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SustainableShaleOilandGas
EmergingIssuesinAnalyticalChemistry
SeriesEditor
BrianF.Thomas
SustainableShaleOilandGas AnalyticalChemistry,Geochemistry, andBiochemistryMethods
VikramRao ResearchTriangleEnergyConsortium,ResearchTrianglePark,NC, UnitedStates
RobKnight UniversityofCaliforniaSanDiego,LaJolla,CA,UnitedStates
Elsevier
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Copyright r 2017ElsevierInc.Allrightsreserved.
PublishedincooperationwithRTIPressatRTIInternational,anindependent,nonprofitresearchinstitute thatprovidesresearch,development,andtechnicalservicestogovernmentandcommercialclientsworldwide (www.rti.org).RTIPressisRTI’sopen-access,peer-reviewedpublishingchannel.RTIInternationalisatrade nameofResearchTriangleInstitute.
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Notices
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DEDICATION
To Campastimes,theIndianInstituteofTechnologyMadrasmagazine, sadlynowdefunct,whereIcutmybabyteethinwriting54yearsago.
LISTOFCONTRIBUTORS
JasonJ.Amsden
NanomaterialsandThinFilmsLaboratory,DepartmentofElectrical andComputerEngineering,DukeUniversity,Durham,NC, UnitedStates
RobKnight
PediatricsandComputerScience&Engineering,Universityof CaliforniaSanDiego,LaJolla,CA,UnitedStates
TimProfeta
NicholasInstituteforEnvironmentalPolicySolutions,Duke University,Durham,NC,UnitedStates
VikramRao
ResearchTriangleEnergyConsortium,ResearchTrianglePark,NC, UnitedStates
NicoleM.Scott
BiotaTechnology,SanDiego,CA,UnitedStates
LukeK.Ursell
BiotaTechnology,SanDiego,CA,UnitedStates
DavidS.Vinson
DepartmentofGeographyandEarthSciences,UniversityofNorth CarolinaatCharlotte,Charlotte,NC,UnitedStates
JoelWalls
IngrainInc.,Houston,TX,UnitedStates
FOREWORD
TheabilityoftheUnitedStatestoutilizedomesticunconventionaloil andgasistheenergyissueoftheday.Cheapenergyfromthesesources isdrivingmanufacturinggrowthinthecountryandsuppressingfuel coststhroughouttheeconomy,theutilitysectorismovingrapidly fromcoalgenerationtonaturalgas,andthecarbondioxideemissions fromtheutilitysectorhavedroppedtotheirlowestsincethe1990s. Afiercedebate,however,hasarisenoverwhetherthistransitionisa netgoodfortheenvironment.Inparticular,manyquestionwhether theclimate,air,andwaterimpactsfromacquiringoilandgasthrough unconventionalprocessesovershadowanybenefitsfromtheuseof acleanerfuel.
Theferocityofthispoliticaldebatehasclearlyoutpaced policymakers’ understandingoftheproblem,aswellastheassessment ofthepotentialsolutions.Also,thespeedoftechnologicaldevelopmentcontinuestoacceleratepastthegovernment’sknowledgeofhow tomonitorandassesstheproblem.Wethusareleftwithapolicy challengelacedwithemotionbutlackingtheinformationneededto makewisepolicy.
Wiseenvironmentalpolicycannotbeconstructedunderthiscircumstance.Toproperlyevaluateandweightheoptions,policymakersneed clear-eyedassessmentsofboththescaleoftheissueandthepotential solutionstotherisks.
Inthisbook,RaoandKnightsuccinctlysummarizethestateof knowledgeonthemanagementoftheenvironmentalrisksofaccessing shaleoilandgas.BystandingonshouldersoftheinvestmentsofentitiessuchastheUSDepartmentofEnergyandtheEnvironmental DefenseFund,andalsotheresearchofmanyexpertsintheacademy (includingmanyofmycolleaguesatDukeUniversity),theauthors seektocreatealibraryofknowledgethatshouldbethe “rawmaterial” forwisepolicy.Theyalsoexplorenewmeasurementtechnologiesby whichwemightinformregulation.
Energyisthelifebloodoftheeconomy andnaturalgasisagame changerinthatitmayprovidethatbloodtooureconomyforyearsto come.Unconventionalnaturalgas,ontheotherhand,couldproveto betooenvironmentallychallengingtomakeitalongertermsolution toourenergyneeds.Whichfuturewepursue,intheend,willdepend ontheissuesexploredinthisbook.
