Offshore Engg services and design

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WINTERTRAININGREPORTON

OFFSHOREENGINEERINGSERVICESANDDESIGN

SUPERVISEDBY-

DHANANJAYBADOLECE(P),11High,ONGC(MUMBAI).

SUBMITTEDBY:-VYSAKHVENUGOPAL

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ACKNOWLEDGEMENT

IsincerelythankMR.DHANANJAYBADOLE,chiefengineerfortakingme

underhisablementorship.

IalsothankOILANDNATURALGASCORPORATIONforgivingmean

opportunitytogetindustrialexposurefromtheexperts.Ialsothankthose

whowereindirectlyinvolvedinhelpingme.

VYSAKHVENUGOPAL

DEPT.OFMECHANICALENGG.

VNITNAGPUR

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ABSTRACT

Ihadanopportunitytoundergovocationaltrainingfor30days(8.12.2013to

08.12.2014)inONGC,Mumbaiatthe11Highoffice.Duringthisperiod,Ihad

anexposuretovariousongoingprojectsandproceduresindifferent

departmentsofoffshoreengineeringservicesoftheorganization.Igotan

opportunitytodiscussandlearnalotabouttheindustrialprocessingand

DevelopmentactivitiesofONGC.

Therearebasicallytwodivisionsunderengineeringservices–Offshore

DesignSection(ODS)andOffshoreWorksDivision(OWD).Duringthetenure

ofthetrainingmyfocuswasmainlyonODS,underwhichthereareseven

disciplines-

• Process

• Piping

• Pipelines

• Instrumentation

• Mechanical

• Electrical

• Structure

Apartfromgettingtheoverviewofallthesedisciplines,Ihavealsoworkedon

asmallprojectontypesandworkingofplatforms,alongwithanoverviewof

thebasicsofdrillingprocesses.

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ABOUTONGC

ONGCLtd.IsrecognizedastheNumeroUnoE&Pcompanyintheworldand

25thamongtheleadingglobalenergymeasuresasper“PlattsTop250”Global

EnergyCompanyRanking2008.ItisthefirstandonlyIndiancompanyto

figureinFortune’s“World’sMostAdmiredCompaniesList,2007”.

ONGCGroupofCompaniescomprisesof

• OilandNaturalGasCorporationLimited(ONGC-TheParentCompany)

• OverseasE&P:ONGCVideshLimited(OVL–awhollyownedsubsidiary

ofONGC),ONGCNileGangaBV(ONGBV-awhollyownedsubsidiaryof

OVL),ONGCAmazonAlaknandaLtd.(OAAL)etc.

• MangaloreRefineryandPetrochemicalsLimited(MRPL-asubsidiaryof

ONGC).

• Value-Chain:OPAL,OMPLetc.

• Services:OMESL,PawanHansHelicoptersLtd.,etc.

• SEZ:MSEZ,DSL.

• Power:OTPC.

OilandNaturalGasCorporationLimited(ONGC)isIndia'sMostValuable

Company,havingamarketshareofabove80%inIndia'sCrudeOiland

NaturalGasExplorationandProduction.ONGCregisteredthehighestprofit

amongallIndiancompanieswithRs.19872Croresintheyear2007-08.ONGC

alsoproducesValue-AddedProducts(VAP)likeC2-C3,LPG,NaphthaandSKO.

ONGCVideshLimited(OVL)isoverseasarmofONGC,engagedinExploration

&ProductionActivities.Ittrans-nationallyoperatesE&PBusinessin10

countries,makingONGCthebiggestIndianMultinationalCorporation.In

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recentyears,ithaslaidfootholdsinhydrocarbonacreageinvariouscountries

includingIvoryCoastandAustralia.ONGCNileGangaBVisawhollyowned

subsidiaryofOVLandhasequityinproducingfieldinSudan.

ONGCenvisagesorganizingImport/InternationalSaleofCrudeOilandExport

ofPetroleumProductsthroughTenderingProcedureforalltheGroup

Companies.However,itwouldberestrictedtotheCompanies/Firms/

VendorsregisteredwithONGConitsapprovedVendorLists.[1]

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1. PRELIMINARIESOFOILANDGASPRODUCTION

1.1 EXPLORATION

Explorationmeansascientificsearchsetbythegeologistsandgeophysicistsforlocatingtheprobableregionsofoilandgas.Ingeneraltermsthisrefertotheentiregamutofsearchforhydrocarbonswiththehelpofgeologicalandgeophysicalsurveysintegratedwithlaboratorydatabackup,selectionofsuitablelocationsofexploratorytest-drillingandtestingofsuchwells.

