Effects of fracture connectivity on S-wave attenuation caused by wave-induced fluid flow

Abstract

We numerically calculated P- and S-wave attenuation caused by wave-induced fluid flow in fractured media. The fractures are modeled as a poroelastic domain much more compressible than the background medium. The numerical approach is based on the solution of Biot’s equations of consolidation using the finite-element method. We used an unstructured mesh which can capture efficiently the large aspect ratio (150) of the fractures by strongly varying the spatial resolution. The main objective was to investigate how and how much the connectivity between fractures affects P- and S-wave attenuation due to wave-induced fluid flow on the mesoscopic scale. Our results showed that S-wave attenuation tends to change drastically in magnitude at a certain frequency due mainly to a shift in frequency of its maximum by more than one order of magnitude. P-wave attenuation was much less sensitive than S-wave attenuation to fracture connectivity in the investigated morphologies. The results led us to conclude that intrinsic S-wave attenuation estimated from seismic data can be a strong indicator of fracture connectivity.