By Karin Vergoth

An aerial view of a drilling oil well in the Bakken Formation in North Dakota. A new study finds that the Bakken region emits 275,000 tons of methane per year.
Credit: S. Haines/USGS.

The Bakken oil and gas field is leaking a lot of methane, but less than some satellites report, and less than the latest Environmental Protection Agency (EPA) inventory for petroleum systems, according to researchers’ calculations. That’s the finding of the first field study measuring emissions of this potent greenhouse gas from the Bakken, which spans parts of North Dakota and Montana. The new study was published today in the Journal of Geophysical Research: Atmospheres.

Researchers found that 275,000 tons of methane leak from the Bakken each year, similar to the emission rate found for another oil-producing region, Colorado’s Denver-Julesburg Basin.

“This study provides a key snapshot of Bakken methane emissions that will help answer the bigger questions: how much methane is the U.S. emitting, where is it coming from, and how is that changing over time?” said Jeff Peischl, a scientist from the Cooperative Institute for Research in Environmental Sciences (CIRES) at the University of Colorado-Boulder working at NOAA and the study’s lead author.

The 200,000 square-mile Bakken Shale formation is one of the country’s top oil-producing regions. At the time of the study in May 2014, the Bakken accounted for 12.5 percent of all crude oil produced in the United States. Only Texas surpasses North Dakota for oil production among states.

Methane is the primary component of natural gas and the second-most common greenhouse gas emitted by human activity in the U.S. Some methane is produced by natural sources such as wetlands, but livestock feedlots, landfills, coal mines, and oil and gas production also add significant amounts of methane to the atmosphere. Pound for pound, methane is significantly more efficient than carbon dioxide at trapping heat in the atmosphere over a 100-year period. Eventually, atmospheric methane reacts to form to carbon dioxide, the most common greenhouse gas, which persists in the atmosphere for thousands of years.

In this study, researchers flew an instrumented NOAA Twin Otter aircraft upwind and downwind of production facilities in the Bakken, and calculated the region’s total methane emissions using a technique called mass balance. The researchers evaluated the chemical composition of the air samples to determine if the methane captured during the flights came from oil and gas operations or other activities, such as livestock feedlots. The majority came from oil and gas, they found.

A map of NOAA-CIRES published studies on oil and natural gas emissions in the U.S.
Credit: CIRES/NOAA.

This study is one of several that are part of an ongoing effort to understand the atmospheric impact of oil and gas drilling across the United States, an effort that has revealed major differences in emission rates among regions and types of oil and gas basins.

The Bakken’s 2014 methane emission rate of 275,000 tons per year is significantly less than estimates generated by satellites for the region between 2006 and 2011. The researchers also compared the measured emission rate for the Bakken to EPA’s 2013 national inventory, the latest year available when the paper was submitted.  EPA only reports total national greenhouse gas emissions from petroleum systems, so researchers calculated the Bakken’s share of the EPA inventoried emissions based on the Bakken’s oil production level.

The EPA, in its 2014 greenhouse gas inventory released last month, increased its estimate of methane emissions from petroleum systems by 2.5 times. The data reported today shows emissions from the Bakken are slightly lower than EPA inventory, scaled to production. Field studies like this one, the researchers say, are vital for improving the accuracy of inventory estimates and satellite-based remote sensing measurements.

Another recent study showed the Bakken leaks ethane, also a component of natural gas, at a rate of about 250,000 tons per year, enough to be detected by atmospheric monitors in Europe.

“Policymakers need good data to make good decisions,” said Tom Ryerson, a scientist at NOAA co-author of the study. “As we transition from coal to natural gas and other sources of energy, it’s important that we understand the climate impacts of the fuel choices we’re making.”

This study is part of a continuing NOAA effort to understand methane emissions from all the major sources in the U.S. and across the globe. This larger effort involves tracking the natural emissions from tropical wetlands and sources in the Arctic, as well as human-caused emissions from landfills, agriculture and animal husbandry, and energy production and use.

—Karin Vergoth is a science writer at CIRES, which is a partnership of NOAA and CU-Boulder. This post originally appeared as a news release on the CIRES website.