Deepwater Horizon Accident Investigation Report

EX99.33dex993.htmDEEPWATERHORIZONACCIDENTINVESTIGATIONREPORTExhibit99.3

DeepwaterHorizonAccidentInvestigationReportSeptember8,2010

ThisisthereportofaninternalBPincidentinvestigationteam.Thereportdoesnotrepresenttheviewsofanyindividualorentityotherthantheinvestigationteam.TheinvestigationteamhasproducedthereportexclusivelyforandattherequestofBPinaccordancewithitsTermsofReference,andanydecisiontoreleasethereportpubliclyistheresponsibilityofBPIthasnotbeenpreparedinresponsetoanythirdpartyinvestigation,inquiryorlitigation.

Inpreparingthisreport,theinvestigationteamdidnotevaluateevidenceagainstlegalstandards,includingbutnotlimitedtostandardsregardingcausation,liability,intentandtheadmissibilityofevidenceincourtorotherproceedings.

Thisreportisbasedontheinformationavailabletotheinvestigationteamduringtheinvestigationavailabilityofadditionalinformationmighthaveledtootherconclusionsoralteredtheteamsfindingsandconclusions.

Attimes,theevidenceavailabletotheinvestigationteamwascontradictory,unclearoruncorroborated.Theinvestigationteamdidnotseektomakecredibilitydeterminationsinsuchcases.Inevaluatingtheinformationavailabletoit,theinvestigationteamuseditsbestjudgmentbutrecognizesthatotherscouldreachdifferentconclusionsorascribedifferentweighttoparticularinformation.

Inthecourseoftheinvestigation,membersoftheteamconductedinterviews,andthisreportdrawsupontheteammembersunderstandingofthoseinterviews.Theinvestigationteamdidnotrecordorproduceverbatimtranscriptsofanyinterviews,nordidtheteamaskintervieweestorevieworendorsethenotestakenbytheinterviewteammembers.Therewereatleasttwoteammemberspresentduringeachinterviewand,inutilizinginformationgatheredfrominterviews,theteamhastakenintoaccountthepresenceorabsenceofcorroboratingorconflictingevidencefromothersources.

Thereportshouldbereadasawhole,andindividualpassagesshouldbeviewedinthecontextoftheentirereport.Discussionoranalysisthatisbased,toanyextent,onworkcarriedoutbythirdpartiesforexample,onlaboratoryorconsultantreportscommissionedbytheinvestigationteam(refertotheappendicesofthisreport)issubjecttothesamequalificationsorlimitationstowhichthatworkwassubject.

Graphicsareoccasionallyusedtodepictinformationandscenariosthesemaybesimplifiedornottoscaleandareintendedonlyasanaidtothereaderinthecontextofthediscussionthattheysupport.

Whereverappropriate,thereportindicatesthesourceornatureoftheinformationonwhichanalysishasbeenbasedorconclusionshavebeenreached.Wheresuchreferenceswouldbeoverlyrepetitiveormightotherwiseconfusethepresentation,evidentiaryreferenceshavebeenomitted.

TableofContentsTableofContentsExecutiveSummary 9

Section1.ScopeoftheInvestigation 13

Section2.TheMacondoWell 15

Section3.ChronologyoftheAccident 21

Section4.OverviewofDeepwaterHorizonAccidentAnalyses 31

Section5.DeepwaterHorizonAccidentAnalyses 49

Analysis5A.WellIntegrityWasNotEstablishedorFailed 51

Analysis5B.HydrocarbonsEnteredtheWellUndetectedandWellControlWasLost 79

Analysis5C.HydrocarbonsIgnitedonDeepwaterHorizon 109

Analysis5D.TheBlowoutPreventerDidNotSealtheWell 141

Section6.InvestigationRecommendations 181

Section7.WorkthattheInvestigationTeamwasUnabletoConduct 189

Appendices 191DeepwaterHorizonAccidentInvestigationReport 3

FiguresandTables

FiguresandTablesFiguresExecutiveSummary

Figure1. MacondoWell 12

Section2.TheMacondoWellFigure1. GeographicLocationoftheLeaseandWell 15Figure2. Geology,OriginalWellDesignandInstalledDepth 16Figure3. ActualCasingRun 19

Section4.OverviewofDeepwaterHorizonAccidentAnalysesFigure1. BarriersBreachedandtheRelationshipofBarrierstotheCriticalFactors 32Figure2. ShoeTrackBarriers 37Figure3. PossibleMovementofSpacerintotheKillLine 40Figure4. HydrocarbonsEnteringtheRiser 43Figure5. MudGasSeparator 45

Section5.DeepwaterHorizonAccidentAnalysesAnalysis5A.WellIntegrityWasNotEstablishedorFailed

Figure1. HydrocarbonZonesandPotentialFlowPaths 54Figure2. PlannedCementSlurryPlacement 56Figure3. PlannedCementFluidLocations 61Figure4. ShoeTrack 69Figure5. FloatCollarConversion 71Figure6. LongString,LinerandLinerwithTieback 75

Analysis5B.HydrocarbonsEnteredtheWellUndetectedandWellControlWasLost Figure1. PositivepressureTest(RealtimeData) 83Figure2. SpacerPlacement 84Figure3. PossibleMovementofSpacerintoKillLine 87Figure4. April20,2010,NegativepressureTest(RealtimeData) 88Figure5.

TypicalDrillersDisplayScreenShowingDataTrendingCapabilityandMudloggersDisplayArea(notDeepwaterHorizon) 90

Figure6. TypicalDrillersCabinonanOffshoreRigSimilartoDeepwaterHorizon 90Figure7. DeepwaterHorizonDrillersCabincirca2001 91Figure8. FlowIndicationGraphShowingAnomalies(RealtimeData) 93Figure9. PressureIncreaseDuringtheSheenTest(RealtimeData) 95Figure10. NormalVersusAbnormalFlowOutSignatureasPumpsShutOff(RealtimeData) 95Figure11. FlowPathBeforeandAfterRoutingtheSpacerOverboard 96Figure12. TypicalVideoCameraDisplaysintheDrillersCabin(notDeepwaterHorizon) 97Figure13. MudPump#2PressureIncreaseat21:17Hours(RealtimeData) 98

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FiguresandTables

Figure14. OLGA WellFlowModelingforFlowConditionwithanOpenAnnularPreventer 100Figure15. InvestigationofPressureResponsesAfterShuttingDownPumps(RealtimeData) 101Figure16. ModeledPressureResponsesResultingfromHydrostaticChangesintheWellbore 102Figure17. InterpretationofWellControlResponse(RealtimeData) 105Figure18.

OLGA WellFlowModelingPredictionofCumulativeGainExcludingPumpedVolumes20:52Hours21:49Hours 106

Analysis5C.HydrocarbonsIgnitedonDeepwaterHorizonFigure1. OLGA WellFlowModelingPredictionofFluidOutflowfromtheRiser 113Figure2. SimplifiedProcessFlowDiagramofSelectedDeepwaterHorizonSurfaceEquipment 114Figure3. SimplifiedDrawingoftheMGS 115Figure4. OLGA WellFlowModelingPredictionofBackpressureandFlowattheDiverterPacker 117Figure5. Photographof6in.VacuumBreakerLineGooseneckVent 118Figure6. PhotographofStarboardOverboardLines 119Figure7. DeepwaterHorizonPhotographShowingaStarboardJetFlame 120Figure8. SchematicofPostulatedHydrocarbonReleaseLocations 121Figure9. VaporDispersionat100Seconds 122Figure10. VaporDispersionat240Seconds 122Figure11. RelevantSurfaceEquipmentDownstreamoftheIBOPat~21:47 123Figure12. DrillPipePressureMeasuredatCementPumpPIandMudPumpPI 124Figure13. MudPump#2PressurePlotShowingLineTestDuringNegativepressureTest 125Figure14. MudPump#2PressurePlotShowingLiftPressureofPRV 126Figure15. IllustrationofWellboreandPositionofHydrocarbonsat21:38HoursifBOPWasClosed 127Figure16. VaporDispersionCaseforDivertingtotheStarboardDiverter 128Figure17. HazardousAreaClassificationMainDeck 130Figure18. CGDLocationsDrillFloorandAbove 132Figure19. CGDLocationsSecondDeck 133Figure20. CGDLocationsMainDeck 134Figure21. PhotographofAftDeckofDeepwaterHorizon 135Figure22. VaporDispersionAftDeck190Seconds 136Figure23. SecondDeckDamageVectorDiagram 137

Analysis5D.TheBlowoutPreventerDidNotSealtheWellFigure1.

DrillPipePressureOLGA WellFlowModelingofDrillPipePressureforaClosingBOPVersusRecordedData 144

Figure2. OLGA WellFlowModelingofWellborePressureforaLeakingandSealingAnnularPreventer 145Figure3. FiniteElementAnalysisofanAnnularPreventer 147Figure4. ModelRepresentationofHydraulicControlforAnnularPreventer 148

DeepwaterHorizonAccidentInvestigationReport 5

FiguresandTables

Figure5. HydraulicAnalysesofanAnnularPreventer 149Figure6. MoonPoolLayoutShowingtheLocationofBlueandYellowMUXReels 151Figure7. TypicalConfigurationofFlexibleHosesintheMoonPool 152Figure8. SimplifiedSchematicoftheAMFControlSystem 153Figure9. DischargeCurvefora27voltAMFBatteryBank 155Figure10. ShearPressureRequirementfor5 /2in.,21.9ppf,S135DrillPipe 157Figure11. HydraulicAnalysesofBSRClosureResponse 159Figure12. RadiographImageofSTLockinClosedPositionTakenbyROVAftertheAccident 161Figure13. LikelyStatusofBOPRamsImmediatelyAfterAutoshearInitiation 163Figure14. RetrievedRiserKinkSectionandItsContents 164Figure15. ASchematicofDrillPipeConfigurationAcrosstheBOPOverTime 165Figure16.

(A)PhotographofSolenoidValve103intheYellowPod(B)TestingofSolenoidCoils 168

Figure17. Photographofa9voltAMFBatteryPack 168Figure18. ROVVideoStillsofLeakingHoseFittingonaShuttleValveintheSTLockHydraulicCircuit 170Figure19. PhotographsofDeepwaterHorizonBOPTCPandEventLogger 174Figure20. BOPWellControlModesofOperation 176

Section6.InvestigationRecommendationsFigure1. BarriersBreachedandtheRelationshipsofBarrierstotheCriticalFactors 181

Tables

Section5.DeepwaterHorizonAccidentAnalyses5A.WellIntegrityWasNotEstablishedorFailed

Table1. HalliburtonCementBlend 57Table2. HalliburtonCementSlurryDensities 57

5B.HydrocarbonsEnteredtheWellUndetectedandWellControlWasLostTable1. InformationAvailableBasedonActivitiesBeingConducted 94Table2. Final9MinutesPriortotheExplosion 103

5C.HydrocarbonsIgnitedonDeepwaterHorizonTable1. TimelineofEventsLeadingUptotheDeepwaterHorizonAccident 111Table2. CGDsonDeepwaterHorizon 131


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Appendices

AppendicesAppendixA.

TransoceanDeepwaterHorizonRigIncidentInvestigationIntotheFactsandCausation(April23,2010) 193

AppendixB. Acronyms,AbbreviationsandCompanyNames 195

AppendixC. MacondoWellComponentsofInterest 201

AppendixD. SperrySunRealtimeDataPits 203

AppendixE. SperrySunRealtimeDataSurfaceParameters 205

AppendixF. RolesandResponsibilitiesforMacondoWell 207

AppendixG. AnalysisDeterminingtheLikelySourceofInflow 211

AppendixH. DescriptionoftheBOPStackandControlSystem 223

AppendixI. DeepwaterHorizonInvestigationFaultTrees (electronicmedia)

AppendixJ. HalliburtonLabResults#73909/2 (electronicmedia)

AppendixK.

LaboratoryAnalysisofCementingOperationsontheDeepwaterHorizon(fromCSITechnologies) (electronicmedia)

AppendixL. Reserved

AppendixM.

SummaryReportGlobalAnalysisofMacondo9 /8inx7inProductionCasing4992ftWaterDepth,GoM(ForMacondoWellInvestigation)(fromStressEngineering) (electronicmedia)

AppendixN. MississippiCanyon252No.1(Macondo)BasisofDesignReview (electronicmedia)

AppendixO.

IndustryComparisonDataonLongStringCasingandCasingLinersintheMacondoWellArea (electronicmedia)

AppendixP. BP/DeepwaterHorizonRheliantDisplacementProcedureOSCG32306(MISWACO) (electronicmedia)

AppendixQ.

