Subsurface Characterization for Secure CO2 Storage in the Pennsylvanian-permian Storage Complex in the Midcontinent Region, U.S.A.

Abstract

Subsurface characterization of target injection and confining zones is essential for developing a safe and successful Carbon Capture Utilization and Storage (CCUS) project. The Integrated Midcontinent Stacked Carbon Storage Hub (IMSCS-HUB) Project is assessing the feasibility of commercial-scale CCUS implementation in the Midcontinent Region of the United States of America (USA) as part of the U.S. Department of Energy-National Energy Technology Laboratory’s (DOE-NETL) Carbon Storage Assurance Facility Enterprise (CarbonSAFE) initiative. The IMSCS-HUB project area is comprised of a carbon dioxide (CO2) source corridor that runs from eastern Iowa to western Nebraska and a stacked CO2 storage corridor that spans across western Nebraska and Kansas, representing the first large-scale CCUS project for the Midcontinent Region. The deep saline reservoirs and caprocks of the IMSCS-HUB stacked storage corridor subsurface make up a Pennsylvanian-Permian Storage Complex which is characterized by thick stratigraphic successions of marine and non-marine sedimentary rocks, (i.e. cyclothems). These stratigraphic successions provide alternating sequences of deep saline formations, oil-bearing reservoirs, shale, and evaporite units that are conducive to vertically stacked CO2 injection for geologic storage and enhanced oil recovery (EOR). Selected areas within the IMSCS-HUB storage corridor have been identified for detailed CO2 storage site characterization in southwest-central Nebraska (Sleepy Hollow Site), in western Nebraska (Madrid Site), and in western Kansas (Patterson Site). As part of the IMSCS-HUB project, characterization wells were drilled, whole and sidewall core were acquired, advanced geophysical well logs were collected, and well testing was conducted the knowledge gaps at the selected storage sites. Regional and site-specific subsurface analyses of the Pennsylvanian-Permian Storage Complex in the Midcontinent Region are conducted to validate caprock integrity through stacked-injection simulations, and to inform the post-injection monitoring plan. The lateral and vertical extents of the formations of interest are defined through well log analysis and geologic mapping. The stress regime is defined using image log data, mini-fracture tests, and drill stem tests. Petrophysical and geomechanical properties of reservoir and caprock intervals are determined through core laboratory testing, advanced well log analysis (sonic and image logs), and well testing (mini-fracture and drill stem tests). The well testing data is also used to determine the fracture pressure gradient/injection pressure constraints. The core laboratory testing includes routine core analysis (porosity, permeability, net confining stress, and grain density), mercury injection capillary pressure, effective permeability, threshold entry pressure, and triaxial compressive strength. The results of the subsurface characterization are used to construct and populate the static earth model and are key inputs for stacked-injection simulations. Three-dimensional simulations assess the baseline stresses in the subsurface and provide information on the fracture gradient to estimate the maximum permissible injection pressure, simulate the mechanical integrity of the caprocks, and evaluate the risk of induced seismic events using an injection scenario of 50 million metric tons, per the CarbonSAFE objective. The IMSCS-HUB project is supported by the U.S. Department of Energy-National Energy Technology Laboratory Agreement No. DE-FOA-0031623.