Top sources of electricity in the U.S. The share of American electricity generated in coal-fired power plants has fallen since 2000  while natural gas and renewable energy sources other than hydropower have gained ground and nuclear power has remained flat. Source: U.S. Energy Information Administration. Graphic: The Conversation / CC-BY-ND

By Anthony J. Marchese and Dan Zimmerle
2 July 2018

(The Conversation) – Natural gas is displacing coal, which could help fight climate change because burning it produces fewer carbon emissions. But producing and transporting natural gas releases methane, a greenhouse gas that also contributes to climate change. How big is the methane problem?

For the past five years, our research teams at Colorado State University have made thousands of methane emissions measurements at more than 700 separate facilities in the production, gathering, processing, transmission and storage segments of the natural gas supply chain.

This experience has given us a unique perspective regarding the major sources of methane emissions from natural gas and the challenges the industry faces in terms of detecting and reducing, if not eliminating, them.

Our work, along with numerous other research projects, was recently folded into a new study published in the journal Science. This comprehensive snapshot suggests that methane emissions from oil and gas operations are much higher than current EPA estimates.

One way to quantify the magnitude of the methane leakage is to divide the amount of methane emitted each year by the total amount of methane pumped out of the ground each year from natural gas and oil wells. The EPA currently estimates this methane leak rate to be 1.4 percent. That is, for every cubic foot of natural gas drawn from underground reservoirs, 1.4 percent of it is lost into the atmosphere.

This study synthesized the results from a five-year series of 16 studies coordinated by environmental advocacy group Environmental Defense Fund (EDF), which involved more than 140 researchers from over 40 institutions and 50 natural gas companies.

The effort brought together scholars based at universities, think tanks and the industry itself to make the most accurate estimate possible of the total amount of methane emitted from all U.S. oil and gas operations. It integrated data from a multitude of recent studies with measurements made on the ground and from the air.

All told, based on the results of our new study, the U.S. oil and gas industry is leaking 13 million metric tons of methane each year, which means the methane leak rate is 2.3 percent. This 60 percent difference between our new estimate and the EPA’s old one can have profound climate consequences.

Methane is a highly potent greenhouse gas, with more than 80 times the climate warming impact of carbon dioxide over the first 20 years after it is released.

An earlier EDF study showed that a methane leak rate of greater than 3 percent would result in no immediate climate benefits from retiring coal-fired power plants in favor of natural gas power plants.

That means even with a 2.3 percent leakage rate, the growing share of U.S. electricity powered by natural gas is doing something to slow the pace of climate change. However, these climate benefits could be far greater.

Also, at a methane leakage rate of 2.3 percent, many other uses of natural gas besides generating electricity are conclusively detrimental for the climate. For example, EDF found that replacing the diesel used in most trucks or the gasoline consumed by most cars with natural gas would require a leakage rate of less than 1.4 percent before there would be any immediate climate benefit.

What’s more, some scientists believe that the leakage rate could be even higher than our estimate. [more]

The U.S. natural gas industry is leaking way more methane than previously thought. Here’s why that matters

ABSTRACT: Methane emissions from the U.S. oil and natural gas supply chain were estimated using ground-based, facility-scale measurements and validated with aircraft observations in areas accounting for ~30% of U.S. gas production. When scaled up nationally, our facility-based estimate of 2015 supply chain emissions is 13 ± 2 Tg/y, equivalent to 2.3% of gross U.S. gas production. This value is ~60% higher than the U.S. EPA inventory estimate, likely because existing inventory methods miss emissions released during abnormal operating conditions. Methane emissions of this magnitude, per unit of natural gas consumed, produce radiative forcing over a 20-year time horizon comparable to the CO2 from natural gas combustion. Significant emission reductions are feasible through rapid detection of the root causes of high emissions and deployment of less failure-prone systems.

Assessment of methane emissions from the U.S. oil and gas supply chain



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