Study Of Best Fracked Wells Finds Low Methane Emissions, Skips Super-Emitters
- September 24, 2013
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The good news: A sample of what are probably the best fracked wells in the country finds low emissions of methane, a potent heat-trapping gas.
The bad news: The study likely missed the super-emitters, the wells that are responsible for the vast majority of methane leakage.
The ugly news: Same as ever — natural gas from even the best fracked wells is still a climate-destroying fossil fuel. If we are to avoid catastrophic warming, our natural gas consumption has to peak sometime between in the next 10 to 15 years, according to studies by both the Center for American Progress and the Union of Concerned Scientists.
If natural gas is a bridge fuel, it has got to be a very short bridge. Otherwise it is merely “a bridge to a world with high CO2 Levels,” as climatologist Ken Caldeira put it last year.
Methane, the primary component of natural gas, is a powerful greenhouse gas — 72 times more potent than carbon dioxide over a 20-year time frame. The largest single source of U.S. methane emissions is the vast network of infrastructure that supplies natural gas. These emissions, if not controlled, pose a significant risk to the climate and regional air quality. In the near term, the opportunity to maximize the lower carbon characteristics of natural gas compared to other fossil fuels rests on whether methane emissions are well understood and whether they can be sufficiently controlled.
This is important work and what seems like small changes in percentages can have a large impact. For example, EPA currently estimates methane escaping during development and delivery of natural gas to be 1.5 percent of total U.S. production, including associated gas from oil wells. Getting that number down to one percent — controlling just a third of the emissions — would have the same climate benefit over the next 20 years as retiring another 10 percent of U.S. coal generation. That’s a big deal, and it’s possible. A key takeaway of the UT study is that emission control technologies, such as so-called green completions (see below), are available and effective at reducing methane emissions….
UT estimates the national methane leakage rate associated with the phase of natural gas extraction to be equivalent to 0.42% of total U.S. natural gas produced. This finding is in line with EPA’s current emission inventory estimate for the production segment of the supply chain….
Physicians Scientists & Engineers for Healthy Energy called the study “fatally flawed,” and posted a detailed critique.
I think there are two key, related issues. First, the EDF FAQ notes:
Nine natural gas companies, out of thousands of producers in the U.S., volunteered for this study. The UT study collected data that characterized the practices at particular sites operated by the participating companies, not industry at large. In 2011, the participants accounted for roughly 12% of all U.S. gas wells, 16% of gross gas production and almost half of all new well completions.
Bill Chameides, Dean of Duke University’s Nicholas School of the Environment, explains what this means in his HuffingtonPost piece:
It could be that this subset of companies — the ones willing to have their sites measured — are the ones that are most careful to limit leakage and thus are not representative of the industry.
You may recall that a major study this August in Geophysical Research Letters from 19 researchers led by NOAA suggested natural gas may be more of gangplank than a bridge. Scientists used a research aircraft to measure leakage and found:
The measurements show that on one February day in the Uintah Basin, the natural gas field leaked 6 to 12 percent of the methane produced, on average, on February days.
The Uinta Basin is of particular interest because it “produces about 1 percent of total U.S. natural gas” and fracking has increased there over the past decade.
How to explain the discrepancy in measured leakage rates? Energy Wire talked to Colm Sweeney, who co-authored the NOAA-led study that found high leakage. He “drove around for an hour in a basin in Texas recently, measuring methane emissions from 23 well pads.” The result:
He found nine wells were clean. Eight wells had emissions enhanced by 20 percent above background. And five wells showed enhancements of methane 100 percent over background. Those are the super-emitters.
The super-emitters are lost in a study released this week by scientists at the University of Texas, Austin, and the Environmental Defense Fund.
Sweeney believes that explains the discrepancy:
The 0.42 percent is the average of a bunch of good actors but not necessarily representative of the real world, Sweeney cautioned.
He compared the exercise to doing a Nielsen survey, in which a poll worker calls 100 people to see how much television they watch. The worker would miss someone in the mountains without a phone who is watching 24 hours of television a day.
“You got your average from those 100, but you are missing the big guys,” he said.
I asked Steve Hamburg, Chief Scientist at the Environmental Defense Fund, about this issue of the super-emitters, which are in some sense the “fat tail” of distribution curve of leaking wells. He replied:
Understanding the relative importance of the ‘fat tail’, a few large emitters influencing overall emissions fluxes, is a key question that EDF has been concerned with since we started working on methane emissions from production of oil and gas. I believe we raised the issue in the literature for the first time in our 2012 paper in PNAS by Alvarez et al.
The UT study was not designed to address fat tails, though the size of the study makes it more likely that in fact they would have included some of the fat tail for the 9 companies sampled, to the degree it exists. To try to understand the potential importance of spatially and temporally rare events in determining the overall methane emissions fluxes EDF contracted with Colm Sweeney and his NOAA team over a year ago to do flyover based estimates of methane emissions from oil and gas operations. We eagerly await publication of those results, but until then it would be inappropriate to discuss that work or any other work that has not gone through peer review. We are also sponsoring a side by side comparison of emissions estimates from a dozen science teams using a diversity of methodological approaches so we can better understand in a structured and rigorous way the strengths and weaknesses of different measurement strategies for different emissions types, including large rare events.
So we should find out soon just how big a role the super-emitters play in overall methane emissions. Ultimately, national standards could be put in place requiring all companies to use the best practices of the low emitters. Enforceable standards, if is combined with real-time on-site monitoring of methane at wells, could help restore confidence in fracked gas as a short-term bridge fuel. Until then, however, the rush to frack seems premature at best, counterproductive at worst.
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