SPE-171295-MS

ImprovingofCleaningEfficiencyofOilPipelinefromParaffin

MikhailS.Turbakov,PermNationalResearchPolytechnicUniversity;EvgeniiP.Riabokon,IFPSchool

Copyright2014,SocietyofPetroleumEngineers

ThispaperwaspreparedforpresentationattheSPERussianOilandGasExplorationandProductionTechnicalConferenceandExhibitionheldinMoscow,Russia,14–16October2014.

ThispaperwasselectedforpresentationbyanSPEprogramcommitteefollowingreviewofinformationcontainedinanabstractsubmittedbytheauthor(s).ContentsofthepaperhavenotbeenreviewedbytheSocietyofPetroleumEngineersandaresubjecttocorrectionbytheauthor(s).ThematerialdoesnotnecessarilyreflectanypositionoftheSocietyofPetroleumEngineers,itsofficers,ormembers.Electronicreproduction,distribution,orstorageofanypartofthispaperwithoutthewrittenconsentoftheSocietyofPetroleumEngineersisprohibited.Permissiontoreproduceinprintisrestrictedtoanabstractofnotmorethan300words;illustrationsmaynotbecopied.TheabstractmustcontainconspicuousacknowledgmentofSPEcopyright.

Abstract

Thepurposeofthispaperistopresentandanalyzewaxdepositionmechanismontheinneroilpipewall.Itisshownthatthefactorssuchaspressure,temperature,wettabilitynatureofwashedsurfaces,velocityoftheoilduringoilpipelinetransportation,aswellasresinasphalteneandhardparaffinconcentrationinthereservoiroilplaykeyroleinthewaxmatterdeposition.Thepiggingtoolwhichremoveswaxdepositsisproposed.Theadvantagesofthistoolarecomparedwithanalogues.Itisshownthattoolincreasesoperationreliability,oilpipelinelife,highgradecleaningofoilpipelineinthecurvedareasandhaslow-costproduction.

Introduction

Theoilfromdifferentfieldsischaracterizedbywidevarietyofchemicalcompositionandphysicalandchemicalproperties.Intermsofphysicsandchemistryoiliscomplexdispersivesysteminwhichtheasphaltensandresinsareimportantelements.Asphaltenemacromoleculesbeinginthecolloidalstatemaybeattractionandprecipitationcentersforthedissolvedinoilresinmolecules.

Formedasphaltene-resincomplex(ARC)interactswithliquidhydrocarbonmoleculesthatareinARC’szoneofinfluence(attractionzone)(AliSetal.,1994).UnderthetemperaturebelowstartingpointofcrystallizationofhardparaffintheybeingtinyelementscoagulatewithARC.Asaresultasphaltene-resin-paraffincomplexesareformed(ARPC).

Tocleanpipelineintheefficientwayfirsofallunderstandingofwaxformationprocessesisrequired.Uptothepresentmomenttheissuesofwaxdepositionmechanisminthepipelinearenotverycleartounderstandunambiguouslyentirecomplexprocess,thus,roleofseveralfactors,whichaffectinnerpipelineflowsinordertopreventwaxdeposition,isevaluateddifferentlyandempiricalapproachisused.Becauseofthesamereasonthetechnologiesaresuccessfulundercertainconditionsbutaren’tunderothers.

Accordingtotheworldexperienceoilrecoveryprocess,oiltreatmentandtransportationisoftenfollowedbythewaxdepositionontheinnerwallofon-fieldequipment,whichsignificantlydecreasesusefulcrosssectionofproductiontubingandpipelinesystemandleadstothedisturbanceoftechnologicalmodeofwells,controlandmeasurementsequipmentandoilcollecting-transportationpipelinesystem.Theaspirationtomaintainoilrecoveryonthedesignlevelleadstoincreaseofequipmentdeterioration,

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Table1—Worldusedtechnologiesofcleaningpipelines

CountryUSAMyanmarAbuDhabiIndiaUSAIran

UnitedKingdomAngolaBangladeshUSA

Nameofobject/field,owner

Trans-AlaskaPipelineSystemYetagunDevelopmentProjectIntelligentPiggingProject

DeenDayalFieldDevelopmentPipelineProject&SlugCatcherprojectWestCoastoffshorein-fieldpipelinePersianBaygaspipeline,

