Potential of the Cambro-Ordovician Knox Carbonates of Illinois as Combined Reservoirs and Seals for Carbon Sequestration

Yaghoob Lasemi, Z. Askari, and H. E. Leetaru
Illinois State Geological Survey, Prairie Research Institute, Champaign, IL, [email protected]

The Cambo-Ordovician succession in Illinois is up to 6000 feet thick and consists of alternating carbonate-dominated and siliciclastic-dominated units. The carbonate units, from base to top, include the Cambrian Franconia Formation, Potosi Dolomite, Eminence Formation, and the Ordovician Oneota and Shakopee Dolomites. The siliciclastic units comprise the Cambrian Eau Claire Formation, Galesville and Ironton Sandstones, and the Ordovician Gunter and New Richmond Sandstones. The siliciclastics thin southward and in the central and southern deep area of the basin, dolomite is the dominant lithology of the Knox succession. To evaluate the potential reservoirs and seals of the Knox deposits for CO2 storage, deep wells in Illinois were studied for petrographic examination and geophysical log correlation.

Detailed facies analysis indicates that the Knox carbonates consist of dolomitized mudstone to grainstone facies (generally preserved in silicified intervals) and relics of bioclasts, ooids, and peloids recording deposition in a shallow marine ramp setting. The dominant lithology of the Knox carbonates is fine to coarsely crystalline dense dolomite. The intercrystalline pore space of the original dolomite was lost as a consequence of later stage diagenetic dolomite overgrowth or cementation. The dense dolomite interval of the Knox succession, therefore, could serve as an effective seal for the encompassing permeable units. In addition to porous and permeable sandstone units, vugular and/or fractured intervals are present within the dolomite of the Knox Group. They are laterally discontinuous and could serve as important reservoirs for carbon sequestration.

AAPG Search and Discovery Article #90154©2012 AAPG Eastern Section Meeting, Cleveland, Ohio, 22-26 September 2012