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1、Chapter7ScaleInhibitorsSomeriskofscaledepositionoccursinmanyoperationsinthepetroleumin-dustry.Scaledepositionhappensparticularlyinproduction,stimulation,andtransport.Scalingcanoccurwhenasolutionbecomessupersaturated,whichoccursmostlyifthetemperaturechangesinthec
2、ourseofinjectionoperations.Also,iftwochemicalsthatwillformaprecipitatearebroughttogether,ascaleisformed(e.g.,ifahydrogenfluoridesolutionmeetscalciumions).Fromathermodynamicperspective,thereisastableregion,ametastableregion,andanunstableregion,separatedbythebinod
3、alecurveandthespinodalecurve,respectively.Thescalemayconsistofcalciumcarbonate,bariumsulfate,gypsum,stron-tiumsulfate,ironcarbonate,ironoxides,ironsulfides,andmagnesiumsalts[943].Therearemonographs(e.g.,CorrosionandScaleHandbook[159])andreviews[414]onscaledeposi
4、tionsavailableintheliterature.ScaleInhibitionTheproblemisbasicallysimilartopreventingscaleinhibitioninwashingmachines;thereforesimilarchemicalsareusedtopreventscaledeposition.Scaleinhibitioncanbeachievedeitherbyaddingsubstancesthatreactwithpotentialscale-forming
5、substancessothatfromathermodynamicsstandpointthestableregionisreachedorbyaddingsubstancesthatsuppresscrystalgrowth.Conventionalscaleinhibitorsarehydrophilic,thatis,theydissolveinwater.Inthecaseofdown-holesqueezing,itisdesirablethatthescaleinhibitorisadsorbedonth
6、erocktoavoidwashingoutthechemicalbeforeitcanactasdesired.However,adsorptionontherockmaychangethesurfacetensionandthewettabilityofthesystem.Toovercomethesedisadvantages,oil-solublescaleinhibitorshavebeendeveloped.Coatedinhibitorsarealsoavailable.Often,scaleinhibi
7、torsarenotappliedassuch,butratherincombinationwithcorrosioninhibitors.ThermodynamicInhibitorsThermodynamicinhibitorsarecomplexingandchelatingagents,suitableforspecificscales.Forexample,forscaleinhibitionofbariumsulfate,commonchemicalsareethylenediaminetetraaceti
8、cacid(EDTA)andnitrilotriaceticacid.ThesolubilityofcalciumcarbonatecanbeinfluencedbyvaryingthepHorthepartialpressureofcarbondioxide(CO2).Thesolubilityincreaseswithdecr
