GHGEmissionsAssociatedwithTwoProposedNaturalGasTransmissionLines
inVirginiai
SummaryofGHGEmissionEstimates
Theprimarypurposeofthiswhitepaperistoestimatepossiblegreenhousegas
(GHG)emissionsassociatedwithseveralproposednewinterstatenaturalgas
transmissionlinesthatwouldrunthroughpartsofVirginia.By“associated”
emissionswemeanthemajorGHGemissionsthatareestimatedtooccur(a)from
operationofthetransmissionpipelines,(b)fromtheupstreamstagesofproduction
andprocessingofthenaturalgasthatisintendedtogointotothosetransmission
pipelines,and(c)fromcombustionofthetransportednaturalgas.(Theanalysis
excludesleaksfromlocaldistributionlines,whichweassumewouldbeavoidedif
thegaswillbecombustedinlargeplantsconnectedcloselytothetransmission
lines;however,localdistributionlinesareamajorsourceofmethaneemissionsand
wouldneedtobeaccountedfor—inadditiontocombustionemissions—ifdeliveries
arefirstmadetolocalgasdistributors.)
Thefourmajorinterstatenaturalgastransmissionlinesandtheirdailythroughputs
ofgasproposedinVirginiaaretheAtlanticCoast(ACP,1.5bcf/day),theMountain
Valley(MVP,2.0bcf/day),theWBXpressProjecttoexpandthecapacityofthe
ColumbiaGasTransmissionpipelineby1.3bcf/day),andtheAppalachian
Connector(upto2bcf/day),foratotalof6.8bcf/day.
OuremissionestimatesfortheAtlanticCoast(ACP)andMountainValley(MVP)
pipelinesaresummarizedinFigures1and2,respectively.Thebasecase(inthe
firstcolumnoftheFigures)isfromapublishedanalysis:thatofLaurenziandJersey
(2013),referredtohereasthe“ExxonMobil”analysissincetheauthorsare
employeesofthatCorporationanduseddatafromdrillingsitesownedbyit.In
additionwedevelopedthreealternativecasesbasedondifferentassumptionsthan
usedintheExxonMobilresults,althoughoneofthosecasesisderiveddirectlyfrom
theExxonMobilresults.Ingeneral,thefourcasesfallintotwopairs(labeled
ExxonMobiland”EX”)thatamounttoalowandahigherestimateofupstream
emissionsofmethane(CH4),whileestimatedcarbondioxide(CO2)remainthesame
forallcases.Withineachpairthedifferenceincarbondioxide-equivalent(CO2eq)
totalemissionsisduetotwodifferentassumptionsabouthowmethaneis
weighted—knownastheGlobalWarmingPotential(GWP)ofmethane.(Moredetail
onthequantitativecontributionsofCO2andCH4inthefourcasesisgiveninTables
1and2inthenextsection.)Forcomparisontothosepipeline-associatedGHG
emissions,aseventhcolumnintheFiguresshowsthetotalreportedemissionsof
GHGsinVirginiain2014fromEPA’sGreenhouseGasReportingProgram.
1
Figure2.GHGEmissionsfromMVPforFourCases
ComparedwithEPAGHGRP2014VAStaBonarySources(MMTCO2eq/year)
100
90
80
70
60
Sta?onarySources
Combus?onofDeliveredGas
50
Transmission&Storage
Produc?on&Processing
40
30
20
10
0
ExxonMobilGWP25
ExxonMobilGWP84
3XGWP25
3XGWP84
VAGHGRP2014
2
TheissueofwhichGWPtochoosecanbebypassedbycomputingthetime-dependent
radiativeforcingdueseparatelytoCO2andCH4.Figure3showstheresultsof
calculationsofradiativeforcingcomputedbyasimplemodel.However,insteadof
showingradiativeforcinginconventionalunitsofwatts/meter2weshowthetotal
thermalheatingeffectontheplanetofGHGemissionsfromallfourpipelineprojects,
consistingoftheradiativeforcingmultipliedbythetotalsurfaceareaoftheEarthplus,
forcomparison,themuchsmallergenerationofheatgeneratedbycombustionofthe
naturalgasdeliveredbythepipelines.NotethatthethermaleffectofCO2persistslong
afteroperationscease(weshowitfor300years),andwilllastforcenturiesafterthat.
ThebasisforthisgraphisexplainedinmoredetailintheDiscussionsectionbelow.
Amoredetailedexplanationoftheresultsisgiveninthenextsection.Asubsequent
section,DiscussionofAssumptionsandResults,describestheunderlyingbasisand
comparesourresultstootherstudiesfromtherecentliterature.Followingthatsection
wepresentsomerecommendationsbasedontheresultsandlessonslearnedin
analyzingtheliteratureonemissionsfromthenaturalgasfuelcycle.
DetailedDescriptionofResults
TheExxonMobilanalysisproducedresultsbasedonemissionvaluesperunitoutputofa
hypotheticalnaturalgaselectricpowerplant(KgCO2eq/MWh),andwescaledtheirGHG
emissionsvaluestocorrespondtothepotentialmaximumnaturalgasthroughputofthe
respectivepipelines(1.5Bcf/dayforACPand2.0Bcf/dayfortheMVP).Wechosethis
studybecauseitwasapartialLCAanalysis(oftheproductionatthewellheadstage),
provideddetailedresultsforprocessstepsseparatelyforcarbondioxide(CO2),methane
(CH4)andnitrousoxide(N2O)emissions,andpertainedtoconditionsspecifictonatural
gasfromhydraulicfracturingproductionintheMarcellusshaleregion,whichis
identifiedasthesourceforthetwopipelinesinquestion,includingsomemeasurements
madeontheCorporation’sownwelloperations.
