| Autor: |
Bhuiyan, M. H., Holt, R. M. |
| Předmět: |
|
| Zdroj: |
Geophysical Journal International; Jul2016, Vol. 206 Issue 1, p487-500, 14p |
| Abstrakt: |
Gassmann's fluid substitution theory is commonly used to predict seismic velocity change upon change in saturation, and is hence essential for 4-D seismic and AVO studies. This paper addresses the basics assumptions of the Gassmann theory, in order to see how well they are fulfilled in controlled laboratory experiments. Our focus is to investigate the sensitivity of shear modulus to fluid saturation, and the predictability of Gassmann's fluid substitution theory for P-wave modulus. Ultrasonic P- and S-wave velocities in dry and saturated (3.5 wt per cent NaCl) unconsolidated clean sands (Ottawa and Columbia) were measured in an oedometer test system (uniaxial strain conditions) over a range of 0.5-10 MPa external vertical stress. This study shows shear modulus hardening upon brine saturation, which is consistent with previous data found in the literature. Analysis of the data shows that most of the hardening of the ultrasonic shear modulus may be explained by Biot dispersion. Isotropic Gassmann's fluid substitution is found to underestimate the P-wave modulus upon fluid saturation. However, adding the Biot dispersion effect improves the prediction. More work is required to obtain good measurements of parameters influencing dispersion, such as tortuosity, which is very ambiguous and challenging to measure accurately. [ABSTRACT FROM AUTHOR] |
| Databáze: |
Complementary Index |
| Externí odkaz: |
|
