Small subset of wells accounts for most methane emissions, researchers say

A small subset of natural gas wells are responsible for most methane emissions from US natural gas production, said a study from the University of Texas at Austin. Researchers cited the two major sources of methane emissions from wells as liquid unloadings and pneumatic controller equipment.

The results were published Dec. 9 in an article in Environmental Science & Technology. Lead researcher David Allen is a UT chemical engineering professor and chair of the US Environmental Protection Agency’s Science Advisory Board.

Allen told reporters that the research team noted a 10% decline in methane emissions from US gas development and production activities compared with what it reported in 2013 (OGJ Online, Sept. 17, 2013).

The latest results stemmed from the 3-year study’s second phase. The first phase of the study involved some of the first methane emissions measurements taken directly at hydraulically fractured well sites.

Both phases of the study were supported by a partnership between the Environmental Defense Fund and 10 oil and gas companies, an independent scientific advisory panel, and the UT study team.

Companies involved were Anadarko Petroleum Corp., BG Group PLC, Chevron Corp., ConocoPhillips, Encana Oil & Gas USA Inc., Pioneer Natural Resources Co., SWEPI LP (Shell), Statoil ASA, Southwestern Energy Co., and XTO Energy Inc.

Separately, the EPA is getting closer to issuing guidance for reducing methane emissions from wells.

The EPA could propose a rule by Dec. 31 regarding methane emissions data that the agency collects from the oil and gas industry as part of the greenhouse gas reporting program, Joe Goffman, EPA associate assistant administrator for climate and senior counsel to the assistant administrator for air and radiation, said during an Environmental Law Institute webinar in November.

President Barack Obama has asked EPA officials to consider whether methane from oil and gas operations should be directly regulated. If additional controls are deemed necessary, the EPA could finalize methane regulations by March 2016.

Allen said the UT study was intended to provide a better understanding of methane emissions. Findings suggest industry can achieve low emissions given the right equipment and procedures.

“We hope the studies provide information as our country and other countries think about policies and what is the smart way to do it,” Allen said.

Separately, Howard Feldman, spokesman for the American Petroleum Institute,  said industry’s investments in new technologies and equipment are paying off.

“This latest study shows that methane emissions are a fraction of estimates from just a few years ago,” Feldman said. “The industry will continue to make substantial progress to reduce emissions voluntarily and in compliance with EPA regulations.”

Study findings

Researchers found 19% of pneumatic devices accounted for 95% of the emissions from those devices. Meanwhile, 20% of the wells that vent emissions to the atmosphere during unloading operations accounted for 65-83% of those emissions.

For pneumatic devices, the study confirmed regional differences in methane emissions as first reported by the study team in 2013. Researchers found methane emissions from pneumatic devices were highest in the Gulf Coast and lowest in the Rocky Mountains.

Pneumatic devices use gas pressure to control the opening and closing of valves. Their emissions are estimated to be among the larger sources of methane emissions from the gas supply chain.

EPA reports 477,606 pneumatic (gas-actuated) devices in use at gas production sites.

“Our team’s previous work established the pneumatics are a major contributor to emissions,” Allen said. “Our goal here was to measure a more diverse population of wells to characterize the features of high-emitting pneumatic controllers.”

The research team measured emissions from 377 controllers at gas production sites and a small number of oil production sites.

High-emitting pneumatic devices were found to involve a combination of devices that were not operating as designed, were used in applications that caused them to release gas frequently, or were designed to emit continuously at a high rate.

In addition, the team’s field study measured emissions from unloadings from wells at 107 gas wells, and Allen said that research represents the most extensive measurement of emissions associated with liquid unloadings currently available in scientific literature.

A liquid unloading is a method of clearing wells of accumulated liquids. Liquid unloading are more frequent in older wells than newer wells, Allen said, noting a statistical correlation between the age of wells and the frequency of liquid unloadings.

Unloadings can involve various lifting mechanisms. Researchers found differences in emissions between wells using plunger lifts and wells without plunger lifts.

Most wells without plunger lifts unload less than 10 times/year with emissions averaging 0.4-0.7 Mg per event. Wells with plunger lifts averaged more than 200 events/year with emissions averaging 0.02-0.2 Mg per event, the study said. Overall, wells with plunger lifts were estimated to account for 70% of emissions from unloadings nationally.

Contact Paula Dittrick at paulad@ogjonline.com.

*Paula Dittrick is editor of the Unconventional Oil & Gas Report.

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