However,whiletheseExxonMobilestimatesareusefulasastartingpoint,theymaynot
berepresentativeofallfrackingoperationsintheMarcellusorothershaleregions.In
fact,otherestimatesofoverallemissionsfromthatregionsuggestmuchhigherfugitive
emissionsofmethane,anditisclearthatsomeoperatorsareresponsibleformuchmore
emissionsperunitofproductionthanothers.Forthatreasonwealsopresentan
alternativesetofestimatesformethaneemissionsfromtheoverallproductionand
processingstage,asdiscussedbelow.Notethatneitheroftheseestimatesappearsto
considertheproblemofpost-productionleaks,which,asdocumentedbySchlumberger,
mayemergemanyyearsafterawellhasbeencappedandtakenoutofoperations.
Figure1andTable1showresultsapplicabletotheACPpipeline,whileFigure2and
Table2showsimilarresultsfortheMVPpipeline.Forsimplicity,weaggregatedthe
originalauthors’moredetailedprocesslevelresultsintothreemajorfuelcyclestages:1
ProductionandProcessing(i.e.,operationsupstreamofthetransmissionline),
TransmissionandStorage,andCombustionofthedeliveredpipelinegas(assumingno
localdistribution).(CO2eqemissionsofN2OareneglectedinTables1&2asrelatively
smallcomparedtotheGHGimpactsofmethaneandCO2emissions.)Webelievethat
assessingGHGemissionsfromallthreemajorfuelcyclestages,notjustthetransmission
pipelinestage,isimportantbecausethesenewpipelinesareintendedtocollectthe
producedgasesandtransportthemtoneworexpandedmarketsinVirginiaandNorth
Carolina,andpossiblyeventoforeignexportterminals.Hence,thepipelineswilltendto
generateoratleastsupportadditionalusesofnaturalgasthatarguablywillresultin
greatergasproductionandcombustionandtheirassociatedemissions.Someofthe
usesmayincludenewindustrialplantsownedbyforeigncompaniesthatareattracted
totheregionbytheavailabilityofcheapernaturalgassuppliesthanavailableabroad.
Pipelineproponentshavebeentoutingsucheconomicdevelopmentasabenefitoftheir
pipelines.
Thetwoprincipleissuesinmakingmethaneleakageestimatesare:1)whatistheactual
leakagerateofmethanefromvariousstagesofthenaturalgasfuelcycle?and2)whatis
theappropriatechoiceofglobalwarmingpotential(GWP)(orothermethod)toapply
whencomparingemissionsofCO2tootherGHGs,especiallytomethane?Thereason
1Thefuelcycleapproachmeansanalysisofoperationalimpactsofallrelevantstages
fromextractionthroughuseanddispositionofwastes;alifecycleanalysis(LCA)
approachextendstheanalysistoconsiderationoftheindirectimpactsofmanufacturing
andtransportingtheequipmentandtherawmaterialsthatgointothestagesandis
evaluatedovertheestimatedlifetimeofthecapitalfacilities.
4
therearefourcolumnsinthetwotablesandfirsttwofiguresisbecausewemade
alternativechoicesforbothofthoseissues.InTables1and2thefirstcolumnisfrom
thegenericestimatesgivenbyLaurenziandJersey(exceptforthescalinguptoeach
pipeline).Notethatthescale-upassumesthepipelinesoperateatfullcapacity
24/7/365becausewehavenoestimatesfromtheproponentsabouttheirplanned
operatingschedule.ThesecondcolumnadjuststhemethaneCO2eqemissionvalues(the
firstcolumnwasbasedonEPA’s100-yearGWPassumptionof25)tothe20-yearGWPof
84fromIPCCAR5whensummingtoobtaintotalCO2eqemissionsfromeachstage.The
thirdandfourthcolumns(3X)increasethemethaneemissionsfromProductionand
Processing(butnotthetransmissionorcombustionstageemissions)bymultiplying
Columns1and2,respectively,byafactorofthreetoreflectresultstypicaloftop-down
highermethaneemissionmeasurementsintheMarcellusandothershalebasins.The
reasonforthischoiceisexplainedbelowintheDiscussionsection.Thosetwo
adjustmentsincreasetheupstreamproductionandprocessingemissionsinColumn4by
afactorof4.9andthetotalsystememissionbyafactorof1.7relativetocolumn1.
(NotethattheCH4emissionvaluesshownintheTablesareinmillionmetrictonnes
(MMT)ofmethane,notCO2eq.)TheCO2eqvaluesfromthefourcolumnsinthetalesare
alsoshowngraphicallyinthebarchartsofFigures1and2.