NationalIranianOilCompanyGaspipelineonMungofield,BPDeepoffshoreoilpipeline,

TheAngolaDeepwaterConsortiumGaspipeline«Bakhrabad-Chittagong»,GasTransmissionCompanyLtdOilpipelinesofPennsylvanianfield

Usedtechnology

Scraperpigging,Intelligentpigging(Fineberg,2013)

Pigging(Intelligentpigging)(Trans-AsiaPipelineServicesFZC,2014)Pigging(Intelligentpigging)(Trans-AsiaPipelineServicesFZC,2014)Pigging(Intelligentpigging)(Trans-AsiaPipelineServicesFZC,2014)Scrapperpiggingϩchemicals(Wylde,2011)Scrapperpigging(Shana,2014)

Scrapperpiggingϩglycol(Offshore,2003)Scrapperpigging(Taxyetal.,2009)Scrapperpigging(AshokeKumar,2011)

Chemicalsolvents,dispersantsϩscrappers(Davis,2008)

increaseofelectricityconsumption(duetohydraulicresistivityincrease)andprobabilityofaccident.Forexample,intensivewaxdepositioncouldtotallyblockwelltubingandannulusincertainareas,whichwouldneedworkoverinordertodewaxthewell(Mordvinovetal.,2008).Theissueofoilupstreamandmainpipelinedewaxingisextremelyrelevantaswell.Theirpurposeistotransportoilconstantlyoverthedistancewhichisupto300kmlong(constructionnormsandrules1.04.03-85).Thatmeansthehighertheclassofthepipelinethebiggerdangeritisrepresentsincaseofpipelineleakandthebiggercouldbetheleakagedistancefromdamagepointtotheinhabitedlocalityorproductionfacilitiesandpremises.Inordertopreventsuchcatastrophicscenarioandtomaintainthepipelinesinthemaximalefficienttechnologicalmodetheyshouldbecheckedandcleanedregularly.Theexamplesofmostspreadandusedtechnologiesarerepresentedinthetable1.

Thetable1belowshowsthatscrapperuseasamechanicalmeanofinnerpipelinewallcleaningfromwaxdepositsisthemostusedmethodcurrently.However,allmentionedtechnologiesarelabor-consuming,hardinuse,notalwaysreliable(dependsonconstruction)andexpensive.

Accordingtothatthereisneedtocreatecleaningmean,whichwouldmeetsuchrequirementsashigherefficiency,reliability,easeoffabricationandlowprice.

Analysisofwaxformationmechanisminpipeline

Fromtheobservationoftechnologicalmodeofmainoilpipeline«Kumkol-Aryskum-Josaly»(Kazakh-stan)thewaxdepositsappearquiteinhomogeneouslyalongoilpipelineduringoiltransportation.Atthefirststageofoilpipeline,wherethetemperatureishigherthanstartingpointofparaffincrystallizationthedepositionisnegligible.Thenthetemperaturebecomeslower,paraffinreleaseintensivelyanditsdepositsbecomesignificant.Nextstageparaffindepositionthicknessdecreasesduetothefactthatoilflowswithalmostconstanttemperaturewhichisequaltogroundtemperatureandmainpartofparaffinwhichdepositsunderthistemperatureisalreadydepositedontoprevioussection.Inparticularintensiveparaffindepositionhappensinthedowntimeperiod,whenoilinthepipelinestartscoolingdown.Thefreezeprocessstartsnearbytheinnerwallofpipelineandspreadstothecentergradually;thevelocityofformationoffreezelayerishighernearbytopwallofpipeline,inotherwordsmostcoldarea.Inthepumpingperiodfreezeparaffinlayerisnotsweptbyoilflowandiskeptinthepipelineuntilsummerseason,whenpipelineandpumpedoiltemperatureincreaseuptothevalue,whichisenoughtosoftenandwashfreezelayer(Dzholdasovetal.,2011).

Fromthisexampleitisobviousthatforefficientpipelinecleaningfromwaxmatterfirstofallitisneededtounderstandwaxdepositsprocessformation(intwoandthreephaseflow).Undertheconditions

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ofoiltemperaturedecreasebelowstartingpointofparaffincrystallizationnucleationandcrystalriseofdendrite-sphericalstructurestartinthesomeactivesurfacepoints,whichconcentrateatthebeginningalongscratch,crackandroughnessingeneral.Graduallyallsurfacebecomescoveredbyparaffinseeds.Onthegrown-upcrystallitesnewcrystalsappearincreasingthetotalthicknessofformeddepositsandmakinggrainysurfacefullofbigamountofbrowsandcavitiesfilledbyoil.

