Borehole Guided Waves Sensitivity to Well Integrity and CO₂ Saturation Changes Beyond the Casing

In this study, we explore the use of different wavefields recorded in VSP surveys to conduct time-lapse seismic monitoring of CO₂ migration in the subsurface. To do so, we perform a series of VSP experiments employing a surface source and an array of borehole hydrophones to establish correlations between the recorded wavefields (e.g., direct, reflected, and guided waves) and the presence of heterogeneities in the formation surrounding the borehole, which may be affected by the presence of CO₂. We analyze changes in seismic signals acquired before and during a CO₂ injection experiment at the Svelvik CO₂ Field Laboratory, focusing on typical VSP attributes used for seismic characterization (e.g., arrival time shifts and amplitude decay of direct waves) and less common wave types (e.g., tube waves) that may provide additional insights into CO₂ presence near the borehole.