More than 14,000 inactive oil and gas wells remain uncapped in the Gulf of Mexico. Leaks from wells could harm marine ecosystems and increase emissions of planet-warming methane, but plugging them would cost billions.
Mark Agerton at the University of California, Davis, and his colleagues collected data from the US Bureau of Safety and Environment on the 82,000 wells drilled in the Gulf of Mexico. While most wells have been plugged and abandoned, they found more than 14,000 are disconnected, despite having been idle for at least five years, a point beyond which they are unlikely to restart the production.
Operators are legally required to plug wells once they are taken out of production, which usually involves a cement plug covered in sediment. Just over 5,000 wells remain active.
Oil leaking from wells, especially those closer to shore, could harm marine ecosystems. Wells near the shore can also leak methane which can then reach the atmosphere. The researchers found that the methane escaping from wells in deeper waters further offshore would be consumed primarily by marine microbes.
The 2010 Deepwater Horizon oil spill, which resulted from a surge of natural gas blowing through a temporarily clogged well, illustrates a worst-case scenario. Unlike this well, however, there are many unplugged wells in operation, and it is unclear what impacts many small chronic leaks might have. “We don’t think about catastrophic eruptions as much,” says Agerton.
An infrastructure bill passed by the US Congress in late 2021 earmarked $4.7 billion to plug orphan onshore and offshore wells, but David Small at the National Resources Defense Council says “there is no way” that all the wells will be plugged. “There are not enough administrative interests or money,” he says.
The researchers estimated that plugging all the inactive wells would cost more than $30 billion; plugging wells in shallow waters alone would cost around $7 billion. For wells in federal waters, the oil companies that dug them are responsible for plugging them — and they remain liable even if a well they drilled is sold to a smaller operator who cannot pay to plug them. In state waters, the cost of plugging such “orphan” wells could fall on the state.
Researchers say U.S. agencies should focus their efforts on shallow-water wells that pose the greatest environmental threat and are the cheapest to plug.