A 2018 explosion at an Ohio natural gas well owned by an Exxon Mobil Corp. subsidiary spewed significantly more methane than the company initially estimated, according to an analysis of satellite images released Dec. 16.
The satellite images also indicate that the amount of methane released during the 20-day event was greater than the annual reported emissions of some European countries, including France, Spain and Sweden.
Methane emissions are the second-largest contributor to global warming but have historically been difficult to monitor and measure. The satellite image analysis paper, published in the Proceedings of the National Academy of Sciences, said the findings indicate that methane emissions around the world could be more widespread than prior studies have estimated.
"These comparisons highlight the importance of accidental emissions for regional- and national-scale emission reporting and inventories, as the lack of incorporating such emissions can lead to significant underestimation of overall emissions," the scientists said in the paper.
Using data gathered during a routine global survey by a satellite known as TROPOMI, scientists were, for the first time, able to both detect and quantify the likely rate of the methane emissions leaked into the atmosphere from a well owned by XTO Energy Inc. in Belmont County that blew out in mid-February 2018 and was not contained until March 7, 2018. After the event occurred, an XTO spokesperson said at the time that the leak rate was likely well below the U.S. Environmental Protection Agency's estimate of 100 MMcf/d.
But satellite data gathered Feb. 27, 2018, the 13th day of the event, showed that the damaged well was emitting about 120 metric tons of methane per hour, or about 156 MMcf/d, which is significantly higher than the company suggested. Moreover, the rate identified for the Ohio well explosion was twice the peak emissions rate of the Aliso Canyon leak in California in 2015.
Assuming that rate reflected the average leakage amounts for the 20-day period, total emissions from the event would have totaled about 60,000 metric tons, which is 3,120 MMcf, or about one-quarter of Ohio's reported annual oil and gas methane emissions. The estimated total emissions from the one event in Ohio was greater than the annual oil and gas emissions for all but three — Germany, Italy and the U.K. — of 15 European countries reviewed in the study.
Exxon spokesperson Julie King said in an emailed statement that the company's scientists are reviewing the study and its assumptions. King also said the company has instituted procedures to prevent events like the Ohio well blowout from happening again. Exxon is "working with government laboratories, universities and others to identify the most cost-effective and best-performing technology, including satellites, that can be adopted by all producers to detect, repair and accurately measure methane," King said.
One path to measuring future emissions could be relying more on additional satellite data, report co-author Steven Hamburg, a chief scientist at the Environmental Defense Fund, said in a statement. Hamburg is co-lead for EDF subsidiary MethaneSAT, which is scheduled to launch a satellite in 2022 designed to measure methane across the globe weekly.
The latest results from the TROPOMI satellite "show the opportunity for satellites to help see and quantify emissions no matter where they are," Hamburg said. "Regular, widespread data like this offers an invaluable tool for industry and public officials alike to understand problems and identify effective solutions."