Geophysicaltechnologygreatlyreducestheriskofdrilling.WellsaredrilledtotestageologicaltheoryormodelthatisgeneratedintheWideAreaGeologicalReviewandvalidatedbyseismicdata.Therelativepositionofrocklayerscanbeimagedfromthepatternsofacousticsoundwavesthatarereflectedfromsubsurfaceformations.Fortwo-dimensional(2D)seismicoperations,fieldcrewsrunparallellinesofsoundrecordersatwideintervalstocoverlargeareasinarelativelyinexpensivemanner.Onceafieldisdiscovered,3Dseismiccanberuninagridpatternwithclosesoundrecorderstodelineatethemostattractiveplacestodrilladditionalwellsanddeterminethearealextentofaformation.[2]

1.2 GASANDCRUDEOILPRODUCTION

Accordingtogenerallyacceptedtheory,CrudeOilisderivedfromancientbiomass.Itisafossilfuelderivedfromancientfossilizedorganicmaterials.Morespecifically,crudeoilandnaturalgasareproductsofheatingofancient

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organicmaterials(i.e.kerogen)overgeologicaltime.Threeconditionsmustbepresentforoilreservoirstoform:somesourcerockrichinhydrocarbonmaterialburieddeepenoughforsubterraneanheattocookitintooil;aporousandpermeablereservoirrockforittoaccumulatein;andacaprock(seal)orothermechanismthatpreventsitfromescapingtothesurface.Withinthesereservoirs,fluidswilltypicallyorganizethemselveslikeathree-layercakewithalayerofwaterbelowtheoillayerandalayerofgasaboveitaccordingtotheirdensities,althoughthedifferentlayersvaryinsizebetweenreservoirs.Becausemosthydrocarbonsarelighterthanrockorwater,theyoftenmigrateupwardthroughadjacentrocklayersuntileitherreachingthesurfaceorbecomingtrappedwithinporousrocks(knownasreservoirs)byimpermeablerocksabove.However,theprocessisinfluencedbyundergroundwaterflows,causingoiltomigratehundredsofkilometershorizontallyorevenshortdistancesdownwardbeforebecomingtrappedinareservoir.Whenhydrocarbonsareconcentratedinatrap,anoilfieldforms,fromwhichtheliquidcanbeextractedbydrillingandpumping.[3]

Prospectsmustbewelldefinedinordertoobtainoilandgasleasesfromlandownerspriortothedrillingofawildcatwellafterthenecessarylandworkhasbeencompleted,thedrillingrigismovedonsiteandcrewswork24hoursadaytodrillaholeforthecalculateddepth.Oncetheholehasbeendrilledtothetargetformation,thewellisloggedwithelectronicdownholemeasurementtoolstorecordthecharacteristicsofthesubsurfacerockformations.Ifloggingindicatesthewellisproductive,itiscasedwithsteelpipeandawellheadofshutoffvalvesisinstalledtoprepareforproduction.Thewelliscompletedbyperforatingholesinthecasingatthedepthoftheproducingformation.Onceasuccessfultestwellorseriesofwellshasbeendrilled,theeconomicpotentialofthehydrocarbondiscoverymustbe

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determined.Thisstepincludesestimatinghowmuchoilandgasispresent(reserves),theprobablesellingprice,thecostofcontinuingtheexplorationeffortaswellasthecostoffullfielddevelopment,andthetaxes,royalties,andotherexpensesassociatedwithproducingtheoilfield.Iftheventurelookspromising,thefinalstepistaken—developmentofanewlydiscoveredfield.[3]

1.3 PROCESSING

Offshoreproductionsconsistofanumberofoperationsthatallowthesafeandefficientproductionofhydrocarbonsfromtheflowingwells.Thekeyoperationsthatwillbeconductedattheoffshoreplatforminclude:

