Fine-grained sediments from the poroelastic perspective

Fine-grained sediments, such silt and clay, are porous media, consisting of solid particles saturated by water; however, the skeletal structure of the solid component is significantly different than that of larger grained sediments such as coarse and fine sands. The modeling of fine grained sediments from the poroelastic perspective, such as the Biot theory, can be challenging. A stumbling block is the frequency dependence of attenuation, which from experimental measurement is shown to be proportional to the first power of frequency, while the Biot theory generally predicts a second power of frequency dependence at low frequencies. One approach to reconcile this difference is based on the distribution of pore sizes [Yamamoto and Turgut, 1988]. When a broad distribution of pore sizes in taken into consideration, the frequency dependence approaches the first power of frequency within a limited frequency band. Another approach is to examine the relaxation process at the grain-grain contact, which is governed by a thin fluid film in the contact region. In fine-grained sediments, the contact region is extremely small and nano-fluid effects must be expected. In this study, a derivation of a poroelastic model, based on the relaxation process associated with the grain contact region will be discussed. [Work supported by the Office of Naval Research, Ocean Acoustics Program.]