Historyofoffshoredrillingunits

Offshoredrillingbeganin1897,just38yearsafterCol.EdwinDrakedrilledthefirstwellin1859.H.L.WilliamsiscreditedwithdrillingawelloffawoodenpierintheSantaBarbaraChannelinCalifornia.Heusedthepiertosupportalandrignexttoanexistingfield.Fiveyearslater,therewere150offshorewellsinthearea.By1921,steelpierswerebeingusedinRinconandElwood(California)tosupportlandtypedrillingrigs.In1932,asteelpierisland(6090ftwitha25ftairgap)wasbuiltmileoffshorebyasmalloilcompany,IndianPetroleumCorp.,tosupportanotheronshoretyperig.Althoughthewellsweredisappointingandtheislandwasdestroyedin1940byastorm,itwastheforerunnerofthesteeljacketedplatformsoftoday.[1]

Contents

1Overview2Thefirstonwaterdrilling3ThefirstMODU

3.1Thefirstoffshoredrillingunittoimplementsubseawellcontrol4Offshoredrillingunitdesignevolution

4.1Thetenderassistdrilling(TAD)unit4.2Thesemisubmersibleunit4.3Growthofoffshoredrillingunits4.4Firstgeneraltionsemiunits4.5Newergenerationsemiunits4.6Thefixedplatformunits4.7Theshipandbargeshapedunits4.8TechnologicaldevelopmentoftheMODU

5Thefutureofoffshoredrilling6References7Seealso8NoteworthypapersinOnePetro9Externallinks

Overview

In1938,afieldwasdiscoveredoffshoreTexas.Subsequently,a9,000ftwellwasdrilledin1941infashionsimilartotheCaliforniawellsbyuseofawoodenpier.WiththestartofWorldWarII,however,alloffshoredrillingactivitieshalted.AftertheendofWorldWarII,thestateofLouisianaheldanoffshorestatewatersleasesalein1945.Thiswasfollowedin1955bythestateofCalifornia(CunninghamShellAct)leasesale,whichallowedexplorationofoilandgassands.[1]Beforethelatteract,coredrillingcouldbedoneonlyuntilashowofoilandgas.Atthattime,alldrillinghadtostopandthecoreholepluggedwithcement.

Thefirstonwaterdrilling

ThefirstonwaterdrillingwasbornintheswampsofLouisianaintheearly1930swiththeuseofshallowdraftbarges.Thesebargeswererectangularwithanarrowslotintheaftendofthebargeforthewellconductor.Canalswere,andstillare,dredgedsothattugscanmobilizethebargestolocations.Later,bargeswerepostedonalatticesteelstructureabovethebarge,allowingthemtoworkindeeperwaterdepthsbysubmergingthebargeonthebaybottoms.Thesebargesusuallyrequiredpilingsaroundthemtokeepthemfrombeingmovedofflocationbywindsandwaves.Thefirstoffshorewell,definedas,outofsightofland,wasstartedon9September,1947byatenderassistdrilling(TAD)unitownedbyKerrMcGeein15ftofwaterintheGulfofMexico(GOM).AnexWorldWarII26048ftbargeservicedthedrillingequipmentset(DES),whichconsistedofthedrawworks,derrick,andhoistingequipmentlocatedonawoodenpileplatform.[2]

TheBretonRig20(Fig.1),designedbyJohnT.Hayward(whowaswithBarnsdallRefiningCo.atthetime),wasalargepostedsubmersiblebargecreditedin1949withdrillingsomeofthefirstwellsintheopenwatersofLouisiana.ItwasdifferentfromtheKerrMcGeebargeinthatallthedrillingequipmentwasononebarge,anditcouldbetowedasacompleteunit.Theunit,whichwasaconversionfromaninlanddrillingbarge,hadtwostabilitypontoons,oneoneachsideofthebarge,thathydraulicallyjackedupanddownasthebargewassubmergedandpumpedout.Thesepontoonsprovidedthenecessarystabilityforthisoperation.TheBretonRig20,laterknownastheTransworldRig40,wasamajorstepforwardbecauseiteliminatedthecostandtimerequiredtobuildawoodenplatformtosupportallorsomeoftheoffshoretyperig.Althoughitdrilledonlyinpredominantlyprotectedbaysinshallowwater(lessthan20ft),theBretonRig20maybeabletolayaqualifiedclaimasbeingthefirstmobileoffshoredrillingunit(MODU).[3][4]

(/File%3ADevol2_1102final_Page_591_Image_0001.png)

Fig.1BretonRig20,aconvertedpostedswampdrillingbargecapableofdrillinginopenLouisianawaterdepthsupto20ftin1949.Retiredin1962.