Mechanicalinclusionsandparticlesformedintheoilvolumegasmicrobubbles(Hermanetal.,1999),electrokineticphenomenaandmagnetoelectricpropertiesofthedispersedphaseintheoilexertsignificantinfluenceontheformationofdeposits.

Beforethebeginningofhardparaffinintensivecrystallizationtheoccurringprocessesaredeterminedbytheinfluenceofintermolecularinteractionforces.Duringtheformationundertheinfluenceofcohesionandadsorptionoflargeparticlesofthedispersedphasestrengthenstheroleoftheforcesassociatedwiththesurfaceelectricchargesandtheeffectofhydrodynamicfactors(particletransport,includinginthedirectionperpendiculartotheflowmotion).

Inadditiontoparaffins,aromaticandnaphthenichydrocarbonsareincludedintherefractorycompo-sitionofhydrocarbons.Theyarestronglypolarized;theirparticlesconnectwitheachothermuchlessandformlessdensedeposits;besidestheyareeasiertodissolve.Thenormalparaffinhydrocarbonsarelesspolarized;theyconnecteasierandformdenseandpoorlysolubledeposits.Ahighcontentofaromaticandnaphthenichydrocarbonsreducesadhesionandcohesion(connectionofmoleculesinphase)theparaffins.Itwasdetermined(Hunt,1996)thatwaxdepositsmayactivelyparticipateintheformationofharderodiblesedimentcomplexcompositionincludingwax,mineralsalts(gypsum,calcite)andironsulfide.Waxmatterplayroleofaprocess«initiator»,asabasisfortheformationofothertypesofdeposits.Duringtheoiltransportationsolidhydrocarbonsadsorbhydrophobicthinfilmduetohighwettabilityofthemetal.Thedifferenceinpotentialandpolaritybetweenthehydrophobizedsurfaceandthesurroundingfluidlayersiscreated.Theformedsaltcrystals,ironsulfideandwaxmatterareattractedtothesurfaceoftubing,downholeequipmentandpipelines.Thestrengtheningprocessofwaxparticlesformationwithliquidtemperaturedecreaseandgasdischargeinfreevaporphasefromtheoilleadtocrystalcoatingandattractionofnewparticlesofsaltandironsulfidesfromthevolumeofliquidtotheformingconglom-erates.Theironsulfideparticlesinthebulkliquidplayroleofcentersofnucleationandgrowthofsaltcrystals.

Theproblemofthewaxdepositsformationandcomplexprecipitationsisreasonablytosolvebyusingchemicalswithapplicationofinhibitorsofsaltformationandtheformationofwaxdeposits,i.e.reagentswithcomplexproperties.Researchandexperimentalexperience(oilandgasdivisionofKrasnoholm-skneftJSC«OCBashneft»)shownhighefficiencyof«ReaponIF»reagent,whichhaspropertiesofdemulsifyingcompound,waxdepositionandcorrosioninhibitor,bactericideinrelationtosulfate-regeneratingbacteria.

Duringtheoilmovementinthepipelineasphaltens,thesmallestcomplexesofasphaltensandresinshydrophobizatemetalsurfaceevenwithpresenceofwaterinthepipelinefluid,thereforethecrystalli-zationofhardparaffinandwaxdepositionformationtakeplaceathighwatercutalso.

V.P.Tronovprovedthatthemechanismofformationofresin-paraffindepositsonthesurfaceofequipmentdoesnotdependontheflowmodeparameter,buttheseparametersentirelydeterminetheintensityoftheprocessofdepositsaccumulationonthesurfaceofpipelinecommunications.Hisresearchshowedthattheprocessofaccumulationofresin-paraffindepositsduetocreationandgrowthofwaxcrystalsdirectlyonthesurfaceisobservedwiththeoilsolventpowerdecreaseonthesurfaceofanytype.Thatmeansiftheinnerpipelinesurfacedoesnothaveprotectinglayerwhichdecreasetheconnectionwithoilparaffintheprocessofwaxdepositionisinevasible(Tronov,1970).Themostreliablecoveringmaterialsforthatareproventobeglassepoxyandpolymercomposites(McCafiinetal.,1984).Suchkindofcoatinginnerpipelinewalltechnologiesiscostly.Useofahydrophilizingchemicaladditivesandchemicalreagent-solventsisalaboriousprocess,expensiveandneedsahighrepetitionrate.

