Quantifying the Predicted Extent of the CO2 Plume for Delineating the Area of Review

Delineating the horizontal extent of the injected CO2 plume is required in the U.S. EPA permit application for UIC Class VI wells. In a heterogeneous reservoir of variable thickness, the three-dimensional plume shape is often irregular. When there exists one or more continuous layers of relatively high permeability, CO2 can move much farther radially from the well in these layers than in other layers. A common approach to defining the footprint of the CO2 plume is to use the maximum radial extent based on gas saturation. Because of the potential for radial fingering and narrow channeling of the gas, this approach may not capture the CO2 mass distribution. Furthermore, using a cut-off CO2 saturation may not be appropriate because it is very difficult to define a value that is appropriate for all sites. We will present a criterion that is based on the distribution of CO2 mass that applies to all sequestration sites regardless of their heterogeneity and/or spatial extent. This approach will be demonstrated for a suite of conceptual models with varying heterogeneity and a variety of injection scenarios.