subsea intervention

OT5301SUBSEASYSTEMSENGINEERING

ASSIGNMENT1SUBSEAINTERVENTION

PREPAREDBY:ASEPNURULHAQ

A0081910M

DEPARTMENTOFCIVIL&ENVIRONMENTALENGINEERINGNATIONALUNIVERSITYOFSINGAPORE

OT5301SubseaSystemsEngineeringAssignment1(SubseaIntervention)AsepNurulHaq(A0081910M)

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Contents1 Introduction..........................................................................................................................................22 SubseaWellIntervention......................................................................................................................32.1 Whatissubseawellintervention?................................................................................................32.2 Whatarethevarioustypeofsubseawellintervention?..............................................................32.2.1 LightIntervention..................................................................................................................32.2.2 MediumIntervention............................................................................................................42.2.3 HeavyIntervention................................................................................................................4

2.3 Whataretheactivitiesofsubseawellintervention?...................................................................42.4 Whataretheequipmentsinvolved?............................................................................................52.5 Whatisusedtointervenethewells?..........................................................................................112.6 Whyyouhavetodosubseaintervention?.................................................................................132.7 Whenyouhavetodo?................................................................................................................132.8 Howmuchisthecostofsubseawellintervention?...................................................................132.9 Whichcompanyofferssubseainterventionservices?...............................................................14

3 SubseaROV/ROTIntervention...........................................................................................................153.1 WhatissubseaROV/ROTintervention?....................................................................................153.2 WhatarethevarioustypeofsubseaROV/ROTinterventionactivity?.....................................153.2.1 Sitesurvey...........................................................................................................................153.2.2 DrillingAssistance...............................................................................................................163.2.3 InstallationAssistance.........................................................................................................173.2.4 OperationAssistance..........................................................................................................183.2.5 Inspection............................................................................................................................183.2.6 MaintenanceandRepair.....................................................................................................20

3.3 HowdoyouperformsubseaROV/ROTintervention?...............................................................203.4 WhataretheequipmentinvolvedinsubseaROV/ROTintervention?......................................203.4.1 ROVInterventionSystem....................................................................................................203.4.2 ROVMachine......................................................................................................................253.4.3 RemoteOperatedTool(ROT).............................................................................................28

Bibliography................................................................................................................................................30


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1 IntroductionSubsea intervention by definition means intervention that is done subsea or underwater. Uponliterature study, writer found that various sources define subsea intervention differently. FromWikipedia& Subsea System Engineering Lecture Notes from Prof. LohWay Lam,writer learns thatsubsea intervention relatesmore towell intervention that is done subsea. Yong Bai define subseaintervention as all types of work that is done subsea by using ROV and coined the term ROVIntervention. In thispaper,writerwill cover thedefinitionof subsea intervention fromboth sources.Belowchartshowswhichcategoryeachdefinitionliestoeasereaderintheunderstandingofwhatisthedifferencebetweenthosedefinitions.

Figure1SubseaInterventionDefinition

Asbothdefinitionofsubseaintervention,theyareentitledtohavetheirownseparatechapterintermsofthekeycomponentsthatthispaperneedstocover,whichare:

o Whatissubseaintervention?o Whatarethevarioustypeofsubseaintervention?o Whatyouhavetodoinsubseaintervention?o Whatisinvolvedinsubseaintervention?o Whyyouhavetodosubseaintervention?o Whendoyouhavetodosubseaintervention?o Howyoudoasubseaintervention?

SubseaIntervention

SubseaWellIntervention

LightIntervention

MediumIntervention

HeavyIntervention

SubseaROV/ROT

Intervention

ROVIntervention

ROTIntervention


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o Howmuchisittodoasubseaintervention?o Whoisdoingsubseaintervention?

This paperwill first cover the definition of subsea intervention byWikipedia and LohWay Lam andcontinuewiththedefinitionofsubseainterventionbyYongBai.

2 SubseaWellIntervention2.1 Whatissubseawellintervention?Asubseawellinterventionisanyoperationcarriedoutonasubseaoilorgaswellduring,orattheendof itsproductive life,thataltersthestateofthewellandorwellgeometry,provideswelldiagnostics,managestheproductionofthewelloractivityrequiredtosafelyabandonssubseawells.2.2 Whatarethevarioustypeofsubseawellintervention?Subsea well intervention falls into 3 types, light intervention, medium intervention and heavyintervention.2.2.1 LightInterventionItuseswirelineandslickline.Activitiesinvolvedare:

o Loggingo Lightperforatingo Zoneisolationo Plugsetting/removal

Figure2LightIntervention


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2.2.2 MediumInterventionItusescoiledtubing,wirelineandslickline.Activitiesinvolvedare:

o Flowlineinterventiono Wellcommissioningo Wellabandonmento Downholepumpchangeouto Acidizingorfracjobo Sandorscalecleanouto Watershutoffo Scrapingo Downholevalveretrievalo Replacemento Casingleakrepairs

2.2.3 HeavyInterventionActivitiesinvolvedare:

o Scalemillingo Completionchangeout/repairo Redrillorsidetracko Christmastreechangeout

2.3 Whataretheactivitiesofsubseawellintervention? Pumping

Thisisthesimplestformofinterventionasitdoesnotinvolveputtinghardwareintothewellitself.FrequentlyitsimplyinvolvesrigginguptothekillwingvalveontheChristmastreeandpumpingthechemicalsintothewell.

