Thermal stability and interactions with sedimentary rocks under typical reservoir conditions of selected pyridines investigated as phase partitioning tracers

ContentslistsavailableatScienceDirect

Upstream Oil and Gas Technology

journalhomepage:www.elsevier.com/locate/upstre

Thermal stability and interactions with sedimentary rocks under typical reservoir conditions of selected pyridines investigated as phase partitioning tracers

Mario Silva

, Helge Stray

, Mahmoud Ould Metidji

, Tor Bjørnstad

aThe National IOR Centre of Norway, University of Stavanger, 4036 Stavanger, Norway

bDepartment of Energy Resources, University of Stavanger, 4036 Stavanger, Norway

cInstitute for Energy Technology (IFE), Department of Tracer Technology, Instituttveien 18, 2007 Kjeller, Norway

a r t i c le i n f o

Keywords:

Partitioning tracers Stability Reservoir rocks New compounds Pyridines

a b s t r a ct

Pyridine, 2-hydroxy-6-methylpyridine,3-hydroxypyridine,and4-methoxypyridineareevaluatedaspotential phase-partitioningoilfieldtracers.Theirstabilityistestedinabrinefor12weeksattemperaturesbetween25°C–

150°C,andatinitialpHvaluesof5,5;7,1;8,0.Interactionswithkaoliniteclay,Bereasandstoneandlimestone arealsoevaluated.Themainresultsareasfollows:pyridineisstableupto12weeksat150°C,andnotinfluenced bytherocksubstratesorpH.2-hydroxy-6-methylpyridinebecomesunstableatT≥50°C,isnotaffectedbythe rocksubstrates,andexihibtsslowerdegradationkineticsathigherpHvalues.3-hydroxypyridineisunstableat T≥75°C,sensitivetothepresenceofkaoliniteinacombinedeffectwithpH,andexihibtsslowerdegradation kineticsathigherpH.4-methoxypyridinedegradesatT≥75°C,ischaracterisedbyastronginteractionwith kaolinite,andisinsensitivetopH.

Thedegradationof4-methoxypyridineintheabsenceofkaoliniteclayfollowspseudofirst-orderkinetics.This compoundcouldindicatethetemperatureinthesweptvolumes,andinconjunctionwithafullyconservative tracerindicatethepresenceofclays.Pyridineexhibitstherequiredstabilityandlackofinteractionwithrock materialstobeusedasPITTtracerinoilreservoirs.However,itispresentinoilsanditsconcentrationlevelsin productionwatersshouldbeevaluatedpriortoitsuse.

1. Introduction

Knowledgeoftheresidualoilsaturation(S_OR)inthesweptvolumes ofoilreservoirscanbeusedbothtoimprovereservoirmanagement,and inthedesignandevaluationofEOR/IORprojects[1,2].Asthenumber ofmaturefields increases[3],suchprojectsbecomemoreimportant toensuretheproductionofhydrocarbonstosatisfyglobaldemand.A partitioninginter-welltracertest(PITT)istheonlydynamictooltomea- sureS_OR intheinter-wellregionofwaterfloodedreservoirs.APITTis basedontheuseofpassiveandoil/waterpartitioningtracers[4].Itwas introducedtotheoilindustryin1971byCooke[5],howeverneverrou- tinelyused.Thepoorknowledgeaboutthebehaviourandgeochemical interactionsofthecompoundsusedasPITTtracersleadtomanyunsuc- cessfultestsinthepast[4,6].Inrecentyears,thistypeoftracertesthas receivedincreasingattentionduetotheimportanceoftheinformation itprovides[7,8].Additionally,asmallnumberofcompoundshasbeen developedforuseasPITTtracers[6,9];additionalPITTtracerswould beuseful.Thestudyoftracercompoundspriortotheiruseonthefield

∗Correspondingauthorat:InstituteforEnergyTechnology(IFE),DepartmentofTracerTechnology,Instituttveien18,2007Kjeller,Norway.

E-mailaddresses:[email protected],[email protected](M.Silva).

iscrucial,notonlytoensuretheaccuracyofthetests,butalsotoeval- uatethepossibilityofusingtracerstoretrieveothertypeofrelevant information[10–12].

Inthisdocumentwepresentthestabilityassessmentperformedon 4pyridinesthatarePITTtracercandidates.Theinfluenceoftemper- ature,pH,time,salinity,anddifferentrockmaterials,onthestability andbehaviourofpyridine,4-methoxypyridine,3-hydroxypyridine,and 2-Hydroxy-6-methylpyridinewasinvestigated.

