Time-lapse (TL) seismic technology has been utilized in CO2 geo-sequestration to verify the CO2 containment within the reservoir. A major risk associated with geo-sequestration is possible leakage of CO2 from the storage formation into upper layers. Therefore, the deployment of carbon capture and storage (CCS) projects requires reliable and fast detection of relatively small volumes of CO2 outside the storage formation. To do this, it is necessary to predict typical leakage scenarios and improve the subsurface leak-detection methods. The upward migrated CO2 will form small secondary accumulations with limited lateral extend. In contrast to petroleum exploration methods, which mostly utilise reflected waves, this spatially small CO2 amounts will produce seismic signals corresponding to diffracted waves. In this work, we present a technique that can enhance CO2 leakage detection based on diffracted wave analysis in time-lapses seismic data. Focusing on diffraction energy, we aim to image small objects with limited lateral extend, such as a plume containing with less than 10,000 tonnes of supercritical CO2. Using seismic forward modelling, we examine the sensitivity of the method to the amount of CO2 leaked into a formation.


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