A Small CO ₂ Leakage May Induce Seismicity on a Sub‐Seismic Fault in a Good‐Porosity Clastic Saline Aquifer

Despite public concerns, only a few CO2 injections into saline aquifers have reported microseismicity. We analyze passive seismic monitoring of small (15,000 tonnes and 0.15 MPa pressure) injection supercritical CO2-rich mixture for Stage 2C the CO2CRC Otway Project (Victoria, Australia), which induced 19 detectable events with maximum moment magnitude MW-0.5. The locations dynamic parameters triggered indicate reactivation fault patch where flowed through fault. Time-lapse images plume reservoir simulations show that occurred when reached this This might be indicative weakening by enabled subsequent pressure variations. Our observations suggest leakage from commercial-scale storage may trigger felt seismicity in overburden without strong overpressure, thus, de-risking workflows should involve detailed study faults.