SPE-115386-PA-Recent Advances in Surfactant EOR

December2011SPEJournal889RecentAdvancesinSurfactantEORGeorgeJ.Hirasaki,SPE,ClarenceA.Miller,SPE,andMauraPuerto,RiceUniversityCopyright©2011SocietyofPetroleumEngineersThispaper(SPE115386)wasacceptedforpresentationattheSPEAnnualTechnicalConferenceandExhibition,Denver,21–24September2008,andrevisedforpublication.Originalmanuscriptreceivedforreview19July2010.Revisedmanuscriptreceivedforreview22December2010.Paperpeerapproved18January2011.SummaryInthispaper,recentadvancesinsurfactantenhancedoilrecovery(EOR)arereviewed.Theadditionofalkalitosurfactantfloodinginthe1980sreducedtheamountofsurfactantrequired,andtheprocessbecameknownasalkaline/surfactant/polymerflooding(ASP).Itwasrecentlyfoundthattheadsorptionofanionicsurfac-tantsoncalciteanddolomitecanalsobesignificantlyreducedwithsodiumcarbonateasthealkali,thusmakingtheprocessapplicableforcarbonateformations.Thesamechemicalsarealsocapableofalteringthewettabilityofcarbonateformationsfromstronglyoil-wettopreferentiallywater-wet.Thiswettabilityalterationincombinationwithultralowinterfacialtension(IFT)makesitpos-sibletodisplaceoilfrompreferentiallyoil-wetcarbonatematrixtofracturesbyoil/watergravitydrainage.Thealkaline/surfactantprocessconsistsofinjectingalkaliandsyntheticsurfactant.Thealkaligeneratessoapinsitubyreactionbetweenthealkaliandnaphthenicacidsinthecrudeoil.Itwasrecentlyrecognizedthatthelocalratioofsoap/surfactantdeter-minesthelocaloptimalsalinityforminimumIFT.Recognitionofthisdependencemakesitpossibletodesignastrategytomaximizeoilrecoverywiththeleastamountofsurfactantandtoinjectpoly-merwiththesurfactantwithoutphaseseparation.Anadditionalbenefitofthepresenceofthesoapcomponentisthatitgeneratesanoil-richcolloidaldispersionthatproducesultralowIFToveramuchwiderrangeofsalinitythaninitsabsence.Itwasoncethoughtthatacosolventsuchasalcoholwasnecessarytomakeamicroemulsionwithoutgel-likephasesorapolymer-richphaseseparatingfromthesurfactantsolution.Anexampleofanalternativetotheuseofalcoholistoblendtwodissimilarsurfactants:abranchedalkoxylatedsulfateandadouble-tailed,internalolefinsulfonate.Thesingle-phaseregionwithNaClorCaCl2isgreaterfortheblendthanforeithersur-factantalone.Itisalsopossibletoincorporatepolymerintosuchaqueoussurfactantsolutionswithoutphaseseparationundersomeconditions.Theinjectedsurfactantsolutionhasunderoptimumphasebehaviorwiththecrudeoil.Itbecomesoptimumonlyasitmixeswiththein-situ-generatedsoap,whichisgenerallymorehydrophobicthantheinjectedsurfactant.However,somecrudeoilsdonothaveasufficientlyhighacidnumberforthisapproachtowork.Foamcanbeusedformobilitycontrolbyalternatingslugsofgaswithslugsofsurfactantsolution.Besideseffectiveoildis-placementinahomogeneoussandpack,itdemonstratedgreatlyimprovedsweepinalayeredsandpack.IntroductionItisgenerallyconsideredthatonlyapproximatelyone-thirdofthepetroleumpresentinknownreservoirsiseconomicallyrecoverablewithestablishedtechnology(i.e.,primary-recoverymethodsusinggaspressureandothernaturalforcesinthereservoir,andsecond-aryrecoverybywaterflooding).Ithaslongbeenanobjectiveoftheindustrytodevelopimprovedprocessestoincreaseoverallrecovery.However,thelowoilpricesthatprevailedfromthemid-1980suntilrecentlyprovidedlittleincentiveforresearchonEOR,especiallysurfactantprocesseswithsubstantialinitialcostforchemicals.Inlightofthecurrenthigherpricesandaccompanyingrevivalofinterest,itseemsappropriatetoreviewunderstandingof,andprospectsfor,surfactantEOR.Addingsurfactanttoinjectedwatertoreduceoil/waterIFTand/oralterwettabilityandtherebyincreaserecoveryisnotanewidea[see,forinstance,UrenandFahmy(1927)].Indeed,afewearlyfieldtrialswheresmallamountsofsurfactantwereinjecteddidproducesmallincreasesinoilrecovery.Theincreaseswereprobablycausedmainlybywettabilitychanges,althoughthedatawereinconclusiveforassessingmechanisms.Theresultswerenotsufficientlypromisingtostimulateuseofsurfactantsonalargerscale.Arelatedlong-heldconceptforimprovingrecoveryistogeneratesurfactantinsitubyinjectinganalkalinesolution(Atkin-son1927),whichislessexpensivethansyntheticsurfactantsandconvertsnaphthenicacidsinthecrudeoiltosoaps.Earlyresultswerenotencouraging,andtherelativeimportanceoflikelyprocessmechanismswasnotunderstood(Johnson1976).OtherreferencestoearlyworkonsurfactantsaregivenbyHilletal.(1973).TwodifferentapproachesstimulatedsignificantadvancesinsurfactantEORprocessesinthe1960s.Thesurfactantsweremadeeitherbydirectsulfonationofaromaticgroupsinrefinerystreamsorcrudeoils,orbyorganicsynthesisofalkyl/arylsulfonates,whichallowedforthesurfactanttobetailoredtothereservoirofinterest.Theadvantagesofthesesurfactantsaretheirlowcost,theirwiderangeofproperties,andtheavailabilityofrawmaterialsinsomewhatlargequantities.Misciblefloodingwasanactiveareaofresearch,butthesol-ventsbeingconsidered,suchasenrichedgasandLPG,exhibitedpoorreservoirsweepbecausetheadversemobilityratiopromotedviscousfingeringandthelowsolventdensityledtogravityover-ride.Seekingasolventmisciblewithoilbuthavingahighervis-cosityanddensity,GogartyandcoworkersatMarathonproposedusingaslugofanoil-continuousmicroemulsionm