On Tuesday, the academic journal Environmental Science & Technology published an issue featuring 10 new peer-reviewed articles investigating the rate of methane leakage from the Barnett Shale region, where the practice of hydraulic fracturing or “fracking” to extract natural gas first took off in the United States.  The studies found that the amount of natural gas leaking into the atmosphere during drilling operations is likely about 1.5 times what the U.S. Environmental Protection Agency (EPA) had previously estimated, with most of the emissions likely caused by just a handful of problem drilling operations.  The findings indicate that more regulations and controls on methane leakage will most likely be required to realize the potential climate benefits of burning natural gas versus coal for electricity generation. 

Even in small quantities, methane leakage is an important part of the climate change equation for natural gas because methane (the primary component of natural gas) is a far more powerful greenhouse gas than carbon dioxide.  Different greenhouse gases are ranked according to their Global Warming Potential (GWP), which describes their warming impact as a multiple of the impact caused by carbon dioxide, the most prevalent greenhouse gas.  By definition, carbon dioxide has a GWP equal to 1.  Methane has an estimated GWP of 28 to 36—indicating that one kilogram of methane released to the atmosphere will cause the same amount of warming as about 28 to 36 kilograms of carbon dioxide.  Thus, controlling methane leakage in the natural gas supply chain is a vital part of reducing the overall greenhouse gas emissions associated with natural gas, even if the actual volume of methane is small. 

The studies published last week in Environmental Science & Technology indicate that natural gas leakage rates might be higher than previously estimated by EPA.  To quantify methane leakage emissions, two methods are typically used. “ Top-down” methods measure the concentration of methane in the atmosphere to approximate how much extra methane is contributed by oil and gas operations, while “bottom-up” methods use measurements directly collected at drilling sites and along the natural gas supply chain.  By conducting a series of coordinated bottom-up methane leakage measurements in collaboration with industry, researchers were able to estimate total methane emissions with a level of accuracy and spatial resolution not previously available.  They found that total emissions from Barnett Shale oil and gas producers were about 1.5 times what EPA had previously estimated, indicating that EPA might be systematically underestimating methane leakage rates. 

Researchers used measurements collected from drilling sites to develop a new estimate of how much methane is leaking into the atmosphere from various locations throughout the Barnett Shale region, which encompasses the Dallas-Fort Worth metro area. ( Source: Lyon et al.) 

Most of the emissions were found to come from a handful of problem sites, which leaked far more methane per unit of gas produced than other natural gas wells.  One study found that 19 percent of total measured methane emissions could be traced to just 2 percent of drilling sites.  Another study attributed 9 percent of total regional methane emissions to just eight high-emitting sites (four gas processing plants, one gas compressor station, and three landfills). 

Controlling leaks in the natural gas supply chain is important because methane leakage could either make or break the climate benefits of fuel switching from coal-fired electricity generation to natural gas.  A 2012 study found that natural gas power generation can achieve immediate climate benefits over coal if leakage rates in the natural gas supply chain are kept below approximately 3.2 percent.  Compare this cutoff point to EPA’s 2009 estimated leakage rate of 2.4 percent and the stakes become clear.  If methane emissions can be controlled and reduced, then natural gas generation (a vital component of EPA’s Clean Power Plan) could provide a climate benefit.  If methane emissions creep above 3 percent, fuel switching could get us nowhere. 

Realizing the climate benefits of natural gas will require controlling methane emissions from oil and gas drilling sites and other parts of the natural gas supply chain.  Fortunately, researchers have shown that methane leakage could be reduced significantly by addressing a handful of problem sites that have greater than normal emissions.  With the right rules and regulations in place, it’s possible for natural gas to play a role in the wider energy transition.