Download - 12 Helgeland
-
7/29/2019 12 Helgeland
1/26
Gas kick due to hydrates in the drillingfor offshore natural gas and oil
! ! !Leif Rune Helgeland
Andreas Andersen Kinn
Ole Flokketveit Kvalheim
Anders Wenaas
Department of Petroleum Engineering and Applied Geophysics
NTNU, Trondheim, November 2012
!
i
-
7/29/2019 12 Helgeland
2/26
Abstract
Dissociationofgashydratesareinvestigatedasapossiblereasonforgaskicksduringdrilling.
Gashydratesaresolidice-likestructurescontaininggasmolecules.Thebasicprinciplesofgas
hydratesandkicksareexplained,andmethodsfordiscoveringgashydratezonesbefore
drillingcommencesarereviewed.AnappraisalwellontheShenziBieldinthenorthernGulfof
Mexicothatmayhavehadahydraterelatedkickisusedasanexample.Gashydratesarealso
investigatedasapossiblecontributiontothe2010DeepwaterHorizonaccident.
Themainfocusisonavoidinggashydrateproblemswhendrilling,describingvariousdrilling
methodsandmuddesignsfoundmainlyinSPEliterature.ManagedPressureDrillingand
drillingwithcasingaredescribedasdrillingmethods.Mudweight,compositionand
temperatureofthemudarefoundtobeimportantfactors.
EarlyidentiBicationofhydratezonesbyacquiringseismicdatawasfoundtobeakeyfactorin
ordertotakepreventiveactionsbeforehydrateproblemsoccur.Itwasfoundthatafurther
understandingofhydratesisneededtoeffectivelysolvethechallengescurrentlyfaced.
ii
-
7/29/2019 12 Helgeland
3/26
Table of contents
1. Introduction! 12. Gas hydrates
!2
2.1.Formation of gas hydrate zones! 42.2.Detection of gas hydrates! 5
3. Gas kick! 74. Drilling through hydrates! 9
4.1.Possible hydrate-related kick in the deepwater Gulf of Mexico! 104.2.Deepwater Horizon did hydrates cause the blowout?! 12
5. Avoiding gas hydrate problems ! 145.1.Drilling techniques to help prevent problems with hydrates [24]! 155.2.Drilling fluid design [25]! 165.3.Cement [27]! 17
6. Discussion! 187. Conclusion! 198. Abbreviations ! 209. References ! 21
iii
-
7/29/2019 12 Helgeland
4/26
1. Introduction
Gashydrateshavealwaysprovidedchallengesinoffshoreproductionofnaturalgasandoil.
Themostcommonproblemispluggingofpipesandsubseaequipment,asubjectthathas
beenthoroughlyinvestigatedanddocumented.Thispaperwillfocusonproblemsregarding
hydratedissociationleadingtokicksduringdrillingoperations.Kicksasaresultofhydrate
dissociationhasnotbeengivenmuchattention,butithaspreviouslybeendocumentedboth
kicksandblowoutscausedbydrillingthroughhydratebearingsediments.
Sincepresenceofhydratescanresultinbothkicksandblowoutsitisimportanttounderstand
thebehaviorofhydrates,wheretheyarelocatedandhowwecanavoidtheproblemsweare
facingtodayregardinghydrates.Currentlythemostprominentdrillinghazardrelatedto
hydratesisunawarenessofitspresenceintheformation.Inordertodrillthroughhydratesin
asafemanner,earlydetectionofitspresenceisakeyfactor.Collectingseismicdataisone
waytomapthepresenceandlocationofhydrates.Ifthedatagivesindicationofhydratesin
theformation,actioncanbetakentosecureasafedrillingoperation.
GashydratesisalsobelievedtohavebeenacontributingfactorintheDeepwaterHorizon
accidentintheGulfofMexico.Formationofgashydrateshamperedthecontainmentofthe
blowoutafterthecatastrophewasafact.
1
-
7/29/2019 12 Helgeland
5/26
2. Gas hydrates
Gashydratesaresolidice-likestructures
containinggasmolecules.Theybelongtoa
groupofsubstancescalledclathrates,whichisa
chemicalsubstanceconsistingofacrystal
structureofonetypeofmoleculetrappingand
containingasecondtypeofmolecule[1].Inthe
caseofgashydrates,watercreatesthecrystal
structureandnaturalgasmoleculesare
trappedinside,asshowninFigure2.1.
Threedifferentstructuresofhydrateshave
beenidentiBied:I,IIandH.Theseareillustrated
inFigure2.2.Gashydratesusuallyforminthe
twoBirststructures.StructureIconsistsof46watermolecules,formingsmallandlargecages.
Thesmallcageisshapedlikeapentagonaldodecahedron(ageometricalshapewithtwelve
BlatfaceseachhavingBiveangels,written512),andthelargecageisshapedlikeahexagonal
truncatedtrapezohedron(14Blatfaces,twelveofthemwithBiveanglesandtwowithsix
angles,written51262).StructureIIconsistsof136watermolecules,alsoformingsmalland
largecages.ThesmallcageisthesameasintypeI,butthelargeoneisshapedlikea
hexadecahedron(16Blatfaces,twelveofthemwithBiveanglesandfourofthemwithsix
angles,written51264)[2].Thesetwostructuresarestabilizedwhengasmoleculesaretrapped
insidethecages[3].
