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A Signal Detection Model to Interpret Safety Tests in Offshore Oil Drilling: A Case Study to Analyze Negative Pressure Test (NPT)
Interpretation in Offshore Drilling
MaryamTabibzadeh,PhDa
DetlofvonWinterfeldt,PhDb
NajmedinMeshkati,PhDb
aDepartmentofManufacturingSystemsEngineering&ManagementCaliforniaStateUniversity,Northridge(CSUN)
bDanielJ.EpsteinDepartmentofIndustrialandSystemsEngineeringUniversityofSouthernCalifornia(USC)
PSAM14,September2018
Outline
! VitalNeedtoOffshoreandDeep-waterDrilling! OffshoreDrillingasaHigh-RiskIndustry! WhyRiskAnalysisPractices?
! AnalyzingHumanandOrganizationalFactors
! ConcentratingonNegativePressureTest! SignalDetectionModelParametricEquations
! ACaseStudytoQuantifytheSignalDetectionModel
! SensitivityAnalysis! SummaryandConclusion
2
OffshoreDrilling:AVitalSourceofOilSupply
(EIA,2016)
3
WellsdrilledintheGulfofMexicobywaterdepthfrom1940to2010(ReporttothePresident,2011,page41)
WhyDeep-waterDrillingIsNoteworthy??
4
OffshoreDrilling&Production:High-RiskIndustry
Offshoredrillingisoneofthehigh-riskindustrieswith“tightlycoupled”and“interactivelycomplex”
operations.
PiperAlpha,NorthSea,1988
Fatalities:167Cost:$3.4Billion
Petrobras36,Brazil,2001
Fatalities:11Cost:$350Million
BPDWH,GOM,2010
Fatalities:11Cost:$40-$50Billion
5
CaseStudy:DeepwaterHorizon(DWH)Accident
! April20,2010! 11peopledied,17injured! 5millionbarrelsofspilled
oil~682000tonsin87days! Hugeenvironmental
damages,influencingsmalllocalbusinesses,andtourism
! Billionsofdollarsofcost
6
7
DWHWasDuetoaSeriesofTechnicalFailures
! Welldesign:• Narrowdrillingmargin
• Longstringinsteadofaliner
! Cementing• Cementmaterial
• Numberofcentralizers
! NegativePressureTest(NPT)misinterpretation! BlowoutPreventer(BOP)failure
! Mud-gasseparator! Alarmsystems
8
HigherRiskofDeep-waterDrilling
! Morecomplexcasingdesigns! Higherpressure! Moredifficultformations! Higheruncertaintyofseismology! Higherchallengesinaccessingthesiteandwellhead! Loweravailabilityofexperiencedpersonnel
9
WhyRiskAnalysisPractices?
“Governmentagenciesthatregulateoffshoreactivityshouldreorienttheirregulatoryapproachesto
integratemoresophisticatedriskassessmentandriskmanagementpracticesintotheiroversightofenergy
developersoperatingoffshore.”
ReporttothePresident,NationalCommissionontheBPDWHOilSpill,2011,Page251
Trade-offbetweenhighriskofdeep-wateroffshoredrillingandtherisingdependenceofoilandgassupplytoit
10
WhyNPT?
NPT
Manageablescopeofwork
Theprimarywayofascertainingwell
integrityinoffshoredrilling
NPTmisinterpretation
wasamajorcontributingcauseoftheDWHaccident
NPT:NegativePressureTest11
SignificanceofNegativePressureTest
“Ifthenegativepressuretesthadbeencorrectlyinterpreted,theblowout,explosion,fire,andoilspillwouldhavebeenaverted.Consequently,theCourtfindsthatthemisinterpretationofthenegativepressuretestwasasubstantialcauseoftheblowout,explosion,fire,andoilspill.”
Findingsoffactandconclusionsoflawphaseonetrial,OilSpillbytheOilRig“DeepwaterHorizon”intheGOM,
TheUnitedStatesDistrictCourtfortheEasternDistrictofLouisiana,September2014,Page65
12
Dissecting“Standard”(Shou
ldbeDone)Negative
PressureTest
13
DWHcrewpracticeofthe
negativepressuretest
4pm
4:53pm4:58pm
5:10pm
5:26pm
5:53pm6:40pm
4pm
4:53pm
4:58pm
5:10pm
5:26pm
5:53pm
6:40pm
WhyHumanandOrganizationalFactors(HOFs)?