1.1. Pyridines

PyridinehasthechemicalformulaC₅H₅Nandastructuresimilarto benzene.Itisaweaklybasic,transparent“yellowish”,flammable,and water-solubleheterocyclicaromaticcompound,withadistincthighly unpleasant smell. Such properties arealso observed in many of the differentsubstitutedpyridines.Manycompoundswithinthisfamilyof chemicalsshowinterestingpropertiesforuseasPITTtracers.Relevant propertiesofthecompoundstestedherecanbefoundinTable1.

https://doi.org/10.1016/j.upstre.2021.100033

Received19May2020;Receivedinrevisedform30January2021;Accepted10February2021

2666-2604/© 2021TheAuthor(s).PublishedbyElsevierLtd.ThisisanopenaccessarticleundertheCCBYlicense(http://creativecommons.org/licenses/by/4.0/)

M. Silva, H. Stray, M. Ould Metidji et al. Upstream Oil and Gas Technology 6 (2021) 100033

Table1

Meltingpoint,boilingpoint,pKa,andoctanol/waterpartitioningcoefficientofthepyridinesselectedaspartition- ingtracercandidates.

Compound Melting point (°C) Boiling point (°C) K OW pKa

Pyridine − 42 115 4,47 5,25 ^∗

4-Methoxypyridine 4 191 5,22 6,58 ^∗

3-Hydroxypyridine 126 329 4,36 4,79 ^∗/8,75

2-Hydroxy-6-methylpyridine 159 275 2,18 4,94 ^∗/9,27

Data Source: NIST chemistry WebBook

∗Valueforthemono-protonatedpyridine.

Pyridineandpolycyclicpyridinederivativeshavebeenreportedin crudeoilsandarecommonlyclassifiedaspartoftheiralkalinefraction [13–15].Theyareresponsiblefor20%–26%ofthetotalnitrogencontent inallcrudeoils[13,14]whichisusually≤1%(wt),and<0.25%(wt) inabout90%ofthem[13].Theotherpyridinederivativesinvestigated underthescopeofthisworkhavenever,tothebestofourknowledge, beenreportedasconstituentsofanytypeofoilreservoirfluid.Thechem- icalindustryusespyridineasraw-materialandintermediateonalarge scale.Itistheprecursortosomepesticides,suchasparaquatanddiquat [16],industriallyusedassolvent,intheproductionofdyes,explosives, pharmaceuticals,etc.[17,18],andisusedasaligand(orbaseunitfor ligands)incoordinationchemistry[19]. 4-Methoxypyridineismostly usedasaligandincoordinationchemistry[20,21],andinthesynthesis ofpharmaceuticalcompounds[22].3-Hydroxypyridinehasbeencon- sideredasaprecursorfortheproductionofnitrogen-richpolymersfor CO₂adsorption[23],usedasadditivetoimproveopticalpropertiesof hydrophilicophthalmiclenses[24],andalsoasprecursorforpharma- ceuticalactiveprinciples[25].2-Hydroxy-6-methylpyridinehasnosig- nificantindustrialuseandweonlyfounditreportedasaligandinthe preparationofmetal-lanthanidecomplexesorspecialmetalcomplexes [26,27].Thewidespreaduseofpyridinesmeansthatmostofthemare availableatlowercostthanthecompoundspresentlyusedasPITTtrac- ers.

Pyridinesareprobablyoneoftheleastobviouschoicesforuseas PITTtracercandidatesbecauseoftwomainissues:i)pyridineitselfhas beenidentifiedasaminorconstituentofcrudeoils;ii)pyridineandits derivativesareweakbases,andthereforepHsensitivecompoundswhen inaqueoussolution.However,thePITTisprimarilydesignedformature oilfieldswherewaterfloodinghasbeenperformedforlongperiodsof time(typicallyyears).Insuchfields,itcanbeexpectedthatachemical equilibrium(orquasi-equilibrium)isestablishedbetweenthehydrocar- bonsandthecirculatingaqueousphase,whichwillkeepthedissolution ofpyridinesinthewateratalowconcentration.Suchconditionswill notaffecttheuseofpyridinesasPITTtracers,asthebackground“noise” willnotcompromisedetectionofthepyridineinjectedastracer.Are- centstudyfoundnoevidenceofthepresenceofpyridineinproduction watersfromeightoilfieldsontheNorwegiancontinentalshelf[28].The useofdeuteratedformsofpyridine,couldalsobeusedtodistinguishthe PITTtracerfromnaturalpyridine.ThepHsensitivityofthisfamilyof compoundscouldindicatepHconditionsinsidetheporousmedium.The partitioncoefficient(K)ofpyridinesvariesasfunctionofpH.