2
Figure 2.1: Gas molecules trapped inside a crystal water
structure [1]
-
7/29/2019 12 Helgeland
6/26
Gasesthatarelikelytoformhydratesalongwithwaterare[4]:
Lightalkanes(methaneandiso-butane)
Carbondioxide
HydrogensulBide
Nitrogen
Oxygen
Argon
Animportantfeatureofgashydratesisthatonecubicmeterofsolidhydratecancontainupto
180standardcubicmetersofgas,dependingonthegas.Methaneisthepredominantgasin
naturaloccurringhydrates,makingup>99%ofhydrateintheoceanBloor[5].Formethane,
thevalueisabout164sm3[6].
Gashydratesformwhenwaterandgassesaremixedatrelativelyhighpressuresand
relativelylowtemperatures.Whilewaterformicecrystalsattemperaturesof0Candbelow,
gashydratescanformattemperaturesabovethisassoonasthepressureishigherthanafew
tensofbars,asshowninFigure2.3.Typicalconditionsforformationofhydratesare
pressuresabove30barsandtemperaturesbelow20C[3].Shallowdepthsoffshorecanhave
3
Figure 2.2: Structures of hydrates [3].
-
7/29/2019 12 Helgeland
7/26
theseproperties,usuallybetween100mand500mbelowtheoceanBloor[4].Thedepth
wheregashydrateswillformiscalledtheGasHydrateStabilityZone(GHSZ).
2.1. Formation of gas hydrate zones
Themethaneingashydratesisformedbybacteriainaprocesscalledanaerobicbacterial
methanogenesis.acteriahavebeenfoundatdepthsofupto800mbelowtheseaBloorin
marinesediments,andcanbeactiveattemperaturesupto113Candpressuresabove1000
bar[8].Thismeansthatthemethanemaybeformedwithinthegashydratestabilityzone
(GHSZ),oritcanmigratefromdeepersedimentsuntilitreachestheGHSZ.Atthisdepth,it
willformgashydratesifwaterispresent.
Gashydratesinoffshoresedimentscanexistinmanydifferentforms.InBinesilt/clayitoften
appearsasnodulesandveins,whileincoarse-grainedsedimentsitoftenformsas
disseminatedgrainsandporeBillings[6].Differentformsofgashydrateoccurrencesare
showninFigure2.4.
4
Figure 2.3: Gas hydrate phase diagram [7].
-
7/29/2019 12 Helgeland
8/26
2.2.Detection of gas hydrates
TobeabletoplanhowtomoveforwardindrillingthroughHydrateearingSediments(HS),
itiscrucialtodetectthezonesbeforedrillingcommences.Inordertodothis,acoustical
methodsareused,speciBicallycollectionofseismicdata.Thepresenceofgashydratesin
sedimentswillbeclearlyindicatedontheseismicdata,asitsacousticvelocityisveryhigh
(around3.3km/s,whichisabouttwicethevelocityofnormalsediments)[9].Two
characteristicsinseismicdataareusedtodetecthydratelocations;ottomSimulating
ReBlection(SR),andaphenomenoncalledblanking.
SRsarethemostwidelyusedindicatorforgashydratezonesoffshore.TheSRsmarkthe
phaseboundarybetweentheGHSZandthefreegaszonebelow.Seismicdatarecordsthe
reBlectionstrength,whichisproportionaltothechangeofacousticimpedance(theproductof
velocityanddensity).Asboththedensityandseismicvelocityinfreegasismuchlowerthan
ingashydrates,theboundarybetweenthezonesproducesaverystrongreBlectioninthe
seismicdata[9].
Inseismicdata,blankingisalocationwherethereisreductioninseismicreBlections,
resultinginanearlyblankzone.Thepresenceofgashydratesinporousmediaincreasesthe
averageacousticalvelocityinthelayers,resultinginreducedvelocitycontraststhatare
5
Figure 2.4: Potential gas hydrate occurrences [6].
-
7/29/2019 12 Helgeland
9/26
requiredtocreatestrongreBlections.Ingashydratezones,blankingwillthereforeoccur
abovetheSR[9].lankingandSRsareshowninFigure2.5below.
6
Figure 2.5: Blanking and BSR [9].
-
7/29/2019 12 Helgeland
10/26
3. Gas kick
ThedeBinitionofakickisBlowofformationBluidsintothewellboreduringdrilling.Formation
Bluidswillenterthewellborewheneverthewellborepressuredropsbelowtheporepressure
(giventhattheporesarepermeable).TheformationBluidwillkickthedrillingmudoutof
thewell,resultinginasuddenincreaseinmudpitvolumeonthesurface[10].
Kickscanbecategorizedintwogroups[11]:
Underbalancedkicks:ThistypeofkickistheresultofmudweightbeinginsufBicientof
keepingtheformationBluidtrapped.Thiscanhappenwhendrillingthroughzones
withhigherpore-pressurethanexpected,ifthedrillingBluidislightenedornotto
speciBicationtobeginwith.
Inducedkicks:Thistypeofkickoccursifdynamicandtransientpressureeffectslower
thepressureinthewell.Forexamplewhenpullingdrillstringoutofthewell.