SummaryoftheEffectofSpacerFluidCompositionandPlacementonNegativepressureTest (electronicmedia)

AppendixR. FluidCompressibilityCalculations (electronicmedia)

AppendixS. FirstSurfaceIndicationsofWellFlowandPitGain (electronicmedia)DeepwaterHorizonAccidentInvestigationReport 7

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AppendicesAppendixT.

ComparisonofEventswithRelevantTransoceanWellControlPolicies,PracticesandProcedures (electronicmedia)

AppendixU. RiserFluidEvacuationtoRigFloor (electronicmedia)

AppendixV. BPDeepwaterHorizonGOMIncidentInvestigationDispersionAnalysis(fromBakerRisk)(electronicmedia)

AppendixW. ReportDynamicSimulationsDeepwaterHorizonIncidentBP(fromaeaddenergy) (electronicmedia)

AppendixX. DeepwaterHorizonBluePodAMFSystemBatteries (electronicmedia)

AppendixY. September2009DeepwaterHorizonFollowupRigAudit (electronicmedia)

AppendixZ. HydraulicanalysesofBOPcontrolsystem(fromUltraDeep) (electronicmedia)

AppendixAA.DeepwaterHorizonBOPModificationsSinceCommissioning (electronicmedia)8 DeepwaterHorizonAccidentInvestigationReport

ExecutiveSummary

ExecutiveSummary

ExecutiveSummaryOntheeveningofApril20,2010,awellcontroleventallowedhydrocarbonstoescapefromtheMacondowellontoTransoceansDeepwaterHorizon,resultinginexplosionsandfireontherig.Elevenpeoplelosttheirlives,and17otherswereinjured.Thefire,whichwasfedbyhydrocarbonsfromthewell,continuedfor36hoursuntiltherigsank.Hydrocarbonscontinuedtoflowfromthereservoirthroughthewellboreandtheblowoutpreventer(BOP)for87days,causingaspillofnationalsignificance.

BPExploration&ProductionInc.wastheleaseoperatorofMississippiCanyonBlock252,whichcontainstheMacondowell.BPformedaninvestigationteamthatwaschargedwithgatheringthefactssurroundingtheaccident,analyzingavailableinformationtoidentifypossiblecausesandmakingrecommendationstoenablepreventionofsimilaraccidentsinthefuture.

TheBPinvestigationteambeganitsworkimmediatelyintheaftermathoftheaccident,workingindependentlyfromotherBPspillresponseactivitiesandorganizations.Theabilitytogatherinformationwaslimitedbyascarcityofphysicalevidenceandrestrictedaccesstopotentiallyrelevantwitnesses.Theteamhadaccesstopartialrealtimedatafromtherig,documentsfromvariousaspectsoftheMacondowellsdevelopmentandconstruction,witnessinterviewsandtestimonyfrompublichearings.Theteamusedtheinformationthatwasmadeavailablebyothercompanies,includingTransocean,HalliburtonandCameron.Overthecourseoftheinvestigation,theteaminvolvedover50internalandexternalspecialistsfromavarietyoffields:safety,operations,subsea,drilling,wellcontrol,cementing,wellflowdynamicmodeling,BOPsystemsandprocesshazardanalysis.

Thisreportpresentsananalysisoftheeventsleadinguptotheaccident,eightkeyfindingsrelatedtothecausalchainofeventsandrecommendationstoenablethepreventionofasimilaraccident.Theinvestigationteamworkedseparatelyfromanyinvestigationconductedbyothercompaniesinvolvedintheaccident,anditdidnotreviewitsanalyses,conclusionsorrecommendationswithanyothercompanyorinvestigationteam.Also,atthetimethisreportwaswritten,otherinvestigations,suchastheU.S.CoastGuardandBureauofOceanEnergyManagement,RegulationandEnforcementJointInvestigationandthePresidentsNationalCommissionwereongoing.Whiletheunderstandingofthisaccidentwillcontinuetodevelopwithtime,theinformationinthisreportcansupportlearningandthepreventionofarecurrence.

TheaccidentonApril20,2010,involvedawellintegrityfailure,followedbyalossofhydrostaticcontrolofthewell.ThiswasfollowedbyafailuretocontroltheflowfromthewellwiththeBOPequipment,whichallowedthereleaseandsubsequentignitionofhydrocarbons.Ultimately,theBOPemergencyfunctionsfailedtosealthewellaftertheinitialexplosions.

Duringthecourseoftheinvestigation,theteamusedfaulttreeanalysistodefineandconsidervariousscenarios,failuremodesandpossiblecontributingfactors.DeepwaterHorizonAccidentInvestigationReport 9

ExecutiveSummaryEightkeyfindingsrelatedtothecausesoftheaccidentemerged.Thesefindingsarebrieflydescribedbelow.AnoverviewoftheteamsanalysesandkeyfindingsisprovidedinSection4.OverviewofDeepwaterHorizonAccidentAnalyses,whileSection5.DeepwaterHorizonAccidentAnalysesprovidesthedetailedanalyses.RefertoFigure1.MacondoWell,fordetailsofthewell.

1 Theannuluscementbarrierdidnotisolatethehydrocarbons.Thedaybeforetheaccident,cementhadbeenpumpeddowntheproductioncasingandupintothewellboreannulustopreventhydrocarbonsfromenteringthewellborefromthereservoir.Theannuluscementthatwasplacedacrossthemainhydrocarbonzonewasalight,nitrifiedfoamcementslurry.Thisannuluscementprobablyexperiencednitrogenbreakoutandmigration,allowinghydrocarbonstoenterthewellboreannulus.Theinvestigationteamconcludedthattherewereweaknessesincementdesignandtesting,qualityassuranceandriskassessment.

2 Theshoetrackbarriersdidnotisolatethehydrocarbons.Havingenteredthewellboreannulus,hydrocarbonspasseddownthewellboreandenteredthe9 /8in.x7in.productioncasingthroughtheshoetrack,installedinthebottomofthecasing.Flowenteredintothecasingratherthanthecasingannulus.Forthistohappen,bothbarriersintheshoetrackmusthavefailedtopreventhydrocarbonentryintotheproductioncasing.Thefirstbarrierwasthecementintheshoetrack,andthesecondwasthefloatcollar,adeviceatthetopoftheshoetrackdesignedtopreventfluidingressintothecasing.Theinvestigationteamconcludedthathydrocarboningresswasthroughtheshoetrack,ratherthanthroughafailureintheproductioncasingitselforupthewellboreannulusandthroughthecasinghangersealassembly.Theinvestigationteamhasidentifiedpotentialfailuremodesthatcouldexplainhowtheshoetrackcementandthefloatcollarallowedhydrocarboningressintotheproductioncasing.

3 Thenegativepressuretestwasacceptedalthoughwellintegrityhadnotbeenestablished.Priortotemporarilyabandoningthewell,anegativepressuretestwasconductedtoverifytheintegrityofthemechanicalbarriers(theshoetrack,productioncasingandcasinghangersealassembly).Thetestinvolvedreplacingheavydrillingmudwithlighterseawatertoplacethewellinacontrolledunderbalancedcondition.Inretrospect,pressurereadingsandvolumebledatthetimeofthenegativepressuretestwereindicationsofflowpathcommunicationwiththereservoir,signifyingthattheintegrityofthesebarriershadnotbeenachieved.TheTransoceanrigcrewandBPwellsiteleadersreachedtheincorrectviewthatthetestwassuccessfulandthatwellintegrityhadbeenestablished.

4 Influxwasnotrecognizeduntilhydrocarbonswereintheriser.Withthenegativepressuretesthavingbeenaccepted,thewellwasreturnedtoanoverbalancedcondition,preventingfurtherinfluxintothewellbore.Later,aspartofnormaloperationstotemporarilyabandonthewell,heavydrillingmudwasagainreplacedwithseawater,underbalancingthewell.Overtime,thisallowedhydrocarbonstoflowupthroughtheproductioncasingandpassedtheBOPIndicationsofinfluxwithanincreaseindrillpipepressurearediscernableinrealtimedatafromapproximately40minutesbeforetherigcrewtookactiontocontrolthewell.Therigcrewsfirstapparentwellcontrolactionsoccurredafterhydrocarbonswererapidlyflowingtothesurface.TherigcrewdidnotrecognizetheinfluxanddidnotacttocontrolthewelluntilhydrocarbonshadpassedthroughtheBOPandintotheriser.


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ExecutiveSummary

ExecutiveSummary5 Wellcontrolresponseactionsfailedtoregaincontrolofthewell.ThefirstwellcontrolactionsweretoclosetheBOP

anddiverter,routingthefluidsexitingtherisertotheDeepwaterHorizonmudgasseparator(MGS)systemratherthantotheoverboarddiverterline.Iffluidshadbeendivertedoverboard,ratherthantotheMGS,theremayhavebeenmoretimetorespond,andtheconsequencesoftheaccidentmayhavebeenreduced.

6 Diversiontothemudgasseparatorresultedingasventingontotherig.OncedivertedtotheMGS,hydrocarbonswereventeddirectlyontotherigthroughthe12in.gooseneckedventexitingtheMGS,andotherflowlinesalsodirectedgasontotherig.Thisincreasedthepotentialforthegastoreachanignitionsource.ThedesignoftheMGSsystemalloweddiversionoftherisercontentstotheMGSvesselalthoughthewellwasinahighflowcondition.ThisoverwhelmedtheMGSsystem.

7 Thefireandgassystemdidnotpreventhydrocarbonignition.HydrocarbonsmigratedbeyondareasonDeepwaterHorizonthatwereelectricallyclassifiedtoareaswherethepotentialforignitionwashigher.Theheating,ventilationandairconditioningsystemprobablytransferredagasrichmixtureintotheenginerooms,causingatleastoneenginetooverspeed,creatingapotentialsourceofignition.

8 TheBOPemergencymodedidnotsealthewell.ThreemethodsforoperatingtheBOPintheemergencymodewereunsuccessfulinsealingthewell.

Theexplosionsandfireverylikelydisabledtheemergencydisconnectsequence,theprimaryemergencymethod

availabletotherigpersonnel,whichwasdesignedtosealthewellboreanddisconnectthemarineriserfromthewell.

TheconditionofcriticalcomponentsintheyellowandbluecontrolpodsontheBOPverylikelypreventedactivationofanotheremergencymethodofwellcontrol,theautomaticmodefunction(AMF),whichwasdesignedtosealthewellwithoutrigpersonnelinterventionuponlossofhydraulicpressure,electricpowerandcommunicationsfromtherigtotheBOPcontrolpods.AnexaminationoftheBOPcontrolpodsfollowingtheaccidentrevealedthattherewasafaultinacriticalsolenoidvalveintheyellowcontrolpodandthatthebluecontrolpodAMFbatterieshadinsufficientchargethesefaultslikelyexistedatthetimeoftheaccident.

Remotelyoperatedvehicleinterventiontoinitiatetheautoshearfunction,anotheremergencymethodofoperating

theBOPlikelyresultedinclosingtheBOPsblindshearram(BSR)33hoursaftertheexplosions,buttheBSRfailedtosealthewell.

Throughareviewofrigauditfindingsandmaintenancerecords,theinvestigationteamfoundindicationsofpotentialweaknessesinthetestingregimeandmaintenancemanagementsystemfortheBOP.

Theteamdidnotidentifyanysingleactionorinactionthatcausedthisaccident.Rather,acomplexandinterlinkedseriesofmechanicalfailures,humanjudgments,engineeringdesign,operationalimplementationandteaminterfacescametogethertoallowtheinitiationandescalationoftheaccident.Multiplecompanies,workteamsandcircumstanceswereinvolvedovertime.DeepwaterHorizonAccidentInvestigationReport 11

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ExecutiveSummaryTheinvestigationteamdevelopedaseriesofrecommendationstoaddresseachofitskeyfindings,andtheserecommendationsarepresentedinthisreport.(RefertoSection6.InvestigationRecommendations.)Therecommendationsareintendedtoenablepreventionofsimilaraccidentsinthefuture,andinsomecases,theyaddressissuesbeyondthecausalfindingsforthisaccident.Theserecommendationscovercontractoroversightandassurance,riskassessment,wellmonitoringandwellcontrolpractices,integritytestingpracticesandBOPsystemmaintenance,amongotherissues.

Withthisreport,theinvestigationteamconsiderstheTermsofReferenceofthisinvestigationfulfilled.(RefertoAppendixA.TransoceanDeepwaterHorizonRigIncidentInvestigationIntoFactsandCausation[April23,2010].)

