14,000 oil and gas wells remain unplugged in the Gulf of Mexico

More than 14,000 inactive oil and gas wells remain uncapped in the Gulf of Mexico. Leaks from the wells could harm marine ecosystems and add to planet-warming methane emissions, 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 Environmental Enforcement on the 82,000 wells drilled in the Gulf of Mexico. While most of the wells have been plugged and abandoned, they found that more than 14,000 are unplugged, despite having been inactive for at least five years, a point beyond which they are unlikely to restart production.

Operators are legally required to plug wells once they are taken out of production, which usually involves a cement cap covered with sediment. A little over 5000 wells remain active.

Oil leaking out of the wells, especially those nearest shore, could harm marine ecosystems. Wells near shore may also leak methane that can go on to reach the atmosphere. The researchers found methane leaking from wells in deeper water further offshore would mostly be consumed by marine microbes.

The Deepwater Horizon oil spill in 2010, which resulted from a surge of natural gas blowing through a temporarily capped well, illustrates a worst-case scenario. Unlike that well, however, many of the unplugged wells are tapped out, and it is unclear what impacts many small chronic leaks could have. “We’re not thinking as much about catastrophic blowouts,” says Agerton.

An infrastructure bill passed by the US Congress in late 2021 dedicated $4.7 billion to plugging orphaned onshore and offshore wells, but David Pettit at the National Resources Defense Council says “there’s no chance” that every well will be plugged. “There’s not enough administrative interest or money,” he says.

The researchers estimated that plugging all the inactive wells would cost more than $30 billion; plugging only wells in shallow waters would cost around $7 billion. For wells in federal waters, the oil companies that dug them are liable for plugging them – and they remain on the hook even if a well they drilled is sold to a smaller operator who can’t pay to plug. In state waters, the cost of plugging such “orphaned” wells could fall to the state.

The researchers say US agencies should focus efforts on the shallow-water wells that pose the greatest environmental threat and are the cheapest to plug.