Methane Emissions from U.S. Natural Gas Gathering and Processing Anthony Marchese 1,*, Daniel Zimmerle 2, Timothy Vaughn 1, David Martinez 2, Laurie Williams 2, Allen Robinson 3, Austin Mitchell 3, Daniel Tkacik 3, R. Subramanian 3, Scott Herndon 4, Rob Roscioli 4 1 Department of Mechanical Engineering, Colorado State University, 2 The Energy Institute, Colorado State University, 3 Department of Mechanical Engineering, Carnegie Mellon University, 4 Aerodyne Research * Principal Investigator, Presentation to the National Oil and Gas Emissions Committee September 10, 2015

2 Methane Emissions from U.S Gathering and Processing Overview Background and Objectives Field Campaign Measurement Results Modeling Approach for National Estimate Model Results Comparison to EPA GHGI and GHGRP

3 Partners Environmental Defense Fund, Anadarko Petroleum, Access Midstream, Williams, SWN, Hess, DCP Midstream* Total Partner Facility Inventory 738 gathering facilities 28 processing plants Study Team Colorado State University (Anthony Marchese, Dan Zimmerle) Carnegie Mellon University (Allen Robinson) Aerodyne Research (Scott Herndon) *DCP provided access to one randomly chosen processing plant but did not provide funding. Methane Emissions from U.S Gathering and Processing Study Team

4 The gathering and processing sectors are defined as all NG industry assets and operations that take place between two custody transfer points: the well site delivery meter and the receipt meter to the transmission sector Gathering and Processing Systems = gathering pipelines, gathering compressor/booster stations and processing plants Methane Emissions from Gathering and Processing Sector Definition Processing Plant Gathering Lines Gathering Facility Gathering pipelines were not measured as part of this study

5 Methane Emissions from Gathering and Processing Gathering Facility CH 4 Emission Sources A gathering facility is a centralized facility that accepts gas from multiple gas wells (10 < N < 100), compresses the gas and sends the gas to a processing plant or to transmission. In many cases these facilities also remove liquid water, water vapor, H 2 S, CO 2. Gathering Compressor Glycol Contact Towers for H 2 O Dehydration Amine Treatment System to Remove H 2 S and/or CO 2 Produced Water and/or Hydrocarbon Condensate Tanks

6 A Subpart KKK processing plant includes much of the same systems as a gathering facility (compression, dehydration, treatment) but also includes systems (often cryogenic) to remove natural gas liquids. These plants are often much larger (and higher NG throughput) than gathering. Cryo-Tower to Remove Natural Gas Liquids (NGL’s) Methane Emissions from Gathering and Processing Processing Plant CH 4 Emission Sources

7 Methane Emissions from U.S Gathering and Processing Motivation and Challenges Very little data exist on CH 4 emissions from processing plants and gathering facilities. No national databases exist for gathering: facility counts, equipment, gathering pipeline miles, etc. The EPA Greenhouse Gas Inventory (GHGI) includes gathering systems (pipelines and facilities) as part of its natural gas production inventory. Very few gathering facilities (≈ 10%) are required to report CH 4 emissions under the EPA Greenhouse Gas Reporting Program (GHGRP). Gathering facilities that are required to report CH 4 emissions report only Subpart C combustion emissions. Processing plants do not report all source categories under EPA GHGRP.

8 The goal of this study was to quantify methane emissions from all U.S. gathering and processing systems and operations: Methane Emissions from U.S Gathering and Processing Objectives of the Study 1.Measure facility-level CH 4 emissions from all partner processing plants (N ≈ 24); 2.Measure facility level CH 4 emissions from randomly selected gathering facilities (N ≈ 120); 3.Compile facility data (e.g. facility count, equipment, NG throughput) using partner (N=768), state and national data bases; 4.Develop a Monte Carlo model to estimate methane emissions from all U.S. gathering facilities (N ≈ 5000) and processing plants (N ≈ 600); 5.Compare model results against existing methane emissions estimates/inventories (e.g. EPA GHGI; EPA GHGRP).

9 Study Partner Assets Study partner assets included 738 gathering facilities and 28 Subpart KKK processing plants located in 13 U.S. states. Methane Emissions from U.S Gathering and Processing Field Campaign

10 Methane Emissions from U.S Gathering and Processing Field Campaign Comprehensive Measurements Facility-level CH 4 emissions were acquired from 16 processing plants and 114 gathering facilities in 13 U.S. states in 20 weeks.