Additionalphysicalevidencemaybecomeavailablefollowingtherecoveryofsubseaequipment.Ongoingactivities,investigationsandhearingsmayalsoprovidefurtherinsight.BPwillconsiderhowbesttoexamineandrespondtofurtherevidenceandinsightsastheyemerge.

ItmayalsobeappropriateforBPtoconsiderfurtherworktoexaminepotentialsystemicissuesbeyondtheimmediatecauseandsystemcausescopeofthisinvestigation.

Finally,giventhecomplexandinterlinkednatureofthisaccident,itmaybeappropriatetofurtherconsideritsbroaderindustryimplications.

Figure1.MacondoWell.12 DeepwaterHorizonAccidentInvestigationReport

Section1.ScopeoftheInvestigation

Section1

Section1.ScopeoftheInvestigationScope

Within24hoursoftheaccidentaboardtheTransoceanDeepwaterHorizon,BPExploration&ProductionInc.requestedthatanaccidentinvestigationteambeformed.MarkBly,BPGroupHeadofSafetyandOperations,wasassignedtoleadtheinvestigationteam.TheinvestigationwasconductedindependentlyfromBPteamsmanagingtheongoingaccidentresponseandregularoperations.

TheTermsofReferencefortheinvestigationwereissuedonApril23,2010.(RefertoAppendixA.TransoceanDeepwaterHorizonRigIncidentInvestigationIntotheFactsandCausation[April23,2010].)UndertheTermsofReference,theinvestigationteamwastoanalyzethesequenceofpertinentevents,thereasonsfortheinitialreleaseofhydrocarbons,thesubsequentexplosionsandfire,andtheeffortstocontroltheflowduringandimmediatelyaftertheaccident.Theinvestigationteamwasaskedtoidentifycriticalfactorsandtheirunderlyingcausesinordertomakeappropriaterecommendations.

Overthecourseoftheinvestigation,theteaminvolvedover50internalandexternalspecialistsfromavarietyoffields:safety,operations,subsea,drilling,wellcontrol,cementing,wellboredynamicmodeling,blowoutpreventer(BOP)systemsandprocesshazardanalysis.

TheaccidentinvestigationfocusedontheeventsleadinguptotheexplosionsandfireonApril20,2010,andonattemptstoactivatethesubseaBOPfromApril21May5,2010,usingsubsearemotelyoperatedvehicles(ROVs).

Theinvestigationteamdidnotexamineotherincidentmanagementactivities,thesinkingoftherigorthespillresponse.

InvestigationProcess

TomeetitsTermsofReference,theinvestigationteamusedBPsinvestigationanalysisprocessinconjunctionwithfaulttreeanalysisandachronology.Theintentwastoidentifycriticalfactors(eventsorconditionsthat,ifeliminated,couldhaveeitherpreventedtheaccidentorreduceditsseverity)andtoexaminepotentialcausalorcontributoryfactorsattheimmediatecauseandsystemcauselevels.Basedonthiswork,theteamdevelopedrecommendationstoenablepreventionofsimilaraccidentsoccurring.DeepwaterHorizonAccidentInvestigationReport 13

Section1.ScopeoftheInvestigationThefaulttreesdevelopedbytheinvestigationteamareincludedinAppendixI.DeepwaterHorizonInvestigationFaultTrees.Afaulttreedepictseachcriticalfactorandtrackspossiblecausesandsubcausesacrossthefaulttreefromlefttoright.Theselinesofinquirywereinvestigatedwiththepurposeofsubstantiatingorrulingouteachcausalhypothesis,andthefaulttreesreferthereadertotherelevantsectionsofthereportfortheinvestigationteamsanalysisandconclusions.Whendevelopingrecommendations,theinvestigationteamaddressedmattersthatwereidentifiedintheinvestigation,whetherornottheywereconsideredcontributorytotheaccident.

SharingInsights

Throughthecourseoftheinvestigation,membersoftheinvestigationteambriefedinternalandexternalpartiessothatinformationthatwaspertinenttotheongoingincidentmanagementactivitieswouldbeavailabletotheresponseteams.Additionally,theinvestigationteamsharedearlyinsightsintoitsanalysisandthepossiblesequenceofeventswithrepresentativesoftheU.S.government.Thisreportsupersedesthoseearlyinsights.Theinvestigationteamhopesthattheinformationandrecommendationsinthisreportwillhelpenablepreventionofsimilaraccidentsinthefuture.14 DeepwaterHorizonAccidentInvestigationReport

Section2.TheMacondoWell

Section2

Section2.TheMacondoWellLeaseandPermits

OnMarch19,2008,BPacquiredtheleasetoMississippiCanyonBlock252intheCentralGulfofMexico(GoM)atMineralsManagementService(MMS)leasesale206.The10yearleasestartedonJune1,2008.BP(65%),AnadarkoPetroleum(25%)andMOEXOffshore(10%)sharedownershipinthelease,withBPastheleaseoperator.TheMacondowellislocatedinMississippiCanyonBlock252.

TheMMSapprovedtheexplorationplanfortheleaseonApril6,2009.MMSapprovedarevisedexplorationplanonApril16,2009.

AnApplicationforPermittoDrilltheMacondowellwasapprovedbyMMSonMay22,2009.Inlinewithnormalpractice,severalApplicationsforPermittoModifyweresubmittedbyBPandapprovedbyMMSthroughoutthedrillingprogram.ThesereflectednecessarychangestotheApplicationforPermittoDrillbecauseofthewellconditionsencountered.

TheMacondowellislocatedapproximately48milesfromthenearestshoreline114milesfromtheshippingsupplypointofPortFourchon,Louisianaand154milesfromtheHouma,Louisiana,helicopterbase.(RefertoFigure1.)

Figure1.GeographicLocationoftheLeaseandWell.DeepwaterHorizonAccidentInvestigationReport 15

Section2.TheMacondoWellWellPlanningandDesign

TheMacondowellwasaninfrastructureleddevelopment,meaningthattheexplorationwellwasdesignedsothatitcouldlaterbecompletedtobeaproductionwellifsufficienthydrocarbonswerefound.BPsprimaryobjectivefortheMacondowellwastoevaluateaMiocenegeologicalformation(M56)forcommercialhydrocarbonbearingsands.(RefertoFigure2.)Althoughtheoriginalwellplanwastodrilltoanestimatedtotaldepth(TD)of19,650ft.,theactualTDwas18,360ft.

TheBPMacondowellengineeringteamworkedinconjunctionwiththeBPsubsurfaceteamandselectedspecialistcontractorstodeveloptheMacondowelldesign.Theteamsestimatedtheporepressuresandstrengthsofthegeologicformationsandusedtheseestimatesindevelopingthedesignbasisforthewell.BylateJune2009,adetailedengineeringdesign,ashallowhazardassessmentandadesignpeerreviewhadbeencompleted.Theoriginalwellplanencompassedallelementsofthewelldesign,includingthewellequipmentandoperations,mud,drillbits,casingdesign,cementplansandpressuretesting.

Theoriginalwellplanconsistedofeightcasingstrings.(RefertoFigure2.)However,duringdrilling,ninecasingstringswereneeded,includinga9 /8in.x7in.productioncasing.

Figure2.Geology,OriginalWellDesignandInstalledDepth.16 DeepwaterHorizonAccidentInvestigationReport

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Section2

DrillingOperationsSummary

InitialdrillingoftheMacondowellbeganwithTransoceanssemisubmersibleMarianasonOctober6,2009,andcontinueduntilNovember8,2009,whenMarianaswassecuredandevacuatedforHurricaneIda.Marianaswassubsequentlydemooredandremovedduetohurricanedamagethatrequireddockrepairs.Aftertherepairs,therigwentoffcontract.

DeepwaterHorizonwasownedandoperatedbyTransoceanandhadbeenundercontracttoBPintheGoMforapproximately9years.Duringthistime,ithaddrilledapproximately30wells,twothirdsofwhichwereexplorationwells.TherigwaschosentofinishtheMacondowellaftercompletingitspreviousproject(theKodiakappraisalwell).

TheMMSapprovedanApplicationforRevisedNewWellonJanuary14,2010,andtheMacondowellplanwasupdatedtoreflectthereplacementofMarianaswithDeepwaterHorizon.OnJanuary31,2010,DeepwaterHorizonarrivedonsite.DrillingactivitiesrecommencedonFebruary6,2010.

AsistypicalofexploratorywellsintheGoM,throughoutthedrillingprocessthewellencounteredporepressuresandfracturegradientsthatdifferedfromthedesignbasis.Thisresultedinchangestothemudweightsandwellcasingsettingdepthsascomparedwiththeoriginaldesign.

DeepwaterHorizondrilledoutthe18in.liner,anda16 /2in.x20in.holesectionwasdrilledto12,350ft.,withindicationsofincreasingporepressure.Alostcirculationzonewasencountered,butthiswasremediedwithlostcirculationmaterials(LCM).Thesubsequentattempttoreturntothepreviousdepthof12,350ft.wasproblematic.A16in.casingwasinstalledatadepthof11,585ft.,whichwasapproximately915ft.shallowerthanoriginallyplanned.

Afterrunningandcementingthe16in.casing,thedrillingofthe14 /4in.x16in.holesectioncommencedonMarch7,2010.OnMarch8,2010,awellcontroleventoccurredthatresultedinthedrillpipebecomingstuck.Thedrillpipecouldnotbefreed,andthelowerpartofthewellborewasabandoned.(RefertoAnalysis5B.HydrocarbonsEnteredtheWellUndetectedandWellControlWasLostofthisreport.)

Arevisedcasingdesignwaspreparedtoaddressthehighformationpressurethathadledtothewellcontrolevent.A9 /8in.drillinglinerwasaddedtoreachthewellsprimaryobjectivesands,andtheproductioncasingwaschangedfroma9 /8in.longstringtoacombination9 /8in.x7in.longstring.TheMMSapprovedtherevisedwelldesign.

Thesubsequentdrillingbypassedtheabandonedwellbore,andthe13 /8in.linerwasrunandcementedinplaceat13,145ft.Thecontingency11 /8in.linerwassetat15,103ft.,andthenew9 /8in.linerwassetat17,168ft.(RefertoFigure3.)

Drillingofthefinal8 /2in.x9 /8in.holesectionstartedonApril2,2010,andcontinueduntilApril4,2010,whenthewellencounteredlostcirculationat18,260ft.Lostcirculationpillswerepumpedtothebottomofthewellbore,andthemudweightwasreducedfrom14.3ppgto14.17ppg.Thissolvedthelostcirculationproblems.FullcirculationwasregainedonApril7,2010,andonApril9,2010,thewellwasdrilledtoafinaldepthof18,360ft.DeepwaterHorizonAccidentInvestigationReport 17

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Section2.TheMacondoWellUponreachingfinalwelldepth,fivedayswerespentloggingthewelltoevaluatethereservoirintervals.Aftertheloggingwascomplete,acleanouttripwasconductedtoconditionthewellboreandverifythattheopenholesectionwasingoodcondition.Partofthisprocedureincludedcirculatingbottomsuptoverifythatnogaswasentrainedinthemud.Uponachievingbottomsup,noappreciablevolumesofgaswererecorded,indicatingthatthewellwasstable.

OnApril16,2010,theMMSapprovedtheprocedurefortemporaryabandonmentofthewell.Atthetimeoftheaccident,the9 /8in.x7in.productioncasinghadbeenrunandcementedinplaceat18,304ft.,andpressuretestinghadbeencompleted.(RefertoFigure3.)Therigcrewwaspreparingforthefinalactivitiesassociatedwithtemporarywellabandonmentwhentheaccidentoccurred.18 DeepwaterHorizonAccidentInvestigationReport

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Section2

Figure3.ActualCasingRun.DeepwaterHorizonAccidentInvestigationReport 19

Section3.ChronologyoftheAccident

Section3Section3.ChronologyoftheAccidentThechronologyofeventsinthehoursleadinguptoandincludingtheDeepwaterHorizonaccidentarepresentedhereasafactualtimelinetoallowastraightforwarddescriptionofeventsastheyunfolded.

Themajoractivitysetscoveredinthistimelineinclude:

EventsPriortoApril19,2010.

FinalCasingRun.

CementJob.

PositivepressureandNegativepressureTests.

WellMonitoringandSimultaneousOperations.

WellControlResponse.

ExplosionandFire.

BOPEmergencyOperations.

Theinvestigationteamconsultedthefollowingprimarysourcestoconstructthischronologyofevents:

Realtimedata:realtimedatatransmissionsfromtheSperrySunloggingsystem.