2. Materialsandmethods 2.1. Materials

Pyridine(≥99%),4-methoxypyridine(≥99%),3-hydroxypyridine (≥98%), 2-hydroxy-6-methylpyridine (≥97%), kaolinite (nat- ural aluminium silicate 125 μm–250 μm with linear formula Al2O3•2SiO2•2H2O) and limestone powder type “BCR-116″ (95.7%

CaCO3+4.3%MgCO3)werepurchasedfromSigma–Aldrich(Sigma–

Aldrich Norway AS, 0252 Oslo). Berea sandstone powder [93.13%

silica (SiO₂), 3.86% alumina (Al₂O₃), 0.11% ferric oxide (Fe₂O₃), 0.54%ferrousoxide(FeO),0.25%magnesiumoxide(MgO),and0.10%

calciumoxide(CaO)](125μm–250μm)wasobtainedbycrushingand sievingsandstonecorespurchasedfromBereaSandstone^TMPetroleum Cores(Ohio,USA).

2.2. Experimentalprocedure

1Lof10 mgL⁻¹solutionoftheselectedpyridineswasprepared in a synthetic brine. The brine was constituted of 36.855 g L⁻¹ of NaCl,0.629gL⁻¹ofKCl,3.814gL⁻¹ofCaCl₂.2H₂O,2.550gL⁻¹of MgCl₂.6H₂O,0.088gL⁻¹ofBaCl₂.2H2O,0.437gL⁻¹ofSrCl₂.6H2O, and0.046gL⁻¹ofNa₂SO₄.ThepHofthissolutionwas5.5.Twoother solutionstotestthecompoundsatpH7.1and8.0werepreparedusing ofNaHCO₃toadjustthepHvalues.

Oxygen was removed from thesolutions throughsonication and spargingwith5mL/minofargonfor20min.Thesolutionswerekept underconstantspargingofargonduringthewholetimeofsampleprepa- ration.4setsofdurexglasstesttubeswereprepared:1setcontaining norocksubstrate,1setcontaining600mgofkaolinite,1setcontaining 600mgofBereasandstone,and1setcontaining600mgoflimestone.

2mLofthesolutionofthetracercandidateswastransferredtothetest tubes. Vacuumwasappliedtotheheadspace ofthetesttubesduring theirheat-sealing.Theexperimentswereperformedintriplicate.The testtubeswerethenincubatedduring12weeksattemperaturesupto 150°Cinthermalcabinets.Thethermalcabinetshadarotationmecha- nismwhichensuredsmoothagitationandhomogeneityofthebulkdur- ingtheexperimentalperiod.Theconcentrationofthetestedpyridines wasmonitoredafter1,3,6,and12weeksofincubation.Thequantifi- cationofthecompoundswasdonebyUPLC-UVwithdetectionat222 and254 nm,by injecting10 μLof thetestsamplesfilteredthrough a 0.45 μmPTFE filterinto the chromatographic system. A “Agilent Technologies1290InfinityII” UPLC(AgilentTechnologies,SantaClara, California,USA)equippedwithaWaters“AcquityUPLCBEH” reversed- phaseC181.7μmpackedcolumn(WatersCorporation,Milford,Mas- sachusetts,USA)wasused.Elutionofallpyridineswasachievedwith agradientwiththreeeluentsinthemobilephase.Thesewereabuffer solutionof5mMNH4HCO2,methanol,andacetonitrile,atatotalcon- stantflowrateof0.5mL/min.Thetotaltimeofthechromatographic runwas10min.

3. Resultsanddiscussion

Resultsarepresentedintheformofremainingfraction(RF)asfunc- tionoftime(t)andtemperature(T).RFofthetestedpyridinesisdefined asC(t,T)/C(t₀,T₀).Analyticaluncertaintyisdeliberatelynotdepicted tofacilitatethereadingofthefigures.Typicalstandarddeviationvalues (𝜎)inthedeterminationoftheconcentrationinthetriplicatereplicas rangefrom0,04to0,08.

3.1. Pyridine

Fig.1depictstheRFvaluesofpyridineasfunctionoftimeandtem- peratureatthedifferentinitialpHvalues.

