New study finds wide variations in gathering systems’ methane samples

Feb. 11, 2015
Samples of methane emissions from 114 natural gas gathering stations and 16 processing plants across 13 states found wide variations in amounts actually released, a recent study revealed. Researchers at Colorado State University in Fort Collins, Carnegie Mellon University, and Aerodyne Research took the samples over 20 weeks starting in October 2013.

Samples of methane emissions from 114 natural gas gathering stations and 16 processing plants across 13 states found wide variations in amounts actually released, a recent study revealed. Researchers at Colorado State University in Fort Collins, Carnegie Mellon University, and Aerodyne Research took the samples over 20 weeks starting in October 2013.

Researchers found facility-level emissions ranging from less than 1 kg/hr to 696 kg/hr, while loss rates—the ratio of methane emitted to the amount of gas flowing through a facility—ranged from less than 0.01% to more than 10%.

A second study of methane emissions samples from gas transmission and storage operations by CSU, Carnegie Mellon, and Aerodyne Research teams found that just 2 of 45 sampled sites accounted for almost as much methane as the other 43 sites combined. It said the two sites’ higher emissions were likely due to a faulty valve.

Anthony Marchese, a CSU mechanical engineering professor who led the first study, said it was, by far, the largest and most comprehensive data set ever collected on direct methane emissions from gas gathering operations. “The results point to the gathering sector likely being a notable source of emissions and identify areas where emission reductions can be achieved,” he said.

The study, which was published on Feb. 10 in the American Chemical Society’s Environmental Science & Technology Journal, also found significant variations among facilities of similar size and type that apparently were driven by inlet and outlet pressure differences and abnormal process conditions.

This resulted in a few sites contributing to a majority of the emissions. For example, the study said about 30% of the gathering facilities accounted for nearly 80% of the methane emissions measured.

Abnormal condition

One sixth of the gathering facilities (with compression and dehydration) were classified as having an abnormal process condition that resulted in larger than expected methane emissions at liquid storage tanks. Emissions at these “abnormal” facilities were an average 300% higher than similar facilities functioning normally.

Processing plants’ methane losses were much lower than at gathering facilities, the study found. None of the processing plants measured had loss rates above 0.6%, it indicated.

“The results of this study and the direct measurements obtained, suggest the majority of emissions can be attributed to a relatively small number of facilities,” said Allen Robinson, the Lane Professor of Mechanical Engineering at Carnegie Mellon who led the study’s field measurements.

“That means we may be able reduce the overall methane emissions from the gathering and processing sectors by focusing on sources at these higher-emitting sites,” he suggested.

The study was one of 16 organized by the Environmental Defense Fund and several oil and gas industry partners to better quantify amounts of methane escaping into the atmosphere from the gas supply chain. Access Midstream, Anadarko Petroleum Corp., Hess Corp., Southwestern Energy Co., and Williams Cos. provided financial support were cosponsors and provided access to facilities. DCP Midstream provided access to one of its processing plants.

This study’s results were released 2 months after one led by the University of Texas at Austin researchers found that a small subset of gas wells was responsible for most methane emissions from US gas production in samples at the wellhead (OGJ Online, Dec. 9, 2014).

Establishes new goal

The Obama administration set a new goal earlier this year to cut the oil and gas industry’s methane emissions from 2012 levels by 40–45% by 2025, and announced a series of actions to put the US on a path to achieve that goal (OGJ Online, Jan. 15, 2015). EDF and 15 other environmental organizations have pressed the federal government to begin regulating methane emissions from oil and gas operations (OGJ Online, Sept. 22, 2014).

Marchese said he was not surprised that there was a difference between gathering systems and processing plants’ methane emissions. “Processing plants are generally much larger and permanently staffed, and are required to report methane emissions to the [US Environmental Protection Agency],” he said. “They also are required by federal law to repair any leaks within five days of detection. Most gathering facilities aren’t subject to those federal regulations.”

Only gathering systems which exceed the 25,000-tonne carbon dioxide equivalent (CO2e) emissions threshold are required to report any methane emissions to EPA and are not subject to the same leak detection and repair regulations, he noted.

Marchese said the comprehensive field study as provided the most methane emissions data so far for the US gas industry’s gathering and processing operations. “Prior to our study, most of the information we had on methane emissions from these facilities originated from studies in the early 1990s,” he said.

An American Petroleum Institute official welcomed the latest study’s findings. “The industry has every incentive to reduce emissions and sell more natural gas to consumers,” said Howard J. Feldman, API senior regulatory and scientific affairs director.

“We’re making remarkable progress reducing emissions, and this progress will continue as operators detect and seal leaks—including leaks from the few high-emitting sites identified in this study,” Feldman said. “Burdensome new regulations would only interfere with our progress reducing emissions and jeopardize production of the clean-burning natural gas that has helped drive US carbon emissions to near 20-year lows,” he said.

Second study’s reach

The second study, which looked at emissions samples from 45 transmission and storage facilities across the country, similarly found that only a few sites were responsible for most of the releases. It also was the most comprehensive methane emissions study conducted so far at these facilities, and its data will be used in a second study due to be release in a few more months to build a model of nationwide estimates which can be compared with EPA estimates, the Interstate Natural Gas Association of America said.

“This finding indicates a need to focus methane management measures on sites and equipment with the highest emissions profile,” said INGAA Pres. Donald F. Santa. “It’s also very consistent with the direction INGAA members are voluntarily taking to reduce emissions.”

He explained that last summer, INGAA members committed to develop industry guidelines for directed inspection and maintenance (DI&M) of natural gas pipeline facilities. DI&M is a well-established and EPA-recognized tool for detecting and mitigating leaks in a cost-effective manner.

While most INGAA members use DI&M, the guidelines will improve consistency and uniformity, which should result in further emissions reductions and help focus efforts on reducing emissions from the pipeline equipment that has the potential to release the most methane, the association said. INGAA also is working with research groups to create a roadmap for developing technological innovations to make DI&M even more effective.

The CSU-led study also identified sources of emissions from gas transmission and storage facilities which are underreported in or excluded from another EPA emissions measurement program, the Greenhouse Gas Reporting Program. Emissions reported in this study were higher than the emissions level reported in the GHGRP because the GHGRP excludes many sources and its reporting methods can under-estimate emissions.

“This finding isn’t surprising,” Santa said. “The GHGRP only covers a small portion of the nation’s natural gas compressor facilities. Under EPA reporting rules, only those facilities with emissions of 25,000-tonne CO2e submit emissions data to EPA. In addition, some facility sources of methane measured for this new study are not included in the GHGRP, such as compressor and valve-related leaks in certain operating modes.”

Contact Nick Snow at [email protected].

About the Author

Nick Snow

NICK SNOW covered oil and gas in Washington for more than 30 years. He worked in several capacities for The Oil Daily and was founding editor of Petroleum Finance Week before joining OGJ as its Washington correspondent in September 2005 and becoming its full-time Washington editor in October 2007. He retired from OGJ in January 2020.