Enhanced Monitoring of Geological CO₂ Injection Through Seismic Attenuation Difference Estimation

Carbon capture and storage (CCS) is critical to mitigating carbon dioxide (CO2) emissions, with geological formations serving as safe reservoirs for CO2 storage. Rigorous monitoring protocols are essential to track subsurface CO2 distribution and potential leakage to ensure the effectiveness and safety of carbon sequestration initiatives. Active seismic monitoring has emerged as a powerful tool for this purpose, offering precision in confirming CO2 sequestration and identifying potential leakage pathways. Seismic attenuation, which indicates fluid changes within reservoirs, has attracted attention due to its sensitivity to reservoir fluid changes. This study presents a novel divergence-based centroid frequency shift (CFS) method for monitoring attenuation changes induced by CO2 injection. The method, derived without assumptions beyond a constant Q model, exhibits frequency independence, enhancing sensitivity to frequency components and facilitating accurate observation of their response to fluid composition changes. Validity and feasibility are demonstrated through application to the Frio II CO2 injection project, which reveals distinct frequency-dependent attenuation changes. Lower frequencies show increased sensitivity to CO2 injection, outperforming conventional monitoring methods that rely on velocity and travel time variations. This method offers increased sensitivity to CO2 injection and provides critical frequency-based features for monitoring CO2 transport and detecting potential leaks.