Long-termstudy(1988-2005)ofmorethan600welldocumentedmajorfailuresinoffshorestructures:approximately80%ofthemajorfailureswereduetoHOFs
LordCulleninthe25thanniversaryofPiperAlpha(2013):“asIdugdowntothebackgroundofwhathappened,Idiscovereditwasnotjustamatteroftechnicalorhumanfailure.Asisoftenthecase,suchfailuresareindicatorsofunderlying
weaknessesinmanagementofsafety.”
ThereisacriticalgapintheliteratureregardingtheexistenceofenoughriskassessmentapproachesanalyzingthecrucialroleofHOFs
ChiefCounsel’sreport(2011)ontheDWH:“whattheinvestigationmakesclear,aboveallelse,isthatmanagementfailures,notmechanicalfailings,werethe
ultimatesourceofthedisaster.”
15
ConceptualRiskAnalysisFrameworkforNPTMisinterpretation
OrganizationalFactors
Decisions/Actions
BasicEvents
16
ConceptualRiskAnalysisFrameworkforNPTMisinterpretation
ASnapshotoftheSignalDetectionModelforNPTInterpretation
! APLeak&WellLeak:Yes/No
! Targetvariable:Finitecontinuous
! Decisions/judgments:OK/NOTOK
18
Possibleflowpathsforhydrocarbon(Sourceofimage:ChiefCounsel’sReport,2011,page39)
LeakintheBOPannularpreventer(Sourceofimage:ChiefCounsel’sReport,2011,page154)
TwoVariablesAffectingourTargetVariable(PressureDeviation)
19
DecisionProcessesinSignalDetectionTheory
PhysicalWorld
SensoryProcesses
Inference&DecisionProcesses
ResponseBehavior
Signaldetectiontheoryanddecisionprocesses(GreenandSwets,1974;DeplanckeandSparrow,2014)
20
SignalDetectionTheory
Hit
FalseAlarmMiss
CorrectRejection
Noise Signal
21
StatesoftheSystem
Classificationofstates:APLeak,WellLeak
! Normalsate:h0:NN
! Abnormalstates:h1:YNh2:NYh3:YY
! P(h0)=P(NN)! P(h1)=P(YN)! P(h2)=P(NY)! P(h3)=P(YY)
22
SignalDetectionModelNotations
Probabilityofeachstatefor(APLeak,WellLeak):
P(APLeak,WellLeak)=P(APLeak)*P(WellLeak)
e.g.P(NN)=P(APLeak=N)*P(WellLeak=N)
23
SignalDetectionModelforNPTInterpretation
Observeavalueforpressuredeviationfromthesystem;AP-EP=d
Whatisthejudgment?Say“H0”(OK)or“H1”(NOTOK)
Say“H0“orOKiff:
:LikelihoodRatio
:Prioroddforstate“hi”comparingto“h0”
:Conditionalprobabilityofthepressuredeviationknowingthatthestateis“hi”
Calculatethecut-offpointvalue“e”forthepressuredeviation:Judgmentis“H1”orNOTOKforanyobservedpressuremorethan“e”
Cij:Costofsaying“Hj”whenthestateis“hi”
SignalDetectionModelRequiredInputs
Thecut-offpointvaluedependsonthreemaininputs:
1) P(hi):Priorprobabilityofthestate“hi”;i=0,1,2,3
2) f(x|hi):Conditionalprobabilityofpressuredeviationforstate“hi”
3) Cij:Costofsaying“Hj”whilethestateis“hi”;i=0,1,2,3andj=0,1
25
ResultsofSignalDetectionModelAnalysis
! Cut-off point value for the above inequality knowing thevaluesforthemainthreeinputs:
e=247psi
! Foranyobservedpressurebuilt-upmorethan247psi:say“H1”orNOTOK
Howapressuredeviationashighas“1400psi”was
acceptedbytheDWHcrew?
26
TheCut-offPointIllustrationandMeaning
0
0.005
0.01
0.015
0.02
0.025
0.03
f(x|h0)
f(x|h2)
f(x|h1orh3)
Pressuredeviation(psi)
27
Bias1:UnderestimatingPriorProbabilityofAbnormalStates
00.10.20.30.40.50.60.70.80.91
Cut-offpoint"e"Vs.P(APLeak=Y)
Cut-offpoint"e"
P(APLeak=Y)
0100200300400500600700800900100011001200130014001500160017001800190020002100
00.20.40.60.81
Cut-offpoint"e"Vs.P(WellLeak=Y)
Cut-offpoint"e"
P(WellLeak=Y)
Bias1:UnderestimatingPriorProbabilityofAbnormalStates-Cont’d
Cut-offpoint"e"Vs.P(APLeak=Y)
Cut-offpoint"e"
P(APLeak=Y)
0
500
1000
1500
2000
2500
Cut-offpoint"e"Vs.P(WellLeak=Y)
Cut-offpoint"e"
P(WellLeak=Y)
RootCausesofBiases
Organizationalfactorsaretherootcontributingcausesofbiases:
! Economicpressure! Personnelmanagementissues! Issuesincommunicationandprocessingofuncertainties! Lackofanintegrated,informedmanagement
30
! There is aneed formore sophisticated riskanalysismethodologies to reducethehighriskofaccidentsandblowoutsinfutureoffshoredrilling.
