CHARACTERIZING GEOLOGIC FEATURES AT THE CONTACT OF PRECAMBRIAN BASEMENT AND THE OVERLYING MT. SIMON SANDSTONE, AND IMPLICATIONS FOR CO2 STORAGE

Geologic carbon storage (GCS) in the Illinois Basin has been carried on for a couple of years as a viable option to reduce the level of CO₂ in the atmosphere. One of the important concerns regarding GCS is injection-induced microseismicity. Detailed characterization of reservoir-scale geologic features is necessary for construction of geological models that can include the spatial variation of geomechanical properties and seismic velocities of the appropriate rock units, and thus allow modeling of subsurface fluid flow. This will thus help improve understanding of the mechanisms of injection-induced microseismicity, so that its occurrence can be better predicted and controlled. A representative geological model is, however, often limited by available geologic data from sparse subsurface data. Consequently, analogue studies of similar depositional environments play an important role in improving understanding of the sedimentary architecture of geologic formations. Analogues provide detailed information on sedimentary structures, geobody geometry and its lateral variability, which are important input variables for geological modeling.

This study focuses on a study of the basement topography in potential CO₂ sequestration sites and the facies at the contact of the Precambrian basement and overlying injection zone of the Mt. Simon Sandstone, which are c. 34m apart from the basement at one injector site. Outcrop photogrammetry and sedimentary logging were used to study an analogue of the Mt. Simon Sandstone, the Lamotte Sandstone in southeast Missouri. This paper will detail the nature of the basement – Mt. Simon contact, and compare these outcrops with core analysis and borehole geophysical data from the Mt. Simon Sandstone GCS site. This analysis indicates that the depositional environments included braided fluvial, eolian, debris flow deposits and interdune deposits that show spatial variability in their thickness and characteristics. Characterization of facies and sedimentology around these Precambrian highs, in terms of their sedimentological and geomechanical properties and spatial variability, can be used to enhance models of the environments of deposition.