by
©Kentollp, e
Thisthesisbcginswilhanoullookoflheoffshoreewfoundlandoilandgasinduslry Whilehydrocarbonresourcesare plentiful. adverse opcrating conditions andriskof impacifromencroachingicebergs leads tochallengesin design. projeclexecutionand opcration.Acceptablerisklevelsregardinghydrocarbonrcleaselolhecnvironmenlhave tobemCI by providingsufficienlproleclion forvulnerJble asselS.A discussiononthe parametcrsinvo!ved in detemliningconlact riskbclwecnIhckcclof anicebcrganda
Forsubsea struclures.many protectionconceplshave bccn considercdforapplicalionin
sclectedconceptformajorfield devclopmenlandproduclionschemesonlhcGrand
Ihatonlyrequirclimitedsubseainfrastruclurc.Otherprotcclionconceptswhichhave
The Pl'otcctionof subseainstallationsrequired forsubscatic-b:ICkdcvclopmentsvia tubularframc prolcctionstructuresisproposedinthcprcsentstudy.Thrccdiffcrcnt gcomctric configurations:J.rcanalyzed.Thelirstconfigurationconsisls ofarectangular
struClurchas alarge circularbascand a smallercircular topponion.withIhctop andbasc conncclcdusingslraightinclinedmcmbcrs.togivclhcappcaranccofalruncatcdconical
structuralresponseofthe framessubjcctcdto iccloading.Primaryfailuremechanisms during ice·subseastructureimeraction areassessed using anenergyapproach.Dcsign loads aree:~timalcdusing asimpleice load modelaccountingforcrushingfailureofthc
Progressinthis research areashould involvcsimulutionofa wider rangeof icc contact cvcnts.ltissuggestcdthatthcfiniteelementmodelbcimprovedtowardcontinuum
substructurcmodelcdusing kinematicconstraintsrepresenting icebergsi eandstability
guidanceandlimeduringthecomplclionoflhisprojectinitsentirCly.lwouldalsolikc 10 exprcssgratitudetoPaulSluckey.Freeman Ralph. and TonyKing fC CRfor
programming knowledge.Ithankthemboth.AlsoIwouldliketothankC C R for providing me with aspaceto work. accessto softwareandvariousreports. andrcscarch
questions,MITACS(www,mitacs.ca)grantedmeanintcrnshipscholarship, for thatI
4 SUBSEAPROTECTIO"~-AIKtV>tW L>
5.2 5
. 2
.,C ,ol .lo ligI,:ebergRisk 59
5.2.2Iceoc'l: e cy,e 0<)
5.2.4lccoc'I:KcCIIJCOmcl.ry
6.4Prescnlllnestigation-Crmingl lodel 110 6.4.1
~~~::~::::~:~~~~:::af::~:;;:i~~::~;~;~~~~;:r~ . . .. ~
6.42~:;
7.2Soil-PileInteraction 118
7.6 FiniteElel11Cllt Mod"I 129
9 CONCLUSIONS&RECOMMENDATIOINS 14
9.1Ice LoadsonSubseaSlructures 9.2Singlc-s~lIcllileWeIlProlectionFrameDcsign
:::
'"
11,
Equipmentrepair/replacementcost Environmentaland equipmenl cleanup cost
Heighlofsubseafacilityabovescabcd lcebcrgdraft Waterlinelcnglhoficeberg
Annualcontact frequencybelweenscouringicebergsandsubseafacilitics Proportionoficebergswilh draftcapableofcontaclingsubseafacility
~l eanwidthoffrcc-noatingkeels Df Effeclivediameterof subseafacility
Normalforce alicebergkeel Horizontalforeealicebergkecl Vertical forceat icebergkeel Slope inglc orstructureface
tv!,,~o\t,~~ Righting momentoficeberg
KG
Distancefrorn keelto center of gravityl~p Waterplanemomenlofincrtia
q,P Ultimate verticalbearing resistance of soil
expccled10 plateauwilhinthenexl fewyearsmeaning newasselsnecdtobcexploiledlo mainlainfullproduclioncapacity.Marginal fieldde\lelopmenl hasacledas a calalysl
The presentsludy begins byreviewing IhecUrrcll1slate oflhe offshore ewfoundland
prodUClionisdcclining.Theissueatlhecoreoflhisworkislhepolentialforicebergkeel
ObjCCIimpactsorinterferencefromtrawlgear.Inicc environOlentsthegoalisiccbcrg avoidance oricebergresistance. Forsubscafacililicsextcndingabovctheoceannooror
contaCI.Thcparamelersinvolvedinthecalculationorriskwithfrec-noJlingand
Thegoalofthisstudy isto assess thcpotentialofprotectingsing1c salcllitc oil producing wcllsusingaslrucluralframe.Toestimategloballoadsimposedduringtheicekeel-
encrgytoworkdonethroughcrushingandpitchandheavemolions.Basedonthe analysis. a simplificalionofthe energy modcl is used.Itisassumed conservativelythat energyisdissipaledincrushingfailurcoficeoverthccontactarca only
ThcloadsdctcmlincdfromthisapproacharclhenapplicdtolheprotCCIionframe using
dcvelopcdtosimulatepile-soilinteraction.soil-struclurcbearing intcractionand global siruclurcrcsponseuponapplicationofmcanglobalicccrushingprcssurcs.Thrce differcnlstrucluralconfigurationsare analyzcd andthcresultsarcdiscusscdindctail Finally.conclusionsofthepresenlsludyaredrawnandrccommcndationsput forthfor
sarcguardrorsinglesubseasatellilewcllinstallalionsagainstice keelconiaci.Theintenl is not to propose this ideaasthebestsolulion,ralhcrtoverirywhelherornolproteclion
Thedcsircd resuhorthc analysis is anearlyoptimalproicciionstruciure.Thefirslstepis
space ror ROYaccess andworkovcr. Thereshouldalsobcsurticientclearanee10 allow
configuralionwillbcmade more nearlyoplimal Ihrough successiveiIcrations.The analysis willbeginwith asimple rectangularrramc. similar toconvcntionalprotcction
Iruncatedconcwilhstraightinclinedmcmbcrs.Thclfuncalcdconewillthcntakcmore oradomedshapcaslhecrrectivcnessorprolcctionfrarncgeomelry(i.c. curved vcrsus
Figure I depicts Europe'slargest fixed-platromlsubscatic·backdcvclopmcllt.the
prodUClionlrcc. lypically calledChristmas(Xmas)Irce.andwellhead.TheXmastrcc comprises valves.spoolsand fillingswilh a primary functionlodircclandcontrolnuid
hasarclalivelylowprofileheightversuslheverticaltrccleading10 areductionincontact
catastrophicfailuremodes.In theeventof a dirccliccbcrgimpaclwithatrcc.prevention
production tubing.Stresscsinducedin theproductiontubing.criticaltorcliablcsafcty valvcopcratioll.willlikc]ybehigherforahorizontaltrccappiic:nionandrccomplcting
polcntiallybcrcalizcdwilhthcimplcmcntationofsufricicnlimpactprolcclion
Figure2providesapproximalcdimcnsionsforatypicalhorizontnItrce used offshore
protectionstructures. ThreeslruclUralconfigurationshavebcenconceived based initially
analyticalcxpressionslhalaccountforthesyslcmenergycomponcntsandicecrushing
Theglobalstructuralresponscofarectangulartubular·framestructure (Figure 3)willbe compared10 thatofa truncated cone slructurc(Figure 4) andthen Ihepotential benefit of introducing curvedmemberswillbcexaminedaSlheprotcctionstrucluretakesa dome- like shapc (Figure5).Thereclangularframeslructure.including piIefoundalion. has an
~
l~
EFigurc4-Truncatcd ConeProlectionStructure
~ ~
PROFILEpotcntialoflheWeslcxtension hasreceived continucdinterest(IiuskyEnergy.2008) ExpansionplansforbOlh thcTerra Nova andHibcrnia ficlds alsoindicatethetrend in harncssinglhe fullpolentialofTewfoundlandandLabrador'soiland gasresourccs.The following figure showsIhe approximatelocatioll ofthcaforcmclllionedfields with
Figure Offshore Newfoundlandand LabradorOilfields(Rigzonc,2008)
Ascosts escalatedue tostrong globaldemandforscrviccs.resourcesandmalerials.itis bccomingincreasinglydifficull 10makeprojectcconomics work.TheWhiteRose Southcrncxpansion.forexamplc,addsonlyaIO%incrcmcnttothestatedoilreserves butwillcost25%ofthcoriginalWhiteRoscdevclopmentbudget(111cCanadianPress.