WellheadandChristmastreemaintenanceThecomplexityofthisoperationcanvarydependingontheconditionofthewellheads.Scheduledannualmaintenancemaysimply involvegreasingandpressuretestingthevalueonthehardware.Sometimesthedownholesafetyvalveispressuretestedaswell.

SlicklineSlicklineoperationsmaybeusedforfishing,gaugecutting,settingorremovingplugs,deployingorremovingwirelineretrievablevalvesandmemorylogging.


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BraidedlineThis ismorecomplex than slicklinedue to theneed foragrease injection system in the rigup toensure theBOPs can sealaround thebraided contoursof thewire. Italso requiresanadditionalshearsealBOPasatertiarybarrierastheuppermastervalveontheXmastreecanonlycutslickline.Braided line includesboth thecorelessvarietyused forheaving fishingandelectriclineused forloggingandperforating.

CoiledtubingCoiledtubingisusedwhenitisdesiredtopumpchemicalsdirectlytothebottomofthewell,suchasinacirculatingoperationorachemicalwash.Itcanalsobeusedfortasksnormallydonebywirelineif the deviation in thewell is too severe for gravity to lower the toolstring and circumstancespreventtheuseofawirelinetractor.

SnubbingAlso known as hydraulic workover, this involves forcing a string of pipe into the well againstwellborepressuretoperformtherequiredtasks.Therigup is largerthanforcoiledtubingandthepipemorerigid.

WorkoverInsomeolderwells,changingreservoirconditionsordeterioratingconditionofthecompletionmaynecessitatepullingitouttoreplaceitwithafreshcompletion.

2.4 Whataretheequipmentsinvolved?Thefollowingaretheequipmentinvolvedinsubseawellintervention.1. TheVessel(WorkPlatform)

o LightinterventionvesselAnexampleofa light interventionvessel is theHelixWellEnhancer.Light interventionvesselusuallyhasthefollowingspecification: DynamicPositioningSystem,toallowthemtomaintainpositionduringsubseaintervention

activity Offshore crane/modulehandling tower, forperforming subsea riserlesswell intervention

services Moonpool,toallowROV/interventiontooldeployment ROVcapabilitysuchasROVcontrolroom Liquidcargodischargesystems,topumpmud/producttowell Operatingdepth600m 100Tecrane 1,100m2maindeckspace 7x7mmoonpool


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Figure3LightInterventionVessel(HelixWellEnhancer)

o MediuminterventionvesselAnexampleofamediuminterventionvesselisUlsteinXBow.AsidefromthebasicrequirementofaninterventionvesselsuchasDynamicPositioningSystem,MoonpoolandROVcapability,amedium intervention vessel usually has larger deck area, crane andmoon pool as detailedbelow: Size:120mlongx25mbreadth Operatingdepth2500m 150TeCrane Deckarea1380m2 8mx8mmoonpool

Figure4MediumInterventionVessel(UlsteinXBow)


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o Heavyinterventionvessel

AnexampleofaheavyinterventionvesselistheQ4000ownedbyWellOps,comparedtolightandmediuminterventionvessel,itskeydifferentiatorare: Semisubmersible,size:95mx64m Operatingdepthin3000m 600Tederrickcrane,350Temaincrane,160Tesecondarycrane 12mx6mmoonpool

Figure5HeavyInterventionVessel(HelixQ4000)


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o OffshoreSupportVesselsSupport vessels transports personnel, cargos, fuel, cement,mud, freshwater, etc to distantdeepwaterfield.Theyhaveanchorhandling,towing,mooring,emergencyresponse/rescueandfirefightingcapacities.Theyarealsoequippedwithdynamicpositioning.

Figure6AkerPSV22OffshoreSupportVessel

o MultipurposeSupplyVessels

MultipurposeSupplyVesselscarryandonloading/offloadingsuppliesandservices tooffshoreinstallations. They also have fire fighting capacities and dynamic positioning capabilities. Thevesselsarealsodesignedtostoreandtransportdrinkingor industrialwater,drillingmud,fuel,methanolorcementandalsoforROVoperations.

