Attenuation in partially saturated rocks

Abstract

Based on limited experimental data, the attenuation of acoustic waves in partially saturated rocks has been suspected to result from the effect of fluid flow. Global flow is accompanied by a viscous energy loss, which results in the attenuation of acoustic waves. In this theoretical study, we explore the effects of global flow and gas saturation level on acoustic wave attenuation. The attenuation predicted by theory is much smaller than that actually supported by experimental data for sandstones at low frequencies (≦1000 Hz). The technique involves the use of Biot's equations of two interacting continua that have been modified to accommodate confined gas and liquid by introducing effective and average values of fluid compressibility, fluid mass, and viscosity.