Two risk metrics for CO2 storage reservoirs with varying domain size, heterogeneity, and injection rate

Two parameters that play the most important role in the appraisal of environmental risk performance at carbon dioxide (CO2) storage sites are the prospective impact of the pore pressure increase and CO2 saturation. In this context, this study investigates the spatiotemporal evolution of pressure buildup and CO2 saturation as a function of flow region's size, average porosity and permeability, and heterogeneity, as well as the injection rate and total volume of injected fluid. The practical importance of this study is to investigate the factors that affect the extent of pressure buildup and areal extent of CO2 plume both during and after injection, which will impact risk assessment as well as influence effective monitoring operations. This study pursues the above objective using two risk metrics that are based on numerical simulations and illustrated using representative models of three realistic storage sites with varying volumetric storage potential and geological settings, all with open geologic systems. The two metrics (the spatiotemporal extent of pressure buildup and CO2 saturation plume, respectively) used in this study are able to capture the geologic (structural and petrophysical) and operational complexities that cannot be incorporated into analytical or semianalytical solutions. The results of this study suggest that in addition to the average permeability, the areal extent of the pressure buildup during the injection period is strongly related to the injection rate, whereas the postinjection period may be more strongly influenced by the reservoir heterogeneity. The areal extent of the saturation plume during active injection is highly correlated to the mass of injected fluid, and the postinjection behavior is impacted by the shape of the reservoir–seal interface. These findings are consistent with other recent studies by the National Risk Assessment Partnership (NRAP) on characteristic reservoir behavior. The results have been used to generate pressure and saturation plume profiles (over time) that can be used to support risk‐based decision making. © 2019 Society of Chemical Industry and John Wiley & Sons, Ltd.