OpenWells :BPsdailyreportingsystementitledOpenWells DrillingMorningReport.

Interviews:witnessaccountscollectedbytheinvestigationteam.

MarineBoardInvestigation(MBI)testimony:testimonygivenduringtheMBIhearingsonMay2629andJuly1923,2010.

DeepwaterHorizonpipingandinstrumentationdiagrams(P&IDs).

Incidentmanagementteam(IMT)reports:recordsfromBPsaccidentresponseeffort.

OLGA wellflowmodeling:transientmultiphasewellflowsimulationsrunbythirdpartyexpertsonbehalfoftheinvestigationteam.

UnifiedCommand:theunifiedcommandoftheDeepwaterHorizonaccidentresponse.

Othersourcesasnoted.

Inthechronology,conclusionsreachedbytheinvestigationteamasaresultofmodelingorcalculationsareshowninitalicswithinbrackets.DeepwaterHorizonAccidentInvestigationReport 21

Section3.ChronologyoftheAccidentEventsPriortoApril19,2010Date Time Description Source

2009October6

SpuddedMacondowellwithTransoceansMarianas.OpenWells

November827

PulledriserandevacuatedMarianasforHurricaneIda.Marianassubsequentlydamagedandmovedtosafeharborrepairs.

OpenWells

2010January31February6

TransoceansDeepwaterHorizononlocationtoreplaceMarianas.

Sixdaysofprejobmaintenanceandtestingofblowoutpreventer(BOP)followed.

DrillingactivitiesrecommencedonFebruary6.

OpenWells

February23March13

Pilotvalveleakof1gpmnoticesonyellowpodofBOPleakreducedafterswitchingtobluepod.

OpenWells

March8 Wellcontroleventat13,305ft.Pipestuckseveredpipeat12,146ft. OpenWells

March1222

Contingencylinerutilized,anewdrillinglinerwasaddedandproductioncasingchangedtoa9 /8in.x7in.longstring.

MineralsManagementService(MMS)approvedchanges.

Macondowellplan

MMSapplications

April56

Strippeddrillpipethroughupperannularpreventerfrom17,146ft.to14,937ft.whileaddressingwellborelosses.

OpenWells

April914

Totaldepthof18,360ft.reachedanddatacollectedforfivedays.Reservoirsandscontainedhydrocarbonsatpressuresofapproximately11,850psi.

OpenWells

April14

HalliburtonOptiCemcementmodelreviewconcludedzonalisolationobjectivescouldbemetusing9 /8in.x7in.longstringasproductioncasing.

Halliburton9 /8in.x7in.ProductionCasingDesignReport

April15

OptiCemmodelupdatedwithopenholecaliperandsurveydata.Inputincluded21centralizersand70%standoffabovethetopcentralizer.

Companyemails

April15 Decisionmadetoorder15additionalcentralizers.Orderplaced. Companyemails

April16 11:51Fifteensliponbowspringcentralizersdeliveredtorigbyhelicopter. OpenWells22 DeepwaterHorizonAccidentInvestigationReport

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Section3(continued)Date Time Description Source

April16

12:4812:53

Mechanicalintegrityconcernsregardingthebowspringcentralizers.Decisionmadenottorunbowspringcentralizers.

CompanyemailsInterviews

April18

20:58

Partiallabtestresults,anewOptiCem modelreport(usingseveninlinecentralizers)andHalliburtonscementingrecommendedprocedurefortheMacondowellcementjobwereprovidedtoBPandHalliburtonstaff.

[CompletelabtestresultsonplannedslurrydesignnotprovidedtoBPbeforejobwaspumped.]

EmailfromHalliburtoninhousecementingengineertoBPandHalliburtonstaff

FinalCasingRunDate Time Description Source

April19

13:30

Completedfinal(production)casingrunto18,304ft.(jobtook37hours).TheshoetrackincludedaWeatherfordfloatcollarinstalledatthetopandareamershoeatthebottom.

OpenWells

April19

14:3016:20

Nineattemptsmadetoestablishcirculation.Circulationestablishedwith3,142psi.

OpenWellsRealtimedata

April19

16:2019:30

Circulationpressureof340psididnotmatchmodelingresultsof570psi.OpenWells

CementJobDate Time Description Source

April1920

19:3000:36

Cementjobpumpedasplannedwithfullfluidreturnsobserved.Bottomplugburstdiskrupturedathigherthanplannedpressure2,900psi.

Cementjobcompletedbumpedtopwiperplugat00:36hours.

OpenWells

Realtimedata

April2000:40

Bledoff5bblsoffluidtoreducedrillpipepressurefrom1,150psito0psi.Noflowobservedafterbleeding5bbls.

Realtimedata

OpenWells

April20

00:4007:00

DrilQuipsealassemblyinstalledinsubseawellhead.Twopressuretestsuccessfullycompleted.Drilledpipepulledoutofriser.

Realtimedata

OpenWells

Interviews

April20

~07:30

BPandserviceprovidersdiscussedrunningcementbondlog(CBL)duringmorningoperationscall.

Decisionmade,inaccordancewithpreestablishedBPMacondowellteamdecisiontree,nottorunCBL.

Interviews


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Section3.ChronologyoftheAccidentPositivepressureandNegativepressureTestsDate Time Description Source

April20

10:5512:00

Successfulpositivepressuretestoftheproductioncasing.

Realtimedata

Interviews

April20

12:0015:04

Drillpiperuninholeto8,367ft.Displacementprocedurereviewedinpreparationformuddisplacementandnegativepressuretest.

At13:28hours,DeepwaterHorizonstartedoffloadingmudtoM/VDamonBankston.

Mudloggertoldassistantdrillerthatpitlevelscouldnotbemonitoredduringoffloading.AssistantdrillertoldmudloggerthatnoticewouldbeprovidedwhenoffloadingtoM/VDamonBankstonceased.

Realtimedata

M/VDamonBankstonlog

Interviews

April20

15:0415:56

Seawaterpumpedintoboost,chokeandkilllinestodisplacemud1,200psilefttrappedinthekillline(i.e.,notbledoff).

Realtimedata

April20

15:5616:53

Atotalof424bblsof16ppgspacerfollowedby30bblsoffreshwaterpumpedintowell.Displacementcompletedwith352bblsofseawater,placingthespacer12ft.abovetheBOP.

[From~16:00hours17:50hours,triptankwasbeingcleaned.Recordedflowdataunreliableduringthisperiod.]

Realtimedata

MISWACOdisplacementprocedure

April20

16:54

Uponshuttingdownpumps,drillpipepresswasat2,325psi.Pressureinkilllineremainedat1,200psi.

Anannularpreventerwasclosedforthenegativepressuretest.

Realtimedata

Interviews

April20

16:5416:56

Drillpipepressurebledfrom2,325psidownto1,220psiinordertoequalizewiththe1,200psionthekillline.

Realtimedata

April20

16:5716:59

Killlineopenedandpressuredecreasedto645psidrillpipepressureincreasedto1,350psi.

Attemptmadetobleedsystemdownto0psi.Drillpipepressuredecreasedto273psi.Killlinepressuredecreasedto0psi.Killlineshutin.

Realtimedata

Interviews

April20

16:5917:08

At16.59hours,drillpipepressureincreased273psito1,250psiin6minutes.

Annularpreventerclosingpressurewasincreasedfrom1,500psito1,900psitocreateaseal.

Theriserwastoppedupwithapproximately50bblsofmudfromthetriptanktoreplacethevolumebledoffthroughthedrillpipe.

[SpacerfluidwasthenacrosstheBOP.]

Realtimedata

MBItestimony


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April20

17:0817:27

Drillpipepressuredecreasedfrom1,250psito1,205psi.Realtimedata

April20

17:17

MudoffloadingfromDeepwaterHorizonmudpitstoM/VDamonBankstonceased.Mudloggernotnotified.

M/VDamonBankstonlog

Interviews

April20

17:2717:52

Drillpipepressurereducedfrom1,205psito0psibybleedingoff15bblsto23bblsoffluidtothecementunit.

Rigcrewandwellsiteleaderdiscussednegativepressuretestprocedure.WellsiteleaderstatedthenegativepressuretestneededtobedoneontheonthekilllineinaccordancewiththeBPplansubmittedtoMMS.

Realtimedata

Interviews

April20

17:5218:00

Killlineopenedtothecementunit.

Cementerbledoff3bblsto15bblsofseawater.Awitnessreportedcontinuousflowfromthekilllinethatspurtedandwasstillflowingwheninstructedtoshutintheline.

Realtimedata

Interviews

April20

18:0018:35

Drillpipepressuregraduallyincreasedto1,400psiover35minutes.Buildprofileshoweddistinctpressurefluctuationsatfairlyuniformintervals.

Realtimedata

April20

18:3519:55

Discussionensuedaboutpressureanomaliesandnegativepressuretestprocedure.

Seawaterpumpedintothekilllinetoconfirmitwasfull.Openedkilllineandbled0.2bbltominitriptankflowstopped.Killlineopenedandmonitoredfor30minuteswithnoflow.

At19:55hours,thenegativepressuretestwasconcludedandconsideredagoodtest.

Realtimedata

Interviews

WellMonitoringandSimultaneousOperationsDate Time Description Source

April2020:00

Internalblowoutpreventer(IBOP)andannularpreventeropenedandpumpingofseawatercommenceddownthedrillpipetodisplacemudandspacerfromtheriser.

Realtimedata

April2020:50 Pumpsslowedforthespacerarrivingatsurface. Realtimedata

April20~20:52[Calculatedthatthewellwentunderbalancedandstartedtoflow.] OLGA modelDeepwaterHorizonAccidentInvestigationReport 25

Section3.ChronologyoftheAccident(continued)Date Time Description Source

April20

20:5821:08

Flowoutfromthewellincreased.

Triptankwasemptiedintotheflowlineatthistime.

[Takingintoaccounttheemptyingofthetriptank,calculatedagainofapproximately39bblsoverthisperiod.]

Realtimedata

Calculations

April20

21:0121:08

Drillpipepressureincreasedfrom1,250psito1,350psiatconstantpumprate.Realtimedata

April2021:08

Spacerobservedatsurface.

Pumpsshutdowntoenablesheentesttobeconducted.

Realtimedata

Interviews

April20

21:0821:14

Withpumpsoff,drillpipepressureincreasedfrom1,017psito1,263in5 /2minutes.

OverboarddumplineopenedduringsheentestSperrySunflowmeterbypassed.

Successfulresultfromvisualsheentestindicatedthatfluidscouldbedischargedoverboard.

[OLGA wellflowmodelingcalculatedthatinflowtothewellduringthisperiodwasapproximately9bbls/min.]

Realtimedata

Interviews

DeepwaterHorizonP&IDs

OLGA model

April20

21:1421.31

Pumpsrestartedtocontinuedisplacement.

Displacedwellfluidsdischargedoverboard.

Drillpipepressureoncontinuallyincreasingtrend.

Realtimedata

Interviews

April20

21:17

Pump#2startedandpressurespikedto6,000psi.[Inferredthatthepumplikelystartedagainstaclosedvalveandthepressureliftedthereliefvalve.]

Realtimedata

MBItestimony

April2021:18 Pumps#2,#3and#4wereshutdown.Pump#1stayedonline(boostline). Realtimedata

April20

~21:1821:20

Toolpusherwascalledtorigfloor.Interviews

April20~21:20

Assistantdrillerwascalledtoeitherthepitroomorthepumproom.

Interviews

MBItestimony

April20

~21:20

Seniortoolpushercalledtoolpusherandaskedhowthenegativepressuretesthadgone.Toolpusherrespondedthatthetestresultwasgood,andthedisplacementwasgoingfine.

MBItestimony

April20

21:2021:27

Pumps#3and#4restarted.Somepressurestartedtobuildonpump#2,reaching800psiat21:27hours.

Realtimedata


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April20

21:2621:30

Drillpipepressuredeclinedby400psiatconstantpumprate.Realtimedata

April2021:30

[Calculatedthatthespacerwasfullydisplacedfromtheriser.]

Realtimedata

OLGA model

WellControlResponseDate Time Description Source

April2021:31 Pumpsshutdownfirstpumps#3and#4,then#1(boostpump). Realtimedata

April20

21:3121:24

Drillpipepressureincreasedfrom1,210psitol,766psi.

~21:33hours,chiefmateobservedtoolpusheranddrillerdiscussingdifferentialpressure.Toolpushertoldchiefmatethatcementjobmaybedelayed.