Figure7HOSStronglineMultipurposeSupplyVessel


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Figure8HOSIronhorseMultipurposeSupportVessel

2. TheSubseaVehicle(InterventionSupport)ThesubseavehicleforinterventionsupportistheROV(remoteoperatedvehicle).

Figure9ROV


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VehicleDutieswithinanInterventionare: Survey(Visualonly)

o Wellpositionestablishment/Depthcorrelationo LeakDetectiono Interfacecondition(priortointervention)o Valvepositionverificationo Connectorpositionverificationo Etc..

WellPreparation(Variesdependingonintervention)o Obstructionremoval(manipulator)o Guideline/Guidewireestablishment(manipulator)o Protectivecoverremoval(manipulator)o Liftlineestablishment(manipulator)o TreeCap/WellheadConnector/etc.o Etc..

WellIntervention(Variesdependingonintervention)o ValveActuatorOverride(TDU/Piston/TTool)o Temporary/Permanento WellheadConnectorOverride(HydJack)o Subassemblyretrieval(SpecTooling/Piston/TTool)o Choke/ControlModule/Cap/MPFM/etc.o Liftlineestablishment(manipulator)o TreeCap/WellheadConnector/etc.o Heavyliftguidance(thrust)o FunctionHotstabbing(Hydraulically/Electrically)o Measuremento Gasket/Sealchangeout(manipulator)o SurfaceCleaning(manipulator/Brush/Jet)o VideoSupporto Etc..

ROVwillbefurtherdetailedinSection3SubseaROV/ROTIntervention.3. TheInterventionSystem(TemporaryWellControl)

TheinterventionsystemprovidestheabilitytoreenteraSubseawell(onatemporarybasis)withavarietyoftools:

o Toeithereffectaphysicalchangeofstateinwello Toestablishdataofwellcondition

It also establishes additionalwell control hardware ontowell, beyond that typically resident inSubsea treeandallows the insertionand removalof intervention tooling into thewell,whilst thewellremainspressurized.


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Figure10SubseaInterventionHardware

4. TheSubseaTree(PermanentProductionControl)

Thesubseatreeispositionedonseabed,locatedonsubseawellhead.Viacontrolsystem,thesubseatreeprovideswellcontrolbetweenwellitselfandseabedpipelinefacilities.

Figure11SubseaTrees

2.5 Whatisusedtointervenethewells?

1. Slickline Monofilamentwireusedtomechanicallyconveytoolsintowellbore. Hightensilewirespooledonandoffapowereddrum


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Figure12Slickline

2. Wireline Multistrandcableformechanicalconveyanceoftools intowellbore,aswellasprovidean

electrical/fiberopticcommunicationpathtotheoperator. Hightensilecablespooledonandoffapowereddrum

Figure13Wireline

3. CoiledTubing

Rolled&Weldedcontinuous lengthofsteel tubingwhich isused toconvey tools,providecommunicationpath,aswellasprovideafluidflowpath.

Coiledtubespooledonandoffareel,utilizinganInjectorsystem. TubecanhaveintegratedWireline


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Figure14OffshoreCoiledTubing

2.6 Whyyouhavetodosubseaintervention?Duringthelifeofafield,interventionsandworkoversareperformedto:

Improve/maintain/optimizefieldrecovery/productionlevels. Repairwellboremechanicalfailures Terminate/suspendproduction

2.7 Whenyouhavetodo?Weneedtoperformsubseainterventionwhen:

Wellproductionrateisdeclining(i.e.duetosandproduction) Damage/scheduledperiodicalreplacementtotheequipment

2.8 Howmuchisthecostofsubseawellintervention?Subsea intervention cost depends on the type of intervention, the vessel used for intervention, thecomplexityandthedurationofintervention.Table1showsthesummaryofsubseainterventioncost.Table1SubseaInterventionCost

LightIntervention MediumIntervention HeavyInterventionInterventionVessel $150K~200K/day $150K~300K/day $360K~840K/daySubseaTree $3,000~6,000KInterventionHardware $6,000~30,000K


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2.9 Whichcompanyofferssubseainterventionservices?The following Table 2 shows some of the prominent companies that provide subsea interventionservices,theserviceprovidedalongwiththecompanysasset.Table2SubseaInterventionServiceProvider

Company ServiceProvided Facilities/VesselAkerSolutions Slickline

WirelineWirelinetractorLoggingWelltestfacilityCoiledtubingFluidhandlingandwellcontrolProcessingConstructionandmaintenance

Skandi Aker (monohull subsea wellinterventionvessel)capableofserviceupto3,000mwaterdepth

Oceaneering WellAbandonment/WirelineServices

HydrateRemediationSubseaPumping

MSVOceanIntervention

WellOps(HelixEnergySolution)

