--> Seal Capacity of Upper Ordovician Units in the Midwest Region: A Quantitative Approach Using Mercury Injection Capillary Pressure

2019 AAPG Eastern Section Meeting:
Energy from the Heartland

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Seal Capacity of Upper Ordovician Units in the Midwest Region: A Quantitative Approach Using Mercury Injection Capillary Pressure

Abstract

The Midwest’s subsurface exhibits a series of potential reservoirs for geologic carbon sequestration opportunities, including depleted oil and gas fields and deep saline aquifer systems. The Upper Ordovician contains many low-permeability units that could serve as regional caprocks to prevent the upward, density-driven migration of supercritical carbon dioxide injected into the units underlying them. These include the Maquoketa Group and equivalent units, which consist of thick and heterogeneous sequences of carbonates, silts, and clay-rich rock units. This heterogeneity results in distinctive sealing potential that, in addition to geomechanical factors, are controlled by the capillary entry pressure and permeability associated to the identified lithologic character. This work uses mercury porosimetry analyses applied to samples from a four-state region (Indiana, Kentucky, Ohio, and Pennsylvania). Mercury injection capillary pressure analysis reveals insightful information about porosity, permeability, pore size distribution, and capillary entry pressure of these samples. This information, combined, allows the quantification of the seal potential of the sequence under study. In addition to Upper Ordovician samples, we analyzed samples from other stratigraphic intervals composed of carbonates and mudstones that will shed light on the effects of lithology on the sealing potential of these units. Results of these evaluations indicate that, assuming 20% pore brine displacement by supercritical CO2, the Upper Ordovician sequences can prevent upward flow from a maximum CO2-column up to 1,500 m. Other units with similar sealing potential that were also evaluated include the Nolichucky Shale and Eau Claire Formation (Upper Cambrian), and the Cincinnati Group, Juniata Formation, Reedsville Shale, and Utica Shale (Upper Ordovician). In conclusion, quantification of the seal capacity of widely distributed units revealed that there is a high potential for safe geologic CO2 storage, but local-scale evaluations at targeted injection sites should be performed to verify our regional-scale results.