! The developed methodology in this study is an attempt of utilizingsophisticatedriskanalysispractices,andthismethodologycanbegeneralizedtootherapplicationsaswell.
! Weproposedastructuredsignaldetectionmodelwithparametricequationsfor it in order to analyze critical decision making situations and involvedbiases.Thismodelcanbeusedindifferentsafety-criticalsystemssuchasoilandgasindustry,healthcare,transportationandfinancialsystems.
! Biases, such as underestimating the prior probability of abnormal states,affect rational decision making and increase the risk of a false negativesituationormisinterpretinganegativepressuretest.
! MisinterpretationofaconductedNPTcanmostlyoccurduetotheconfluenceofdifferentbiasesratherthanjustonespecificbias.
! Organizationalfactorsaretherootcausesofinvolveddecisionmakingbiases.
SummaryandConclusion
31
Acknowledgements
! Petroleumengineeringexperts:
" Mr.StanChristman,retiredExxonMobilexecutiveengineeringadvisor
" Mr.FredDupriest,retiredExxonMobilchiefdrillingengineerandlecturerattheTexasA&MUniversity
" Mr.RogerGatte,BPretiredwellssuperintendent" AretiredExxonMobilWorldwidedrillingmanager
32
Thankyou!
MaryamTabibzadeh,PhD
DepartmentofManufacturingSystemsEngineering&ManagementCaliforniaStateUniversity,Northridge(CSUN)
References• Aven,T.,Sklet,S.,andVinnem, J.E. (2006)“BarrierandOperationalRiskAnalysisofhydrocarbon
releases (BORA-Release); Part I: Method description”. Journal of Hazardous Materials, 137 (2):681-691
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• Bea,R.(2011)PersonalCommunication.UniversityofCaliforniaBerkeley,memberoftheNationalAcademyofEngineering,December6
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• BOEMRE Report (2011) “Report Regarding the Causes of the April 20, 2010 Macondo WellBlowout”. The Bureau of Ocean Energy Management, Regulation, and Enforcement (BOEMRE).September14
• BPreport(2010)“DeepwaterHorizonAccidentInvestigationReport”.BritishPetroleum
• Chief Counsel’s Report (2011) “Macondo, the Gulf oil disaster”. National Commission on the BPDeepwaterHorizonOilSpillandOffshoreDrilling
• Christman, S. A. (2013) Personal Communication, Retired ExxonMobil executive engineeringadvisor,December13
References• Deplancke, A. and Sparrow, L. (2014) “Signal Detection Theory”, Presentation file,
http://ureca.recherche.univ-lille3.fr/sparrow/TLDocs/cours1314/PPNSA_UE7_SDT_2012.pdf,Accessdate:February24,2014
• Dupriest,F. (2014a)PersonalCommunication,RetiredExxonMobilchiefdrillingengineer,LectureratTexasA&MUniversity,January18
• Garcia, J. A. (2013) Personal Communication, Retired ExxonMobil Worldwide Drilling Manager,November25
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• NAE/NRC Report (2011) “Macondo Well Deepwater Horizon Blowout: Lessons for ImprovingOffshoreDrillingSafety”.NationalAcademyofEngineeringandNationalResearchCouncil (NAE/NRC).TheNationalAcademiesPress,Washington,D.C.
