NETL study identifies key methane emitters along US gas supply chain

Feb. 20, 2017
About 1.7% of the methane in the US natural gas supply chain is emitted between extraction and delivery, according to a 2-year study by analysts at the US Department of Energy's National Energy Technology Laboratory.

About 1.7% of the methane in the US natural gas supply chain is emitted between extraction and delivery, according to a 2-year study by analysts at the US Department of Energy's National Energy Technology Laboratory.

Gathering systems, which the study called a significant and previously overlooked emissions source, and pneumatic controllers at production sites were two of the top contributors, data from a series of ground-based field measurements indicated.

Identifying the magnitude and sources of methane emissions will allow producers to prioritize opportunities to reduce emissions of the potent greenhouse gas, NETL said. The report, "Synthesis of Recent Ground-Level Methane Emission Measurements from the US Natural Gas Supply Chain," appears in the April 2017 issue of the Journal of Cleaner Production.

It said that gathering systems, which move gas from the wellhead to processors, represented 22% of methane emissions along the gas supply chain, while pneumatic devices that intentionally release gas into the atmosphere to control line pressure were responsible for 10% of the total.

Another emissions category, unassigned emissions, made up 19% of the gas supply chain's methane emissions, the study said. Rather than a single, unified emissions source, the category includes multiple sources, including a small number of production sites with atypically high emission rates, production equipment that requires maintenance, and intermittent wellhead maintenance events.

Future efforts may attribute unassigned emissions to specific sources, NETL said. For its synthesis report, it said it used new data from studies funded by the Environmental Defense Fund that were representative of the US gas supply chain from production through distribution.

These studies measure, model, and report methane in different ways, creating a need to compile the results in a clear and consistent manner, NETL said, adding that it used its own natural gas life cycle analysis tool to synthesize this new data.

NETL said the recent study shed new light on methane emissions along the gas supply chain in the US, as well as revealing the knowledge gaps and sources of uncertainty that must be addressed through further study.

Future research may include geographically diverse measurement studies that can provide a better understanding of regional variability and may validate emission measurements by using a combination of component and site-level measurements, it said.