A unified model for characterizing wave propagation in a microcracked porous background with intersecting fractures

Summary

Natural fractured reservoirs or artificially hydraulically fractured networks typically exhibit hierarchical microstructures characterized by porous backgrounds permeated by microcracks and intersected by macroscopic fractures. Prior theoretical frameworks predominantly decouple micro- and macro-scale heterogeneities, thereby overlooking the interplay between pore-scale squirt-flow dissipation and fracture-induced wave attenuation. By integrating microcracked porous wave-motion theory with fracture scattering theory, we present a unified model for characterizing wave propagation in fluid-saturated microcracked porous rocks with intersecting fractures. Five distinct attenuation mechanisms are concurrently incorporated: squirt flow at the microcrack scale, wave-induced fluid flow (WIFF) at both fracture-background and fracture-fracture mesoscales, elastic scattering, and Biot's global flow. The results show that microcrack density primarily affects matrix stiffness and shifts the attenuation of squirt flow to lower frequencies. In contrast, microcrack aspect ratios control the characteristic frequency and its coupling with fracture-related mechanisms. Fluid mobility governs the frequency range of WIFF and Biot flow, with high mobility potentially creating attenuation gaps where scattering-induced velocity drops disappear. The model also accommodates multiple-aspect-ratio microcrack systems and extends to planar fractures as linear-slip interfaces, enabling realistic characterization of anisotropic shale reservoirs. This unified approach provides a comprehensive basis for interpreting seismic dispersion and attenuation in complex fractured formations relevant to hydrocarbon exploration and reservoir monitoring. In parallel fractures and zero microcrack-limiting cases, our model predictions agree well with those of existing models.