| Abstract: | Accurate S-wave velocities for shallow sediments are important in performing a reliable elastic inversion for gas hydrate-bearing sediments and in evaluating velocity models for predicting S-wave velocities, but few S-wave velocities are measured at low effective pressure. Predicting S-wave velocities by using conventional methods based on the Biot-Gassmann theory appears to be inaccurate for laboratory-measured velocities at effective pressures less than about 4-5 megapascals (MPa). Measured laboratory and well log velocities show two distinct trends for S-wave velocities with respect to P-wave velocity: one for the S-wave velocity less than about 0.6 kilometer per second (km/s) which approximately corresponds to effective pressure of about 4-5 MPa, and the other for S-wave velocities greater than 0.6 km/s. To accurately predict S-wave velocities at low effective pressure less than about 4-5 MPa, a pressure-dependent parameter that relates the consolidation parameter to shear modulus of the sediments at low effective pressure is proposed. The proposed method in predicting S-wave velocity at low effective pressure worked well for velocities of water-saturated sands measured in the laboratory. However, this method underestimates the well-log S-wave velocities measured in the Gulf of Mexico, whereas the conventional method performs well for the well log velocities. The P-wave velocity dispersion due to fluid in the pore spaces, which is more pronounced at high frequency with low effective pressures less than about 4 MPa, is probably a cause for this discrepancy. |
| Genre: | USGS Numbered Series |
| ProdID: | 98537 |
| Citation Author: | Lee, Myung W. |
| Citation Contributing Office: | Central Energy Resources Science Center |
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| Citation Language: | ENGLISH |
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| Citation No Pagination: | N |
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| Citation Online Only Flag: | Y |
| Citation Phsyical Description: | iv, 13 p. |
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| Citation Publisher: | U.S. Geological Survey |
| Citation Series: | Scientific Investigations Report |
| Citation Series Code: | SIR |
| Citation Series Number: | 2010-5138 |
| Citation Search Results Text: | Predicting S-wave velocities for unconsolidated sediments at low effective pressure; 2010; SIR; 2010-5138; Lee, Myung W. |
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| Citation Year: | 2010 |
| Type: | citation/reference |
| Text: | Predicting S-wave velocities for unconsolidated sediments at low effective pressure; 2010; SIR; 2010-5138; Lee, Myung W. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/sir_2010_5138.jpg |
| URL (INDEX PAGE): | http://pubs.usgs.gov/sir/2010/5138/ |
| Date Other: | Thu, 22 Jul 2010 00:00 -0500 |
| Publisher: | U.S. Geological Survey |