Riser based and riserless ThroughTubingWellInterventionSaturationdivingIRMSlicklineServicesElectricLineServicesCoiltubingServicesCementingServicesStimulationServicesWell Testing and Production FlowbackServicesSubseatreeinstallationandrecoveryRiser based and riserless subsea wellandfielddecommissioningFlowlineandumbilicalabandonmentCasingCuttingandwellheadrecoverySurface drilling and surface casing

WellEnhancer Seawell Q4000


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installationSlimHoleDrillingRiglesssubseawellabandonmentConstruction: including tiein andinstallationofheavyumbilical and smalldiameterridgedflowlines.Pipelineblockageremediation.EmergencyWellControlsupport.

VetcoGrey Tooling Systems and Equipment fordiverless, ROV based InterventionOperations:TieinandConnectionToolsComponentReplacementTooling

InsertChokesSubseaControlModulesMultiphaseFlowmeters

CleaningToolsInspectionToolsROVToolingSkidsTorqueToolsSpecialPurposeTooling

3 SubseaROV/ROTIntervention3.1 WhatissubseaROV/ROTintervention?Subsea intervention is anyoperation carriedout subseautilizingROV (remotelyoperated vehicle)orROT(remotelyoperatedtool),suchas:

Sitesurvey; Drillingassistance; Installationassistance; Operationassistance; Inspection; Maintenanceandrepair.

Aboveactivitieswillbedetailedinthefollowingsection.3.2 WhatarethevarioustypeofsubseaROV/ROTinterventionactivity?3.2.1 SitesurveyAsitesurveyhastobecarriedoutbeforeoffshoreactivitiessuchasdrillingandinstallationtoobtaintheseabedsprecisebathymetryandproperties.


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Figure15SeabedMappingwithanROV

Detailedseabedmappingthroughprecisebathymetrymaybeperformedbyaseabedreferencesystemwithdifferentialpressuresensorsandacousticdatatransmission,whichmaybedeployedandretrievedby an ROV. Seabedmapping can also be performed by an ROV carrying amultibeam echo sounder(MBE)or a sidescan sonar (SSS) as shown in Figure 15.A subbottomprofiler (SBP) for subbottomprofilingmaybeusedtoassessthequalityofseabedpropertiesforoffshoreinstallationfoundation.3.2.2 DrillingAssistanceDrillingactivitiesforproductiondrillingandcompletionnormallyinclude:

DeploymentofacousticunitssuchastranspondersorbeaconsbyanROVforsurfaceorsubseapositioning;

BottomsurveybyvisualobservationfromaROVwithvideoandstillcameras; Structuresettingandtesting(ifneeded)ofpermanentguidebase(PGB),temporaryguidebase

(TGB),Xmastree,BOP,etc.; Asbuilt(bottom)surveybyROVvisualobservationwithsupplementalequipment.

During the entire process, the observation taskswith video cameras (oftenwith scanning sonar assupplemental acoustic observation)make up themajority ofROV drilling assistance. Tasks includeconductingthebottomsurvey,monitoringthe loweringofthestructureandtouchingdown,checkingthestructuresorientationandlevelwithagyrocompassandbullseye,respectively,andperforminganasbuilt survey. Some necessary interventionworkmay have to be donewith ROVs or ROTs duringstructuresettingandtesting:

Acoustictransponderorbeacondeploymentandrecovery; Debrispositioningandremovalfromseabedandtree,includingdroppedobjects;


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StructurepositionassistancewithROVpull/push; Guidewiredeployment,recovery,andcuttingduringemergencyconditions; Rigging(e.g.,shackleconnectionanddisconnection); Cementcleaningonguidebasewithbrushorwaterjet; Valveoperationwithhydraulictorquetoolorhydraulicstabin; ROVoperableguideposts,replacement,andpinpullrelease; ControlpodreplacementifsuitableforROV(otherwiseROT); Anodeinstallationbyclampandcontactscrew.

3.2.3 InstallationAssistanceTheinstallationofasubseaproductionsystemfromthewatersurfacetotheseabedcanbedividedintotwoparts:

Subseaequipmentinstallation(e.g.,manifolddeployment,landing); Pipeline/umbilicalinstallation(e.g.,initiation,normallayandlaydown).

