Underground gas storage in salt cavern September 2009

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EnecogasspeicherUndergroundgasstorageinsaltcavern

September2009

Q.A.L.VNoordoven

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AbstractTheDutchnationalenergycompanyEnecoisintheprocessofimplementingalargeprojectinvolvingthestorageofgasinsaltcavernsinEpe,Germany.Forshort‐termgastradingandflexibilityinthegasmarketEnecointendtoleasetwocavernstill2030withanoptiontoleasetill2060.ThecavernsareleachedbySalzgewinnungsGeselschaftWestfalen(SGW).Thiscompanyhasproducedbrinefromthisareasincethe1972.Thetwocavernswillhaveageometricalvolumeof500000m3and400000m3,andwillbeoperatedbetween40and210bar,resultinginaworkinggasvolumeof170millionm3.Enecoexpectstheprojecttocontributetoanincreasedsecurityofsupplyandliquidityofthenorth‐WestEuropeangasmarket.Tocompletethisproject,EnecoGasspeicherteamaskedmetogiveacompleteoverviewofheproject.Andtogiveallparametersinvolvedinthisproject.Thispaperwilldescribetheprojectinsomemoredetail.

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Tableofcontent:Enecogasspeicher.................................................................................................................................................. 1

Abstract ............................................................................................................................................................. 2 Introduction....................................................................................................................................................... 4

1.Solutionmining .................................................................................................................................................. 4 1.1Introduction:................................................................................................................................................ 4 1.2 Miningprocess:........................................................................................................................................ 4

2. Hydrocarbonstorage ..................................................................................................................................... 6 3. EnecoGasspeicher ......................................................................................................................................... 9

3.1introduction................................................................................................................................................. 9 3.2 Stratigraphy ........................................................................................................................................... 10 3.3 Wells ...................................................................................................................................................... 12 3.4 Installation ............................................................................................................................................. 13

4.1 Storageparameters ................................................................................................................................... 13 4.2Gashydrates .............................................................................................................................................. 15 Temperature.................................................................................................................................................... 16 4.3.Rockmechanicsinsalt.............................................................................................................................. 16

4.3.1.Creepofrocksalt .............................................................................................................................. 17 4.3.2.Primarycreep .................................................................................................................................... 18 4.3.3.Secondarycreep................................................................................................................................ 18

4.4Permeability .............................................................................................................................................. 18 4.5Cavernspacing........................................................................................................................................... 19 4.6Subsidence................................................................................................................................................. 20 4.7Storagepressure........................................................................................................................................ 20 4.8Cavernsabandonment .............................................................................................................................. 22

5 Conclusionsandrecommendations: ............................................................................................................. 23 6Data................................................................................................................................................................... 24 7References ........................................................................................................................................................ 25

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IntroductionSinceJuly2004,marketliberalizationforgasaswellforelectricityiseffectiveforallgroupsofcustomers,includingresidentialcustomers.Distributioncompanies,likeEneco,andothershippersnowadaysimportgasfortheirownportfolios,whereasinthepre‐liberalizationerathedistributioncompaniespurchasedtheirgasrequirementsfromtheformerlyintegratedGasunie.(Hoelen,Q.,vanPijkeren,G.,Teuben,B.,Steenbergen,B.,Breuning,P.)Theenergycompaniescanusestoragefacilitieslikesaltcavernfortheirownflexibility.Enecoplanstousenaturalgasstorageforcommercialreasons;

• tooffermoretradingopportunities

• increaseprofitsbyshort‐termgastrading• Reducecostsrelatedwithpeakloaddemands

Thenaturalgasstorageisfacilitatedinasaltcavernleachedoutbysolutionmining.Inthisreportarelistedthevariousmethodsforsolutionmining,thestorageparameters,thelithologyandtherockmechanics.Alsoare

listedtheEnecoGasspeicherplanforundergroundgasstorageandsomerecommendations.

1.Solutionmining

1.1Introduction:

Miningistheprocessofextractingoreormineralsfromtheground.Solutionminingisaprocessofrecoveringminerals;itisprimaryusedforsaltminerals.Saltsolutionminingistheminingofvarioussaltmineralsbydissolvingthemwithwaterandpumpingtheresultingbrinetothesurface.Waterorundersaturatedbrineisinjectedthroughawelldrilledintoasaltbedlayertoetchoutacavernorvoid.Thebrineisextractedforprocessing.Itusuallytargetssaltsatdepthsgreaterthan400metersandupto2800metersintheBaradeelconsessionintheNetherlands.(Breunese,J.,vanEijs,R.,deMeer,S.,Kroon,I.)Atdepthsgreaterthan2000meterongoingsaltcreeptendtoreducecavernsize.

InChinabrinewellsareusedformorethan2000years,especiallyintheScechuanandYunnanprovinces.MarcoPoloreportedannualproductioninasingleprovinceofmorethan30000tons.Withbamboopoles

theyleachedshallowsaltformations.InLorraine,France,thefirstsimplewellsweresunkbyhandasearlyasintheyear858.Andby1830intheUSAthereweremorethan60brinewellsinoperationintheOhioregion.

Theadvantageofsolutionminingoverconventionalminingorsurfaceevaporationisthatproductqualityandtheextractingoperationisnotdependentofclimateorrockstrengthandisnotdangerousforpersonneland

equipment.Solutionminingcanexploitfoldedanddisturbedbedsordeeplyingstrata,conventionaltechniquesarenotcommonlyusedinthesesituations.

1.2 Miningprocess:Thedesignofasaltsolutionwellconsistsoftwoormorecolumnsofsteelpipes(figure1).Freshwaterneeded

forthesolutionprocessispumpedintothewelltocreateacavityinthetargetedsaltbyleaching,thefollowingleachingfluidscanbeused:

‐ Surfacewaterfromrivers‐ Wellwater‐ Seawater‐ Waterfromsewage/purificationplants‐ Undersaturatedbrinefromothercaverns‐ Condensatefromsaltproductionplants.

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Theresultingbrineisthenreturnedtothesurfacefortheprocessingandrecovery.

Thefirststepinsolutionminingsaltistodrillaborehole,largeenoughfortherequiredpipesandcasings.

Solutionwellsarewiderthanoil,gasorwaterwells.Nearthesurfacetheboreholeisthewidest.Thesurfacecasingiscementedinplacetopreventanyleakageandcontaminationofgroundwater,alsotopreventablow

out.Thefinalcasingstringissetatsomedepthbelowthetopofthetargetsalt,sothatduringdissolutionasetthicknessofsaltremainsinplace.Insomewellsthereisanotherstringthatcontrolsthethicknessofthefluid

blanket.Afluidblanketisusuallypumpedintoasolutioncaverntopreventrapidupwardleachingandapossiblecollapseofthecavernroof.Blanketfluidisinertsoitdoesnotdissolvethetargetsalt.

Figure1a:Methodofdirectcirculation. Figure1b:Methodofindirectcirculation

Therearetwomethodsfordevelopingandshapingcavernsasseeninfigure1.

