Feasibility study on time-lapse FWI using a multi-shallow-wells VSP acquisition

He Liu, Xin Fu, Daniel O. Trad, Kristopher A. Innanen

Monitoring injected CO₂ with high spatial and temporal resolution is essential for verifying storage security in Carbon Capture, Utilization, and Storage (CCUS) projects. However, conventional approaches—particularly surface 4D seismic surveys and deep observation wells—are costly and operationally restrictive, driving the need for lower-cost, scalable geophysical monitoring strategies. In this work, we assess the feasibility of a multi–shallow-well VSP acquisition as a cost-effective alternative to the conventional combination of surface seismic and a single deep VSP well. Using full-waveform inversion (FWI), we systematically compare multiple shallow VSP wells with a traditional deep-well + surface seismic across a seiries of controlled time-lapse scenarios, including source-location non-repeatability, wavelet mismatch, random noise, near-surface velocity inconsistency, and biased initial velocity models. Numerical experiments demonstrate that a seven–shallow-well VSP configuration can generate baseline and time-lapse results that are comparable to—or under several non-repeatability conditions, more robust than—the conventional acquisition. The multi–shallow-well geometry shows reduced sensitivity to 4D noise and consistently recovers the time-lapse anomaly even in the presence of significant near-surface perturbations and moderate initial-model errors. These results indicate that densely distributed shallow VSP wells offer a technically effective and economically scalable pathway for next-generation CO₂ monitoring projects.