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Asaresult,thecalculationofwaxdepositionpreventionconditionslooksmuchmorelogicalandeliminatestheneedforcleaningactivities.

Thus,ifthelistofconditions(thatisbelow)inwhichtheparaffinisinthedissolvedstatearemaintainedinthepipeline,useofcleaningtechnologiesisnotrequired.

1.Flowtemperature,changeinwhichleadstothechangeofphaseflowsandchangesinthecompositionofoil.

2.Saturationpressure,belowwhichthegaspassesintothefreevaporphase,andalsodisturbsthebalanceofthehydrocarbonsystem.

3.Thelevelofroughnessandhydrofobisationofequipmentthatincreasestherateofwaxformation(Mordvinovetal.,2010).However,takingintoaccountthelevelofdevelopmentofmajorfieldsintheRussianFederation,adherenceofthoseconditionsisdifficult.Asaresult,inmostcases,oilpipelineexploitationiscomplicatedbywaxformationbecausetheresinandasphalticcomplexesbegintodepositalreadyinthewell.Insuchcasesitisnecessarytousethetechniquetodeterminethedepthofstartpointofdeposition,oneofwhichisconsideredtobe«Themathematicalmodelfordeterminationthedepthofthestartpointoftheintensivewaxingintheoilwells»(Turbakov,2011).Accordingtocalculations,andbasedontheconditionsofformationandchemicalcompositionofthewaxpickingofpossiblechemicalreagentsisdone(inordertoaddthemintooilflowtopreventwaxformationandincreaseperiodbetweentubingcleaningprocedures)(Turbakov,2011,Turbakovetal.,2012).

Thecarriedoutanalysisshowedthatthemostcommonwaytopreventtheformationandremovalofparaffinonthenumberofdevelopmentsandtechnologiesoftheirapplicationisuseofchemicalreagents,i.e.agentsofdifferentclasseswhichservefordifferentpurposeswhilewaxdepositionpreventionandremoval.Asarulesuchkindofagentsdoesnotinteractwithprocessedfluids.

Chemicalagainstwaxdepositionaresubdividedintoagentsandtheirmixture(solvents,solutionsofsurfactants)andcompositionsforpreventingtheformationofparaffindeposits(inhibitors).Recently,thegrowingproblemofwaxdepositionshasgivenapushtothelarge-scaleuseofchemicalmethodsandresearchinthisarea.

Hydrocarbonsolvents

Aneffectivemethodofremovingparaffinfromthewellandsurfaceequipment,oilpipelineistheuseofsolventsonthebasisoflightoilfractions,thecompositionsoflightoilfractions,naphthenicandaromatichydrocarbons,aswellassurfactants,byproductsandwasteofvarioussurface-activesubstancesproduc-tion(Yukletal.,1988).

Intensivepipeparafinizationsectionsarealsowashedwithsolvent.Incaseofwellcleaningitsundergroundequipmentandthepipelineatashortdistancearecleaned.Surfactantsasadditivestosolventsincreasedispersingpropertiesofremovers.However,theyincreasethecostofreagentsby20Ϭ25%.

AsitistypicalinRussiaFederation,lighthydrocarbons(hexanes,gasoline,solvents,andaromaticfractions),reformingcatalysisproducts(Stabikar)andcompositesolventsbasedonthem«SNPCH-7R-14»and«FLEK»(Turbakov,2011)arewidelyusedashydrocarbonsolvents.

Waxdepositioninhibitors

Incaseofwaxhighformationrateseveralpromisingmethodsofphysicalandchemicalinfluence,includingchemicalinhibitors,areexercised.

Mostoftheinhibitorscurrentlyavailableinthemarketofoilrecoveryreagentsrefertothetypeofso-calledhydrofilizators,mixturesofmultifunctionalhydrophilicsurfactants(McCafiinetal.,1982).Theirfunctioneffectsonadsorptiononmetalsurfaceswithaconstantlyrenewableandsustainablein

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dynamicshydrofilizationaccordingtothefilmmechanism.Suchkindofmechanismpreventswaxformation(Mirsaetal.,1995).Theadvantagesoftheseinhibitorsincludetheeffectiveperformanceunderconditionsofincreasingwatercutandpossibilitytoinputthereagentintheintervalofthebeginningofwaxdeposition.Surfactants,wettingagentsarepolycomponent,andasaconsequence,aremultifunc-tional;theyarewater-soluble,thereforenotapplicableforinhibitorprotectionofequipmentduringrecoveryandtransportationofhighlyparaffinicwaterlessoil.

