Transcript
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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”
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