TimProfeta
PREFACE
Thelastsentenceofthisbookreads, “Thatwhichcannotbemeasured, cannotberegulatedorotherwisecontrolledorexploited.” Thisembodiestheessentialmotivationforthebook.Toputthatinperspective, Iquotethelastlinesfromapreviousbookofmine:
Low-costenergyisatidethatliftsallboatsofeconomicgrowth.Shalegasis apowerfulsuchtide.Ithasburstuponussounexpectedlythatwehave becomerattledbytheflotsamitcarriedwithit.Thisauthorconcludesthat theflotsamismanageable,allowingustoenjoythebenefitsofthetide.
Byflotsam,Imeanttheenvironmentalbaggage.AlthoughIstillsubscribetothisconclusion,Ihaveincreasinglycometobelievethatcurrent measurementtechniquesareinadequateforthespecialcircumstances surroundingthisresource,whichnowimportantlyincludesoil,inadditiontothegasmentionedinthequote.
WhenIwasapproachedaboutabookinthisspace,Ivieweditas anopportunitytodrawattentiontothedeficitinavailablemeasurementcapabilityanddosomethingtoaddressit.Iwasintheenviable positionofadvisingtwoexcitingdevelopmentsthatwererighton point.Oneisashoebox-sizemassspectrometerwiththeresolutionofa laboratorymachine,thusenablingdetectionandspeciationofallmannerofmolecules,nottheleastofwhicharevolatileorganicchemicals (VOCs).VOCsarenotcurrentlyregulatedatwellsiteperimeters.In fact,onlyrecently,in2016,hastherebeenpromulgationofbenzene regulationonrefineryperimeters.Theportablemassspectrometer couldwellbeacaseofbettermeasurementemboldeninglegislation,as wellasvoluntarycompliance.
TheseconddevelopmentistheuseofsubsurfaceDNAsequencing tocharacterizeoilandgasreservoirsthroughstudiesofmicrobial populations.Thisisexpectedtoimproverecoveryeconomics,thus addressinganotherlegofthesustainabilitystool.Myco-author,Rob Knight,aworldauthorityonmicrobiomesinhumansanddeveloper ofmanyofthekeydataanalyticaltechniques,wasvitalfordoingjusticetothatpartofthebook.
Fugitivemethaneemissionsfromoilandgasoperationsarebeing scrutinized,andtheissueissomewhatcontroversial.TheEnvironmental DefenseFundhastakenaleadinfundingthequantificationoftheproblem.ItandtheUSAdvancedResearchProjectsAgency Energy (ARPA-E)oftheUSDepartmentofEnergyhavefundedinnovation toimprovedetectionmethods.Boththequantificationandthedevelopmentsaredescribedinsomedetail.
Inthefaceofafuturewithlowoilprices,sustainabilityimportantly includesmeasurestodrivedownthecostperbarrelproduced. Althoughthepricetoplaycertainlyincludesenvironmentalcompliance,resiliencytoseveredropsintheworldpriceisrequired.Theanalyticalmethodsinsupportofimprovingrecoveryeconomicscomprise aninterestingblendofchemistry,geochemistry,andbiochemistry. Nevertheless,thereisnosuggestionofacomprehensiverecipeforsuccess.Thisismerelyanattempttofillthetoolboxofthefolkslooking toaddressthisobjective.
Theentirebookhasasolutionsflavor,inthebeliefthatregulations aremorelikelytobeadheredtoifcost-effectivealternativesexist. Voluntarycompliancewillalsobeencouraged.Processmeanstomonetizethegasthatwouldotherwisebeflaredisanexampleofasolution thatisnotasimplesubstitutionofbetterperformingequipment.In general,thebookisintendedtobetechnicalbutapproachable. VikramRao
ACKNOWLEDGMENTS
Manycontributedwithreferences,reviewsofthetext,andothermanner ofsupport.Thosewithsignificantcontributionsareidentifiedbychapter here.Allcommentsthatfollowarethoseoftheleadauthor(VR).
JasonAmsden(DukeUniversity)providedmuchinsightandmaterial,includingfigures,forChapter4,ParticulateMatterandVolatile OrganicChemicals.DavidVinson(UniversityofNorthCarolinaat Charlotte)conductedanexhaustiveandinformativereviewofearly draftsofChapters5,MethaneinGroundwater,and6,Potentialfor LiquidContaminationofGroundwater,keepingmehonestonthegeochemistry.JoelWalls(IngrainInc.)madevaluablecontributionstothe text,andprovidedmanyofthefigures,forChapter7,Illuminatingthe Reservoir.LukeUrsellandNicoleScott(BiotaTechnology)werevery influentialwithregardtoChapter9,SubsurfaceDNASequencing: ANewToolforReservoirCharacterization.JonathanThornburg, DorotaTemple,andBrianStoner(allRTIInternational)providedkey insightsforChapters3,DetectionofMethaneandAmelioration,and 4,ParticulateMatterandVolatileOrganicChemicals.