provinceiscxpcctcd toreachthe 00,0Cl0BarrclspcrDay(BPD)rnarkwithproduction
expansionoftheindustry.largcrstand-alonefielddevclopmcntsorsmallerficld developmclltwithtie-backstoexistinginfrastrueturcisrequired.Park(2007)discussed productiontrcndsfor thethreecurrcnt producingfieldson theGrandBanks:in2007.a30 pcrccntdecrcascinproductionwasprcdictcdby201I.WithoutadditionaldevclopmcnI
Thcmajorilyofoiland gas aClivityhasbccnfocused in IheJcannc O'ArcBasinwhichis onlyoneoffourbasinsonlheGrandBankswilhthcgcophysicalcharaclcrislicsofoil- bearingrock.AlldiscoveriesonlheGrandBankslodalc have bceninlhisbasinwhilc
Therearc approximatcly4million hcclaresundcrliccnscin thcoffshorcarcasof
cxplorationliccnscsgranlcdforlesslhanaquartcrofthclotalavailablctcrrilory.Asa rcsultofthrccscparatcbidscallcdbytheCNLOPBin2006,sixncwcxplofationlicenses havebccngrantcdforsixparcelscomprisingatOlalof 604,647heclarcs.Threcofthese parccls,whichmakc up approximalcly13%ofthetOlal area, arclocalcdin theJeanne O'ArcBasinwhilethercmaining area is in theWeslcrnNewfoundland and Labrador offshoreregion(OepanmenlofNaturalResources.Gov. NL.2008). Thenumberof
e328wells hadbeen spudded (spuddingis Ihevery start ofdrillingon anewwell).
eIOlalinduslryexpendilurcswasapproximalc!yS2Ibillion(>l.8billionon
barrelsofnaturalgasliquidshadbeen discovered(Departmentof Natural
thaI Ihere isalargeenoughriskof accidentalloading.Ihensomemeansofprotection mustbcprovidcdtoprotectagainsllheseloads.Protcctionframesapplywhenthere isa risk ofdroppedobjectimpact loads orsnagloads (fishing gcar. anchors).Workis currcntlyongoingfortheassessmentofprolcctionstrocturcstowithslandstrongerand
requircmcntsforovcr-trawlableand droppedobjecl protectionstruClures.Maximum loadscxpeclCd fromdroppcdobjcct impaclsand fishinggcararestj pulatcd.Foralllulti-
is givenas 50 kJ. Amaximum load of1 MNfrOIlltraw[ground rope snagis given in the progressive collapselirnitSlate(PLS) for anon-overtrawlablcInon-snag-frccstructure
Figure8-GravitySubseaProtection(GSP)Framc(ArupEnergy.2(08)
Fail-safe wellfeaturesplay averyimportantrole whenevalumingrcquircmentsfor wellhcadprotection.Currcntly.failsafesystemsareadoptedasapart ofthedesignon everywell drilled andpcrformanimportantsafetyfunction.espcciaIlyforoffshorc installatiolls.Thcscsafctysystclllsarerequircdloprcvcntinjurytopcrsons.damagcto
Subscacomplctions,whichincludeintcgralwcllheadcomponellts.shouldbedcsignedto
type of fail-safe systcmsadoptcdforwell installations is thesubsurface safety valve
emergencysuchas awellheadfailure.Thcsafely-valvcsyslcmisdesigned 10befail-
Perhaps Ihe mosl regulatedcomponemofanoil andgaswell. theSCSSYIllustsatisfy stringenttechnical. qualityandoperational requirements.1l1Cinduslry has madc huge
rcliability.Thcfigurcbclowil1ustratcsthedcvelopmcntinDappcrtypc downholesafcty
Historic"TR-SCSSV(fbppef)ReIl~
I.. ... . .. ,~ i [j]
~~
bylheFoundationrorScienlificandlnduslrialResearchallheorwegianlnslituteor Technology(SINTEF)andiscurrcnllymanagcdbyWclhnaslcr.Thissludyrcmainslhc largestyelundcrtakcnintosubsurtaccsarely-valveopcrationalcxpcricncc
SarClY valvcsshouldbeinstalled atsurficicntdepthin thcproductionstring10maintain inlcgrilyaslhcyorrcramajor riskorenvironmcntal dalllagcircompromiscd.Orrshorc
inlhctubing stringatlcast30 mbelowthcseanoor.as slipulatcdbylheCNOPBunder
Ananalysispcrrormcd byDoha(2007)providesinsight inlothcsarcrangcordcpthsat whichccrtaindownholecomponenlsmaybescl.Significantstresseswereround IObc noncxiSlcntat typicalSCSSY inSlallalion Icvels.ReliancconSCSSY's andotherrail sarcsystemsorrersanobvioussolutionrorrcductioninovcmllriskandup-rronl
ponionoflhe XmasIree.canbeplacedundera safcly class 2dcsignationascenain componcntsdonolcontribulcgrcatlytowellintcgrily.Thiswouldeffcclivelyreducclhc
unprolcctedwcllinslallalionwouldbereduccdtoapproximatcly9.7xlO-jwilhoulice managcmcnl.Thcsccstimatesprovidemolivationforfunhcrstudyofthcstrucluml
Foran unprolccted well. Fowlow(2007)cslimatesan icebcrgcontacIprobabilityof9.6x 100Byrefining safelyclass designalionsoflheChriSlrnasIree.approximatclyl7%of the lrcc areacanbcneglected. achieving aCOlllaclprobabilityreductionof17%.C-
giveniecbcrgconlaclhasoccurred.isapproxirnatclyO.097.lntegrating lhis suggeslion as well as an SCSSV probabilily offailurcofO.027anoverallblowout probabilityof9.7
51.1 years.Fowlow(2007)uses a moreconservative valucof36.7. whichresulted from
for Olhcr polcnlialleaksources.In addition.thedalasct may notaccounlforlheinlcnded
resultingfrom icebcrgcontaciand thecorrcsPOndingeffectonSCSSVreliabilityand
Tokeep rescrvoir Ouidsseparatefrom Iheenvironmentlhercareasericsofbarriersina wcllcomplction.Primarybarricrsareinfull-timedircclconlactwithhydrocarbons sccondarybarriersexist as abackup incaseofa primarybarrierfailurc andlcniary
Doha(2007)pcrformed afault tree analysis10roughlyprcdiciIheovcrallprobabilityof failurcofallwc]lintcgritycomponcnls.Failurcofproduclionlubingand annulus
11lbinghungcrandlwoSCSSV·sbe]ow.Thcscvalveshavehighrcliabililiesand Iheir combinedcffonsgivea probability offailureofapproximalcly 8 xI0.7.TIlcunnulus barricrs-packers.ca.<;ingjoinls.tubing hangerseals.andannularisolulionvalvcs-givea mlichgrcalcrovcrallprobabilityoffailurcofO.987.Thcresullingprobabilityof hydrocarbonrclcaselolheenvironmcntisapproximalclyO.OI27.Thisfaulttrccanalysis waspcrformedgivingthercliabilityofallpolenliallcaksourccsequalweight.when in
TYPICALWFltHfAQPROTECTIVf ENCIQ$I!RfCO T
FigureI I Proteclive ShellerConccpt(PctroleumDirCClorate.Gov.NL.1981) DORISEngineering perfonneda dctailcdstudy in1999 on altemativcstogloryholes
protectonctothrcesubscatcmplatcswhichrcquirca muchlargerstnlcturcthanwouldbe requiredbyasingle satellilc well.Noncthcless.thecstimalcdiccbcrgloadingand ncccssaryslrtlcturcsidcslopewouldapply.1l1cminimumheightwaschosenaslOm
scabed,Ahorizonlaltrce.usuallyaround5mhighwouldrcqllircastructureabOlll8m high,Figurel2iliustratesthetypicaiproIcctionsiructurcarrangcmcnLAnicecrushing strengthof2MPawasutilizedindeterminingiceloadswhichrangcdfrom arcsultanlof
Figure12-TypicaIProtcclionStruclureArrangement(DorisEnginccring,I999) Thefollowingpoinls briefly outlineIhevarious slructures considered
~Iopingfacedesign andexternalshellof concreteorstcel.Tobefloaledand
wcightversionwasconsideredtoreduceinstallationweighLThisversionwould
separatelyconstructedandtransported elcmel1ts.Similartothemonolithicrigid
• Piled segmental rigidstructure; this solutionwasshown lorequircalargenumber ofpilesloresistthelatcralloadsandthereforewas nOIinvestigatcdfurther
,Ilpecledleading10 the requircmcnlforaconsidernbleamounlofaddilional
AnOlhcrapproachthalhasbccnc,Ilamincdisthcconslruclionofaprotcclivcbcrmaround
practicalityofthisconccplisrcstrictcdbythecxtcnsivc:lmountofslrUcluralmatcrial
BOllomscouringicebcrgshavelraversedregionsofg]oryholcinstallalionsal depthsof uploI.5minlhepast(C1ark.Hclheringlon.Zavitz.&O'NeiI.1997).Thclevelof unccnainlyand prudenceforeslablishingaconservalivcdcsign basiswilhrespccl10 safelylargclshasled reccm developmenlson IhcGrand Banks,namclyWhitcRoseand
Opcngloryholcsoriginatcdwhendrillingaclivitybcganinshallowwaterrcgionsin Ihe
incorporatedopcngloryholcsprovidingabout411lofscour proICClion(Carrick. Delong.