Forcomparison,Virginia’stwolargestsourcesofCO2eqGHGemissionsin2014werethe
Chesterfield(7.22MMT)andClover(5.67MMT)coal-firedpowerplants.TheColumn1
totalinTable1fromtheACPpipeline(40.7)iscomparabletothetotalcontributionfrom
the177GHGsourcesinVirginia(49.4MMTCO2eq)fromEPA’sGreenhouseGas
ReportingProgram(GHGRP)in2014,whilethetotalinTable2fromtheMVPpipeline
considerablyexceedsit.2(However,onlypartoftheemissionsinTables1and2would
occurinVirginia.)TheseVirginiaGHGRPvaluesalsoarecomparedagainstthepipeline
valuesinFigures1and2.Obviouslythecomparabletotalsforthehighermethane
emissionsassumedinColumns3and4ofthetwotableswouldbeevenhigher,butonly
Columns1and3shouldbecomparedwithEPA’sGHGvaluessincethelatteralso
assumeaGWPof25.Emissionsfromtheothertwoproposedpipelineswouldnearly
doublethetotalemissionsfromtheACPandMVPforatotalof185MMTCO2eqataGWP
of25inthebasecase,theExxonMobilrates,or3.7timestheEPAGHGRPtotalfor
Virginia.
2ThisisbasedonEPA’s“Flightdatabase”fromtheirGreenhouseGasReportingsystem,
butthatdatabaseexcludesGHGemissionsfromonshoreoilandgasproductionatthe
statelevel,henceitdoesnotincludetheemissionsfromcoalbedmethaneextraction
operationsinVirginia,forexample.Also,thelistof177largesourcesincludessomethat
reportedzeroemissionsin2014comparedwithsubstantialemissionsinprioryearsand
EPAgenerallyassumestheGHGRPreportedemissionsunderestimateactualtotals
somewhat.Onlylargesourcesarerequiredtoreport,andthedatabasedoesnotinclude
transportationandmanysmallsources
5
TABLE 1. Generic GHG Emission Estimates for the ACP Pipeline
GHG Emissions by gas
and fuel cycle stage
Production & Processing
CO2 (MMT CO2/year)
CH4 Losses (MMT CH4/year)
Total CO2eq Emissions (MMT/year)
Transmission & Storage
CO2 (MMT CO2/year)
CH4 Losses (MMT CH4/year)
Total CO2eq Emissions (MMT/year)
ExxonMobil* Adjusted
Top-Down Top-Down
(w/CH4
ExxonMobil* Higher CH4 Higher
GWP=25
(w/CH4
Leakage
CH4
over 100
GWP=84
Estimate** Leakage
years)
over 20
(w/CH4
Estimate**
years)
GWP=25) (w/CH4
GWP=84)
3.60
0.107
6.3
3.60
0.107
12.6
3.60
0.321
11.6
3.60
0.321
30.6
1.27
0.058
2.7
1.27
0.058
6.1
1.27
0.058
2.7
1.27
0.058
6.1
Combustion of Delivered Gas
CO2 (MMT/year)
31.7
31.7
31.7
31.7
Grand Total GHG Emissions
40.7
50.4
46.0
68.4
(MMT CO2eq /year)
* ExxonMobil means the ANALYSIS analysis of Laurenzi & Jersey (2013); note that
this was a generic analysis, not specific to the ACP pipeline. The values here
represent a conversion from their numbers in terms of emissions/MWh into
emissions/SCF, which are multiplied times the ACP capacity of 1.5 Bcf/day to get the
MMT/year values shown here. These values assume full-time operation 24/7/365.
** Assumes 3 X ExxonMobil CH4 Production & Processing emissions (see
discussion)
6
TABLE 2. Generic GHG Emission Estimates for the MVP Pipeline
GHG Emissions by gas and fuel
cycle stage
ExxonMobil*
(w/CH4
GWP=25
over 100
years)
Adjusted
ExxonMobil*
(w/CH4
GWP=84
over
years)
Top-Down
Higher
CH4
Leakage
Estimate**
(w/CH4
GWP=25)
Top-Down
Higher CH4
Leakage
Estimate**
(w/CH4
GWP=84)
Production & Processing
CO2 (MMT CO2/year)
CH4 Losses (MMT CH4/year)
Total CO2eq Emissions (MMT/year)
Transmission & Storage
CO2 (MMT CO2/year)
CH4 Losses (MMT CH4/year)
Total CO2eq Emissions (MMT/year)
Combustion of Delivered Gas
CO2 (MMT/year)
Grand Total GHG Emissions
(MMT CO2eq /year)
4.8
0.143
8.4
4.8
0.143
16.8
4.8
0.428
15.5
4.8
0.428
40.8
1.7
0.077
3.6
1.7
0.077
8.1
1.7
0.077
3.6
1.7
0.077
8.1
42.3
42.3
42.3
42.3
54.3
67.2
61.3
91.2
* ExxonMobil means the ANALYSIS analysis of Laurenzi & Jersey (2013); note that
this was a generic analysis, not specific to the MVP pipeline. The values here
represent a conversion from their numbers in terms of emissions/MWh into
emissions/SCF, which are multiplied times the MVP capacity of 2.0 Bcf/day to get the
MMT/year values shown here. These values assume full-time operation 24/7/365.