NocleartrendisobservablefortheRFvaluesofpyridine(Fig.1) asfunctionoftime,temperature,andpH.Thevariationsobservedcan

Fig.1.RFofpyridineasfunctionoftimeandtemperatureofincubation.(A) InitialpH5.5;(B)InitialpH7.1;(C)InitialpH8.0andnorocksubstrateinany ofthesamples.

beattributedtoanalyticaluncertainty.Thus,resultsshowthatpyridine exhibitsthestabilityrequiredforuseasPITTtracer.Massconservation iscriticalforthisapplication.

3.2. 2-Hydroxy-6-methylpyridine

2-Hydroxy-6-methylpyridine(resultsinFig.2)isonlystableatatem- peratureof 25°C.Unsuccessfulattempts(notpresentedinthisdocu- ment)todevelopakineticmodelforthedegradationof2-hydroxy-6- methylpyridineweremade.

Fig.2.RFof2-hydroxy-6-methylpyridineasfunctionoftimeandtemperature ofincubation.(A)InitialpH5.5;(B)InitialpH7.1;(C)InitialpH8.0andno rocksubstrate.

ThedecreaseinRFvaluesof2-hydroxy-6-methylpyridineobserved atmildtemperaturesof50°Cand75°Calsosuggeststhatthiscompound maybepronetomicrobialdegradation.Therateofdegradationof2- hydroxy-6-methylpyridineappearstobelowerwithincreasinginitial pHvalues.Thiseffectisparticularlynoticeableforshorterincubation periodsandhighertemperatures.Asthetimeofincubationincreases,re- sultssuggestthattemperaturebecomesthepredominantdrivingforce behindthedegradationprocess,andinfluenceofpHbecomeslessclear.

Thus2-hydroxy-6-methylpyridineisnotaneffectivecandidatetocon- siderasPITTtracer.Furthermore,thedifficultyinaccuratelydescribing

M. Silva, H. Stray, M. Ould Metidji et al. Upstream Oil and Gas Technology 6 (2021) 100033

Fig.3.RFof3-Hydroxypyridineasfunctionoftimeandtemperatureofincu- bation.(A)InitialpH5.5;(B)InitialpH7.1;(C)InitialpH8.0andnorock substrate.

thedegradationofthiscompoundleadsustoconcludethatitismost likelyinappropriateforanyuseastracer.

3.3. 3-Hydroxypyridine3-Hydroxypyridine

Fig.3isstableattemperaturesupto75°Cand12weeksofthermal incubation.Microbialactivityisunlikelyattemperatureswheredegra- dationisobserved.Theuseof3-hydroxypyridineasmassconservative tracercouldstillbeconsideredinlowtemperaturereservoirs,typically onshorelowdepthones,orinenvironmentalapplicationssuchasas-

sessmentofnear-surfacecontaminationsbynone-aqueousphaseliquids (NAPL). Effortstoidentifydegradationproductswereunfruitful.The thermallydrivendegradationof3-hydroxypyridineappearstobeslower athigherpHvalues,however,thisprotectiveeffectisnotsufficientto compensateforthetemperatureeffect.3-Hydroxypyridineisunlikelyto haveanyapplicationastracerinanoilreservoir.

3.4. 4-Methoxypyridine

4-Methoxypyridine degradesattemperatures≥75 °Cwith noin- fluencefrompH(Fig.4).Thissuggestathermallydrivendegradation mechanism.

Therateatwhichthedegradationof4-methoxypyridineoccursis notlinear.Thus,isnotzeroorderandispossiblyconcentrationdepen- dent.FurthertreatmentofthevariationofRFvaluesofthiscompound wasperformedwiththeintentionofassessingtheaccuracyofafirst order kineticdegradation modelin describingtheexperimentaldata.

Anaccuratekineticdegradationmodelopensthepossibilityofusing4- methoxypyridineasanactivetemperatureprobetoretrieveinformation abouttemperatureorthermalfrontsinreservoirs.

3.5. Influenceofrocksubstrate

Three rock materials (Berea sandstone, limestone and kaolinite) wereusedas“model” reservoirrockstoevaluateinteractionwiththe pyridines.Thesematerialsdonotrepresentallthemineralsthatwould beencounteredinanoilbasin,buttheyarerepresentativeofthemost commonsedimentconstituentsandallowforthescreeningofawide rangeofpossibleeffectsandinteractionswiththecompoundsinvesti- gated.