NATURAL SEABED
DifficultgroundcondilionscrealcdtcchnicalchallcngcsforbolhlheTcrr30vaand WhilcRosegloryholeexcav3tions.Cost implicationsoflargeopcn gloryholes provide reasolllocrC3lccheaperahemalives.WilhancstimalcdcoslofS9.55MMCDN(2007).
gloryholcsarenotarcasonableicebergconlacldcfcnscsolutionforsinglcs31cllitc
typically6tolOmctcrsindiamcteranduplo20mdcpth.lnstallationwouldnorrnallybe carricdoUlfromadrillingrig.Thesiloisinstallcdpriortocomrncncclllclllofdrilling opcrations,Thcsilohasawcakpointatapre-dctermincdclcvationbelowsealevel.In the caseoficeberg impacl. thesiloisshearedattheweak poillt andlhcuppcrpartofthe silois sacrificed.leavingthe lowerpartofthcsilo,thc wcllhcadandthcChrislmaslreein
Afieldlrialin199010assessthefeasibililyofusingTornado Drill@technologyshowed
NATURAL SEABED
scgmcntbyslopcdexcavatedsidewalls.Soilreinforcemcntfabricmay bc appliedto the sloped excavationsif necessary toavoid soil slippage.Aninnerprotectiveshieldcould alsobc incorporalcdto protcct theproduclion equipment fromdebrisand makecleanup
multi-wellclustertie~backdevelopmentsfrom a riskandcost perspective.The modified casedholeconceptwasfoundtobcthemostattractiveoptionfromacombincd cost and
asscmblyconsisisofallcomponenisessentialformainiainingwcllintcgrily.Thc
damageduring shear linkaClivalionabreakawayflangcmaybcincorporalcdabovclhe
special runninglools andconsumablccaisson malcrialsarcrequired(Fowlow.2007)
ThiseonccplhasbccnimplementcdonfiveexplorationwellsollthcGrand Banksby
asproductioll weltsif thefields arcfound 10beeornmcrciallyviablcatalalcrdalc.As discusscdbyFowlow.CFER(1988)invcsligalcdthecollapscbchaviorofthcsel.067m caissoncomplclions10 assessthceffectiveness ofthcintended proteclionsystem.While lhcrelativclyunsophisticaled analysis yiclded favorablcrcsults.unccrtainliesincaisson strength andsoil parameterswere sufficienttosuggcslthai inSOlllCSituationscaisson
CAlSSOO
l S l(S
TOPOFWElLHOO
FigurcI7-CaissonComplelionMcthod(Fowlow.2007)
pipcbcncaththcoccanfloor(Oceanlnduslry,1978).Thcabovc-mudlincheightwas signilicantlyrcduccdlo4'6'"(approximatelyl.5m).MaSlcr valvesandothercritical portions ofthesyslcmaresunk toarequired dcplhandarcdesigned 10 au(omatically shut
notincludcanycriticalpressure-containingcomponenlsandinthisparliclilardcsignis coveredbya protectivedome.New design(caturcs(orthis conccptwereprototypcd.
Figurc18-CamcronlronworksCaissonComplclionSyslcm("OccanIndustry.1978)
TheconccplproposcdbyDoha(2007)uscsoffthcshelfcomponcnlsandcanbeinstallcd using standardprocedurcs;aconvenicnccfeaturc whichwould increaseatlractivcllCSSof anyncwconccpl.Thcdiffcrcncebetwecnthisconccptandthccaissoncomplclion syslcmisthcnon-rcquircmenlforalowerlrecasscmbly.lnSlcad.asinglcisolalionball valveisinstallcd abovclhc tubing hanger. BClwccnthelubinghangcrand wcaklinkin Ihecaissoncomplclionsyslcm.thercconsislsa]owcranduppcrtrccasscmbly compared
tubing.Theintention ofthe pipe-in-pipecross scctionistodecreascstiffnessattheshear
Figure 20-Arrangcmcntof ShearLink WellheadSystem(Doha,2(07)
ofthisconccptis that nospecial tools.cxtraexcavation or vcsscIrequirement beyonda drillingrigarcrequiredforinstallation ofsub-mudlinc casingandtubinghangers.All
major factorin the relative economic attractiveness ofthis coneepl.Adownfallofthis conceptis thaiwhile shearlinks arcinlcnded10rclievehorizontalloading.theywould
not prevent damage fromsignificantvertical forces.Thcvcrticalforccscrcatcdduring IhcinleraclionprocessmaycomprcSSlheshcar-linkdisconncctmcchanisminhibiling
opcrationofwellintegritycomponcnts.lnasamplccalculmion,Doha(2007)assumes
in estimatingan ovcrallrisk levelof1.27x 10-6, which isless than lhclargctsafcly1cvcl
oflxl0·S.lfwcassumeicemanagementisunsucccssfullhecstimaIcis increased10
Alhree year program by GERTH(GroupcmenlEurop cndeRccherchesTechnologiqucs surlcsHydrocarbures)started in 1976 withthe objcctive ofdclining andstudying a
designofasix-momh.per-yearproduclion schemeasillustrated by Figurc21(secDuval
To place critical componcnlSoUI of range of scouring icc kccls il wasdccidedloplacelhe cquipmcnl on Ihc boltom ofa gloryhole. ThcXmas tree slood at a height of4 mwilha5
pUIinplace10avoidfillingby soil cave-ins.Tubinghangcrswerclocatcdinalm caissonapproximalclyl7mbclowlhccxcavationbonom.Thccaissoncornplclion syslcmconsislcdofalowerlreeassembly (slim conncctor and lowcrmaslcrvalvcblock) anduppcrtrcc asscmbly(uppcrfailsafcmUSlcr block. wcak point,cxtcnsion,wye divcrtcr,wcllvcrticalacccsssyslem,nowlincconncctionsystcm).Thccrilicalprcssure- COlilainingcomponentsarclocaledbclowlhewcakpoinl. TIlcwcakpoint isincorporatcd inlhisparticulardesignasasafetymeasureinthe improbablccventofaniccbcrgkccl scouringdeepenough toimpacithcsubsea structure.Thetwohydraulicallyconlrollcd
Thisconccplincludcs three sepur.lleproteclionschemcs in onc: opcn gloryholc.cascd glory hole. and caisson complelion.ForapplicaliononthcGrandBanksorinanyothcr
design rorsarety hashadyears to developsincethis study.Thenovellyoroperalingin
Figurc21-Multi-ProtectionCol1cept(Duvaletal.,1980)
developmentinorrshore iceenvironments.Anindepthriskanalysisis conductedror eachconceptaswellasadetailednelcostanalysis.Orseveralnovclconceptsprcscntcd.
onlythe XmasIrCCwithdownholeweakshcar planeandthemodificdcascd gloryhole
optionswere deemedworthy offunherslUdy duetothcir favorability fromcommcrcial.