• ProducedHydrocarbonSeparation

• GasProcessing

• OilandGasExport

• Well-Testing

• ProducedWaterTreatmentandInjection

• Utilitiestosupporttheseprocesses

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ThePipelinesandRisersfacilityusesSubseaproductionwells.ThetypicalHighPressure(HP)wellheadatthebottomright,withitsChristmastreeandchoke,islocatedontheseabottom.Aproductionriser(offshore)orgatheringline(onshore)bringsthewellflowintothemanifolds.Asthereservoirisproduced,wellsmayfallinpressureandbecomeLowPressure(LP)wells.Thislinemayincludeseveralcheckvalves.Thechoke,masterandwingvalvesarerelativelyslow,thereforeincaseofproductionshutdown,pressurebeforethefirstclosedsectioningvalvewillrisetothemaximumwellheadpressurebeforethesevalvescanclose.Thepipelinesandrisersaredesignedwiththisinmind.Shortpipelinedistancesisnotaproblem,butlongerdistancesmaycausemultiphasewellflowtoseparateandformsevereslugs,plugsofliquidwithgasinbetween,travellinginthepipeline.Severesluggingmayupsettheseparationprocess,andalsocauseoverpressuresafetyshutdowns.Sluggingmightalsooccurinthewellasdescribedearlier.Sluggingmaybecontrolledmanuallybyadjustingthechoke,orwithautomaticslugcontrols.Further,areasofheavycondensatemightforminthepipelines.Athighpressure,theseplugsmayfreezeatnormalseatemperature,e.g.ifproductionisshutdownorwithlongoffsets.Thismaybepreventedbyinjectingethyleneglycol.CheckvalvesalloweachwelltoberoutedintooneormoreofseveralManifoldLines.TherewillbeatleastoneforeachprocesstrainplusadditionalManifoldsfortestandbalancingpurposes.TheCheckvalvessystemshavebeennot

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includedinthediagramtoavoidcomplexityofthediagram.Thewell-streammayconsistofCrudeoil,Gas,Condensates,waterandvariouscontaminants.Thepurposeoftheseparatorsistosplittheflowintofractions.Themainseparatorsaregravitytype.AsmentionedtheproductionchokereducesthepressuretotheHPmanifoldandFirststageseparatortoabout3-5MPa(30-50timesatmosphericpressure).Inlettemperatureisoftenintherangeof100-150degreesC.Thepressureisoftenreducedinseveralstages,threestagesareused,toallowcontrolledseparationofvolatilecomponents.Thepurposeistoachievemaximumliquidrecoveryandstabilizedoilandgas,andseparatewater.Alargepressurereductioninasingleseparatorwillcauseflashvaporizationleadingtoinstabilitiesandsafetyhazards.Animportantfunctionisalsotopreventgasblow-bywhichhappenswhenlowlevelcausesgastoexitviatheoiloutputcausinghighpressuredownstream.Theliquidoutletsfromtheseparatorwillbeequippedwithvortexbreakerstoreducedisturbanceontheliquidtableinside.EmergencyValves(EV)aresectioningvalvesthatwillseparatetheprocesscomponentsandblow-downvalvesthatwillallowexcesshydrocarbonstobeburnedoffintheflare.Thesevalvesareoperatedifcriticaloperatingconditionsaredetectedoronmanualcommand,byadedicatedEmergencyShutdownSystemTherealsoneedstobeenoughcapacitytohandlenormalsluggingfromwellsandrisers.Othertypesofseparatorssuchasverticalseparators,cyclones(centrifugalseparation)canbeusedtosaveweight,spaceorimproveseparationTherealsohastobeacertainminimumpressuredifferencebetweeneachstagetoallowsatisfactoryperformanceinthepressureandlevelcontrolloops.ThesecondstageseparatorisquitesimilartothefirststageHPseparator.Inadditiontooutputfromthefirststage,itwillalsoreceiveproductionfromwellsconnectedtotheLowPressuremanifold.Thepressureisnowaround1MPa(10atmospheres)andtemperaturebelow100degreesC.Thewatercontentwillbereducedtobelow2%.Anoilheatercouldbelocatedbetweenthefirstandsecondstageseparatortoreheattheoil/water/gasmixture.Thiswillmakeiteasiertoseparateoutwaterwheninitialwatercutishighandtemperatureislow.Theheatexchangeisnormallyatube/shelltypewhereoilpassesthoughtubesinacoolingmediumplacedinsideanoutershell.ThethirdstagebasicallyusesaFlash-Drum.FurtherreductionofwaterpercentageisdoneintheGDU(GasDehydrationUnit).Onaninstallationsuchasthis,whenthewatercutishigh,therewillbeahugeamountofproducedwater.Watermustbecleanedbefore

