采油化学Word格式.docx
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采油化学Word格式.docx
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Theseparatedsaltwaterstillcontainscertainamountsofresidualoil,wherenowpreferentiallyoil-in-wateremulsionsareformed.Theseparationoftheresidualoilisnecessaryinoilfieldwaterpurificationandtreatmentforecologicandtechnicalreasons,becausethewaterisusedforsecondaryproductionbywaterflooding,andresidualoilvolumesinthewaterwouldincreasetheinjectionpressure.
Thepresenceofwater-in-oilemulsionsoftenleadstocorrosionandtothegrowthofmicroorganismsinthewater-wettedpartsofthepipelinesandstoragetanks.Attherefinery,beforedistillation,thesaltcontentisoftenfurtherreducedbyasecondemulsificationwithfreshwater,followedbydemulsification.Crudeoilswithhighsaltcontentscouldleadtobreakdownsandcorrosionattherefinery.Theobjectofusinganemulsionbreaker,ordemulsifier,istobreaktheemulsionatthelowestpossibleconcentrationand,withlittleornoadditionalconsumptionofheat,tobringaboutacompleteseparationofthewaterandreducethesaltcontenttoaminimum.
Thereareoil-solubledemulsifiersandwater-solubledemulsiflers,thelatterbeingwidelyused.Emulsionsarevariableinstability.Thisvariabilityislargelydependentonoiltypeanddegreeofweathering.Emulsionsthathavealowstabilitywillbreakeasilywithchemicalemulsionbreakers.Brokenemulsionswillformafoamlikematerial,calledrag,whichretainswaterthatisnotpartof
thestableemulsions.Themosteffectivedemulsifiermustalwaysbedeterminedfortheparticularemulsion.Demulsifiersareoftenaddedtotheemulsionatthewellheadtotakeadvantageofthetemperatureofthefreshlyraisedemulsiontohastenthedemulsificationstep.
Waterflooding
Duringimprovedoil-recoveryprocesses,waterfloodingoftheoilisapplied.Theentrainedwaterformsawater-in-oilemulsionwiththeoil.Inaddition,saltssuchassodiumchloride,calciumchloride,andmagnesiumchloridemaybedissolvedintheemulsifiedwater.
OilSpillTreatment
Demulsifiers(specifically,oilspilldemulsifiers)canbeappliedtooilspillsinlowconcentrations.Theypreventmousseformationforsignificantperiodsoftimeandcausealargereductioninoil-waterinterfacialtension.Thebestofthesewasfoundtopreventemulsificationatdosagesaslowas1partinhibitorto20,000partsoffreshoilat20°
C[273].Atdosagesof1:
1000,attemperatureshigherthan10°
C,thechemicalalsoresultsinsignificantandrapiddispersionoftheoil.Forverylowtemperaturesorhighlyweatheredoil,theperformanceofthechemicalfallsoffsharply.
DesiredProperties
Demulsifiersforcrudeoilemulsionsshouldmeetthefollowingproperties:
•RapidbreakdownintowaterandoilwithminimalamountsofresidualWater•Goodshelflife•Quickpreparation
MechanismsofDemulsifieation
StabilizationofWater-OilEmulsions
Thestabilizationofwater-oilemulsionshappensasaresultoftheinterfaciallayers,whichmainlyconsistofcolloidspresentinthecrudeoil—asphaltenesandresins.Byaddingdemulsifiers,theemulsionbreaksup.Withwater-solubledemulsifiers,theemulsionstabilizersoriginallyinthesystemwillbedisplacedfromtheinterface.Inaddition,achangeinwettingbytheformationofinactive
complexesmayoccur.Conversely,usingoil-solubledemulsifiers,themechanism,inadditiontothedisplacementofcrudecolloids,isbasedonneutralizingthestabilizationeffectbyadditionalemulsionbreakersandthebreakupresultingfrominterfaceeruptions.
InterfacialTensionRelaxation
Theeffectivenessofacrudeoildemulsifieriscorrelatedwiththeloweringoftheshearviscosityandthedynamictensiongradientoftheoil-waterinterface.Theinterfacialtensionrelaxationoccursfasterwithaneffectivedemulsifier.Shortrelaxationtimesimplythatinterfacialtensiongradientsatslowfilmthinningaresuppressed.Electronspinresonanceexperimentswithlabeleddemulsifiersindicatethatthedemulsifiersformreversemicellelikeclustersinthebulkoil.Theslowunclusteringofthedemulsifierattheinterfaceappearstobetherate-determiningstepinthetensionrelaxationprocess.
PerformanceTesting
Thetrial-and-errormethodofchoosinganoptimaldemulsifierfromawidevarietyofdemulsifierstoeffectivelytreatagivenoilfieldwater-in-oilemulsionistime-consuming.However,therearemethodstocorrelateandpredicttheperformanceofdemulsifiers.