caissoncomplctionsystcm.Astrucluralbascdfinitcclcmcntanalysis wasconductcd to prcdictstructuralrcsponseofawellheadtoiccbcrgcontacl.Optimallevclsforkey componcnts ofthecomplctionaresuggested.Rcsultsofariskanalysisbasedoncontact frequency and availablereliability data showthe potcntialeffecl.S ofincluding downhole
AsdiscusscdbyDoha(2007),itwouldnOlbceconomicallyfcasibleforrcscrvoirs1css
protection.A recommendation for newsubscaprotcction ideaswasputfonh
Fowlow(2007)pcrfonned an in-deplh risk andcost studyforlhcvariousprolcction concepts.Single welldevc[oprnentscenarios as wcllasmulti-wellclusterarrangcmenls were analyzed.Theannualcontactprobabilily wascalculalcd foreachconccplulilizing
effccts oficebcrg managementwithan assumed 85%cffectivencss.Fromapurely risk based pcrspective. assuminglhal icc keelcontact resultsin a wellblowout.it was suggestcd Ihalopcnglory holesandmodifiedcasedgloryholesarcIhemostfavorablc
rcduccd byshortcningthespacingbctwcen Xmastrcesin thcclustcr.Fowlow(2007) suggcstedchangingtheminimumwellspacingfrom25mtoiOmtorcducccontact
Thecostofdevelopinganoilfieldisgenerallyhighcroffshorccwfoundlandthanin
costanalysiswasundertaken for the aforcmcntioncd wellhead protectionconcepts.The net cost ofa particularsystemis evaluatedusingthe followingexpression
whcreC,\,yisthenetincrcmcntalsystcmcostequaltotheincrcmentalCAPEX cost
(Cc"nJt)plusIhe costofriskfromicebergs (CIfI~K).Costofriskcanbecxpressed as
where,flistheannualprobabilityoficebcrgcol1tact.Risequipmcntrepair/rcplacclllcllt cost, Eiscnvironrncntal andequipmcntc1canupcost.pis costof lossproduclion.and
singlcsatellitewelldevelopmentbasedon nctcost. WhilcanunprOlcclcdwellwithand
thrcsholdsafclylimitoflO·5,basedonlheassumptionthalicebcrgcontact causesawell
comparisonof the associalcdcosls foreachconcepl.CAPEX hasthcgreatcslinfluence
~ O 0A--.- - ---a-I
I ··IA--.-~ ~
Figurc22-UnitNormalizcdCAPEX&CostofRisk(Fowlow.2007)
Thc majorilyoficebergsthat find lheir way 10 thc Grand BankscalveoffoflheWcst
JccbcrgslravclorthinlheWcslGreenlandCurrcnl.lhenSouthinthcBaffinand
2003).Figure230utlineslhcgcncraltrajcetoryoficebcrgslhatmaydriftinloregionsof
Icebcrgsrnaybcfreely-floatingortheymayalsocolllcintocontactwiththeseabcd causingscours (gouges)or pirs.Itis worthnoting thatthcCanadianterm'scour is synonymouswiththeU,S,term·gougc'.Thenumbcroficebcrgswhichenterthe Grand
iccbcrgseasonextends fromarchthroughJune.Whileiccbcrgs arc greatsJ --ctaclesfor
Acceptablesafetyorreliability targetsas~ociatedwithsubseainstallations inice
orrshorccodcsprovidcthebcsidesignguidancerelatingtoGrandBanksiccissucs
inslallalion isIhercfore Ix10..Up 10aboul tcncntiticsc bctrcalcdindividuallyatthisan
safctylcvclbcmaintainedatlxlO-l.therebyincreasingthesafctyrcquircmentforeach
orinjection wells.the environmental impact willbclcss scvereandthercforcthcsafcty
watcrlincstructurcsbeseparatc from Ihcgcneralseaiccloadproblem.lcebergloadsfor
Theyshowed thccffectoflowering Ihevertical profilehcighlofasubscainstallationon
bctwcen10and10·Jwhich is 100 highfor a safely classIinstallation evenIhoughafull well blowoul isnolnecessarilyaresultofimpaci. A main rccommcndalion from this papcrwastoasscss Iherisk loslruclurcsthatprolrudc above thescaOoorbysimulationof
To assessiccbcrgrisk10subseainstallations whichprotrudcabovcIhc mudline we need
10iairiskoficeberglsubscasifUciureimpacl.Figurc24showstheimportanceof
3 XIO-3
00510152025303540455055 StructureDiamcter(m)
Table Areal Densityfor Degree~~~~~~~~~knstainingMajorDevelopments onthe
~~77/~1.26
~
1.61
1.53~ 1~
~.f
'
1.06 1.03
InareportbyCan:ncc ConsultantsLtd.(1999).studiesbyBrooks(1985).EI-Tahanand Davis(1985)and Miller andHOlzel(1985)werediscussed. Brooks (1985) showed that aniceberg'swatcrlinc 1cngthis greaterthan itsdraft inabOlll92%ofthccascsanalyzcd
rclationshipwussatislicdforl97outof214iccbcrgs(approxirnately92%).Miltcrand HOllCI(1985)foundiccbergwidlh(maximumdimcnsionmcasurcdperpcndicularlo Icnglhaxis)was85%oftheicebcrglength. Fromthisrcsult.c1osccorrelationbctwccn
D=l.03exp(O.70+0.78In(L)+E,,) whcrccllisanormallydistribulcdrandoOlvariablewithamcanofOandstandard
Arecent reportonicemanagement(AMEC Earth&Environmcnlal.R.F.McKenna&
Figure PcrcenlugeofFrcc-FloatingKeelsCapable of1mpacI(C-CORE.2007)
Anexpressionrelating normalized iccbergwidlh(w*)to normalizedhcighlabovcthc
w*=-9.31:::*'+5.30z*+O.26
no nprofiles andrecommendationismadc loincorpor::ucdata frommanyicebergs:
~0.9
~o.a :
~O.S
~O••
00 .2 M:':~Z~,~''''''''':'(I'o\<I~ftl '' .
~
angCMCanValUC 100m> Draft>90m a.22m/s I05m>Draft>85m 0.24m/s IIDm>Draft>80m a.30mtsFull Region a.34m/s
On-shelf a.32m/s
Off-shelf O.35m/s
·r~ r=
·l l ·~ .~'.
l ~ ~--
~l '''~ ~ I
4~,
LongitudeFigurc28-DriftSpccdStudyRcgion(Stuckcy.2008)
Fieldspecific cstirnatcsofmeandriftspccdshouldconsiderthewutcrdcplhrangcofthc faciliticscornprisingthesubseaficldlayoul.ltisconscrvalivclouseancstirnatcforthc clllircstudyregioninlhc above figure. Thefollowingparagraphisareview of other prcviouscSlimatcs ofmeandriftspced. however.IhercccntworkdonebyStuckey(2008)
IOO.OOOkm2)includcSlheortheastGrandBanks.F1emishPassandthewestemportion
scourdcnsitywasO.56scourslkm2andindcpthsgrcalcrthanll0mamcandclisilyor O.86scourslkm2.ThevariabilityinlocallcvcISorscourdcnsityisnotcd:thcrcare
rcgionandameandensityofl.2-1.3scourslkm!bctweenIOO-I50mwaterdepth(K.R
incorporated inlotheGBSC. Ameanscour dcnsilyor2.64scourslkm2was de(ermined forlhel50km2rcgion
Geological Inference-UpperBound Geologicallnference-LowerBound 8.3xIO-
Scourdepths aredirticulttomeasureconsistentlyduc (oinformationfrom various
(Mycrs&Campbcll,1996)areincloseagreemcnt;forwaterdepthsrangingfrom80-120
through anexamplepcninenttothisstudy.Thethcoryforthisapproachwasfirst prescntcd by Sandcrson(1988),whodevelopcdthc method todelcrmincthcfrcquencyof
mclhodsrequiringcstimatcsoficebcrgnux.Thcfollowingformulacarcrecentlyused
wherc'7is thcannual averagearealdensityofice ergs,ristheproportionoficcbcrgs withdraftscapableofcontaclingthefacilily,Wflisthc meanwidthoffree-noating icebergkeelsatthetopofthcfacility,Uisthemcanicebergdriftspeed,andO/is
'iJ
=0.032X((cOS(4~;:~.~; ~X IO'(IO-· J ",-'
(46.67+21)XO.34",/,x3.16xIO'slY'=2.26xlO-Jy,.-'
whcrep,isthcscourrate,LJisthemeanscourlcngth'W:kisthemeanscouring 1ccbergkcelwidthatlhelopoftheslruclurc,andOjisthccffectivc slructurcdiameter
'l.=7xl0-4km-lyr-lxlO-6kmljm2(72m+21m)x650m
=4.23xIO~5
q=qf+q,
=2.26xIO-J+4.23xIO'
=2.3IxlO-J
RClum pcriods forcontactwilheachtypcofapproaching icebcrgcanbcdetemlinedby laking the inverseofthe contact frequencies. Thcrclurnpcriodforcontaci wilh a freely- floatingiccberg isapproximately 442 yearscomparcdwith23633 yearsforascouring iccbcrg.llisclcarthatfreely-floaling;ccbergsdominalccontactrisklosubsea
Theaddilionalcomacl risk frompining iccbcrgs (iccbcrgslhalcrcaICroundor oval fcalUfcsonthcscabcd)willbenegligiblcwhencomparcdtolhcriskfmlllfree-floating
Tablc5-lnpul ParamelersforTotalContaclProbabilityofaSubscaFacility ProtrudingAbovcIhcMudlinc
Df
O.79~~;:~ee
SCClion5.2.4/Croasdaleelal (2000)
insccondplacewilh 5 percentof operalionsfollowed by watercannons.nclS.andlwo--
insomc carlyreports.ha ibeendismisscd duc 10 theassocialcddangers(Barronela!..
