Precambrian topography and site assessment for carbon sequestration potential in the Mt. Simon Sandstone

The Cambrian Mt. Simon Sandstone underlies one of the largest concentrations of coal-fired power plants in the world and this formation may provide one of the most significant carbon storage resources in the United States. The Mt. Simon is over 2600 feet ( approximately 792 m) thick in portions of the Illinois Basin and has been used for natural gas storage for over 50 years. Sequestration sites are commonly evaluated by studying the local structure and confirming the presence of both a reservoir facies and an impermeable seal that is not breached by significant faulting. However, an assessment of any potential Mt. Simon sequestration site must also include knowledge of the paleotopography prior to deposition of this regional sandstone. Such information is critical in evaluating likely thickness and facies variations across the structure due to changes in paleo-water depth. The Mt. Simon Sandstone directly overlies Precambrian basement granitic or rhyolitic rocks and the unconformity between the two units is speculated to be in the 100's of millions of years in age. In places there was at least 1000 feet ( approximately 305 m) of topographic relief on the top of the basement surface prior to Mt. Simon deposition. The Mt. Simon is thin or not present on topographic basement high areas, whereas the low areas have thicker Mt. Simon. The paleotopography on the basement has been observed at outcrops, during subsurface drilling, and on seismic reflection data. Any potential site must, at the minimum, have seismic reflection data, calibrated with drill-hole information, in order to evaluate the presence of Precambrian topography and its impact on Mt. Simon thickness and facies variations.