CO2 as Injection Gas for Enhanced Oil Recovery

NTNU–NorwegianUniversityofScienceandTechnologyDepartmentofPetroleumEngineeringandAppliedGeophysics__________________________________CO2asInjectionGasforEnhancedOilRecoveryandEstimationofthePotentialontheNorwegianContinentalShelfbyOddMagneMathiassenChiefReservoirEngineerNorwegianPetroleumDirectorateTrondheim/Stavanger,May2003________________________________PartIofIICO2injectionforEnhancedOilRecovery2___________________________________________________________________________ACKNOWLEDGEMENTIwouldliketothankmysupervisorProfessorOleTorsæterattheNorwegianUniversityofScienceandTechnologyforexcellentguidingandhelpinmyworkwiththisthesis.Iwouldalsoliketothankmyemployer,theNorwegianPetroleumDirectorate,forgivingmetheopportunityandtimetocompletethethesis.MythanksalsogotomycolleaguesMr.GunnarEinang,Mr.SørenDavidsenandMr.JanBygdevollforvaluablediscussionswhileworkingwiththisthesis.Finally,IwouldliketothankDr.EricLindebergandseniorresearcherIdarAkervollattheSintefResearchforvaluableinformationonCO2relatedissues.SUMMARYThemainobjectiveofthisthesisistoinvestigatethepossibilityofusingCO2asinjectiongasforenhancedoilrecoveryandestimatethepotentialofadditionaloilrecoveryfrommatureoilfieldsontheNorwegianContinentalShelf(NCS).BecauseofthelackofCO2datafromoffshoreoilfields,aliteraturestudyonCO2floodexperienceworldwidewasundertaken.Inaddition,thephysicalpropertiesofCO2andCO2asasolventhavebeenstudied.TheliteraturestudymakesitpossibletoconcludethatCO2hasbeenanexcellentsolventforenhancedoilrecoveryfromonshoreoilfields,especiallyintheUSAandCanada.Almost30yearsofexperienceandmorethan80CO2projectsshowthattheadditionalrecoveryisintheregionof7to15%oftheoilinitiallyinplace.Theestimationisbasedonspecificfielddataforallfieldsandreservoirsincludedinthethesis.CO2dataarelimitedtostudiesandreservoirsimulationsfromForties,Ekofisk,BrageandGullfaks.SinceFortiesisaUKoilfield,mostofthedatausedarefromthethreeNorwegianoilfields.Thisthesisincludesalloilfieldscurrentlyinproduction.Fieldsunderdevelopment,fieldswithapprovedplanfordevelopmentandoperation(PDO),ordiscoveriesunderevaluationarenotincluded.However,theymayhavepotentialforuseofCO2inthefuture.ThecandidatesarescreenedaccordingtotheircapabilityofbeingCO2flooded,basedoncurrentindustryexperienceandmiscibilitycalculations.Thenamodelbasedonthemostcriticalparametersisdeveloped.Finally,riskanalysisandMonteCarlosimulationsareruntoestimatethetotalpotential.Applyingthemodeldevelopedandcompensatingforuncertainties,theadditionalrecoveryisestimatedbetween240and320millionSm3ofoil.ThispotentialconstituteslargeincreasesinoilproductionfromtheNorwegianContinentalShelfifCO2canbemadeavailableatcompetitiveprices.Forsomeofthetimecriticalfields,immediateactioniscalledupon,butforthemajorityofthefieldsdealtwithinthisthesis,CO2injectioncanbepostponed5yearsormore.CO2injectionforEnhancedOilRecovery3___________________________________________________________________________TABLEOFCONTENTSACKNOWLEDGEMENT.........................................................................................................2SUMMARY...............................................................................................................................2TABLEOFCONTENTS...........................................................................................................31.INTRODUCTION..............................................................................................................52.THEPHYSICALPROPERTIESOFCO2.........................................................................62.1PhasetransitionsandphasediagramforCO2........................................................92.1.1Phaseequilibrium...............................................................................................92.1.2TheClausius-Clapeyronequation..................................................................102.1.3Solid-LiquidEquilibrium...............................................................................102.1.4Solid–VapourEquilibrium.............................................................................112.1.5Liquid-VapourEquilibrium............................................................................122.1.6Phasediagramcalculatedfromthederivedequations.....................................122.2CO2-rockandfluidinteractions..............................................................................132.2.1PVTconditions.................................................................................................132.2.2CO2hydrates.....................................................................................................132.2.3Wettability........................................................................................................132.2.4Scale.................................................................................................................142.3Injectivityabnormalities...........................................................................................142.3.1Injectivityincreases........