Secure CO2 geological storage necessitates robust monitoring methods to provide assurance of CO2 storage. Pressure monitoring above the injection zone is a method to detect potential CO2 leaks into overlying formations. We built a CO2 storage model to characterize pressure changes above the injection zone due to both hydraulic connection and undrained loading. The model considers the existence of a CO2 injector and: (1) a fault either leaky or sealing, (2) a leaky abandoned well, (3) a leaky injector, and (4) a second injector. The results show that changes of pore pressure above the injection zone caused by partially undrained loading can be as large as ~1% of the pressure increase in the injection zone for the chosen reservoir model. The pore pressure in the above-injection zone increases up to a maximum value of ~15 kPa within ~10 days followed by a gradual decay with time in the absence of leaks, while CO2 migration through leaky paths favors a higher (typically one order of magnitude larger) yet more gradual pressure increase through direct fluid communication. Monitoring of pressure changes due to partially undrained loading in the above-injection-zone is a feasible technology to track the CO2 plume but requires high precision pressure measurements.
The successful development of carbon dioxide (CO2) storage necessitates robust monitoring methods to detect potential CO2 leakage into overlying formations and provide assurance for permanent CO2 trapping (Kim & Hosseini, 2015; Meckel et al., 2008). On-surface monitoring (such as 4D seismic and InSAR mapping) can capture large geophysical features but is limited by high costs, laborious interpretation, and a large buffer zone of signals imposed by the overburden (Arts et al., 2004; Rutqvist et al., 2010). Monitoring in the injection zone (IZ) enables direct access to the zone of interest and offers early leak detection, but remains limited to a few observation wells and small sampling volumes (Ajo-Franklin et al., 2013; Hovorka et al., 2006; Zeidouni & Pooladi-Darvish, 2012b, 2012a). Pressure monitoring above the injection zone (AIZ) is a new approach to monitor CO2 injection and detect undesirable migration of fluids from the injection zone to overlying formations (Liebscher et al., 2013; Park et al., 2012). AIZ pressure monitoring is less costly than on-surface seismic monitoring, covers a wider area than the IZ monitoring, and has the potential to detect leaks into overlying formations (Hosseini et al., 2018).