SPE-129976-MS-P-A Comprehensive EOR Study Using Lo

SPE129976AComprehensiveEORStudyUsingLowSalinityWaterinSandstoneReservoirsM.B.Alotaibi,R.M.Azmy,andH.A.Nasr-El-Din,TexasA&MUniversity,allSPEmembersCopyright2010,SocietyofPetroleumEngineersThispaperwaspreparedforpresentationatthe2010SPEImprovedOilRecoverySymposiumheldinTulsa,Oklahoma,USA,24–28April2010.ThispaperwasselectedforpresentationbyanSPEprogramcommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).ContentsofthepaperhavenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).ThematerialdoesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.Electronicreproduction,distribution,orstorageofanypartofthispaperwithoutthewrittenconsentoftheSocietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.TheabstractmustcontainconspicuousacknowledgmentofSPEcopyright.AbstractIthasbeenreportedthattheionicstrengthofinjectionwatercanhaveamajorimpactontherecoveryofhydrocarbonsduringwaterfloods,withincreasedrecoveryresultingfromtheuseoflowsalinitybrines.Understandinghowthewaterandoilchemistryaffectsthefinalrecoveryfromaphysicochemicalpointofviewisnecessaryinordertooptimizelowsalinitywaterfloodingprocess.Itisclearfromtheliteratureoverthelasttwodecadesthatwettabilityisconsideredakeyfactorinachievingthelowsalinityeffect.Optimumionicstrengthandconditionsforlowsalinityfloodwithrespecttowettabilityisstilluncertain.Inthisstudy,weintegratenewcorefloodapparatususingcoresamples,upto20inchlength,tomimicandunderstandcrudeoil/water/rockinteractions.Thecorefloodexperimentsareconductedunderbothsecondaryandtertiaryrecoverymodes.Weappliedcontactanglemethodtostudyrockswettability.Reservoirrocksandstock-tankcrudeoilsample(westTexas)areutilizedinallexperiments.Syntheticbrinesvaryinginsalinity(upto174kppm)aretestedunderelevatedtemperatureandpressureconditions.Asionexchangeplaysacrucialroleinchangingwettability,chemicalanalysesareperformedontheeffluentsamples.Moreover,Zetapotentialisdeterminedforsandstonerocksandselectedclaysasafunctionofionicstrength.Residualoilsaturationisdeterminedwithallvariationinwettability,brinesalinity,andtemperatureconditions.Somecorefloodtestsgiveanincrementalincreaseinproducedoilasdecreasingtheinjectionbrinesionicstrength.Experimentalresultsindicatethatadjustingbrinesalinitymayenhanceoilrecoveryundercertainconditions.Thispapergivesanewinsightintooptimumsalinityandprovidesbetterunderstandingofinteractionbetweeninjectedbrine,theoil,andtherockatdownholeconditions.IntroductionTheobjectiveofthispaperistoinvestigateiflowsalinitywaterismoreeffectivethannormalbrineinwaterfloodingoperation.Lessattentionhasbeengiventothechemistryofinjectionwater.Lowsalinitywaterflooingistypicallyintherangeof500to5,000partspermillion(ppm)oftotaldissolvedsolids(TDS),andnomorethan6,000ppm.Thispaperstructuredintofoursections:1)wettabilitystudyusingcontactanglestechnique,2)Lowsalinitywatereffectonrocksurfacecharges,3)corefloodexperiments,and4)aqueoussolutionanalysisusingatomicabsorption.Ourpapercontributestotheliteratureintwoways.Thefirstcontributionistoexplaintherock’swettabilityperformanceusingsurfacecontactangle.Theothercontributionistodeterminethewatersalinityeffectonoilrecovery,surfacechargesandionsexchange.LiteratureReviewWaterfloodandoilrecoverymechanisms.Salinityoftheconnateandinvadingbrinescansignificantlyinfluencerockwettabilityandoilrecoveryatreservoirtemperature.Sandstonereservoircoresshowedgreaterresponsetofloodingwithlowsalinitywaterthanoutcroprocks.Crudeoil-brine-rock(COBR)interactionsplayedamajorroleinanyincreaseintheoilrecovery(TangandMorrow1997;Morrowetal.1998;Loahardjoetal.2007).RepresentativecoresfromAlaskafieldreservoirsweretestedusingreservoirbrines,ultra-lowsalinitylakewater,andNaClsolution.Secondaryrecoveryexperimentsreducedresidualoilsaturationatlowandhightemperatureconditions(Patiletal.2008;Agbalakaetal.2009).Recoveryimprovementduetolowsalinitywaterinjectionwasalsonoticedwithdifferentcrudeoilcharacteristics,andconnatebrinesalinities(Webbetal.2008).Numeroussandstonefieldswerewaterfloodedusinglowsalinityformationbrine(1,000ppm)(Robertsonetal.2003;2SPE129976Robertson2007).Crudeoilandrocktypes,particularlythepresenceanddistributionofkaolinite,bothplayadominantroleintheeffectthatbrinecompositionhasonwaterfloodoilrecovery.Toconfirmlaboratoryresults,singlewellchemicaltracer(SWCT)testswereappliedindifferentfields.Fieldresultsindicatedthatlowsalinitywatertechniqueappearstobeeffectiveatsalinitylevelsofnearly5,000ppmorless(McGuireetal.2005)Severalcorefloodexperimentsshowedthatlowsalinitybrineimprovedtheoilrecoveryforbothsecondaryandtertiarymodes,butsometimesforonlyoneortheother(ZhangandMorrow2006;Zhangetal.2007).Inadditiontoproductiondataanalysis,detailedchemicalcompositionoftheproducedwatersupportedtheincrementalrecoveryduetolowsalinitywaterinjection.Also,resultsindicatedthatnoadverseeffectssuchasporepluggingorclayswellingowingtofinesmigrationwereobserved(Lager