GEOMECHANICAL ASSESSMENT OF SUB-KNOX FORMATIONS FOR SAFE CO2 INJECTION STUDY IN THE MIDWEST U.S

Recent advances in research on carbon sequestration have raised the question regarding integrity of subsurface storage reservoirs, in terms of interplay among poro-elastic properties, CO₂ injection rate and potential subsurface deformation. This study presents the results from integrated rock property characterization and coupled flow-geomechanical simulations for CO₂ injection in the Sub-Knox formations at three sites in the Midwest U.S. The main objectives of this work are to investigate the vertical variation of poro-elastic properties to better define the injection unit, and understand the fate of CO₂ upon long-term injection into the site.

We used various petrophysical and geomechanical measurements from core samples and advanced well logs (such as multi-component sonic, resistivity image, and nuclear magnetic resonance) to analyze porosity, permeability, Young’s modulus, Poisson’s ratio, principal stresses, and others. All these parameters were integrated to subdivide the Sub-Knox formations into various geomechanical units, which are comparable to certain flow-zone units. Next, these parameters were chosen as input to coupled flow-geomechanical simulations at various rates of CO₂injection to analyze corresponding stress-field response in the reservoir and caprock.

Preliminary results show that the Basal Sandstone Formation may be considered as a favorable reservoir for CO₂ injection, where it has combination of suitable geomechanical properties, porosity, permeability, and required overburden. The Basal Sandstone Formation consists of seven poro-elastic units, out of which four units have higher rigidity compared to three others. Detailed characterization of sedimentary formations, in terms of poro-elastic properties is critical to delineate suitable CO₂-injection-units for storage, and use these units as a guide to geologically meaningful reservoir simulation.