| Autor: |
Brian E. Hornby, Craig D. Johnson, Karl S. Coyner, John M. Cook |
| Rok vydání: |
1997 |
| Předmět: |
|
| Zdroj: |
SEG Technical Program Expanded Abstracts 1997. |
| DOI: |
10.1190/1.1885560 |
| Popis: |
Primary compaction of a water-saturated China Clay was studied using controlled ultrasonic laboratory measurements. Ultrasonic velocities were recorded using a custom built compaction cell that incorporates ultrasonic compressional and 4-component shear wave transducers oriented parallel and perpendicular to the direction of axial stress. The effect of primary compaction on porosity and on compressional wave slowness was investigated and empirical relations for porosity and velocity versus effective stress derived. Changes in P-wave slowness are found to be linear with changes in porosity during primary compaction, with the result that the Wyllie time average relationship is valid for this sort of compacting sediment. In addition, the development of anisotropy during compaction was investigated and showed an increase in P-wave anisotropy (c) to 5 percent for axial stress to 93 MPa. Unloading to 16 MPa resulted in a further increase in anisotropy to more than 8.5 percent. This increase in elastic anisotropy during the unloading phase is consistent with the results from a theoretical modeling study that shows that anisotropy will increase with increasing porosity for clay supported sediments (clay compacts or shales) with a fixed clay-platelet alignment. An interpretation of these results is that the microstructure of the clay compact is largely determined during primary compaction, and during the unloading phase the principle effect on the anisotropy is due to the porosity increase, and any effects due to variations in the clay microstructure during unloading are secondary. burden stress with an accompanying increase in anisotropy (e.g. Kaarsberg, 1958). In this study measurements of ultrasonic velocity and porosity are taken a a function of primary compaction. Porosity/velocity relationships are examined as well as the development of elastic anisotropy during primary compaction. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
|
