The potential of borehole seismic monitoring techniques at the field scale for leakage and well integrity assessment in CO₂ injection projects

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 then analyze the changes in those seismic signals by comparing data recorded before and during a CO₂ injection experiment carried out at the Svelvik CO₂ Field Laboratory. We focus on VSP attributes typically employed for seismic characterization (e.g., arrival time shifts and amplitude decay of direct waves) as well as on wave types which are not commonly used (e.g., tube waves) but may provide additional information regarding the presence of CO₂ in the vicinity of the borehole.