Realtimedata

MBItestimony

April20

21:3621:38

Overa90secondperiod,drillpipepressuredecreasedfrom1,782psito714psiandthenincreasedfrom714psito1,353psi.

[Inferredtohavebeencausedbyopeningandclosinga4in.valveonthestandpipemanifold.]

Realtimedata

OLGA model

April2021:38 [Calculatedthatatapproximately21:38,hydrocarbonspassedfromwellintoriser.] OLGA model

April20

21:3821:42

Drillpipepressureheldbriefly,thendecreasedsteadilyfrom1,400psito338psi.Realtimedata

April20

~21:4021:48

Chiefelectriciandeisolatedpump#2.

Chiefelectricianobservedfourpersonnel(includingtheassistantdriller)completingrepairofthepressurereliefvalveonpump#2atthetimeheleftthearea(~21:48hours).

MBItestimony


Section3.ChronologyoftheAccident(continued)Date Time Description Source

April20

21:4021:48

~21:40hoursMudoverflowedtheflowlineandontorigfloor.

~21:41hoursMudshotupthroughderrick.

~21:41hoursDiverterclosedandflowroutedtomudgasseparator(MGS)BOPactivated(believedtobelowerannularpreventer).

[DrillpipepressurestartedincreasinginresponsetoBOPactivation.]

~21:42hoursM/VDamonBankstonwasadvisedbyDeepwaterHorizonbridgetostandoff500mbecauseofaproblemwiththewell.Theshipbegantomoveaway.

~21:42hoursDrillpipepressureincreasedsteadilyfrom338psito1,200psiover5minuteperiod.

~21:44hoursMudandwaterexitedMGSventsmudraineddownonrigandM/VDamonBankstonasitpulledawayfromrig.

~21:44hoursToolpushercalledwellsiteleaderandstatedtheyweregettingmudbackandthattheyhaddivertedtothemudgasseparatorandhadeitherclosedorwereclosingtheannularpreventer.

~21:45hoursAssistantdrillercalledtheseniortoolpushertoreportthatThewellisblowingout...[thetoolpusher]isshuttingitinnow.

~21:46hoursGashissingnoiseheardandhighpressuregasdischargedfromMGSventstowardsdeck.

~21:47hoursFirstgasalarmsounded.Gasrapidlydispersed,settingoffothergasalarms.

~21:47hoursRoaringnoiseheardandvibrationfelt.

~21:47hoursDrillpipepressurestartedrapidlyincreasingfrom1,200psito5,730psi.

[ThisisthoughttohavebeentheBOPsealingaroundpipe.Possibleactivationofvariableborerams[VBRs]at21:46hours.]

~21:48hoursMainpowergenerationenginesstartedgoingintooverspeed(#3and#6wereonline).

Realtimedata

Interviews

MBItestimony



Section3ExplosionandFireDate Time Description Source

April20

21:49

Rigpowerlost.SperrySunrealtimedatatransmissionlost.

Firstexplosionoccurredanestimated5secondsafterpowerloss.

Secondexplosionoccurredanestimated10secondsafterfirstexplosion.

RealtimedataInterviewsMBItestimony

April2021:52:57

MaydaycallmadebyDeepwaterHorizon.

M/VDamonBankstonlog

April20

~21:5221:57

Subseasupervisorattemptedtoactivateemergencydisconnectsequence(EDS)fortheBOPatthepanelonthebridge.Lightschangedonpanel,butnoflowwasobservedontheflowmeter.

Lowermarineriserpackagedidnotunlatch.

DeepwaterHorizonmasterannouncedtheactivationoftheEDSat21:56.

MBItestimonyInterviews

April20

~22:0023:22

Transferof115personnel,including17injured,toM/VDamonBankston.

11peopleweredeterminedtobemissing,andsearchandrescueactivitiesensued.

U.S.CoastGuardarrivedonsiteat23:22hours.

MBItestimony

April22 10:22 DeepwaterHorizonsank. UnifiedCommand

April23 17:00 Thesearchforthe11missingpeoplewassuspended. UnifiedCommandBOPEmergencyOperationsDate Time Description Source

April2122

18:0001:15

Remotelyoperatedvehicle(ROV)operationswereinitiated.

ROVattemptedhotstabinterventionstocloseVBRsandblindshearrams(BSRs)ROVattemptswereineffective.

IMTreports

April22~02:45

ROVsimulatedautomaticmodefunctionAMFinanattempttoactivateBSR.Wellcontinuedtoflow.

IMTreports

April22~07:40

Onthethirdattempt,ROVactivatedautoshearfunction.(BSRthoughttohaveclosed.)Wellcontinuedtoflow.

IMTreports

April25May5

SeventeenfurtherattemptsbyROVsusingsubseaaccumulatorstoclosevariousBOPramsandannularpreventers.Wellcontinuedtoflow.

IMTreportsDeepwaterHorizonAccidentInvestigationReport 29

Section4.OverviewofDeepwaterHorizonAccidentAnalyses

Section4Section4.OverviewofDeepwaterHorizonAccidentAnalyses

Introduction

Thissectionprovidesanoverviewofthedetailedanalysesundertakenbytheinvestigationteam.TheinvestigationteamconsidersthefindingsandconclusionsfromthedetailedanalysesastrongfoundationfortherecommendationsinSection6.InvestigationRecommendationsofthisreport.

Acomplexandinterlinkedseriesofmechanicalfailures,humanjudgments,engineeringdesign,operationalimplementationandteaminteractionscametogethertoallowtheinitiationandescalationoftheDeepwaterHorizonaccident.Multiplecompanies,workteamsandcircumstanceswereinvolvedovertime.

Theinvestigationpursuedfourprimarylinesofinquiry,basedontheinitialreviewoftheaccidentevents.Fortheaccidentanditsaftermathtohaveoccurred,thefollowingcriticalfactorshadtohavebeeninplace:

Wellintegritywasnotestablishedorfailed.

Hydrocarbonsenteredthewellundetectedandwellcontrolwaslost.

HydrocarbonsignitedonDeepwaterHorizon.

Theblowoutpreventer(BOP)didnotsealthewell.

Theinvestigationofthiscomplexaccidentbecamefourlinkedinvestigationsintothefactsandcausesunderlyingthesecriticalfactors.(RefertoSection5.DeepwaterHorizonAccidentAnalysesofthisreport.)Usingfaulttreeanalysis,variousscenarios,failuremodesandpossiblecontributingfactorswereconsidered.Eightkeyfindingsemerged:

1. Theannuluscementbarrierdidnotisolatethehydrocarbons.

2. Theshoetrackbarriersdidnotisolatethehydrocarbons.

3. Thenegativepressuretestwasacceptedalthoughwellintegrityhadnotbeenestablished.

4. Influxwasnotrecognizeduntilhydrocarbonswereintheriser.

5. Wellcontrolresponseactionsfailedtoregaincontrolofthewell.

6. Diversiontothemudgasseparatorresultedingasventingontotherig.

7. Thefireandgassystemdidnotpreventhydrocarbonignition.

8. TheBOPemergencymodedidnotsealthewell.DeepwaterHorizonAccidentInvestigationReport 31

Section4.OverviewofDeepwaterHorizonAccidentAnalysesInFigure1,theeightblocksrepresentthedefensivephysicaloroperationalbarriersthatwereinplacetoeliminateormitigatehazards.Theholesrepresentfailuresorvulnerabilitiesinthedefensivebarriers.Theeightkeyfindingsarerepresentedbytheholesthatlineduptoenabletheaccidenttooccur.

Figure1.BarriersBreachedandtheRelationshipofBarrierstotheCriticalFactors.

Ifanyofthecriticalfactorshadbeeneliminated,theoutcomeofDeepwaterHorizoneventsonApril20,2010,couldhavebeeneitherpreventedorreducedinseverity.Section5.DeepwaterHorizonAccidentAnalysesofthisreportdocumentstheinvestigationteamsanalysisandconclusionsregardingeachkeyfindingorbarrierbreach.

Background

DeepwaterHorizon,whichwasbuiltin2001,wasafifthgeneration,dynamicallypositionedsemisubmersibledrillingunit.Theunitemployedanautomateddrillingsystemanda15,000psiratedBOPsystemandhadoperatedinwaterdepths(WD)greaterthan9,000ft.Therighaddrilledwellsupto35,055ft.inthenineyearsithadbeenownedandoperatedbyTransoceanundercontracttoBPinthedeepwaterGulfofMexico.

TheMacondowellwasanexplorationwellinMississippiCanyonBlock252in4,992ft.WD.Thewellhadbeendrilledto18,360ft.fromitslastcasingpointat17,168ft.ThewellpenetratedahydrocarbonbearingMiocenereservoirandwasdeemedacommercialdiscovery.ThedecisionwasmadetotemporarilyabandontheMacondowellandcompleteitasaproductionwellinthefuture.32 DeepwaterHorizonAccidentInvestigationReport


Section4Atthetimeoftheaccident,thefinalstringofcasinghadbeenrunintothewell,andthecementbarrierhadbeenputinplacetoisolatethehydrocarbonzones.Integritytestshadbeenconducted,andthetop8,367ft.ofmudwasbeingcirculatedoutusingseawaterinpreparationfortemporaryabandonmentofthewell.TheremainingstepsweretosetacementpluginthecasingandtoinstallalockdownsleeveonthecasinghangersealassemblypriortodisconnectingtheBOPandsuspendingthewell.

Forthepurposesofthisreport,theBPMacondowellteamreferstoBPsHoustonbasedwellsteamthatworkedontheMacondowell,excludingBPscementingservicesprovider(Halliburton)andalsoexcludingtheBPwellsiteleadersaboardDeepwaterHorizon.

TherigcrewdescribesTransoceansrigcrewleaderswhowereaboardDeepwaterHorizon(seniortoolpusher,toolpushers,drillersandassistantdrillers)collectively,ortotheindividualsinoneormoreoftheseroles,andincludespersonnelactingattheirdirection.ReferencestotheBPwellsiteleadersaretothedayandnightwellsiteleaderswhowereaboardDeepwaterHorizon.

ReferencestomudloggersaretheHalliburtonSperrySunmudloggerswhowereaboardDeepwaterHorizon.MlSWACOprovidedthemudengineers.

KeyFinding1.Theannuluscementbarrierdidnotisolatethehydrocarbons.

Theannuluscementbarrierfailedtopreventhydrocarbonsfrommigratingintothewellbore.Theinvestigationteamsanalysisidentifiedaprobabletechnicalexplanationforthefailure.InteractionsbetweenBPandHalliburtonandshortcomingsintheplanning,design,executionandconfirmationofthecementjobreducedtheprospectsforasuccessfulcementjob.

A9 /8in.linerwassetinplaceat17,168ft.priortodrillingtheproductionsectionofthewelltoatotaldepthof18,360ft.Thislastholesectionwasdifficulttodrillduetoareductioninfracturegradientatthebottomofthewellbore.Thisconditionrequiredselectingthecorrectmudweighttomaintainoverbalanceontheformationwhileavoidingfluidlossestothewell.

Consideringthenarrowmarginbetweenporepressureandfracturegradient,anumberofdifferentoptionswereevaluatedpriortoselectingthedesignfortheproductioncasingstring,cementformulationandplacementplan.

Theinvestigationteamreviewedthedecisiontoinstalla9 /8in.x7in.longstringproductioncasingratherthana7in.productionliner,whichwouldhavebeentiedbacktothewellheadlater,andconcludedthatbothoptionsprovidedasoundbasisofdesign.

Theinvestigationteamfoundnoindicationthathydrocarbonsenteredthewellborepriortoorduringthecementjob.Todeterminehowthehydrocarbonsenteredthewellafterthecementjob,theinvestigationteamassessedthecementslurrydesign,cementplacementandconfirmationoftheplacement.


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CementSlurryDesign

Duetothenarrowmarginbetweenporepressureandfracturegradient,theaccuracyofcementplacementwascritical.SeveraldesigniterationswereconductedbyHalliburtonusingtheOptiCemwellboresimulationapplicationtoestablishanacceptableslurrydesignandplacementplan.Acomplexdesignforthecementjobwithbaseoilspacer,cementingspacer,lead(cap)cement,foamcementandtailcement,wasrecommendedandimplemented.

TheHalliburtonandtheBPMacondowellteamstechnicalreviewsofthecementslurrydesignappearedtobefocusedprimarilyonachievinganacceptableequivalentcirculatingdensityduringcementplacementtopreventlostreturns.Otherimportantaspectsofthefoamcementdesign,suchasfoamstability,possiblecontaminationeffectsandfluidlosspotentialdidnotappeartohavebeencriticallyassessedintheprejobreviews.