Inthedirectcirculationmethod,feedsolventisinjectedthroughthetubingstringanddissolvesthesaltatthebottomoftheformation.Thebrineisthendrawnoutthroughtheannularspacebetweenthetubingstring

andthefinalcasing.

Intheindirectcirculationmethodfreshwaterisinjectedbetweenthetubingandthecasing.Thissystemiscalledthe“topinjectionmethod”.Bythetopinjectionmethodthewaterentersthesaltdepositatthetopof

theformationandstartstodissolvethesaltneartheroof.Thesaltbrineflowsdownwardtothebottomofthetubingwhereasumpeffecthasbeenproducedbythepumpdrawingonthetubing.Thesumpisaleftoverof

thebrineproductionoftheinhomogeneousrocksalt.Thebrineispumpedfromthewellandthenitisreadytobeprocessed.

Underthedesignscenario,stringscanberotatedandraisedasthecaverngrowsandthebottomfillswithdebris.

Whenasingleholesolutionminingwellisfirstdrilled,theflowratethroughthecavityandupthepipeisussuallykeptverylowtomaintainhigherbrineconcentration.Aftersomeyearsthesurfaceareaandthecavity

volumeincrease,theextractedbrineflowcanberaised.

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Leachingratesandthusconstructiontimesvarywiththeamountanddegreeofsalinityofthewaterinjected.Itiscommontofindthatforeverysevencubicmetersoffreshwaterinjected,avolumeofonem3isleached(Leith,2001).Leachingratesarenormallyexpressedastheamountofwaterorbrinecirculatedandcanreachratesof1600m3perday.IntheU.S.,leachingratesof320,000m3to400,000m3peryeararecommon(Leith,2001).Constructionratesforthetwo150,000m3solution‐minedcavernsatHuntorfinGermanywereanaverageofabout360m3ofsaltperday,atamaximumcirculationof600m3perhour.Eachcavernwascompletedinabout14monthsandittookafurtherfivemonthstoremovethebrinefromeachofthecaverns(Leith,2001).

Figure2:Constructionforsaltleaching.

Therearetwomethodsofsaltproduction.

Thesingle‐wellmethodofsolutionmininginvolvesthedrillingofasinglelargediameterdrillholeintoasaltformation.Acasingisusedintheholetostopthewallsfromcaving.Asecondtubingafsmallersizeisthen

placedinthecaseddrillhole.Thesinglewellmethodismostlyappliedfordeepersaltformations.

Thetwowellmethodofsolutionminingisbasedondrillingtwoidenticalwellsintoasaltbodyatadistancefromtenthstoseveralhundredsofmeters.Onewellisassignedasproductionwellandtheotherforinjection.

Severalwellmethodsstartsinthesamewayassingle‐wellmethodsolution,formingtwocaverns.Aftercompletion,highpressurewaterisappliedattheinjectionwellinordertocausehydraulicfracturing.The

brineisthendrawnfromtheproductionwell.Thevolumeofwaterwillonlyrisesotheproductionwilldecreasealso.Themainconcerninthestabilityofthelargecavernsisroofcontrol.Forthistypeofminingis

thedepthofsaltsolutionlimitedto300‐500meters.ThatiswhyinEpethismethodisnotused.

2. HydrocarbonstorageCrudeoil,LiquefiedPetroleumGas(LPG)andlighthydrocarbonscanbesafelystoredintheundergroundstoragefacilities.TheearliestoilstorageincavernswasinCanadaduringWorldWarII.In1949LPGwas

storedincavernsinTexas,USA.Inthepastdecadesnaturalgasisstoredin(salt)caverns,undergroundmines,aquifers,oil‐andgasfieldsinincreasingvolumes.ThefirststorageofnaturalgasinasaltcavernwasatUnity

Saskatchewan,intheUSA,in1959.Nowadaystherearemanysaltcavernsusedforoilandgasstorage

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worldwide.Intotalover600undergroundgasstoragefacilitiesareused.Figure3.presentsasummaryoftheinstalledworkinggasvolume(106m3)bynations.

Saltdepositsareextensivelyusedforundergroundstorageofhydrocarbonsandotherproductsaswellasforwastedisposal.Thestoragecavernsinsaltdepositsareconstructedbythesolutionprocessdescribedinthe

previouschaptersolutionmining.Today’sbrineproducersarealsoawareofthepotentialstorageopportunities.Onereasontomakethecavernistheirbrinefeed,butontheotherhandtheyproducetight

cavernsuitableforstorage.Therenttheyreceivefromenergycompaniesareofgreatamounts.Thestoragecavernshavetomeetthecriterianecessarytoassurestableandtighthighpressure,subsurfacestorage

vessels.

Figure3:Undergroundstoragefacilitiesintheworld

Naturalgashasbecomeaprimesourceofenergyworldwide,especiallyinresidentialheatingandgas‐fired

powerplants.Traditionallythedemandfornaturalgasisusuallyhigherduringwinter,partlybecauseitisusedforheatinginresidentialandcommercialsettings.Storednaturalgasplaysavitalroleinensuringthatany

excesssupplydeliveredduringthesummermonthsisavailabletomeettheincreaseddemandofthewintermonths.However,withtherecenttrendtowardsnaturalgasfiredelectricgeneration,demandfornaturalgas

duringthesummermonthsisnowincreasing,becauseoftheneedofmoreelectricityinsummermonths,forairconditioningforexample.Naturalgasinstoragealsoservesasinsuranceagainstanyunforeseenaccidents,

naturaldisasters,orotheroccurrencesthatmayaffecttheproductionordeliveryofnaturalgas.Naturalgasstorageplaysavitalroleinmaintainingthereliabilityofsupplyneededtomeetthedemandsofconsumers.

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Figure4:workinggasvolumebynations

GermanyisinthelastdecadestheleadingstoragecountryofWesternEurope.AccordingtoCEDIGAZ,Germanyhasanestimated713Bcfofworkingnaturalgasstoragecapacity,thelargestamountintheEUand

thefourth‐largestintheworld.Thecapacityisspreadamong43facilities.In1976thefirstGermangasstoragefacilitywascreatedinasaltcavern.Figure5givesthedevelopmentandplanningofnewgasstoragefacilities.

Intherecentyearsitisatrendtousesaltcavernforgasstorage.

Figure5:GasstorageinGermany

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3. EnecoGasspeicher

3.1introductionForshort‐termgastradingandflexibilityinthegasmarketEnecointendtoleasetwocavernstill2030withan

optiontoleasetill2060.Thecaverns,namedEpeS81andEpeS82,areleachedbySalzgewinnungsGeselschaftWestfalen(SGW).ThecavernsarenearthevillageEpe,inNorth‐RhineWestfaleninGermany.Itislocatednear

theborderwiththeNetherlandsandispartofthetownGronau.ForyearstheEpeareaisthecentreofsaltsolutionmining,becauseofthethicksaltformationunderground.TheSGWhasintheEpeareaover90

caverns.Theywerefirstusedforbrineproductiononly.LatertheSGWusedthecavernsforstorageofvariouschemicalsandgases.

