--> --> Quantifying CO<sub>2</sub> Storage Efficiencies of Geologic Depositional Environments

Eastern Section Meeting

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Quantifying CO2 Storage Efficiencies of Geologic Depositional Environments

Abstract

Storage efficiency (E), the ratio of the injected volume of CO2 to the accessible pore volume, quantifies CO2 storage potential in a reservoir. Storage efficiency is used to make storage resource assessments and to determine distribution of the CO2 at geological carbon storage sites. A single range of E is typically applied to all depositional environments. This work is intended to improve site selection and screening processes by using numerical modeling to quantify E ranges for eight depositional environments, namely deltaic, shelf clastic, reef, non-reef shelf carbonate, strandplain, fluvial deltaic, fluvial-alluvial, and turbidite. Depositional environments were interpreted from core and geophysical log data, and geologic models were developed based on selected Illinois Basin formations. For example, three unique models for non-reef shelf carbonates were created based on the Mississippian Ste. Genevieve Limestone, the Devonian Geneva Dolomite, and the Silurian Racine Formation at Johnsonville, Miletus, and Forsyth fields, respectively. At Johnsonville, the Ste. Genevieve contains northeast-southwest trending, elongated oolite shoals and microcrystalline dolomite layers which both form reservoirs. The Geneva at Miletus consists of a regional high-porosity interval with secondary porosity formed through dolomitization and dissolution, possibly enhanced on paleotopographic highs over Silurian reefs. At Forsyth, the reservoir is a lenticular, dolomitized wackestone to grainstone body in the Racine. However, the models were designed to be representative of the different depositional environments and not of any particular field. Features in cratonic and non-cratonic basins differ in scale but exhibit similar reservoir characteristics, allowing comparisons between depositional environments in the Illinois Basin and other United States basins. Geologic and petrophysical data from these fields were used as constraints in the development of geocellular models, which were upscaled for flow simulations. Geologic structures such as domes were removed from the geocellular models because they influence fluid movement and limit lateral flow of CO2, significantly increasing E regardless of the depositional environment. Reservoir simulation of CO2 storage in the different depositional environments is ongoing. Preliminary simulation results predict that baseline E can be increased using operational injection and well completion techniques optimized for CO2 storage.