(i.e.,thenumberanddimension)isacomplexprocessthatinvolvesproduc-tionforecastandeconomics.Thefirststepwastoidentifyaproperreservoirmodelthatprojectstheproductionperformancesofmultipletransversefractures.Usually,fracturing-designsoftwarecontainsaproductionmod-uletoestimatepre-andpost-fractur-ingperformances,but,often,theyareverysimpleandnotabletohandletransverse-fractureorcomplexsce-nariosaswereplannedwiththesehorizontalmultifracturedwells.Thereservoirmodelfocusesmainlyontheoverallproject,withlimitedcapabili-tiesregardingdetailednear-wellboremodeling,whichisnecessarywithtransversemultiplefractures.Differentscenarioswereanalyzedtomaximizeproductionresultsandrecoveryfactorfromthethreelow-permeabilitylayersoftheFoukandaDreservoir.WellDesignOnthebasisofreservoir-andfractur-ing-modelresults,theselectedgeneralThisarticle,writtenbySeniorTechnologyEditorDennisDenney,containshighlightsofpaperSPE119140,“MultipleTrans-verseFracturinginOpenHoleAllowsDevelopmentofaLow-PermeabilityRes-ervoirintheFoukandaField,OffshoreCongo,”byAlbertoCasero,SPE,LorisTealdi,SPE,RobertoLuisCeccarelli,SPE,AntonioCiuca,SPE,Giamberar-dinoPace,SPE,Eni;BradMalone,SPE,Schlumberger;andJimAthans,SPE,PackersPlusEnergyServices,pre-paredforthe2009SPEHydraulicFracturingTechnologyConference,TheWoodlands,Texas,19–21January.Thepaperhasnotbeenpeerreviewed.MultipleTransverseFracturinginOpenHoleEnablesDevelopmentofaLow-PermeabilityReservoirTIGHTRESERVOIRSForalimitedtime,thefull-lengthpaperisavailablefreetoSPEmembersatwww.spe.org/jpt.JPTOCTOBER20094748JPTOCTOBER2009well-designconceptwasahorizontalwellwithmultipletransversefrac-tures.BecausetheDreservoirhasthreedifferenttargetsorlayers(fromthetop,D1,D2,andD3),thedrainwaschosentobesubhorizontaltocrossallthethreelayers,witheachlayertargetedbyasinglefracture.Thiswasacontingencychoiceincasetheshalebarrierspreventedfracture-heightgrowthacrossthedifferentlayers.TheexceptionwasZoneD3,whichrepresentedthebesttarget,withtwofracturetreatmentsplanned(thesecondfracturetreatmentwasconsideredabackup).Thedirectionofthewellwascho-seninthemostlikelydirectionofminimumstresstoobtaintransversefractures.Thelengthofthedrainwaschosentoachieveoptimumspacingconsideringthereservoirextension,numberoffractures,andgeologicalconstraints.Thewellwasplannedtoreach80°deviation(azimuth237°)withintheDreservoirswitha450-m-longdrain.Thedesigncon-sideredcaprockintegrity,potentialofwaterchannelingfromawaterlayerabovethereservoir,andthepositionoftheoil/watercontact.CompletionSelection:ContinuousPumpingMultistageSystem(CPMSS)Arecentapproachusesasystemthatbecomesapermanentcompletionliner.Thissystemusesaseriesofexternalmechanical-elementpackersthatareintegraltothedeployedlinerinstrategicplacesforisolation.Asliding-sleevevalveisplacedbetweeneachpairofthepackersandisreferredtoasafracport.Useofthepack-ersallowssegmentingthewellboreintoselectedzonesforstimulation.Packerscanbeusedincasedholetostraddleperforationsorinopenholewellborestosegmentthecompletion.Toselectivelyopenfracportsprogres-sivelyupthecompletion,progres-sivelylarger-diameterceramicballsaredroppedthatlandonabeveledseatbeloweachport.Theseatingballenablesapplyingpressuretocreateadownwardforcethatwillshiftthesleevetotheopenpositionwhileiso-latingthepreviouslyplacedfracturesthroughthedeeperports.TheCPMSScompletionassem-bly,includingfourfracturingports,wasrunintothewellondrillpipe.Theproductionlinerwas41/2-in.,13.5-lbm/ftcasingbetweenthedown-holetools.Originally,theisolationpackerswereplannedtobeapproxi-matelyequallyspacedasincased-holecompletionsintheKitinafield.Later,itwasdecidedtoruntheisolationpackersinverycloseproximitytoeachofthefracturingportstoensurethatthefractureswerespacedproper-lyalongthewellborebyconstrainingthefracture-initiationpoint.CompletionRuninHole:RedundancyHelpedHavingplannedinadvanceforafourthbackupfracturetreatmentprovedveryimportantandhelpedmaintainthethree-fracturescenar-iodespitetheinabilitytoreachtheplannedtotaldepthwiththeCPMSSbottomholeassembly.Thesettingtoolwaspulledfromthewell,andafracturing-sealassem-blywasrunintothewellandlandedinthesealboreoftheliner-hangerpacker.Thenthetubingannuluswasisolatedwiththeblowoutpreventeratthesurface.Duringthefractur-ingtreatment,annuluspressurewasmaintainedbyarigpumpandthepressurewasmonitoredbyboththerigcrewandthefracturingcontrol-monitoringsystem.FracturingExecutionOncetheCPMSSlinerassemblywasrunandset,allthefracportsandaccesstotheopenholeannuluswereclosed.Theinitialfractureportwasopenedwithpressuredifferential.Aftertheinitialfracportwasopenedhydraulically,eachsequentialportwasopenedwithaballsizedspecificallytoaseatmadeforthatzone.Theballalsoactedtoisolateanyfracturedintervalsbelowthetargetedintervalduringthefracturingoperation.ProductionResultsThreefractureswereplacedintheformation,asshowninFig.1,rath-erthanthefourfracturesinitiallyplanned.Thispreviouslyabandonedzonehadasignificantstartuprate—greaterthan3,000BOPD—andafter1yearofproduction,itwasstillcapableofproducing1,500BOPD.Thispro-ductionrepresentsone-thirdofthetotalFoukandafieldproductionof4,500BOPD.AnotherimportantachievementisthatWellFoukanda109producesbynaturalflow.Artificialliftwouldhavebeenrequiredinthecaseofnofracturing.Themid-termproductionperformancealignswiththeoriginalreservoirmodel.ThesecondwelloftheFoukandaDdevelopmentwasplannedtobedrilledandmultifrac-turedbytheendof2008byuseofthesameapproachandtechnologyasappliedinWellFoukanda109.JPTFig.1—RepresentationoffinalcompletionwiththreefracturesinWellFoukanda109.
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