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dischargetosea.Oftenthiswatercontainssandparticlesboundtotheoil/wateremulsion.Theenvironmentalregulationsinmostcountriesarequitestrict,italsoplaceslimitsotherformsofcontaminants.Thisstillmeansuptoonebarrelofoilperdayfortheaboveproduction,butinthisform,themicroscopicoildropsarebrokendownfastbynaturalbacteria.Variousequipmentareused,Firstsandisremovedfromthewaterbyusingasandcyclone.Thewaterthengoestoahydrocyclone,acentrifugalseparatorthatwillremoveoildrops.Thehydrocyclonecreatesastandingvortexwhereoilcollectsinthemiddleandwaterisforcedtotheside.Finally,thewateriscollectedinthewaterde-gassingdrum.Dispersedgaswillslowlyrisetothesurfaceandpullremainingoildropletstothesurfacebyflotation.Thesurfaceoilfilmisdrained,andtheproducedwatercanbedischargedtosea.Recoveredoilinthewatertreatmentsystemistypicallyrecycledtothethirdstageseparators.Thegastrainconsistofseveralstages,eachtakinggasfromasuitablepressurelevelintheproductionseparator’sgasoutlet,andfromthepreviousstage.Incominggasisfirstcooledinaheatexchangerandgoesintothecompressors.Forthecompressoroperateinanefficientway,thetemperatureofthegasshouldbelow.Thelowerthetemperatureisthelessenergywillbeusedtocompressthegasforagivenfinalpressureandtemperature.Temperatureexchangersofvariousformsareusedtocoolthegas,Theseparatedgasmaycontainmistandotherliquiddroplets.Liquiddropsofwaterandhydrocarbonsalsoformwhenthegasiscooledintheheatexchanger,andmustberemovedbeforeitreachesthecompressor.Ifliquiddropletsenterthecompressortheywillerodethefastrotatingbladesforwhichgasispassedthroughascrubberandreboilersystemtoremovetheremainingfractionofwaterfromthegas.Whenthegasisexported,manygastrainsincludeadditionalequipmentforfurthergasprocessing,toremoveunwantedcomponentssuchashydrogensulfideandcarbondioxide.Thesegasesarecalledsourgasandsweetening/acidremovalistheprocessoftakingthemout.

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1.4 TRANSPORTATION

ThegaspipelineisfedfromtheHighPressurecompressors.Oilpipelinesaredrivenbyseparateboosterpumps.Forlongerpipelines,intermediatecompressorstationsorpumpstationswillberequiredduetodistanceorcrossingofmountainranges.

2. OFFSHOREDESIGNSECTIONS

2.1 PROCESS

Thisdisciplinelaysouttheinitialspecificationsrequiredfortheprocessplatformintheoffshore.Anyprocessplatformisthegatheringanddistributionpointforallthepipelinesi.e.wellfluidlines,liftgaslinesandoilexportlinefortankerloading.Alltheprocessingfacilitiesi.e.separation,producedwatertreatment,gascompressionanddehydration,gassweeteningisinstalledonthisplatform.Inaddition,therearetestingfacilitiesfortestingofproductioncomingfromindividualplatforms.

Therefore,usingmanysoftwarelikeASPENHYSYS,SMARTPLANTetc.theprocessdisciplineunderODSdraftsoutthebasicplansforanyoffshoreprocessplatform.ThevariousdiagramslikePFDs(ProcessFlowDiagram)andP&IDs(Pipingandinstrumentationdiagram)arebeingdesignedbythepeopleofthisdiscipline.Aftertheprocessdesigniscompletedthefeasibilitystudyforthedesignedprocessiscarriedoutforfuturebiddingandfinalizationforthedesign.

2.2 PIPING

ThepipingdisciplineunderODSlooksafterthepipesontheprocessplatform.Plantlayoutanddesignofpipingsystemsconstitutesamajorpartofthedesignandengineeringeffort.Basicallythefollowingarethemaintaskscarriedoutbythisdiscipline:

• Pipingandinstrumentationdiagrams(P&IDs)

• Pipingdesignandengineeringprinciples

• Terminology,symbolsandabbreviationsusedinpipingdesign

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• Pipingmaterials

• Pipingspecificationsandpipingcodes

• Componentsofpipingsystems-fittings,flangesandvalves[5]

ThemainbaseforallthecalculationsisHoopStressforallthestresscalculationsandwallthickness.Wallthicknessselectionisoneofthemostimportantandfundamentaltasksindesignofoffshorepipelines.Whilethistaskinvolvesmanytechnicalaspectsrelatedtodifferentdesignscenarios,primarydesignloadsrelevanttothecontainmentoftheinternalpressure

Thisdisciplineusesvarioussoftwareandstandardcodesforthedesignpurposes.Amongthestandardcodes,ONGCfollowstheASMEB31codeforpressurepipingofanumberofindividuallypublishedsections.ThecodesusedareB31.3(ProcessPiping),B31.8(Gastransportationanddistributionpipingsystem)andB31.4(Pipelinetransportationsystemsforliquidhydrocarbonsandotherliquids)

2.3PIPELINES

PipelinesareusedforanumberofpurposesinthedevelopmentofoffshorehydrocarbonresourcesTheseincludee.g.:

• Export(transportation)pipelines

• Pipelinebundles.