Theinstallationmethodsforsubseaequipmentmaybedividedintotwogroups.Largesubseahardwarewithweightsover300tonne(metricton)canbeinstalledbyaheavyliftvesselwherethecranewireislongenoughtoreachtheseabedandthecraneisusedtobothputtheequipmentoverboardandlowerit.Asoft landingtotheseabedmayberequiredusinganactiveheavecompensationsystemwiththecrane.Alternatively, itmaybe installedwithadrilling toweronadrilling rig,whichcanhavea liftingcapacityuptoabout600tonne.Forsmallersubseahardware (maximumapproximately250tonne),anormalvesselequippedwithasuitablecraneforoverboardingthehardwaremaybeused.Thevesselnormallywouldnothavealongenoughcranewiretotheseabed,sothehardwareistransferredfromthecranewiretoawinchwithahighcapacityandalongenoughwireforloweringtheequipmenttotheseabedoncethehardwarepassesthroughthesplashzone. Inboth installationgroups,ROVsareusedforobservationandverificationandforengagementandreleaseofguidewiresandhooks.Subsea structures arewidely positioned underwater using the long baseline (LBL)method inwhichtransducersusedforpositionmeasuring,agyrocompassfororientationmeasuring,adepthsensorfordepthmeasuringmaybemountedontostructurebypackage(s)thatwillberetrievedbytheROV.TheorientationcontrolmaybeassistedbytheROV,andtheROVhastoverifyviacamerathatthestructureis aligned and level before the structures final setdown. ROVsmay also be used to install chokes,multiphasemeters, and subsea controlmodules. For seal pressure tests, ROVs can be used for hotstabbing.ROVscanbeused toassist in the installationofadeadanchor forpipeline/umbilical laying initiation.TheycanalsobeusedtoconnectthepullinlineforJtubeorItubeinitiation.Duringnormalinstallationandpipeline/umbilicallaydown,thetouchdownpointisoftenmonitoredwithROVsinfrontandbehind.The connections between subsea production equipment and flowlines and subsea equipment andumbilicalsmaybecompletedthroughflyingleadsfromtheumbilicalterminationassembly(UTA)tothetree/manifold,well jumper fromthetreetothemanifold, jumper fromthemanifoldtothePLET.The


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flying leadsmaybehandledandpulled inbyanROVdirectly.Jumperscanbedeployed fromavesselwithspreaderbar(s),andthenpositionedandconnectoractuatedwiththeassistanceofanROV.3.2.4 OperationAssistanceMainproductionactivitiesnormallyinclude:

Flowcontrol by chokes and valves operated by hydraulic actuators through control pods andumbilicalsorexternallybyROVorROTintervention;

Monitoringofflowtemperatureandpressurebyrelevantmeasurementmeters; Chemicalandinhibitorinjectionforcorrosion,waxing,andhydrateformationresistance; Flowseparationofliquids,gases,andsolids(filtering); Flowboostingbypumping; Flowheatingorcooling.

Duringtheoperationphase,ROVsarenormallynotrequiredexceptfornoncriticalvalveactuationandpossiblyintermittentstatuschecks,takingsamples,etc.3.2.5 InspectionInspectionmaybeneededonaroutinebasisforthestructuresexpectedtodeteriorateduetoflowlinevibration,internalerosion,corrosion,etc.Inspectionincludes:

Generalvisualinspection,includingcathodicmeasurementsandmarinegrowthmeasurements; Close visual inspection additionally requiring physical cleaning for close visual inspection, CP

measurements,andcrackdetectionbymeansofnondestructivetesting(NDT); Detailed inspection including close visual inspection, crack detection, wall thickness

measurements,andfloodedmemberdetection; Routinepipeline inspection including trackingandmeasurementofdepthof cover forburied

pipelines,whichisalsoapplicableforcontrolumbilicalsandpower/controlcables.


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Figure16PolatrakROVIITipContactCPProbe

Cathodicprotection(CP)potentialmeasurementsmaybecompletedbyCPprobeasshowninFigure16.ThistypeofmeasurementisnormallycarriedoutbyaworkclassROV.CleaningmaybeperformedbyanROVwithbrushingtoolsorhighpressurewetjetsandgritentrainmentasshowninFigure17.

Figure17RotatingBrushToolandWaterJettingTool

CrackdetectionmaybeperformedbyanROVwithmagneticparticle inspection (MPI),eddy current,alternatingcurrentfieldmeasurement(ACFM)methods,etc.


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3.2.6 MaintenanceandRepairMaintenance activities include repair or replacement of modules subject to wear. Maintenance isnormallyperformedbyretrievingthemoduletothesurfaceandsubsequentlyreplacingitwithaneworothersubstitutemodule.Retrievalandreplacementhavetobeanticipatedduringsubseaequipmentdesign.Somemodulessuchas multimeters, chokes, and control pods are subject to removal and replacement. A completedreplacementmayhave tobecarriedoutdue to the significantwearonordamage tononretrievablepartsofsubseaequipment.Due to the difficulty and expense ofmaintenance and repair, the operationmay be continuedwithregularmonitoringifthedamagedmoduleisnotreadilyreplacedanddoesnotpreventproduction.3.3 HowdoyouperformsubseaROV/ROTintervention?Thereare2methodsthatareusedtocompletethosetasks,whichare:

1. ROVs(remoteoperatedvehicles)forinspection,cleaning,andsoon,and2. ROTs(remoteoperatedtools)formodulereplacementandsubseatiein.

