Poromechanical modeling of CO2 sequestration in exploited gas fields

Injection of CO2 in an exploited faulted gas field is simulated with the aim at investigating the poro-mechanical consequences of the sequestration. A long-term injection until the initial reservoir pressure is exceeded by as much as 40% over a period of 150 years is addressed. The process is analyzed from a poro-mechanical point of view using a FE-IE (Finite Element Interface Element) model. The results show that the ground surface rebound due to the overpressure generated by the CO2 storage partially mitigates the land subsidence experienced by the area because of the previous gas field depletion. Activation of faults lying close to the reservoir boundary occurs before being reached by the CO2 plume, so there is little chance for a CO2 escape. The caprock is shown to preserve its integrity with the shear stress approaching the limiting state prone to the rock failure on a local scale only, thus not jeopardizing the overall effectiveness of the sequestration.