Pressure Monitoring above the Injection Zone for CO₂ Geological Storage

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.