New Study Sheds Light on Methane Leakage from Natural Gas
Natural gas wells represent a significant source of U.S. greenhouse gas (GHG) emissions, as many of them leak methane, which is more than 20 times more potent than carbon dioxide. But while scientists know that “fugitive methane” is a concern, there’s much uncertainty about the full extent of the problem. A new study from the University of Texas—developed in partnership with the Environmental Defense Fund and nine natural gas production companies (Anadarko, BG Group, Chevron, EnCana, Pioneer, Shell, Southwest, Talisman, ExxonMobil)—sheds some light on this perplexing issue.
The study focuses on the pre-production and production stage of hydraulically fractured shale gas wells, which accounted for roughly half of methane emissions from natural gas systems in 2011. The research shows that while methane leakage is a significant problem, natural gas companies can take —and in some cases, already are taking—cost-effective measures to reduce these dangerous emissions. It also reveals a few particular focus areas to help curb natural gas’s climate impact.
Three major takeaways are important to note, including:
1) Results Are Largely Consistent with EPA Inventory Estimates, with Two Important Caveats
Overall, the study finds that total production-stage methane leakage is consistent with U.S. Environmental Protection Agency (EPA) estimates, as published earlier this year in the 2011 GHG emissions Inventory. However, there are significant differences when you look at the details.
Emissions occurring during the well completion flowback stage of the production process were significantly lower than EPA estimates. This discrepancy is partly explained by the fact that UT researchers conducted their measurements in 2012, as new rules from EPA that require the increased use of reduced emission-completion (REC) technologies were beginning to go into effect. Also, RECs proved to be more effective at capturing methane than previously assumed. EPA had estimated that well completions account for roughly one-quarter of all production-stage methane emissions. However, because most of the studied wells were using RECs, UT researchers estimate that this activity only accounts for 1 percent of total production-stage emissions.
The lower-than-expected leakage estimate for well completions was counterbalanced by much higher-than-expected emissions from other parts of the natural gas production process. This is especially true in the use of pneumatic devices, which vent natural gas into the atmosphere. UT researchers found that pneumatics produce roughly 30 percent of production-stage methane emissions, nearly twice the level previously estimated by EPA.
2) This New Study is an Important Piece of the Puzzle, but Doesn’t Reveal the Whole Picture
To put this study in context and understand its broader implications, perhaps the most important question is: To what extent do its results represent the complete picture of production-stage methane emissions from across the country? In that sense, we know that this study has some important limitations. Researchers took direct measurements of equipment and operations at nearly 500 natural gas wells, which represented roughly 1 percent of total gas production in 2012. Though this study only surveyed a small fraction of the more than 500,000 U.S. wells in production today, it included a very significant sample size.
It is certainly reasonable to compare this new study's findings with emissions estimates published in the EPA GHG Inventory (the most comprehensive picture of GHG emissions from all U.S. sources). However, it is also reasonable to assume that the UT study – which was completed with the voluntary participation of companies that were collectively responsible for roughly half of all well completions in 2011 – is only partially representative of the conditions industry-wide. Because most of the measurements for this study occurred in the vicinity of brand new wells (i.e., those undergoing hydraulic fracturing to initiate production), these results are likely closer to industry best practices and not necessarily common practice. Two issues to note include:
For well completions, best practices –such as reduced emission completions—are increasingly becoming common practice and will be required by law for all hydraulically fractured natural gas wells by 2015. Therefore, the UT study findings may be viewed as largely representative of standard industry practice for this particular process.
However, for equipment used in the routine production of natural gas—such as pneumatic devices—the measurements in this study are more representative of what can be achieved rather than what is commonly achieved at all of the existing wells around the country. In order for the thousands of other wells in the United States to achieve a comparably low level of emissions to those observed by this study, all production companies would need to conduct more frequent leak-detection and repair and replace their aging high-bleed pneumatics with lower-bleed devices.
The study also came up with highly variable emissions estimates from its limited measurements of liquids unloading operations (a common well-maintenance activity used for all natural gas wells), where a small number of measured events contribute to a large percentage of total emissions. Report authors have said that they will conduct additional research to better understand why emissions levels vary so widely for liquid unloadings and other processes. A more complete picture will also emerge soon, as results are published from a related “fly-over” study, wherein methane emissions from some of the same well fields measured for this report were simultaneously measured by aircraft.
3) The U.S. Needs New Policies to Reduce Sector-Wide Emissions
The UT study confirms that the EPA's recent 2012 regulations of volatile organic compounds from the oil and natural gas sector, which requires RECs for all hydraulically fractured and re-fractured natural gas wells, was an important and appropriate first step to limit harmful production-stage emissions. The study also confirms that methane leaks from well production sites are a significant problem. In order to meet its commitment to reduce nation-wide emissions by 17 percent by 2020 and curb climate change, the United States needs policies to ensure that natural gas companies are switching-out leaky equipment and more aggressively conducting routine leak detection and repair. In our April 2013 working paper, Clearing the Air, WRI found that these actions are cost-effective and result in significant GHG reductions from natural gas systems.
A Need for Better Data
Long before this most recent study began, there has been a lack of public trust and a call for greater transparency from the oil and gas industry. Many environmental and public health concerns remain unaddressed from a regulatory standpoint, even as an increasing number of companies step up to voluntarily disclose more and more details about the environmental footprint of their operations. The companies that participated in this study should be recognized for their leadership and commitment to provide better data and transparency.
Ultimately, we need more measurements from more wells and from fly-over surveys, which are being conducted as part of a broader, related measurement campaign organized by the Environmental Defense Fund. This work will help to give us a fuller picture of the issue of fugitive methane emissions, providing greater transparency and helping federal and state policymakers take the necessary steps to reduce harmful pollution.
- LEARN MORE: Download WRI's working paper, Clearing the Air: Reducing Upstream Greenhouse Gas Emissions from U.S. Natural Gas Systems