11 Methane Emissions from the G&P Sectors Dual Tracer Gas Method Roscioli, J. R., Herndon, S. C., et al (2015). Measurements of methane emissions from natural gas gathering facilities and processing plants: measurement methods. Atmos. Meas. Tech., 8, C 2 H 2 Tracer Release Point Mobile Laboratory Tracer Release Vehicle

F CH4 = F tracer x ΔC CH4 ΔC tracer Facility-level methane emissions are determined from downwind CH 4, C 2 H 6 and tracer gas (C 2 H 2, N 2 O) measurements Uncertainty = error + interference + other Methane Emissions from the G&P Sector Dual Tracer Gas Method Onsite tracer release Downwind measurement C 2 H 2 tracer N 2 O tracer CH 4 C2H6C2H6

Weighted Average Facility-Level Emissions of CH 4 Example Result of C/D Facility Weighted average: ±19.9 kg/hr

14 Methane Emissions from the G&P Sectors Facility-Level CH 4 Emission Rates 9% Emitter (660 kg/hr) Mid-Size C/D Station (9.5 MMscfd) Three (3) 1150 HP recips Noticeable venting from PW Tanks 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) High Emitters: 25 facilities had methane loss rates > 1% 1%

15 Methane Emissions from the G&P Sectors Facility-Level CH 4 Emission Rates Facility-Level Methane Emissions (kg/hr) and Loss Rate(%) 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

16 Methane Emissions from the G&P Sectors “ Back of the Envelope” Estimates Gathering Facilities (0.42% CH 4 loss rate) x (421 Tg CH 4 gathered in 2012) ≈ 1770 Gg ( ≈ 4500 facilities) x (56 kg/hr/facility) ≈ 2200 Gg Subpart KKK Processing Plants (0.08% CH 4 loss rate) x (287 Tg CH 4 processed in 2012) ≈ 230 Gg ( ≈ 600 facilities) x (170 kg/hr/facility) ≈ 890 Gg Median loss rates (%) and facility-level emission factors (kg/hr/facility) can provide order of magnitude estimates of how the emissions might scale nationally. Even without a sophisticated model, the experimental results indicate that methane emissions from gathering facilities are substantial (≈ 30% of entire NG supply chain methane emissions).

17 Methane Emissions from the G&P Sectors Development of National Estimate Issues for Scale Up: Facility size varies over several orders of magnitude (0.1 to 1000 MMscfd) Emissions vary with throughput. Large variation in emissions for a given throughput range. Natural gas can flow through multiple gathering/boosting stations during transit from the production site to transmission. Scale Up of CH 4 Measurements to National Estimate Scale up to a national estimate requires: Accurate facility count of all gathering facilities and processing plants Average natural gas throughput (MMscfd) or proxy such as installed compressor engine power for each facility

18 Gathering Facility Data Methane Emissions from the G&P Sectors Development of National Estimate Natural gas facility lists (with installed compressor engine data) were obtained from state air permit data from AR, CO, OK, TX, NM, PA, WY and LA - these states account for ≈ 83% of U.S. natural gas production. The initial lists contained production sites, gathering facilities, processing plants and transmission stations.

19 Establishing Confidence Intervals for State Gathering Facility Inventories Methane Emissions from the G&P Sector Development of National Estimate Gathering facility lists (200<N<1000) were generated from the state NG facility lists using company names, industry segment codes, equipment types (i.e. engine make/model/HP) and satellite imagery. To establish confidence intervals in the facility counts, a random sample was drawn from each original list (1500 < N <10,000) and the initial facility designation was compared “double blind” by two independent experts. Gathering Not Gathering Marchese, A.J., Zimmerle, D.J, Vaughn, T. L. et al (2015). Methane emissions from United States natural gas gathering and processing. Environ. Sci. Technol /acs.est.5b02275.

20 Gathering Facility Counts Methane Emissions from the G&P Sector Development of National Estimate StateData Source Identified Gathering Facilities Known Partner Gathering Facilities Identified Partner Gathering Facilities Extrapolated Gathering Facilities AR Arkansas Department of Environmental Quality CO Colorado Oil and Gas Conservation Commission LA Louisiana Department of Environmental Quality NM OK Oklahoma Department of Environmental Quality PA Pennsylvania Department of Environmental Protection - Bureau of Air Quality TX Texas Commision on Environmental Quality * WY Wyoming Department of Environmental Quality

21 Methane Emissions from the G&P Sectors Development of National Estimate Monte Carlo Simulation Scheme (Gathering) Installed compressor engine power is used as a proxy for facility natural gas throughput. For each facility in a state database, an emissions value is randomly drawn from among the 10 sampled facilities with closest HP. Experimental uncertainty and uncertainty in facility count included. Process is repeated for 50,000 iterations. Annual gathering methane emissions (Gg) and confidence intervals predicted for each state in the model from median and 97.5% confidence intervals. Colorado: 69 (+25/-21) Gg of CH 4 from 193 (+46/-35) facilities

