To better understand injection and post‐injection flow processes and the entrapment of supercritical CO2 during geological carbon sequestration in a carbonate reservoir, the pore system was analyzed in 66 Cambrian‐Ordovician carbonate samples from several locations in the midwestern USA. This work employed standard microphotography from thin sections, helium porosimetry for porosity and permeability, and mercury injection capillary pressure analysis, aiming to understand which elements of the pore system dominantly control the overall flow and CO2 storage potential in the subsurface. In particular, mercury injection capillary pressure analysis has been fundamental in understanding several petrophysical properties of rocks, including porosity, permeability, and the pore‐size distribution of the samples under study. This work analyzes mercury injection capillary pressure data and proposes a petrophysical subdivision of the samples into four petrofacies, based on values of porosity, permeability, and capillary entry pressure. This system aims to predict the portions of the studied carbonate sequence that are more likely to have a higher potential for injectivity and storage, and to better understand how porosity, permeability, capillary entry pressure, and pore size all play a role in ensuring both buoyant and capillary trapping mechanisms to secure the injected supercritical CO2. Results from this investigation suggest that in these Cambrian‐Ordovician carbonate reservoirs, pore size inversely correlates with capillary entry pressure, and that permeability does not always have a direct relationship with pore size but rather relates to the overall interconnectivity of the complex pore system.