Improving thin-bed resolution: Application of a sparse-layer inversion on 3D seismic observations from the In Salah carbon dioxide storage project

The In Salah carbon dioxide storage project in Algeria has injected more than 3 million tons of carbon dioxide into a thin water-filled tight-sand formation. Interferometric synthetic aperture radar range change data revealed a double-lobe pattern of surface uplift, which has been interpreted as the existence of a subvertical fracture, or damage, zone. The reflection seismic data found a subtle linear push-down feature located along the depression between the two lobes thought to be due to the injection of carbon dioxide. Understanding of the CO2 distribution within the injection interval and migration within the fracture zone requires a precise subsurface layer model from the injection interval to above the top of the fracture zone. To improve the resolution of the existing seismic model, we applied a sparse-layer seismic inversion, with basis pursuit decomposition on the 3D seismic data between 1.0 and 1.5 s. The inversion results, including reflection coefficients and band-limited impedance cubes, provided improved subsurface imaging for two key layers (seismic horizons) above the injection interval. These horizons could be used as part of a more detailed earth model to study the CO2 storage at In Salah.