PETROFACIES AND RESIDUAL SATURATION IN A CAMBRIAN-ORDOVICIAN CARBONATE RESERVOIR FOR GEOLOGICAL SEQUESTRATION USING MERCURY POROSIMETRY

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 systems of sixty-six Cambrian-Ordovician carbonate samples from multiple states in the Midwest United States were analyzed. Standard microphotography from thin sections, helium porosimetry, and mercury injection capillary pressure (MICP) analysis were utilized to assess which elements of the pore system are dominantly controlling the overall flow pathways and CO₂ storage potential in the subsurface. In particular, MICP was fundamental in determining the petrophysical properties of the rock units, including porosity, permeability, and the pore-size distribution. Analyses of MICP data suggested a petrophysical subdivision of the samples into four petrofacies: (a) high permeability and porosity and very low capillary entry pressure; (b) medium-high permeability and porosity and low capillary entry pressure; (c) low permeability and porosity and high capillary entry pressure; and (d) very low permeability, low porosity, and very high capillary entry pressure. This subdivision can be used to predict what portions of the studied carbonate sequence are more likely to have a higher potential for injectivity and storage and to better understand the roles that porosity, permeability, capillary entry pressure, and pore size distribution play in ensuring both injectivity and storability of the injected supercritical CO_2.