Crosslinked Borate HPG Equilibria and Rheological CharacterizationWord文件下载.docx

Crosslinked Borate HPG Equilibria and Rheological CharacterizationWord文件下载.docx

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DowellSchlumberger

*SPEMembers

Copyright1993,SocietyofPetroleumEngineers,Inc.

ThispaperwaspreparedforpresentationattheSPEInternationalSymposiumonOilfieldChemistryheldinNewOrleans,LA,U.S.A.,March2-5,1993.

ThispaperwasselectedforpresentationbyanSPEProgramCommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthors）.Contentsofthepaper,aspresented,havenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthors）.Thematerial,aspresented,doesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.PaperspresentedatSPEmeetingsaresubjecttopublicationreviewbyEditorialCommitteesoftheSocietyofPetroleumEngineers.Permissiontocopyisrestrictedtoanabstractofnotmorethan300words.Illustrationsmaynotbecopied.Theabstractshouldcontainconspicuousacknowledgmentofwhereandbywhomthepaperispresented.WriteLibrarian,SPE,P.O.Box833836,Richardson,TX75083-3836,U.S.A.Telex,163245SPEUT.

Abstract

Viscoelasticpropertiesofhydroxypropylguar（HPG）crosslinkedbyborateionswerestudiedusingsteadyshearanddynamicoscillatoryshearexperiments.Chemicalequilibriainvolvingboricacid,borateions,andborateionsassociatedwithcis-diolsitesonthepolysaccharidechainsdeterminethenumberofcrosslinks.TheseequilibriaarefunctionsoftemperatureandpH,andthustherheologyoftheborategelsdependontemperatureandpH.Dynamicoscillatorymeasurementsonpolymersolutionscrosslinkedbyboraxwereperformedoverthetemperaturerangefrom10'

Cto65°

C,andthepHrangefrom6.35to9.5.Thestorageandlossmoduliobeytime-temperaturesuperpositionsothatmastercurvescanbeconstructedover6decadesinfrequency.Leibler,etal.haverecentlyproposedatheoryfortherheologyofassociatingpolymersystems.Followingthistheory,wehavesubtractedthesolutionmodulifromthegelmoduliandtheresultingreducedmodulidatafollowasingletimeconstantMaxwellmodel.Steadyshearexperimentswereperformedincapillarytubesattwodifferentdiameterstodeterminewallslip.Theshearratesstudiedweresuchthatthechainsdonothavesufficienttimetorelaxcompletely.Byanalysingthedatafromthetwotubes,thegelwasfoundtoslipatthewall.Threedifferentregionswereseeninthestress-shearratebehaviorofthesegels.Atlowrates,thestressincreasesrapidlywithshearrate.Atintermediateshearrates,thestressremainsconstantandat

highshearrates,thestressincreasesslowlywithrateandthegelisfoundtoslipinthisregion.Theactualstress-shearratebehaviorafteraccountingforslipandslipvelocitiesweredetermined.

Introduction

Watersolublepolymerscanbecrosslinkedtoformwater-swellablegelsusinganumberofcrosslinkingchemistries.Examplesincludecovalentlycrosslinkedgelsusedincontrolleddrugreleaseorassoftcontactlenses1"

6,gelsformedbyhydrogenbondingsuchasphotographicgelatins7,gelatinfoods8oragarosegelsforelectrophoresis9,gelsformedbyhydrophobicinteractions10'

11,orgelsformedusinginorganicmetalions12"

15asthecrosslinkingspeciesinhydraulicfracturingoperations.

Inthispaperwepresentastudyofthegelationofhydroxypropylguarbyborateions.Thevariousequilibriumreactionsbetweenborateionsandsugarresiduesarepresented,followedbythedynamicoscillatorybehaviorandsteadyshearbehaviorofHPGcrosslinkedbyboraxgels.Thesurprisingresultisthattheborate"

gels"

obeythelawsoftime-temperaturesuperpositionjustlikelinearpolymermeltsorsolutions.ThesuperpositionshiftfactorsshowanArrheniusdependenceontemperaturewhichisinaccordwiththeborateionequilibriathatgovernscrosslinking.TheshifteddataarefittedwithasinglerelaxationtimeconstantMaxwellmodel,

whichmeansthattherelaxationbehaviorofguarandHPGgelscanbepredictedfromasinglemastercurveandfromtheknownshiftfactorsforpHandtemperature.Thesteadyshearexperimentswereconductedintwocapillarytubestoinvestigatewhetherthegelslipsatthewall.Theexperimentswereperformedatshearratesgreaterthanthecriticalshearrate（whichistheinverseoftherelaxationtime）predictedfromtheelasticmodulidata.Atshearratesgreaterthanthecriticalshearrate,thegelbehaveslikeanelasticsolidratherthanafluidandslipoccursatthewall.

Guaris'

anaturallyoccurringpolysaccharidewhichiscomposedofalinearbackboneof（1-4）PlinkedD-mannoseunitswith（1-5）a-linkedD-galactoseunitsrandomlyattachedassidechains16Themolecularweightofguarisabout2X10^.Guarisderivatizedtoformhydroxypropylguar（HPG）orcarboxymethylhydroxypropylguar（CMHPG）becausethepropylationstepreducestheamountofinsolublecelldebrisinthefinalsolutions.ThestructureoftherepeatingunitofguaranditsderivativesisshowninFig1.

