Measuring Methane Leaks from Natural Gas Drilling
Posted September 17, 2013
There has been a lot of cross-talk over the last couple of years about how much methane leaks from the natural gas production and distribution system. Most of what has been said and written was based on analyzing and reanalyzing a very limited data set. Yesterday a team of scientists led by David Allen at the University of Texas expanded the available data with the publication of their study of methane emission measurements made at 190 onshore natural gas sites in the United States. The results of this study are important and interesting, but don’t expect them to settle the controversy over the environmental consequences of natural gas production and use.
Before delving into the findings of the Allen et al. study let’s review the bidding. Natural gas is primarily methane. Burning it to generate electricity emits less than half as much carbon dioxide than burning coal at typical power plants of each type, but unburned methane that leaks into the atmosphere is at least 25 times more powerful at trapping heat than carbon dioxide (over a 100 year period) and as much as 100 times more powerful (over a 20 year period). So even a little methane leakage significantly diminishes the global warming benefit of switching from coal-fired to gas-fired power plants, and a leak rate greater than about 4 percent could wipe it out. Technologies to reduce methane leaks are available and often profitable, as NRDC showed in our Leaking Profits report last year. The goal should be to ensure than methane leaks are well below one percent of production.
Having a lower emissions rate than coal is of course a very low bar—to solve the climate crisis we need to boost energy efficiency and switch to renewable, zero-emission sources of energy as quickly as possible. Still, like it or not, the United States uses a lot of fossil fuel and will for some time, so it’s important to know what the total global warming impact really is, and even more important to reduce it as quickly as possible.
EPA is tasked with keeping the official tally of global warming pollution from all significant sources in the United States. Its latest estimate is that “natural gas systems” (from production through distribution) emit 6.9 million metric tons of methane, which is about 1.3 percent of total natural gas production. Of this total, 2.5 million metric tons comes from the upstream, production part of the system according to EPA. Many in the natural gas industry assert that this estimate is too high, while some critics claim it is way too low. What do the new data show?
Allen et al. only looked at the production part of the system and their overall estimate for this comes in a little below EPA’s, at 2.3 million metric tons. Dig a little deeper and things get more interesting.
In EPA’s emissions inventory the largest share of emissions from natural gas production is from the process of completing hydraulically fractured wells, when injected fluids flow back up the well before regular gas production can begin. A lot of methane can be mixed in with these fluids and if nothing is done to control it that methane escapes into the air. EPA estimated that the emissions from such “completion flowbacks” in 2011 amounted to 654 thousand metric tons. Based on their measurements of methane emissions from 27 well completions Allen et al. estimate that annual emissions from completion flowbacks are only 18 thousand metric tons (with an uncertainty range of 5-27). It turns out that this huge difference is not due to different estimate of how much methane is contained in the flowback fluid—EPA and Allen et al. have similar estimates for such “potential emissions”—rather Allen et al. found that two thirds of the wells completions they measured took steps to prevent methane emissions, and those steps were extremely effective. The remaining wells had much lower potential emissions to begin with, so overall Allen et al. found that the actual emissions from well completions were only 2 percent of the potential emissions. EPA, by contrast, had assumed that actual emissions were 50 percent of potential emissions. Some of this difference may be due to changes in some company practices from 2011 to 2012 (when the measurements were made) and the well completions sampled by Allen et al. may not be representative of overall industry practice.
The good news is that under EPA regulations issued in April 2012 most fracked natural gas wells will have to capture or flare methane during well completions staring in 2015. So whether or not Allen et al.’s estimates are representative today, their measurements show that these regulations will be effective. They would be even more effective if they were implemented sooner, applied to existing wells, and extended to oil wells and hybrid wells that produce a combination of oil and gas.
Largely offsetting their lower emissions estimate for well completions, Allen et al. measured a higher leak rate from pneumatic controllers and other equipment than given in EPA’s emissions inventory. The substantial emissions from pneumatic devices, 580 million metric tons according to Allen et al., make them the largest identified source of methane from the production phase of the natural gas system. EPA should move quickly to establish performance standards that will cut down on this waste and source of pollution. A mandatory leak detection and repair program could cut down on other significant emission sources measured in the study.
By bringing hard data to the table Allen et al. have made a major contribution to the debate about natural gas, but you can expect the debate to continue for lots of legitimate reasons:
- The measurements reported in this study represent a very small sample of the roughly half-million natural gas wells in the United States. There is no guarantee that the sample is fully representative of the industry as a whole given that the firms which chose to participate might be expected to have lower methane leak rates than average.
- The measurements pertain to only a small slice of the natural gas supply chain. Even within the production sector Allen et al. only had enough data to make independent estimates for about half the emissions given in EPA’s inventory. Measurements on the rest of the supply chain are expected to be published over the next 15 months and additional data are also coming in from EPA’s emission reporting requirements.
- Methane leaks are only one of many environmental problems with natural gas drilling, which threaten the safety of our air, our drinking water, and our communities.
One thing is clear. Regardless of how much methane is currently leaking into the air, natural gas is still a fossil fuel and the sooner we end our addiction to fossil fuels the better, for the health of families, our communities, and our climate.
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