• Flowlinestotransferproductfromaplatformtoexportlines

• Waterinjectionorchemicalinjectionflowlines

• Flowlinestotransferproductbetweenplatforms,subseamanifoldsandsatellitewellsThedesignofpipelinesisusuallyperformedinthreestages,namely;

1. Conceptualengineering,

2. Preliminaryengineeringorpre-engineering,

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3. Detailengineering.[6]Fig2.1Thepipelinecontrolforanyoffshoreplatform

Fig2.2Flowlinedesignprocess

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Fig.Belowshowsthelayingofthesubseapipeline,anumberofpiecesofpipesareweldedonthebargeandtheassemblyismadetoshiftslowly,theassemblyactsasathreadandlaydownontheseabed

Fig2.3LayingofSubseapipelineontheseabed.

2.4INSTRUMENTATION

InstrumentationdisciplinecomesintoplayaftertheprocessplatformhasbeendesignedbytheprocessdesignsectionwiththehelpofaP&ID.Thisdisciplinehelpsincontrollingandautomatingalltheprocessparametersinvolvedintheoffshoreaswellasintheonshoreprocessplatforms.

Thevariouscontrollinginstrumentslookedafterbythisdisciplinemaybeeitherpneumaticorelectronic.Itdealswiththemeasurementofpressure,temperature,flow-rateswiththehelppressuretransducers,temperaturesensors(RTD,Thermocouplesetc.)andflowmetersrespectively.Instrumentationdisciplinealsotakescareofthe“ShutDownPanel”whichshutsdownalltheprocessesincaseofanemergency.

2.5ELECTRICAL

Everypowerplantneedsoneortheotherwayelectricalpowerforitsproperfunctioning.Foranoffshoreplatformitrequireshugeelectricalpowertorunallthemechanicaldevicesemployed,livingquarterselectricalconsumption

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andalsosomepowertorunvariousinstruments.

ForanygeneralplatformofONGC,itrequiresabout20-25MWormorepowertorunthesystem.Toproducesuchlargeamountofpowerischallenging.ForthisONGChasitsownpowerproductionunitwherepowerisgeneratedbyaportionofthenaturalgasproduced.TherearehugeGasTurbineUnits(GTU)forpowerproduction.Alsothecircuitbreakerstationisinstalledontheplatformitself.ForsomeotherpurposeswhichmayrequiresmallpowersayfewKWs,powerisgeneratedbytherenewablesourcesofenergylikesolarenergy,windenergyetc.

2.6MECHANICAL

TheMechanicaldevicessuchasTurbines,Compressors,Pumps,HeatExchangersetc.arethebasicsforaplanttooperateandsuchdevicesareincludedundertheMechanicaldisciplineforbothrunningandmaintenanceofthesame.Asmallintroductionaboutthemainmechanicalunitsoperatinginaoffshoreprocessplatformisgivenbelow

2.6.1GasTurbines

GasTurbinesareusedforthepowerproductionbyrotationoftheturbineshaftbysteamgeneratedduetoheatgeneratedbyburningaportionofnaturalgasproduced.Anefficientgasturbineusedinapowerplantproducesabout10-15MWofpowerunderoptimizedconditions.Specialcareistakenfortheinletgasenteringintotheturbineaswetgasmaycorrodethebladesoftheturbineandalsoreducestheefficiencyfurthermoreduetocorrosionitmaycosteconomiclosstotheplant.

2.6.2GasCompressors

Agascompressorisamechanicaldevicethatincreasesthepressureofagasbyreducingitsvolume.Compressorsaresimilartopumps:bothincreasethepressureonafluidandbothcantransportthefluidthroughapipe.Asgasesarecompressible,thecompressoralsoreducesthevolumeofagas.Liquidsarerelativelyincompressible,whilesomecanbecompressed,themainactionofapumpistopressurizeandtransportliquids.Normallyathreestagecompressionsystemisappliedinagasbasedpowerplant.[7]

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Belowarethedifferenttypesofgascompressors:

Thecentrifugaltypesaremostlyusedingasplants.