Hydroxypropylguariscrosslinkedbyboraxtoformborate-crosslinkedHPGgel.The

borateion（B（OH）4~）istheeffectivespeciesincrosslinkinganditsconcentrationisafunctionofpH,temperatureandtheconcentrationofboraxandpolymerinthesolution.Theequilibriumreactionsforborateionsinaqueoussolutionhavebeenstudiedpreviously17,18.Sodiumborate（borax）dissociatescompletelytoformboricacid,

B（OH）3jandborateions,B（OH）4~,

B4C>

7'

+7H20->

2B（OH）3+2B（OH）4

（1）

andanacid-baseequilibriumisestablishedbetweenboricacidandmonoborateions,

Ka

B（OH）3+H2Q;

>

B（OH）4+H+

（2）

ThepKaofthereactionisbetween9.0-9.2.Themonoborateionsreactwiththecis-hydroxylgroupsinguarorHPGtoformcrosslinks.Thebindingconstantofthemonoborateiontosinglehydroxylgroupsismuchweakerthanthebindingconstanttocis-hydroxylsandcanbeneglectedinthefollowingmass-actioncalculations.Inordertostudythecomplexationchemistry17'

21,mostofthestudiesintheliteraturewereperformedwithsimplepolyolslikepentanol17,1-2propanediol19andwithmodelsugarslikemethyl-a-Dgalactopyrannosideandmethyla-Dmannopyrannoside18.Sincegalactopyrannosideandmannopyrannosidearetherepeatingunitsinguar,similarreactionsareexpectedtooccurbetweentheborateionsandthehydroxylgroupsinguarsolution.Werepresentthevariousreactionsschematically,

whereAreferstothepolyol（i.e.asinglegalactopyrannosideorgalactopyranosideunitwithasinglecis-hydroxyl）,B"

referstoB（OH）4'

andAB'

A2B‘arethe1:

1and2:

1complexstructuresformedbythereactionofapolyolwithaborateionandtwopolyolswithaborateionrespectively.Therheologicalpropertiesoftheborate-crosslinkedgelsdependstronglyonthenumberofeffectivecrosslinks,i.e.theconcentrationofA2B'

.AmodeltopredicttherelaxationtimeforareversiblycrosslinkedpolymersinconcentratedsolutionormeltregimehasbeenpresentedbyLeibler22.

RheologyofHPGiBnrateGels

TheconsistencyofthecrosslinkedHPGgelchangesfrompolymersolutionathightemperaturesorlowpHvalues（aboutpH7.0）,tosolidgelsatlowtemperaturesandhighpHvalues（aboutpH9-9.5）.ThepHandtemperatureeffectsarisefromtheboricacidequilibria（Eq.2）andtheArrheniusdependenceoftheequilibriumconstantsontemperature.ThepropertiesofcrosslinkedborategelsindynamicoscillatoryshearhasbeenstudiedbyPezronetal23andKesavanandPrud'

homme24.Thegelsweresubjectedtodynamicoscillatorysheartodeterminethemodulusandrelaxationtime.Steadyshearexperimentswereperformedincapillarytubesatshearrateshigherthanthecriticalshearrate,whichisthereciprocaloftherelaxationtime,sothatthegeldoesnothaveenoughtimetorelax.

DynamicBehaviorofHPGcrosslinkedbvBoraxgels

ExperimentalProtocol:

The

compositionandpreparationofthesolutionisasfollows:

Add500mlofdeionizedwaterinablenderandstiritsothatitformsashallowvortex.Then,add2.4gmofguar（Dowell

Schlumberger,Inc.,Tulsa,OK）orHPG（HiTekPolymersInc.,Louisville,KY,Lot#39-18-014T）,0.6gmofsodiumdiacetate（CelanesePlasticsandSpecialitiesCompany,Jefferstown,KY,WSP-OS-1015-02）,0.6gmofborax（FisherScientific,lot794671）and0.125mlof25%glutaraldehydesolutioninwater（EastmanKodak,lot#EllA）.Stirthesolutionforabout2-3minutesintheblenderandthentransferitforfurthermixinginarollermixerforabout20-24hours.ThepHofthesolutionisincreasedbyaddingsmallquantitiesofINNaOHsolution.Thesolutionimmediatelygelsduetotheformationofboratecrosslinks.Auniformgelisproducedbyheating（to'

melt'

）thegeltoabout65‘Cforabout15minutesandsubsequentlycoolingthesolution.Thesolutionisstirredwhenitishotandthisprocessisrepeatedseveraltimes（from2-5timesdependingonthepHofthegel）toproducethehomogeneousgel.

RheologicalmeasurementswereperformedonaRheometricsFluidsSpectrometerII（RheometricsInc,Piscataway,NJ）usingaCouettegeometrywhoseinnerbobandoutercupradiiare16and16.925mm,respectively,andlengthis33.3mm.Strainsweepexperimentswereinitiallyperformedonthesampletodeterminethelinearviscoelasticregion,wherethemodulusisindependentofstrain,andsubsequentmeasurementswereperformedwithinthelinearregion.Strainvaluesbetween5and50%wereuseddependingonthestrengthofthegel.

Thestorageandlossmodulibehaviorof0.48%HPGsolutiona