USING SEISMIC ATTRIBUTES TO EVALUATE LOWER PALEOZOIC AND PRECAMBRIAN STRUCTURE BENEATH A CARBON CAPTURE AND STORAGE SITE, ILLINOIS BASIN

The Illinois Basin - Decatur Project (IBDP), located in the Illinois Basin at Decatur, Illinois, represents one of the premier sites for evaluating technologies for Carbon Capture and Storage. A dedicated high-resolution 3D seismic data set constrains the possible relation of injection-related microseismicity to structural discontinuities in the Lower Paleozoic and Precambrian beneath the site. Interpretation workflows using 3D seismic attributes have previously revealed coherent patterns of discontinuities in the deep Precambrian basement underpinning the IBDP site. Our study extends this previous work by applying a similar sequence of attribute workflows to the Cambrian Mt. Simon Sandstone that constitutes the injection zone and to the shallow Precambrian basement immediately beneath it. Multiple attribute volumes have been generated, including maximum curvature, cosine of phase, semblance, and spectral decomposition. Microseismic events were then populated in a 3D workspace along with the seismic attribute solutions. Co-rendering curvature and cosine of phase in time-slice views yields coherent patterns that correlate well with the location and azimuthal orientation of microseismic hypocenters. These attributes are good proxies for geomorphic shapes, as they largely ignore seismic amplitude, and focus on boundaries and 3D reflector geometry. They thus aid in visualization of faults and stratigraphic terminations. In order to provide geological “cross-section” views, cosine of phase data were co-rendered on the vertical face of the amplitude volume. 3D rendering of the attributes revealed correlation of microseismicity with shallow dipping (<20^o) discontinuities in the uppermost Precambrian basement. The reflector discontinuities are especially discernible using the cosine of phase overlay on the amplitude volume. The shallowness of the dip can provide insights on the response of the basement to its tectonic stress history as well as to the inducing of microseismic events related to injection. This represents a departure from previous interpretations, which have delineated steeply dipping or near-vertical discontinuities.