Anisotropic Anelastic Fresnel-Volume-Migration of the Asse 3D Seismic Data Set

In 2020, a comprehensive 3D reflection seismic survey was conducted over the Asse salt structure in Lower Saxony, Germany, to support the retrieval of radioactive waste from the salt mine. While the data has already been processed using conventional seismic imaging techniques, we present the results from applying the Fresnel-Volume-Migration (FVM) approach that we extended for considering anisotropy and anelastic attenuation. These enhancements aim to provide a more detailed and accurate characterization of the Asse region’s complex geology, which is crucial for the safe planning and execution of the waste retrieval process.

A wavefront construction (WFC) technique was employed to calculate the required Green’s functions for 3D anisotropic (TTI) velocity models. The WFC method was further extended to also calculate compensation traveltime fields (t*) for spatially varying Q-models. These t*-fields were then incorporated into the migration process to account for amplitude decay, phase shifts and dispersion due to anelastic attenuation, ultimately leading to a more accurate representation of subsurface reflectivity.

The method was applied to both synthetic 2D data as well as 3D subsets of the Asse seismic data set. Migration with anelastic compensation effectively corrected amplitude losses and phase distortions in the synthetic data. Furthermore, applying the anisotropic FVM to the 3D Asse data set significantly improved image quality. Additionally, the migration was performed in Common Offset Gather (COG) domain to facilitate muting of the corresponding Common Image Gathers (CIGs) and thereby significantly enhancing the quality of the resulting images.

Our study highlights the critical importance of integrating both anisotropy and anelastic attenuation into 3D seismic imaging to obtain reliable, high-resolution subsurface images. Accurate positioning and characterization of reflectors are essential for performing further quantitative seismic processing, e.g. AVO (Amplitude Versus Offset) analysis, which, in turn, facilitates more precise geological interpretations. The seismic imaging advancements developed here also offer promising applications for other applications, e.g. for mineral exploration, geothermal reservoir characterization, as well as within the radioactive waste disposal site selection process.