GeraldT.Pollard(HowardAssociates,LLC)patientlyeditedthe copy;hislastingcontributionwasmyintroductiontoStrunkandWhite, nodoubtafeebleattemptatreducingtheloadoffuturecopyeditors. DayleJohnson(RTIInternational)enduredartisticsuggestionsfromthe engineerauthorandoutdidhimselfwithabrilliantcoverdesign.
CHAPTER 1 1
Background
Thatwhichdoesnotkillme,makesmestronger.
(Wasmichnichtumbringt,machtmichstärker).
FriedrichNietzsche, TwilightoftheIdols
Shaleoilandgasmayhavepermanentlyalteredtheenergylandscape. Theyburstuponthefossilenergyscenewithasuddennessthatinitially defiedprediction.Muchoftheuncertaintywasduetothefactthatthe typeofreservoirbeingexploitedwasdramaticallydifferentfromthe conventionalone.Theterm “unconventionalreservoir” wasascribed tothisrock.Therelativelynewtechniquesofhorizontaldrillingand hydraulicfracturingwereessential.Bothofthesetechniques,butespeciallythelatter,hadsomeenvironmentalbaggage,especiallyinstates suchasPennsylvaniathatwereunpreparedwithadequateregulations. Productionmethodswereinefficientlargelybecausethereservoirwas notadequatelyunderstood.Thisbookaddressestheanalyticalmethodsandassociatedsciencenecessarytopermitefficientexploitation whilesimultaneouslyprotectingtheenvironment.Hadmethodssuch astheseexistedintheearly2010s,andregulationsemboldenedby themputinplace,muchoftheuncertaintyengenderedtodatecould havebeenavoided.
OIL
Ascant6yearsago,noteventhemostaggressivecrystalballgazers couldhavepredictedtheeventsof2014,whenshaleoilproduction rampeduprapidlyenoughtobethedeterminingfactorofworldoil price.Bylate2014,thepriceofoilhalved.Pricesinearly2016plumbed
newrecentdepthsdowntoUS$25perbarrel.TheOrganizationofthe PetroleumExportingCountries(OPEC)’sresponsewastomaintain productionandnotpropupthepricewithproductioncuts.Awidely reportedmotivationofatleastSaudiArabia,amemberofOPEC,was todriveouthighercostshaleoilproducers.Shaleoilproductioncertainlyhaddroppedbyearly2016,butresiliencycreptin.Production costswereslashedinpartwithcostreductionbytheservicecompanies butmostlythroughefficiencyinnovation.Animportantcomponentof thisgameofchickenisarealisticappraisalofhowlowthe profitablebreakevencostofshaleoilcango.Thetimeframeisafactor aswell,asdescribedlater.
What,then,aretheprospectsforshaleoilproducerssurvivingthe Saudigambit?Wetreatthenaturalgasissueseparately.Themarkets aredifferent,andtheonlymaterialeffectofoilpriceisonliquefied naturalgas(LNG)pricing;thisisdiscussedlater.ThesurvivalofUS shaleoilisdependentonthreefactors.Themainfactoristheabilityto produceitprofitablyatdepressedoilprices.Thesecondistheability toovercomeenvironmentalhurdles,becausedoingsomayrepresent thepricetoplay.Lastly,shaleoilproduction,unlikeconventionaloil recovery,literallyoccursinthebackyardsofcitizenswhoarenotused tothisactivity.Thesethreefactorsadduptothestandarddefinitionof sustainability:Withoutprofit,thereisnoenterprise,butitcannotbeat theexpenseofeithertheenvironmentorthewellbeingofthecitizens inthelocalityoftheindustry.
Asaconsequenceoftheforegoing,thisbooksquarelyaddressesall threeelementsofsustainableproduction.Thishydrocarbonsourceis newand,consequently,nowhereclosetooptimizedwithregardtoeconomicsofproduction.Forexample,onlyapproximately5%oftheoil inplaceintheaverageplayisbeingproduced.Thepercentageforconventionaloil,bycontrast,isinthemid-thirties.Modestgainsinthe 5%figurewillhaveasignificantimpactonprofitability.However, thesegainsrequirecapabilitiesnotcurrentlyinthetoolboxofpractitioners.Duringtheperiod2013to2015,theindustryfocusedon improvingefficiencyinlogisticsanddrillingpractices.Itisnowcommonformultiplewellstobeplacedonpads.Thefollowingbox describesthisphenomenon,whichhasbenefitstotheenvironmentin additiontotheeconomicsofdrilling.
