Rapid-repeat time-lapse vertical seismic profile imaging of CO2 injection

In a Carbon Capture and Storage (CCS) project, monitoring CO2 during the injection period is crucial for ensuring both the safety and effectiveness of the injection process. Real-time observation of CO2 behavior allows for adjustments to injection parameters to enhance performance and enables the refinement of reservoir simulation models to more accurately predict plume migration. Achieving this with seismic surveys requires significantly shorter intervals between surveys compared to conventional monthly or yearly timescales. This study aims to identify an effective seismic monitoring method, encompassing both acquisition design and imaging technique, for capturing the short-term, dynamic subsurface changes resulting from CO2 injection. We present images generated through elastic full waveform inversion (FWI) applied to rapidly repeated time-lapse vertical seismic profile (VSP) field data. The data were acquired using a fixed source shooting across an injection plume at approximately 15-minute intervals over several days. These images, created from a combination of sparse geophone data and dense distributed acoustic sensing (DAS) data, provide clear snapshots of transient subsurface changes near the injection well. The results are further validated using a synthetic inversion experiment, demonstrating that the combined geophone and DAS-VSP approach offers a cost-effective and informative monitoring solution for CCS projects.