FRACTURE ANALYSIS IN THE MOUNT SIMON SANDSTONE AND IMPLICATIONS FOR CARBON SEQUESTRATION

The Cambrian Mount Simon Sandstone is a mature quartz arenite that is commonly the basal siliciclastic unit in the subsurface throughout the Illinois Basin and the Midwest region. Active research is being done on the formation to determine and demonstrate the reservoir capabilities of this unit for carbon dioxide sequestration programs. The Mount Simon Sandstone ranges from fine-grained, well-sorted eolian sandstone to poorly-sorted alluvial conglomerates. Changes in grain size, composition, cementation, and stratigraphic sequence all play a role in determining fluid migration though the reservoir. Many of the Mount Simon cores which have been recovered from within the Illinois Basin have captured fractures which range in size and orientation through the formation. Fractures include multiple types of deformation bands, and open fractures filled with authigenic cements. Observed deformation band types include compaction bands, disaggregation bands, shear bands, dilatation bands, and possible phyllosilicate bands. It is known that fractures can act as fluid-flow pathways and, if cemented, indeed have in the past. Zones of brittle deformation and cemented fractures can act to reduce porosity, and could potentially block fluid flow through the reservoir. Conversely, open fractures could act as conduits to flow and potentially compromise the integrity of this reservoir. The goal of this research is to analyze a set of newly obtained cores which show evidence of fracturing in the Mount Simon Sandstone and provide a detailed analysis of their geometry, association with sedimentary facies, potential origin, and any apparent fluid-related diagenesis. All of these factors may influence porosity and permeability of the reservoir and therefore affect the movement and storage potential of carbon dioxide in the subsurface.