** Assumes 3 X ExxonMobil CH4 Production & Processing emissions (see
discussion)
_____________________________________________________________________________________________
DiscussionofAssumptionsandResults
Thetwoprincipleissuesinmakingtheseestimatesare:1)whatistheactualleakage
rateofmethanefromvariousstagesofthenaturalgasfuelcycle,and2)whatisthe
appropriatechoiceofglobalwarmingpotential(GWP)(orothermethod)toapplywhen
comparingemissionsofCO2tootherGHGs,especiallytomethane?Bothofthose
questionshavebeenissuesforseveraldecades.Neitheriscompletelysettledtoday.We
haveapproacheditinourestimatesbychoosingalowerandhighervalueforeachfactor,
andalsoproducedaseparateanalysisthatobviatestheGWPissue.
7
Theissueofleakageratesremainsunresolvedandaverycontroversialtopic.Theway
chosenheretorepresentarangeofopiniononleakageratesfromtheupstream
productionandprocessingstagesistoshowalowerestimate(theso-calledExxonMobil
values,whicharesimilartoEPA’semissionfactors)vs.ahigherestimate(the“3X”
or”Top-DownHigher”valuesinColumns3&4)asexplainedfurtherbelow.
ChoiceofGWP.TheGWPissueisnowquitewellunderstoodscientificallybutremains
controversialinthepolicyandpoliticalarenas.TheissuewithaGWPselectionisthat
theUNadopteda100-yearGWPaspartoftheKyotoProtocol.EPAalsoadoptedit
becauseoftheneedtohaveaspecificwaytoweightvariousGHGsandvalueemission
tradeoffsandtobeconsistentwithInternationalreportingrequirements.However,for
otherpurposessuchasevaluatingmitigationstrategiesandlonger-termtradeoffs,many
climatescientistsandpolicyanalysts,includingthelatestIPCCreports,nowunderstand
itslimitations.Forstrategicpurposestherearealternativesolutionsforcharacterizing
therelativeimpactsavailableintheliterature(e.g.,Alvarezetal.2012)thatrenderthat
choiceirrelevant.However,forsimplicityherewesimplycomputemethaneeffectsfor
twowidelydifferentvaluesoftheGWPtoillustratetherange:EPA’svalueof25(that
wasbasedontheIPCCAR42007reportfora100-yeartimeframe)andwasusedby
LaurenziandJersey,andtheIPPCAR52013valueof84fora20-yeartimeframe.We
believethatthelatestscientificestimatesshouldbeappliedandthatthereisno
scientificjustificationforpreferringa100-yearovera20-yearvalues,especiallysince
manyoftheGHGmitigationgoalsoftheU.S.(forexample,theU.S.pledgetotheUNFCCC
processfor2025)willoccurovermuchshorterperiodsoftime,closertoa20-year
period.
WealsoshowinFigure3theresultsofasimplemodelthatshowsthetemporal
evolutionofplanetaryheatingduetotheemissionsofCO2andCH4(separately)plus
heatingfromcombustionofthedeliveredgasesfromallfourpipelineprojects.Forthis
chartweusedthehighermethaneemissionrates(columns3and4inthetables).
PlanetaryheatingfromtheGHGemissionsmeanstheincrementalradiativeforcingat
thetopoftheatmosphereduetotheemittedgases.Oursimplemodelissimilartothat
describedbyAlvarezetal.2012,althoughweuseupdatedparametersbasedonthe
latestestimatesoftotalgreenhousegasconcentrationsintheatmosphereanddisplay
ourresultsinabsolutetermsasplanetaryheating.Ourmodelwillbedescribedinmore
detailinasubsequentpaper.ThisapproacheliminatestheneedforusingGWPsand
providesmoreinformation.
ProductionandProcessingStages.EstimatesofGHGemissionsfromnaturalgas
production,processingandgatheringpipelinetransportoperationsdifferwidelyand
currentlyareverycontroversial.Briefly,thereisanunresolveddisconnectbetweentwo
generalapproachestoestimatingemissions:so-calledbottom-upmethodsthatsumup
measurementsand/orgenericemissionfactor-basedestimatesforindividualoperations
andequipmentintheoverallprocess,versustop-downmethodsbasedonmeasuring
concentrationsofmethaneintheatmosphereforsomeregioninwhichtherearenatural
gasand/oroilproducingoperations,thentranslatingthosemeasurementsinto
estimatesofemissionsassociatedwithnaturalgasandoilproduction,processingand
8
otherstages(dependingonwhatoperationsareoccurringinthestudyregion).Those
twoapproachesleadtoestimatedemissionsthatcandifferbyasmuchasanorderof
magnitude.Figure4belowshowssomeexamplesoftop-downcomparedwithEPA
bottom-upestimates.Notethatseveraltop-downestimatesshowninFigure4havea
medianvalueofabout10%leakage,comparedwiththeEPAestimatebetween1and2%.
Tables1and2beginwithoneestimate(Columns1&2)ofabottom-upapproach,the
Exxon-Mobilstudy,whichisnearthelowerendoftherangeofsuchestimates,(although
thereareevenlowerones).Itamountstoabout1.12%leakageofmethanefromthe
upstreamproductionandprocessingstagesofMarcellusshalefracking,inparticularin
theSouthwesternPennsylvaniapartofthatregion.Wealsogivehypothetical(3X)
estimates(Columns3&4)(basedonmultiplyingtheExxonMobilresultsbyafactorof
3)thatwebelievearerepresentativeofthemiddleofthetop-downestimatesandalso
arecomparabletothehigherendofbottomupestimates),whichisequivalentto
upstreammethaneemissionsofabout3.4%.TheExxonMobilresultsformethane
emissionappeartoberoughlyinthesamerangeassomeotherbottom-upestimates
nearthelowend,includingvaluesbasedonEPA’sGreenhouseGasEmissionInventory.