Whileselectingwaxreagents-inhibitorsandreagents-removersitisneededtotakeintoaccountfollowing:

levelofresearchofthereagentanditspreparedness(accordingtothelevelofstudy)foruse;thereagentimpactonthequalityoftheproducedproduct(ontheoilcollectionandpreparationprocesses,onthequalityofcommercialoil);

●technologicalpropertiesofthereagent(easeofuse,dosing,safetyatwork,effectivepreventionwaxformation);

●economicindicators(capitalexpenditures,operatingcosts).

●●

Anothertypeofwaxreagentsinhibitorsisdetergents-dispersants.Duringinjectionintothesystemtheyareworkingontheprocessofcrystallizationofthesolidcomponentsofoilonthemacromolecularlevelwiththeformationoftheadsorptionlayerofreactantmoleculesonsmallembryoniccrystalshydrocar-bons.

Bydoingsotheabilityofsolidcomponentstosticktogetherisdecreasedaswellastobedepositedontheinnerwallsofoil-fieldequipments.Theirmechanismofthisactionhasphysicalnature.Forexample,thesameeffectgivesheatingofoilwithcrystallizedparaffin,whenasdetergents-dispersantsthereareasphaltene-resinoilcomponents(Newberryetal.,1984).Excepttheeffectivewaxpreventionunderwellsandpipelinesconditionsanotheradvantageofdetergent-dispersantisthatsometimesnotlesseffectiveprotectionfromsedimentsinreservoirsbyretainingsuspensionofmicrocrystalsinthevolumeofoil.Adisadvantageofsuchinhibitorsisthatthereisneedtodelivertheirmainmasspointatatemperatureabovetheoilsaturationbyparaffintemperature(whichmaybeinthewellitself)andincreaseddosesoftheinhibitorproportionallytotheamountofsolidoilhydrocarbon.

Anothergroupincludesdepressant,thesubstancethatcaneffectivelymodifythetermsofwaxcrystallization,reducingthetendencyofindividualmoleculestothenucleationandsubsequentformationon-crystalstructures(Sifferman,1979).Advantagesanddisadvantagesofthisgroupareidenticaltotheabove-describedinhibitorsofdetergent-dispersants.

Ifthementionedaboveinhibitingwaxadditivesarerepresentedmainlybysurfactantsofdifferentclasses,thegroupofmodifiershasdifferentchemicalnature,similartothenatureofsolidmethane-naphthenicoilhydrocarbon.Underthetemperaturesofaboutthesaturationtemperatureofoilbyparaffinthesereactantsinteractwithmoleculesofsolidhydrocarbons,modifyingthesystembygivingittherequiredcomplexofproperties.

Waxcrystalsmodificationmechanism,whenwaxisdepositing,couldbedifferent.Thechoicesare:

modifierprecipitatesoutofsolutionatatemperatureslightlyhigherthanthecloudpointoftheoilandformsnumerousnucleationsites;

●modifierprecipitatesoutofsolutionatthecloudpointofoilandaco-crystallizingsolidhydrocarbons;

●modifierprecipitatesoutofsolutionatlowertemperaturethanthecloudpointandabsorbstheformedcrystals.

●

Crystalmodifiersareoligomericandpolymericmaterials,e.g.polyethylene,copolymeresters,deriv-ativesfrompolyhydrocarbonsandothers.Themainadvantageofmodifiersistoholdparaffindispersed

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inoilallthewayfromdownholetotherefinery.Thisdeterminesthebenefitoftheiruseincomparisonwithothermethodsandtechnologiesagainstwaxdeposition.

Fromthesegroupsofinhibitorsthemosteffectiveismodifiers(Pisula,1995).Itshouldbenotedthatinthedomesticofpetrochemicalindustrytheproductionofcomplexoligomericandpolymericcompo-nentsfortradestateofinhibitors-modifierisunderdeveloped.