ThefollowinglablcgivesIhcresultsof the analysisbascdonthesetwodcfinitions oflow
Tablc6-lccManagemenIOperationaISucccss(BarronctaI..2005)
provides a goodfitto empirical dataforareasranging0.6 m2106rn2.Todelcnninelocal icc pressures(I,.)correspondingtoanexceedanccprobability (p~)thefollowing
I
whcrcpcanbedctenninedwithknowledgeofmcanevcntduration/andcontact
Thctcnnpfcprcscntslhenumberofeventspcrunillimc.Contaclfn.--quency-which
(ramming ofKigoriakvessel. mean dural ioncquals 0.7 s).ItisaSSUllledhcrclhalcach cOlltaclqualificsasanevcntforfurtherdctailsandcxplanationscc(JordaancluI..1993)
prcssufc-:ucurclationshipsforca1culationofglobal iccforces.Globalicccrushing pressure canbccstim:lIcdbythe pressure-area relationship
P=CI'A"'
whcrcC,,=JandD1.=-0.4maybetakenasmcanglobalvalues,dcpcndingonthe applicillion.Jordaandiscusscshowlheseresultswcrcdcrivedrromabeslfitanalysislo ship ram data(Jordaan. 2(01).BothCl'andD"canbclakenmndomlylocxlcndthe
rangeofrcalislicphysicalsituations.ThemeaniSlakcn in thisstudy as ameans of
ltisrecognizcdthathighlocalpressuresmayexislonsmallcrarcas.LocaIpressure
curve in Figure 30.Focusing on the10.000 yearlocalpressure curveilis evident that local prcssures at areasgrcatcrthanaround13m2acluallydipbclowpressuresexpectcd globally.At the pointwhcrcthesc curvesinlcrsectutransition fromlocal to global
mcanglobal prcssurccalculatedforlheincrcmcntal area incontaCl.lfforcxamplcwe assumcfullcnvc!opmentofasingletubu!armcmber(withanormalprojcclcdareaof approxim<ltcly7m2)uponinitialcontactthcarcaisalrcadyclosctothclocal to global
thispreliminary analysis.Iheeffectsofhigh local pressuresoversmallcontactareaswill
procoourcs may bcstcapture Ihisresponsc mechanismand isarecommendedcourscof
value.
I
' 5.45s
~ . .
l00yrlocaJ-Mean~
, . ~
I, i
Figure LocalPressure-Are~~~:~:_~~e~~~~:~Return Period&MeanGlobal
Iceberg eels scour IhescabcdwhenIheydrift inlowalcrdcpthsshallowerlhantheir
playcdakcyrolcinthcmodeJ.whichbalancedscabedrcaclionforccs.cnvironmcnlal
iccbcrghydrostalicsisascnsitivcparamctcrinrnodclingthcscourprocess.Limilcd
hydroslalicsand conscqucntlyleads tosignificant differencesin rnodclcdscQurlcngths
and scouring icebergs were considered.Bascdonlhecontaclarea,aforccwascalculalcd fromthe sampled pressure. ContaCI areasrcsulting fromfree-noaling andscouring iccbcrgswcrcconsidercdin the analysis.Pressure wasassurned todevelop uniformly over the entirerigid-bodycontacl area and allimpaclSwereassumedlobedirccthils
with drarts capable of impactingasmcllilcwell5.5rnin heightwillpitchsllflicicntlyto allowthekeel topass overthelOPOflhestruclurc.Forlhercmaindcrof theiccbcrg population,Ihcdistancerequired lodissipatcthckincticencrgyoflheiceberg was calculalcd based oninilialicebcrgdriftvelocily, icebergmass andimpactforceappliedal
cebeT Force(MN) Momenl(MN·m)
rg ype Mean Std. Mean Sid.
Free-noalin 3.3 4.3 9.2 6.6
Scourin 11.9 8.2 18.710.3
excccding2.8m210eSlimaieice keelforces onahernalivcproteclionSlntcturcs for the
loads ranged from a rcsultanl40MN-200MNonstruclureswhichvaricd grcallyin
iccbcrgs withsubseasilos would bein theorderofIO-30MNwithsignificantdownward
iccbcrgs.Thcsignificanldownwardsforcesmayhavebccnaresultofconservatismin
estimatingicecrushingpressures.ThecoerficientC,.istakenas7andlhecxponcnlD,.
sacrificial wcll cquipment belocaledabovclhcscabedand crilical cquipmcntbeinslalled
Figure31-Gcometry ofTruncated Cone(NorthAtlantic Offshore EnginecringAlliance.
Aspart oflhestudy,lhcdelerminationoficebergloadsbycncrgyconscrvationand mOlllcntumconservationapproaches was invcsligated,Aswell.anumericalmodclof iceberg mOlionwas accomplishedusingthediscreteelcmenlcompuler packagcknownas
A recentstudyby Gudmcstad andLiferov(2007)assesscd iccloadsof an ice-ridgekccl onarigidsubseaslructure.Twosimplified2DnumcricalmodclsweredcvclopcdlO
cohesion,kcclangle ofinternalfriction). Thcanalysiswaspcrformcdforshallow.
intcnncdialCwatcrdCplhsinicc covered walcrs. Asamplcoutputgraphshowed annual cxcccdanccprobabilityversus comaclforcepcrmClcr(width)for alOmwidcslruclure cxtcnding5rnabovcthcmudlinein30mwaterdcpth.ltwasdelcrmincdthatkccldeplh orcontaclhcight.hasgreatestsensitivity.Possiblcintcractionsccnarioswcredcveloped
Confinedkccls,with lhehighdriving forcesOflhcsurroundingicc
noe
werepresumed10 eithershcaratlhckeel. orfaillocally and/or globally,Rcsultsoflhcanalysisshowed thai inall but two cascs,local propagating failure wasthe mechanism that limilcdthe kcclTheenergyapproach describedherein followsthe samcprocedureoutIinedinthcl996
rclalionshipshad tobcmodifiedaccordingly: cxplanmionis given throughout this
Iccloadsimpartedon asubseastructurecanbcestilllatcdusingan applicalionofthc work.energyprinciple.Uponimpact.thcinitialkineticcnergyoftheiccbergwillbc dissipatedthroughcrushingof the icc keel(indentation energy),rotation andheaveofthe iccbcrg,andstrainenergydissipated by the majorload carrying componentsofthe
Energy.2<XXJ).TheapplicalionoflheenergyapproachinlhissludydoesnOIaccount for
wherc E istheinitial incticenergyofthciccbcrg.E i )lheencrgyabsorbedin sliding(orcrushing).E.lhcenergyinliflinglheieebcrg.andEI'inrol31inglheicebcrg
whcrcmisrn3ss.c..isanaddedmasscoefficicnlandl'islhcasSUlllcddriftspcedoflhc
walcrsurroundingtheiceberg.Theadded rnasscoefficienl< nvarybctweenQ.OSfora
cxtrclllclyhighnorlllalforcesarcgcncratcdoncontacLNorlllalandfrictionalforcescan
The momentgeneralcddue to Ihe forcesatIhckeelcanbccalcu]aled bymulliplyingeach forcecomlXmentbyilSpcrpcndiculardislancctolheccnlcrofgravilyoftheiccbcrg
Fromlhccenterofgravityoflheicebcrg.e,ande arelhehorizonlal andvertical
bcequalcd10 therightingmoment todetenninelhcamountofinduccdrolalion.Righling
stability.Itisthereforc importantto integratestabilitycalculalions whenconsideringthe
M"~Iu'"tGMsin a whereGMislhedistaneefromthecenlcrofgravitytothemctacentric height and is
where is thesubmergedordisplacedvolume.ThedislanceGM isgivenby
whcrcKB is thcdislancefrom Ihekeel10 cenler ofbuoyancy.8MisIhcdislanccfrom theccntcrofbuoyancytothemetacenlricheighlandGKisthedislancefromthekeel10
whereI..,.isthemomentofinenia ofthe waterplane arca. and isthesubmerged or displaced volume.Equation 6-15can thenbercarranged as follows
~M"••••
~M,,,.,,".=(/.,'p'g-BGll)sinO
Ifwcassurnclhatforsmallangles.sinB:=B.thccxprcssioncanbefurlhersimplificd
aniccbcrgsome anglewilhoutperfonningdctailcdslabilityca1culations.Foraninitial
shapcdiccbcrgwillbccxamined,Thekeyparametcrsfromahydrostaticanalysiswillbe
