Deep, saline aquifers in the US have sufficient capacity to sequester a century’s worth of CO2emissions from the nation’s coal-fired power plants, according to a research team at the Massachusetts Institute of Technology who published their findings in the Proceedings of the National Academy of Sciences on April 3.
The findings substantially refine estimates of the storage capacity of these reservoirs, which the Global CCS Institute recognizes as having the most promising potential of any geological storage option. Previous measures of their capacity in the US spanned from a few years’ of CO2 emissions, to tens of thousands of years’ worth.
Earlier assessments tended to oversimplify the problem, leading to the wide range. “We felt that there was such a big disparity in numbers out there that CCS deserved a closer look,” team leader Ruben Juanes, MIT’s ARCO Associate Professor in Energy Studies in the Department of Civil and Environmental Engineering, told The New York Times.
MIT researchers improved the accuracy of these estimates by building a more detailed mathematical model. Previous models were “missing some of the nuances of the physics,” said Christopher MacMinn, a doctoral researcher and co-author of the study, via a press release.
The MIT team modeled micron-scale fluid dynamics to better understand how liquefied CO2 is trapped in deep saline aquifers. Including some 20 parameters, the team designed the mathematical model to be flexible enough to evaluate the potential of saline aquifer formations at the scale of hundreds of miles, and in different regions of the US.
“The key is capturing the essential physics of the problem,” said Michael Szulczewski, a doctoral researcher and co-author of the study, “but simplifying it enough so it could be applied to the entire country.”
Using glass beads to simulate the way liquefied CO2 would percolate through the tiny poor spaces of deep rock formations, the approach helped the MIT team to better understand rates of injection and how the CO2 is sequestered through the dynamics of capillary trapping and solubility trapping. Of key concern was estimating the pressure and rates of CO2 injection necessary to prevent fracturing of the reservoir or its over-capping structures.
The study “demonstrates that the rate of injection of CO2 into a reservoir is a critical parameter in making storage estimates,” said Howard Herzog, a senior research engineer with the MIT Energy Initiative and another co-author of the PNAS paper, in a release.
While this study is focused on the saline aquifers in the US, the method can be extended to similar geologies around the world, MacMinn added.
The abstract for the paper, Lifetime of carbon capture and storage as a climate-change mitigation technology is published at PNAS.
Also, below is a video where Juanes and his team members explain their work. The first half-minute or so is a basic overview of carbon storage. Stick with it; starting around 0:45 Szulczewski goes into greater detail of the model’s approach to the subsurface dynamics of CO2 injection.