ThefirstMODU

ThefirsttrulyoffshoreMODUwastheMr.Charlie,designedandconstructedfromscratchbyOceanDrillingandExplorationCo.(ODECO),headedbyitsinventorandpresident,DocAldenJ.Laborde.TheMr.Charlie(Fig.2)wasapurposebuiltsubmersiblebargebuiltspecificallytofloatonitslowerhulltolocationand,inasequenceoffloodingthesterndown,endeduprestingonthebottomtobegindrillingoperations.WhentheMr.CharliewenttoitsfirstlocationinJune1954,Lifemagazinewroteaboutthe

novelnewideatoexploreforoilandgasoffshore.[5]TheMr.Charlie,ratedfor40ftwaterdepth,setthetoneforhowmostMODUswerebuiltintheGulfofMexico(GOM).Usually,aninventorsecuredinvestors,inthiscaseMurphyOil,andthenfoundacustomerwithacontracttodrillfor,inthiscaseShellOil,allowingbankloanstobeobtainedtobuildtheunit.

(/File%3ADevol2_1102final_Page_592_Image_0001.png)

Fig.2Mr.Charlie,thefirstpurposebuilt(June1954)openwaterMODUratedfor40ftwaterdepth.Retiredinlate1986andnowamuseumandtrainingriginMorganCity,Louisiana.

Becausetheshelfdroppedoffquickly,andwaterdepthsincreasedrapidlyofftheshoreofCalifornia,theapproachtherewasentirelydifferentfromthatintheGOM.RigswereinstalledonsurplusWorldWarIIshiphullsmodifiedtodrillinafloatingpositioncomparedwithsittingasubmersiblebargeontheoceanbottom,asdoneintheGOM.Oilcompaniesformedpartnershipsorproceededindependently,butMODUswerenotdesignedandconstructedbycontractdrillingcompaniesinCalifornia.Alldesignandconstructionwasdoneinahighlysecretivemannerwithlittlesharingofknowledge,becausetechnologywasthoughttogiveanedgeinbiddingforstateoilandgasleases.Beforetheleasingofoilandgasrightsin1955,oilcompaniescoredwithsmallrigscantileveredoverthesidemidshipofoldWorldWarIIbarges.Thesebargesdidnothavewellcontrolequipmentortheabilitytorunacasingprogram.Theycouldonlydrilltoadesignatedcoredepthwiththeunderstandingthatiftheydrilledintoanyoiland/orgassands,theywouldstop,setacementplug,andpulloutofthecorehole.Thesecorevesselswerehighlysusceptibletowaveaction,resultinginsignificantroll,heave,andpitch,whichmadethemdifficulttooperate.

Thefirstoffshoredrillingunittoimplementsubseawellcontrol

WithleasingfromthestateofCaliforniatoexploreandproduceoilandgas,wellcontrolandtheabilitytorunmultiplestringsofcasingbecamemandatoryandrequiredatotallynew,unproventechnology.ThefirstfloatingdrillingrigtousesubseawellcontrolwastheWesternExplorer(Fig.3)ownedbyChevron,whichspuddeditsfirstwellin1955intheSantaBarbaraChannel.Othersfollowedquickly,withallofthemconcernedaboutthemarineenvironmentandtechnologytoallowdrillinginroughweather.In1956,theCUSS1wasbuiltfromanotherWorldWarIIbarge.Theunit,builtbytheCUSSgroup(Continental,Union,Shell,andSuperiorOil),was260ftlongandhada48ftbeam.TheCUSSgroupeventuallyevolvedintowhatisnowGlobalSantaFe.

