Study ties outsize methane emissions to some oilfield equipment

WASHINGTON — As federal regulators mull new mandates to curb methane leaks from the oil sector, new research suggests two major sources are techniques to dislodge fluid from wells and the pneumatic devices used to control valves at the sites.

The research from the University of Texas at Austin, with support from the Environmental Defense Fund and 10 natural gas companies, reveals that a large portion of methane emissions from oil and gas production can be traced to small subset of outlier wells and equipment.

For instance, about 19 percent of the pneumatic devices monitored by the research team accounted for 95 percent of the emissions from pneumatic devices. And 20 percent of the wells that vent emissions to the atmosphere during “unloading” operations designed to dislodge fluids accounted for 65 to 83 percent of those emissions.

Even so, the research documents a decline in methane emissions from the development and production of natural gas — now 10 percent lower than the same research team found in a 2013 study.

Oil industry representatives also cheered the researchers’ finding that most of the sites recorded low to no emissions — a sign, they said, that companies are investing in equipment needed to mitigate methane.

Howard Feldman, director of regulatory and scientific affairs at the American Petroleum Institute, said the report demonstrates “industry-led efforts to reduce emissions through investments in new technologies and equipment are paying off.”

The study also confirms wide regional differences in the amount of methane leaking from pneumatic controllers that use gas to manipulate valves and other devices at well sites. Emissions from those devices were highest in the Gulf Coast and the lowest in the Rocky Mountains region.

Mark Brownstein, an Environmental Defense Fund vice president, speculated the regional variations could be tied to the “history of more comprehensive regulation of air emissions from oil and gas operations” in Rocky Mountains states, particularly Colorado and Wyoming.

“The results in this study speak to the value of those kind of leak detection and repair requirements,” he said. “The idea that you’ve got a certain subset of pneumatic devices that are responsible for a large proportion of emissions in the study suggests proper operation and maintenance is an important strategy for keeping emissions low overall.”

The Environmental Protection Agency and the Interior Department are considering a combination of regulations and voluntary programs that would rein in methane, a powerful heat-trapping pollutant that is the primary component of natural gas. After releasing a series of white papers earlier this year, the EPA is expected to decide its next steps later this month.

The study published Monday in the journal Environmental Science & Technology is unique in the way it measured methane emissions — directly at their source, including pneumatic controllers and wells with liquid unloading operations.

Liquids unloading operations are designed to remove fluid that, over time, can suppress gas production and keep it from flowing freely and easily out of a well. One method is a plunger-lift operation that involves first shutting in wells to stop them from flowing, then sending a plunger down the well and allowing pressure to build up. Once it does, a controller opens a valve and the gas-propelled plunger lifts liquid to the surface.

The plungers can be triggered automatically or manually. And in some cases, the flow may be diverted to a storage tank at atmospheric pressure.

According to the lead researcher, David Allen, a chemical engineering professor at UT-Austin’s Cockrell School of Engineering, the most reliable indicator of emissions wasn’t the precise technique used but the amount of times those unloading events were triggered. Some natural gas wells are vented just one or two times a year, while others will vent thousands of times annually, Allen said. “That is the dominant determinant of whether you have a high-emitting well.”

For pneumatic controllers, leaks averaged about the same whether the devices were designed to continuously vent gas or do so intermittently, sometimes with brief spikes up to 150 standard cubic foot per hour.

Roughly two-thirds of the high-emitting controllers documented in the study probably “were not operating as designed” and may be in need of repairs or replacements, Allen said.

It is unclear how many of those pneumatic controllers are in operation in the United States. An EPA greenhouse gas inventory documents about half a million of the controllers in use at the half million natural gas wells in the United States. But Allen noted that researchers saw an average of 2.7 of the devices at each of the wells they visited.