Gathering and Processing
FORT COLLINS - Researchers led by Colorado State University have published the latest results from the largest, most comprehensive study ever conducted on methane emissions from natural gas gathering facilities and processing plants.
The study, published on August 18, 2015 in the journal Environmental Science & Technology, used data from methane measurements conducted at 114 natural gas gathering facilities and 16 processing plants in 13 states over 20 weeks to develop an estimate of total methane emissions from all U.S. gathering and processing operations. The latest publication is the third manuscript published to date from the CSU gathering and processing study.
Methane Emissions from the Natural Gas Supply Chain
The primary component of natural gas, methane is a greenhouse gas many times more potent than carbon dioxide when released into the atmosphere unburned. The nation’s vast natural gas infrastructure – including wells, compressor stations, processing plants, pipelines, and storage facilities – constitutes the largest industrial source of methane emissions in the United States. The gathering and processing study is part of a series of methane emissions studies organized by Environmental Defense Fund, representing the largest measurement campaign of the U.S. natural gas infrastructure to date.
Natural Gas Gathering and Processing
Gathering facilities collect and compress natural gas from multiple wells then send the gas to a transmission line or a processing plant where ethane and natural gas liquids are removed. In addition to large natural gas-powered compressors, both gathering and processing facilities include equipment such as liquid separators, dehydration systems, acid gas removal systems and liquid storage tanks. Processing plants also include additional systems to remove the ethane and/or natural gas liquids. While all processing plants are required to report methane emissions under EPA’s Greenhouse Gas Reporting Program, very few gathering facilities are currently required to report methane emissions.
The study found that 0.47 % of the methane produced domestically is lost during gathering and processing operations. According to the study, methane emissions from gathering systems are equivalent to 30 percent of overall methane emissions from natural gas operations in the current U.S. EPA Greenhouse Gas Inventory (currently estimated at 6,186 Gg).
The researchers also identified opportunities to improve the two federal programs that track methane emissions from the natural gas supply chain, EPA Greenhouse Gas Reporting Program (GHGRP) and EPA Greenhouse Gas Inventory (GHGI). The GHGI does not explicitly break out gathering facilities as a category separate from field production. The CSU study team, which also included researchers from Carnegie Mellon University and Aerodyne Research, analyzed the current production inventory to determine the appropriate fraction of emissions to assign to gathering, and the results were eight times higher than the best interpretation of EPA data for gathering facilities. The majority of the methane emissions from gathering and processing operations were attributed to normal operations of gathering facilities. Researchers found that methane emissions from gathering facilities are substantial – 1,697 Gigagrams (Gg) per year — while emissions from processing plants are less than half that amount — 505 Gg per year. These emissions are equivalent to the amount of natural gas consumed annually by 3.2 million U.S. homes and represent a potential loss of $390 million in revenue to producers.
Processing plant methane emissions are reported to the GHGRP. Depending on the type, many processing plants are also subject to regulations that require companies to periodically monitor their facilities for leaks and make a first attempt to repair any leaks found within five days. Gathering facilities are not presently subject to those regulations and only a small fraction of gathering facilities report methane emissions to the GHGRP.
The study compared processing plant emissions to those in the GHGRP and found methane emissions from processing plants were three times higher than the GHGRP. Currently, methane emissions reported from gathering facilities are very low — less than 1 Gg per year – because very few of these facilities are required to report methane emissions according to current EPA rules. The EPA has proposed a rule that would require gathering systems to report methane emissions.
The CSU team did not measure emissions from natural gas gathering lines in this study. Future studies need to be conducted to accurately determine the total amount of gathering pipelines in the U.S. and their methane leakage rates.
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. doi:10.1021/acs.est.5b02275.
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) 3219-3227.
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, 2017-2035. Additional Data.