(/File%3ADevol2_1102final_Page_593_Image_0001.png)

Fig.3WesternExplorer,thefirst(1955)floatingoilandgasdrillingMODUthatusedsubseawellcontrol.Retiredin1972.

Theoriginaldesignershadnoexamplesorexperiencestogoby,sonoveltyandinnovationwerethecourseoftheday:

TorqueconvertersonthedrawworkswereusedasheavemotioncompensatorsRotariesweregimbaledtocompensateforrollandpitchThederrickwasplacedatmidshipoveraholeinthevesselcalledamoonpool.Blowoutpreventers(BOPs)wererunoncasingtotheseafloorReentryintothewellwasthroughafunnelabovearotatinghead(riserlessdrillingisnotnewMudpitswereplacedinthehullwithmudpumpsLivingquarterswereadded

Itwasanexcitingandamazingtime,consideringthateveryonewasstartingwithablanksheetofpaper.

Fig.4showstheHumbleSM1drillingbarge(2043413ft)builtandownedbyHumbleOilandRefiningCo.(nowExxonMobil)in1957.Fig.5showsthesubseaequipmentusedtodrillthewells.Notethatithasnomarineriser.TheHumbleSM1drilled65wellsforatotalcostof$11.74/ft,aboutdoublethecostoflanddrillingatthetime,inanaveragewaterdepthof159ftandwithamaximumwelldepthof5,000ft.Theunitaveraged8.93daysperwellanddrilledanaverageof324ft/D.Unfortunately,theunitsankinastormin1961whileonloantoanotheroperator.[6]Attheinsistenceofinsuranceunderwriters,theAmericanBureauofShipping(ABS)wroteandimplemented,in1968,thefirstindependentcodes,guidelines,andregulationsconcerningthedesign,construction,andinspectionsofMODUhulls.

(/File%3ADevol2_1102final_Page_594_Image_0001.png)

Fig.4HumbleSM1,afloatingMODUdesignedandoperatedbyHumbleOil&RefiningCo.(nowExxonMobil)in1957.Oneofanumberoftopsecretdrillingunitsofthemid1950s.CourtesyofExxonMobilDevelopmentCo.

(/File%3ADevol2_1102final_Page_595_Image_0001.png)

Fig.5HumbleOilandRefiningCo.sHumbleSM1subseadrillingsystemusedoffshoreCalifornia.CourtesyExxonMobilDevelopmentCo.

Offshoredrillingunitdesignevolution

WiththeMr.Charlie(bottomfounded)andWesternExplorer(floating)asthefirstMODUs,anotherconceptforaMODUshowedupintheformofajackup(/Jackups).Thistypeofunitfloatedtolocationonahullwithmultiplelegsstickingoutunderthehull.Onceonlocation,thelegswereelectricallyorhydraulicallyjackeddowntotheoceanbottom,andthenthehullwasjackedupoutofthewater.Withthisapproach,astableplatformwasavailablefromwhichtodrill.InWorldWarII,theDeLongspudcanjackswereinstalledonbargesforconstructionand/ordocks.TheDeLongtyperigs(Fig.6)showsanexample,theGusI)werethefirstjackupsbuiltin1954.[7]Althoughjackupsinitiallyweredesignedwith6to8legsandthenafewwith4legs,thevastmajorityofunitstodayhave3legs.TheGusIwasconstructedwithindependentlegs.TheLeTourneauCo.builtforZapataCorp.thefirstlatticelegjackup,theScorpion(Fig.7),whichhadindependentlegswithspudcans.Tothisday,LeTourneaucontinuestospecializeinlatticelegtypejackupMODUs.

(/File%3ADevol2_1102final_Page_596_Image_0001.png)

Fig.6WithaDeLongtypejackingsystem,theGusI,builtin1954andratedfor100ftwaterdepth,wastheforerunnerofthemodernjackup.Initially,twobargesthatwereeventuallyjoinedpermanently,buttheunitwaslostinastorm.

(/File%3ADevol2_1102final_Page_597_Image_0001.png)

Fig.7LeTourneausScorpionbuiltforZapata(nowDiamondOffshoreDrillingInc.)in1956for80ftwaterdepthasanindependentlegjackup.Lostin1969.