Kicksduetohydratedissociationwillbeexplainedinchapter4.
Whendetectingakick,itisimportanttotakeactiontopreventfurtherlossofcontrolofthe
well.Fordrillersitisimportanttobeabletopredictgasbehavior,assmallvolumesofgascan
bepotentiallydangerousbecauseofthehugeexpansion.
Ifthemaximumallowedannularshut-inpressureishigherthanthecasingpressure,killing
thewellisthestandardprocedure.Inordertokillawell,anewoverbalanceintheborehole
7
Figure 3.1: Formation fluid entering wellbore [10]
-
7/29/2019 12 Helgeland
11/26
mustberestored.Pumpingdrillingmudwithhigherdensityrestoresthisoverbalance.There
aretwomainkilling-methodsusedintheindustrytoday[12]:
Drillersmethod,inthismethodtheformationBluidisdisplacedbeforeinjectingthekill
mud.Thisisthemostcommonmethodofrestoringanoverbalanceafterakickhas
beendetected.
Engineersmethodorthewait&weightmethodasitisoftencalled,increasesthemud
weightandstartspumpinginkillmudimmediately.
Failuretotakeproperactionwhenakickisdetectedcaninworstcasescenariosleadtothe
developmentofablowout.AblowoutistheuncontrolledBlowofreservoirBluidsintothe
wellbore.Themosttroublesomeblowoutsaretheundergroundblowouts,wherereservoir
BluidfromazonewithhighpressureBlowsintoazonewithlowerpressurewithinthe
wellbore[11].UndergroundblowoutsareverydifBiculttobringundercontrol,anditmay
takemonthstostoptheblowout.Ablowoutcanresultinseriousdamage.Lossofhumanlives,
largematerialandeconomicallossesarecommon.
8
-
7/29/2019 12 Helgeland
12/26
4. Drilling through hydrates
WhenHSaredrilledthroughachangeinpressureandtemperaturemayoccurandcausethe
hydratestobecomeunstable[13].Asexplainedinchapter2,if1m3ofmethanehydrate
dissociate,itwillproduce164m3methanegas.Whenavolumechangelikethathappensitwill
resultinakick,orinworstcasescenarioablowout.Attheshallowdepthswheregashydrates
usuallyareencountered,theblowoutpreventer(OP),riser,choke-andkilllinesare
normallynotinstalled[4].Hydratedissociationintheformationmaycauseproblemswith
wellborestabilityandsubsurfaceequipment,whichcanleadtoreducedefBiciencyandsafety
issuesofdrillingoperations.Gashydratescanalsobeencounteredatgreaterdepthswhenthe
OPandriserareinstalled.Equipmentonsurfaceandsubsurfacearemoreexposedtodanger
inthiscasebecausetherapidlyincreaseinvolumewillinvolveahugestrainonthe
equipment[4].Wellboreinstabilityduetohydratedissociationismainlycausedbytwo
problems:
Whenthehydratesdissociateinthewellbore,thedrillingmudwillexperiencea
reductionindensityandachangeinrheologyduetodissolvedgas.Thismayleadtoan
enlargementofthewellboreandevencollapseofthehole.
Whenhydratesdissociate,thesurroundingsedimentsmayexperienceanincreasein
permeabilityandareductioninstrength[13].
WhendrillingthroughHS,severalproblemscanbeencountered.Someoftheseare:
Subsidence,stuckpipe,gasleakingontheoutsideofthecasingandaninefBicientcementjob.
AnotherproblemisthatthedrillingwindowinHSisnotwellunderstood.Whendrilling
throughgashydratesyouneedtostayabovethecollapsepressure,belowthefracture
pressure,andatthesametimemanagethedissociationtemperatureandpressureofthe
hydrates[15].Failuretodothiscanleadtoagaskick.
WhendissolvedgasBlowstowardsthesurface,hydratesmayagainform.Someofthe
problemsthatmaybeencounteredonsubsurfaceequipmentaredescribedbelow[4]:
ChokeandKill-lineplugging:ThiscausesdifBicultyintheuseofthelinesduringwell
circulation
9
-
7/29/2019 12 Helgeland
13/26
PlugformationatorbelowtheOP:Well-pressuremonitoringbelowtheOPs
becomesimpossibleordifBicult
Plugformationaroundthedrillstringintheriser,OPsorcasing:Makesthedrill
stringmovementaproblem
PlugformationbetweenthedrillstringandOPs:Thiscausesproblemsinthefull
closureoftheOPswhennecessary
PlugformationintheramcavityoftheOPs:CausesdifBicultyinopeningtheOPs
fully.
UnawarenessofHSwhendrillingawelliscurrentlythemostprominentdrillinghazard.
[15].Inthefuturewearemostlikelyforcedtodrillindeeperwaters,arcticenvironmentsand
possiblyproducehydratesasasourceofenergy.Inordertodothisinasafemannerweneed
tounderstandandcontroltheproblemswecurrentlyarefacingregardinggashydrates.
4.1.Possiblehydrate-relatedkickinthedeepwaterGulfofMexico
AnappraisalwellontheShenziBieldinthenorthernGulfofMexicoexperiencedissuesrelated
topossiblehydrateformationsaftercementingthe22casing.Thewaterdepthatthis
particularwellis1323meters.Insuchgreatwaterdepthsthepressureandtemperature
conditionsareidealforhydratestoforminastablestructure.
