Their estimate is that the yearly damage is equal to one day's usage by the United States of crude oil, or 1/365th of the yearly damage done by the U.S. from crude oil usage.
https://uk.reuters.com/article/us-us...-idUKKBN23N1NL
The group is among an array of regulators, activists and federal agencies now seeking out abandoned wells from the U.S. Northeast to California. The heightened interest in the climate threat posed by the wells started with a 2014 study by Princeton graduate student Mary Kang, who was the first to measure methane emissions from old drilling sites in Pennsylvania. She concluded in 2016 that abandoned wells represent 5% to 8% of total human-caused methane emissions in the state.
“It’s not like they leak for one year, and then they stop,” said Kang, now a professor of civil engineering at McGill University in Montreal. “Some of these have been there maybe for 100 years. And they are going to be there for another 100 years.”