Laboratory Measurements of Velocity and Attenuation in Sediments

Journal Article · Tue Jun 08 04:00:00 EDT 2004 · Published in: Society of Exploration Geophysicists, Tulsa, vol. 2, no. 2, July 1, 2004, pp. 32

OSTI ID:15014302

Zimmer, M A; Berge, P A; Bonner, B P; Prasad, M

Laboratory measurements are required to establish relationships between the physical properties of unconsolidated sediments and P- and S-wave propagation through them. Previous work has either focused on measurements of compressional wave properties at depths greater than 500 m for oil industry applications or on measurements of dynamic shear properties at pressures corresponding to depths of less than 50 m for geotechnical applications. Therefore, the effects of lithology, fluid saturation, and compaction on impedance and P- and S-wave velocities of shallow soils are largely unknown. We describe two state-of-the-art laboratory experiments. One setup allows us to measure ultrasonic P-wave velocities at very low pressures in unconsolidated sediments (up to 0.1 MPa). The other experiment allows P- and S-wave velocity measurements at low to medium pressures (up to 20 MPa). We summarize the main velocity and attenuation results on sands and sand - clay mixtures under partially saturated and fully saturated conditions in two ranges of pressures (0 - 0.1 MPa and 0.1 - 20 MPa) representative of the top few meters and the top 1 km, respectively. Under hydrostatic pressures of 0.1 to 20 MPa, our measurements demonstrate a P- and S-wave velocity-dependence in dry sands around a fourth root (0.23 -0.26) with the pressure dependence for S-waves being slightly lower. The P- velocity-dependence in wet sands lies around 0.4. The Vp-Vs and the Qp-Qs ratios together can be useful tools to distinguish between different lithologies and between pressure and saturation effects. These experimental velocities at the frequency of measurement (200 kHz) are slightly higher that Gassmann's static result. For low pressures under uniaxial stress, Vp and Vs were a few hundred meters per second with velocities showing a strong dependence on packing, clay content, and microstructure. We provide a typical shallow soil scenario in a clean sand environment and reconstruct the velocity profile of such a sediment packet.

• Research Organization: Lawrence Livermore National Laboratory (LLNL), Livermore, CA
• Sponsoring Organization: USDOE
• DOE Contract Number: W-7405-ENG-48
• OSTI ID: 15014302
• Report Number(s): UCRL-JRNL-205155
• Journal Information: Published in: Society of Exploration Geophysicists, Tulsa, vol. 2, no. 2, July 1, 2004, pp. 32, Journal Name: Published in: Society of Exploration Geophysicists, Tulsa, vol. 2, no. 2, July 1, 2004, pp. 32 Journal Issue: 2 Vol. 2
• Country of Publication: United States
• Language: English

Related Subjects

58 GEOSCIENCES
ATTENUATION
PHYSICAL PROPERTIES
PRESSURE DEPENDENCE
S WAVES
SEDIMENTS
SHEAR PROPERTIES
ULTRASONIC WAVES
VELOCITY