10
Figure 4.1: Graphical sketch displaying the problems that may be encountered when drilling through HBS [4]
-
7/29/2019 12 Helgeland
14/26
Thedrillingoperationwasperformedasfollowing:The22casingwasdrilledtoadepthof
2203metersMDandcementedinplace.WhenthecementreturnsreachedtheseaBloor,a
minorannularBlowofBluidizedsedimentsdroppingfromthecementportsweredetectedbya
subsearemotelyoperatedvehicle(ROV).Furtherdrillingoperationswhereputonholdfor
overaweektocheckandrepairequipment.DuringthisweektheROVdetectedadecreasein
BlowofBluidizedsediments,untilonlybubbleswereBlowingslowlyoutofthecementports
whichwerepartiallycloggedwithhydrates.TheROVcollectedsomesamplesofthebubbles
anditwasdeterminedtobe100%methane.Thedrillingwasresumedand16casingwasset
insaltat3560meters.TheROVdetectedthattheBlowrateofbubblesincreasedduringboth
drillingoperationsandwhenthecasingwascementedinplace.Ontheotherhand,adecrease
ofbubbleBlowrateweredetectedwhendrillingoperationswereputonholdforleakofftest
andequipmentrepairs.AccordingtotheinformationfromtheROVtheBluidizedsediments
seemstobearesultofanexothermicreactionduringcementingandthecirculationofwarm
drillingmudthroughthewell.ThisevidencestronglysuggeststhattheBluidizedsediments
andsubsequentgasbubbleswerearesultofdissociatedin-situgashydrates[17].
asedonthefactthatBluidizedsedimentsandbubbleswereBlowingoutofthecementports,
animproved3DseismicobtainedfrommeasurementswhiledrillingwasscreenedforSRs
andothergeophysicalindicationsofhydratedeposits.Amaximumnegativeamplitudeextractionwasgeneratedonthesurfacetoapproximately914metersbelowmudlineto
identifypossiblehigh-amplitudegasanomalies.Theresultsgaveseveralindicationsof
shallowgasanomalies,theshallowestatonly405metersbelowmudline.Aplotofthegas
anomalieswheremadeandiscalledaSR,whichisexplainedinchapter2.2.
Althoughhydratedissociationinthisparticularcasedidnotnegativelyimpactthedrilling
operation,besidesstoppingdrillingforaweek,itisworthnoticingthatmassivedissociation
ofhydratescouldpresentapotentialrisk.Earlyobservationsofpossiblehydratedissociation
arethereforepreferred.Possibletechniquesfordeterminingtheamount,distributionand
presenceofhydratesaregeotechnicalinvestigations,MeasuringWhileDrilling,borehole
wirelineloggingandseismicinversions[17].
.
11
-
7/29/2019 12 Helgeland
15/26
4.2.DeepwaterHorizondidhydratescausetheblowout?
Thesemi-submersiblerigDeepwaterHorizon
experiencedagasreleaseandasubsequentexplosionat
21:49CentralTimeonthe20thofApril2010[18].The
blowoutoccurredwhendrillinganexploratorywellin
theMacandoBieldintheGulfofMexicoat1500meters
seadepth.Therewere126personsworkingontherig
atthetimeoftheaccident,whereaselevenpersonslost
theirlives[19].
Complicationsfromthecementjobareconsideredas
oneofthereasonstotheaccidentatDeepwaterHorizon.Halliburtonperformedthecement
job[20].Just20hoursbeforetheaccident,cementwaspumpeddownthewelltosetcasing[21].TheseabedintheGulfofMexicoiswellknownforcontainingvastamountsofgas
12
Figure 4.2: 3-D seismic showing gas anomalies, this kind of plotting is called a BSR. [17]
Figure 4.3: Incident site [19]
-
7/29/2019 12 Helgeland
16/26
hydrates.Aswillbeexplainedinchapter5.3,thesettingofcementleadstoreleaseofheat.
Thecementwillbeindirectcontactwiththeformation,asitispumpedbetweenthecasing
andtheformation.Onetheoryisthattheheatreleasedfromthecementcouldhaveaffected
thestabilityofgashydratesintheformation,leadingthemtomelt.Anotheristhatmeltingof
hydratesduringdrillingcreatedlargecavesinthewell,sothatwhencementwaspumped,it
wasnotsufBicienttocementtheentirecasinginplace.Furthermeltingofthehydrateswould
thenleadtoagaskickoutsidethecasing,andwithnocementtostopthegas,itwouldreach
thesurface.Survivorsoftheaccidentexplainedthatjustbeforetheexplosion,thepressure
hadbeenreducedinthedrillcolumnandheatwasappliedtosetthecementsealaroundthe
wellhead.Anexpandingbubbleofmethanethenbrokethroughvarioussafetybarriersbefore
explodingontheplatform[22].
Gashydratesalsoplayedamajorroleinthefailureofcontainingtheleakduringdrillingofthe
reliefwell.Pconstructeda100tonnedomeplanningtoplaceitovertheleak,guidingtheoil
throughafunneltobecollectedonavessel,asshowninBigure4.4.Thedomewasplacedover
theleakthe7thofMay.Tendayslatertheyconcludedthattheoperationwasafailure.Asoil
andgaswastransferredupthefunnel,thegasreactedwithwatertoformgashydrates,and
quicklypluggedthepipe[20].