2.6.3HeatExchangers

HeatExchangersexchangesheatbetweentwofluids,InONGCheatexchangerusedisthetubeandshelltype.Mainlytheseunitsareusedduringcrudeoilcomponentsseparationinwhichaportionofthecrudeoilisheatedandpassedthroughtubesandotherportionispassedthroughshellinthiswayexchangeofheattakesplacereducingtheviscosityofthefluidwhichisnecessarytoavoidvortexformationandmaintainalmostlaminarflowwithin

thepipeswhichhelpsinavoidingcondensateformation.Alsosince

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compressorsrequirethetemperatureoftheenteringgastobelowforitsefficientworkingtemperatureexchangersofvariousformsareusedtocoolthegas.

2.6.4KnockOutDrums(KOD)

Theknockoutdrumsisusedfortheseparationofgasandoilfromthesalinewater.Mainlytheprincipleinvolvedisthegravityseparation(baffleplatesarepresentinsidethem)inwhichthecomponentsareseparateddependingontheirdensity.

2.6.5Pumps

Pumpsarebasicallyusedfortransportingincompressiblefluidslikecrudeoilbycreatinglargepressuredifferenceforitstransportationalongpipelines.PresentlyinONGCcentrifugaltypepumpsareusedforgeneralpurposes.

2.7STRUCTURE

Structuredisciplinedesignsthesupportingstructureoftheplatformandthetopsideconsideringthestressanalysiscriteria.TheyusemanysoftwarelikeSACS,MicroStationetc.forthedesignpurposes.

2.7.1SupportingStructures

Thesupportingstructureonwhichtheplatformrestsisdividedinto:

1. Jackets

2. FPSO(Floatingproductionstorageandoffloading)

3. Jackuprigs

4. Semi-SubmersiblePlatform

5. Gravitybasedstructures

6. Spar

2.7.1.1Jackets

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Jacketsarebroadlyclassifiedinto3/4/6/8legged,dependinguponthesurfaceareaoftheplatformrequired.Ajacketcanbeusedonlyforsmallerdepthsay60-70metersasthejacketstructurerestsontheseabed,atypicalfour-leggedjacketisshownbelow.Thejacketsupportsasub-framewithproductionequipmentandaccommodationdeckontopofit.Thejackethastobetransportedonabargetoitsinstallationsiteatsea.Whileinstallingjacketontheseabedsteamhammeringisdonewhilepilingthemforstability.Sometimesskirtpilesarealsogivenforprovidingsupporttothebiggerjacketstructure.Theotherprocesseswhichareinvolvedwhileinstallingthejacketare:cementingoflegsofjacket,provisionofthemudmatatthebase,batteringofthelegs(singlebatterononesideanddoublebatterontheotherside,thisisdoneinordertoletthebargeapproachtotheplatformtoinstallthedrillrigs),provisionfortheriserisalsoincludedinthedesign.

2.7.1.2FPSO

AFloatingProduction,StorageandOff-loadingvessel(FPSO)isgenerallybasedontheuseofatankerhull,whichhasbeenconvertedforthepurpose.Suchvesselshavealargestoragecapacityanddeckareatoaccommodatetheproductionequipmentandaccommodation.Whenconvertingoldtankersforthispurpose,specialattentionhastobepaidtothefatiguelifeofthevessel.

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2.7.1.3Jack-UpRigs

Ajack-upisamobiledrillingunitthatconsistsofaself-floating,flatbox-typedeckstructuresupportingthedrillingrig,drillingequipmentandaccommodation.Itstandson3or4verticallegsalongwhichtheplatformcanbeself-elevatedoutofthewatertoasufficientheighttoremainclearofthehighestwaves.Drillingoperationstakeplaceintheelevatedconditionwiththeplatformstandingontheseabed.Thistypeofplatformisusedfordrillingoperationsinwaterdepthsuptoabout100m.Jack-upsspendpartoftheirlifeasfloatingstructures.Thisiswhensuchplatformsaretowedtoanewlocationbymeansofocean-goingtugs.Inthismode,thelegsareliftedupandextendupwardsovertheplatform.