TheabovemethodusesROVandROTwhichwillbeexplainedinthefollowingsection.3.4 WhataretheequipmentinvolvedinsubseaROV/ROTintervention?3.4.1 ROVInterventionSystem

Figure18ROVSystem


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AnROV systemused in subseaengineering,as shown inFigure18,canbedivided into the followingsubsystems:

ControlroomondeckforcontrollingtheROVsubsea; WorkoverroomondeckforROVmaintenanceandrepair; Deckhandlinganddeploymentequipment,suchasAframeorcrane/winch; UmbilicaltopowerROVsubseaandlaunchorrecoverROV; TethermanagementsystemtoreducetheeffectofumbilicalmovementontheROV; ROVforsubseaintervention.

3.4.1.1 ROVCategoriesROVcanbedividedintofiveclassesassummarizedinTable3.Table3ROVClasses

Class GeneralDefinition DetailedDefinitionI Pureobservation Pure observation vehicles are physically limited to video observation.

Generally they are small vehicles fittedwith video cameras, lights, andthrusters. They cannot undertake any other taskswithout considerablemodification.

II Observationwithpayloadoption

Vehiclescapableofcarryingadditionalsensorssuchasstillcolorcameras,cathodicprotectionmeasurementsystems,additionalvideocameras,andsonar systems.Class II vehicles shouldbe capableofoperatingwithoutthelossoforiginalfunctionwhilecarryingatleasttwoadditionalsensors.

III Workclassvehicles Vehicles largeenough to carryadditional sensorsand/ormanipulators.Class III vehicles commonly have a multiplexing capability that allowsadditional sensors and tools to operate without being hardwiredthrough the umbilical system. These vehicles are larger and morepowerfulthanClassesIandII.ClassIIIAWorkclassvehicles150hp

IV Seabedworkingvehicles

Seabedworking vehicles maneuver on the seabed by a wheel or belttraction system, by thruster propellers or water jet power, or bycombinationsofanyofthesepropulsionmethods.ClassIVvehiclesaretypicallymuch largerandheavierthanClassIIIworkclass vehicles, and are configured for specialpurpose tasks. Such taskstypically include cable andpipeline trenching, excavation,dredging andotherremotelyoperatedseabedconstructionwork.

V Prototypeordevelopmentvehicles

Vehiclesinthisclassincludethosebeingdevelopedandthoseregardedasprototypes.SpecialpurposevehiclesthatdonotfitintooneoftheotherclassesarealsoassignedtoClassV.TheAUViscurrentlyassignedtoClassV.


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3.4.1.2 TopsideFacilitiesSuitable deck area and deck strength, external supplies, and ease of launch and recovery should beprovidedondeckforsafeandefficientoperationofROVs.ROV control stations vary from simple PC gaming joysticks to complex and large offshore controlcontainers/roomson theplatformor vessel.The control stations contain videodisplaysand a setofoperator/ROV interface controlling mechanisms. A typical control container consists of operatorconsole,lighting,electricaloutlet,firealarmandextinguishers,etc.3.4.1.3 ROVLaunchandRecoverySystems(LARS)The LARS consists of awinch,winch power unit, crane/Aframewith fixed block, and ROV guidingsystem.Generallyspeaking, launchand recoveryactivitiescanbeachievedbyasimple ropewithuplift force.However, to facilitate thedeploymentand recoveryof the rope,a reel/drum isused,andamotor isusuallyusedtorotatethereelandprovidetheupliftforce.Themotormaybeeitherahydraulicmotororanelectromotorwith/withoutagearboxusedtoreducetherotaryspeedand increasethetorqueforce.Thesystemofmotor,reel/drum,baseframe,andotherancillarystructuressuchasabrakeandclutchisnormallycalledawinch.Afixedblock,sustainedattheendofacraneboom/Aframebeam,isusedtochangetheupwarddirectionoftherequiredwinchforcetoadownwarddirectionandpositionthewinchonthelowerstructure,forexample,thedeck.TorestrainROVmotionwhileitisbeingloweredfromtheairtothewatersurfaceaLARSisused.Thishelpsprevent,forexample,damagetotheumbilicalbythebilgekeelifsidedeploymentisbeingused.TheLARSmaybeequippedwithadockinghead,cursor,orguiderails,asshowninFigure19,Figure20,andFigure21.