Thereareanumberofgeneralissueswithmostbottom-upstudies,includingthe
difficultyofassuringthatindividualmeasurementsmadetodetermineemissionfactors
arerepresentativeofthebroaderindustryoperations,andthatmostmeasurements
havebeenmadebyorincloseassociationwiththeproducingindustrythathasavested
industryinshowinglowemissions.(Itisdifficulttomakedetailedmeasurementsata
sitewithouttheoperator’scooperation,andtherealwaysisaquestionaboutwhether
theoperatormaydothingsdifferentlywhenheknowsresearchersorgovernment
inspectorsarepresent.)
Theparticularhigh-endestimateformethaneleakageweusehere(3.4%)iscomparable
tothetop-downresultsreportedinthestudybyPetronetal.(2014),viz.4.1±1.5%.
However,thatpertainedtonaturalgasproductionfromacombinationofoilandgas
wellsandsupportinginfrastructure.Thatstudyinvolvedatmosphericstudiesusing
variouscombinationsofground-basedairmonitors,aircraftmeasurements,andother
measurementsofmethaneandVOCconcentrations.Therehavebeenrelativelylarge
uncertaintyboundsontop-downmethods.(SeeboundsshowninFigure4below,but
alsothenewerZavala-Araizaetal.,2015studydiscussedbelow.)Theadvantageoftopdownestimatesisthattheytendtocaptureallthemethaneemissionsinaregion,
includingnaturalgasindustrysourcesthatmayhavemuchhigheremissionsthan
representedbyemissionfactors(andthereismuchevidencethatafewlargeleakage
sourcesaccountforadisproportionatecontributiontototals).Theirresultwas
nowhereneartheworst-caseleakageexampleamongtopdownstudies,someofwhich
foundvaluesofmethaneleakageontheorderof10%ormore,asshowninFigure4.A
leakagerateof3.4%isalsoconsistentwithhigherestimatesusingbottom-upmethods
fromtheliterature[forexample,seeBrandtetal.(2014)].Atmosphericmeasurements
donotmeasureCO2emissions,soweusethesameCO2estimatesfromLaurenziand
JerseyinthiscolumninTable1.Alsonotethatatmosphericmeasurementsdonot
necessarilycapturealltheindirectLCAvaluessincesomeofthosemayapplyto
9
operationsoutsidetheproducingareas,butthosetendtobethesmallerpartofthetotal
emissions.
AveryrecentreportbyZavala-Araizaetal.(2015)reconcilesbottom-upandtop-down
estimatesintheBarnettshaleoilandgas-productionregionofTexas.Itaugments
conventionalbottom-upinventories,accountsforhighemitters,andcomparesthemto
top-downaircraftstudiesinwhichethanemeasurementsareusedtocorrectfor
biogenicsources.Theirbottom-upinventoryis1.9timesestimatedemissionsbasedon
theEPAGHGIprogram,andrepresentsamethaneleakagerateof1.5%(1.2—1.9%).
TheAircrafttop-downmeasurementsoffossilmethaneaveragedabout10%higherthan
thebottom-upestimates,butstillwithinthetop-downuncertaintybounds.Those
resultsfortheBarnettregionindicateasignificantlysmallerleakageratethanthe
Petronetal.(2014)resultsobtainedintheDenver-Julesburggasandoilproduction
region.
TheZavala-Araizaresults(amethaneleakagerateof1.5%forupstreamproductionand
processingstages)suggestamediumleakagecaseinbetweenourbaseExxonMobil
valueandthe“Higher3X”leakageestimateof3.4%incolumnsthreeandfour.Ofcourse,
neitherofthoseestimatesfromotherbasinsnecessarilypertainstotheMarcellusshale
gasproductionregion,sowecannotsaywhetherourassumedmediumandhighvalues
intheTablesandFiguresareconsistent.Wedonotclaimthatthevalueof3.4%used
hereisavalidupperestimatefortheMarcellusregion,butonlythatitillustratesthe
potentialimpactofahigherestimatethatisslightlysmallerthanatop-downresultfrom
anotherregionthatinvolvedparticularlycomprehensivemeasurements.
AreportbyMarcheseetal.(2015)givesestimatesofemissionsfromthegasprocessing
andgatheringpipelinestages(whichstagesareincludedinourestimatesofProduction
andProcessing).Generallytheyfoundthattheirmeasurementsof16gasprocessing
plantswereevenlowerthanEPA’semissionfactors,butmeasurementsof114gathering
pipelinefacilitieswereoftenmuchhigherthanEPAemissionfactors.Afewofthe
smallergatheringfacilitiesappeartohaveleakageratesexceeding10%ofgas
throughput,butmostweremuchlessthanthat.Marcheseetal.didconcludethat:
“WhilethereisuncertaintyindetermininggatheringfacilityemissionsfromtheEPA
GHGI,theresultsofthisstudysuggestthattheGHGIsubstantiallyunderestimates
emissionsfromgatheringfacilities.