Amajorevolutionforthejackupdesignwastheintroductionofthecantilevereddrillfloorsubstructure(Fig.8)inthelate1970sandearly1980s.Asfixedplatformsgotbigger,theslotjackupscouldnotswalloworsurroundtheplatformwithitsslotcontainingthedrillingequipmenthowever,thecantileverunitscouldskidthecantileveroutovertheplatformafterjackingupnexttoit.Beforethecantileveredsubstructure,alljackupshadslots,usually50ft.square,locatedintheaftendofthehull.Duringtows,thesubstructurewasskiddedtothemetacenterofthehull,butduringdrillingoperations,thesubstructurewasskiddedaftovertheslot.Thederrickand/orcrowncouldbeskiddedport/starboardtoreachwellsoffcenterjustliketodaysunitsdo.

Thewaterdepthrangeformostoftheearlyslotandcantileverdesignswasfrom150tojustover300ft.Cantileverdrillfloorcentershadareachof40to45ftaftoftheafthulltransom.variabledeckload(VDL)(/MODU_equipment_and_capabilities)ratingswere3,500to5,000kips.

Inthelate1990s,premiumorenhancedjackupsweredesignedandbuilt:

Theycouldcarrymuchlargerdeckloads(7,000kips)Theycoulddrillindeepwaterdepths(400ft)Theyhadmorecapabledrillingmachinery(7,500psihighpressuremudsystemsand750tonhoistingequipment)Theyhadextendedcantileverreach(atleast70ft.)Theyhadlargercantileverloadratingsofdoubleormoretheearlierunits(some>2,500,000lbm)

(/File%3ADevol2_1102final_Page_598_Image_0001.png)

Fig.8LeTourneaus116Ccantileveredjackupwithdrillfloorcantileveredoverafixedplatform.Today'sworkhorsedesignofjackups.CourtesyLeTourneau,Inc.

Thetenderassistdrilling(TAD)unit

TheTAD(/Tender_assist_drilling_(TAD)_units)conceptwasusedtodrillthefirstoffshoreoutofsightoflandwellintheworld.Initiallyusedasanexplorationmethod,ithasevolvedintoadevelopmenttool.Thefirsttenderswereshapedlikebarges,butsomearenowshapedlikeshipsforbettermobilizationspeeds.

Basically,theDES(DrillingEquipmentSet)consistsofthederrick,hoistingequipment,BOPs,andsomemudcleaningequipment,reducingtherequiredspaceandweighttobeplacedonthefixedplatform.Therestoftherigislocatedonthetenderhullmoorednexttothefixedplatform,including:

MudpitsMudpumpsPowergeneratorsTubularsandcasingstorageBulkstorageAccommodationsFuelDrillwater

Thisapproachturnedouttobeaverycosteffectivewaytodrillfromsmallfixedplatforms.Unfortunately,inmildandespeciallysevereweather,themooringlinescouldfail,withthehullfloatingaway,asitoftendidinaGOMnorther.Today,mostTADsoperateinbenignorcalmenvironmentsintheFarEastandWestAfrica.

Thesemisubmersibleunit

In1992,thefirstsemisubmersible(semi)(/Semisubmersibles)SeahawkTAD(Fig.9)wasconvertedfromanoldsemiMODU.Thesemihullofferssuperiorstationkeepingandvesselmotionscomparedwithshiporbargeshapedhulls:

Inasemihull,thewavetraincanmovethroughthetransparenthullwithoutexcitingittoheave,roll,andpitch,unlikeamonohullThelowerhullofthesemiisbelowthewateratadeeperdraft.ThecolumnsofferareducedareatoexcitethehullTheworkplatformormaindeckisaboveallwaveaction

TADsareseeingnewuseondeepwaterproductionplatforms,suchasspars,tensionlegplatforms(TLPs)(/Fixed_platform_rigs),anddeepwaterfixedplatforms,whichoperatebeyondjackupwaterdepths.

(/File%3ADevol2_1102final_Page_599_Image_0001.png)

Fig.9Worldsfirstpurposebuilt(conversion)semiTADunitSeahawk.Convertedin1992fromasemiMODU.CourtesyAtwoodOceanics.