22 Monte Carlo Simulation: Gathering Results Methane Emissions from the G&P Sectors Development of National Estimate Total annual emission of methane (Gg) from all gathering facilities in the states of AR, CO, LA, OK, PA, TX and WY, and extrapolated U.S. results. State Number of Gathering Facilities Annual Emission of CH 4 from Gathering Facilities (Gg) 2012 CH 4 Gathered (Gg) Modeled CH 4 Loss Rate (%) AR214 (+43/-38)53 (+20/-25)19, % (+0.10%/-0.08%) CO193 (+46/-35)69 (+25/-21)28, % (+0.09%/-0.07%) LA364 (+62/-124)104 (+42/-36)50, % (+0.08%/-0.07%) NM282 (+82/-82)96 (+40/-33)20, % (+0.20%/-0.16%) OK1103 (+132/-132)322 (+56/-52)34, % (+0.16%/-0.15%) PA247 (+22/-7)70 (+16/-14)37, % (+0.04%/-0.04%) TX1012 (+304/-101)616 (+124/-118)126, % (+0.10%/-0.09%) WY382 (+77/-66)86 (+25/-22)34, % (+0.07%/-0.06%) Total States in Model 3,797 (+768/-587)1,417 (+158/-154)351, % (+0.05%/-0.04%) Total U.S.4,549 (+921/-703)1,697 (+189/-185)420, % (+0.05%/-0.04%)

23 Monte Carlo Simulation Results for Processing Methane Emissions from the G&P Sectors Development of National Estimate Cumulative distribution function of predicted total annual emission of methane (Gg) from all U.S. Subpart KKK processing plants. Model results predict 506 Gg +55/-52 Gg for normal operation. Processing: 506 (+55/-52) Gg of CH 4 from 592±14 Subpart KKK plants

24 Processing Methane Emissions from the G&P Sectors Comparison to EPA GHGI 2014 EPA Inventory of CH 4 emissions (Gg) for processing plants under normal operation is 851 Gg, which is higher than our estimate of 506 Gg (+55/-52 Gg) Majority of CH 4 emissions in processing inventory are from compressor fugitives and exhaust. Observations from the field campaign suggest differences in reciprocating and centrifugal compressor activity data: 3890 reciprocating 1473 centrifugal

25 Gathering. The 2014 EPA Greenhouse Gas Inventory (GHGI) embeds gathering systems (pipelines and facilities) within its natural gas production inventory. Methane Emissions from the G&P Sector Comparison to EPA GHGI We tabulated all source categories in the EPA GHGI production inventory common to both gathering and production. A total of 1,431 Gg of methane emissions are attributed source categories common to both gathering and production. The model results for gathering facilities alone (1,697 Gg) are greater than all of the source categories common to both gathering and production in the EPA GHGI (1,431 Gg).

26 Methane Emissions from the G&P Sector Comparison to EPA GHGI Gathering. The 2014 EPA Greenhouse Gas Inventory (GHGI) embeds gathering systems (pipelines and facilities) within its natural gas production inventory. We then used field observations to estimate the fraction of the combined inventory to assign to “gathering”. Based on this approach, we estimate that only 404 Gg of the combined GHGI inventory is attributed to gathering sector, of which on 226 Gg is attributed to gathering facilities. The relatively small fraction of activity data assigned to “gathering” is consistent with Allen et al (2015) observations that suggest a high volume of equipment at production sites: 124,000 heaters 495,000 separators 36,000 dehydrators 12,000 compressors 1,608,000 pneumatic controllers 247,000 liquid tanks

27 Comparison of measured annual equivalent methane (Mg) for the sampled processing plants (N=16), average annual emissions reported under the 2011 to 2013 EPA CHGRP for the same processing plants (N=16) and all processing plants that reported emissions for which average daily natural gas throughput was available (N=246). The total methane loss rate for the 246 plants that reported under the GHGRP was 0.044%, which is less than 1/4 of our modeled loss rate of 0.18%. Methane Emissions from the G&P Sectors Comparison to GHGRP: Processing Approximately 50% of the reported CH 4 emissions in both the larger GHGRP (N=246) and the sampled plant dataset (N=16) were less than 200 Mg, whereas only 2 of 16 annualized CH 4 measurements were below this value.

