An Assessment of Carbon Sequestration Options in the Mt. Simon of the Illinois Basin

Leetaru, Hannes¹, Scott M. Frailey¹, David G. Morse¹, Robert J. Finley¹ (1) Illinois State Geological Survey, Champaign, IL

Deep, saline water-bearing reservoirs offer the greatest potential for sequestration of large volumes of CO₂. In the Midwest, the most significant saline reservoir is the Mt. Simon Sandstone. The Mt. Simon underlies one of the largest concentrations of coal fired power plants in the world and this sandstone may provide one of the most significant carbon storage resources in the United States. An assessment of any potential Mt. Simon sequestration site must include knowledge of its depositional history, current structural configuration, and seal. An understanding of Mt. Simon geology alone is not adequate for addressing the public concerns for a safe repository for the permanent sequestration of CO₂. For example, although there can be as much as 2,000 feet of Mt. Simon sandstone present, numerical flow modeling suggests that CO₂ would migrate vertically and be primarily trapped in the uppermost part of the formation. Therefore, site assessment must also be concerned with the integrity of the caprock, formation capacity and injectivity, and vertical heterogeneities that would slow the upward migration of CO₂ and allow greater interactions with CO₂, water, and rock.

Another public concern is whether the deep native saline waters would discharge into shallower outcrops, subcrops, or into freshwater regions of the same formation. Preliminary estimates using pressure transient theory indicates small pressure (1< psi) changes occur 30 – 40 miles away from a single well after 30 years of injecting 1 Mtonne/year.