Growthofoffshoredrillingunits

Thingswereoffandrunninginthe1950s,withnumerousoperatorsgettingintotherigownershipandoperationbusinessandnewdrillingcontractorsbeingformedeveryyear.Intheearly1960s,ShellOilsawtheneedtohaveamoremotionfreefloatingdrillingplatforminthedeeper,stormierwatersoftheGOM.ShellnoticedthatsubmersiblesliketheMr.Charlie,nownumberingalmost30units,wereverymotionfreeafloatcomparedwithmonohulls.Theideawastoputanchorsonasubmersible,usesomeoftheCaliforniatechnologyforsubseaequipment,andconvertasubmersibletowhatisnowknownasasemisubmersibleorsemi.Thus,in1961,thesubmersibleBluewaterI(Fig.10)wasconvertedtoasemiamidmuchtechnologicalsecrecy.Infact,inthemid1960s,ShellOilofferedtheindustrythetechnologyinaschoolpricedatU.S.$100,000perparticipantandhadlotsoftakers.

(/File%3ADevol2_1102final_Page_600_Image_0001.png)

Fig.10WorldsfirstsemiMODU,BluewaterNo.1,convertedin1961/1962byShellOilfromasubmersiblehull.Lostin1964.

ThencametheOceanDriller,thefirstsemibuiltfromthekeelup(Fig.11).TheOceanDriller,designedandownedbyODECO,wenttoworkforTexacoin1963,withthemooringandsubseaequipmentownedbytheoperator,aswascommoninthe1960s.Theunitwasdesignedforapproximately300ft.ofwaterdepth,withthemodeltestsofthehulldoneinDocLabordesswimmingpool.TheOceanDrillercouldalsositonbottomandactasasubmersible,whichitdidwellintothe1980s.

(/File%3ADevol2_1102final_Page_601_Image_0001.png)

Fig.11Worldsfirstpurposebuilt(1963)semiMODU,OceanDriller.Unitcouldoperateasasemiorsubmersible.Retiredin1992andscrapped.CourtesyODECO(nowDiamondOffshoreInc.).

Firstgeneraltionsemiunits

Mostofthefirstgenerationunitscouldsitonbottomordrillfromthefloatingpositionasahedgeagainstunemployment.Theshapeandsizeofthefirstsemisvariedwidelyasdesignersstrivedtooptimizevesselmotioncharacteristics,riglayout,structuralcharacteristics,VDL,andotherconsiderations.Thegenerationdesignationofsemisisaveryloosecombinationofwhentheunitwasbuiltorsignificantlyupgraded,thewaterdepthrating,andthegeneraloveralldrillingcapability.

Newergenerationsemiunits

Intheearly1970s,anew,secondgenerationsemiwasdesignedandbuiltwithnewer,moresophisticatedmooringandsubseaequipment.Thisdesigngenerallywasdesignedfor600ftwaterdepth,withsomeextendingtogreaterthan1,000ft.TheOceanVictoryclass(Fig.12)wastypicaloftheunitsofthisera,whichconcentratedheavilyonreducingmotionsoftheplatformcomparedwithincreasedupperdeckVDLrating.Manywerebuilt,and,inthemiddletolate1980s,anumberofthirdgenerationsemisweredesignedandbuiltthatcouldmoorandoperateingreaterthan3,000ftofwaterdepthandmoresevereenvironments.Manyofthethirdgenerationunitswereupgradedinthe1990stoevendeeperwaterdepthratingswithmorecapabilitiesandbecamefourthgenerationunits.Withafewexceptions,theoperatingdisplacementoftheseunitswentfrom18,000longtonsinthe1970stomorethan40,000longtonsinthe1980s.

(/File%3ADevol2_1102final_Page_602_Image_0001.png)

Fig.12ODECOsmulticolumnsecondgenerationsemiOceanVictoryclassofearly1970s.UnitshownistheOceanVoyager,drillingintheNorthSeaintheearly1970s.Thisdesignprovedstructurallyveryattractiveforupgradetofourthandfifthgenerationunits(seeFig.14.14).