rOlatcuponinitialconlact.lesseningtheamountofenergytobcdissipalcdlhrough crushingoflhekecl.Encrgystoredinheavedisplacemcntwillinturnaddenergytothe systemintheformofpolentiaIenergy:thenet balancewilllikely benegligibletowards lhedissipationofcnergy.Thefollowingpamgmphsprovidctheprocedurcfor
Assumingbasckccl widlh.sidc+slopcangle(a)and height(II) allowsforcalculationof theradius ofthetopareaofthelruncatedcone(refertoFigurc33),Withthegcometry cstablishcd.hydrostaticscanbeused lorcso]vckcyparamctersrcquircdtodetcrmincthc stabilityofthcassumcdiccbergshape.Toobtainthcdcsircddraft.theheightcanbe adjustcdandIhe hydrostatics performed iteratively:thcfoliowingdcscribeslhisprocess
Aftcrsclcclingabascradius.side-slopcanglcandhcight.lhctopradiuscanbccalculated bysirnpletrigonornetry.Thevolumeoflltruncatcdcone(inthisCllsc,thcvolullleofice)
whereII,rb'andt;areilluslratedin Figure33.Theweightofthe icc(\V..-~)whichis equaltOlhe buoyantforce (FB).canthenbecaleulalcd bymultiplyingthevolumeofice by the unilwcight.assumingthe densily of icc isapproximatcly92kglm
densilyofseawaterisl025kglm3
V'""'_'''''''N=~
(Eq.6-25)required;a solutioncanbeachievediterativelyorusingasolverloolsuchasgoalseckin excel. Furthermore.changeslolhegeometry(i.e.overallheighl)canbemade to achieve thedesireddra t
importantindcxofslubilityatsmallanglesofrolation.Sincewcaredealingwilh symmctricgcometry in thisexample. there isno need todislinguishbclwccnlongitudinal
can bccalculatcdbyequalion 6-14.The locationof the cCnlcrof gravityforatruncated
G="-["~(,,;~:.,;.:~)')]
calculatcdusingcquation6-16,where/Mpforacircularwalcrplanccrosssectionalareais
AflCrcalculatingthese key parameters.itisrelatively simple10 ca!cu]alctheslability v evOffthegivenshape.takingadvantageofthesmallangle approximation. WithsurticienlaccuracyforallpracticalpurposcsthedistanceGZcan
foragivenangleofrolation.Knowingtheseparamctersrclaledloiccbergslabilily
goometryduclorolationoftheicebergarenol accounledfor. The normaIcontaclareais
pres~urccan be approximatedby the nominalpressure-area relalionship givingnormal
willbea sharpincrease.andIhe accumulation of area will continue onIinearlylhcreafler
angleofthe strUClureand thecoefficientoffriclionbelweenIhekeclandslruclurcface Figurc 34illustratesthe growth ofthe contactarea wilhhorizonlalpenctrationaswcllas lhcnorrnalandcomponent forccs.Theappticdmorncntatthekeelisthencalculated cnablingrcsolutionoflherotalionangle.Wecan alsosolvc forlhe verticalupliftasthe
displacemelllS.the workdone bysurge.heaveand pitchmotionscan bedelcrminedby intcgralion.Thecumulativesumofenergicsaftcreachincrclllcntiscomparcdtolhe
ofenergiesfromeachoontributingmechanismwithincrementalpenctrationuntilallof theenergyhasbecndissipatcd.asindicatcdbythc·%TotaIWorkDonc·linc. Fromlhis figure we can scethatcrushingencrgy increascs rapidlyatfirst due to the fact that thc
1 ~1 --- )f1 =~;-~ I
1 1LjJ ~
00.5 .5 .5 5.5
Figure5·Work DonevcrsusPenetration-Trunc:.lledConelcebergGeometry
Figurc -WorkDoncversusPenelralion-TruncatcdConcIccbcrgGeometry Tocslablishan uppcrooundeslimateofinitialstability. andconverselyaloweroound cSlimalCoflhe energydissipaledthrough rotation. wecansimulalc arectangularprism shapc.ThisprcsumptionisbasedonlhcidcathatlhcbalanccofmOlllcnlsaboutthc CClltcrofgravitywill bc zero asthe horizontalandverticalforccsapplied al the keeland the moment armswill bcpracticallythesame.Thccalculationprocedureisthesame as forthcpreviousexarnple, asidefrom thedifferenccingeolllctry.Thcfollowingtublc
Figure37.ContactArea&ForccversusPcnctr.i1ion-TabularlccbergGeomelry Ascanbcsccnin Figure39.nearlyallofthc workisdone bycrushing ofthekecl.The
stabililyincornparison tothe previousshape.Thcothcrfactorwhichcontribulcsgrearly
ccntcrlincofthciccberg.Theappliedmorncntatthckcclabollllhc ccntcrofrotalionis equal lOthehorizontal forceatthekeel multiplied bythedistancefrom thcpointof
horizontaldistunce isonlyasmallamountlesslhan the verticaldiSlance.thererorethe applied momentatthekeelis muchlowerthanforthepreviouscase.Frollltheresults prescntedinthcfollowingtwo figures.itisclearthatthemajorilyofenergyisdissipatcd throughcrushing bcforetheiceberg comeslOrest aftcr surging almost5111
l~
~15~
3 3
Figurc3S-WorkDoneversusPcnclralionforTabularlccbergGcomclry
~ ....
~
0.00.51.01.52.02.53.03.5.04.55.05.511.0
Figure %Work Done versusPenetration-Tabular JccbcrgGcomctry
TheparallelaxislheoremforcompositesectionsisusedlofindGandB.Anelliptical
Thesubmerged volumcandwatcrplanemomentofincrtiaarecalculalcdtodclermincIhe
than the proportion from pitching. Thisislikclyduclolhcdiffercnccin theslopeof the
Ihcorclicnllycamc toreSI it had pilchcdabouijusl greatcrthan 0.23°which closely agrees wilhnmcan pilchof0.24°presenlcd ina similarmodcl used to prcdicIiceberg dynamic
'.,
n/s
Figure41-Conlacl Area&Force versusPenetr.tlion-Mcan Iceberg Geol1lclry
:~L21J . . __
In =~~-I
~
00.5 1 1.5 2 2.5 3 3.5 4 4 5 5
Figure42-WorkDoneversusPenClration-MeanlcebcrgGeomclry
r ! : ' =0 ,'" "" =:~:nW:Dono I
i ~ ~
00.511.5 2 2.5 3 3.5 .55
Figure43-%Work Done versusPenelration-MeanIccbcrgGeometry
dissip31edcntirclythroughcrushingoflhckcclmaybcconscrvativcincases whcrcthc initial pointofcont3ct isfar fromthe ccntcrof rotalionofthcicebcrg.Thcrccolllmended courseof actionistoscalecxisting iccbcrgprofilcs of icebergs suchlhatlheywillhavc sufficicnldrafttoirnpactasubscaslructureofagivcn height inugivcnwulcrdcplh.For cachiccbcrg.lhcstabilityuboutthcvaryingdircctionsshouldbcdclcrmincd Rcprcscntativc contactgeomctrycan beassumcdtoproduccacontactarca-pcnctration
TheiccbcrginFigure 44forexample willbehavcdifferclltly based on the poinlof contacl.ThcmctacentricheightwillchangeaboutdiffercntuxesasweIIasthe distance
produce verydifferent results withchangein theoricntationofimpacl.Applicationof thcMonte Carlo approachisrecommcnded10 cover awiderange oficcberg profiles Wilh
arcmadclosimplifytheloadtransferproccss.Sccnariosarcclcvclopcdtoasscsslhc structural responscofaprolcctionframeto loadsrepresentative Oflhosclhalwoutdbe imposcdduringcontactwilhanicekeel.Althoughawidcf:lIlgeoficcbcrgloadevclllS
Iheicc-structurcinleractionproccssforconlaclwilhscabcdinstallations.Basedonthis assumption.horizontal forces generated byice crushing pressuresandsurgepenetralion willbeuscdconservativelytocalculalelotalworkdone.Sincehcaveandpitchmolions
0.01.02.03.04.05.06.01.08.09.010.011.0
'''crt
, '"
~ :
I: ··· ·· .• =:'~_I
~ :
0 1 2 3 4 5 8 1 8 9 1 0 1 1
0m I
'00 ---
f
I / .. 0;._.-,....
1/
0 3 5 1011
Figurc53-WorkDone inCrushing versusenc r runcion cDomeStruclure)
1.