Thesignificantresultswereachievedinthedevelopmentofchemicalmethodsofpreventingtheformationofwaxdeposition,howeverhighcostofeffectivereagentsnotallowtousethemon-fieldinrequiredvolumes,inparticularduetovarietyofcompositionandpropertiesofreservoirfluidsanddifferenceinconditionsifthewellsandoilpipelinesystems.Ifafterapplyingtheselectedoptimalmethodscompleteavoidanceisnotpossible,thenthemostrational(mostefficient,leasttime-consumingandhasalowprice)isamechanicalmethodofpipelinecleaning.

Waxcompositioniscomplexandunstableoverthetimeandindifferentpartsofthesystem,whichcomplicatesproblemofitsdeposits.Themainoilpipeline«Kumkol-Aryskum-Zhosaly»exampleshows,thatevenifatthebeginningofthepipelinewax-dissolution-in-liquidconditionsaresupported(thiscanbeachievedeithernaturallyorbyinstallinglinesofelectricheating),thenfurther,attheparticularsection,theywilldepositanyway.Moreover,inconditionsoflowtemperaturesthisphenomenonisinevitable.Hence,periodicmechanicalpipelinecleaningisanintegralprocedureintheupstreamfieldandmainpipelines.

Duringmechanicalpipelinecleaningsuchtoolsasspacers,balls,brushandscraperforsprings,pistons,torpedoesandultrasonicdeviceswithmovingjetvanesareused.

Theworkprincipleofsomeofthemisbasedonmovementwithfluidflow,removingdepositsfromtheinnerpipelinesurfaceandtheirpushing(adisadvantageofthesetoolsispipelineseparationthatleadstotheaccumulationofparaffinandpipelineblockage).Other’sprincipleisremovalofsediments,theirdilutionandwashingoutwithfluidflowpassingthroughthebypassholesoftool(disadvantagesare:pointleachingofsolidsphase,crushingandcompactionofsolidprecipitation,lowreliabilitywhilelongnotachievementoftherequiredpressuredropandhence,lowlifetime;corrosion).

Descriptionoftheproposedpipelinecleaningtechnology

Inordertoimproveandspeeduptheprocessofcleaningtheinnerpipelinesurfaceitisneededtocreatealow-viscosityfluidflowwithfineparticlesofwax,rustandimpuritiesaheadofthetool.Incaseoftoolswithmovingjetvanesunliketorpedoes,pistonsandseparatorspulverizedsolidsphaseaheadofthetoolmixeswiththeliquidandformahomogenizedflowandisentrainedinthedrivingdirection.

ThepiggingtoolforcleaningpipelinesfromparaffinhasbeendevelopedinthePermNationalResearchPolytechnicUniversity(theDecisionofpatentissue09.06.14,request󰀂2013118313).Itcontainsbody1whichismadeasahollowhemisphereofelongatedelasticmaterial,suchasoil-resistantrubber,withaprofoundcut.Alongtheaxisofrotationofthepigthroughmetaltube2isinstalledandfixedinthebody1bycurvedwashers3andnut4.Ontheoutersideofthebody1onthetube2figuralnut5isscrewed,onwhichthefluoroplasticwasher6andthecuff7areplanted.Fixedfluoroplastichollowsleeve8andvane9arefixedbynut4andplacedoncuff7.Vanechannels9areconnectedwiththeinnercavityofthetube2throughtheholes10madeoverthediameterofthetube2.Cuff7andthesleeve8haveholesalignedwiththeholes10.Ontheoppositesidesofthevane9theholes11areplaced.ModelofthepigisshownontheFigure1.

Pigisinstalledinthepipelinethroughthelaunchingchamberandretrievedthroughthereceivingchamberrespectively.Insidethepipelinepigmovesunderpressuredifferencebetweenitsinletandoutletinthedirectionofliquidflow.Viathroughmetaltube2installedinthebody1manufacturedwithprofoundcutononesidethepartliquidgetsintothehollowvane9withtheholes11,outofwhichflowswithhighvelocity,creatingareactiveforceofrotationprovidingthescrapping-offsomeofinnerwallparaffindepositsbyvane’sends.Theparaffinmixeswithliquidandbecomeshomogenizedflow.Double

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Figure1—Piggingtoolforcleaningofoilpipelinefromwaxdeposits

bypasssystemofworkingfluidthroughthemetaltubeandthevaneprovidesreliableblurandstemseparatedwaxdeposits.