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References• Perrow,C.(1984)“NormalAccidents:LivingwithHigh-RiskTechnologies”.BasicBooks,NewYork• Report to the President (2011) “Deep Water; the Gulf Oil Disaster and the Future of Offshore
Drilling”,NationalCommissionontheBPDeepwaterOilSpillandOffshoreDrilling• Skogdalen, J.E.andVinnem, J.E. (2012) “QuantitativeRiskAnalysisofOilandGasDrilling,Using
DeepwaterHorizonasaCaseStudy”.ReliabilityEngineeringandSystemSafety.100:58-66
• SINTEFexecutivesummary(2011)“TheDeepwaterHorizonAccident:Causes,LearningPointsandRecommendationsfortheNorwegianContinentalShelf”
• Tabibzadeh,M.(2014)“ARiskAnalysisMethodologytoAddressHumanandOrganizationalFactorsin Offshore Drilling Safety:With an Emphasis on Negative Pressure Test”, Doctor of PhilosophyDissertation,UniversityofSouthernCalifornia,LosAngeles,California,May2014
• Tabibzadeh,M.andMeshkati,N.(2014)“LearningfromtheBPDeepwaterHorizonAccident:RiskAnalysis of Human andOrganizational Factors in Negative Pressure Test”, Environment SystemsandDecisions,34(2):194-207,http://dx.doi.org/10.1007/s10669-014-9497-2
ProjectionofDeep&UltraDeep-waterDrilling
Librafield;Brazil:
! OffRiodeJaneirocoast! 7000meters~23000ftdepth! 8-12billionbarrelsofoil
Economist,October26,2013
SignificanceofNegativePressureTestSlide38
TheHonorableDr.DonaldWinterinhisinterviewwithPlatts:BPDeepwaterHorizon
wasprecipitated“notbyapieceofhardware,butbythedecisiontoproceedtotemporaryabandonmentinspiteofthefactthatthenegativepressuretesthadnotbeenpassed”(November4,2013).
ConceptualRiskAnalysisFrameworkforNPTMisinterpretation
16
Observationsfromthe3-LayerConceptualModel
! Organizationalfactorsarerootcausesofaccumulatederrorsandquestionabledecisions/actionsmadebypersonnelandmanagement.
! Thefirstthreeorganizationalfactorswiththehighestinfluence:
1. PersonnelManagementissues2. Issuesincommunicationandprocessingofuncertainties3. Economicpressure
ConditionalProbabilitiesandWellCharacteristics
! Specificationsandrangeofeachconditionalprobabilitydistributionforthetargetvariableineachstatedependsontheanalyzedwellcharacteristics,suchasdepthofdrilling,depthofdisplacement,formationcharacteristics,andtypeandamountofusedfluids(e.g.oilbasedmudvs.waterbasedmud,spacer)
! ConsideredvaluesforeachconditionalprobabilityarebasedoncharacteristicsofawellliketheMacondo.
Forexample:Whenthereisleakingintheannularpreventer(state“h1”),foracaseliketheDWH,basedonthe421bblsofusedspacer,intheworstcase,thebottomofthespacercanbeat8367ftandthetopatabout3000ft.
ParametricDecisionMakingEquations-1
Say“H0“orOKiff:
1.1
2.1
ExpectedvalueforsayingorjudgingHiafterobservingthevalue“d”fromthesystemforourtargetvariable
ParametricDecisionMakingEquations-2
Bysubstitutingtheequality(2.1)in(1.1):
Bysimplifyinginequality(1.2):
Fortheexpectedcost:1.3
1.2
1.4
Post-MortemAnalysisoftheDWHNPT
UnderwhatcircumstancescouldtheDWHcrewacceptthenegativepressuretestresultswithapressurebuilt-upof“1400psi”?! Basicscenario:
• P(APLeak=Y)=0.01• P(WellLeak=Y)=0.02• C20/C01andC30/C01=2000
Cut-offpoint=247psi
! Scenario1:• P(APLeak=Y)=0.01• P(WellLeak=Y)=0.00001• C20/C01andC30/C01=300
Cut-offpoint=837psi(Whichisstilllessthan1400psi)
! Iftheabovecostratiosreduceto250:thecut-offpointwillbeinfinity,whichmeansacceptingthetestforanyobservedpressurebuilt-up;nomatterhowhighitis.
RootCausesofBiases
Organizationalfactorsaretherootcontributingcausesofthestatedbiases:
! Economicpressure;ifthereistoomuchpressureoncostandtimesaving,that can cause underestimation of the described cost ratio (cost ofacceptingthetestforanabnormalstatetothecostofrejectingthetestforanormalstate).
! Personnel management issues; if personnel does not receive propertrainingordoesnothaveenoughexperience,thatcancausethedescribedbiases.
! Issuesincommunicationandprocessingofuncertainties;ifmanagersdo not communicate the risk of complex operations such as NPTprocedurestopersonnel,thatcancontributetothedescribedbiases.
! Lackof integrated, Informedmanagement;existenceofno integratedfeedbacksystemfrommanagers (bothonshoreandoffshore) to thecrewcancontributetothedescribedbiases.