4 Brigham Young University, P.O. Box 24606, Provo, UT 84602,

The Ordovician St. Peter Sandstone and Cambrian Mt. Simon Sandstone are saline reservoirs that underlie much of the Illinois Basin. Both are used for natural gas storage in the northern part of the basin and are currently being evaluated as reservoirs in which to successfully sequester carbon dioxide. However, no St. Peter or Mt. Simon gas storage projects have been undertaken in areas where these reservoirs are deeper than 4,500 ft. In the deeper part of the basin, relatively few wells (approximately 25 wells) have penetrated these saline reservoirs and thus seismic reflection data are necessary for characterizing the nature of the reservoirs and the geometry of the traps that contain them.

Although the Mt. Simon is over 2,000 feet thick in the northern part of the Illinois Basin, seismic reflection data and well logs suggest that it is thin or absent over local Precambrian paleo-highs south of this depocenter. In some cases, the Mount Simon may truncate onto the flanks of these paleo-highs. The geometry of these traps can be identified by the thinning and termination of seismic reflector packages. The character of the internal stratigraphy within these reservoirs and the overlying confining strata can also be assessed using seismic data. Commonly, structure maps on shallower horizons defined by oil and gas wells are used to project the deeper structure. In the Illinois Basin, the shallow and deeper strata are not necessarily structurally aligned; the crests can be laterally offset by thousands of feet. In some cases deep-seated faults penetrate only these lower Paleozoic strata and can only be accurately mapped with 3-D seismic reflection data.

AAPG Search and Discovery Article #90059©2006 AAPG Eastern Section Meeting, Buffalo, New York