13
Figure 4.4: Dome placed over the leak [23]
-
7/29/2019 12 Helgeland
17/26
5. Avoiding gas hydrate problems
HShasbeendrilledthroughsuccessfully,eventhoughtherehavebeenreportedcasesof
blowoutscausedbyhydratedissociation.othinitialformationcharacteristicsandbottom-
holeconditionslikemudtemperatureandpressure,willdecidetheamountofgashydrate
thatisdissociated.
TodrillsafelythroughHS,wehavetodevelopabetterunderstandingofgashydrates,so
thatweareabletoidentifyproblemsthatmayoccurandhowtopreventthem.Some
techniquesadoptedsofar[13]:
CoolingthedrillingBluid.
Increasingthemudweighttostabilizethehydrates,butavoidingfracturingtheHS.
AddingchemicalinhibitorsandkineticadditivestothedrillingBluidtopreventhydrate
formationandtoreducehydratedestabilizationintheformation.
Acceleratingdrillingbyrunningcasingimmediatelyafterhydratesareencountered
andusingacementofhighstrengthandlowheatofhydration.
Tostaywithinasafeoperationalenvelopewhendrillingthroughgashydrates,youhaveto
assesstheallowabledrillingparameters:
MudWeight
Composition
Temperature
Youalsohavetoevaluatefactorslike[13]:
EffectofdrillingBluidonheatingtheformationandchangingthestressesandpore
pressure
Effectofheatontheformationsthermodynamicstabilityofthehydratesandwellbore
stability
EffectofreductioninHSstrengthandlossofcohesionduetohydratedissociation.
Therefore,modelingwellborestabilityinHSrequiresconsiderationofvariousmechanisms
14
-
7/29/2019 12 Helgeland
18/26
GashydratescancauseproblemsbothduringandafterHSareencountered.Whendrilling
through,piecesofhydratearecarriedupbytheBluidandturnedintogasbecauseofpressure
andtemperaturechanges.Oncepastthezone,gashydrateatthefrontoftheholecancontinue
todissociateduetotemperatureandpressureinthemud.othscenariosreleasesgasintothe
mud,alteringitsrheology,whichcanbedangerousifnottakenintoconsiderationwhen
designingthemud.Soitisimportanttochoosetherightdrillingmethodandmud,todeal
withtheissuebothduringandafterdrilling.
5.1. Drilling techniques to help prevent problems with hydrates [24]
ManagedPressureDrilling(MPD)
MPDhaveauniqueapplication,itisadrillingprocessusedtocontrolthepressureproBile
throughoutthewellbore.MPDtechniquesmaypreventformationinBluxbyascertainingthe
pressuresinthewellborewithintheenvironmentlimits.Itallowsforfastercorrectiveaction,
asitmayincludecontrolofbackpressure,Bluiddensity,Bluidrheology,annularBluidlevels,
circulatingfrictionandholegeometry.ThisprovidesbettercontrolifformationinBluxis
encountered,whichmeansthatthistechniquecanbeusedinwellswithnarrowpressure
windows.
SlimandInsulatedMarineRiser
Drillingindeep-seaandcoldwater,thereisaneedforinsulatedrisers.Slimmerrisermeans
thereturnswillhavehighervelocity.WhendrillingthroughHStherewillbelesstimefor
heattransfertowarmthereturns,whichagainminimizesthedissociationofhydrates.
Drillingwithcasing
Theformationmightberatherfragileandthewellboreshouldbecasedasquicklyaspossible.
Aone-tripdrillingsystem,thatcarriescasingwithitandthepossibilityforfastcementing
couldbetheanswer.Drillingwithcasingsolvesthis.Insteadofdrillpipe,casingisusedand
cementedinplaceassoonasthesectionisdrilled.Thisprotectswellborefromtheformation
andHSandpreventsinBlux.
15
-
7/29/2019 12 Helgeland
19/26
5.2. Drilling fluid design [25]
WhendesigningadrillingBluidtobeagashydrateinhibitor,characteristicsincludedshouldbe[26]:
Lowestpossibledensitywithmaximumhydratesuppression
CompatibilitywithmostcommondrillingBluidcomponents
CompatibilitywithmostsaltstobalancehydratessuppressionandBluiddensity
Provideshaleinhibitionforadequateboreholeanddrillcuttingsstability
Ashydratescanforminpipes,OP,risersetc.itisimportantthatonceawellisintheGHSZ,
hydrateinhibitors/suppressorsareaddedtothedrillingBluid.
Wellsarebeingdrilleddeeper,andtheneedforimprovedandcustomizeddrillingBluidto
handlethevaryingconditionisneeded.Itmustdealwithchangingmudlinetemperaturesto
preventhydratesfromformingandmaintainingthedrillingBluidproperties.Agoodwaytodo
thisismakingsalinedrillingBluids,whichmeansaddingsalts.Thishasprovensuccessfulin
wellsdowntoabout2300minthegulfofMexico.HighperformancedrillingBluidsisagoodwaytohelpstophydratesfromblockingtheOPandchokelines.TheNorthSeahasalower
mudlinetemperature,sothermodynamicinhibitorsmaynotbesufBicienttopreventhydrates
fromformingandadditionaladditivesmightbeneeded.
