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Mt. Simon Sandstone as a Carbon Sequestration Sink in the Illinois Basin

Hannes Leetaru, David G. Morse, Scott M. Frailey, and Robert Finley
Illinois State Geological Survey, Champaign, IL

The Cambrian age Mt. Simon Sandstone is a saline reservoir that underlies most of the Illinois Basin at depths from close to surface to over 16,000 feet. It is overlain by shales of the Cambrian age Eau Claire Formation and is underlain by Precambrian granites. The Mt. Simon reservoir sandstone has porosities up to 14 percent and permeabilities of over 100 mD. Mt. Simon gas storage fields indicate that the Eau Claire is an effective seal for gas containment.

The upper 200 feet of the Mt. Simon is composed of sandstone beds that are commonly no more than 20 feet thick and separated from each other by thin zones of discontinuous shale or low permeability siltstone. Three-dimensional reservoir modeling of the upper Mt. Simon demonstrates the lack of laterally extensive correlative shale barriers that would vertically compartmentalize the reservoir; instead the shales behave as baffles that impede but do not stop reservoir communication. Wireline logs suggest that below the upper Mt. Simon there are additional porous reservoir sandstones with potentially stacked reservoir strata 100's of feet thick. Although the Mt. Simon is over 2000 feet thick in the central part of the basin, seismic reflection data and well logs suggests that it is thin or absent over local Precambrian paleo-highs near the edge of the basin.

The long history (almost 50 years) of successful natural gas storage in the Mt. Simon indicates that this saline reservoir could provide successful containment for carbon dioxide sequestration and that further detailed evaluation is warranted.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005