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Bakken wells drove a sudden reversal of global decline in ethane emissions

Emissions had been falling worldwide — until production surged at a single regional source.

The emissions measured over the Bakken are 10 to 100 times larger than producers have been reporting to regulators, according to research published Friday in the journal Geophysical Research Letters.
REUTERS/Andrew Cullen

Oil and gas production in North Dakota’s Bakken formation is the key culprit in a worldwide rise  in atmospheric levels of a potent greenhouse gas that also contributes to ozone formation near the Earth’s surface.

Moreover, the emissions measured over the Bakken are 10 to 100 times larger than producers have been reporting to regulators,  according to research published Friday in the journal Geophysical Research Letters.

The gas at issue is ethane, a hydrocarbon that ranks No. 3 behind carbon dioxide and methane as a driver of the greenhouse effect and global warming. Also of concern is its contribution to poor air quality when it reacts with sunlight and other atmopheric chemicals to create eye- and lung-irritating ozone, which can be harmful to certain crops and has heat-trapping properties of its own.

According to an announcement from the University of Michigan, where the paper’s chief author, Eric Kort, teaches in the department of climate and space sciences and engineering:

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Globally, the atmosphere’s ethane levels were on the downswing from 1984 to 2009. The gas gets into the air primarily through leaks in fossil fuel extraction, processing and distribution. Scientists attributed its declining levels to less venting and flaring of gas from oil fields and less leakage from production and distribution systems.

But in 2010, a mountaintop sensor in Europe registered an ethane uptick. Researchers looked into it. They hypothesized that the boom in U.S. oil and gas brought about by hydraulic fracturing could be the culprit — even a continent away.

Ethane concentrations have been increasing ever since.

Huge surges in production

Zeroing in on the Bakken, where oil and gas production have surged in the last dozen years – oil production went 3,500-fold from 2005 to 2015, while gas went up by a factor of 180, with the sharpest increases coming after 2009 — the researchers flew over its oil fields in a light aircraft equipped with air-sampling gear.

Their measurements, made over a 12-day period in May 2014, determined that the Bakken’s ethane output to the atmosphere amounted to about a quarter-million U.S. tons per year. From the paper (with citations and some technical notes omitted, and emphasis added):

This estimate indicates that the growth rate in emissions from the Bakken alone reached a sustained level in 2012 … sufficient to cancel half the average long-term decline rate in global ethane emissions.

This is consistent with the hypothesis that the large increase in U.S. oil and gas production has led to a reversal in the declining atmospheric ethane burden, and highlights the disproportionate role played by the Bakken region, which represented only 2% of shale gas production in the U.S. in May 2014 and yet emitted 1-3% of total global ethane emissions.

The very heavy composition of raw gas in the Bakken shale helps explain the relatively high emissions. Other shale plays in the U.S. have notably lower ratios [of ethane to methane].   

One of many compounds that make up natural gas — second only to methane in volume at the wellhead — ethane is also a significant byproduct of oil refining. It escapes from leaky drilling, storage and transport equipment, and large amounts are who deliberately vented in the course of extraction, even though it has value in making a variety of industrial chemicals required for manufacturing plastics (think polyethylene).

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In the Bakken, the researchers say, their sampling found an ethane/methane mix indicating that most of the emissions arrived in the atmosphere as raw gas, not byproducts of processing operations.

A byproduct of fuels production

Worldwide, energy production accounts for about two-thirds of atmospheric ethane; natural seeps and miscellaneous sources, like big forest fires, add the rest.

The Kort team’s finding as to the ethane/methane ratio over the Bakken,  according to a good piece in the Washington Post, “could have big implications for future methane assessments.”

In many oil and gas fields, methane is often the primary natural gas present — sometimes accounting for up to 90 percent or more of the gas that is released during extraction. Ethane often tends to be present in smaller proportions. In the Bakken, however, the researchers found that ethane accounted for nearly 50 percent of all the natural gas composition, while methane was closer to 20 percent.

This is important because researchers sometimes use trends in global ethane emissions to make assumptions about the amount of methane that’s being released by fossil fuel-related activities. While it’s possible to measure the total methane concentration in the atmosphere, it’s difficult to say exactly where that methane came from, because there are so many possibilities: thawing permafrost in the Arctic, emissions from landfills and agriculture are just a few examples.

 But because ethane is primarily emitted as a byproduct of fossil fuel development — and because methane and ethane tend to be emitted together in those cases — researchers sometimes use trends in global ethane emissions to make assumptions about how much of the Earth’s methane output can be attributed to oil and gas development.

According to the Associated Press, the Kort study has the attention of the U.S. Environmental Protection Agency, which has had its own difficulties arriving accurate estimates of methane emissions; a spokesman said the findings were under review and added that a tightening of federal limits on methane emissions ought to help with the ethane problem as well.

Detection “a game changer’

And North Dakota’s top environmental health official said the state has bought a new camera that detects otherwise invisible gases at the source leak, adding that he thought companies weren’t necessarily venting the stuff deliberately.

“It’s a game changer,” Dave Glatt told the AP. “A lot of the companies thought they were in good shape, and they looked through the camera and saw they weren’t.” 

The Kort paper notes that production in the Bakken has slowed somewhat since their surveys, which presumably would also bring a reduction in ethane emissions.

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And while ozone formation downwind from drilling zones was happening at fairly slow rates during the study, because of cold springtime temperatures, they suggest that ethane plumes could push communities out of compliance with federal air quality standards in warmer months.

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The paper, “Fugitive emissions from the Bakken shale illustrate role of shale production in global ethane shift,” can be read here without charge.