ThecavernsarelocatedintheZechsteinsaltformation.ThedrillingprocessforwellS81startedFebruary

2002,S82startedJanuary2003.ThevolumeofS81cavernmeasuredinApril2006,was129029m3.Theleachingprocesswasnotfinishedyetinthatperiod.InJuly2006thevolumeofS82was133801m3.The

cavernsareconnectedwithgasstoragefacilities.FromHengelointheNetherlandsanapproximately21kilometerlongnaturalgaspipelineisconnectedtothisnaturalgasstoragefacility.Thegaswillbetransported

fromHengelotothegasstoragefacilityinEpe,therethegasisinjectedintothecavernswiththehelpoftwocompressorsthatcanoperateatamaximumcapacityof100,000m3/heach.Thegasisthenwithdrawnfrom

thestoragefacilitybacktotheDutchsupplynetwork.Beforethegascanbeusedagainitspressureisreducedinthegastreatmentplant.Furthermore,thehumidityisextractedfromthegas.

Theplannedcavernlayout:

Cavern Width(m) Height(m) Depth(m) Volume(m3) TimetoleachEpeS81 60 243 1357 519.000 2003‐2012EpeS82 66 171 1283 395.000 2003‐2010Table1,plannedlayout.

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3.2 Stratigraphy

Figure6:PreliminarydepthmapoftheBaseZechsteinGroup(resultingfromtheSPBApilotmappingproject)

Thecommongoalofstratigraphystudiesisthesubdivisionoflayeredrocks.Itcantellusmuchabouttheprocessesaffectingthedepositionofsediments.

TheevaporaterocksoftheZechsteinformationwerelaiddownbytheZechsteinSea,anepicontinentalorepeiricseathatexistedintheGuadalupianandLopingianepochsofthePermianperiod.TheZechsteinSea

occupiedtheregionofwhatisnowtheNorthSea,pluslowlandareasofBritainandthenorthEuropeanplainofTheNetherlands,GermanyandPoland.InitsownerathecontinentwaslocatedneartheEarth'sequator

wherehightemperaturesandaridconditionsfacilitatedevaporationasseeninfigure7.

Figure7:LocationofthecontinentinthePermera.

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TheZechsteinformationitselfconsistsofatleastfivedepositionalcyclesofevaporaterocks,whicharecalledZ1toZ5respectivelyandishardlytectonicallydeformed.Inthegroup,atwofoldsubdivisioncanbemadebaseduponthedepositionalcharacterintomarineevaporatedepositsinthelowerpartofthegroup(i.e.,theZ1,Z2andZ3Formations)andplaya‐typedepositsintheupperpart(theZ4andZ5Formations)(Geluketal.,1997).Aplayaisadryorephemerallakebed,generallyextendingtotheshore.Suchflatsconsistoffine‐grainedsedimentsinfusedwithalkalisalts.

Figure8:Lithology.

TheZechstein1saltintheEpeareaisconsideredofgoodqualityandrelativelypurewith99%NaCl,itistheWerraSteinsalz,Na1.AndtheformationisabeddedZechsteinsaltformationwithchangesinthicknessof

rocksaltmassanddepthofthesalttop.ThethicknessoftheZechstein1saltinwellS81isabout370meters,thethicknessofthewerra‐steinsalzinwellS82isabout300meters.Furthermore,therearefaultsexisting

eitheratthebasisofthesaltlayeroratitstop.Thefaultsatthesaltbasisaresyngeneticregardingthegenesisoftherocksaltmassandhavecreatedaspecialgeotectonicstructureatthesaltbasis,calledfaultzone.

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Figure9:ThicknessoftheZechsteinsaltformation

Inthenorthernandwesternpartofthedeposittherockmassatthesaltbasisischaracterizedbysignificantfaultzoneswithathrowofhundredandmoremeters.Theothercavernsshowthatthefaultsystemsatthebasisandabovethesaltdepositarenotthesame.Thereforethesaltrockmassitselfseemstobenotdestrengthenedbythefaultsystems.Theavailableborelogs(seeappendix)showsandstone,shaleandanhydrite.BelowtheWerra‐saltathickanhydritelayerexistswithanormalthicknessofabout100mandmore.Belowthisanhydritelayerthecarboniferousrockmassfollowswhichconsistsofchanginglayersofsandstone,siltstoneandclaystone.(Lux,Wermeling,Bannach)

3.3 WellsTheEnecowells(S81andS82)areclusterwells.Clusterwellpadsallowmultiplecavernstobecreatedbeneathalargepadandarecheaperalternativetosinglewellpads.Theyhavealowerinfrastructurecostsandland

arearequirements.Howevercomparedtothesinglewellpads,theysufferfromlessflexibilityinongoingplanningandmaintenance.Casingsareacriticalfeatureinclusterpadwells,especiallyforhydrocarbon

storage.

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Figure10:Clusterwellpads,deviatedwellfigure11:Installation,wellpadandwelllocation.

3.4 InstallationTherearetwomethodsbywhichgasisinjectedintoundergroundstorageandbothmethodswillbeused

dependingonthepressureofthegasinthepipelinecomparedtothegasinthecavernatthetimeoftherequiredinjection.Ifthepressureinthepipelineishigherthanthepressureinthecavern,thegaswillflow

freefromthepipelineintothecavernwithoutanyadditionaleffort.Thisoccurswhenthegasinventoryinthecavernisatalowlevel.Ifthepressureinthepipelineislowerthanthepressureinthecavern,thegaspressurewillbeincreasedbyusinggascompressors.

Thesetwomethodsarealsousedinthewithdrawalprocessonlyinreverse.Ifthepressureinthecavernishigherthanthepipeline,thegaswillfreeflowoutofthecavernintothepipeline.Ifthepressureinthecavern

islessthanthepipelinepressure,thegaswillbecompressedusingthesamecompressors.Instorage,gasabsorbswater,whichthenhastobeseparatedtopreventanycorrosionorgashydrateformationinthe

pipeline.Thefirststepinvolvesseparatingtinyfreedropsofwaterfromthegasstreamintheso‐calledfreewaterknockoutprocess.Apreheaterheatupthegastopreventanygashydratesformationintheprocessing

facilitieswhenpressureisreducedforthegassupplygrid.Thegasisnowjustasitwaswhenitwasoriginallydeliveredtothestoragefacility.

Theusabilityoftheinjectionandwithdrawalcapacitiesisaffectedbythefillinglevelofthestoragefacility.

Onceacertainlevelofvolumeisinjected,thepressureinsidethestoragefacilityissohighthattheoriginalinjectioncapacityisnolongercompletelyavailable.Accordingly,belowacertainvolumewithdrawn,the

pressureinsidethestoragefacilityisnolongersufficienttomaintaintheentirewithdrawalcapacity.

4.1 Storageparameters Thereareseveralvolumetricmeasuresusedtoquantifythefundamentalcharacteristicsofanundergroundstoragefacilityandthegascontainedwithinit.Forsomeofthesemeasures,itisimportanttodistinguishthe

characteristicofafacilitysuchasitscapacity,andthecharacteristicofthegaswithinthefacility.

