One major source of these missing emissions, Rutherford said, is liquid storage tanks. Some emissions are intentional – such as “flashing,” in which dissolved methane under pressure escapes when the pressure is reduced. “It’s like opening a beer,” Rutherford analogized. “It’s liquid as long as there is high enough pressure, but if you release the pressure, the gas quickly escapes.” But much is due to operator errors, such as when a technician accidentally leaves a hatch open or separation equipment malfunctions. The combination of the two leads to very high emissions from storage tanks, although storage is only one component among many where Rutherford and Brandt point the finger.

The upshot of their new methane inventory is twofold, Brandt said. The first is awareness. It highlights a key shortfall in the current modeling that is used to make important environmental decisions and spotlights specific activities that should be targeted for remediation or regulation. Second, he said, the goal is not to replace existing models, but to provide a useful baseline tool upon which to base modifications to those models to make future inventories more accurate.

To that end, Rutherford has been making the rounds talking to state and federal regulators as well as oil and gas producers about the findings of the new model and how they can best make use of the lessons learned.

“It is helpful simply to identify that there is a problem,” Rutherford said. “But, beyond that, our model offers up some clear actionable steps to improve our inventories and ways operators can adjust their practices that could really make a difference in reducing the amount of methane entering the skies.”

Adam Brandt is also a senior fellow at the Precourt Institute for Energy. Evan Sherwin, postdoctoral scholar at Stanford, is also a co-author. Additional co-authors are from Harrisburg University of Science & Technology, the Joint Institute for Strategic Energy Analysis at the National Renewable Energy Laboratory, the California Air Resources Board, Colorado State University and the Environmental Defense Fund.

This research was funded by the California Air Resources Board. Additional support was provided by Novim.

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