SpreadingPressure
Theperformanceofdemulsifierscanbepredictedbytherelationshipbetweenthefilmpressureofthedemulsifierandthenormalizedareaandthesolventpropertiesofthedemulsifier.Thesurfactantactivityofthedemulsifierisdependentonthebulkphasebehaviorofthechemicalwhendispersedinthecrudeoilemulsions.Thisbehaviorcanbemonitoredbydeterminingthedemulsifierpressure-areaisothermsforadsorptionatthecrudeoil-waterinterface.
CharacterizationbyDielectricConstant
Thedielectricconstantcanbeusedasacriterionforscreening,ranking,andselectingdemulsifiersforemulsionbreaking.Inastudy,thedielectricconstantsofemulsionsanddemulsifiersweremeasuredusingaportablecapacitancemeter,andbottletestswereconductedaccordingtotheAPIspecification.Theresultsshowedthatthedielectricconstantscanbeusedeffectivelytoscreenandrankdemulsifiers,whereasaconfirmatorybottletestshouldbeconductedonthebestdemulsifierstoassistintherapidselectionofthemosteffectivedemulsifier.
ShakerTestMethods
AstudybyEnvironmentCanadaandtheU.S.MineralsManagementServiceattemptedtodevelopastandardtestforemulsionbreakingagents[586].Ninetypesofshakertestmethodsweretried.Althoughtheresultsarecomparablewithdifferenttests,astablewater-in-oilemulsionmustbeused
toyieldreproducibleresults.Testswithunstableemulsionsshowednonreproducibleandinconsistentresults.
ViscosityMeasurements
Watercontentandviscositymeasurementsincertainsystemsshowacorrelationtoemulsionstability.Theviscosityprovidesamorereliablemeasureofemulsionstability,butmeasurementsofthewatercontentaremoreconvenient.Mixingtime,agentamount,settlingtime,andmixingenergyimpact
theeffectivenessofanemulsifier.
Screening
Withoutknowingthestructureindetail,nuclearmagneticresonance(NMR)informationcanbecompiledby13Conthestructureusingthechemicalshifts.Thechemicalshiftscanbecorrelatedwithotherdata,suchasbottletests,andevaluatedbystatisticalmethods.Inaseriesofexperimentalwork
usingprincipalcomponentanalysis,NMRdataandbottletestdatawereusedtoclustermorethan100demulsifiersintoonlyafewdistinctlydifferentchemicalgroupsascharacterizedbytheNMRdata.Similarchemicaltypeshadsimilardemulsificationperformance,whichmeansthatdemulsifierevaluationscanbemadebasedondemulsifierchemistry.Onlyafewofthedistinctlydifferent
emulsifiersneedtobetestedbeforetheoptimizationprocedeurecanstart.BecausethechemicalcharacterizationbyNMRimagingtakesonlyafractionofthetimeofabottletest,itispossibletomorerapidlyfocusonoptimizingthedosageofthedemulsifier.
ClassificationofDemulsifiers
Thechemicalsusedasdemulsifierscanbeclassifiedaccordingtotheirchemicalstructureandtheirapplications.Withthelatterrespect,amaindivisionforwater-in-oilandoil-in-waterapplicationsexists.Furthermore,thedemulsifierscanbeclassifiedaccordingtotheoiltypeused.Fromtheviewofchemicalclassification,twomajorgroupsexist:
•Nonionicdemulsifiers•Ionicdemulsifiers.
CommonPrecursorChemicals
Polyalkyleneoxidesaresubstancesofthefollowinggeneralstructure:
Themostimportantadditivesarepolyethyleneoxide,polypropyleneoxide,andpolybutyleneoxide.Theyarealsoreferredtoaspolyalkyleneglycols,butthisnameiscorrectstrictlyforderivativesof1,2-diols.Polypropyleneoxidehasamolarmassof250to4000Dalton.Thelowermolecularhomologuesaremisciblewithwater,whereasthehighermolecularpolypropyleneoxidesaresparinglysoluble.Theyareformedbythepolyadditionof,forexample,propyleneoxidetowaterorpropanediol.Thesimplestexamplesaredi-andtri-utetrapropyleneglykol.Therearealsoblockcopolymersfromethyleneoxideandpropyleneoxide.Polytetramethyleneglycol(polytetrahydrofuran)isformedbyringopeningpolyetherificationoftetrahydrofuran.Branchedpolyalkyleneoxidesareformedusingpolyfunctionalalcoholssuchastrimethylolpropaneandpentaerythrite.Theproductsareliquidsorwaxesdependingonthemolarmass.Polyalkyleneoxidesareoftenprecursorsfordemulsifiers.
Polyaminesareusuallyopenchaincompoundswithprimary,seconda
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