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Totalgascapacity: Themaximumvolumeofgasthatcanbestoredinanundergroundstorage facility.

Totalgasinstorage: Thevolumeofstorageintheundergroundfacilityataparticulartime.cushiongas: thevolumeofgasintendedaspermanentinventoryinastoragereservoirto

maintainadequatepressureanddeliverabilityratesthroughoutthewithdrawalseason.

Workinggascapacity: Thetotalgasstoragecapacityminuscushiongas.Workinggas: Thevolumeofgasinthereservoirabovethelevelofbasegas.

Workinggasisavailabletosell.Withdrawal: Mostoftenexpressedasameasureoftheamountofgasthatcanbe

delivered(withdrawn)fromastoragefacilityonadailybasis.The deliverabilityofagivenstoragefacilityisvariable,anddependsonfactors

suchastheamountofgasinthereservoiratanyparticulartime,the pressurewithinthereservoir,compressioncapabilityavailabletothe

reservoir,theconfigurationandcapabilitiesofsurfacefacilitiesassociated withthereservoir,andotherfactors.

Injectioncapacity: Thecomplementofthedeliverabilityorwithdrawalrate.Itistheamount ofgasthatcanbeinjectedintoastoragefacilityonadailybasis.The

injectioncapacityofastoragefacilityisalsovariable,anddependsonfactors comparabletothosethatdeterminedeliverability.Bycontrast,theinjection

ratevariesinverselywiththetotalamountofgasinstorage:itisatitslowest whenthereservoirismostfullandincreasesasworkinggasiswithdrawn.

Cyclingreferstothestoragefacility’sabilitytocompletetheinjectionandwithdrawalofworkinggas.

Traditionallyreservoirstorageisdesignedtocompleteonecycleineachyear.Recentmarkettrendshaveproducedtheneedforstoragefacilitiescapableofcompletingmultiplecyclesperyear.

Noneofthesemeasuresarefixedbecausetheratesofinjectionandwithdrawalchangeasthelevelofgasvarieswithinthecavern.Thefacility'stotalvolumecanvary,temporarilyorpermanently,asitsdefining

parametersvary.Storagefacilitiescanwithdrawcushiongasforsupplytomarketduringtimesofheavydemand,althoughthisgasisnotintendedforthatuse.

boundaryconditionsgivenbyBergamt

- MinimumpressureincavernPminisgivenaround40bar.- Therecannotbeapressuredrop(dPmax)of10barinoneday.- MaximumpressureingascavernPmaxisaround210bar.- GeometricvolumeVcisconstant.

- Maximuminjection/productioncapacity- Maximumgasvolume:Pmax*Vc- Maximumworkinggasvolume:(Pmax‐Pmin)*Vc- Maximumgasvolumechangeperday:(dPmax/Pmax)*(Pmax*Vc)=dPmax*Vc- Maximumavarageinjection/productieperhour:dPmax*Vc/24- Minimumcycletimewithworkinggasvolume:2*((Pmax‐Pmin)*Vc)/dPmax*Vc))=2*(Pmax‐

Pmin)/dPmax

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Example

Vc

1mlnm3

Pmax 210barPmin 40bardPmax 10bar

Maximumgasvolume 210mlnm3MaximumWGV 170mlnm3Maximumgasvolumechangeperday 10mlnm3Maximalinjection/production 0,417mlnm3/hour

Cycletime 34days

4.2GashydratesIfthebrineinthesumporonthewallshaveahigherwatervaporpressurethanthepartialpressureofthe

watervaporintheinjectedgas,waterwillmovefromthesesourcesintotheinjectedgas.Watervaporingascaverncancausetwoproblems,thepresenceofwatercancausegashydratesandpossiblemetalcorrosionin

thepipelinecanoccur.Inthelongergasstoragecyclestheequilibriumofthegasandbrinevaporcanbereached.

Gashydratesarecrystallinewater‐basedsolidsphysicallyresemblingice,inwhichgassesaretrappedinside

"cages"ofhydrogenbondedwatermolecules.Withoutthesupportofthetrappedmolecules,thestructureofhydrateclathrateswouldcollapseintoconventionalicecrystalstructureorliquidwater.

Hydrateshaveastrongtendencytoagglomerateandtoadheretothepipewallandtherebyplugthepipeline.

Onceformed,theycanbedecomposedbyincreasingthetemperatureand/ordecreasingthepressure.

InEuropethewatercontentlimitationis70mg/m3at70bar.Thisconcentrationiscapableofallowinghydratestoformifthetemperaturesbecomelowenough.Hydratestakeasignificanttimetogrowtolargesizesand

theywilldecomposerapidlyifexposedtolowpressuresandwarmtemperatures.

Figure12:MethaneHydratestabilityfield

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Whenoperatingwithinasetofparameterswherehydratescouldbeformed,therearestillwaystoavoidtheirformation.

• addingchemicalscanlowerthehydrateformationtemperatureand/ordelaytheirformation

• Replacingbrinewithorganicliquids

• Sumpcoverage

• Caverndrying

Theseoperationsareconsideredenoughtoavoidformation.

TemperatureThetemperatureofrockincreaseswithdepth,atypicalvaluebeingatemperaturerateof45°Cper1000m,

butcavernsareleachedoutusingsoftwaterpumpedfromariver,lakeorshallowaquiferwhosetemperatureiscooler.Brinetemperatureattheendofleaching,isclosetothesoftwatertemperatureandsignificantly

smallerthanrocktemperature.Duringconstructionofnaturalgasstoragecavernsbysolutionmining,thetemperaturedistributioninthesurroundingsofthecavernisextensivelydisturbed.

Whenthecavernremainsinactive,afterleachingiscompleted,theinitialtemperaturedifferenceslowly

resorbswithtime,duetoheatconductionintherockmassandheatconvectioninthecavernbrine(Berest,Broaurd,Karimi‐Jafari).

Duringgaswithdrawal,theexpansionofgascausescoolinginthecavern.Thenecessaryenergyforexpansion

workissuppliedbytheheatcontentofthegasitself.Thehigherthewithdrawalrate,thelessisthetimeavailableforheattransferatthecavernwall.Therefore,thegastemperaturedecreasesmorerapidly.The

extremecaseisanadiabaticexpansionwithoutanyheattransferatthewall.

Inthiscase,thepreviouscoolingofthesaltrockbythesolutionminingprocesshasanegativeeffect.Becauseofaconsiderabledecreaseintemperature,theriskofdevelopinggashydratesincreases.Gashydratesdevelop

incaseofhighpressureandlowtemperature,aswellasinthepresenceofwater.Thegaswithdrawalratehastobereducedorwithdrawaleveninterruptedinordertoavoidpressureandtemperatureconditionswhen

hydratescandevelop.(WaldenS.)

