Simplified physics model of CO2 plume extent in stratified aquifer‐caprock systems

The extent of plume migration as injected CO2 displaces the native reservoir fluids is a crucial performance metric to ensure safe and effective geologic sequestration. In this paper, we develop and validate a simplified physics model for the outer extent of CO2‐brine interface in a stratified aquifer‐caprock system. This involves quantifying the total storage efficiency, which is defined as the product of the volumetric sweep and displacement efficiencies, based on simulations covering an extensive parameter space of different reservoir and caprock properties. We model CO2 injection into a 2‐D radially symmetric brine‐filled reservoir with vertical permeability variations that is in hydraulic communication with a caprock. Based on insights from a suite of detailed numerical simulations of our system, the most important terms in the simplified model for total storage efficiency involve the relative permeability model followed by integrated measures of reservoir heterogeneity. A relationship is established for the plume extent at the end of injection from the amount of CO2 injected and the storativity (porosity‐thickness product) of the reservoir.