Theevidencereviewedsuggeststhatthecementslurrywasnotfullytestedpriortotheexecutionofthecementjob.Theinvestigationteamwasunabletoconfirmthatacomprehensivetestingprogramwasconducted.Thetestresultsreviewedbytheinvestigationteamindicatedthatonlylimitedcementtestingsuchasthickeningtime,foamdensity,mixabilityandultrasoniccompressivestrength,wasperformedontheslurryusedintheMacondowell.Thetestsrevieweddidnotincludefluidloss,freewater,foam/spacer/mudcompatibility,staticgelstrengthtransitiontime,zerogeltimeorsettlement.

ToevaluatetheeffectivenessoftheHalliburtoncementslurrydesignthatwasused,theinvestigationteamrequestedathirdpartycementinglab,CSITechnologies,toconductaseriesoftests.Totestthecementslurrydesign,arepresentativeslurrywasformulatedtomatch,ascloselyaspossible,theactualslurryusedfortheMacondowell(theinvestigationteamdidnothaveaccesstotheactualHalliburtoncementandadditivesthatwereusedforthejob).

Theresultsofthesetestsindicateditwasnotpossibletogenerateastablenitrifiedfoamcementslurrywithgreaterthan50%nitrogen(byvolume)atthe1,000psiinjectionpressure.FortheMacondowell,amixtureof55%to60%nitrogen(byvolume)wasrequiredat1,000psiinjectionpressuretoachievethedesignmixtureof18%to19%nitrogen(byvolume)foamcementatdownholepressureanddownholetemperatureconditions.

ThesethirdpartytestresultssuggestthatthefoamcementslurryusedfortheMacondowellwaslikelyunstable,resultinginnitrogenbreakout.

Theinvestigationteamidentifiedcementslurrydesignelementsthatcouldhavecontributedtoafailureofthecementbarrier,includingthefollowing:

Thecementslurryyieldpointwasextremelylowforuseinfoamcementing,whichcouldhaveincreasedthepotential

forfoaminstabilityandnitrogenbreakout.

Asmallslurryvolume,coupledwithlongdisplacementandtheuseofbaseoilspacer,couldhaveincreasedthe

potentialforcontaminationandnitrogenbreakout.

Adefoameradditivewasused,whichcouldhavedestabilizedthefoamcementslurry.

Fluidlosscontroladditiveswerenotusedforcementingacrossthehydrocarbonzone,whichcouldhaveallowed

formationfluidstopermeatethecement.34 DeepwaterHorizonAccidentInvestigationReport

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Section4

Conclusion

BasedonCSITechnologieslabresultsandanalysis,theinvestigationteamconcludesthatthenitrifiedfoamcementslurryusedintheMacondowellprobablywouldhaveexperiencednitrogenbreakout,nitrogenmigrationandincorrectcementdensity,whichwouldexplainthefailuretoachievezonalisolationofhydrocarbons.Nitrogenbreakoutandmigrationwouldhavealsocontaminatedtheshoecementandmayhavecausedtheshoetrackcementbarriertofail.

CementPlacement

Effectivecementplacementisnecessaryfortheisolationofpermeablehydrocarbonzones.TheMacondowellcementplacementplanwastoplacethetopofcement(TOC)500ft.abovetheshallowestidentifiedhydrocarbonzoneincompliancewithMineralsManagementService(MMS)regulations.

The500ft.TOCdesignwaschosento:

Minimizeannulushydrostaticpressureduringcementplacementinordertoavoidlostreturns.

Avoidcementingintothenextcasingstringandcreatingasealedannulus.Asealedannuluswouldhaveincreasedthe

riskofcasingcollapseorburstduetoannularpressurebuildupduringproduction.

Whentheplacementmodelwasrunusing21centralizers,theresultsindicatedthatthepossibilityofchannelingabovethemainhydrocarbonzoneswouldbereduced.The7in.casingstringthathadbeenpurchasedforthejobwassuppliedwithsixinlinecentralizers.Anadditional15sliponcentralizersweresourcedfromBPinventoryandsenttoDeepwaterHorizon.TheBPMacondowellteamerroneouslybelievedthattheyhadreceivedthewrongcentralizers.Theydecidednottousethe15centralizersduetoaconcernthatthesesliponcentralizerscouldfailduringthecasingrunandcausethecasingtolodgeacrosstheBOP.Tomitigatetheriskofchannelingassociatedwithusingfewercentralizers,thesixinlinecentralizerswerepositionedacrossandabovetheprimaryhydrocarbonzones.

Conclusion

Althoughthedecisionnottouse21centralizersincreasedthepossibilityofchannelingabovethemainhydrocarbonzones,thedecisionlikelydidnotcontributetothecementsfailuretoisolatethemainhydrocarbonzonesortothefailureoftheshoetrackcement.

PlanningforTemporaryAbandonment

Thecementjobwaspumpedwithexpectedvolumesandmudreturns.TheBPMacondowellteamusedfinalliftpressureandreturnstodeclareasuccessfulcementplacement.AfterdiscussionwithMacondowellcontractorsandconsistentwithadecisiontreedevelopedbytheteam,theteamdecidedthatnofurtherevaluationwasneededatthattime.


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BPsEngineeringTechnicalPractice(ETP)GP1060ZonalIsolationRequirementsDuringDrillingOperationsandWellAbandonmentandSuspensionspecifiesthatTOCshouldbe1,000ft.aboveanydistinctpermeablezones,andcentralizationshouldextendto100ft.abovesuchzones.Ifthoseconditionsarenotmet,asinthiscase,TOCshouldbedeterminedbyaprovencementevaluationtechnique,suchasconductingacementevaluationlog,whichwouldtypicallybedoneduringthecompletionphaseofthewell.Theinvestigationteamhasnotseenevidenceofadocumentedriskassessmentregardingannulusbarriers.

Conclusion

EvaluatingliftpressureandlostreturnsdidnotconstituteaprovencementevaluationtechniqueperSection5ofETPGP1060.BynotconductingaformalriskassessmentoftheannuluscementbarrierspertheETPrecommendations,itistheviewoftheinvestigationteamthattheBPMacondowellteamdidnotfullyconformtotheintentofETPGP1060.

AformalriskassessmentmighthaveenabledtheBPMacondowellteamtoidentifyfurthermitigationoptionstoaddressriskssuchasthepossibilityofchannelingthismayhaveincludedtherunningofacementevaluationlog.

OverarchingConclusionforKeyFinding1

Improvedengineeringrigor,cementtestingandcommunicationofriskbyHalliburtoncouldhaveidentifiedthelowprobabilityofthecementtoachievezonalisolation.

Improvedtechnicalassurance,riskmanagementandmanagementofchangebytheBPMacondowellteamcouldhaveraisedawarenessofthechallengesofachievingzonalisolationandledtoadditionalmitigationsteps.

KeyFinding2.Theshoetrackbarriersdidnotisolatethehydrocarbons.

Aftertheannuluscementdidnoteffectivelyisolatethereservoir,amechanicalbarrierfailureenabledhydrocarboningresstothewellbore.Theinvestigationteamconsideredthreepossibilitiesforingress:

Ingressthroughtheshoetrackbarriers.

Ingressthroughthecasinghangersealassembly.

Ingressthroughtheproductioncasingandcomponents.

Availableevidenceandanalysisconductedbytheinvestigationteamleadsittoconcludethatinitialflowintothewellcamethroughtheshoetrackbarriers.


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Section4

TheShoeTrack

Threepossiblefailuremodesforthefloatcollarwereidentified:

Damagecausedbythehighloadconditionsrequiredtoestablishcirculation.

Failureofthefloatcollartoconvertduetoinsufficientflowrate.

Failureofthecheckvalvestoseal.

Atthetimethisreportwaswritten,theinvestigationteamhadnotdeterminedwhichofthesefailuremodesoccurred.

Conclusion

Basedonavailableevidence,hydrostaticpressurecalculations,OLGA wellflowmodelingandanalysisofdatafromtheMacondowellstatickillonAugust4,2010,hydrocarbonsenteredthecasingthroughtheshoetrack.Therefore,theshoetrackcementandthefloatcollarmusthavefailedtopreventthisingress.Theinvestigationteamhasnotestablishedwhetherthisfailurewasattributabletothedesignofthecement,contaminationofthecementbymudinthewellbore,comminglingofcementwithnitrogenduetonitrogenbreakoutfromthenitrifiedfoamcementslurry,swappingoftheshoetrackcementwiththemudintherathole(bottomofthewell)orsomecombinationofthesefactors.


Theshoetrackcomprisedafloatcollarwithtwocheckvalves,7in.casingandaportedreamershoe.(RefertoFigure2.)Ifhydrocarbonsbreachedtheannuluscementbarrier,ingresstothecasingshouldhavebeenpreventedbythecementintheshoetrackandthecheckvalvesinthefloatcollar.

TheentranceofinitialinfluxandflowthroughtheshoewasconfirmedbyextensiveOLGA wellflowmodelingofwellboreflowdynamicsandcomparisontopressuresandflowsobservedintherealtimedata.

Theinvestigationteamidentifiedthefollowingpossiblefailuremodesthatmayhavecontributedtotheshoetrackcementsfailuretopreventhydrocarboningress:

Contaminationoftheshoetrackcementbynitrogen

breakoutfromthenitrifiedfoamcement.(RefertoKeyFinding1.)

Contaminationoftheshoetrackcementbythemud

inthewellbore.

Inadequatedesignoftheshoetrackcement.

Swappingoftheshoetrackcementwiththemudin

therathole(bottomofthehole).

Acombinationofthesefactors.

Figure2.ShoeTrackBarriers.

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TheCasingHangerSealAssembly

Thecasinghangersealassemblywasrunandinstalledaccordingtotheinstallationprocedure,andthepositivepressuretestverifiedintegrityoftheseal.Atthetimeoftheaccident,thesealassemblywasnotyetmechanicallylockedtothewellheadhousing.

Inthisscenario,engineeringanalysisidentifiesthatitispossibleforthesealassemblytobeupliftedifsufficientforceisapplied.Upliftforcesapproached(ifthecasingwassecuredbycement),butdidnotreach,loadssufficienttounseatthesealsduringthenegativepressuretest.However,theanalysisindicatesthatwithsustainedflowfromthereservoir,thetemperatureofthecasingstringwouldhaverisen,therebyaddingtheupliftforceresultingfromthermalelongationofthepipe.Inthiscase,itisplausiblethatthesealassemblycouldhaveliftedandanadditionalflowpathcouldhavebeenestablishedafterthewellhadbeenflowingforasustainedperiod.

Conclusion

Theinvestigationteamhasconcludedthatinitialflowintothewellborewasthroughtheshoetrack,notthroughthecasinghangersealassembly.Thissupportstheconclusionthattheupliftforcesduringthenegativepressuretestdidnotunseatthesealassembly.Withnolockingmechanisminstalled,thermalstressescausedbysustainedhydrocarbonflowfromthereservoirthroughtheshoetrackmayhavesubsequentlyopenedaflowpaththroughthesealassembly.

TheProductionCasingandComponents

Theproductioncasingconsistedofacasinghanger,a9 /8in.productioncasing,a9 /8in.x7in.crossoverjointanda7in.productioncasing.Theinvestigationteamreviewedmanufacturingdata,inspectionreports,installationreports,casingrunningoperationsandpositivepressureintegritytests.Acasingdesignreviewwasconductedusingtheactualwellboreconditions.

Conclusion

Theinvestigationteamconcludesthattheproductioncasingandcomponentsmetalltherequireddesignconditionsandthatitishighlyunlikelythatacasingfailuremodecontributedtothelossofwellcontrol.

KeyFinding3.Thenegativepressuretestwasacceptedalthoughwellintegrityhadnotbeenestablished.

Approximately10 /2hoursafterthecompletionofthecementjob,thepositivepressureintegritytestcommenced.Followingsuccessfulcompletionofthepositivepressuretestto2,700psi,thenegativepressuretestwasconducted.


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Section4

Theobjectiveofthenegativepressuretestwastotesttheabilityofthemechanicalbarriers(shoetrack,casinghangersealassemblyandproductioncasing)towithstandthepressuredifferentialsthatwouldoccurduringsubsequentoperations:thereductionofhydrostaticheadtoseawateranddisconnectionoftheBOPandriser.

Theinvestigationteamconcludesthatthenegativepressuretestresultsindicatedthatwellintegrityhadnotbeenestablished.Thissituationwasnotrecognizedatthetimeofthetest,therefore,remedialstepswerenottaken.