Whentheformationofhydratesisconsidered,thepresenceofwaterasapreconditionforthisisalsorelated

tothecooledrock,butnowinapositivesense.Whilemeasuringthewatercontentinnaturalgasstoragecaverns,itwasnoticedagainandagainthattherewasarapidincreaseofwatercontentofgasinthelower

partofthecavern.Therefore,itcanbeconcludedthatthiswetgasisimmobileandthusnotinvolvedintheconvectionflowintheupperpartofthecavern.Besidelossofheatduetoevaporationatthebrinesurfacein

thecavernsump,considerablecoolingofthissectionduringsolutionminingcanbeassumedbecauseofthelongdurationofinfluenceofthecoldwater.Nevertheless,withregardtothesequestions,eachcavernshould

beregardedindividually,asconsiderablespecificdifferencesbetweencavernsmayexist.(WaldenS.)

Thetemperaturedistributioninthesurroundingsaltbodywillaffectthegastemperatureinthecavernintheshortandlongterm.Becauseoftheheatreservesintherock,thecoolingeffectofthesolutionminingprocess

willdecreaseinthecourseoftheoperationtime.Buttheinitialtemperaturegradientcanneverbereachedagain,duetoconvectionflowinthegasphaseanddisturbancescausedbygasinjectionorwithdrawal

activities.(WaldenS.)

4.3.RockmechanicsinsaltThebehaviorofcavernsandminescanonlybeunderstoodandpredictedbytakingintoaccountthecreepandotheraspectsofsalt.Butthemechanicalbehaviourofsaltisofaveryhardcomplexity,andseveralaspectsof

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itarestillopentodiscussion.InallthearticlesIreadyouseealotofdifferentwaystodescribesaltmechanics.Iwilltrytogivesomeaspectsofmechanicalbehaviorofsalt.Undercertainloadingconditionssaltmaybecomepermeableorfailincompressionorfractureundertension.Fracturingcanresultinfluidorgaslossesfromacavernorfloodingofacavern,whenaconnectiontoan

aquiferhasbeenaccidentallyestablishedbyfracturing.

4.3.1.CreepofrocksaltRocksaltcreepisusuallyinthreestages:primary,secondaryandtertiary.Primarycreepcomponentsmaybe

negligibleforgeologicalstudies,becauseitstimescaleisverysmall.Butresearchersareindebatewhetherornotprimarycreephastobetakenintoaccountinthecaseofminingandstorageinsalt.Theshortertheperiod

ofloadingandthelowerthetemperature,themoreimportanttheprimarycreepcomponentbecomes.Temperatureisaveryimportantparametercoveringthecreepofrocksalt,sinceallmechanismsunder

considerationarethermallyactivated.(Breunese,J.Netal.)

Secondarycreeprepresentsanequilibriumstatebetweenstrainhardeningandrecoveryprocesses.Tertiarycreepisusuallyattributedtoexpansionandisthephaseofafulldisintegrationofthepolycrystalstructure.

Figure13schematicallyillustratestheformofcreepcurvesasobtainedwithuniaxialcreeptests,whichare

unconfinedcompressiontestswithaconstantload(σ=const.),usedtoobtaintime‐dependentmechanicalproperties.

Thestressσleadstoelasticdeformationsεel,whichnotdependontime,aswellastocreepdeformationsεc

dependingontime.IfthecreepstressσissmallerthanastressσF,theso‐calleduniaxialyieldstress,the

increaseofthecreepdeformationwithtime,i.e.thecreeprate islargestafterapplyingthecreepstress

andthenconvergestoaconstantvalue.Thecreepdeformationcan,inthiscase,besubdividedintotwo

components.Oneisthesocalledprimarycomponentofthecreepdeformationεp,whichconvergestoaconstantvalueanddoespracticallynotanymoreincreaseafteracertaintime.Therefore,theprimarycreepis

alsocallednon‐steadycreep.Theothercomponentisknownassecondaryorsteadystatecomponentofthe

creepdeformationεs;itincreaseslinearlywithtimeinanuniaxialcreeptest( =const.).IfthecreepstressislargerthantheyieldstressσF,thecreepcurveusuallyhasapointofinflection.Aftera

delayedcreepatthebeginning,anacceleratedcreepprocessstartsassoonastheinflectionpointispassed,finallyleadingtoacreepfailure(seefigurebelow).Thisbehaviorcanbeinterpretedbyatertiarycreepportion

εt,increasingoverproportionallywithtimeandbeingsuperimposedtotheelastic,primaryandsecondarydeformationcomponents.

Figure13:Primary,secondaryandtertiarycreepinanuniaxialcreeptest

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4.3.2.PrimarycreepPrimarycreepisdependentontemperature.Therelationbetweenstressandstrainratecanbegivenbya

powerlawfunction.ThislawiscalledthecreeplawofMenzel‐Schreiner(1972).

Thislawwithanextensionofatemperaturefunction(theArrheniusfunction):

)n

Wherevaluesβcanbecalculatedtorangebetween0.33and0.44.Wherenrangesbetween9to15.TemperatureT(K),gasconstantR(8.314J/K/mol)andactivationenergyQ(J/mol).

4.3.3.SecondarycreepAtrelativelyelevatedtemperatures(500–1000˚K)andlowstrainrates,secondarycreepstartstoplayan

importantrole.Strainiscausedbydirectedstress.Thesecondarycreeplaw(Poirier1972,Fransen1993)is:

Poiriermentionsarangeofmfrom4to7.

However,noteveryproblemrequiresthedeterminationofallparameters.Asalreadymentioned,stressessmallerthantheyieldstressonlyleadtoelasticaswellasprimaryandsecondarycreepdeformations.Insuch

cases,thestress‐strainbehaviorofthesaltrockiscompletelydescribedbytheparametersE,ν,Ep,ηp,m,aandn.Inlong‐termstudies,thesecondarycreepoftenprevails,becausethestressalterationsduetoan

opening'sexcavationand,thus,theprimarycreepdeformationsarelimitedwithrespecttotime.Insuchcases,theprimarycreepdeformationsmaybeneglectedsothatonlytheparametersE,ν,aandnarenecessaryto

describethestress‐strainbehavior.

Mainfeaturesofsteady‐statecreeparecapturedbythefollowingsimplemodel(Norton‐Hoffpowerlaw):ε ̇=A e^(((-Q)/RT) ) (1/(n+1)) (∂/∂σ) [(√3J2)n+1

WhereJ2isthesecondinvariantofthedeviatoricstresstensor;A,n,Q/Raremodelparameters.

Toslowdownthecreepeffectitisimportanttokeepthepressureclosetolithostaticandtheshearstressesclosetozero.InthecaseofEnecoGasspeicheritisnotfavourabletokeepthepressureclosetolithostatic

pressure.Toslowdownthecreepeffecttherehastobeanhealingperiod,wherethegaspressureinthecavernisclosetothelithostaticpressure.