MultiwellPads
Fig.1.1 isaschematicofatypicalmulti-wellpad.Theprincipalfeature istheabilitytodrillmultiplewellsfromasinglelocation.Typically,but notalways,therigsinthepadmoveonrailstothenewlocation.This takesseveralhours,comparedtoseveraldaysfornormaloperations. Conventionalpracticerequiresarigtobepartlydisassembled,moved, andreassembled.Consideringthatwellsarecurrentlybeingdrilledand completedinlessthan20days,thesavingsintimearehighlymaterial withmulti-wellpads.AnoperatorinColoradodrilled50wellsfrom asinglepadon4.6acresanddrainedareservoirof640acres. Environmentalbenefitsincludelesssurfacedisturbanceforthesamesubsurfaceacreageaccessedandfeweraccessroadsforthetransportof water,sand,andotherfracturingrelatedmaterials.Alargerpadalsohas thecriticalmasstoaffordablyinstallprocessesforenvironmentalcompliance,includingwatertreatmentfacilitiesandairemissionstestingequipment.TheColoradoexampleisunusualinitssize.Mostpadshave4to 15wells,inpartbecausethesubsurfaceaccessiblefromalargepadmay notbeunderleasetotheoperatorofthewells.
Figure1.1Amultiwellpad. Courtesy OilandGasJournal.
NATURALGAS
Naturalgasisaregionalcommodity,unlikeoil,whichisfungibleand hasaworldprice.Theexceptionistherelativelyrecentphenomenonof LNG.Chillingnaturalgas,primarilymethane,to 162 Catatmosphericpressureconvertsittoaliquidthatcanbetransportedlongdistancesifkeptatapproximatelythattemperature.Thisisachievedby deliberatelyboilingoffsmallquantities.Thelatentheatofevaporation chillstheliquid.Inships,theresultantgasisretrievedandusedasfuel. Atthedestination,LNGisreturnedtothegaseousstateinregasterminals.Allthreestepstogetherhaveaconsiderablecost.Naturalgasis pricedinUS$permillionBritishthermalunits(MMBTU).Athousand cubicfeet(Mcf)ofnaturalgashasanenergycontentofapproximately 1MMBTU,sothemarketpriceisoftenquotedasUS$perMcf.
ThedeliveredLNGpricewilladdbetweenUS$4andUS$6per MMBTUtotheproductioncost,dependingonfactorssuchasdistanceshipped.Thiseffectivelyensuresaregionalelementtopricing. Duetoshalegas,thenaturalgaspriceintheUnitedStateshas declinedtobetweenUS$2andUS$4duringthelastcoupleofyears, andithasrecentlybeenatthelowerendoftherange.TheUSEnergy InformationAdministrationforecaststhepricetobebelowUS$6for atleastthenexttwodecades.ThepriceinEuropeandAsiaisdriven bythepriceofthe “lastcubicfoot,” whichwouldbeLNGsourced.As aresult,productswithahighnaturalgascomponent,aseitherraw materialorfuel,areseverelydisadvantagedinthoseareasrelativeto theUnitedStates.Thishascausedaninfluxofmanufacturingcapital intotheUnitedStatesfromabroad.Inthechemicalindustryalone, newcapitalofapproximatelyUS$150billionhasbeencommitted.Ina fewyears,whentheseplantsareupandrunning,naturalgasdemand willincrease.Infact,italreadyhasincreased:Naturalgasisnow (early2016)inparitywithcoalforelectricityproduction.Despitethis displacementofcoal,naturalgaspricesremaindepressed.Newuses arenecessaryforasubstantialrise.Importantly,unlikethecaseof shaleoil,thelownaturalgaspriceisself-inflicted.Abundancecaused theimbalance.Nocartelisinplay.Normalsupplyanddemandeconomicswilldictateprice.
TheaforementionedappliesonlytotheUnitedStates.IncountriesinwhichLNGsetsthemarginalprice,theplummetinoilprice hashadaprofoundimpact.Inmostcountries,medium-term
deliverycontractsforLNGarepeggedtothepriceofoil.Thus,in 2015,thepricedroppedinconcertwiththedropinoilprices,and thefuturepriceremainsuncertain.ThepriceinAsiawasupto US$19perMMBTUinearly2014;inearly2016itwasclosetoUS$9. AllofthisstillleavestheUnitedStateswithaconsiderableadvantageinthemanufactureofchemicalssourcedfromnaturalgas. Consequently,USpriceswilllikelyfirmovertime.Thesignificance isthatinnovationincostreductionmaynotbeascriticalforgasas itisforoil.Demandcreationismoreimportant.Thechallengesare similar,andtheoilsidemayhavedonethegasindustryafavor.For oil,itisamatterofinnovateorperish.Gasproductionwillbea beneficiary.Ontheenvironmentalside,theissuesaresimilarbut possiblyslightlymoreacuteforgasbecausegasismoremobilethan oil.Thegainstobemadeusingmethodsinthisbookandelsewhere willcertainlyapply.
