Carbon dioxide geological storage monitoring based on effective fluid bulk modulus with time-lapse seismic data

Carbon dioxide geological storage stands as one of the core technologies for attaining carbon neutrality goals, with time-lapse seismic emerging as the key technique for monitoring. As a robust fluid factor, the effective fluid bulk modulus can delineate the spatial distribution of stored carbon dioxide in geological formations. Elastic inverse scattering theory has been extended to carbon dioxide geological storage monitoring leveraging time-lapse seismic data. Within the framework of elastic scattering theory, the baseline medium is defined as the reference medium, while the monitoring medium corresponds to the perturbed medium. The discrepancy in subsurface physical properties between the baseline and monitoring medium is treated as the property variation between the reference and perturbed medium. The baseline and monitoring seismic data are regarded as the background wavefields and measured full wavefields, respectively, and the differential data is designated as the scattered wavefields. Based on the above hypothesis, we derive a linearized and qualitative approximation of reflectivity variation using perturbation theory, with this variation being explicitly correlated to changes in the effective fluid bulk modulus. By incorporating the seismic wavelet effect into the reflectivity approximation as the forward solver, we further propose a practical pre-stack inversion approach within a Bayesian framework. This approach enables the direct estimations of effective fluid bulk modulus changes from time-lapse seismic data. The efficacy of the proposed approach is validated via examples, which demonstrate that it can yield stable estimations of effective fluid bulk modulus variation, thereby providing a novel technical means for monitoring changes during carbon dioxide geological storage.