Syntheticbasedmud
Syntheticbasedmudisalowtoxicityoilbasedmud.Dependingonthepressure,themudwill
absorbthegasandreducetheamountofgasreachingtheOPsandchokelines.
KineticInhibitorsandCrystalModiiers
Anotherwayistoslowdowntheprocessandpreventtheagglomerationofgashydrate
formation,onewaytodothatisbyusingcrystalmodiBiers.Thisisaprocessthatusesmostly
polymericandsurfactant-basedchemicalstoalterthenucleation(aphysicalreactionthat
occurswhenpartsofasolutionstartstoprecipitateout)andgrowthofhydratecrystals.Can
alsousekineticinhibitorstopreventcriticalnucleifromappearingandbythatinhibiting
formation.Thesechemicalswillnotstopgashydratesfromdissociating,butinhibiting
16
-
7/29/2019 12 Helgeland
20/26
formationofitinpipes,OPetc.Thechallengewiththismethodisthesurfaceacitivityofthe
kineticinhibitorandchoosingtherightchemicalsinhighsalinitydrillingBluid.
Gashydratepills
Gashydratepillscontainhighlyinhibitiveformulationsandcanbeutilizedwhenneeded.This
meansthatthepillsareplacedinOPs,chokeandkilllinesetc.andwhenagaskick,shut
downorabandonmentoccurs,thesepillsareactivated,preventinggashydratefromforming.
5.3. Cement [27]
Ascasingisruninthehole,ithastobecementedinplaceasfastaspossibletostabilizethe
wellbore.Cementhasanexothermicreactionwithwater,heatingthecement.Thehydration
ratedependsonthevariouscomponentsofthedrillingBluidandalsoonthetemperatureof
thesurroundings.Deepwaterwellsarearealchallengeconsideringthelowsurrounding
temperatures.Lowertemperatureswilldecreasethehydrationrate,causingthecementtoset
moreslowly.Theheatreleasedwillthenhavemoretimetodestabilizethegashydratesand
possiblyweakenthecement.Tobeabletodealwiththisproblem,cementdesignedto
preventdestabilizationofgashydrateshastobeused.Ingredientshavetobechosen
dependingonwellpropertiesandtestingtheadiabatictemperaturerisetoBindamixthatdo
notreleaseheatabovethehydratedestabilizationpoint.OneexampleofthiscanbeusingC2S
insteadofC3S,asC2Sonlyreleasesalmostathirdoftheheattothesurroundingscompared
toC3S.
2C3S+6HC3S2H3+3CH;H=-114KJ/mole
2C2S+4HC3S2H3+3CH;H=-43KJ/mole
IfrunningcasingasquicklyaspossibleafterdrillingpasttheHSzoneandchoosingtheright
cementslurry,youcanavoidalotofproblemsandmakeasaferwell.
17
-
7/29/2019 12 Helgeland
21/26
6. Discussion
Therehasonlybeenreportedminorincidentsofkicksduetohydratedissociationduring
drilling.Asweareforcedintocolderenvironments,suchasthearctic,thismaybecomea
morecommonproblem.Hydratescanbeencounteredatshallowdepthsandprettymuchall
overtheglobe.Thevastdistributionofhydratesgivesreasontobelievethatkicksdueto
hydratedissociationoccurfairlyoften.
Dissociationofhydratesmayhavebeenacontributingfactorintheblowoutaccidenton
DeepwaterHorizon.Whetherornotthisactuallywasacontributingfactor,israther
uncertain.ItisdocumentedandwellknownthattheGulfofMexicocontainsvastamountsof
gashydrates,whichposestheopportunitythathydratesmayhavedissociatedandcreateda
largebubbleofmethane.IfthiswasthecaseonDeepwaterHorizon,itmayalsohaveoccurred
inotherplacesaswell.
InordertoBindmorehydrocarbonsinthefuturewearemostlikelyforcedintoareaswhere
hydratesarestronglypresent.Whetherornothydrateswillposeadrillinghazardinthese
areasissomewhatunclear,butiflargeamountsofhydratesareencountereditmaypose
someseriousrisksthatshouldbetakeninaccountduringwellplanning.
18
-
7/29/2019 12 Helgeland
22/26
7. Conclusion
Thispaperhasexplainedanddiscussedhydratechallengeswhendrillingforoffshorenatural
gasandoil.Gaskicksasaresultofhydratesarenotcommonintheindustrytoday,butitis
likelytoseemoreofthisinthefutureastheindustrypushesforwardtolookfor
hydrocarbonsinmoreextremelocations.
HydrateswerealsoinvestigatedasapotentialcontributorintheDeepwaterHorizonaccident.
Hydrateswasfoundtobeapossiblecontributingfactortotheaccident,anditmadeattempts
oflimitingtheextentofthedamagesharder.Attemptstoplaceadomeontopofthewell
failedduetohydratespluggingthepipe.
Differentmethodsofalteringthemudpropertyanddifferentdrillingtechniqueswere
investigatedaspreventivemeasuresagainsthydrateforming.EarlyidentiBicationofhydrate
zonesbycollectionofseismicdatawasalsofoundtobekeytoensurethatpreventiveactions
canbetakenbeforehydrateproblemsoccur.
