Much like an exploration play, defining a carbon dioxide (CO₂) storage target starts with understanding the subsurface. This requires the integration of all available data, from core descriptions to seismic interpretation. Unfortunately, in the areas and reservoirs not traditionally explored for oil and gas, these data are rare to nonexistent. The Cambrian–Ordovician Knox Supergroup dolostones of western Kentucky qualify as one of these types of potential injection targets. With a database of about 25 well logs, a loose two-dimensional (2-D) seismic grid, a few whole cores, and a few well tests, a geologic model of the Knox in western Kentucky was constructed to help understand the potential for CO₂ storage in these rocks.

Initially, ideas for porosity development in the predominantly tight Knox dolostones were based on geologic models of the age-equivalent Ellenburger and Arbuckle Formations. In these formations, karsting plays a dominant role. Evaluation of several Knox whole cores, however, indicated only minor epikarst zones in intervals with very low porosity. Most of the porosity development is associated with large dolomite crystal-lined vugs that are interpreted to have precipitated from hydrothermal fluids. Borehole image logs also seem to point toward vugs and fractures as significant contributors to porosity.

Interpreted core and log data were integrated with 2-D seismic interpretations to produce a geocellular model that was used for flow simulation of potential CO₂ injection volumes and rates within the Knox Supergroup dolostones. Initial indications are that the Knox Supergroup dolostones have the potential to accept the large volumes of supercritical CO₂ necessary for a CO₂ storage site, although a significant number of wells may be required. To further assess this model, the Kentucky Consortium for Carbon Storage drilled a well in 2009 to test the CO₂ injection capacity of the Knox Supergroup and potential secondary targets. Further evaluation of the sealing capacity of the overlying tight carbonates and shales was also done using whole cores taken in this test well to assess their ability to permanently contain injected supercritical CO₂.