Modeling of seismic attenuation and anisotropy in fractured media: an integrated VSP study

Fracture-induced anisotropy and seismic attenuation strongly influence wave propagation in fluid-saturated reservoirs but remain difficult to characterize simultaneously from conventional seismic observations. This study presents an integrated vertical seismic profiling (VSP) workflow for quantifying azimuthal velocity anisotropy and attenuation in naturally fractured carbonate reservoirs. Layer-stripping tomographic inversion of zero-offset and single-offset VSP data is first applied to estimate layer-specific anisotropic P - and S -wave velocity models. These models are subsequently combined with interval quality factors ( Q ) derived from the zero-offset VSP to construct a layered horizontally transverse isotropic (HTI) viscoelastic rock-physics model based on anisotropic Gassmann theory. The resulting model is used to generate synthetic multi-azimuth VSP wavefields, enabling investigation of the azimuthal dependence of seismic velocity and attenuation. The modeled azimuthal responses are interpreted alongside fracture orientations derived from formation microImager (FMI) logs. The results reveal systematic azimuthal variations in both seismic velocities and quality factors, demonstrating that fracture-induced anisotropy is the dominant control on wave propagation within the reservoir. Maximum P -wave velocities occur for propagation parallel to the dominant fracture orientation, whereas minimum velocities are observed in the fracture-normal direction. Within the reservoir interval (2800–3200 m), the modeled quality factor varies from approximately 82 in the fracture-parallel direction to approximately 100 in the fracture-normal direction, reflecting enhanced wave-induced fluid-flow attenuation and scattering associated with compliant, fluid-filled fractures. Above the reservoir, background Q values increase to approximately 125–170, indicating lower attenuation in the overlying formations. The close agreement between the modeled azimuthal Q response and the FMI-derived fracture orientations demonstrates that azimuthal attenuation provides a robust indicator of fracture geometry. The proposed framework establishes a quantitative relationship between fracture orientation and seismic attenuation, providing an effective tool for fracture characterization and reservoir evaluation in naturally fractured carbonate systems.