Porosity characterization and diagenetic facies analysis of the Cambrian Mount Simon Sandstone: Implications for a regional carbon dioxide sequestration reservoir

The Cambrian Mount Simon Sandstone is being assessed for its potential as a reservoir for geological sequestration, long term storage of injected carbon dioxide in the Illinois Basin. The Mount Simon Sandstone is the basal siliciclastic unit in the sedimentary sequence that overlies Precambrian crystalline basement and is conformably overlain by the Eau Claire Formation. Thickness of the reservoir varies from a few hundred feet in the southern Illinois Basin to over 2,500 ft to the northern part of the basin. The Mount Simon Sandstone\u27s candidacy as a CO2 sequestration reservoir is due in part to its depth, widespread lateral extent, high estimated capacity, and appropriate geologic setting. The Mount Simon Sandstone is a mature quartz to arkosic arenite, with significant spatial variations in mineralogy, porosity, and diagenetic and depositional influence on reservoir properties being studied regionally. Prior to this study, increased pressure solution and quartz overgrowth precipitation with depth have been interpreted as the primary porosity reduction mechanism, however, this work demonstrates that there are multiple other factors that influence porosity. Petrographic image analyses were conducted on 150 thin sections from a range of depths across the Illinois Basin to assess the distribution of effective porosity and characterize pore types. Four dominant and four subordinate types of pores have been identified and illustrate different types of porosity with depth. Samples from shallow depths indicate that the depositional environment was the primary influence on the development of porosity. Deeper samples exemplify higher amounts of diagenetic influence with variable extremes of greater porosity development by either dissolution or cementation. The samples with the highest porosity at depths appropriate for CO2 sequestration show significant dissolution porosity in zones with relatively high feldspar abundance. Authigenic cements are found to influence porosity by reduction of effective pore space. Ten diagenetic facies were interpreted based on authigenic mineralogical composition and abundances, degree of dissolution, and lithological differences. Diagenetic facies were mapped across Indiana and Illinois and to see how the diagenetic processes impact reservoir development. Understanding details of this reservoir\u27s composition is essential for predicting mineral reactivityand identifying potential fluid flow pathways for effectively storing CO2