Modellazione geomeccanica di faglie in applicazioni di segregazione geologica di gas serra e stoccaggio sotterraneo di idrogeno

Storing fluids in underground reservoirs plays a crucial role in energy management and climate change mitigation, enabling, among other applications, the efficient storage of methane (CH4) for energy supply stabilization, carbon dioxide (CO2) for greenhouse gas reduction, and hydrogen (H2) as a renewable energy carrier. However, the safe and effective utilization of these reservoirs requires a comprehensive understanding of their mechanical behavior under varying storage conditions to predict how fluid injection and consequent pressure changes influence fault stability and rock deformation. Following a literature review that identifies critical knowledge gaps, particularly regarding the impact of hydrogen in subsurface environments and its effects on reservoir rocks, this dissertation investigates safety issues related to subsidence and the reactivation of pre-existing faults. The last concern is especially significant when the target reservoir is located in a faulted basin, where human activities can trigger (micro-) seismic events. By integrating conceptual and real-field analyses, we employ a 3D Finite Element (FE) simulator that couples frictional contact mechanics in faulted porous rocks with fluid flow in order to simulate both cyclic and non-cyclic storage phases. Specifically, the study examines the mechanisms of fault reactivation during the lifecycle of an underground gas storage site, including the potential for “unexpected” events under stress conditions that would not typically be expected to cause failure. The results demonstrate how geological configuration, geomechanical properties, and reservoir operating conditions can increase the risk of fault reactivation after primary production, particularly during cushion gas injection, injection/withdrawal cycles (for CH4 and H2), or storage phases (for CO2). These findings are further validated through the simulation of a real-world CO2 storage case in a partially depleted reservoir in Italy, incorporating the complexities of actual geological settings, mechanical properties, and pressure conditions.