Injection-rate histories and well placement influence fault yielding during CO2 geological storage

Abstract Safe CO 2 storage requires injection designs that manage both when faults yield and how yielding spreads, yet temporal schedules and well layouts are often evaluated separately. We developed a two-dimensional quasi-static hydromechanical model of immiscible CO 2 –brine flow around an offset normal fault and compared constant and variable-rate histories, well-placement configurations, and well–fault distances over 30 d. Coulomb failure function (CFF) threshold attainment with frictional weakening defined modeled onset; failure-area ratio and maximum shear plastic strain served as within-mesh comparative indicators of domain-scale localization. The simulations reveal a hierarchy of controls: injection rate primarily governs pressure buildup and onset timing; rate history reorganizes transient stress paths and localization; and well placement and distance redistribute pressure and yielding across the fault. Higher rates increased the within-mesh failure-area ratio, whereas variable histories produced distinct responses that cannot be attributed to cycling alone because peak rate and shut-in transitions were confounded. Local threshold indicators and domain-scale metrics were complementary rather than interchangeable: temporal onset, spatial extent and deformation intensity were distinct response dimensions. These findings motivate joint optimization of injection schedules and well layouts against both temporal onset and spatial localization, while providing model-scale guidance for early quasi-static risk screening rather than predictions of seismicity, dynamic rupture or long-term stability.