Thepressuredifferenceanddiameterofthetubedeterminerateofthepigadvanceinthepipeline.Theworkliquidfromthetubeentersaheadnotyetcleanedpipelinesidethatprovidesblurandstemofseparatedwaxfromtheinnerpipelinesurface.Thus,pulverouswaxisnotdepositontotheoutersurfaceofpigaheadrotatingvaneandnotpushedthroughthepipeline,butwashedbyliquidjetfrommetaltube,whichfacilitateswallcleaning.Thepressureontheinletofpig(upto60bars)contributesgradecontactbetweenthebodyandpipelinewalls.Thatdoesnotallowwaxdepositstoentercleanedsideandpushespigwhichprovidesreliablecleaning.

Asimilardevice,butwithoutthebypassvanesystemhasbeentestedonthepipeline«Nojovka-Mishkino-Kiengop»(Permregion-RepublicofUdmurtia),whichcapacityaftersixyearsofoperationwasdecreasedbyahalfduetowaxdeposits.Theoperationtook15days,buttheinitialpipelinecapacitywasrestored(Grebnev,2006).Upgradeddevicehasperforationsinthelongitudinalandtransversedirectionsoftherotaryvanecreatingjetsofworkingfluid,whichcreatesconditionsforacceleratingthepassageofthedevicethroughthepipelineandprovidesmoreeffectivecleaningoftheinnerpipelinesurfacefromthedeposits.

Highpigpassablenessiscausedbyhisflexiblebodyandshortlength(0,6m).

Thedevicehasthemanufacturesimplicity;sizeofthebodyismoldedtorequireddiameter.

Atthesameupstreampipelinesthroughlaunchingandreceivingchambersasimplifiedversionofthepigwithoutabypasssystemisrun,whichleadstocompletecleaningofthepipelineinareasofcurvaturesduetotheshortlengthoftheflexiblebody.

Conclusions

–Theroughnessoftheinnerpipelinewallandmetalsurfacesofwellequipmentcreatesfavorable

conditionsformoreintensivewaxmatterformationsandotherdeposits.

–Formationofasphaltenedepositsoccurontheinnerwallofthepipeline.Thethicknessofdepositsformedincreaseswithtime,whichleadstoanincreaseinhydraulicresistanceduringmovementofliquidsorliquidmixturesthatleadstotechnologicalmodefailureofwells,measurementandcontrolequipmentandpipelineoilcollectionandtransportationsystems.Intensivewaxmatterdepositioncanleadtoacompleteblockageoftubingandannularincertainareas,causingtheneedofworkoversinordertodewaxing.

–Increaseoffluidvelocityinapipelinereducestherateofwaxformationcontributestodetachmentofsedimentparticlesfromparafinizationsurfacesandtheirremoval.Byincreasingtheflowratethecoolingrateoftransportedinthepipelineliquiddecreases.

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–Waxdepositionremovalfromtheinnerpipelinesurfacecouldbedonebymechanicalmeans(scraper),thermaltreatments(heaters,etc.)andhydrocarbonsolvent(paraffinremovers).

–Forthewaxdepositionwithhighconcentrationofresinsandasphaltene(asphaltenetype)removersofrefiningmaterialandpetrochemicals,includingnaphthenicandaromatichydrocarbonsshouldbeused.

–Reagentsaredepressantpreventcrystalgrowthandtheformationofsolidstructures.Suchagentsaremosteffectiveatlowconcentrationsofasphaltensandresins.

–Forthewaxdepositionofcomplexstructuretheuseofremovers,representingamixtureofparaffinicandaromatichydrocarbonsismoreefficient.

–Improvingoftheefficiencyofactivitiestopreventformationandremovalofwaxdepositsrequiresthecreationandoperationsystemoftheon-fieldandlaboratorystudy,controloftechnologicalprocess,directlyrelatedtothedifficultiesduringthecollectionandtransportationofoil.

–Absenceofrubbingpartsoftheproposedpiggingtoolforcleaningoilpipelinesfromwaxdepositsandthesmallnumberofconnectingnodesincreasethereliabilityandservicelifeofthepipeline.–Theshortlengthofthecleaningpigprovideshigh-qualitycleaningofthecurvedpipelineduetoitsflexibility.

–Thelowcostandresourceconsumptionmaketheproposedpiggingtoolmoreattractiveinfrontofforeignanalogues.

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