Inthelate1990s,thefifthgenerationunits,suchastheDeepwaterNautilusshowninFig.13,becameevenlarger(>50,000longtondisplacement)andmorecapable.Theseunitscanoperateinextremelyharshenvironmentsandingreaterthan5,000ftwaterdepth.Somesecondandthirdgenerationsemishavebeenconverted,givenlifeextensionstotheirhullsandupgradestotheirdrillingequipmentsoastobeclassedasfourthgenerationunits.Fig.14showsasecondgenerationOceanVictoryclassunit(seeFig.12)

thatwascompletelyupgradedtoafifthgenerationunitcapableofmooringandoperatingin7,000ftwaterdepth.NotetheadditionofcolumnblistersforincreasedVDL,50%increaseindeckspace,andtheadditionofriserstorageandhandling.Alimitednumberofthird,fourth,andfifthgenerationsemishavedynamicpositioning(DP)assistorfullDPstationkeepingcomparedwithaspreadmooringsystem.

(/File%3ADevol2_1102final_Page_603_Image_0001.png)

Fig.13DeepwaterNautilus,oneofthenewlybuiltfifthgenerationultradeepwatersemisthathasDPassistforitsspreadmooringsystem.NotespreadcolumnsforincreasedVDLandstability.CourtesyTransoceanInc.

(/File%3ADevol2_1102final_Page_604_Image_0001.png)

Fig.14OceanBaroness,oneoftheOceanVictoryclass(Fig.12)secondgenerationsemisupgradedtoafifthgenerationunit.Noteblisteradditionstocolumn,deckexpansion,andmuchlargerderrick.ThissemialsodidsurfaceBOPworkinMalaysiain2003,alongwithsettingtheworldsrecordselfcontainedspreadmooringwaterdepth(6,152ft).CourtesyDiamondOffshoreDrillingInc.

Thefixedplatformunits

Fiftyyearsago,fixedplatforms(/Fixed_platform_rigs)hadlandrigsplacedonthemtodrillandcompletewells.Todaysplatformrigshavebeenrepackagedsothatthey:

Optimizetherigup/loadouttimeRequirelessspaceArelighterHavemoredrillingcapabilities

Drillingplatformrigsarestillcommon,buttodaysunitslookfardifferentfromthoseof30or40yearsago.Conventionalplatformrigsareusuallyloadedoutwithaderrickbarge.Somelargeplatformsmayhavetwodrillingunitsonthem.

Toeliminatethecostlyderrickbarge,selferectingmodularrigshavebeenbuiltforlightworkoversandfordrillingtomoderatedepths.Largerunitsthathavethecapabilityofa1millionlbmhookloadhavebeenbuiltthatarelightweight,easiertorigup/loadout,andselferecting.TheadventofsparsandTLPsindeepwater,wherespaceanddeckloadarecritical,hasgeneratedevenamoresophisticatedmodulardeepwaterplatformrig,whichishighlyspecializedtothestructureonwhichitsits(Fig.15).Theseplatformrigs:

ArenotselferectingAreuniquetothestructuretheyareplacedonAregenerallyverylightUsuallyhavelimiteddrillingequipmentcapabilities

(/File%3ADevol2_1102final_Page_605_Image_0001.png)

Fig.15Exampleofhighlyspecializedandsitespecificmodularfixedplatformrigsusedonspars,deepwaterfixedplatforms,andTLPs.ThisunitisonaTLPintheGOM.CourtesyHelmerich&PayneIntl.DrillingCo.

Bythemid1960s,thejackupdesignedrigsweredisplacingsubmersiblesinincreasingnumbers.Jackupshadmorewaterdepthcapabilitythaneventhelargestsubmersibles(somecouldoperatein175ftwaterdepth),[7]andtheydidnotslideofflocationinsevereweather.Fromthispointon,jackupandsemidesignswererefinedandmadelargerandmorecapablefromadrillingandenvironmentalstandpoint.

Theshipandbargeshapedunits

ShipandbargeshapedfloatingMODUs(/Conventional_ship_and_bargeshaped_rigs),initiallyattractivebecauseoftheirtransitspeedandeaseinmobilizations,decreasedinnumberassemisandjackupsbecamemorepopular.OneexceptionwastheDPdrillship,whichheldlocationoverthewellborebyuseofthrustersandmainscrewpropulsionratherthanaspreadmooringsystem.