However,thesesimpleapproximationsarepoorlysuitedforundergroundstoragecaverns,wherecaverngaspressurevariessignificantlywithtime.Theseformulaedoesnotcapturethetransienteffects,whichplayamajorroleinthiscontext.(Vouilleetal.andHugout)

4.4PermeabilitySaltsbehaveinamannersomewhereinbetweenaductilematerial(likesteel)andabrittlemanner(likehard

rock).Insufficientbondingstrengthandnonuniforminternalstressesleadtomicro‐crackswhenloadedunderthewrongconditions.

Theelasticbreakdownpressureistheoreticallymorethantwicethelithostaticpressureforanisotropicstress

fieldinelasticrock Howeverelasticbreakdownisneverreachedat

thislevel.Accordingtoalotoftheories,thestressesaroundtheboreholedropasaresultofcreep,ifthe

19

boreholepressureisforalongtimebelowthelithostaticpressure.Whentheboreholeispressuredfast,thetangentialstressesbecometensileatapressurethatisbelowtheelasticbreakdownpressure.Butacreep

relatedstressdropwillhavesomeeffectinthebreakdownpressure.

Byenteringthecrystalboundaries,fluidsnolongersupportthesalt,insteadtheydecreasethecrystalline

stressesandthesaltstrength.Anotherimportantfactorforthepermeabilityisthehydraulicfracturing.Itisasourceofcavernleakagebecauseofthefracturesitgeneratesinthesaltmass.Saltpermeabilityisstrongly

influencedbythestateofstress.Especiallystresses,liketensileorhighdeviatoricstresses,developedatthecavernwall.Theyoccurwhentheinterncavernpressureisveryhighorverysmall.Soafastpressurebuildup

willleadtoahigherbreakdownpressure,sincemicrocrackandfluidintrusiontaketime.

Sowecansaythatbyfluidintrusionsaltbehavesasifitwasapermeablematter.Themaximumfluidexcesspressureinanundergroundcavern,withrespecttotheminimuminsitustressisequaltothetensilestrength.

Therealproblemisusuallythe“piping”orcasing,thecementedwellthatconnectsthecaverntotheground

surface.Correctandstrongwelldesignspreventmostleakages,testingisnecessarytoensurethatthereisacceptabletightness.

4.5CavernspacingFordevelopingnewcavernsthestressdistributionandconcentrationaroundandbetweencavernsisimportant.Forstressevaluationitisnecessarytoknowthevirginstressofthesaltdepositandthemechanical

propertiesofthesalt.Stressdistributionaroundmultiplecavernsisverycomplicated.Thedomainofstressinteractionbetweensaltcavernsisdifficultmatter,becauseplasticitysolutionsindicatethatstressesbeyond

theyieldzonesurroundingacavernaregreaterthatwouldbepredictedbyanelasticsolution.Asafeformationofmultiplewellsisachievedbyatrigonallayoutofsinglewells.Asseeninfigre14thedistance

betweenthewellshavetobe2*diameterofthecavern+2*pillarzone+2*radiusofthecavern

figure14:Determinationofcavernwellspacing

20

4.6SubsidenceItisawell‐knownfactthatnaturalsolutionofconcealedsaltbedsbycirculatinggroundwaterleadstosubsidenceofthelandsurface.Inaddition,subsidenceandimpactsonhydrologeologicalregimesoccuratmanyundergroundminingoperations,causingchangestosurfacelandforms,groundwaterandsurfacewaterflow.Allsolution‐minedcavernsconvergeastheyverygraduallyshrinkduetosaltcreep(Bérest&Brouard,2003).Theshapeanddepthofthesubsidencebowlvaryaccordingtomanyparameters.Likecavernvolumes,depth,spacingbetweencaverns,rockpropertiesandtheproductionrateandscenario.Veryrapidsqueezefromasinglecavernisbelievedtoresultinanarrowbowlbecausesaltsqueezesoveralimitedarea.Slowsqueezefromasinglecavernresultinawidebowlbecausethesqueezeisspreadoveralargerarea.Tocontrolsubsidence,itisofgreatimportancetodesignaproperthicknessofsaltpillarabovethecavern.Thebestcontrolofcavernsubsidenceisachievedbyatrigonallayoutofsinglewells.Thecollapseofacavern

leadstodamageofthesurfaceonlyinthecaseofshallowsolutionmining.Atgreaterdepth(likeover1000meter)destructionofthegroundsurfaceisimpossible.

Severalmathematicalmodelshavebeendevelopedfortheanalysisofsubsidence.Allofthemhavesomedrawbackbecausetheydonotheldthediscontinuousnatureofrocksaltinmind.

Therehastobesomefeaturesheldinmind:

‐ Squeezevolumesarenotthesameasleachingvolumes

‐ Thedipofthesaltlayers‐ Theelasticpropertiesoftheoverburden

‐ Theoccurrenceoffaults‐ Thesaltmassisuniformlydeformed.

BecausetheEpeareaisaruralareaitisveryimportantthatsubsidenceismonitoredconstantly.Theverticalmagnitudeofthesubsidenceitselftypicallydoesnotcauseproblems.Onlyfordrainageitcauseproblems.Moredangerousistheassociatedsurfacecompressiveandtensilestrains,curvature,tiltsandhorizontal

displacement.Thesefactorscausetheworstdamagetothenaturalenvironment,buildingsandinfrastructure.

4.7StoragepressureDeterminationofthemaximumstoragepressureinthecavernisafunctionofseveralvariables:design

specifications,regionalpressureandknowntemperaturegradients.Calculationsvaryfromcompanytocompanyandsitetosite.Themostimportantfactistheoverpressuringofthecasingshoe.Hightemperature

effectsarenotthatimportant,butthelithostaticpressurecalculatedfromwelllogsisimportant.

Lithostaticpressureisapressure,equalinalldirection,causedbytheweightoftheoverlyingrocks.Lithostaticpressureindicesastressinrocks.Whentheelasticlimitoftherockisreached,itwillchangeshapeinnon‐

reversiblefashion.Thelithostaticpressureatdepthzisgivenbytheformulabelow.Whereρ(z)isthedensityoftheoverlyingrockandgistheaccelerationduetogravity.Andp0isthedatumpressure,thepressureatthe

surface.IntheattachmentyoufindthecalculationofthepressureinthetwoEnecowells.

Temperatureaffectstheminimumstoragepressurebecausethehigherthetemperature,themorelikelycreepandclosurewilloccur.Highertemperaturealsoaffectsthemaximumallowablediameterofthecavern.Itismoredifficulttocalculatetheminimumpressureforinhomogeneoussalt.Maximumsafeoperatingpressuresforareservoirdependonfourprimaryfactors:

•Themechanicalpropertiesofthereservoirandoverburden

•Theinsitustressesandfracturepressureinthereservoir

21

•Stressesinducedinthereservoirbygascycling;and,•Stressesinducedinthecaprockmaterialbygascycling

FromSMRIresearchworkonthedeterminationofthemaximuminternalcavernpressureforgasstoragecavernsitisknownfurther,thattheshapeofthecavern’sroofhasamajorinfluence.

Tohavesafegasstoragethemaximumallowableoperatingpressure(MAOP)isapercentageofthecalculated

rockpressure.