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Figure19SnubberRotatorDockingHead

Figure20WireGuidedCursor


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Figure21GuideRailSystem

3.4.1.4 UmbilicalandTMSOnecharacteristicdifferencebetweenanROVandanautonomousunderwatervehicle(AUV),isthattheROV has an umbilical that runs between the support vessel and the ROV to transporthydraulic/electronicpower from thevessel to theROVand informationgathered from theROV to thesurface. The AUV, on the other hands, is a robot that travels underwaterwithout tethering to thesurface vessel/platform. An ROV is usually armoredwith an external layer of steel and has torquebalance capacity. Thediameter andweightof theumbilical shouldbeminimized to reduce thedrag


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forceduetowavesandcurrentsaswellasliftingrequirementsduringlaunchandrecoveryoftheROVfromthewatertothesurface.Normallytheumbilicalhasnegativebuoyancy,andtheumbilicalmaybeattachedwith buoyancy, for example, every 100 m (328.1m) to avoid entanglements between theumbilicalandsubseaequipmentortheROVitselfduringshallowwateroperation.A tethermanagementsystem (TMS) isused todeploy theROV fordeepwaterapplicationswhere theumbilicalwith negative buoyancy can launch and recover the TMS and ROV. The connection cablebetweentheROVandTMScanbeanumbilicalcalledatetherthathasarelativelysmalldiameterandneutralbuoyancy.TheTMS isjust likeanunderwaterwinchformanagingthesofttethercable.ATMShastwosignificantadvantages:

1. ROVscanbemovedmoreeasilyduetodeletingtheforce impliedbytheumbilical,whichmaybethesameastheflyingresistanceoftheROV itself inawaterdepthof200m(656.2ft)andincreaserapidlywithincreasingwaterdepth.

2. ThereisnoneedtousetheROVsownthrusterstogettheROVdowntotheworkingdepthneartheseabed.ApoweredTMS, i.e., installingsomethrusterstoTMScagesmaybecarriedouttoaccountforlargedragforceonTMSduetosignificantcurrents(e.g.,currentvelocityof1to1.5knots)insomeareas.

TheTMSisdesignedtomanagethetetherandcanbeeitherattachedtoaclumpweight,mainlyfortheobservation ROV, or to a cage deployment system, as shown in Figures 238 and 239,mainly forworkclassROVs.3.4.2 ROVMachine3.4.2.1 CharacteristicsConfigurationMostworkclassROVshavearectangularconfigurationandanopenAlbasedframethatsupportsandprotectsthethrustersforpropulsion,underwatercamerasformonitoring,lightsandotherinstrumentssuchasclosedcircuittelevisionforobservation,thegyrocompassforheadingdetection,depthgaugesfor depth detection, an echosounding device for altitude detection, and scanning sonars forenvironmentinspection.MostROVsarenearneutralbuoyancyunderwater.Theydohavea littlebuoyancy tomake sure theROVs can float to thewater surface during emergency conditions or if they break. An ROVmovesdownwardwith a vertical thruster. Generally, the buoyancy is provided by synthetic foammaterialabovetheAlbasedROVframe.AnROVsweightistypicallyintherangefrom1000to3500kg.ExamplescanbeseenfromthetableinAnnexAofAPIRP17H.ThehigherbuoyancycenterandlowerweightofgravityensurethattheROVprovidesgoodstabilityperformance.


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OperationDepthTraditionally,ROVshadbeendesignedandbuiltforoperationsinwaterdepthsof100to1000m(328to3280ft),primarilysupportingdrillingoperations, includingseabedsurveys,water jetting,andseal ringinstallation, as well as providing light construction support and inspection work. These ROVs havepayloadcapacitiesofaround250kgwithpowerrangingfrom40to75hp.Astheoilandgasindustryhasprobedintodeeperanddeeperwaters,demandhasincreasedforROVsthatprovidediverless solutions for such tasks as remote interventions andpipeline/umbilical tieins.Table4liststheoperationalwaterdepthsoftypicalROVs.PayloadThepayloadcapacityofanROVislimitedby:

ROVpower; Structuralintegrity; Manipulatorloadantorquecapacity; Currentcondition.

