A test of a simple model of the acoustic velocity in marine sediments Available to Purchase

A simple physical model is proposed for the dependence of the acoustic velocity of marine sediments on the porosity and lithology. The model is tested for clay‐rich marine sediments using data from the Deep Sea Drilling Project, but has also been successfully used to calculate the acoustic velocity in consolidated and unconsolidated carbonate sediments. The model is a combination of the Wood [A. B. Wood, A Textbook of Sound (Macmillan, New York, 1941)] and Wyllie [Wyllie et al., Geophysics 21, 41–70 (1956)] (time average) models: Any medium may be thought of as composed of one fraction that is comparable to a slurry of particles in suspension and a second that consists of a rigid grain matrix. As the porosity decreases, so too does the fraction of slurry that makes up the sample. A slurry has essentially no shear strength, and thus the bulk compressibility is expressed as the weighted mean compressibility of the solid and fluid components. The rigid matrix velocity is determined using the time average equation. The variation of the grain (zero‐porosity) velocity with lithology is similarly represented using the time average equation. The net bulk velocity is then taken to be the inverse of the weighted mean travel time for each of the component fractions. This approach could simplify the modeling of acoustic velocity variations given an independent measure of the porosity, or vice versa.