Physical properties of sidewall cores from Decatur, Illinois

To better assess the reservoir conditions influencing the induced seismicity hazard near a carbon dioxide sequestration demonstration site in Decatur, Ill., core samples from three deep drill holes were tested to determine a suite of physical properties including bulk density, porosity, permeability, Young’s modulus, Poisson’s ratio, and failure strength. Representative samples of the shale cap rock, the sandstone reservoir, and the Precambrian basement were selected for comparison. Physical properties were strongly dependent on lithology. Bulk density was inversely related to porosity, with the cap rock and basement samples being both least porous (<3 percent) and densest (~2.6 grams per cubic centimeter [g/cc]). Permeability was highest in the reservoir sandstones (10-15 to 10-18 meters squared [m2]) relative to the cap rock and basement rocks (<10-21 m2). Young’s modulus was distinctly higher in the basement rocks (45 to 80 gigapascal [GPa]) compared to the cap rock and sandstones (19 to 57 GPa). Poisson’s ratio for the sandstones varied widely (0.14 to 0.27), but the highest values were similar to the cap rock and basement rocks (0.24 to 0.28). These physical properties reflect the layered structure of the reservoir and adjacent rocks at the Decatur site. However, within the sandstone there is a great deal of lithologic variety, accounting for the large range in physical parameters for this geologic unit.