Forsafegasstorageinsaltcaverntheruleofthumbarethefollowingequationsinbar.

Fortherockpressure: Prock=0.22*depth

Formaximumgaspressure: Pmax=0.18*depth

Minimumgaspressure: Pmin=0.3*Pmax

IntheEnecocaseItookapercentageof10percent:Cavern Depth(m) Rock

pressure(bar)

Maxgaspressure(bar)

Mingaspressure(bar)

Calculatedrockpressure(bar)

Calculatedmaxgaspressure(bar)

EpeS81 1357 298.5 244.3 73.3 278.3 250.5EpeS82 1283 282.3 230.9 69.3 270.1 243.9

Figure14:pressurevsdepthFornatural‐gasstorage,littlebrineisleftatthebottomofthecavern.Gaspressurebuildsupwhengasis

injectedanddropswhengasiswithdrawn.Thedangerfortheenvironmentcanonlybecausedbywellheadfailure,thegasvolumeofthefullcavernwouldbeexpelledbuttakesseveralweeks,dependinguponthe

initialgaspressureandheadlossesthroughthewell.Thegascloudwouldmoveupwardrapidlyanddisperseinthehigheratmosphere.Insomecases,thecloudcouldkindleatanearlystage,but,ifitdoesnot,theriskof

explosionwouldbesmall(Berestetal.)

22

4.8CavernsabandonmentWhenthecavernswillnotbeusedanymore,thecavernwillusuallybefilledwithbrine.Thisismaybethecase

fortheEnecocavernsin2030.Cementwillbepouredinthewellandcasing.Afterthecavernissealed,thebrinepressurewillbuildup.Thefinalvalueofcavernbrinepressureisthemostimportant.

Assaltcreepstowardacavern,thecavernbrineisforcedinasmallerroom,anditspressurebuildsupinasealedcavern.Aftersometime,theprocessbecomesslowerasthecavernpressurebecomeshigher,ultimatelystoppingwhenthecavernpressureisequaltogeostatic(Pi=P¥),afterseveralcenturies(Wallnerand

Paar,1997)

TheauthorsBérestandBrouard,fearthatbrinepressureeventuallyreachafigurelargerthanthegeostaticor

lithostaticpressure,leadingtohydrofracturing.Whichcanleadtoupwardbrineflowthroughfracturesandpollutingdrinkablewater.Themainfactorsofbrinepressurebuilduparecaverncompressibility,saltmass

creep,saltpermeability,leaksandbrinethermalexpansion.

23

5 Conclusionsandrecommendations:

Thegeotechnicaldesignofgasstoragecaverninrocksaltisacomplextask.Astherearenogeneralaccepteddesigncriteriaavailable,alotofdifferentdesignmethodsdoexistallovertheworld.Itisageneral

understandingthatthedemandsofstaticstabilityandtightnessaswellaspublicsafetyatthesurfacemustbeguaranteedbythedesignandtheoperationofthesegeotechnicalconstructions.

Stressfieldscausedbythepresenceofacavernresultincreepatanyshearstressandanyinsitutemperature.

Cavernvolumereductionwithtimeaccompaniedbysurfacesubsidenceisanimportantconsequence.Bykeepingthepressureclosetolithostaticandtheshearstressesclosetozero,theeffectofthoseareslowed

down.Becauseitisnotfavorabletherehastobeahealingperiodeverywhile.

Inthecourseofsolutionminingoperationsforconstructinganaturalgasstoragecavern,aconsiderable

amountofthermalenergyiswithdrawnfromthesaltrock.Thereasonliesintheuseofacoldleachingfluidandtheconsumptionofenergyinthedissolutionofsalt.Duringgaswithdrawal,thegascoolsdowndueto

expansion.Thiscoolingeffectispartlycompensatedbyheatsupplyfromtherock.Themoretherockisalreadycooledbythesolutionminingprocess,thelessfavourablearetheconditionswithregardtogas

withdrawal.Theseconditionshavetobeheldinmindwithregardtoformationofgashydrates.

Theproblemofwaterevaporationfromthecavernsumpintothestoredgashassofarnotbeensolved.ThatiswhytheEnecofacilitymustbeequippedwithgasdryingsystem.Ifthegascontainstoomuchwaterthereisa

possibilityforformationofgashydrates.

Gashydrates: • Avoidoperationalconditionsthatmightcauseformationofhydratessuchaspressureand

temperature

• Temporarilychangeoperatingconditionsinordertoavoidhydrateformation;

• Preventformationofhydratesbyadditionofchemicalsorinhibitors

Thepositionofthecavernisimportantforthestabilityofthecavern.Therearemanyparametersthatplayimportantroles,includingroofshape,distancetothetopofthesaltformation,spacingbetweentwoadjacent

caverns,anddistancefromthedomeflanks.

Abandonmentofthecavernshastobestudiedmoreclosely,especiallythehydrofracturingfearedbytheauthorsBérestandBrouardandWallnerandPaar.

Cyclesandstorageparameterscanbeeasilycalculatedbysoftwarespeciallydesignedforundergroundgasstoragefacilities.LikeSaltCavernGasStorageToolboxbyGasTechnologyInstitute,PipelineResearchCouncilInternationalandTechnicalToolboxesitcontainsamathematicalsimulatortocreatealternativedetaileddesignsimulationscalculatingtransientwellheadpressuresandtemperatures,feasibilitycalculationsformeetingpotentialgasnominations,hydrateformationrestrictionsetcIrecommendEnecotopurchasethissoftwaretooltounderstandanduseitfortheirgasstorageproject.Forfurtherquestionsorrecommendationstheauthorwillbegrateful.

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6Data

MainAttributes MetricUnitsInstalled max/planned/undeveloped Working Gas Volume 106 m³(Vn))Cushion Gas Volume incl. inj. + indig. 106 m³(Vn))Peak Withdrawal Rate 106 m³(Vn)/h)Nominal Withdrawal Rate 106 m³(Vn)/h)Last Day Withdrawal Rate 106 m³(Vn)/h)Injection Rate 106 m³(Vn)/h)Installed Compressor Power (MW)Areal Extent Storage Reservoir (km²) Minimum Storage Pressure @ Datum Level (bar) Maximum Allowable Storage Pressure @ Datum Level (bar) Initial Reservoir Pressure @ Datum Level (bar) Pressure Datum Level below Surface m Depth Top Structure/Cavern Roof m Maximum Depth of Storage Structure m Net Thickness m Porosity (average) % permeability mD Reservoir Temperature (°C) Cavern Height average m Cavern Diameter average m Distance between Caverns average m Convergence Rate of Caverns %/ year Total Convergence of Caverns % Gasquality Hsup (kWh/m³)

25

7References‐ MessberichtSolvay‐ GeologischeD.Albes,15apr2003,GeologischerBerichtzurKavernenbohrungEpeS81,Dipl.

