Quantifying atmospheric methane emissions from oil and natural gas production in the Bakken shale region of North Dakota

We present in situ airborne measurements of methane (CH₄) and ethane (C₂H₆) taken aboard a NOAA DHC‐6 Twin Otter research aircraft in May 2014 over the Williston Basin in northwestern North Dakota, a region of rapidly growing oil and natural gas production. The Williston Basin is best known for the Bakken shale formation, from which a significant increase in oil and gas extraction has occurred since 2009. We derive a CH4 emission rate from this region using airborne data by calculating the CH₄ enhancement flux through the planetary boundary layer downwind of the region. We calculate CH₄ emissions of (36 ± 13), (27 ± 13), (27 ± 12), (27 ± 12), and (25 ± 10) × 103 kg/h from five transects on 3 days in May 2014 downwind of the Bakken shale region of North Dakota. The average emission, (28 ± 5) × 103 kg/h, extrapolates to 0.25 ± 0.05 Tg/yr, which is significantly lower than a previous estimate of CH₄ emissions from northwestern North Dakota and southeastern Saskatchewan using satellite remote sensing data. We attribute the majority of CH₄ emissions in the region to oil and gas operations in the Bakken based on the similarity between atmospheric C₂H₆ to CH₄ enhancement ratios and the composition of raw natural gas withdrawn from the region.