TheMarchesestudyindicatesthatemissionsfromgatheringlinesmaybeconsiderably
largerthanestimatedintheExxonMobilanalysis.However,suchincreasedmethane
emissionspresumablywouldalreadybeaccountedforinbroadregiontop-downstudies
thatarethebasisforourmediumandhighermethaneestimates,sotheredoesnot
appeartobeaneedtofactorthatintoourresultsincolumnsthreethroughsix.
Arecentreport,ConcernedHealthProfessionalsofNewYorkReport(2015),foundthat
(p.52-57):
10
“Leakagefromfaultywellsisanissuethattheindustryhasidentifiedandforwhichit
hasnosolution.AccordingtoSchlumberger,oneoftheworld’slargestcompanies
specializinginfracking,aboutfivepercentofwellsleakimmediately,50percentleak
after15years,and60percentleakafter30years.DatafromPennsylvania’s
DepartmentofEnvironmentalProtection(DEP)for2000-2012showovernine
percentofshalegaswellsdrilledinthestate’snortheasterncountiesleakingwithin
thefirstfiveyears.Leaksposeseriousrisksincludingpotentiallossoflifeor
propertyfromexplosionsandthemigrationofgasorotherchemicalsintodrinking
watersupplies.
“Leaksalsoallowmethanetoescapeintotheatmosphere,whereitactsasamore
powerfulgreenhousegasthancarbondioxide.Indeed,overa20-yeartimeframe,
methaneis86timesmorepotentaheataccumulatorthancarbondioxide.Thereis
noevidencetosuggestthattheproblemofcementandwellcasingimpairmentis
abating.Indeed,a2014analysisofmorethan75,000compliancereportsformore
than41,000wellsinPennsylvaniafoundthatnewerwellshavehigherleakagerates
andthatunconventionalshalegaswellsleakmorethanconventionalwellsdrilled
withinthesametimeperiod.Industryhasnosolutionforrectifyingthechronic
problemofwellcasing/cementleakage.”
CombustionStage.CO2emissionsfromthenaturalgas-firedcombustion(e.g.,power
plant)stagedependmainlyontheamountofgasconsumed,whichinthiscaseissimply
thethroughputofthepipeline,andslightlyonthecompositionofnaturalgas(which
changestheCO2percubicfoot).EffectivelyweusedthelatterfactorfromLaurenziand
JerseysincetheybaseditontypicalpipelinenaturalgasproducedintheMarcellusshale
region(ratherthanEPA’snominalemissionfactor).Anycombustionuseofthe
transmissionlinenaturalgasthroughputwouldgivethesameresult.However,natural
gasdeliveredfurtherforusethroughlocaldistributionlineswouldhavehigheroverall
CO2eqemissionsbecauseofthesubstantialextraleakageofmethaneinmany
distributionsystems.GHGemissionspublishedbyLaurenziandJerseyfromthisstage
arejustfromcombustion,arenotbasedonalifecycleanalysis,anddonotaccountfor
anyleakageofmethaneorunburnedmethaneinthepowerplantexhaustorprecombustionhandling.WhilewecouldnotfindadefinitiveemissionfactorfromEPAfor
methanespecifictoNGCCpowerplants,NETL(2010)givesthefactor8.56E-06
kg/MWhforNGCCplants3.ThatwouldbenegligiblecomparedwiththeCO2emissions.
TransmissionandStorage(T&S)Stage.Ourbaseestimateforthisstageisbasedona
differenttreatment.TheExxonMobilanalysisdidnotbasetheirestimateonalife-cycle
analysisoradetailedcalculationofemissionsfrompipelinefacilities.Rather,ittakes
3Methaneemissionfactorsvarywiththetypeofcombustionprocess;methaneandN O
2
emissionsfromsimplegasturbinesandotherenginesusedtopowerpipeline
compressorsarenotassmall;e.g.,EPA’sAP-42GHGemissionfactorsfornaturalgasfiredturbinesare0.003lb/MMBtuforN2Oand0.0086forCH4,whichtogetheramount
toabout1.4%oftheCO2emissionswhentheAR520-yearGWPsforthosegasesare
applied(268forN2O).
11
2009EPAestimatesoftotalT&SfugitivemethaneemissionsandtotalCO2from
compressorstocalculatetheratiotototalnaturalgaswithdrawalsthatyear.That
resultsinanaverageleakagerateof0.45%ofmethaneandanaverageamountofCO2
emissionsof82Kg/MMScfoftransportedgas.Weonlyhavelimitedinformationabout
thetwoproposedpipelines,suchaslengths,sizes,compressorhorsepower,and
maximumgasthroughputperday.Theredonotappeartobeanyemissionfactors
availabletoestimatepipelineemissionsbasedonlyonthoseparameters.Giventhose
limitationsandthegenericnatureofinformationfromtheLaurenziandJersey(2013)
paperabouttheassumptionsanddatafortheiremissionestimatesoftheTransmission
andStoragestage,itdidnotappearfeasibletoestimatehowtheirgenericestimatesof
methaneshouldscalewithvariouspipelineparameters,otherthanadirectscalingwith
pipelinethroughputcapacity.WealsonotethatGHGemissionestimatesfromthe
pipelineproponentsdonotyetappeartobeavailable.Thatmayespeciallybeimportant
forthedirectemissionvaluesforpipelineoperations.TheanalysisofLaurenziand
Jersey(2013)assumesa0.45%CH4leakrateintransmissionbuttheydonotstate
specificassumptionsabouttransmissionmiles,compressorHPandotherfactors.
