AbstractWe present a reservoir management approach for geologic CO2 storage that combines CO2 injection with brine extraction. In our approach, dual-mode wells are initially used to extract formation brine and subsequently used to inject CO2. These wells can also be used to monitor the subsurface during pre-injection brine extraction so that key data is acquired and analyzed prior to CO2 injection. The relationship between pressure drawdown during pre-injection brine extraction and pressure buildup during CO2 injection directly informs reservoir managers about CO2 storage capacity. These data facilitate proactive reservoir management, and thus reduce costs and risks. The brine may be used directly as make-up brine for nearby reservoir operations; it can also be desalinated and/or treated for a variety of beneficial uses.