t
~: : ~. .m
~911 KtUm"3
~:: ~ 6.8m
Figure 54-SoilStfcngthProfileNW AnchorPile White RoseFicld(Doha.2007)
Each pileconncclcdto thestructureis modclcd as aseparate entitybasedonthe assumplion thatsingle-pileload and dcncctioncharactcrislicswillnotbcaffcclcdby adjaccOIpilcs.Generally,forpilcspacinggrcalcfthancightdiamclcrs.pilegroupeffecis maynot have10 beevaluutcd(A.P.1..2000).Empirical methods. basedonmodeland
r~;~ .. ,~m~"""1
1 2EJ
where Nyand Nrarcbcaringcapacityfaclorsforverticalslripfootings.loadcd verticallyinthedownwarddircclion.YistheeffectivesoilunitweighLristhctola]soil
q,.p=cN,.D
arclati edislacementofa roimate orgranularf soilsand
N, = [cot(¢+o.OOI)~eXP[Jrtan(¢ +o.OOI)]tan'(45+¢+~·OO I)- I}
N'=CXP(Jrtan¢ltan'(45+~)
Figure57-PlottedValues ofVcrti~allli~~~:~n;~~faCiIYFactors(AmericanLifelines
dislance6qJandremainsconSlanilhercafler.lnthcpresentsludyilis assumedIhalthe
Load.displacemenlrclalionshipsforlubularmembersofoffshorcstrucluresimpacted by
toolforasubsealubular-frameproleclionstruclurethcsamcfonnulaecanbeapplied.By applyingforces resulting frompressuresrcpresenlaliveoficccrushing slrcnglh. we can approximalclydclenninerequiredmembersizestoprcvenlcxcessiveplaslicindenlalion
whcrc islheforccandfreprescntsthcclaSlicdisplaccmclll,EisYoung'sModulus,'/
lengthof theconlactarea along the directionoflhetubc.Thecharaclcristiclength isa
discussed by Bai(2003).anempiricalcquationwasobtuincdlhrough Ihcanalysis of linearfinilcshcllclementanalysisresultsandindentationtcsIS.Ameanvalue isfound10
F.=2CT,T'L,;/D
indcnlation .can be calculatedusingascmi~cmpiricalequation.Throughenergy
unloadingpoinl.ThclocaldisplacemenlallhcloadpoilllforaloadlargcrlhanPois
As as3mplccalculalion.scicCIu tubularmemberwith adiameterofO.9m. andthickness
clasticandplasticdisplacernentsareot",,18.36mmando/,=24.62mm.ASSllminga
prediclSlhe hardening behavior in theplaslic regionoflheSlrcss-slraincurve (Wikipedia
gradcs(Walkcr&\Villiams.I995).Figure 59showsasample slrcss·SIfain curvefor x-
2.55 12.03 2.23 13.67
(·52 17.99
(·56 1.66
(·60 1.48 18.99
(·65 25.58
-70 1.13 27.13
0.86 37.00
rade lee . t a Pa
. l. 1.0'lt. 1. . . 3. 3. .
modeledusingthcsameelementsasforpilcs(B31).Pipescclionsarcdefined for the
pileandslruclural member response isbasedonTimoshcnkobeam Ihcoryassuming
dcftncd by nonlinearspringelcmenls in twolransversedircctionsandthelongilUdinal
oninpulparamclcrs(struclUrcdimensions.lubularmcmbcrsizc.pilcdcplhandsizc.and
prolcclionstructureislhcncrcatedandtiedtolhepilcfoundation,The loadapplication is
approachpreviouslydescribcd.Thcloadslcpsareenlcrcdinloanaulomalcdinputfile gencrator whichcreatestheinpulfilc10bccvaluatcdbyABAQUS/SIandardwith
andvcrificationlhroughsimplestruclumlmodcls.hisrccognizcdlhatstrcssintcnsity
analysisandcalibralionofthcftnitcelementmodclisrecolllmendcd
The following OowchanoUllinesIheoverallanalysisprocedure.Themuinidea is that
Thisscclion presentstheresultsoflhefinileelement analysesdescribedin thepreceding chapler.Thcre.'wltsarefirSlillustratedforthcrectangularframemodcl.Theeffectof incorpor•.uingcurved versusslraight membersisthenshown throughcomparisonofthe structuralresponse of thetruncated cone anddome models.Basedon the outcome of
NoteIhat Ihefigurcsprovided arescaled toimprove visibility ofthedeformaliontrends:
undeformcdgcomelriesareprovidedinScction5.Conlaclarcasarchighlighledand
Tablel4-lnputPararnetersforRectangularFrameGlobalStruclural ResponseAnalyses
cified) 8.3kN/m
~~ .\ \ ,~~' I I
2
~ =O.9m
30°keel ..D/I=3530°keel
L. [
Figure60-GlobalStructuralResponseofRectangularFrameProteclion Struclure(2.5x magnification)
Figure61-Comparison ofTruncatedConeand DOlllC Structures(2.5x)
nf
,~
---.-:~, ~;~
I
r ·~~r " , "
60°keelI L, I
,f \~~:f \
~"" fI·
60°keel
L. L.
Figure63-ComparisonofTruncatedConeandDome Struclurcs(2.5x)· Continued
I , fl :::/Fl
Figure64-Comparison ofTruncatedConeand DomeStruclUrcs (2.5x)-Continued
configuralionsproviding increased verticalsupportfor lhecircularbasemodelscould
requiremenlforlhelruncalcdconcanddomcgcomctries.Thercclangularconfiguration
lhecircularbasc.adjaccntlomembcrsundcrdircctpressurc.forthcothcrshapcs.Since
thcsidcofimpaclhave displaced inwards about 0.9 m. Thcinlcmclionwith the30"keel
grcatcrvcrticalcomponemrcsultingin lesshorizonlaldisplacemcnt than ilscountcrpan
Focusing on the frame response with D/I=25in Figure 60.the pointoffirslyieldoflhe
Figure 65.The area bctween lwoconseculivevcrticallines reprcsents aloadslcp.At lhispointIhcicekeel has surged about 3 melcrs and about27oflheassumedinilial
Figure65-HorizomaIForce-PenetralionCurvc-LoadSlcpScgmcnIs
In aside-by-sidccomparisonofthelruncatcdconcanddolllcmodclsiheresults shown in
Figure61-Figure64consislcnllydemonslralelheimprovcdeffcclivcnessoflhedome- likcstructureinconlrollinghighvcrticalloadsimposcdbythc600kcel.Comparisonof
Figure 64. Theadded stirrnesssendslherorceslhroughlhe pathorleastrcsistanceto the
To improvethe perronnanceorthetruncatedcone or domc modcls ilisrecommcndcdto
thcywouldlikclybcmorecompetcntinlhccascororr-ccntcricckcclcontact
rcctungulurrralllcconfiguration increasesits attractivencss.Theinclincdsections cXlcndingrromeachside orthcintcrior rramecouldpotcntiallybcconstructcdand
createunique andeXlrcmechallcngesinevery aspeCIofnew developmentslargeand
ApolCntialsolUlionfor Ihe prolcctionof single satellite wellswas presented.Thrcc separateconligurtions were consideredunderthecategory ofatubular frame proteclion
Theencrgyapproachwasemployedwilhconsidermionoficebcrgstabilityforsirnple shapes10asscssgloballoading.Theinilialkincticenergyofsampicicebergs was cqualcd 10thcworkdone incrushingfailureoftheicckeel over the contactnrca.andthe
simplificationoftheenergyapproachwhich conscrvalively assumcdcrushing failure cxc!usively-inlicuofbcttcrunderslanding-wasusedtoprcdicliceloads whichwere
prediclcd foreachslructuralconfiguration and adiscussionofthcrcsullscnsucd
Thcrcclangularframcconfiguralionbchavcdwcllundcrlhcprcdictcd globalloads.The
highvcnicalprcssurcswithoutincrcasingthcrnernbersizcrclmivc10therectangular frarncrnodcl:vcnicalsliffcningwasrccomrncnded.lncomparingthelruncaledconcand
bcrequircdlhallhearea-penelrationrelalionshipbcafunclionoflhckeelshapeofcach discrclclysimulated profile.Dirccl.cenlralinteraclioncvcnlswilhiccbergsltavcling horizontally havebcen assumed in the currcnt study.Itisrecollllllcnded10extend loadingscenariostoincorporalenon~ccnlralconiaciwhich wouldinducerotation about Ihevcrticalaxis.Thepotentialforverticalimpactfromaniccbcrgwilhsignific3n1heave
Apotentialavenuc10 caplurevarying stabilityand keclgeomctryislocmploy dislributionsoficcbcrgmelaccntricheight(withassociatcdmassandvclocitytcrms)and keel angle.Withkcclangle.thearea-penctrationrclationshipcanbccstirnatcdbascdon cOlltactwithknowIlSlructurcgeolllctry.Frolllthearea-pcnctralioncurvc.thccrushing pressurccanbccaJculatcdfrolllwhichthe normalforcecanbec:IJculatcd andrcsolvcd accordingly.Theapplicd horizontalandvcrticalforccsatthekccldetcrlllinehow much theicebcrg willpitchandheavedependingon the stability ofthe icebcrg.which is represenledbyits metacentricheighL Arnorcaccuraledcscriptionoftheloadpath duringIhcice-structurcintcractioncanbcachieved byupdating thepositionoflhckeel withrcspcctlothcstruclureaftereachincrcmcnlofhorizonlalpcnctration
tnkc advantageof theCoupledLagrangianEulerianapproachedbeingdcvclopcdin ABAQUS.although the conSlilulive models for ice wouldbe a significantchallcngc
Furtherwork ondefining keel geometry isrccommcndedtoasscss thegcncralpolcnlial forkcelprolrusions10induce local member failurc.Inaddilion101his.lheeffects of localiceprcssurcsonlubularmembersshouldbeasscsscdto furtherundersland potential
SinccpileinstallationontheGrand-Banksmaybcdifficult.itmayprovebeneficialto consideran alternative means toeslablishadequalclatcralrcsiSlance.Thcmaindownfall
vessel support)andlogislicsoplimization is needed. Oncc theslruCluralframe
"Oce:mlnduslry.".(1978.ovember).Belowmlld-Unell·ellcompleliollsystemlessells iceberg.anc!lor.lrawldamage.Oceall/lldllstry.13(11)64·65
Allen.S.(2000).OTCI1919-GlobalanalysisorwellheadprOlcctiongloryholesrorlerra nova.OffshoreTec!lllologyCOIl!erellceProceedillgs,Houslon.TX.1-13
ArupEncrgy.(2008).Gravitysllbseliprolecliofl(GSP).Rctricvcd04121.2008.rrom http://www.arup.comJaceplatforms/downloads/GSP.pdr
Bai.Y.(2003).orrShorcslructuresunderimpaclloads.Marille.\·trllct/lraldesigll(lstcd ..
