As many as 11,445 giant underground gas storage wells in the United States have only a single barrier to failure preventing the leak of massive amounts of methane into the atmosphere, a new report has found.
That means 64% of the country’s gas storage wells have a design that may be susceptible to a “single point of failure,” found researchers, after analyzing leakage incident reports submitted to federal regulators and studies pf past leakage events. The new result is nearly three times previous estimates.
“That population is a lot larger than we had estimated, or other researchers had estimated with state [data],” Greg Lackey, study co-author and researcher at the U.S. National Energy Technology Laboratory, told Inside Climate News.
The results come just over a year after roughly 16,000 tonnes of methane escaped a reservoir in Pennsylvania’s Rager Mountain gas storage field, forcing thousands to leave their homes and taking four months to contain.
Notably, all but one of Pennsylvania’s 49 gas storage fields were found to have at least one potential single point of failure well. The new research estimates that big gas leaks like that of Rager Mountain—or Aliso Canyon, California, in 2015—account for 98% of leakage emissions from underground natural gas storage (UNGS) operations.
“Considering that there are potentially thousands more single-point of failure wells at UNGS facilities than previously estimated, improved characterization and management of these wells is needed,” the study warns.
Natural gas companies store reserves of gas to maintain a stable supply amid demand fluctuations and seasonal changes, short-term supply disruptions, or to meet short-term peak demand. The reserves are often located underground in depleted and repurposed gas fields, emptied salt caverns, or aquifers. Though the study focused on UNGS in the U.S., its natural gas markets and infrastructure are tightly integrated with Canada’s, where UNGS capacity comprises depleted reservoirs, with a smaller amount in salt caverns.
The infrastructure needed to fill and extract gas from these spaces uses components like wellheads, casings, and tubing. But many of these components are at risk of failing because they’re old or were repurposed from older infrastructure. The Rager Mountain leak, for example, occurred when a 57-year old well suffered unexpected corrosion from exposure to water, air, and organic matter through an open valve.
It was these components that the study analyzed for single point of failure risks. On average, a total of 448 leaks occurred during the study period—an average of 75 wells experiencing a casing, wellhead, or tubing leak each year, with casings and wellheads the most common sources of failure. Human intervention—from incorrect operation or damage caused by outside force—was the most common (39.3%) cause of well leakage events, while leaks due to corrosion produced significantly higher emissions compared to other causes.
The researchers did not find any differences in risk between different types of UNGS sites, though the majority of facilities included in the study were depleted oil and gas reservoirs.
The Rager Mountain blowout was the most significant leak in years, but it was still smaller than Aliso Canyon, which also followed a single point of failure event. The U.S. government response is still taking shape, including a requirement for baseline risk assessments on all wells by 2027, and new rules on methane leaks and repair. A planned federal fee on “waste” methane would affect gas storage, as well, Inside Climate says.
But leaks from gas storage “are only one part of the industry’s methane problem,” the news story states. “Such facilities also are at risk of dramatic blowouts that are hard to control because they are connected to large, pressurized reservoirs of gas.”
More research is needed to hone the data and identify which wells have the greatest risk of a future blowout, Lackey said. Researchers need more information about each well’s design and construction.
“What you don’t get insight into is how many other casings there are, or where the locations of cement are,” he told Inside Climate, describing additional barriers that would lower the risk.