PITTSBURGH (TNS) — Low-producing wells pump out just 6% of U.S. oil and gas each year but account for roughly half of the climate-warming methane that escapes from all of the nation’s oil and gas well sites, according to a new peer-reviewed study led by the Environmental Defense Fund.

The problem is especially concentrated in Pennsylvania and the broader Appalachian region, the researchers found, where about 180,000 generally decades-old, marginal well sites account for almost a third of the total methane emissions that come from low-producing wells nationwide.

The paper, which was published this week in the journal Nature Communications, defines low-producing wells as those that produce less than 15 barrels of oil equivalent a day. In Pennsylvania and across the country, many of those wells are exempt from regular leak checks that are required at bigger wells.

”The methane footprint of these small wells is enormous and can’t be ignored,” said Mark Omara, a scientist with the Environmental Defense Fund and the study’s lead author. He said collectively, they have the same climate impact every year as 88 coal-fired power plants.

Draft rules proposed by the U.S. Environmental Protection Agency to curb methane releases from new and existing wells would exempt sites from ongoing monitoring if they are expected to release less than 3 tons of methane per year, which is generally equivalent to the low-producing well site threshold used in the study. The EPA estimated that only 14% of well site fugitive emissions come from sites with lower-producing wells.

But federal regulators are also considering a supplemental proposal this year that could require low-producing wells to conduct regular monitoring.

Methane traps 86 times as much heat in the atmosphere as carbon dioxide over 20 years but degrades more quickly. It is a primary focus of international efforts to address climate change rapidly in the short term.

In the oil and gas industry, lost methane is also a waste of a valuable product. The researchers said methane that escapes from low-producing wells is worth about $700 million a year at 2019 prices.

According to the study, “avoidable maintenance-related issues” are a key driver of methane emissions at low-production well sites, “particularly at older sites that tend to suffer from prolonged lack of attention from their owners or operators.”

”Routine emissions monitoring and repair has the potential to yield large emission reduction benefits,” the authors found.

In Pennsylvania, state rules set to take effect this spring will require new quarterly or annual leak monitoring at only 95 of the state’s 27,000 producing conventional well sites, because the rest produce too little oil or gas to qualify, according to the state Department of Environmental Protection.

Still, state regulators expect the rules to cut methane emissions from conventional well sites in half, largely because they require even low-producing sites to replace equipment that intentionally vents methane with less leaky parts.

Trade groups representing conventional oil and gas companies in Pennsylvania have said most of the industry’s wells in the state are owned by small, family-owned businesses and produce an average of less than 1 barrel of oil equivalent a day.

”Less production equates to low or no emissions,” the Pennsylvania Grade Crude Oil Coalition and other groups wrote to the EPA in January.

EPA’s proposal would require each low-producing well site to calculate its methane emissions as a baseline to determine if routine leak detection is warranted. Even that calculation would put conventional oil and gas operators “in serious financial jeopardy,” the groups wrote.

According to the Environmental Defense Fund study, 77% of marginal wells in the U.S. are owned by companies that operate over 100 well sites each and that had average revenue of $335 million in 2019. Less than 4% of low-producing well sites are owned by companies that have 10 or fewer sites.

In recent years, one company, Diversified Energy Co., has accumulated more than a fifth of the 100,000 active conventional wells in Pennsylvania.