4D Seismic Monitoring with Diffraction-Angle-Filtering for Carbon Capture and Storage (CCS)

Carbon capture and storage (CCS) is a key technology that directly removes industry driven CO₂ to achieve carbon neutrality. In the process of CCS, it is necessary to monitor whether injected CO₂ is properly stored and not leaking. The behavior of CO₂ can be investigated using a 4D seismic survey that compares seismic data before and after injection. We proposed a two-step monitoring with diffraction-angle filtering (DAF) to effectively locate the CO₂ plume. Because DAF allows us to control wavenumber components, the gradient of full-waveform inversion (FWI), which is the first step, is composed of low-wavenumber components, and reverse time migration (RTM) for seismic imaging is carried out with high-wavelength components. To verify our method, we implemented FWI and RTM with and without DAF using the velocity model in the Volve oil field in the North Sea. Numerical examples show that the CO₂ plume is properly detected from the difference between baseline and post-injected survey and the extension of the reflective boundary is improved compared to the results of the conventional method. With our proposed method, local minima problem is mitigated in FWI, and the boundaries between layers can be clearly distinguished in RTM.