There are hundreds of thousands of abandoned oil and gas wells in the United States. These underground shafts are inches wide and miles deep and need to be filled and capped to limit greenhouse gas emissions and safety risks.
Plugging spent crude oil wells with a bio-oil made from plant-based leftovers like corn stalks and forest debris could be a possible solution with a two-birds-one-stone appeal, based on research led by Iowa State mechanical engineering professor Mark Mba-Wright (’07,’08, ’10).
“On the one hand, you have these underutilized waste products. On the other hand, you have abandoned oil wells that need to be plugged. It’s an abundant resource meeting an urgent demand,” Mba-Wright says.
The core of the proposed system is fast pyrolysis, a process of transforming dried particles of biological material into liquid bio-oil by exposing them in an oxygen-free environment to a few seconds of intense heat exceeding 1,000 degrees Fahrenheit. Various uses for bio-oil have been identified, and more are being studied. It’s a research focus at Iowa State’s Bioeconomy Institute, where Mba-Wright is an associate director.
The plant matter used to make bio-oil holds carbon pulled from the air as carbon dioxide. So injecting carbon-rich bio-oil into underground shafts acts as a form of sequestration, permanently removing its carbon from the atmosphere.
Based on research by Mba-Wright’s team, a network of 200 mobile biooil production facilities across the U.S. could be an economically and technically feasible expansion of the technology, which is already in limited commercial use. In a recent study, they estimated that the proposed system of small bio-oil units could sequester carbon dioxide for about $152 per ton. That would make bio-oil sequestration competitive with the dominant method of removing atmospheric carbon, direct air capture, with less upfront investment.
“One of the innovations here is that you can do carbon capture with units the size of a skid loader or a combine. You can start small,” Mba-Wright says. “We’re trying to show carbon removal doesn’t need to be either/or. There are a lot of opportunities.”
In the system envisioned in Mba-Wright’s analysis, each mobile fast pyrolysis unit would process about 10 tons of feedstock a day. In the Midwest, the main biomass source studied was corn stover, the portion of the plant left in the field after harvest. That could generate a new revenue stream in rural farming communities, an associated benefit that direct air capture doesn’t offer.
“Bio-oil from Midwestern farmlands is a win-win strategy for farmers and energy companies to meet society’s growing demand for clean energy solutions,” he says.
