Can CO2 storage cause earthquakes? What is the maximum possible earthquake magnitude resulting from CO2 injection? Here, as a theoretical case study we investigate these questions using coupled hydromechanical modeling with multiphase flow and seismological variables for quantifying earthquake magnitude and energy. Our simulations consider transient fluid flow and stress coupling, and the evolution of fault properties. We simulate CO2 injection into a reservoir-caprock system bounded by a subvertical normal fault subjected to different extensional stress regimes and over a range of initial fault permeability values. For our assumed system and injection rate, the simulation results show that sudden stress drop and fault slip primarily initiated along the fault portion intersecting the storage reservoir after a few months of injection when a sufficiently high reservoir pressure has been reached. The size of the rupture area, and consequently, the earthquake magnitude and energy, depends on initial horizontal-to-vertical stress ratio and fault permeability, which strongly influences the size of the pressurized area, and subsequent stress variations.
