by Bob Shively, Enerdynamics President and Lead Instructor

Natural gas has recently replaced coal-fired generation as the dominant form of generation in the U.S. From the standpoint of power plant emissions of greenhouse gases (GHG) this is good news. On average, gas-fired generation emits less than 50% of the amount of GHG emitted by the equivalent output of coal generation.

In fact, GHG emissions from the power sector in the U.S. declined by 13% in the decade ending 2014. Once data becomes available for 2015 the decline will be even more dramatic given the ongoing switch to gas generation.

But, there is a catch to this seemingly good news.  Uncombusted methane (methane typically makes up over 90% of natural gas carried in a pipeline) is a much more potent GHG than the carbon dioxide released when natural gas combusts. 

The U.S. Environmental Protection Agency (EPA) has determined that methane has a Global Warming Potential (GWP) that is 28 to 36 times greater than the equivalent amount of carbon dioxide. Given that, even though much less methane is released, it still made up 11% of the U.S. human-caused GHG release in 2014[1].  This means that natural gas that is released during production or during its journey through the gas system prior to its combustion at the power plant is negating some of the benefits of converting coal to gas generation.   

Methane losses through the gas delivery system are called fugitive emissions. According to the Environmental Defense Fund (EDF) recent data suggests fugitive emissions are significantly higher than previously thought. In fact, EDF states that 2013 fugitive gas emissions have over a 20-year period “the same climate impact as over 200 coal-fired power plants”[2].

As EDF points out, “the lost gas is worth $1.4 billion at 2015 prices,” meaning that gas producers and pipeline companies have an interest in solving the problem that goes beyond being good environmental citizens. The good news is that fugitive emissions are a solvable problem once the source of emissions can be identified. 

A couple of years ago, an environmental scientist told me about his work in a gas field in Wyoming where he and his colleagues could not understand a new high concentration of methane that their instruments were measuring. Then one evening, he fell into conversation with someone who worked at a gathering pipeline company who told him that they had recently changed their procedures resulting in frequent purposeful blow-out of their pipelines. (For those not familiar with the term, blow-out means releasing gas into the air in order to clear the line for maintenance or other planned procedures.) His rapid calculations showed that the unexplained source of methane was now explained and could be addressed through new pipeline operating procedures.

                   Source: NASA/JPL-Caltech/University of Michigan

Since then, scientists from various organizations have become active in identifying unexpected concentrations of methane and then identifying their causes. The photo above shows a concentration of methane in the Four Corners areas of Colorado and New Mexico (see the red/orange on the map) that is reportedly the size of Delaware. Researchers from NASA’s Jet Propulsion Laboratory and the California Institute of Technology spent the last two years identifying the sources of the methane by using low-flying aircraft with spectrometers. They recently published their findings in the Proceedings of the National Academy of Sciences. The research team discovered 250 sources of methane in the region ranging from gas wells, storage tanks, pipelines, and processing plant. 

But interestingly, two-thirds of the emissions came from only 25 sources. Asset operators in the region have already taken action. The result is that gas companies increase production and emissions are reduced. So it’s now feasible to find fugitive emissions and, in many cases, fix them through relatively minor actions. A key outstanding question is whether the industry will do so voluntarily or whether government regulations are required.

Footnotes:

[1] See EPA, Overview of Greenhouse Gases, https://www.epa.gov/ghgemissions/overview-greenhouse-gases

[2] See EDF, David Lyon, EPA Draft Says Oil & Gas Methane Emissions Are 27 Percent Higher than Earlier Estimates, http://blogs.edf.org/energyexchange/2016/02/23/epa-draft-says-oil-gas-methane-emissions-are-twenty-seven-percent-higher-than-earlier-estimates/