pp.285-304).Kidlinglon.Oxrord.UK:ElscvicrScicnccLld
C-CORE.(2001 b). e erlo t s/sl se el illsr l tioll l (C-COREilJe i ReportNo.R01-COI Version2)
le l e er lo t so l s l se ll el i sr ioll tlli e i t t e ll report(C-CORE ReportNo.ROI·COI(Addendurn.VersionI))
C~C~~~'i~~~ld).lcebergrisktopi/Jelilles{If iterose(C-CORE Report o.OO-C45
C-CORE.(2007).S (SIRAM)-I re\·iew(C-COREReportNo.R-06-017-480v2.0)
DuvaI.J.J..Mercier.G..&Morin.P.(1980.January).AseasoflaloilprodllctioflSc"eme foriceberg-iflfestedl\·aters/lxJrl2/.0ceatl/t1dllslr)'./5(1)25-26
Environl1lcntCanada.(2003).Jcebergmigrllliolliflnllladicmll·lIIers.Retrieved6l412008.
2008. fromhllp:/lice-glaces.ec.gc.ca
Exprosorl.(2006}.\Vellmasler(1M):Reliabilil)'ofwellcomIJlefiotleqllipmem.Retrieved 11120.2006.rromhup:/Iwww.exprosoft.comlproduclslI?drlWeIIMasterWeb.pdf FMC Technologies.(2008).SulioilHydrogullfahRetrieved04121. 2008. from
hUp:/Iwww.rmctechnologies.comlSubsealProjectsINorway/SI3toiIGuIlfaks.aspx Fowlow.D.C.(2006).\Vellheadprorecliollcollceprsfol'slIb!u::amargiIIaldel'e/opmetlts-
gralldba1lksojllellfowul/llIu/.h.:elech2006.Banrr.Canada.I-8
Fuglem.M .. Muggcridge.K..&Jordaan.I.(1999).Designlo:ldca1culalionsforiccbcrg impacls.lmemmiollalJollrfla/ojOjfshorealldPo/al'ElIgilleerillg.9(4) Gabr.M. A..Lunnc.T..&Powell. J.J.(1994).P-yanalysisorlatcrallyloadedpilesin
clayusingDMT.JollrflafojGeoteclmicafElIgi/leeriflg.f20(5).816-837
GudmCSlad.O.T..&Lifero....P.(2007).DcsignofsubscacquipmcntlowithSlandforces fromice.Proceedi"gsofPOAC-07.Dalian. China. 787·797 Hauch.S..&Bai.Y.(2000).Bendingmomentcapacityofpipcs.O// lofOffslrorela
MeclulllicslllldArcticEugilleeritlg.I22(4).242·253
IntcrnationallccPalrol(lIP).(2008).WhalarellJesizeslilld.~/l(IfJe.\"oJicebergs?
RClric...cd06/25.2008.fromhttp://www.uscg.milllanlarealiip/faqllcebergs5.shtml Jackson.K.(1993.May).Innovation andcost-cuttingthc kcytosucccsssubsca
IElcctronicversionl.TheOi/mall.(5)96-98
Jordaan.J.J.•Press.D.. Milrord. P.(I999) Iceberg Dalabases and Verificalion PERD/CHC Report20-41. March.1999
Lcc.M.M.K.(1999).Strcngth.strcssandrractureanalysesoforrshorclUbularjoints usingfinitec]cmenls.JOllrnalofColIstrllcriOlllllSleel Re. earch.5l(3).265-286 Lolh.W.(2006).lnPikcK.P.(Ed.).Re:Directioflollproject-sacrijic:;alTreeiShear
plalle
PAL.(2001).The2001 iceberg seaSOI/Oll Ihegrafldbaflks,jillalreport!orthegra"d IXlllksmallagememteam.PALEnvironmcntalScrviccs PAL.(2002).Tile2002iceberg seasoll 011thegrafldbaflks,jillalreport!orlhegralld
ballhmllllagememteam.PALEnvironmcntalScrviccs PAL.(2003).Tile2003 icebergseaso/l 011tllegralldballks,jillalreport!or/he grand
ballhm llIgemeflfteam.PALEnvironmcntalScrviccs PAL.(2004).The2004icebergseaSO/l011tllegrandballh.jillafreporr!or/"egrand
banks/l/aJlagemell,tealll.PALEnvironmcntalScrviccs
Randolph.M.F.(2003).Scicnceandcmpiricisminpilcfoundaliondesign Geoteclmiqlle, 53(10).847-875
Reese.L.
c..
Cox.W.R,,&Koop.F. D.(1974).OTC2080-Analysisoflaleratlyloaded pilesinsand.O!fs"oreTec"noJogyConferenceProceedillgs.l-louston.TXRigzone(2008).Map: EasICalladitmO!fs"oreOilfieJds.RctrievcdOclober7.2008 fromhup:/Iwww.ngzone.comlnewslimagedelail.asp?imgid=2974
sand;~~;~~~.J~~~~~88).IceMechanics.Risksto Offshore Siructures.Graham&
landards or ay. . O O slandard - desigllo!sleel!JrIIcll/res. ysaker.
Norway: SiandardsNorway
WikipcdiaConlribulors.(2008).Ramberg-osgo(J{lrelatiollsltip.Rclricvcd03129.2008.
fromhllp:llen.wikinedia.org/wiki/ramberg-osgoodrelationship?oldid-198827830
pile thickness wasnotspccifiedin theavailable litcralurc.soa D/t ralioof25was
-UndrainedShearSb'ergth(kPa)- wtbu denPf Sl.nl kPa)
10 20 30 0 50 10 70 10
Figurc66-Assumed Undrained Shear StrengthProfile(Karlsrudctal..1993)
isappro imalcly2 A comparisonorbending momcntresponse rora20k'loadalso
Figure67-Horizontal Load vcrsusLatcralDisplacclllcntinCiay
-4-20 2 4 6II 101214161820
Figure68-DepthversusBcndingMomcntSinglcPilcinClay
Inastudywhichexamincdscicnceandempiricismin foundationdcsign.analytical
2003).AsdiscllsscdbyRandolph.thcmclhodofJardincandChow.known<lsthcMTD
diamclcrpilcof50mm wallthickncss.Thcpilccmbcdmentdcplhwastakenas100m.
inclaysoilwilh propcrtiessimilar 10those foundoffshoreWCSIAfrica.Theeffeclive
unitweightwastakenas 3.5kN/mJandundrainedshearstrength(kPa)isapproximated
l , :
Figure69-Undraincd Shear Strength andShaftFrictionversusDcpthinCiay
displacemenloblainedfromtheMTDmcthodandthe APIguidelines arecomparedin
/
0510152025 0 5 0 5
crnbcddcdtoadcpthofapproximatc]y22minsanclwithanintcrnalanglcorrrictionof 39°andancffcclivcunilwcightofI0.4kN/m3.Thcwalcrtablcwasrnaintaincdabovc lhcgroundsurface during loading10 simulalc conditionswhich wouldexist at anoffshore
pile. bcginning with a loadof small magnitude.Groundlinedisplaccmclllsandbending
pararnetcrsofthc field testwercrnatchcdinthenumericalanalysis.Rcsultsshowedgood agrccrncntbetwccnmeasured andpredictedgroundlinedcncctions(sccFigure71) with anaverage errorofapproximately 16.5.Abcndingmomemcurvcwasgiveninthe reportfor a 266k.Nlateral load. Figure72 displays a cOlllparison of the calculatedand measuredbendinglllomentcurveforthe266kNload.Excellcntagreclllcntisachieved
~ j l::
:!: ::~
75o 5Groundlineut.,.IDllplac:emenllmm)10 15 20r
25 ~0~_;ded ~ .... ~ I
Figurc71-HorizomalLoadversusL.lIcralDisplaccmcntinSandA 1994sludybyAI-Shafeielal.involvedtestingandanalysisoftensionand eomprcssionloadsonO.6lmdiarnetersleelpilesdrivcnlol8mdepthindcnsesand Figure 73showsacornparisonbetween Iheidealized bilinear t-z curveapproximatcd usingtheAPIguidelinesand themeasured t-zcllrvcfrornthcphysicaltcslat2mdeplh
I
~p"""""'1
~
o 0.002 0.00 0.006 0.008 0.01
