A feasibility evaluation method for seismic monitoring of CO₂ geological storage based on reservoir simulation and pre-stack time-lapse AVO inversion

Deep saline aquifers are critical reservoirs for CO₂ geological storage. To evaluate their storage capacity and monitor CO₂ plume migration, this study constructs a numerical simulation model for CO₂ storage in the sandstone reservoirs of the Utsira Formation in Sleipner area, and predicts reservoir elastic parameters by combining the Hertz-Mindlin formula with the Gassmann equation. On this basis, an evaluation workflow integrating reservoir simulation, rock physics, forward modeling, and pre-stack inversion is established through AVO/AVA forward modeling and pre-stack time-lapse inversion. The results indicate that reservoir P-wave velocity is most sensitive to changes in CO₂ saturation, decreasing significantly with increasing saturation and exhibiting a distinct critical saturation threshold, beyond which the velocity variation tends to level off. Amplitudes of pre-stack angle gathers are sensitive to saturation variations within the low-saturation range; however, as saturation further increases, the amplitude response tends to saturate. Pre-stack time-lapse inversion results of synthetic data demonstrate that time-lapse variations in P-wave impedance can stably and quantitatively indicate the migration pathways and spatial distribution of the CO₂ plume, exhibiting good robustness against random noise, whereas S-wave impedance inversion results are relatively sensitive to noise. This study verifies the applicability of the proposed workflow for CO₂ geological storage monitoring through a synthetic data model, providing a theoretical basis and reference for relevant monitoring methodology research.