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Abstract

Multiple approaches are under development to mitigate the release of potentially harmful human-generated CO2 into the atmosphere. Geologic carbon sequestration is one such process by which CO2 that would otherwise be vented to the atmosphere is liquefied, injected, and stored in the pore space of a subsurface reservoir. The Cambrian Mount Simon Sandstone (MSs) is a targeted reservoir for CO2 sequestration in the Illinois Basin. The goals of this research are to analyze a set of subsurface samples related to ongoing CO2 sequestration demonstrations in the Illinois Basin. These samples contain evidence of small-scale fractures and deformation bands in the MSs. We provide a detailed analysis of their geometry, association with sedimentary facies, potential origin, and any apparent fluid-related diagenesis. Core samples displaying fractures were analyzed visually to characterize the sandstone and fracture geometry, and at higher resolution using thin section transmitted light petrography. Scanning electron microscopy with energy dispersive X-ray analysis (SEMEDX) was used to analyze even smaller-scale structures along with select geochemical properties. Observed fracture types in the MSs include: 1) deformation bands and 2) open fractures filled with authigenic cements. Observed deformation band types include a) compaction bands, b) shear bands, and c) cemented dilatation bands. Low porosity/permeability deformation bands have the potential to block fluid migration, while open fractures create secondary porosity/permeability. These small-scale deformational structures can impact the routes that migrating fluids will travel along, therefore directly impacting CO2 sequestration operations.

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