Rather,theyassumeafractionoftotalEPAestimatesforpipelineCH4leakageand
compressorCO2emissionsin2009basedonthefractionofgrossgaswithdrawals.The
ACPandMVPtransmissionpipelines,totaling554.6milesand294miles,respectively,
maynotbetypicalofthelengthandleakageratesimplicitintheLaurenziandJersey
analysis.Itwouldbedesirabletoupdatethoseestimateswhenmorespecific
informationbecomesavailable.
Subramanianetal.(2015)recentlypublishedanonsitestudyofcompressorstation
emissions.Itincludesmeasurementsofmethaneemissionsfrom47transmissionline
compressorandstoragesites.Thisisclaimedtobethemostcomprehensivesetof
measurementssincethe1996jointEPA/GasResearchInstitutestudy.However,the
measuredfugitivemethaneemissionestimatesvarybyseveralordersofmagnitude
amongstationsandthestudyfoundnocorrelationbetweenemissionsandcompressor
horsepower.Thoseresults,togetherwithresultsofotherstudies,indicatethatthere
arelargevariationsinemissionsamongdifferenttechnologiesusedinequipment,
probablyintheamountofeffortcompaniesspendonmaintenanceofthingslikesealson
compressors,valves,andleaks,andperhapsalsointheeffortsspentonmonitoringto
detectleaks.4Becauseofthewidevarianceintheseresultsandthelackofclear
correlationtopipelineparameterssuchastotalhorsepowerandsizeofpipeline,we
wereunabletousetheresultstoreplaceorcomparedirectlywiththoseofthe
ExxonMobilstudy.
4AnEPAbackgroundstudy,EPA(2014),preparedforanalysisofaproposedNSPS
standard,estimatedthefollowingmethaneemissionsachievablepercompressorfor
eachofthethreetypesoftransmissioncompressor:27.1metrictonne/yearfor
reciprocating,126forcentrifugalwithwetseals,and15.9forcentrifugalwithdryseals,
butthoseestimatesapparentlydonotincludealltheothercomponentsatacompressor
station,whichinpracticecancontributesubstantialemissionsduetoleakage,venting
andexhaustemissions.
12
Zimmerleetal.(2015)publishedarecentstudyoftheU.S.naturalgastransmissionline
andstoragesystem(T&S)methaneemissions.Thisstudy’sestimatedoverallUS
transmissionandstoragesectoremissionsfor2012as1503Gg/yr,whichwerewithin
theirstatisticaluncertaintyofEPA’sGHGIestimatedvalueof2071Gg/yr.Theyalso
foundsuperemitterstationsthatappeartobeduetoequipmentorcontrolmalfunctions.
OnecancomparethoseleakageestimateswiththeU.S.totalvaluethattheExxonMobil
studyusedasthebasisfortheirgenericestimateofpipelineemissions,whichwas2,115
Gg/yrfor2009,or0.45%oftotalgasproduction.Sincetotalgrosswithdrawalsin2012
wereabout16.5%largerthanin2009,theZimmerlestudyvalueof1503Gg/yr
correspondstoamethaneleakagerateofabout40%lessthantheExxonMobilstudy,or
about0.27%ofgrosswithdrawals(apparentrangeof0.23to0.39%).However,bothof
thoseestimatesrefertoaveragesoveranationalmixofdifferentpipelinesofdifferent
sizes,agesandcapacities,soitisquestionablewhethertheycanbeapplieddirectlyto
specificnewtransmissionpipelineprojects.TheZimmerleetal.studyincludesthe
resultsfromSubramanianetal.(2015)atindividualcompressorstationandstorage
sites,butapparentlyextendstheanalysis.Theyfitalltheirresultstoseveraldifferent
modelsinordertodrawconclusionsabouttheoverallpopulationofsites,includingthe
U.S.totalT&Semissionscitedabove.However,itagainitisdifficultforustointerpret
thoseresultsintermsofspecificestimatesfortheACPandMVPpipelines.
13
Fig.4.ChartfromSchneisingetal.(2014).(Figureandcaptioncopied
directlyfromFigure7oftheirreport)
14
ConclusionsandRecommendations
ThepotentialtotalGHGemissionsassociatedwiththesetwoproposednew
pipelinescouldgreatlyincreaseemissionsfromthisregionfordecadesintothe
future.Hence,inanerawhereclimatechangemitigationwillrequirereducingGHG
emissionssharply,decisionmakersneedtoconsiderwhetherapprovalofthese
projectsisconsistentwithnationalandinternationalgoalsforclimatemitigation.
