A Small CO<sub>2</sub> Leakage May Induce Seismicity on a Sub‐Seismic Fault in a Good‐Porosity Clastic Saline Aquifer
Stanislav Glubokovskikh, Erdinc Saygin, S. A. Shapiro, Boris Gurevich, Roman Isaenkov, David Lumley, Rie Nakata, Julian Drew, Roman Pevzner
Abstract
Abstract Despite public concerns, only a few CO 2 injections into saline aquifers have reported microseismicity. We analyze passive seismic monitoring of a small (15,000 tonnes and 0.15 MPa pressure) injection of supercritical CO 2 ‐rich mixture for Stage 2C of the CO2CRC Otway Project (Victoria, Australia), which induced 19 detectable events with maximum moment magnitude M W ‐0.5. The locations and dynamic parameters of the triggered events indicate a reactivation of a small fault patch where CO 2 flowed through the fault. Time‐lapse seismic images of the plume and reservoir simulations show that the reactivation occurred when the CO 2 plume reached this fault. This might be indicative of a fault weakening by the plume that enabled subsequent reactivation by pressure variations. Our observations suggest that a leakage from a commercial‐scale storage may trigger felt seismicity in the overburden without strong overpressure, thus, the de‐risking workflows should involve a detailed study of small faults.