Duringthenegativepressuretest,thewellwasplacedinanunderbalancedstatewhenhydrostaticpressureinthewellborewasreducedbelowreservoirpressure.

Toprepareforthistest,mudintheboostline,chokeline,killline,drillpipeandupperpartoftheproductioncasingwasdisplacedtoseawater.Toprovideseparationbetweenthemudandtheseawaterinthecasing,aspacerwaspumpeddownthedrillpipeaheadoftheseawater.

Withtheheavierfluidsinposition,theannularpreventerwasshuttoisolatethehydrostaticheadofthefluidsintheriserfromthewell.Atthistime,theannularpreventerdidnotsealaroundthedrillpipe,resultinginheavyspacerleakingdownpasttheannularpreventer.Afteradjustmentoftheregulatorhydraulicpressurefortheannularpreventer,aneffectivesealwasestablished.Theresidualpressureof1,260psiinthedrillpipewasbledofffromthewell.Accordingtowitnessaccounts,15bblsoffluidreturnsweretaken.Theinvestigationteamsanalysisindicatesthatapproximately3.5bblsshouldhavebeenexpected.Thisexcessflowfromthedrillpipe,withthewellinanunderbalancedcondition,shouldhaveindicatedtotherigcrewacommunicationflowpathwiththereservoirthroughfailedbarriers.

TheBPMacondowellteamprovidedbroadoperationalguidelinesforthenegativepressuretest.Therigcrewandwellsiteleaderwereexpectedtoknowhowtoperformthetest.Therigcrewbeganthenegativepressuretestbymonitoringthedrillpipeflow.Accordingtowitnessaccounts,thiswastherigcrewspreferredpractice.However,theApplicationforPermittoModify(APM)toMMSfortheMacondowelltemporaryabandonmentstipulatedthatthenegativepressuretestshouldbeconductedbymonitoringthekillline.Thewellsiteleadernoticedthediscrepancyandafteradiscussionwiththerigcrew,preparationsforcontinuingthenegativepressuretestweremadebybleedingthekillline.Accordingtowitnessaccounts,between3bblsand15bblsofseawaterflowedfromthekillline,whichwasthenshutin.

From18:00hoursto18:35hours,thedrillpipepressureincreasedfromapproximately50psito1,400psi.Toresumethenegativepressuretest,thekilllinewasfilledandthenopened,0.2bblsflowed,andnofurtherflowwasobservedfromthekilllineduringa30minuteperiodofmonitoring.Thedrillpipepressurewasconstantat1,400psi.


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Figure3.PossibleMovementofSpacerintotheKillLine.

Thispressureof1,400psionthedrillpipewasmisinterpretedbytherigcrewandthewellsiteleaders.Accordingtowitnessaccounts,thetoolpusherproposedthatthepressureonthedrillpipewascausedbyaphenomenonreferredtoasannularcompressionorbladdereffect.Thetoolpusheranddrillerstatedthattheyhadpreviouslyobservedthisphenomenon.Afterdiscussingthisconcept,therigcrewandthewellsiteleadersacceptedtheexplanation.Theinvestigationteamcouldfindnoevidencethatthispressureeffectexists.

Theinvestigationteamhasidentifiedtwopossiblereasonsthatflowdidnotexitthekillline:

Thekilllinemayhavebeenpluggedwithsolidsfromthespacer.(RefertoFigure3.)

Thesystemmaynothavebeenlinedupcorrectlyavalvemayhavebeeninadvertentlyleftclosed.40 DeepwaterHorizonAccidentInvestigationReport


Section4

Conclusions

Theinvestigationteamconcludesthatthelackofflowfromwhatwasbelievedtobeanopenkillline,coupledwiththeerroneousexplanationforthe1,400psionthedrillpipe,ledthewellsiteleadersandtherigcrewtotheincorrectviewthatthenegativepressuretestwassuccessfulandthatwellintegritywasestablished.Thewellsiteleadersandtherigcrewmaintainedthisviewdespitethecontradictoryinformationof1,400psionthedrillpipeconnectedthroughthewellboretothenonflowingkilllinewith0psi.

Theguidelinesforthenegativepressuretest,acriticalactivity,didnotprovidedetailedstepsanddidnotspecifyexpectedbleedvolumesorsuccess/failurecriteria.Therefore,effectiveperformanceofthetestplacedahigherrelianceonthecompetencyandleadershipskillsoftheBPandTransoceanrigleaders.

KeyFinding4.Influxwasnotrecognizeduntilhydrocarbonswereintheriser.

AfundamentalrequirementforsafeDrillingandCompletions(D&C)operationsistomaintaincontrolofthewellandpreventinfluxofhydrocarbons.Duringallphasesoftheseoperations,fluidreturns,pressureandflowindicatorsshouldbecontinuouslymonitoredtodetectinfluxintothewellassoonaspossible.OntheMacondowell,therigcrewapparentlydidnotrecognizesignificantindicationsofhydrocarboninfluxduringthedisplacementoftherisertoseawater.

Followingthenegativepressuretest,theannularpreventerwasopened,andthehydrostaticheadoffluidintheriserreturnedthewelltoanoverbalancedstate.Therigcrewbeganthedisplacementofthemudintherisertoseawater.Asthemudwasdisplacedfromtheriser,thepressureatthebottomofthewellboredecreased.AnalysisofOLGA wellflowmodelingindicatesthatthewellbecameunderbalancedagainatapproximately20:52hours,andhydrocarboninfluxresumed.Therateofinfluxwouldhavegraduallyincreasedasthewellbecamemoreunderbalancedwithheavierfluidsbeingdisplacedbylighterseawaterandhydrocarbons.Flowincreasefromthewellwasdiscernableintherealtimedataafterapproximately20:58hours.

Theinvestigationteamsanalysisoffluidvolumesshowsanapproximategainof39bblsby21:08hours.Nowellcontrolactionsweretakenatthattime,indicatingthatthisfluidgainwasnotdetected.

Simultaneousendofwellactivitieswereoccurringandmayhavedistractedtherigcrewandmudloggersfrommonitoringthewell.Theseactivitiesincludedpreparingforthenextoperation(settingacementpluginthecasing),bleedingofftherisertensionersandtransferringmudtothesupplyvesselM/VDamonBankston.



TheinvestigationteamdidnotfindevidencethateithertheTransoceanrigcrewortheSperrySunmudloggersmonitoredthepitsfrom13:28hours(whentheoffloadingtothesupplyvesselbegan)to21:10hours(whenreturnswereroutedoverboard).

At21:08hours,thespacerreachedthetopoftheriser,andtherigcrewshutdownpumpingoperationstocompleteasheentestpriortodischargingthespacertothesea.Duringthesheentest,therigcrewconfiguredtheflowpathtoroutethespaceroverboard.Thisflowpathbypassedthemudloggersflowmeterandthemudpitstherefore,fluidflowcouldnolongerbemonitoredatthemudloggersconsole.However,drillpipepressureshouldhavebeenobservableatthemudloggersconsole,andflowanddrillpipepressureshouldhavebeenobservableatthedrillersconsole.

Duringthesheentestbetween21:08hoursand21:14hours,themudpumpswereshutdown,andrealtimedatashowedflowcontinuinganddrillpipepressureincreasingby246psi.Therigcrewapparentlydidnotrecognizetheseindicationsofflow,anddisplacementwasrecommenced.

AnalysisofOLGA wellflowmodelingsuggeststhatby21:30hourstherewouldhavebeenapproximately300bblsofhydrocarboninfluxinthewell.

At21:31hours,themudpumpswereshutdown.Witnessaccountsindicatedthataconversationbetweenthetoolpusherandthedrillertookplaceontherigfloorregardingdifferentialpressure.Between21:31hoursand21:34hours,thepressureonthedrillpipeincreasedbyapproximately560psi.

Analysissuggeststhatbetween21:31hoursand21:41hours,withthepumpsshutdown,thewellwasunloadingatanaveragerateofapproximately60bpmto70bpm.Analysisalsosuggeststhathydrocarbonsdidnotentertheriseruntilapproximately21:38hours.(RefertoFigure4.)Theinvestigationteambelievesthatthefirstwellcontrolactiontakenbytherigcrewwasat21:41hours.

Conclusions

Analysisindicatesthatthefirstindicationsofflowfromthewellcouldbeseenintherealtimedataafter20:58hours.Therigcrewandmudloggerseitherdidnotobserveordidnotrecognizeindicationsofflowuntilafterhydrocarbonsenteredtheriseratapproximately21:38hours.Thefirstwellcontrolresponselikelyoccurredat21:41hours.

TheTransoceanWellControlHandbookstatedthatthewellwastobemonitoredatalltimes.However,thepolicydidnotspecifyhowtomonitorthewellduringinflowtesting,cleanuporotherendofwellactivities.



Section4

Figure4.HydrocarbonsEnteringtheRiser.

KeyFinding5.Wellcontrolresponseactionsfailedtoregaincontrolofthewell.

Whenwellinfluxoccurs,rapidresponseiscritical.Therigcrewneedseffectiveproceduresandmusteffectivelyimplementthemtomaintaincontroloverdeterioratingconditionsinthewell.

Keymembersoftherigcrewneedtobetrainedanddemonstratecompetency.Theiractionsneedtobecorrectandimmediate,especiallywhencontrolofthewellhasbeenlostandtheflowofhydrocarbonshasescalated.



WitnessaccountsandrealtimedatawerecombinedwithOLGA wellflowmodelingtoinferwhichactionsweretakenbytherigcrewpriortotheexplosion.Althoughitisuncertainwhattherigcrewactionswere,separateindicationsandanalysessupportthefollowingevents.

Atapproximately21:40hours,witnessaccountsindicatedthatmudfloweduncontrolledontotherigfloor.RealtimedataandfurtherwitnessaccountssuggestthattherigcrewattemptedtocontrolthewellbyclosinganannularpreventerintheBOPatapproximately21:41hours.Thisfirstactionwastoolatetopreventthereleaseofhydrocarbons,whichwerealreadyintheriser.Modelingsuggeststhattheannularpreventerdidnotfullysealaroundthedrillpipe,allowinghydrocarbonstocontinueenteringtheriser.

Therigcrewdivertedhydrocarbonscomingthroughtherisertothemudgasseparator(MGS),whichwasquicklyoverwhelmedandfailedtocontrolthehydrocarbonsexitingtheriser.Thealternativeoptionofdiversionoverboardthroughthe14in.starboarddiverterlinedidnotappeartohavebeenchosenthisactionwouldprobablyhaveventedthemajorityofthegassafelyoverboard.

Realtimedataindicatedthatat21:47hours,drillpipepressurerosefrom1,200psito5,730psiwithinoneminute.Thiswaslikelycausedbytheclosureofoneortwovariableborerams(VBRs),whichsealedtheannulus.Atapproximately21:49hours,rigpowerandrealtimedatawerelost.Witnessesrecallanexplosionontherig,followedcloselybyalargerexplosion.Aftertheexplosions,firescontinuedontherig.

Thesubseasupervisorattemptedtoactivatetheemergencydisconnectsequence(EDS)sometimeaftertheexplosion.ThiswouldhavesealedthewellanddisconnectedtheriserfromtheBOPstack.Therewerenoindicationsthatthesequenceactivated.

Conclusions

Noapparentwellcontrolactionsweretakenuntilhydrocarbonswereintheriser.Theactionsthatweretakenafterthatdidnotcontrolthewell.

Anannularpreventerwaslikelyactivatedat21:41hours,anditclosedaroundthedrillpipe.Itfailedtosealtheannulusforapproximatelyfiveminutes,allowingfurtherflowofhydrocarbonsintotheriseruntiltheannuluswassealedat21:47hours,likelybytheclosureofaVBR.

Thediversionoffluidsoverboard,ratherthantotheMGS,mayhavegiventherigcrewmoretimetorespondandmayhavereducedtheconsequencesoftheaccident.

Transoceansshutinprotocolsdidnotfullyaddresshowtorespondinhighflowemergencysituationsafterwellcontrolhasbeenlost.Wellcontrolactionstakenpriortotheexplosionsuggesttherigcrewwasnotsufficientlypreparedtomanageanescalatingwellcontrolsituation.



Section4

Figure5.MudGasSeparator.

KeyFinding6.Diversiontothemudgasseparatorresultedingasventingontotherig.

TheMGSremovesonlysmallamountsofgasentrainedinthemud.Onceseparated,thegasisventedtotheatmosphereatasafelocation.WhentherigcrewdivertedhighflowtotheMGS,thesystemwasoverwhelmed.