Thefirstunitdevelopedinthemid1960s,althoughnotanoilandgasexplorationunit,wastheGlomarChallenger,whichwasdesignedandownedbyGlobalMarine(nowGlobalSantaFe),andcontractedbytheNationalScienceFoundationfordeepseacoringaroundtheworld.ThisvesselconfirmedthetheoryofshiftingcontinentalplatesFollowingtheGlomarChallengerinthelate1960stoearly1970swereanumberoffirstgenerationDPoilandgasdrillships,suchastheSedco445Subsequently,inthemiddletolate1970s,thesecondgenerationDPunitsweredeveloped,suchastheBenOceanLancer.TheBenOceanLancerwasanIHCHolland

Dutchdesign,whichalsoincludedtheFrenchrigsPelerinandPelican,whichwereownedbytheFrenchcompanyForamer(nowPride).Theseunitscoulddrillinupto2,000to3,000ftwaterdepth,hadbetterstationkeepingabilityinmoderatemetoceanconditions,andhadbetteroveralldrillingcapabilitiesDPshipsofthelate1990sandearly2000scanoperateingreaterthan10,000ftwaterdepthandaretwotothreetimeslargerthantheearlierDPships,withextremelycomplexstationkeepinganddualactivitydrillingsystems

Dualdrillingconsistsbasicallyofsomedegreeoftwocompletederricksanddrillingsystemsononehull,sothatsimultaneousoperations,suchasrunningcasingwhiledrillingwiththeotherderrick,canbeperformed.Theseunitsareveryexpensivetobuildandoperate,butcanovercometheircostwithsupposedlyhigherefficiency.Theyshouldbereviewedforpossibleuse,undertherightconditions,asanalternativetostandardsingleoperationunits.Examplesofsuchconditionsinclude:

BatchdrillingasubseatemplateLargedevelopmentprojectsoveratemplateDeepwatershortwellsWellsituationsinwhichmorethanoneoperationcanbenefittheoverallplan

TechnologicaldevelopmentoftheMODU

Theoffshoredrillingindustryhashadspurtsofconstructionanddesignimprovementsoverits50yearhistory.ThefirstwastheconceptionoftheMODUsinthemid1950s,followedbyamildbuildingperiodinthemid1960s.Intheearly1970s,thereweresignificantnumbersofjackupsandsemisubmersiblesbuilt.However,themajorboomofthelate1970sandearly1980shasbeenunmatchedinnumbersofrigsbuilt.Startinginthelate1980s,anumberofdrillingcontractorsupgradedrigsbuiltinthe1970sandearly1980stodeepwaterdepths,moresevereenvironmentalratings,andbetterdrillingabilitiesratherthanbuildingnewunits.Theconceptwasthatdeliveryandcostcouldbecutinhalfcomparedwithanewbuild.Somedrillingcontractorshavesuccessfullybuilttheirentirebusinessplanaroundconversioninsteadofnewbuild.

Sincetheoilandgasbustofthemid1980s,therehasonlybeenonespurtofnewbuilding,andthatwasinthelate1990s.Mergersandbuyoutsofdrillingcontractorsandrigsdominatedtheindustryfromthemid1980stothemid1990s.Onedrillingcontractor,GlobalSantaFe,monthlypublishesapercentagenumberrelatedtodayrateandcostofbuildinganewunit.A100%ratingmeansnewunitscanbebuiltprofitablyhowever,thepercentagenumberhaslingeredinthe40to60%rangeoverthelast15yearsorso,withspurtsinto80%.Byitsnature,thedrillingbusinessisbuiltonoptimismforthefuturethatmaynotalwaysshowproperreturnsoninvestmentintermsofnewbuildsorconversions.Highonhopeandthefuture,thecontractdrillingbusinesshashistoricallynotbeenconservativeandhasnotfollowedgenerallyacceptedrulesofinvestment.

Intheearly2000s,theaverageageofthefleetwasmorethan20years,withsomeunitsmorethan30yearsold.Fewarelessthan5yearsold.Somehavebeenupgradedandhavehadlifeextensions,whichmeansthat,withgoodcareandmaintenance,thebasichull,ifitand/ortherigarenotrenderedtechnologicallyobsolete,maylastmorethan40years,asdounitsinthedredgingbusiness.

