Direct phase determination of S‐wave velocities from acoustic waveform logs
| Autor: | J. D. Ingram, T. Parks, E. E. MacKnight, C. F. Morris |
|---|---|
| Rok vydání: | 1985 |
| Předmět: | |
| Zdroj: | GEOPHYSICS. 50:1746-1755 |
| ISSN: | 1942-2156 0016-8033 |
| DOI: | 10.1190/1.1441864 |
| Popis: | A new technique for producing S-wave logs from borehole acoustic waves has been developed. The procedure is based on direct phase calculations for time‐windowed waveforms obtained with an acoustic logging tool. A window is positioned over the S-wave portion of the signals, and window moveout is chosen to give zero‐phase differences in a band of frequencies across the array of receivers. A major issue in application of this method is the error introduced by windowing and by interfering signals such as casing arrivals, residual P-waves, and modes propagating in the borehole. Examples using synthetic data are presented illustrating these errors and the means of reducing them. A capture effect, characteristic of phase methods, may be exploited to reduce the effect of interference. Examples are presented showing logs made in different lithologies using a conventional two‐receiver long‐spacing tool. A pulsed transmitter was used with energy in a frequency range 10 to 20 kHz. In hard formations there is little difficulty in obtaining good shear logs. In softer formations, with reduced shear amplitudes, the problems caused by interfering waves become more severe. Careful choice of frequency bands used in the analysis can reduce interference problems and may improve logs in soft formations. |
| Databáze: | OpenAIRE |
| Externí odkaz: |
|