Althoughsomesolutionswereproposedinthispapertopreventhydrateproblemsitwas
foundthatafurtherunderstandingofhydratesisneededtoeffectivelysolvethechallenges
ahead.
19
-
7/29/2019 12 Helgeland
23/26
8. Abbreviations
OP-lowoutpreventer
SR-ottomSimulatingReBlection
GHSZ-Gashydratestabilityzone
HS-HydrateearingSediments
MPD-ManagedPressureDrilling
ROV-RemotelyOperatedVehicle
20
-
7/29/2019 12 Helgeland
24/26
9. References
[1]: Skalle, P., Pressure control during oil well drilling, Chapter 7, Special offshore safety issues,
second edition: Ventus Publishing,http://bookboon.com/en/textbooks/geoscience/pressure-control-
during-oil-well-drilling (accessed 3 October 2012).
[2]: Wikipedia, Clathrate hydrate [online]. http://en.wikipedia.org/wiki/
Clathrate_hydrate#Natural_gas_hydrates (accessed 17 October 2012).
[3]: Sinquin, A., Palermo, T. and Peysson, Y.: Rheological and Flow Properties of
Gas Hydrate Suspensions, Oil and Gas Science and Technology Journal.
[4]: Amodu, A. A., Drilling through gas hydrate formations: possible problems and suggested
solutions, MS thesis, Texas A&M University, Texas, Houston (August 2008).
[5]: Dillon, W.P. and Max, M.D., Oceanic Gas Hydrates, Chapter 6,Natural Gas Hydrate in
Oceanic and Permafrost Environments, 2003.
[6]: Thomas, C. P., Methane hydrates: Major energy source for the future or wishful thinking?,
SPE-71452, paper presented at the SPE 2001 Annual Technical Conference and Exhibition, New
Orleans, Louisiana, U.S.A., 30 September-3 October 2001. http://dx.doi.org/10.2118/71452-MS.
[7]: Sandengen, K., Hydrates and Glycols [online], Downloaded from:http://www.ipt.ntnu.no/
~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdf (accessed 5 October 2012).
[8]: Dillon, W.P. and Max, M.D., Oceanic Gas Hydrates, Chapter 8,Deep Biosphere: Source of
Methane for Oceanic Hydrate, 2003.
[9]: Dillon, W.P. and Max, M.D., Oceanic Gas Hydrates, Chapter 13, The U.S. Atlantic
Continental Margin; the Best-Known Gas Hydrate Locality, 2003.
[10]: Skalle, P., Pressure control during oil well drilling, Chapter 1,Introduction.
[11]: Schlumberger Oilfield glossary, Blowout [online]. http://www.glossary.oilfield.slb.com/
Display.cfm?Term=blowout (accessed 19 October 2012).
[12]: Skalle, P., Pressure control during oil well drilling, Chapter 4, Standard killing methods.
21
http://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://dx.doi.org/10.2118/71452-MShttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.glossary.oilfield.slb.com/Display.cfm?Term=blowouthttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://www.ipt.ntnu.no/~jsg/undervisning/naturgass/lysark/LysarkSandengen2010.pdfhttp://dx.doi.org/10.2118/71452-MShttp://dx.doi.org/10.2118/71452-MShttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://en.wikipedia.org/wiki/Clathrate_hydrate#Natural_gas_hydrateshttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drillinghttp://bookboon.com/en/textbooks/geoscience/pressure-control-during-oil-well-drilling -
7/29/2019 12 Helgeland
25/26
[13]: Khabibullin, T., Falcone, G. and Teodoriu, C., Drilling Through Gas Hydrate Sediments:
Managing Wellbore Stability Risks, SPE-131332, June 2006. http://dx.doi.org/10.2118/131332-
MS.
[14]: Kadaster, A. G., Millheim, K. K. And Thompson, T. W., The planning and drilling of hot ice
#1 Gas hydrate exploration well in the Alaskan arctic, SPE/IADC-92764, paper presented at the
SPE/IADC Drilling Conference, Amsterdam, TheNetherlands, 23-25 February 2005. http://
dx.doi.org/10.2118/92764-MS.
[15] Qadir, M. I., Gas hydrates: A fuel for future but wrapped in drilling challenges, SPE-156516,
paper presented at SPE/PAPG Annual Technical Conference, Islamabad, Pakistan, 22-23November
2011. http://dx.doi.org/10.2118/156516-MS.
[16]:Nimblett,J.N.,Shipp,R.C.andStrijbos,F.,GasHydrateasaDrillingHazard:Examples
fromGlobalDeepwaterSettings,OTC17476,paperpresentedatthe2005Offshore
TechnologyConference,Houston,Texas,U.S.A.,2-5May2005.http://dx.doi.org/10.4043/17476-
MS.
[17]: Williamson, S. C., McConnell, D. R. and Bruce, R. J., Drilling Observations of Possible
Hydrate-Related Annular Flow in the Deepwater Gulf of Mexico and Implications on Well
Planning, OTC 17279, paper presented at the 2005 Offshore Technology Conference, Houston,
Texas, U.S.A., 2-5 May 2005. http://dx.doi.org/10.4043/17279-MS.