ThemaximumdifferencebetweenRF(t,T)valuesintheexperiments withandwithoutrocksubstrateencounteredforeachofthetestedcom- poundswiththeir±2𝜎errorbarsareshowninFig.5.

Themaximumdifferencesencounteredforpyridineand2-hydroxy- 6-methylpyridineareallwithinanalyticaluncertainty.Thesetwocom- poundshavenosignificantinteractionwiththerockmaterialsandtheir useisnotlimitedbythenatureofthereservoirrocks.

RFvaluesof4-methoxypyridinearenotsignificantlyinfluencedby thepresenceofBereasandstoneandlimestone,butdramaticallyinflu- encedbythepresenceofkaolinite.Inthepresenceofthisclay,themaxi- mumdifferenceinRFvaluesreachesabout0,77.Thus,anyfieldapplica- tionconsideringthiscompoundasapossibletracershouldbeperformed withextremecaution.However,thisalsosuggeststhatthiscompound canpotentiallybeusedtoretrieveinformationaboutthepresenceand distributionofkaoliniteandperhapssimilarclays.

3-Hydroxypyridineisalsoinsensitivetothepresenceofsandstone andcarbonaterockmaterialsandsensitivetokaoliniteinacombined effectwithpH.Fig.5clearlydepictsadecreaseinthemaximumdif- ferencesbetweenRFinexperimentswithnorocksubstrateandexperi- mentswithkaolinitewithincreasingpHvalues.

Excluding the differences observed at 150 °C, results in Fig. 6 show that there is a clearpH dependence on the interactionof 3- hydroxypyridinewithkaolinite.

ThelowerthepHoftheexperiment,thelargeristhedecreaseinthe concentrationof 3-hydroxypyridine inthepresence ofkaolinite.The pKavalue(Table1)for3-hydroxypyridinium(theprotonatedformof 3-hydroxypyridine)is4.79.Thus,asthepHdecreasestheconcentration oftheprotonatedspeciesincreases,whichcouldmakeitmorereactive withtheinterlayerionsinthekaolinite.Theuseofkaoliniteascatalyst inreactionsinvolvingbothorganicandinorganiccompoundshasalso beenreported[29,30].Thus,anotherpossibleexplanationforthereduc- tionoftheRFof3-hydroxypyridinewithpHisthatkaoliniteiscatalysing areactionbetween3-hydroxypyridiniumandoneofthemetalliccations presentinsolution.

Thepossibilitythatkaoliniteisadsorbingeithertheprotonatedform of3-hydroxypyridineoritsotherpossibleproductsisnotlikelybecause

Fig.4.RFof4-methoxypyridineasfunctionoftimeandtemperatureofincu- bation.(A)InitialpH5.5;(B)InitialpH7.1;(C)InitialpH8.0andnorock substrate.

theadsorptionshouldbeafunctionoftemperature.Whateverthecause ofreductionoftheRFof3-hydroxypyridineinthepresenceofkaolin- itemeansthatitwillnotsurvivelongatdetectableconcentrationsin reservoirsedimentscontainingthisclay.

3.6. Kineticsofdegradationof4-methoxypyridine

Thethermalstabilitydataof4-methoxypyridinewasanalysedusing afirstorderkineticmodel..ChangesinC_A/C_A0(RF)at75°C,100°C, 125°C,and150°CareshowninFig.7.

Fig.5.MaximumdifferencesencounteredinRFvaluesbetweenexperiments withrocksubstrate(rs)andexperimentswithoutrocksubstrate±2x𝜎inRF (t,T).(KA)kaolinite,(BS)Bereasandstone,(LS)limestone.(A)InitialpH5.5;

(B)InitialpH7.1;(C)InitialpH8.0.

TheLn(C_A/C_A0)inFig.7werelinearlyregressedasfunctionoftime ofincubation.Forfirstorderkinetics,theapparentrateconstantofthe reaction(k)(weeks⁻¹)ateachtemperatureisthecorrespondingslopeof thelinearregression.WiththelinearisedArrheniuslaw[k(T)asfunc- tionof1/T]theapparentactivationenergyofthereactionandthepre- exponentialfactor(A)wereobtainedwiththeresultpresentedinEq.(1). 𝑙𝑛

(𝐶_𝐴 𝐶_𝐴0

)

=−1,86× 10⁷.𝑒^{−56,𝑅4×10𝑇 3} .𝑡 (1)

M. Silva, H. Stray, M. Ould Metidji et al. Upstream Oil and Gas Technology 6 (2021) 100033

Fig.6. MaximumdifferencesencounteredinRFvaluesof3-hydroxypyridine betweenexperimentswithkaolinite(KA)andexperimentswithoutrocksub- strate(rs)asfunctionoftemperatureandpH.

