Characterization of Diagenesis and Porosity in the Mount Simon Sandstone in the Illinois Basin: Implications for a Regional CO2 Sequestration Reservoir
The Cambrian Mount Simon Sandstone has been targeted as an important geologic reservoir for carbon dioxide sequestration in the Illinois Basin and throughout the Midwest region. Given its presumed reservoir quality, proximity to underlying Precambrian crystalline basement, and the suitability of the overlying Eau Claire Formation as a confining unit, the Mount Simon may serve as a high capacity, spatially extensive reservoir that is ideal for long term sequestration of injected CO2. However, details of the controls on spatial changes in petrophysical characteristics of this reservoir including the nature of the porosity and authigenic mineralogy are not well understood. These factors have important implications on the effectiveness of the storage capacity, injectivity, and security of the Mount Simon as a sequestration reservoir. Previous studies have suggested an exponential decrease in porosity from over 40% near the surface to less than 1% at the maximum depths of 15,000 ft. However, at mid-level depths, where carbon dioxide injection is most plausible, porosity varies over nearly that entire range, suggesting more complex controls beyond simple compaction on porosity. The loss and formation of porosity in the Mount Simon is a result of a complex history of both physical and chemical diagenesis that varies with depositional facies and subsequent groundwater chemistries. Mount Simon core samples representative of varying formation thicknesses and depths in the Illinois Basin were examined petrographically and mineralogically to characterize authigenic minerals and diagenetic textures, with special emphasis on quantifying the amount and character of porosity. Image analysis software of digital micrographs was used to quantify the porosity percentage and identify classes of pores. Characterization of porosity and diagenetic facies will better constrain the factors influencing heterogeneity within this complex and significant reservoir.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009