Wehavechosentofocusontechniquesthatenablebetterilluminationofthereservoir.Thisbookisnotintendedtobeacomprehensive treatiseonreducingthecosttoproduceabarrelofoil.Althoughthat iscertainlythemostappropriatemetric,wefocussimplyonnewand emerginganalyticaltechniquesthatenablethatobjective.Thetwo techniquesfeaturedrelyonrecentadvancesindataacquisitionand associateddataanalytics.Oneusessophisticatedelectronmicroscopy toestimatereservoirrockproperties.Theotherusesthemicrobiometo identifyrockwithgreaterproductionpotential.Thesecondisderived fromexistingdataanalyticsassociatedwiththehumanmicrobiome andonthefactthatDNAsequencingcostshaveplummetedbyfour ordersofmagnitudeinrecentyears.
Formationevaluationmethodsperfectedoverthelast80yearsor soarenowseenasapplicableprimarilytoconventionalreservoirs. Tofurtherconfoundmatters,thehighcostofformationfracturing leftlessroomforcostlyreservoirestimationoperationssuchas sophisticatedlogginginhorizontalwells.Theresultwastheaforementionedlowrecoveryrate.WhileoilpriceswerenorthofUS$100 perbarrel,therewasnotmuchincentivetoimproverecoveryfactors.Furthermore,wemostcertainlydonotimplythatthemethods describedhereinaretheonlymeansforimprovingreservoirunderstanding.Wehopethebookwillstimulatefurtherresearch.
ENVIRONMENTALCONSIDERATIONS
Thesefallroughlyintotwobuckets:waterandair.Eachwellcanconsumeupto6milliongallonsofwater.Thewaterismostlyfresh,so theindustrycompeteswithotherusers,whichisespeciallypernicious inrecentdroughtconditions.Onlyabout10to35%ofinjectedwater returnstothesurfaceasflowback.Thewaterleftbehindcanaffectreservoirperformance,butitisflowbackthathasthepotentialtocontaminatefreshwatersourcesandisthereforethebasisformuchofour discussion.Manyoftheanalyticaltechniquesforassessingcontaminationarenotnew,butsomearenotwidelyknownintheindustry. Theirapplicabilityisdiscussedindetail,especiallyinthegeochemical context.Forexample,intheeventofaquifercontaminationbymethane,onecanusethesetechniquestopredicttheageoftherockfrom whichtheoffendingfluidwasderived.Theycanalsodecipherwhether thesourcewasterrestrial.Thishasimplicationsforculpabilityand remedialaction.
Airemissionsfromshaleoilandgasoperationsrequiresignificant investigation.Analyticaltechniquescontinuetobeinadequate.For example,volatileorganicchemicalsarenotcurrentlymeasuredatthe perimeterofoperationsbecausedoingsoiseconomicallynotfeasible. Existingstudiesarelargelyphenomenologicalwithregardtohealth outcomesinproximalpopulations.Wedescribeanemergingtechnologywiththepotentialtoidentifyandquantifyairborneorganicmoleculespreciselyatamultiplicityoflocationsatrelativelylowcost.Also describedisthemeasurementofparticulatematter(PM10and PM2.5),whichisimplicatedinmorbidityandmortality.Oneofthe underlyingbeliefsoccasioningthisbookisthatcost-effectiveanalytical techniquescouldinformlegislationandpossiblyemboldenit.Inits June2015decision,theUSSupremeCourtgaveclearinstructionto theUSEnvironmentalProtectionAgencytotakeintoaccounttheeconomicsofenforcementpriortopromulgationofrules.
Fugitiveemissionsofmethanehavefacedintensescrutinysince 2011.Newanalyticalmethodshaveemergedandmorearebeing researchedtoidentifysourcesandquantities.Directreleasetothe atmosphereisincreasinglyuncommon,inpartduetothescrutiny. However,flaring(combustion)isthenormwhennoprofitableoutlet canbefoundforthegas.Thehighestvolumesofflaringareforgas associatedwithoilproductionandforwhichnoexportpipelinesexist.
Inefficientburnersresultinreleaseofaromaticcompoundssuchas benzeneinadditiontocarbondioxide.Becauseharnessingofgasthat wouldotherwisebeflaredhasthepotentialtocreateeconomicvalue, somediscussionofrecentadvancesinthatspaceisincluded.Viable economicalternativesarepowerfulincentivesforcompliance.
Manyfactors somepredictable,othersnot feedintothisnew phenomenonofshalepetroleumwithitstechnological,economic,environmental,geopolitical,andsocialramifications.Theadvancesinanalyticalmethodsdescribedhereinarelikelytohaveimplicationswell beyondtheoilpatch.