Fig.7. Ln(RF)of4-methoxypyridineasafunctionoftimeandlinearregressions ateachtemperature.InitialexperimentalpH7.1,norocksubstratepresent.

Theapparentactivationenergyofthereactionis56,4kJ/moland A=1,86×10⁷.

TheaccuracyofthemodelwastestedbycomparingitspredictedRF valueswiththeexperimentalones.Twoadditionaltestsamples(2.2) werepreparedtoobtainRFafter2and4weeksofincubation.Experi- mentalRFvalues±2𝜎intheirdeterminationvsRFvaluespredictedby thekineticmodelarepresentedinFig.8.

4. Conclusions

The stability of pyridine, 2-hydroxy-6-methylpyridine, 3- hydroxypyridine, and 4-methoxypyridine was evaluated at relevant reservoirtemperatures(25°Cto150°C),pH(5,5;7,1and8,0),with elevatedsalinity,andinthepresenceofsandstone,carbonate,andclay materials.

Resultsshowthatpyridineisnotdegradedduringthe12weeksof experimentatalltestedtemperatures.Itisalsoinsensitivetothepres- enceoftherockmaterialsandpHvariations.Thus,pyridineappearsto befullystableandcanbeconsideredasanactive(partitioning)mass conservativereservoirtracer.Sinceithasbeenreportedasaconstituent ofcrudeoilsamplesof producedwatersfromthefieldmustbe tested thoroughlypriortotheuseofthiscompound.

2-hydroxy-6-methylpyridineisonly stableat25 °Cduringthe12 weeksoftesting.Thestabilityofthiscompoundissomewhatinfluenced

Fig.8.ExperimentalvspredictedRFvaluesof4-methoxypyridinebetween75 and150°C.Theuncertaintyof±2𝜎isnotdepictedforvaluesunderthelower analyticalthreshold(RF=0,05).

bypH,becomingmorestableatmorebasicvalues.Thiseffectismore evidentinexperimentsathightesttemperaturesandshortincubation times.No significantinteractionwasobserved between 2-hydroxy-6- methylpyridineandanyoftherocksubstrates.Resultsareinconclusive aboutthenatureofthedegradationphenomena,andmicrobialaction cannotbeexcluded.Thus,anypossibleapplicationbasedonthiscom- poundastracerintheoilfieldishighlyunlikely.

3-Hydroxypyridine isfullystableup to50 °Cduring12 weeksof incubation.Athighertemperatures,thermallydrivendegradationwith influencefromthepHconditionsisobserved.Therateofdegradation decreasesslightlyasthepHincreases.3-Hydroxypyridineisinsensitive tothepresenceofBereasandstoneandlimestone,butastrongeffect onitsstabilityisobservedunderthepresenceofkaoliniteincombina- tionwithpH.Resultssuggestthatkaoliniteismostlikelycatalysinga reactionbetweentheprotonatedspeciesofthiscompoundandacation presentinthebulk,asnotemperatureeffectisobservablewhichwould suggestanadsorptionphenomenon.

4-Methoxypyridine isstablefor12 weeksup to50°C.Thermally drivendegradationofthiscompoundisobservedatallothertestedtem- peratures.Astronginteractionwithkaolinitecausesalargedecrease of theRF values of this compound in thewhole range of tempera- tures tested.Thenatureof thisinteractionisuncertain,asnodegra- dationproductswereidentified.Thistracercandidateisnotaffectedby thepresenceofsandstone,limestoneorpHvariations(inthestudied range)bythemselvesorincombinationwithotherfactors.Thedegra- dationof4-methoxypyridineiswelldescribedbyapseudofirst-order kineticmodelwithoutparticipationofotherchemicalspecies.Theap- parentactivationenergyandthepre-exponentialfactoroftheArrhe- niusequationofthethermaldegradationweredetermined.Theuseof 4-methoxypyridinetoretrievethermalinformationfromthereservoiris suggested.

DeclarationofCompetingInterest

Theauthorshavenoconflictofintereststodeclare.

