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PreparationofPotassiumFormate&MicromaxCompletion&DrillingFluids

Introduction

WereceivedarequesttoformulateaPotassiumFormate/Micromaxcompletionfluidat16ppg&4250f.ThisfluidwasintendedtoreplaceCesiumFormatebrineusedonHPHTcompletions.

ThesuccessfulresultsofthistestingbyElkemhavebeencompleted.SubsequenttothisthecustomeraskedElkemtoformulateaPotassiumFormate/Micromaxdrillingfluid,againat16ppg&4250f.Thetestingforthishasalsobeensuccessfullycompleted.

Theresultsofthesuccessfulformulationsarepartofthisreport.Alsoincludedaredescriptionsoftheprocessbywhichweobtainedourresults,theproblemswehad&ourrecommendations(intheattachedappendix)forsuccessfullytestingofpotassiumformatefluidsathightemperatures.

CompletionFluid

Therequirementsforthiswerefora16ppgfluidstableto4250ffor14days&withminimalsag.Theresultantformulationissimple,usingminimumadditivestoproduceacompletionfluidwithnorequirementforfluidloss,butwithminimalsag.

Asepiolite,PangelHV,wasusedtoprovideextrasuspension&adispersant,ESMD2,wasusedasadeflocculanttopreventflocculationoragglomerationduringsustainedhightemperatureaging.Theresultswithminimalsag,evenafter14daysstaticat4240f,areshownbelowinTable1:

Table116ppgPotassiumFormate/MicromaxCompletionFluid

Additives in order of addition Mixing Time Conc in gram Conc in gram Conc in gram Potassium Formate Brine (SG1.57) 650 650 650 Soda Ash 5 0.35 0.35 0,35 Pangel HV Viscosifier 5 8 8 8 ESM D2 Dispersant 5 4 4 4 Micromax 10 268 268 268 Mud Weight, ppg 16.0 16.0 16.0

Heat Aged at ( 4240f ) BSHA

ASHA 7 days 4240f BSHA

ASHA 10 days

4240f BSHA

ASHA 14 days

4240f 600 rpm 62 93 62 124 62 130 300 rpm 39 68 39 94 39 92 200 rpm 31 58 31 81 31 79 100 rpm 23 45 23 67 23 63 6 rpm 12 25 12 45 12 37 3 rpm 11 23 11 40 11 34 PV @ 120F, cP ( 50 C ) 23 25 23 30 23 38 YP, lb/100ft2 16 43 16 64 16 54 10 sec Gel, lb/100ft2 18 20 18 25 18 26 10 min Gel, lb/100ft2 21 21 21 26 21 26 pH 9 12.88 9 13.0 9 12,2 Supernatant liquid ( ml ) 0 0 0 Density Top 2.15 1.91 1,98 Density Bottom 2.20 1.95 2,08 Sag Factor 0.506 0.505 0,512

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DrillingFluid

Therequirementsforthepotassiumformate/Micromaxdrillingfluidwerefor16ppg@4250fwithlow,upperendrheologytoprovidelowECDs,minimalsag&anHPHTfluidlossof

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Descriptionof&RecommendationsforTestingaPotassiumFormateFluidatHighTemperature

Formulating&testingsaturatedpotassiumformatefluids,especiallyatultrahightemperatures,presentcertainissuesnotseeninotherwaterbasefluids:

a) Potassiumformateisextremelysolubleinwateratupto77%w/w.Thisresultsinleavinglittlefreewatertodissolveadditives.Accordingly,whenaddingaproductrequiringsolubilisation,suchasafluidlosscontrolpolymer(Dristemp,Kemsealetc),sufficienttime&energyisneededtoallowdissolutiontotakeplace.Oneoftheconsequencesofagingathightemperaturemaybethatthesepolymerssaltout,evenifproperlydissolvedpriortoaging.Therefore,theuseofcertainpolymersmayprovetobeimpossibleabovecertainconcentrationsathightemperature.Whenintendingtouseasaturatedpotassiumformatefluiditisrecommendedto:

I. PrehydratepolymersinwaterII. AddsaturatedpotassiumformatebrineIII. Addpowderedpotassiumformatetobringtheresultingfluiduptosaturationwrtpotassium

formate

Nondissolvingadditivessuchassepiolite(PangelHV),Micromax,CaCO3etcdonotrequireprehydration,butdoneedsufficientsheartoproperlydisperse.

