Laboratory and numerical experiments of wave propagation in media with fluid-filled fractures

Understanding how fractures and fluids can influence elastic-wave propagation remains a complex puzzle, driving the exploration of the relationship between fluid properties and P-wave propagation through fractured media. Unraveling fluid viscosity and density from P-wave recordings still poses challenges, and the literature does not provide univocal answers. Therefore, we conduct both laboratory and numerical experiments to examine the effects of fluid viscosity and density on P-wave propagation when fractures are interpreted in terms of the linear-slip model. The medium consists of stacked aluminum discs with parallel horizontal fractures. We consider 1, 5 and 10 fractures and use water, silicone oil and honey as infill materials. In the laboratory, we obtain the static and dynamic, normal and tangential compliances of parallel fluid-filled fractures. We performed numerical simulations using the discontinuous Galerkin method, incorporating the dynamic compliances obtained from the experiments. Our laboratory findings indicate that fluid density correlates positively with P-wave velocity, transmission coefficient, and quality factor. Furthermore, there is an inverse correlation with the number of fractures. In addition, the normal and tangential fracture compliances and their ratio vary between dry and saturated conditions and decrease when the number of fractures increases. The static compliance is, in general, higher than the dynamic. The numerical results showed good agreement in discriminating between different fluids, although numerical attenuation was slightly underestimated compared to experimental observations. The results highlight the impact of fluid properties on wave behavior in fractured media and provide insights into wave sensitivity to fracture characteristics.