A multi-mechanism model of wave-induced fluid flow in porous media with considering capillary effect

When an elastic wave propagates through a porous medium, various types of pore fluid flow may occur due to local structural heterogeneities, resulting in wave dispersion and attenuation. A theoretical model for elastic P-wave propagation in porous media is developed, which integrates multiple fluid-flow mechanisms into a unified framework. Explicitly, the proposed model addresses squirt flow (SF) within the solid matrix, patchy fluid flow (PFF) between different fluid phases, global fluid flow (GFF) of Darcy-type flow, and capillary effects. The model is validated against experimental data for CO2-saturated Berea sandstone (0.1–1000 Hz), successfully reproducing the observed velocity dispersion and attenuation characteristics. In particular, two distinct attenuation peaks are identified at 0.1 Hz and 100 Hz, corresponding to the characteristic frequencies of squirt flow and patchy fluid flow, respectively. Furthermore, it accurately captures the essential features of the capillary effect, particularly the phenomena of elastic softening and capillary hysteresis. Additional validation using water-saturated limestone data (2–500 Hz) further confirms the robustness and applicability of the proposed model under varying saturation conditions. Overall, the proposed model underscores the pivotal role of capillarity and the interplay of multiple fluid-flow mechanisms in controlling acoustic wave behavior, providing a comprehensive framework for describing wave propagation in porous media across a broad frequency range.