A recent techno-economic assessment led by Professor Mark Mba-Wright at Iowa State University examines an innovative path for carbon removal: using bio-oil derived from plant waste to seal abandoned oil wells-also known as orphan wells-while locking away carbon dioxide (CO) deep underground.

Using waste streams like corn stover, forest debris, and other biomass, the process begins with fast pyrolysis, a high-temperature, oxygen-free treatment that converts dried plant material into liquid bio-oil, biochar, and usable gas. The biochar can be used to improve soil quality, while the gas powers parts of the process.

The study models a system of 200 mobile pyrolysis units, each able to process about 10 tons of feedstock per day, producing roughly 5.3 tons of bio-oil and 2.5 tons of biochar daily per unit. Building each mobile unit is estimated to cost about $1-2 million, and for the system to break even, the bio-oil must sell for at least $175 per ton.

In terms of carbon sequestration, the estimated carbon abatement cost is about $152 per ton of CO when using mixed biomass, and approximately $100 per ton for wood-based feedstocks.

The U.S. has more than 123,000 documented orphaned oil and gas wells, with estimates ranging from 310,000 to 800,000 undocumented abandoned wells. Traditional well-plugging methods-such as cement-often cost up to $1 million per well.

Besides environmental benefits, this approach could create new revenue streams for farmers by monetizing agricultural residues, reduce loterm well-capping costs, and stimulate rural economic activity. Farmers could also use biochar to enrich soil, potentially reducing input costs like fertilizer and enhancing land value.

However, challenges remain. Bio-oil is chemically unstable, acidic, and corrosive, requiring careful management in transport and injection. In addition, regulatoryworks are not yet fully developed for using this material in underground applications.

Still, researchers say this strategy compares favorably to other carbon removal technologies such as direct air capture-particularly because it uses existing infrastructure, distributes production through mobile units, and delivers multiple co-benefits for agriculture and climate goals.