Whenanannularpreventerappearedtobeactivatedat21:41hours,thewellwasflowingatahighrate,andhydrocarbonfluidswereabovetheBOPAsthehydrocarbongasexpanded,theflowofgas,oil,mudandwatertothesurfacecontinuedatanincreasingrate.

Theinvestigationteamconcludesthat,atapproximately21:41hours,therigcrewdivertedtheflowofhydrocarbonstotheMGS.(RefertoFigure5.)TheMGSisalowpressuresystem,anditsdesignlimitswouldhavebeenexceededbytheexpandingandacceleratinghydrocarbonflow.Themain12in.gasoutletventfromtheMGSwasgooseneckedatitsterminusontopofthederrick,anditventedgasdownontotherig.SeveralotherflowlinescomingfromtheMGSvesseldirectedgasontotherigandpotentiallyintoconfinedspacesunderthedeck.



Theinvestigationteamdeterminedthatlargeareasoftherigwereenvelopedinaflammablemixturewithinminutesofgasarrivingatthesurface.

Conclusion

ThedesignoftheMGSsystemallowedtheriserfluidstobedivertedtotheMGSvesselwhenthewellwasinahighflowcondition.WhentheMGSwasselected,hydrocarbonswereventeddirectlyontotherigthroughthe12in.gooseneckedventexitingtheMGS,andotherflowlinesdirectedgasbackontotherig.

KeyFinding7.Thefireandgassystemdidnotpreventhydrocarbonignition.

Foroperatingenvironmentswherehazardoussubstancescouldbepresent,secondarylevelsofprotectivesystemsarenormallypartofthedesignphilosophy.OnDeepwaterHorizon,thesecondarylevelsofprotectivesystemsincludedafireandgassystemandtheelectricalclassificationofcertainareasoftherig.

Thefireandgassystemdetectshydrocarbongasandinitiateswarningalarmswhenacceptablelimitsareexceeded.Forsomealarms,anautomatedfunctioninitiateswhenhydrocarbongasisdetectedbeyondacceptablelimits.Thisautomatedfunctionprimarilypreventsgasingresstovulnerablelocationsthroughtheheating,ventilationandairconditioning(HVAC)system.Whengasisdetected,thefireandgassystemclosesthedampersandshutsofftheventilationfans.

Areasontherigareelectricallyclassified,basedontheprobabilityofthepresenceofhydrocarbons.Equipmentinelectricallyclassifiedareasmustmeetdesigncodecriteriathatreducethepossibilityofprovidinganignitionsource.

Becauseofthelowprobabilityofhydrocarbonsbeingpresentbeforeawellproduces,onlyasmallareaofDeepwaterHorizonwaselectricallyclassified.Thetwomainelectricallyclassifiedareaswerewithintherigfloorandunderthedeck,wherethemudreturningfromthewellcouldconveysomeresidualhydrocarbons.Ifaflammablemixturemigratedbeyondtheseareas,thepotentialforignitionwouldbehigher.

DeepwaterHorizonengineroomHVACfansanddamperswerenotdesignedtotripautomaticallyupongasdetectionmanualactivationwasrequired.Thisdesignwasprobablyselectedsothatfalsegasdetectiontripswouldnotinterruptthepowersupplytothethrusters,whichkeepthedynamicallypositionedrigonstation.TheHVACsystemlikelytransferredagasrichmixtureintotheenginerooms,causingatleastoneenginetooverspeed,creatingapotentialsourceforignition.

Theinformationusedtocompletetheanalysisisbasedonpre2001documentationtherefore,someoftheequipmentdetailsandsystemdesignsmayhavechanged.However,intheviewoftheinvestigationteam,itisunlikelythatanysuchdifferenceswouldsignificantlyaffecttheconclusionsdrawn.



Section4

Conclusion

Thefireandgassystemdidnotpreventreleasedhydrocarbonsfromreachingpotentialignitionsources.

KeyFinding8.TheBOPemergencymodedidnotsealthewell.

NoneoftheemergencymethodsavailableforoperatingtheBOPweresuccessfulinisolatingthewellbore.Thedifferentmethodsavailablewerenotfullyindependenttherefore,singlefailurescouldaffectmorethanoneemergencymethodofBOPoperation.Ultimately,theonlywaytoisolatethewellattheBOPwastocloseasinglecomponent,theblindshearram(BSR)thatramhadtoshearthedrillpipeandsealthewellbore.

EmergencyDisconnectSequence

Toisolatethewellaftertheexplosion,thesubseasupervisorattemptedtooperatetheEDSthatwouldclosetheBSR,sealingthewellbore,anddisconnectthelowermarineriserpackage(LMRP).TheEDSrequiredacommunicationsignaltobesentthroughoneoftwomultiplex(MUX)cablesroutedthroughthemoonpool,whichwouldhavebeenaffectedbytheexplosionsandfire.WitnessaccountsindicatedthatanattemptwasmadetoactivatetheEDSapproximately7minutesaftertheinitialexplosion.TheLMRPdidnotdisconnect,andhydrocarbonscontinuedtoflow,indicatingthattheBSRdidnotseal.

Conclusion

TheexplosionsandfireverylikelydamagedtheMUXcables,disablingtheEDSmeansofclosingtheBSR.

AutomaticModeFunction

Theautomaticmodefunction(AMF)oftheBOPactivatestheBSRtoshearthedrillpipeandsealthewellboreintheeventofcatastrophicfailureofthemarineriser.TwoindependentcontrolpodsontheBOPinitiatetheAMFsequencetoclosetheBSRifspecificconditionsaremet(i.e.,whenelectricalpower,communicationsandhydraulicpowerarealllosttobothcontrolpods).Accordingtowitnessaccounts,duringtheattempttoactivatetheEDS,therewasalowaccumulatoralarmontheBOPcontrolpanel,indicatinglossofhydraulicsupplypressure.TheAMFconditionswereverylikelymetuponthedamagetotheMUXcablesandlossofhydraulicsupplypressureaftertheexplosion.

TheAMFrequiresatleastoneoperationalcontrolpodtoinitiateandcompletethesequence.BoththeblueandyellowcontrolpodsfromDeepwaterHorizonBOPwereretrievedaftertheaccident,andtheirAMFfunctionalitywastested.Insufficientchargewasdiscoveredonthe27voltAMFbatterybankinthebluepod,andafailedsolenoidvalve103wasdiscoveredintheyellowpod.Iftheseconditionsexistedatthetimeoftheaccident,neitherpodwouldhavebeencapableofcompletinganAMFsequence.



Conclusion

TheAMFinitiationconditionswereverylikelymetsoonafterthefirstexplosion,buttheAMFsequenceverylikelycouldnothavebeencompletedbyeithercontrolpod,duetothefailedsolenoidvalve103intheyellowpodandaninsufficientchargeonthe27voltAMFbatterybankinthebluepod.

InterventionbyRemotelyOperatedVehicle

TheautoshearfunctionisdesignedtoactivatetheBSRuponinadvertentdisconnectionoftheLMRP.EvidenceindicatedthattheBSRclosed33hoursaftertheexplosion,whenaremotelyoperatedvehicle(ROV)activatedtheautoshearfunction.

ThoughtheBSRappearedtohavebeenclosed,theinvestigationteamhasnotbeenabletodeterminewhyitfailedtosealthewell.Potentialcausesexaminedbytheinvestigationteamincluded:

SealfailureduetotheprevailingflowconditionintheBOP

Insufficienthydraulicpowertoshearthedrillpipeandsealthewellbore.

NonshearablepipeordebrisacrosstheBSR.

BOPMaintenanceandTesting

AreviewofBOPmaintenanceandtestingrecordsprovidedbyTransoceanindicatedinstancesofanineffectivemaintenancemanagementsystemforDeepwaterHorizon.Exampleswere:

InDecember2007,thebatteriesinthebluepodwerefullydepletedwhentheBOPwasbroughttothesurface.

TherewerenoindicationsthattheAMFandROVinterventionsystemsweretestedatthesurface,asrequiredby

Transoceantestingpolicy,priortosubseadeploymentontheMacondowell.

Cameronreportedthatanonoriginalequipmentmanufacturer(nonOEM)partwasfoundonsolenoidvalve103

duringtheyellowpodexamination.

Thediagnosticsystemsdidnotappeartohavebeenutilizedeffectivelyinallcasestoidentifyandremedydefectsincriticalcomponents.SolenoidvalvecoilfaultsandhydraulicsystemleaksprobablyexistedontheBOPpriortotheaccident.

Conclusion

TheBOPmaintenancerecordswerenotaccuratelyreportedinthemaintenancemanagementsystem.TheconditionofcriticalcomponentsintheyellowandbluepodsandtheuseofanonOEMpart,whichwerediscoveredafterthepodswererecovered,suggestthelackofarobustTransoceanmaintenancemanagementsystemforDeepwaterHorizonBOP.


Section5.DeepwaterHorizonAccidentAnalyses

Section5

Section5.DeepwaterHorizonAccidentAnalysesIntroduction

Theinvestigationprocess,includingtheidentificationofcriticalfactors,wasoutlinedinSection1.ScopeoftheInvestigationofthisreport.Theteamexaminedpotentialcausalorcontributoryfactorsforeachcriticalfactor.Theanalyses,5A5D,containkeyfindingsandconclusionsthatareassociatedwiththecriticalfactors.TherecommendationsforallfourcriticalfactorsaresetoutinSection6.InvestigationRecommendationsofthisreport.

Thefourcriticalfactorsandtheirassociatedkeyfindingsare:

Analysis5A.CriticalFactor:WellIntegrityWasNotEstablishedorFailed


KeyFinding2.Theshoetrackbarriersdidnotisolatethehydrocarbons.

Analysis5B.CriticalFactor:HydrocarbonsEnteredtheWellUndetectedandWellControlWasLost

KeyFinding3.Thenegativepressuretestwasacceptedalthoughwellintegrityhadnotbeenestablished.

KeyFinding4.Influxwasnotrecognizeduntilhydrocarbonswereintheriser.

KeyFinding5.Wellcontrolresponseactionsfailedtoregaincontrolofthewell.

Analysis5C.CriticalFactor:HydrocarbonsIgnitedonDeepwaterHorizon

KeyFinding6.Diversiontothemudgasseparatorresultedingasventingontotherig.

KeyFinding7.Thefireandgassystemdidnotpreventhydrocarbonignition.

Analysis5D.CriticalFactor:TheBlowoutPreventerDidNotSealtheWell

KeyFinding8.TheBOPemergencymodedidnotsealthewell.DeepwaterHorizonAccidentInvestigationReport 49

Section5.DeepwaterHorizonAccidentAnalysesAsnotedinSection4.OverviewofDeepwaterHorizonAccidentAnalysesofthisreport,theBPMacondowellteammeansBPsHoustonbasedwellteamthatworkedontheMacondowell,excludingBPscementingservicesprovider(Halliburton)andalsoexcludingtheBPwellsiteleadersaboardDeepwaterHorizon.

TherigcrewmeansTransoceansrigcrewleadersaboardDeepwaterHorizon(seniortoolpusher,toolpushers,drillersandassistantdrillers)collectively,ortotheindividualsinoneormoreoftheseroles,andincludespersonnelactingattheirdirection.ReferencestotheBPwellsiteleadersaretothedayandnightwellsiteleadersaboardDeepwaterHorizon.

ReferencestomudloggersaretotheHalliburtonSperrySunmudloggersaboardDeepwaterHorizon.ReferencestocementersaretoHalliburtonscementoperatorsaboardDeepwaterHorizon.MlSWACOprovidedthemudengineers.50 DeepwaterHorizonAccidentInvestigationReport

Analysis5A.WellIntegrityWasNotEstablishedorFailed

Analysis5A

Analysis5A.WellIntegrityWasNotEstablishedorFailed1Introduction

Thelossofwellintegritywascausedbyafailureoftheannuluscementbarrierthatallowedhydrocarbonstoflowintothewellboreannulus.Failureofoneormoreofthemechanicalbarriers(i.e.,theshoetrack,thecasinghangersealassemblyortheproductioncasingandcomponents)allowedhydrocarbonstoflowtothesurface.

Thisanalysisfocusesonthedesignandinstallationoftheannuluscementandmechanicalbarriers.

Throughtheinvestigationteamsreviewandanalysisoftheavailableinformation,theteamdeterminedthefollowingkeyfindings:


KeyFinding2.Theshoetrackbarriersdidnotisolatethehydrocarbons.DeepwaterHorizonAccidentInvestigationReport 51

Documents

Deepwater Horizon Accident Investigation Report