‐ GeologischeD.Albes,15apr2003,GeologischerBerichtzurKavernenbohrungEpeS82,Dipl.‐ Abschluβbericht,febr.2003,SGWEpeS81

‐ Abschluβbericht,jan.2003,SGWEpeS82‐ Lux,Karl‐Heinz(1984),GebirgsmechanischerEntwurfundFelderfahrungimSalzkavernenbau“Ein

BeitragzurEntwickulungvonPrognosemodellenfurdenHohlraumbauimduktilenSalzgebirge”,Enke.

‐ J.A.IstvanandC.W.Querio,1983,StorageofNaturalGasinSaltCaverns.‐ M.L.Jeremic,1994,Rockmechanicsinsaltmining,A.A.Balkema

‐ RichardE.Goodman,Introductiontorockmechanics,2ndeditionJohnWiley&sons‐ P.A.Fokker,Thebehaviorofsaltandsaltcaverns,Thesis,1995

‐ Kurstedt,A.(2007):SalzbergwerkEpe–VonderSolegewinnungzumgrößtenKavernenspeicherEuropas.Bergbau9/2007;Essen.

‐ Th.E.Wong,D.A.J.Batjes&J.deJager,GeologyoftheNetherlands,RoyalNetherlandsAcademyofArtsandSciences,2007.

‐ HowardL.Hartman,SeeleyW.Mudd,SMEMiningEngineeringHandbook,SME,1992

‐ Von Sedacek R.,Untertage-Gasspeicherung in Deutschland, ‐ Breunese,J.N.,vanEijs,R.M.H.E.,deMeer,S.,Kroon,I.C.,Observationandpredictionoftherelation

betweensaltcreepandlandsubsidenceinsolutionmining.TheBarradeelcase.NetherlandsInstitute

ofAppliesGeoscienseTNO,Fall2003conference5‐8October,Chester,UnitedKingdom‐ Hoelen,Q.,vanPijkeren,G.,Teuben,B.,Steenbergen,B.,Breuning,P.,gasstorageinsaltcaverns

“aardgasbufferZuidwending”TheNetherlands,23rdWorldGasConference,Amsterdam2006‐ Berest,P.,Brouard,B.,Safetyofsaltcavernsusedforundergroundstorage

‐ Bishop,WilliamM.,Areexamninationofgashydratesandnaturalgaswatercontentandtheiraffectoncavernoperations,2004

‐ ZieglerK.,GerstädtP.,HilscherA.,SafetyConceptforanLPGUndergroundStorageinGermany,2002‐ RiekenbergR.,HartmannU.,StaudtmeisterK.,Zander‐SchiebenhöferD.,Recommendation of

maximum cavern pressures for the gas storage caverns at Huntorf on the basis of three- dimensional numerical models, 2004

‐ Allen Marr W., Feasibility Study For the storage of cold compressed natural Gas in underground solution mined bedded salt caverns, 2006

‐ Brouard B., Bérest P.,Karimi-Jafari M., Thermal Effects in Salt Caverns, 2007 ‐ Berger, H., Zündel, F., Walden, S., Water in Gas Storage Caverns – Problems and Solutions, 2002 ‐ Sloan, E.D., Clathrate Hydrates of Natural Gases, 1990 ‐ Brouard B., Bérest P.,Karimi-Jafari M., Subsidence, Sinkholes and Craters above Salt Caverns, 2008

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‐ http//www.eia.doe.gov/pub/oil_gas/natural_gas/data_publications/natural_gas_monthly/historical/

2002/2002_05/pdf/nym_all.pdf‐ www.UGSnet.de‐ http://gisos.ensg.inpl-

nancy.fr/UserFiles/File/PM_2005/PM05_pdf/T4_T6/Berest_1%20et%20al.pdf‐ Creep:http://www.geofoon.nl/nr12art2.pdf‐ http://www.brouard-consulting.com/articles/nancy-post-mining.pdfdeepsaltcaverns

abandonment‐ http://www.cadlm.fr/%5Cworkshop%5Cdoc%5Cproceedings/BerestBBDG.pdf‐ http://www.saimm.co.za/events/0309isrm/downloads/0301‐Erichsen.pdf‐ www.tno.nl

‐ http://cdl.niedersachsen.de/blob/images/C51249629_L20.pdf‐ http://www.saltinstitute.org/symposia/symposium6/haddenhorst.pdf‐ http://www.igu.org/html/wgc2006/WOC2database/index.htm

‐ http://www.rwe.com/generator.aspx/produkte/storage‐fee‐computer/epe/language=en/id=227662/page.html

‐ http://www.saltinstitute.org/symposia/symposium6/istvan.pdf

‐ http://www.gie.eu.com/index.html‐ http://www.eia.doe.gov/emeu/cabs/Germany/NaturalGas.html

27

Bijlage1:StratigraphyS81andS82

StratigraphyS81

system years group foundation meter

quartiar 5 1950

LowerCretaceous 112‐145,5 basissandstone 203,2 2250

middlebuntsandstein 299 2230

solling‐hardegsenFolge 109,4

withHardegsensandstone 27,9

detfurthfolge 81,7

WithClay 27

Withsandstone 54,7

volpriehausensandstone 107,9

Withvolpriehausensandstone 30,3

untererBundsandstein 359,7 2230

BernburgFolge 136,3

CalvordeFolge 190,1

zechsteinubergangsfolge 33,3

ZechsteinZ4 6,9 2240

pegmatitAnhydrite 1,4

252

RedsaltClay 5,5


UpperLeineAnhydrite 3,6

LeineSaltrock 0,8

mainAnhydrite 1,5

Plattydolomite 43,7

253

GreySaltclay 2,6


Basalanhydrite 31,1

254,5

Dolostone 16,6


UpperWerra‐Anhydrite 13,5

WerraRocksalt 368,3

LowerWerraAnhydrite 15,7

Latepermian

258

lithostaticpressure27831480Pa

28

StratigraphyS82

system years group foundation meter density

quartiar 5 1950

LowerCretaceous 112‐145,5 basissandstone 215,8 2250

middlebuntsandstein 311,9 2230

solling‐hardegsenFolge 109,2

withHardegsensandstone 27,6

detfurthfolge 83,6

WithClay 27,1

Withsandstone 56,5

volpriehausensandstone 119,1

Withvolpriehausensandstone 24,6

lowerBundsandstein 384,5 2230

BernburgFolge 153,7

CalvordeFolge 201,6

zechsteinubergangsfolge 29,2


pegmatitAnhydrite 1,6

252

RedsaltClay 4,3


UpperLeineAnhydrite 3,9

LeineSaltrock 1,2 2185

mainAnhydrite 0,8 2168 Plattydolomite 33,5

253

GreySaltclay 1,7


anhydrite 24,6 2900

stassfurtsalt 3,8 2240

Basalanhydrite 24,6

254,5

Dolostone 11,3


UpperWerra‐Anhydrite 14,9

WerraRocksalt 296,3 2168

LowerWerraAnhydrite 13,2

Latepermian

258

BreuneseJ.Netal. lithostaticpressure 27013161Pa

29

Locationwells

Underground gas storage in salt cavern September 2009

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