Acknowledgments

TheauthorsacknowledgetheResearchCouncilofNorwayandthe industrypartners, ConocoPhillipsSkandinaviaAS,AkerBP ASA,Eni NorgeAS,MaerskOil,acompanybyTotal,StatoilPetroleumAS,Nep- tuneEnergy NorgeAS,Lundin NorwayAS,HalliburtonAS,Schlum- bergerNorgeAS,WintershallNorgeAS,andDEANorgeAS,ofTheNa- tionalIORCentreofNorwayforsupport.

References

[1] R. Khaledialidusti , S. Enayatpor , S.J. Badham , C.T. Carlisle , J. Kleppe , An innovative technique for determining residual and current oil saturations using a combination of Log-Inject-Log and SWCT test methods: LIL-SWCT, J. Pet. Sci. Eng. 135 (2015) 618–625 .

[2] O. Dugstad , S. Viig , B. Krognes , R. Kleven , O. Huseby , Tracer monitoring of enhanced oil recovery projects, in: A. Haugan (Ed.), Proceedings of the Sixth International Conference On Tracers and Tracing Methods, Tracer 6, E D P Sciences, Cedex A, 2013 .

[3] A. Muggeridge , A. Cockin , K. Webb , H. Frampton , I. Collins , T. Moulds , P. Salino , Re- covery rates, enhanced oil recovery and technological limits, Philos. Trans. A Math.

Phys. Eng. Sci. 372 (2014) 20120320 .

[4] C. Serres-Piole , H. Preud’homme , N. Moradi-Tehrani , C. Allanic , H. Jullia , R. Lobin- ski , Water tracers in oilfield applications: guidelines, J. Pet. Sci. Eng. 98-99 (2012) 22–39 .

[5] C.E.J. Cooke , Method of Determining Fluid Saturations in Reservoirs ” (US Patent 3,590,923), Esso Production Research Company, USA, 1971 .

[6] M. Silva , H. Stray , T. Bjørnstad , Stability assessment of PITT tracer candidate com- pounds: the case of benzyl alcohols, J. Pet. Sci. Eng. 167 (2018) 517–523 . [7] M. Sanni , M. Al-Abbad , S. Kokal , Ø. Dugstad , S. Hartvig , O. Huseby , Pushing the

envelope of residual oil measurement: a field case study of a new class of inter-well chemical tracers, J. Pet. Sci. Eng. 163 (2018) 538–545 .

[8] M. Silva , H. Stray , T. Bjørnstad , Stability assessment of PITT tracer candidate com- pounds – The case of pyrazines, J. Pet. Sci. Eng. 182 (2019) 106269 .

[9] S.O. Viig , H. Juilla , P. Renouf , R. Kleven , B. Krognes , O. Dugstad , O.K. Huseby , Ap- plication of a new class of chemical tracers to measure oil saturation in partitioning interwell tracer tests, in: Proceedings of the SPE International Symposium On Oil- field Chemistry, Society of Petroleum EngineersThe Woodlands, Texas, USA, 2013 . [10] M.C. Adams , J. Davis , Kinetics of fluorescein decay and its application as a geother-

mal tracer, Geothermics 20 (1991) 53–66 .

[11] M. Schaffer , K.R. Idzik , M. Wilke , T. Licha , Amides as thermo-sensitive tracers for investigating the thermal state of geothermal reservoirs, Geothermics 64 (2016) 180–186 .

[12] J.S. Tang , Propagation of phenol in aquifer with reversible adsorption, in: Proceed- ings of the Go-Expo Gas and Oil Exposition and the 4 Annual Canadian International Petroleum Conference and the 54 Annual Technical Meeting of the Petroleum So- ciety of CIM: Global Challenges and Technology Integration, Petroleum Society of CIM, Canada, 2003 .

[13] G.H.C. Prado , Y. Rao , A. de Klerk , Nitrogen removal from oil: a review, Energy Fuels 31 (2017) 14–36 .

[14] P.J. King , F. Morton , A. Sagarra , Chemistry and physics of petroleum, in: G.D. Hob- son, W. Pohl (Eds.), Modern Petroleum Technology, Applied Science Publishers, Barking, U.K., 1973 .

[15] E. Bae , J.-.G. Na , S.H. Chung , H.S. Kim , S. Kim , Identification of about 30,000 chemi- cal components in Shale Oils by Electrospray Ionization (ESI) and Atmospheric Pres- sure Photoionization (APPI) coupled with 15 T Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR MS) and a comparison to conventional oil, Energy Fuels 24 (2010) 2563–2569 .