PART I I AirEmissions
Andifyougazeforlongintoanabyss,theabyssgazesalsointoyou. (UndwenndulangeineinenAbgrundblickst,blicktderAbgrundauch indichhinein.)
FriedrichNietzsche, BeyondGoodandEvil
CHAPTER 2 2
FugitiveMethaneandEmissionsFromFlaring
Shaleoilandgasproductionhasresultedintwotypesofatmospheric emissionsthathaverecentlycomeunderscrutiny.Fugitivemethaneis usuallydefinedasgasthatisreleasedtotheatmosphereinadvertently. Weaddtothatthecategoryofdeliberaterelease,inpartbecauseitis asignificantcomponent.Onemechanismisaresultofusingequipment thatinherentlyleakswhenoperated;whetherthatmaybeclassifiedas deliberateispartlyintherealmofsemantics.Inmanyinstances,especiallyinthecaseofgasproducedinassociationwithoil,thegasis flaredinsteadofvented.Ineithercase,anthropogenicgreenhousegas isaddedtotheatmosphere.Someofthesepracticeshavealwaysbeen presenteveninproductionfromconventionalreservoirs.Theemissions fromflaringofassociatedgasarestillfargreaterworldwidefromnonshalesourcesthanfromshaleoperations.Inthischapter,wedetailthe sources,andinChapter3.wediscusstheanalyticalmethodsrequired todetect,quantify,andamelioratethem.
Becausethisfieldofinquiryisnew,weaddressrecentmitigation measures.Anotherreasontodiscusseconomicalmitigationisthat sustainableproductioncouldwellrequireitinsomemeasure.Ifthe leakagerateexceedsacertainproportionoftotalproduction, theneteffectofshalegasontheenvironmentcouldwellbenegative comparedtoalternatives. 1 Thiswillsurprisemanybecausegasis viewedascleanerthanotherhydrocarbons,certainlycoal.That iscorrect:Burninggasproduceslessthanhalfthecarbondioxideas burningcoal.(Ofcourse,coalhasotherimportantemissions,such asparticulatematterandmercury,whichareabsentfromnatural gas.Note,however,thatNO x captureinthecombustionprocessis donewithammonia,andasmallamountofnitratesofammonia canresult,whichareparticulatematter.)WereportonthequantificationofthisdifferencebytheEnvironmentalDefenseFund (EDF),inparticularitscalculationofthepointatwhichtheamount
ofproducedgaslosttotheatmosph erebeginstonegatetheinherent advantageofgas.Tosomedegree,thislimitingstatemaynotbe relevantbecauseitisknownfromanEDF-sponsoredstudythat conventionaltechnologyalone,ifimplemented,canmitigateavery highfractionoftheemissionsveryeconomically. 2 Innovative technologiesarebeingactivelysought,someofwhicharealludedto inChapter3.Collectively,therefore,onemaybeentitledtosome bullishnessonshaleoilandgasasan etpositivefortheenvironment comparedtothealternatives.
SOURCESOFMETHANELEAKAGE
Methanemayleakoutateverystageintheproductionanddelivery system. Fig.2.1 isasketchofthesystemfromthepointofproduction totheenduse.Notshown,butdiscussedlater,isnaturalseepageon landandintheocean,mostlymethanehydrates,whichareplentiful. AccordingtoaUSGeologicalSurveyestimate,thetotalpotentialgas fromthissourceisgreaterthanthatfromallfossilfuelproduction operationscombined.
Inthesimplestterms,thechainbeginsatthewellsites.Thesemay beindividualwellsor,asisbecomingincreasinglycommon,acluster ofwellsonwhatisknownasapad(seeChapter1).Thegasmaybe fromawelldesignedtoproducenaturalgasorfromanoilwellthat alsoproducessomegas.Thislastisknownasassociatedgas.Thegas issentawayfromtherigsiteongatheringlines.Thesearesmalldiameterpipelines,usuallywellunder10inchesindiameter,as opposedtointerstatepipelines,whichare36or40inchesindiameter. Althoughsmall,gatheringlineshaveaninstalledcostofmorethan US$1.5millionperinch-mile.Thus,eachmileofa5-inchlinecosts approximatelyUS$7.5million.Thishighcostisthereasonsomelines aredeferreduntillaterinthelifeofthesitewhenthereismorecertaintyoftheeconomicviabilityoftheprospect.