[18]: Rogers, S.,BP oil spill: the official Deepwater Horizon disaster timeline [online]. http://
www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timeline (in press;
published online 9 September 2010, accessed 11 October 2012).
[19]: BP, Deepwater Horizon accident [online]. http://www.bp.com/sectiongenericarticle800.do?
categoryId=9036575&contentId=7067541 (accessed 24 October 2012).
[20]:JonesJ.C.,The2010GulfCoastOilSpill2010,Birstedition:VentusPublishing,http://
bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spill(accessed21
October2012).
[21]:Shoegren,E.,Cementing Becomes One Focus In Gulf Oil Probe [online]. http://
www.npr.org/templates/story/story.php?storyId=126536457(inpress;publishedonline5
May2010,accessed17October2012).
22
http://www.npr.org/templates/story/story.php?storyId=126536457http://bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spillhttp://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timelinehttp://dx.doi.org/10.4043/17279-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.2118/156516-MShttp://dx.doi.org/10.2118/156516-MShttp://dx.doi.org/10.2118/92764-MShttp://dx.doi.org/10.2118/131332-MShttp://dx.doi.org/10.2118/131332-MShttp://www.npr.org/templates/story/story.php?storyId=126536457http://www.npr.org/templates/story/story.php?storyId=126536457http://www.npr.org/templates/story/story.php?storyId=126536457http://www.npr.org/templates/story/story.php?storyId=126536457http://bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spillhttp://bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spillhttp://bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spillhttp://bookboon.com/no/laereboker/petroleum-gas-olie/the-2010-gulf-coast-oil-spillhttp://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.bp.com/sectiongenericarticle800.do?categoryId=9036575&contentId=7067541http://www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timelinehttp://www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timelinehttp://www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timelinehttp://www.guardian.co.uk/news/datablog/2010/sep/09/bp-oil-spill-deepwater-horizon-timelinehttp://dx.doi.org/10.4043/17279-MShttp://dx.doi.org/10.4043/17279-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.4043/17476-MShttp://dx.doi.org/10.2118/156516-MShttp://dx.doi.org/10.2118/156516-MShttp://dx.doi.org/10.2118/92764-MShttp://dx.doi.org/10.2118/92764-MShttp://dx.doi.org/10.2118/92764-MShttp://dx.doi.org/10.2118/92764-MShttp://dx.doi.org/10.2118/131332-MShttp://dx.doi.org/10.2118/131332-MShttp://dx.doi.org/10.2118/131332-MShttp://dx.doi.org/10.2118/131332-MS -
7/29/2019 12 Helgeland
26/26
[22]: Schwartz, N. and Weber, H. R., APNewsBreak: Series of failures led to rig blast [online].
http://www.businessweek.com/ap/financialnews/D9FIBKV00.htm (in press; published online 7
May 2010).
[23]: BBC News, Oil spill in Gulf of Mexico in maps and graphics, [online]. http://
news.bbc.co.uk/2/hi/8651333.stm (in press; published online 10 May 2010, accessed 29 October
2012).
[24]: Hannegan, D., Todd, R. T., Pritchard, D. M. and Jonasson, B., MPD Uniquely Applicable to
Methane Hydrate Drilling, SPE-91560, paper presented at the SPE/IADC Underbalanced
Technology Conference and Exhibition, Houston, Texas, U.S.A., 11-12 October 2004. http://
dx.doi.org/10.2118/91560-MS.
[25]: Ebeltoft, H., Yousif, M. And Sgrd, E., Hydrate Control During Deepwater Drilling:
Overview and New Drilling-Fluids Formulations, SPE-68207, March 2001. http://dx.doi.org/
10.2118/68207-PA.
[26]: Halliday, W., Clapper, D. K. and Smalling, M., New Gas Hydrate Inhibitors for Deepwater
Drilling Fluids, IADC/SPE-39316, paper presented at the 1998 SPE/IADC Drilling Conference,
Dallas, Texas, U.S.A., 3-6 March 1998. http://dx.doi.org/10.2118/39316-MS.
[27]: Ravi, K. And Moore, S., Cement Slurry Design to Prevent Destabilization of Hydrates in
Deewater Environment, SPE-113631, paper presented at the 2008 Indian Oil and Gas Technical
Conference and Exhibition, Mumbai, India, 4-6 March 2008. http://dx.doi.org/10.2118/113631-MS.
http://dx.doi.org/10.2118/113631-MShttp://dx.doi.org/10.2118/39316-MShttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/113631-MShttp://dx.doi.org/10.2118/113631-MShttp://dx.doi.org/10.2118/39316-MShttp://dx.doi.org/10.2118/39316-MShttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/68207-PAhttp://dx.doi.org/10.2118/91560-MShttp://dx.doi.org/10.2118/91560-MShttp://dx.doi.org/10.2118/91560-MShttp://dx.doi.org/10.2118/91560-MShttp://news.bbc.co.uk/2/hi/8651333.stmhttp://news.bbc.co.uk/2/hi/8651333.stmhttp://news.bbc.co.uk/2/hi/8651333.stmhttp://news.bbc.co.uk/2/hi/8651333.stmhttp://www.businessweek.com/ap/financialnews/D9FIBKV00.htmhttp://www.businessweek.com/ap/financialnews/D9FIBKV00.htm