Interpreting attenuation in partially saturated sandstone using measurements of local fluid pressure and numerical modeling of fluid flow in poroelastic media

Abstract

Summary An inedited laboratory technique combined with 3D numerical modeling was used to investigate attenuation in a partially saturated Berea sandstone sample. The workflow consists in measuring both transient fluid pressure and attenuation in extensional mode at frequencies between 1 and 100 Hz. Measurements for large water saturation such as 97% show a significantly frequency-dependent attenuation at room pressure and temperature. Biot’s equations of consolidation are solved with the finiteelement method to verify that the observed frequencydependent attenuation is caused by wave-induced fluid flow on the mesoscopic scale. Both measurements of transient fluid pressure and attenuation could be reproduced by numerical results using a patchy saturated model having same total saturation as the laboratory rock sample. This demonstrated that the measured transient fluid pressure, resulting from fluid flow, was the cause for the fluid-related attenuation observed in the laboratory measurements. We conclude that wave-induced fluid flow on the mesoscopic scale is the dominant mechanism for seismic attenuation in partially saturated Berea sandstone at room pressure and temperature.