Gatheringlinesusuallyconnecttoaprocessingplant.Here,the largerliquidmoleculesareremovedasnaturalgasliquids,usually bychilling.Propane,butane,andnaturalgasolineareseparatedand sold.Someethaneisalsoremoved.Pipelinespecificationslimitthe thermalcontentofgasto1.1millionBritishthermalunits (MMBTU)perthousandcubicfeet(Mcf)ofnaturalgas.Ethane
typicallyhasanenergycontentof1.78MMBTUperMcfcompared toanominal1.0MMBTUformethane,soevenasmallpercentage ofethaneraisesthecalorificvalue.Sinceearly2014,ethanehasnot hadareadymarket,withpricessometimeslowerthanthatfor naturalgas.Thisisinpartbecause,unlikepropaneandbutane,it hasnoconsumeruse.Theonlyutilityisasarawmaterialforthe manufactureofethylene,andethylenecapacityintheUnitedStates islowcomparedtotheethanesupply.Furthermore,allbut3of the39ethanecrackersareontheGulfCoast,farfrommuchofthe ethaneproduction.Producerswillputasmuchethaneasallowable intothepipeline.
Figure2.1Naturalgassupplychain.
Uponexitfromtheprocessingplant,thegasgoestoacompressionstationtoallowlong-distancetransport.Therearefour principaldestinations,asshownin Fig.2.1 .Factoriesusingnatural gasasafuel,suchassteelmills,andthosethatuseitasaraw material,suchasmethanol-orammonia-producingplants,gettheir supplydirectlyfromtheinterstateline.Powerplantsalsogetit directly.Athirddestinationisstoragefacilities,usuallyunderground,commonlytoppedupbeforethewintermonths.Finally, thereisthe “ citygate, ” fromwhichtherearemultipledestinations, includingindustry,homes,andlocalstorage.Insomecases,power plantsarealsofedfrombeyondthecitygate.
Thisdetaileddescriptionofthesupplychainisgivenbecausemost oftheelementsareassociatedwithfugitiveemissions,butwithdifferentmechanisms,and,moreimportantforthisbook,oftenwithdifferentmethodsofdetectionandquantitation.
PRODUCINGWELLS
Thewellpadhastwoclassesofmethaneleakage:equipment-related andasaconsequenceofthefluids-extractionprocess.Inthefirstcategoryarehatchesandcoversoffluid-filledcontainerswithinadequate sealing.Valvesandgasketsarealsoclassifiedinthiscategory. Thefracturingprocessinvolvesinjectionofhigh-pressurefluidtofracture therockandinduceartificialpermeabilityinthereservoir.Atsomepoint, fluidreturnstothesurface,andthisischaracterizedasflowback. Flowbackwaterwillbringwithitacertainquantityofnaturalgasfrom thereservoirrock.Themixtureissenttoaseparatortankwherethegas iseasilyremoved.Inmanyinstances,itiseitherusedonsitefor powergenerationaftersomeconditioningtreatmentorsentto thegatheringlineforexporttotheseparationplant.Earlyindevelopmentofthesite,gatheringlinesmaynothavebeenputinplace.In thiscase,theoperatorhastwochoices:releasetotheatmosphereor burninaflare.Themoreenvironmentallybenignoptionofflaringis increasinglybeingchosen.Quantificationofthisisongoinginthe EDF-sponsoredstudyattheUniversityofTexasatAustin.3
Thesecondcategoryofemissionsistheoperationknownasliquids unloading.Occasionally,theproductionfromagaswellisimpededby
theaccumulationofassociatedliquidsatthebottomofthewell. Acommonmeansofremovingthemisbyblastingtheliquidwith high-pressuregasfromthereservoir.Whenthefluidsmixturegetsto thetop,thegasportionisvented.Analternativethatavoidsmuchof thisfugitiveemissionistheuseoftheplungerlift.Thismethodcalls forshuttinginthegasproductionandtheninsertingtheplungertothe bottom.Whenthewellisopened,thesealsaroundtheplungerallow pressuretobuildbelowit,andthisliftsit.Theaccumulatedliquidrises andiscollected.Alltheenergyfortheliftcomesfromthereservoir pressure,sothemethodiseconomical.Asidefromtheenvironmental benefit,littlegasislostfromsale,althoughthereissomefugitiveemissionwithcurrentdesigns.A2012surveyshowedthatlessthanhalfof wellsusethismethod,sothereisroomforbetterpractices. “Roomfor betterpractices” isaconstantrefrain.
Pneumaticdevicesintheflowsystemusethegaspressureintheline toactuatedevicessuchasvalves.Someoftheserequireasmall amountofthegastobleedoutasadesignfeature.Low-bleeddevices areclassifiedasemittinglessthan6standardcubicfeetperhour,and high-bleeddevicesareclassifiedasemittinggreaterthan6standard cubicfeetperhour,oftenasmuchas30.Somedevices,suchasfluid levelcontrollers,areintermittent.Theusualremedyforthisistouse onlylow-bleedones.Actuationbycompressedairinsteadofthehighpressuregasinthelineisbestenvironmentallybutismoreexpensive.