[16] S. Shimizu , N. Watanabe , T. Kataoka , T. Shoji , A. Nobuyuki , S. Morishita , H. Ichimura , Pyridine and pyridine derivatives, Ullmann’s Encyclopedia of Indus- trial Chemistry, Wiley-VCH, 2000 .

[17] S.-m. Liu , C.-.H. Wu , H.-.J. Huang , Toxicity and anaerobic biodegradability of pyri- dine and its derivatives under sulfidogenic conditions, Chemosphere 36 (1998) 2345–2357 .

[18] J. Shen , Y. Chen , S. Wu , H. Wu , X. Liu , X. Sun , J. Li , L. Wang , Enhanced pyridine biodegradation under anoxic condition: the key role of nitrate as the electron accep- tor, Chem. Eng. J. 277 (2015) 140–149 .

[19] H.M. Ahsan , B.K. Breedlove , S. Piangrawee , M.R. Mian , A. Fetoh , G. Cosquer , M. Ya- mashita , Enhancement of electrocatalytic abilities for reducing carbon dioxide: func- tionalization with a redox-active ligand-coordinated metal complex, Dalton Trans.

47 (2018) 11313–11316 .

[20] S.Y. Desjardins , K.J. Cavell , J.L. Hoare , B.W. Skelton , A.N. Sobolev , A.H. White , W. Keim , Single component N-O chelated arylnickel(II) complexes as ethene poly- merisation and CO/ethene copolymerisation catalysts. Examples of ligand induced changes to the reaction pathway, J. Organomet. Chem. 544 (1997) 163–174 . [21] F.A. Mautner , M. Traber , R.C. Fischer , K. Reichmann , R. Vicente , Synthesis and char-

acterization of pseudohalide-metal(II) complexes with 4-methoxypyridine as co-li- gand, Polyhedron 144 (2018) 30–35 .

[22] K. Yamada , M. Brousseau , W. Honma , A. Iimura , H. Imase , Y. Iwaki , T. Kawanami , D. LaSala , G. Liang , H. Mitani , K. Nonomura , O. Ohmori , M. Pan , D.F. Rigel , I. Umemura , K. Yasoshima , G. Zhu , M. Mogi , Discovery of a novel piperidine-based inhibitor of Cholesteryl Ester Transfer Protein (CETP) that retains activity in hyper- triglyceridemic plasma, J. Med. Chem. 60 (2017) 8466–8481 .

[23] M.C. Gutiérrez , D. Carriazo , C.O. Ania , J.B. Parra , M.L. Ferrer , F. del Monte , Deep eutectic solvents as both precursors and structure directing agents in the synthe- sis of nitrogen doped hierarchical carbons highly suitable for CO 2capture, Energy Environ. Sci. 4 (2011) 3535–3544 .

[24] D.-.H. Kim , A.Y. Sung , Preparation and characterization of ophthalmic polymer con- taining pyridine group and platinum nanoparticles with initiator behavior using photo and thermal polymerization, J. Nanosci. Nanotechnol. 18 (2018) 7027–7032 . [25] S. Kaviani , M. Izadyar , The possibility of iron chelation therapy in the presence of different HPOs; a molecular approach to the non-covalent interactions and binding energies, J. Mol. Struct 1166 (2018) 448–455 .

[26] A. Chakraborty , J.E. Yarnell , R.D. Sommer , S. Roy , F.N. Castellano , Excited-state processes of Cyclometalated Platinum(II) charge-transfer dimers bridged by hydrox- ypyridines, Inorg. Chem. 57 (2018) 1298–1310 .

[27] J.G. Ma ł ecki , J. Mrozi ń ski , K. Michalik , Structural, spectroscopic and magnetic prop- erties of Mn(II), Co(II) and Ni(II) complexes with 2-hydroxy-6-methylpyridine lig- and, Polyhedron. 30 (2011) 1806–1814 .

[28] M. Silva , T. Bjørnstad , Determination of phase-partitioning tracer candidates in pro- duction waters from oilfields based on solid-phase microextraction followed by gas chromatography-tandem mass spectrometry, J. Chromatogr. A 1629 (2020) 461508 . [29] T.P. Vorlicek , G.R. Helz , Catalysis by mineral surfaces: implications for Mo geochem- istry in anoxic environments, Geochim. Cosmochim. Acta 66 (2002) 3679–3692 . [30] T.J. Strathmann , A.T. Stone , Mineral surface catalysis of reactions between FeII and

oxime carbamate pesticides, Geochim. Cosmochim. Acta 67 (2003) 2775–2791 .