Methane Emissions from the US Natural Gas Infrastructure R Subramanian Scott Herndon, Rob Roscioli, Austin Mitchell, Dan Zimmerle, Anthony Marchese, and Allen Robinson

Funding, data, technical input: Environmental Defense Fund Kinder-Morgan NiSource TransCanada Dominion Williams Enable Dow INGAA Anadarko Access Midstream SWN Hess DCP*

3 Methane Emissions from Transmission and Storage

Transmission & Storage Sector 300,000 miles of pipelines ~2000 compressor stations Older facilities often reciprocating compressors Powered by gas reciprocating engines Newer/larger units centrifugal compressors Driven by gas turbines Source: US EIA,

Top-down & bottom-up measurements at 45 compressor stations Compressor Types CategoryNumber GHGRP reporters Reciprocating compressors only Centrifugal compressor only Both types Sites with at least one compressor running Transmission Storage8 (10)27015 Total45 (47) GHGRP reporters: facilities that emit over 25,000 MT-CO 2 e/year Sixteen states, six partner companies, eleven weeks of parallel direct onsite and tracer flux measurements

Bottom-up: Direct Onsite Measurement of Methane Emissions Modeled on EPA GHGRP protocol, but more comprehensive Leak detection with FLIR thermal imaging Measure emissions with Hi-Flow, acoustic devices, turbine meters, bags Issues: Accuracy of some techniques questionable Some leaks may not be detected due to adverse wind Not all detected leaks are safely accessible Time-consuming for comprehensive measurements and at larger sites

“Top-Down” Downwind Dual Tracer Flux: Facility-Level Emission Rates N2ON2O C2H2C2H2 CH 4

Onsite & Tracer Flux Data: Details Reciprocating-only sites Centrifugal-only sites Facility-level CH 4 Emissions (SCFM)

Direct Onsite vs Tracer Flux: Mostly Agree

Onsite does not capture super- emitters Super-emitters: Sites emitting over 300 SCFM methane

GHGRP: NOP rod-packing venting not reported, OEL/connector emission factors low

GHGRP emission factors not appropriate for engine exhaust methane

The fat tail: super-emitters skew emissions distributions Cumulative Fraction of Sites Cumulative Methane Emissions (SCFM) Cumulative Fraction of TF Methane Emissions

14 Processing Plant Gathering Lines Gathering Facility Gathering pipelines were not measured as part of this study Methane Emissions from Gathering and Processing

15 G&P Field Campaign Tracer flux measurements at 16 processing plants and 114 gathering facilities (of Partner inventory of 28 & 738 facilities.)

16 G&P: Facility-Level Methane Emissions (kg/hr) & Loss Rate (% throughput) Mitchell, A.L., Zimmerle, D., Marchese, A.J., Robinson, A.L. et al. Measurements of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results. Environ. Sci. Technol., 49 (5) Median Loss Rate 0.42% Gathering: 56 kg/hr/facility Median Loss Rate 0.08% Processing: 170 kg/hr/facility

17 Mitchell, A.L., Zimmerle, D., Marchese, A.J., Robinson, A.L. et al. Measurements of Methane Emissions from Natural Gas Gathering Facilities and Processing Plants: Measurement Results. Environ. Sci. Technol., 49 (5) facilities had methane loss rates > 1% 1% 9% Emitter (660 kg/hr) Mid-Size C/D Station (9.5 MMscfd) Three (3) 1150 HP recips Noticeable venting from PW Tanks G&P: High- Emitters

18 9% Emitter (660 kg/hr) Mid-Size C/D Station (9.5 MMscfd) Three (3) 1150 HP recips Noticeable venting from PW Tanks At 22 of the 114 sampled gathering facilities, substantial venting was observed from liquids storage tanks and the methane emissions from these gathering facilities was 3X compared to facilities in which substantial tank venting was not observed. G&P: 9% emitter

Modeling Paper Measurement Paper From measurements to modeling Field Campaign Engineering Estimates Study Onsite Estimate Tracer Flux Measurement GHGRP Result Per Facility Comparison National Model Additional Data Sources Additional Partner Meas. GHGI & GHGRP National Comparisons

Summary Significant new measurements of methane emissions from the T&S and G&P sectors Tracer flux quantifies site-level methane emissions Includes* measurement of exhaust methane Quantifies super-emitters Make EPA GHG Reporting Program comprehensive Include all major emission sources and sectors Use updated emission factors, if not direct measurements Remove the 25,000 MT-CO 2 e reporting threshold Better identify and quantify super-emitters 10% of sites => 50% of T&S emissions 30% of sites => 80% of gathering emissions

Questions?

EPA T&S methane inventory Current: Emission factors: 1996 EPA/GRI (15 compressor stations) and 2010 ICF data Activity factors: Pipeline miles scaled to 1990s survey, with some modifications Future? Can we use the GHGRP data from ~500 compressor stations?

Downwind tracer flux: Facility- level Methane Emission Rates Lamb et al. (1995) used sulfur hexafluoride (SF 6 ) as tracer We use nitrous oxide (N 2 O) and acetylene (C 2 H 2 )

Tracer Flux: Method Assumptions Methane and tracer(s) equivalently dispersed Check correlation between methane and tracer(s) Second tracer verifies assumption All methane sources at a site captured downwind Dual tracers (up to 200m apart) encompass the site No other source of tracers Upwind and downwind transects with tracers off Background-corrected methane from target site Upwind transects Use ethane as a signature for natural gas methane

Ethane: Signature for natural gas emissions Ethane lifetime ~2 months, compared to ~10 years for methane Plume dominated by natural gas ethane, not background The Aerodyne TILDAS provides mobile 1-Hz ethane measurements Downwind Plume Measurements Partner-provided Gas Composition

Tracer flux: From plume capture to methane emission rates Uncertainty ±17% (dual tracer correlation) to ±34% (area plumes) Methane (ppm) Ethane (ppb) Acetylene (ppb) N 2 O (ppb)

Onsite Estimate vs Tracer Flux 1 standard ft 3 /min = 1.15 kg/hour

The EPA GHG Reporting Program From 2011, mandates reporting of CO 2, CH 4, N 2 O Only facilities that emit over 25,000 MT-CO 2 e (annualized)