Experimental Evidence of Biot's Dynamic Compatibility Using Seismoelectric Measurements under Varying Saturation
Résumé
In porous media, P-wave propagations may be associated to conversions of mechanical into electrical energy known as seismoelectric (SE) effects. SE phenomena may be expressed as a dynamic transfer function linking coseismic SE field (E) to seismic acceleration (ü) through numerous porous medium properties. To measure transfer function E/ü, we developed a laboratory experiment in unconsolidated sediment (quartz sand). Investigations focused on the impact of water saturation over the coseismic SE field. While varying saturation, the E/ü ratio experienced a switch in polarity at a particular saturation S∗due to a mechanical coupling β, identified as the fluid/matrix relative displacement ratio. This particular behaviour at critical saturation S∗appears to be a direct observation of Biot's dynamic compatibility, causing the coseismic electric field to drop to zero in the absence of relative pore/fluid displacements. Hence the coseismic SE field, that allowed to electrically observe the signature of a poroelastic phenomenon, seems a relevant indicator of dynamically compatible states. In the meanwhile, the transfer functions could become a new tool for characterization of fluid distribution within pores. © ASCE.