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2.7.1.4Semi-SubmersiblePlatform

ASemi-SubmersiblePlatformconsistsofarectangulardeckstructuresupportedby4to8surface-piercingverticalcolumnsstandingonsubmergedhorizontalfloaters.Thesevesselshavegoodmotioncharacteristicsanddonotrequiretheheadingchangedasthepredominantdirectionoftheweatherchanges.Thevesselsaremooredbymeansof8to12catenarymooringlinesconsistingofchainsorcombinationsofchainandwire.Partsofthepipelinestransportingtheoiltothefloaterhavetobeflexibletoallowforthewaveinducedmotionsofthefloater.Theseflexiblepipelineshavetobesufficientlystrongandresilienttowithstandhighpressuresandtemperaturesofthecrudeoilaswellasthecontinualflexingduetothefloatermotions.

2.7.1.5GravityBasedStructures

GravityBaseStructures(GBS)areappliedtoremotefieldsindeepandharshwatersinthecentralandnorthernpartoftheNorthSea.Theyconsistofacombinationofanumberoflargediametertowers,placedontopofalargeareabasewhichcontainsalsostoragecapacity.Pilingtotheseabedisnotrequiredbecauseofthelargesizeofthebaseandthe

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massofthestructure,buttheseabedhastobelevelled.Thetowerssupportasub-framewith

aproductionequipmentandaccommodationdeckontopofit.

2.7.1.6Spar

Sparisbasicallyamonoleggedplatformofsmallersurfaceareaandismostlyemployedforlargerdepthsofmorethan1km.Allthebasicfacilitiesareprovidedontheplatformforthevariousproductionpurposes.

2.7.1.7TensionLegPlatform

ATensionLegPlatform(TLP)consistsofasemi-submersibletypehullwithforinstancefourverticalsurface-piercingcolumnsstandingonunderwaterfloatersandsupportingalargerectangulardeck.Ateachofthefourcornersofthefloater,pretensionedtethersextendverticallydownwardstofoundationtemplateswhicharepiledintotheseabed.Duetotheverticaltendons,whicharepre-tensionedtosuchadegreethattheyneverbecomeslack,anyverticalmotionoftheTLPwillbeeliminated.Thisallowsforsteelpipeline

connectionsbetweenthewellsandthefloater,withouttheneedforflexiblesectionsofpipelines.[9]

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2.7.2Topside

Thetopsideisastructurerestingonasupportingstructurehavingallthebasicfacilitiesfortheprocess,unmannedplatforms.Theyaredividedinto:

1. CellarDeck

2. Sub-CellarDeck

3. HeliDeck

4. LivingquartersDeck

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3.DRILLINGPROCESSES

Amajordifferencebetweenonshoreandoffshoredrillingisthenatureofthedrillingplatform.Inaddition,inoffshoredrillingthedrillpipemustpassthroughthewatercolumnbeforeenteringthelakeorseafloor.Offshorewellshavebeendrilledinwatersasdeepas10,000ft(305m).

Thefollowingtextprovidesanoverviewofdrillinginoffshoreenvironments:

3.1DRILLINGTEMPLATES

Offshoredrillingrequirestheconstructionofanartificialdrillingplatform,theformofwhichdependsonthecharacteristicsofthewelltobedrilled.Offshoredrillingalsoinvolvestheuseofadrillingtemplatethathelpstoconnecttheunderwaterdrillingsitetothedrillingplatformlocatedatthewater’ssurface.Thistemplatetypicallyconsistsofanopensteelboxwithmultipleholes,dependingonthenumberofwellstobedrilled.Thetemplateisinstalledinthefloorofthewaterbodybyfirstexcavatingashallowholeandthencementingthetemplateintothehole.Thetemplateprovidesastableguideforaccuratedrillingwhileallowingformovementintheoverheadplatformduetowaveandwindaction.

3.2DRILLINGPLATFORMS

Therearetwotypesofbasicoffshoredrillingplatforms,themovabledrillingrigandthepermanentdrillingrig.Theformeristypicallyusedforexplorationpurposes,whilethelatterisusedfortheextractionandproductionofoiland/orgas.Avarietyofmovablerigsareusedforoffshoredrilling.Drillingbargesareusedinshallow(<20ft[<6m]waterdepth),quietwaterssuchaslakes,wetlands,andlargerivers.Asimpliedbythename,drillingbargesconsistofafloatingbargethatmustbetowedfromlocationtolocation,withtheworkingplatformfloatingonthewatersurface.Inveryshallowwaters,thesemaybesunktorestonthebottom.Theyarenotsuitableforlocationswithstrongcurrentsorwindsandstrongwaveaction.Likebarges,jack-uprigsarealsotowed,butonceonlocationthreeorfourlegsareextendedtothelakebottomwhiletheworkingplatformisraisedabovethewatersurface;thus,theyaremuchlessaffectedbywindandwatercurrentthandrillingbarges.