Technologicallyobsoletemeansthattheunitneedstohave:

1.Uptodatefeaturessuchas:

Topdrive,Mudsolidscontrol,Pipehandlingequipment,etc

2.Enoughpowertorunallthenewequipment

Thefleetin2003stoodatapproximately390jackups,170semis,30ships,and7submersibles.Fixedplatformrigsnumberabout50,andTADsnumberabout25.

Thefutureofoffshoredrilling

Theconsensusisthattheoffshoredrillingbusinesswillcontinuetogrow,withemphasisontechnicalbreakthroughstoreducedrillingcosts.Theindustryhasdemonstratedthatitcandrillinwaterdepthsuptoandmorethan10,000ft.,andcanoperateinthemostsevereenvironments,butallataveryhighcostthatcanrunintohundredsofthousandsofdollarsperday.Ultradeepwaterwellscostingmorethan$50millionarecommon,andsomewellshavecostmorethan$100million.Itisverydifficulttojustifywellsthatcostthismuchgiventherisksinvolvedindrillingtheunknown.Thechallengetotheoffshoreindustryistodrillsafelyandeconomically,whichmeanstechnologyofeconomics,withsafety,environment,security,andpersonnelhealthallplayingalargerole.

References

1. 1.01.1Silcox,W.H.,etal.1987.OffshoreOperations.InPetroleumEngineeringHandbook,secondedition.Richardson,Texas:SPE,Chapter18.2. Barnes,K.B.,andMcCaslin,L.S.Jr.1948.GulfofMexicoDiscovery.Oil&GasJ47(March18):96.3. MobileRigRegister,eighthedition.2002.Houston,Texas:ODSPetrodata.4. Howe,R.J.1966.TheEvolutionofOffshoreMobileDrillingUnits.DrillingandProductionPractice.API66120(http://www.onepetro.org/mslib/app/Preview.do?

paperNumber=API66120&societyCode=API).5. Laborde,A.J.1997.MyLifeandTimes.NewOrleans,Louisiana:LabordePrintCompany.6. Harris,L.M.1957.HumbleSM1OffshoreExplorationVessel,PetroleumEngineeringProjectReport.LosAngeles,California:HumbleOilandRefiningCo.,

ProductionDepartmentCaliforniaArea.7. 7.07.1Howe,R.J.1986.EvolutionofOffshoreDrillingandProductionTechnology.PresentedattheOffshoreTechnologyConference,Houston,Texas,58May.OTC

5354MS.http://dx.doi.org/10.4043/5354MS(http://dx.doi.org/10.4043/5354MS).

Seealso

PEH:OffshoreDrillingUnits(/PEH%3AOffshore_Drilling_Units)

Tenderassistdrilling(TAD)units(/Tender_assist_drilling_(TAD)_units)

Semisubmersibles(/Semisubmersibles)

NoteworthypapersinOnePetro

T.F.MarucciandD.E.McDaniel1970.SafetyofMobileOffshoreDrillingUnits,OffshoreTechnologyConference,2224April.1321MS.http://dx.doi.org/10.4043/1321MS(http://dx.doi.org/10.4043/1321MS)

Externallinks

AmericanBureauofShipping(ABS)(http://www.eagle.org/)

(https://www.onepetro.org/search?q=Historyofoffshoredrillingunits) (http://scholar.google.ca/scholar?q=Historyofoffshoredrillingunits)

(http://www.worldcat.org/search?q=Historyofoffshoredrillingunits) (http://wiki.seg.org/index.php?

title=Special%3ASearch&redirs=1&fulltext=Search&ns0=1&ns4=1&ns500=1&redirs=1&title=Special%3ASearch&advanced=1&fulltext=Advanced+search&search=History

ofoffshoredrillingunits) (http://wiki.aapg.org/index.php?

title=Special%3ASearch&profile=advanced&fulltext=Search&ns0=1&ns4=1&ns102=1&ns104=1&ns106=1&ns108=1&ns420=1&ns828=1&redirs=1&profile=advanced&search=Historyofoffshoredrillingunits)