Seismic Waves Do Sense Fracture Connectivity: Experimental Validation

Abstract

Fracture connectivity is a key parameter controlling fluid flow throughout the Earth´s crust.While some theoretical and numerical studies suggest that seismic waves are sensitive to fractureconnectivity, an experimental validation of this critically important phenomenon was so far unavailable. In this study, we present a novel methodology for fabricating synthetic analogs of rock samples containing connected and unconnected fluid‐saturated fractures with well‐constrained geometric characteristics. Using a low‐frequency forced‐oscillation apparatus, we show that the P‐wave velocities are higher in samples with unconnected fractures than in those with connected ones. Complementary numerical simulations corroborate these findings and indicate that the dominant mechanism behind the observed differences is wave‐induced fluid pressure diffusion within connected fractures. Our results provide direct experimental evidence that, for otherwise identical fracture networks, the presence of interconnectivity produces a measurable reduction in P-wavevelocity at seismic frequencies, which is consistent with that previously predicted by correspondingnumerical models. This, in turn, opens new and important perspectives for the seismo‐hydrauliccharacterization of fractured rocks.