Giventheobservedwidevariationinmethaneemissionsandtheveryhightotal
potentialGHGemissions,itisimportantthatthetransmissionpipelinecompanies
andFERCprovidecompletelife-cycleestimatesofmethaneandCO2emissionsfrom
theirprojectsfortheEISfortheirproposedpipelineprojects,togetherwithdetailed
documentationoftheirassumptionssothatthepotentialGHGemissionsandother
environmentalimpactsofthepipelinestagecanproperlybejudged.Itisclearthat
expandinggasusageandsupportingitwithnewpipelinesandproductionimplies
substantiallygreatertotalGHGemissionsthanappearwhenagenciesoradvocates
focusononlyonestageatatimeandignoretheindirectimpactsoftheimmediate
project.
FERCmustrecognizethattheemergingworldcommitmenttocutGHGemissions,as
evidencedbytherecentUNFCCCCOP21agreementinParis,willmeanthatthe
operatinglivesofnewnaturalgasinvestmentsarelikelytobesubstantiallyshorter
thanthetraditionalassumptionthatapipelinewilloperateforthirtyormoreyears.
Expandinginvestmentsbasedonsuchrosyassumptionswillleadtosubstantial
strandedinvestments,inadditiontoincreasedglobalwarmingfromexcessiveGHG
emissions.Theseareamplegroundsforrejectingcertificateapplicationsfor
expandednaturalgaspipelinecapacity.Ataminimum,pipelineinvestorsshouldbe
placedatriskforunder-recoveryofinvestmentsasaresultofovercapacityfor
transportationofnaturalgasthatcannotcontinuetobeburnedathistoric,letalone
expanded,levelsforseveraldecadesintothefuture.
Furthermore,ifFERCdecidestoalloweitheroftheproposedpipelinestoproceed,it
shouldrequiredetailedmaintenanceandemissionmonitoringplansfornewand
associatedexistingpipelinesandcompressorstationsadequatetopreventleaksand
detectallreleasesofmethanetotheatmosphereinatimelyfashionsothat
substantialleakscanquicklyberemedied,bothforpublicsafetyandtominimizethe
climateimpactsofGHGemissions.
References
Alvarezetal.(2012):Alvarez,R.A.,etal.,“Greaterfocusneededonmethaneleakage
fromnaturalgasinfrastructure”,PNAS,109,6435–6440,April24,2012.
Brandtetal.(2014):Brandt,A.etal.“MethaneLeaksfromNorthAmericanNatural
GasSystems”,Science343,733(2014)DOI:10.1126/science.1247045
15
ConcernedHealthProfessionalsofNewYork,“CompendiumOfScientific,Medical,
AndMediaFindingsDemonstratingRisksAndHarmsOfFracking(Unconventional
GasAndOilExtraction)”ThirdEdition(October14,2015),p.52-57.
“ExxonMobilReport”LaurenziandJersey(2013):Laurenzi,J.,andG.Jersey,“Life
CycleGreenhouseGasEmissionsandFreshwaterConsumptionofMarcellusShale
Gas”,Env.Sci.&Technol,dx.doi.org/10.1021/es305162w.
Marcheseetal.(2015):Marchese,A.J.,etal.,“MethaneEmissionsfromUnitedStates
NaturalGasGatheringandProcessing”,DOI:10.1021/acs.est.5b02275
Environ.Sci.Technol.
NETL (2010): “LifeCycleAnalysis:NaturalGasCombinedCycle(NGCC)Power
Plant“,DOE/NETL-403/110509.
Petronetal.(2014):Pétron,G.,etal.(2014),“Anewlookatmethaneand
nonmethanehydrocarbonemissionsfromoilandnaturalgasoperationsinthe
ColoradoDenver-JulesburgBasin”,J.Geophys.Res.Atmos.,119,6836–6852,
doi:10.1002/2013JD021272.
Schneisingetal.(2014):Schneising,O.,J.P.Burrows,R.R.Dickerson,M.Buchwitz,
M.Reuter,andH.Bovensmann(2014),Remotesensingoffugitivemethane
emissionsfromoilandgasproductioninNorthAmericantightgeologicformations,
Earth’sFuture,2,doi:10.1002/2014EF000265
Subramanianetal.(2015):“MethaneEmissionsfromNaturalGasCompressor
StationsintheTransmissionandStorageSector:MeasurementsandComparisons
withtheEPAGreenhouseGasReportingProgramProtocol”,
DOI:10.1021/es5060258,Environ.Sci.Technol.2015,49,3252−3261
EPA (2014): EPA OAQPS, “ OilandNaturalGasSectorCompressorsReportforOil
andNaturalGasSectorCompressorsReviewPanel”,April2014.
G.Vaidyanathan,“Whichoilandgascompaniesareleakingthemostmethane?”
http://www.eenews.net/climatewire/2015/06/26/stories/1060020954(June26,
2015).
Zavala-Araizaetal.(2015):Zavala-AraizaD.etal.,“Reconcilingdivergentestimates
ofoilandgasmethaneemissions”,
www.pnas.org/cgi/doi/10.1073/pnas.1522126112
Zimmerleetal.(2015):“MethaneEmissionsfromtheNaturalGasTransmissionand
StorageSystemintheUnitedStates”,Environ.Sci.Technol.2015,49,9374−9383.
16
iPreparedfortheVirginiaChapterSierraClubwithcontributionsbyRichardH.Ball,Ph.D.,volunteer
SustainableEnergyChair,WilliamPenniman,Esq.,volunteerConservationChair,andKirkBowers,
PE,PipelinesProgramManager,VirginiaChapter.
17