TRANSMISSIONLINES
Thetransmissionsystemcommencesatthegasprocessingplant,which canhavesomefugitiveemissions.However,thelargestcontributoris thenextstepintheline,thecompressorstation.Thegasiscompressed tomakeitflowthedistancerequired.Thefuelforcompressionisalmost alwaysgasfromthepipeline,andthecombustionproducesCO2 and someunburnedmethane.However,mostemissionsarefromleaksin variouspartsofthesystem,especiallythecompressorseals,andduring maintenance.Asaclass,thisistheworstactorinthechain.2 Many alternativedesignsformitigationhavebeenputforth.Theygenerally aremoreexpensive,sopolicyactionmayberequiredtominimizethis source.Thenextworstactorispneumaticactuationdevices,but,asdiscussedpreviously,meansofmitigationexistatrelativelylowcost.
Oneofthedestinationsalongthetransmissionlineisstorage.Most commonisstorageinafieldthatproducedgasatonetimebutisnow depleted.Thisisthelowestcostmeans.Thefieldsareusuallydistributedclosetotransmissionlinesandhenceareconvenient.Themost versatilearesaltcaverns.TheseareusuallyneartheGulfCoast.Salt bodiescanbehollowedoutbycirculatingwaterthroughthem.Salt cavernsarealsousedforoilstorageintheStrategicPetroleum Reserve.Neitherofthesestoragemeansisparticularlycitedasanavenueforfugitiveemissionsotherthanfrompneumaticvalvesoperating ongaspressure.
Theotherdestinationforgasispowerplants.Sometimestheyare ontheothersideofthecitygate.
BEYONDTHECITYGATE
Industrialanddomesticcustomersaresupplied.Urbandistribution systemsarestronglyimplicatedinfugitiveemissions,especiallyinolder emplacementsthatuseunprotectedsteelandcastironpipingthathas deteriorated.Theseaccountfor50%ofallemissionsand70%ofemissionsintheeasternUnitedStates.Arecentstudy4 showedthatcity methanereleasesaredramaticallylowerthanthoselistedinthemost recent2011USEnvironmentalProtectionAgency(EPA)report becausethatreportreliedonacomprehensivestudydonein1992. Fig.2.2 showstheupdatedvalues.
ThefindingsofLambetal.4 arenotsurprisingfortheequipment sectorbecauseonewouldexpectimprovements,especiallywheninthe directcontrolofindustrialcompaniesasopposedtoconsumers.The watchwordisleakedgasisgasthatisnotsold.Thefindingsalsoimply thatsignificantreplacementofoldpipeshasoccurred.Lambetal.also notethateasternUScitiesareinmuchworsecondition.Notethevery largeerrorbarsin Fig.2.2,representinghighuncertaintyinthestatistics.ThisisverylikelyduetothesmallsamplescomparedtotheEPA numbers,whicharevoluminousbutold.Recentstudieshaveemerged forWashington,DC,Boston,andNewYorkthatpaintableakerpicture.5,6 However,wherepipeshavebeenreplaced,theimprovements havebeensignificant,asdemonstratedinthreecitiesintheeastern UnitedStates.7
Figure2.2UpdatedUSinventoryofmethaneemissionsfromlocaldistributionsystems. LambBK,EdburgSL, FerraraTW,HowardT,HarrisonMR,KolbCE,etal.DirectmeasurementsshowdecreasingmethaneemissionsfromnaturalgaslocaldistributionsystemsintheUnitedStates.EnvironSciTechnol2015;49 (8):5161 5169
METHANEHYDRATESANDTHEIRROLEINGLOBALWARMING
Methanehydratesareice-likemoleculescontainingmethane.Theyare ubiquitousandplentiful.AccordingtotheUSGeologicalSurvey,they arebyfarthemostplentifulhydrocarbonsourceintheworld.They arediscussedinthisbookbecausetheyareknowntoseepatratesthat havenotbeenproperlyquantified.Inpartbecausemanyofthedepositsareinmarineformations,theseepageisnoteasilydetectable.There isabeliefinmanycirclesthatglobalwarmingwillacceleratetheseepage.Thepossiblemechanismforthiswillbecomeevidentlater.
Methanehydratesarealsoknownasmethaneclathrates.Theseare verylargemolecules,notunlikethebuckyballformofC60,whosediscoverybySmalley,Curl,andKrotowasrecognizedwiththeNobelPrizein 1996andisthebasisformajoradvanceswithcarbonnanotubes.Thelatticecomprisingwater(ice)hasintersticesfilledwithmethanemolecules.
