Elastic properties of overpressured and unconsolidated sediments
Bulletin
2214
By: Myung W. Lee
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Abstract
Differential pressure affects elastic velocities and Poisson?s ratio of sediments in such a way that velocities increase as differential pressure increases. Overpressured zones in sediments can be detected by observing an increase in Poisson?s ratio with a corresponding drop in elastic velocities. In highly overpressured sands, such as shallow water flow sands, the P-to S-wave velocity ratio (Vp/Vs) is very high, on the order of 10 or higher, due to the unconsolidated and uncemented nature of sediments. In order to predict elastic characteristics of highly overpressured sands, Biot-Gassmann theory by Lee (BGTL) is used with a variable exponent n that depends on differential pressure and the degree of consolidation/compaction. The exponent n decreases as differential pressure and the degree of consolidation increases, and, as n decreases, velocity increases and Vp/Vs decreases. The predicted velocity ratio by BGTL agrees well with the measured velocity ratio at low differential pressure for unconsolidated sediments.
Suggested Citation
Lee, M.W., 2003, Elastic properties of overpressured and unconsolidated sediments (Version 1.0): U.S. Geological Survey Bulletin 2214, 10 p., https://doi.org/10.3133/b2214.
| Publication type | Report |
|---|---|
| Publication Subtype | USGS Numbered Series |
| Title | Elastic properties of overpressured and unconsolidated sediments |
| Series title | Bulletin |
| Series number | 2214 |
| DOI | 10.3133/b2214 |
| Edition | Version 1.0 |
| Year Published | 2003 |
| Language | ENGLISH |
| Description | 10 p. |