b) ThenaturalpHofsaturatedpotassiumformatebrineisalkaline.Thebrineusedinthisstudywasaround10.Thepotassiumformatepowderwasstronglyalkalinewhenaddedtothefluidtosaturateit.WithouttreatmentthiswouldresultinpHvaluesof>11bothbefore&afteraging.TopreventhydrolysisofadditivesitisrecommendedtoreducethepHusingformicacid,beforeaging,toca9.5.Furthertreatmentafteragingmaybenecessary

c) DespitereducingthepHbeforeagingitisrecommendedtobufferthefluidwithNa2CO3orNaHCO3.Thereasonforthisistomaintainanequilibriumawayfromdecompositionoftheformate

d) Formatesdodecomposeathightemperature,butthereisamuchgreaterdegreeofdecompositionunderlabtestingthanoccursinthefield.CabotinboththeirFormateManuals&inconversationhaveexplainedthelargedifferencebetweenresultsachievedinlabtesting&thoseachievedinthefield.Essentially,labresultsshowmoredecomposition&corrosion,whichtheyhavenotseenoccurringinthefield.Theyattributethistothefollowing:

I. FormatedecompositiontoCO,CO2orH2isanequilibriumprocessII. TestcellscontainheadspacegassuchasN2,CO2orairinamuchhigherproportiontothat

experiencedinawell.Thislargeramountofgasleadstomoredecompositionbecausethereactiongasesescapeintotheheadspace&delayequilibriumbeingreached

III. Labtestingisconductedatlowpressure(100sofPSI).HPHTwellsareathighpressure(thousandsofPSI)&equilibriumisreachedearlier.Higherpressurerestrictsdecomposition

IV. Labtestcellsaremadeofstainlesssteelalloyscontaininge.g.nickel,whichactascatalystsinthepotassiumformatedecompositionreaction

V. Wellscontaintubularscoveredincorrosionproductssuchasmillscale,whichpoisonsuchcatalyticactivity

Insummary,labderivedfiguresformaximumoperatingtemperaturesaresignificantlyexceededinthefield&thetemperaturelimitsofusingpotassiumformatesshouldnotbebasedonmostofthelabworkpreviouslyconducted.TestsdonebytheWoodsHoleInstusingspecialequipmentdeterminedthat:

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Thedecompositionofformatebrineswill,underrealistichydrothermalconditions,reachequilibriumrelativelysoon.

Themajorproductofformatedecompositionisbicarbonate,whichisalreadypresentinformatebrineasacomponentofthepHbuffer.Somecarbonateisalsoformed,whichisthesecondpHbuffercomponent.

Byaddingextracarbonate/bicarbonatebuffertothebrine,itshouldbepossibletoformulateathermallystableformatefluid.Suchafluidreachesequilibriumafterjustaveryminordegreeofdecomposition.

e) Becausemoredecompositionoccurswhilsttestinginlabconditions,manytestscanbedifficulttorunaccurately.AtthehightemperaturesappliedheretheproductionofH2&CO2resultedinsignificantfoamingofthemudinthetestcell.Suchfoamingcancompromisetestssuchasthesagfactor.Forrheologyorfluidtestingitisbettertoallowthesampletobegentlystirredbeforerunningtheteststopermittheremovaloftheentrainedgases

f) Agingcellsusedtotestformatebrinesaresubjecttocorrosionfromthedecompositionproducts.Therefore,itisrecommendedtouseTeflonlinersuptoca3900f&glasslinersabovethat

Conclusions

Thetestingofwaterbasefluidsathightemperaturesisadifficultprocess.Manychemicalreactionsareaccelerated&additivesmaydegradefrome.g.oxidationorhydrolysis.However,itiswellknownthattheuseofformatesextendsthetemperaturerangeofmanypolymers,primarilythroughtheantioxidativenatureoftheformates.However,athightemperaturesunderlabconditions,formatefluidsdecomposeatlowertemperaturesthanoccurinthefield.Thiscausesproblemsineffectivelyformulating&testingsuchfluids.Despitethesedifficultieswehavesuccessfullyformulated&testedbothacompletion&adrillingfluidto16ppg&4200f.Todothiswediscovered:

Astrictprocess(asdetailedabove)needstobefollowedtosuccessfullytestformatesathightemperature Althoughmanypolymershavetheirtemperatureoperatinglimitssignificantlyextendedinformates,high

concentrationsofsuchpolymersmayresultinthemsaltingoutathightemperature.Therefore,thechoiceofpolymeradditiveisnotobviousfromitschemistry&requirestestingtodetermineitssuitabilityforsuchanapplication

Dristemp,PACLV,&CaCO3(20)weretheonlyfluidlossadditivestosuccessfullywork(together)undertheprescribedconditions

Adeflocculant,ESMD2,isneededtoensurerheologicalstabilityundertheseconditions Asuccessfulformulationhasbeenachievedmeetingthecustomersrequirements