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3.3DRILLINGTECHNIQUES

Severaltypesofdrillingtechniquesarecurrentlyemployedinoilandgasdrilling:straightholedrilling,directionaldrilling,horizontaldrilling,airdrilling,andfoamdrilling.Regardlessofthedrillingtechnique,awellistypicallydrilledinaseriesofprogressivelysmaller-diameterintervals.

3.3.1StraightHoleDrilling

Instraightholedrilling,thewellboreisverticalanddeviatesbynomorethan3degreesanywherealongthewellbore,andthebottomofthewelldeviatesbynomorethan5degreesfromthestartingpointofthewellboreatthedrillingplatform.Withstraightholedrilling,thedrillbitmaybedeflectedifitcontactsfaultzonesordippingbedsofhardrocklayers.

3.3.2DirectionalandHorizontalDrilling

Directionaldrilling(alsotermedslantdrilling)involvesthedrillingofacurvedwelltoreachatargetformation.Directionaldrillingisemployedwhenitisnotpossible,practicable,orenvironmentallysoundstoplacethedrillingrigdirectlyoverthetargetarea.Directionaldrillingisespeciallyusefulforoffshorelocations.Withdirectionaldrilling,itmaytakeseveralthousandfeetforthewelltobendfromdrillingverticallytohorizontally.

3.4WELL-COMPLETION

Onceawellhasbeendrilledandverifiedtobecommerciallyviable,itmustbecompletedtoallowfortheflowofoilorgas.Thecompletionprocessinvolvesthestrengtheningofthewellwallswithcasingandinstallingtheappropriateequipmenttocontroltheflowofoilorgasfromthewell.Casingconsistsofastackedseriesofmetalpipesinstalledintothenewwellinordertostrengthenthewallsofthewellhole,topreventfluidsandgasesfromseepingoutofthewellasitisbroughttothesurface,andtopreventotherfluidsorgasesfromenteringtherockformationsthroughwhichthewellwasdrilled.[11]

4.CONCLUSION

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Engineeringservicesplaysavitalroleintheoffshoredesign.Itimpartsextensivesupportinthedesigningandprocessingofvariousoffshoreproductiontakingplaceinthesea.Itlooksafteranumberofvariousdepartmentsandhenceitsimportancecanbecomparedtononewhenthequestionofimplementingandexecutingtheprocesscomes.

OilandgasindustrythushasahugeroletoplaynotonlyinthegenerationofpowerbutaswellasblossomingIndia’seconomy.TheyarethemajorcontributorsinIndianeconomyandhencecontinuouseffortsarebeingmadefortheirexplorationinthenearfuture.

Finally,summingitupweconsiderourselvesfortunatetobeapartofIndia’stycooncompanyforOil&GasProduction,thoughforashorttenureonly.Wehadagreatexposuretotheoilandgasindustryduringourtrainingasitcontinuouslyfacilitatedusdevelopingourknowledgetothewhere-aboutofoilandgasindustry.

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5.REFERENCES

[1]IOGPTONGC,2009,ONGCCompositeCatalogue.

[2]Tamareck,Oct2002,“CONVENTIONALOILANDGAS,GEOPHYSICALEXPLORATION”

[3]ExcerptsforRocktalk,Vol7No.2ColoradoGeologicalSurvey.

[4]ONGC,“GlimpsesofProductionandprocessengg.ppt”

[5]2009,Fundamentalsofprocessplantpipinganddesign.

[6]ELSEVIEROCEANENGINEERINGBOOKSERIESVOLUME3,“PipelinesandRisers”

[7]Adocumentontheinternet–“Wikipedia.org/gascompressors”

[8]Adocumentontheinternet-“IntroductiontoCentrifugalCompressorsandKnockOutDrums”

[9]JournéeJ.M.J.,MassieW.W.,DelftUniversityofTechnologyFirstEdition,“OFFSHOREHYDROMECHANICS”

[10]Adocumentontheinternet-HyundaiHeavyIndustriesCo.Ltd.,Offshore&Engineering

[11]November,2005,“OILANDGASEXPLORATIONANDDRILLINGTECHNOLOGY”