Bakken field leaking methane at 275 mtpa, less than satellite and EPA estimates
WASHINGTON D.C. -- The Bakken oil and gas field is leaking a lot of methane, but less than what some satellites report, and less than the latest Environmental Protection Agency (EPA) inventory for petroleum systems, according to the 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.
A new study by the National Oceanic and Atmospheric Agency (NOAA) and the Cooperative Institute for Research in Environmental Sciences (CIRES) finds the Bakken oil and gas field in North Dakota leaks about 275 mtpa of methane.
The work was published in the Journal of Geophysical Research: Atmospheres. This emission rate is similar to that for another oil-producing region, Colorado’s Denver-Julesburg Basin.
The Bakken’s 2014 methane emission rate 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.
“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, the study’s lead author and a scientist from the CIRES at the University of Colorado Boulder working at NOAA. Co-authors include scientists from NOAA, the University of Michigan, Stanford University, and the University of California, Davis.
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% of all crude oil produced in the United States. Only Texas surpasses North Dakota for oil production among states.
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.
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 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 the 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.
“Policymakers need good data to make good decisions,” said Tom Ryerson, study co-author and NOAA scientist. “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.”