PayloadcapacitiesfortypicalROVsarelistedinTable4.Table4OperationalWaterDepth&PayloadCapacityofTypicalROVs

ROVName OperationalWaterDepth(m)

PayloadCapacity(kg)

Challenger 1572 113Hysub60 2000 PioneerHP 1500 100SuperScorpio 914 100MRV 1500 220Diablo 2000 250TritonXLS 3000 300SCV3000 3000 100HydraMagnum 3144 227HydraMillennium 3144 318INNOVATORTM 3500 Maximum 499


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3.4.2.2 NavigationSystemThenavigationofROVincludesgeneralnavigationandaccuratenavigation.Thedeckreckoningmethodand hydroacousticmethod are used for general navigation. The hydroacousticmethod is themostwidelyusedtodayviatheLBLsystem, inwhichthere isaresponderarrayontheseabed,at leastonetranspondersetontheROV,andonereceiversetonthevessel.Accurate navigation is used to lead the ROV to the target object. A gyrocompass provides the ROVheading and a viewing system is used that comprises imaging sonar/low light cameras and lights.Normallythepowerofasubsealightisbetween250and500W.AnROVmightalsohave750to1000Wofpowerforlargelightsand100to150Wofpowerforsmalllights.ThereisalsoacubicTVtoprovide3Dobjectconfigurations,that is,toobtaindataabouttargetthicknessanddistancebetweentheROVandthetarget.3.4.2.3 PropulsionSystemThepropulsionsystemforanROVconsistsofapowersource,controllerforanelectricmotororaservovalvepackforahydraulicmotor,andthrusterstoadjustthevehiclecondition(trim,heel,andheading)andtopropelthevehiclefornavigatingfromtheTMStotheworksite,andviceversa.Being themainpartof anROVpropulsion system, theunderwater thrusters are arranged in severalways to allow for proper maneuverability and controllability of the vehicle through asymmetricalthrustingandvaryingtheamountofthrust.Thethrustersneedtobeadequatelysizedforcounteringalloftheforcesactingonthevehicle,includinghydrodynamicandworkloadforces.Thereareawiderangeofthrustersfromelectricallypoweredtohydraulicallypowered.Ingeneral,electricalthrustersareusedforsmallervehicles,whilethehydrauliconesareusedforlargerandworkclassvehicles.Typicalelectricandhydraulicthrusterexamplesareshown inFigure22TypicalElectricandHydraulicThrusters.WhenselectingthrustersforanROV,thefactorsofpower,efficiency,pressure,flow,weight,size,andforward/reversecharacteristicsshouldbetakenintoaccount.


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Figure22TypicalElectricandHydraulicThrusters

3.4.2.4 ViewingSystemA wide range of underwater video cameras are used in ROVs for viewing purposes, typically fornavigation,inspection,andmonitoring.Cameraimagesensorsincludelowlightsiliconintensifiedtargets(SITs),chargecoupleddevices(CCDs),andHADsforhighdefinitionimages.SomecamerasareequippedwithLEDlightsprovidingilluminationforcloseupinspectionandeliminatingtheneedforseparatelighting.Imagescapturedbyacameraaretransmittedasvideosignals through the tetherandumbilical toavideocapturedeviceon thewatersurface.3.4.2.5 ManipulatorsAnROVisnormallyequippedwithtwomanipulators,oneforROVpositionstabilization,normallywithafive function arm, and the other for intervention tasks, normally with a sevenfunction arm.Manipulatorsystemsvaryconsiderablyinsize,loadrating,reach,functionality,andcontrollability.Theymaybesimplesolenoidcontrolledunitsorservovalvecontrolledposition feedbackunits.Theendofthearm is fittedwithagripper,usuallyconsistingof twoor three fingers thatgrasphandles,objects,andstructuralmembersforcarryingoutanactivityorstabilizingtheROV.3.4.3 RemoteOperatedTool(ROT)AnROTsystemcanbedividedintothefollowingsubsystems,asshowninFigure23:

Deckhandlinganddeploymentequipment,suchasAframeorcrane/winch; ControlsroomondecktocontroltheROTsubseaoperation; WorkoverroomondeckforROTmaintenanceandrepair;


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Umbilical/liftwiretopowertheROTsubseaanddeployorrecoveranROV; TheROT.

Figure23ROTSystem

AROT ismainlyusedformodulereplacement/changeoutandflowlinetiein,bothofwhichrequireahandlingforcelargerthanthatofanROV.ROTsareusuallydeployedonliftwiresoracombinedliftwire/umbilical,andthelateralguidanceispoweredbyanumbilicalwithdedicatedthrusters,ROVassistance,orguidewires.The ROT system should provide for safe locking of the replacement module during handling,deployment,normaloperation,andemergencyconditionssuchaspowerfailure.TherearethreegenerationsofROTfortieintools:

AfirstgenerationROTistwoseparatetoolsthatpullinandconnectindividually. AsecondgenerationROTisacombinedtoolthatpullinsandconnectstogether. AthirdgenerationROTisanROVmountedpullinandconnectiontool.


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BibliographyYongBai,Q.B.(2010).SubseaEngineeringHandbook.Houston,USA:Elsevier.YongBai,Q.B.(2005).SubseaPipelines&Risers.Elsevier.LohWayLam.SubseaSystemEngineeringLectureNotes.NUS.Variousinternetwebsite

Subsea InterventionAssignment 01(1)

subsea intervention

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