28 Comparison of national estimate of CH 4 emissions from U.S. natural gas gathering systems and processing plants with 2014 EPA Greenhouse Gas Inventory and 2013 EPA Greenhouse Gas Reporting Program. Methane Emissions from the G&P Sectors Comparison to EPA Programs

29 Methane Emissions from the G&P Sectors Methane Loss Rates National estimate of total CH 4 emissions (Gg) and rate of CH 4 loss (%) for U.S. natural gas gathering and processing systems (gathering lines, gathering facilities and processing plants). Comparisons are made against the 2014 EPA GHGI. Gathering Facilities Gathering Lines a Processing Plants (Normal Ops) Processing Plants b (Blowdowns) Total Study Results Total CH 4 Emissions (Gg) 1697 (+189/-185) (+55/-52) (+245/-237) Sub-category CH 4 Loss Rate c (%) 0.40%0.04%0.18%0.01% U.S. Natural Gas Supply Chain CH 4 Loss Rate d (%) 0.33%0.04%0.10%0.01%0.47% EPA GHGI Total CH 4 Emissions (Gg) 226 e ,296 Sub-category CH 4 Loss Rate c (%) 0.05%0.04%0.30%0.01% U.S. Natural Gas Supply Chain CH 4 Loss Rate d (%) 0.04% 0.17%0.01%0.25% a. Unmodified from EPA GHGI estimates, includes pipeline leaks, blowdowns and mishaps b. Unmodified from EPA GHGI estimates, includes routine blowdowns and venting c. Normalized by 421 Tg of total CH4 gathered in 2012 and 287 Tg of CH4 processed in d. Normalized by 513 Tg of total production of CH4 for e. As derived from apportionment of combined gathering /production inventory as described in SI Section S.6.2

30 1.Facility-level CH 4 emissions were measured at 16 processing plants: median CH 4 loss rate < 0.1% 2.Facility-level CH 4 emissions were measured at 114 gathering facilities: median CH 4 loss rate = 0.42% 3.Scale up modeling results suggest annual methane emissions of 1,697 Gg from ≈ 4,600 gathering facilities and 506 Gg of methane emissions from ≈ 600 Subpart KKK processing plants. 4.The total rate of methane loss from gathering and processing is estimated to be 0.47% when normalized by 2012 annual production. 5.Methane loss during gathering and processing is equivalent to the annual natural gas consumption from 3.2 million U.S. homes and has a value of $390 Million. Methane Emissions from Gathering and Processing Summary of Major Findings

31 Methane Emissions from Gathering and Processing Summary of Major Findings 6.Estimated methane loss from processing plants (546 Gg) is less than EPA GHGI (891 Gg) but higher than EPA GHGRP (179 Gg). 7.Estimated methane loss from gathering facilities (1,697 Gg) is higher than EPA GHGI (≈ 226 Gg) and EPA GHGRP (<0.5 Gg). 8.Not all source categories for processing plants are reported under GHGRP and very few gathering facilities (<10%) are required to report any methane emissions under current regulations. 9.Observations from field campaign suggest that emissions can be reduced from gathering by incorporating systems and/or practices to quickly identify and repair high emitting gathering facilities. 10.Emissions from gathering pipelines were not measured. Future studies should be conducted to better quantify total length and emission factors.

32 Methane Emissions from Gathering and Processing Publications 1.(August 2015) Marchese, A.J., Zimmerle, D.J, Vaughn, T. L., Martinez, D.M., Williams, L., Robinson, A.L., Mitchell, A.L., Subramanian, R.A., Tkacik, D.S., Roscioli, J.R. and Herndon, S.C. (2015). Methane emissions from United States natural gas gathering and processing. Environ. Sci. Technol /acs.est.5b (May 2015) Roscioli, J. R., Yacovitch, T. I., Floerchinger, C., Mitchell, A. L., Tkacik, D. S., Subramanian, R., Martinez, D. M., Vaughn, T. L., Williams, L., Zimmerle, D., Robinson, A. L., Herndon, S. C., and Marchese, A. J. (2015). Measurements of methane emissions from natural gas gathering facilities and processing plants: measurement methods. Atmos. Meas. Tech., 8, (February 2015) Mitchell, A.L., Marchese, A.J., Zimmerle, D.J, Vaughn, T. L., Martinez, D.M., Williams, L., Robinson, A.L.,, Subramanian, R.A., Tkacik, D.S., Roscioli, J.R. and Herndon, S.C. (2015). Measurement of methane emissions from natural gas gathering facilities and processing plants: measurement results. Environ. Sci. Technol., 49 (5) The paper published today in Environmental Science and Technology is the third paper published to date on this study:

33 Methane Emissions from the G&P Sector Backup Slides