Three Democratic U.S. lawmakers asked the head of ConocoPhillips for more information about a month-old natural gas leak from an oilfield in northern Alaska and implications for its nearby project on public lands.

U.S. Representative Raul Grijalva, the chairman of the House Committee on Natural Resources, and two other Democrats sent a letter to Ryan Lance, the chairman and CEO of ConocoPhillips, asking why it took a month to identify the leak at its Alpine field and control it.

More than 7.2 MMcf of natural gas, the main component of which is the potent greenhouse gas methane, escaped from the oilfield, the company and regulators said this month.

The leak temporarily cut oil production at Alpine, one of the largest conventional onshore oil fields developed in North America in the past 25 years, by about a third. Trace amounts of gas may continue to escape from the site, ConocoPhillips said in a video.

The lawmakers also asked why the company temporarily evacuated about 300 of its own personnel even as it publicly denied the leak was a threat to human health and safety.

"How close was this leak to becoming something more severe such as a blowout or explosion?" the lawmakers said in the letter.

Citing reports that the primary source of the leak was a well that was not fully cemented, they asked, "Is it standard industry practice to build wells that are not fully cemented?"

Grijalva asked ConocoPhillips what the leak's implications are for its proposed Willow project inside the National Petroleum Reserve-Alaska, a 23 million-acre (9.3 million-hectare) area on Alaska's North Slope that is the largest tract of undisturbed public land in the U.S. Grijalva's committee has jurisdiction over oil and gas resources on public lands.

Dennis Nuss, a company spokesperson, said ConocoPhillips is reviewing the letter and that Willow has undergone "extensive environmental and permitting reviews" that began in 2018.

After peaking at more than 2 MMbbl/d of crude production in 1988, Alaska's oil output has been waning, hurt by reduced investment and better opportunities in the shale fields in other states. In 2021, the state produced just 437,000 bbl/d, according to the U.S. Energy Information Administration.

The Willow project holds an estimated 600 MMbbl of oil, or more than the amount currently held in the U.S. Strategic Petroleum Reserve, the country's emergency supply stored in caverns along the Gulf Coast.