The Fluidal Interface is Where the Action is in CO2 Storage

Summary We examine the mechanical integrity of a deep saline aquifer during the injection of supercritical CO2. The analysis is conducted with a numerical scheme of the capillary pressure and nonwetting pressure for multiphase flow. In this study, unidirectional hydromechanical coupling is considered: fluid pressure and phase saturation influence mechanical stress via the momentum equation, while feedbacks to fluid pressure from mechanical deformation are not considered. Caprock stability is monitored in time, referenced to the potential for hydraulic fracture and shear slip along an optimally oriented shear plane for a suite of injection pressures. For reasonable parameter values and the chosen aquifer geometry, significant mechanical failure (and potential breach of integrity) is expected in the shale caprock for all but low injection rates. This indicates that the analysis of the hydromechanical response is crucial for proper selection of injection sites, injection rates, and total storage capacity.