DENVER (AP) — From Colorado's high desert to the wooded hills of northwest Pennsylvania, millions of deserted oil and gas wells plunge thousands of feet into the earth after fossil fuels have been pumped out, combusted and released as carbon dioxide. They have long been symbols of pollution.

Colorado lawmakers are considering a new solution that would give these wells a redemptive purpose: deep receptacles to trap carbon for millennia.

The idea is to keep carbon locked away in biochar — a special type of carbon-rich charcoal that's made from burning organic matter such as plants at high heat and little to no oxygen. The hope is that defunct oil and gas wells could be plugged using biochar. This would not only filter dangerous gas leaks but also keep carbon out of the atmosphere and prevent it from forming carbon dioxide, a greenhouse gas.

Lawmakers in Colorado's Democrat-controlled statehouse want to launch a study to assess if biochar would work to plug orphaned wells, and they plan to discuss it Thursday afternoon.

If successful, experts say using biochar to help fill a portion of the over 3 million abandoned oil wells nationwide could help slow climate change.

The bill would, in part, direct Colorado State University to review current research and run new tests to answer a number of questions. Those include the efficacy of biochar's filtration properties, the tonnage of carbon that could be sequestered, and even how the substance would interact with its subterranean environment.

Carbon naturally cycles through Earth's ecosystems, floating in the atmosphere as carbon dioxide before being snatched up by little bluestem grasses, ingested by grazing bison on the prairie, and when the animal keels over and begins decomposing, returning to the atmosphere as carbon dioxide.

But extracting fossil fuels has unearthed carbon — formed out of ancient plant matter over eons — that's been stored underground largely since the Mesozoic Era, the age of dinosaurs over 65 million years ago.

"Where we need to focus is: How do we not only stop putting excess carbon into the cycle but can we take measures to take carbon out of the cycle permanently?" said Rep. Karen McCormick, a Democrat and one of the bill's sponsors. "That's where I see biochar having a great benefit."

North of Denver in the small town of Berthoud, one company already makes biochar and sells it to governments and farmers. On a recent day at Biochar Now's facility, a tractor drove across the muddy yard, its bucket holding shards of wood bound for a new life as biochar. Nearby, dead logs were stacked in neat piles. They were likely either killed by invasive beetles in Rocky Mountain forests or were casualties of a 2021 wildfire near Boulder, the most destructive in state history.

What they have in common, said James Gaspard, the company's co-founder, is that they'd otherwise be doomed to rot in a landfill, oozing CO2. Instead, the wood debris is loaded into large kilns, where the heat burns at three times the temperature of fire and the oxygen is sucked from the chamber in a process called pyrolysis. What's left is biochar.

Biochar has a carbon structure closer to a diamond, said Jim Ippolito, a professor at Colorado State University. Unlike a decomposing bison, biochar pulls carbon out of the cycle.

While diamonds might last forever, biochar isn't far behind and can keep the carbon atoms inert — unable to form C02 — for centuries if not thousands of years.

And like diamonds, biochar's pitch-black flakes and dust shimmer. It's lightweight — like popcorn — and porous like a sponge, which is why it already has an international market.

From Colorado, Biochar Now ships bags of the substance nationwide and to other countries including Canada. Biochar is deployed at wastewater treatment plants as a filter, in soil to retain nutrients and in streams to pull out pollutants.

That's partly why it's being proposed to plug oil and gas wells. It could help absorb dangerous gases such as methane that still seep from abandoned shafts. The plugging process includes pouring concrete at certain points in the wellbore — the vertical shaft — and can include stuffing the remaining space with a combination of fillers like sand, gravel or clay.

The Colorado study will determine if biochar could make up a portion of the slurry pumped into wells, and if it could be used as an ingredient in the concrete that's poured as the plug.

Colorado's oil and gas industry association said it "looks forward" to working with McCormick in finding the best use for biochar.

If passed, the measure would let scientists to take a key step forward in assessing whether biochar in wells is a viable form of carbon sequestration.

"That's what we need to prove, back this up with hard data, so that we can say: 'Hey Louisiana, hey Mississippi, hey Texas, you can see what we are doing here,'" McCormick said.

___

Jesse Bedayn is a corps member for the Associated Press/Report for America Statehouse News Initiative. Report for America is a nonprofit national service program that places journalists in local newsrooms to report on undercovered issues.