Acoustic velocity and attenuation of unconsolidated sands: An experimental and modeling study

I have developed a sonic frequency apparatus (1–10 kHz) that utilizes resonance to measure the acoustic velocities and attenuation of both extensional and torsional waves in unconsolidated materials (e.g., sands, clays and sediments) under hydrostatic confinement. The basic equations and methodology for correcting these effects are given and applied to a dry Monterey sand to determine the shear and Young's moduli and attenuation over an effective pressure range of 0–9 MPa. Comparison of my measured data with theoretical granular contact models gives insight into the seismic wave propagation in unconsolidated sands.; The effects of water saturation and pressure on the velocity and attenuation of seismic waves in unconsolidated sands are investigated using the newly-designed apparatus and methodology in the laboratory. Two kinds of pore fluid distribution are achieved with water injection and de-gassing methods, and an X-ray CT scanner is used to obtain the images of pore fluid distribution. There is not significant difference in velocities for the different pore fluid distributions. Measured velocities are in favorable agreement with theoretical predictions based on Gassmann's equations. At all effective pressures, V _P of the fully-water-saturated sand is larger than that of the dry sand, implying that water in pore space stiffens the rock, causing an increase in the rock's bulk modulus. For the partially-saturated sand, the attenuation of compressional wave is larger than that of torsional wave, and both of them increase with water saturation.; The effects of pore fluid saturation and distribution on seismic velocities are further studied based on numerical simulations of seismic wave propagation in fluid-saturated porous media. The calculated results indicate that numerical modeling based on Biot theory gives the same compressional velocity V_P as Gassmann's equations if the pore fluids are mixed in such a fine scale that the induced pore pressure increments can equilibrate with each other. (Abstract shortened by UMI.)...