Sonic well logging methods and apparatus for processing flexural wave in optimal frequency band
US5587966A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | Oct 13, 1994 |
| Grant date | Dec 24, 1996 |
| Priority date | — |
| Expiry date | Oct 13, 2014 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01V1/48
- WIPO fieldMeasurement
- WIPO sectorInstruments
Abstract
Methods for determining an optimal frequency band for processing of flexural waves according to bias-corrected STC or QSTC are disclosed. A preliminary estimate of the formation shear slowness S and a determination of the borehole diameter D are first obtained, and the flexural waves are processed in a frequency band having a center frequency f.sub.c which is a function of preliminary estimate of S and the product of that estimate of S and diameter D. Where the preliminary estimate of S indicates a slow formation, f.sub.c is chosen as 0.6/SD. Where the estimate indicates a fast formation, f.sub.c is chosen as 0.2/SD. In other or all formations, a smooth function such as [0.2+((0.8/.pi.) arctan ((S-100)/100))/SD] can be used to choose the center frequency. Alternatively, if errors in the environmental parameters can be estimated statistically, they can be used to select an optimum center frequency. Once f.sub.c is chosen, the filter parameters which define the bandwidth of the filter used in the Fourier transform of QSTC and in bias-corrected STC are preferably normalized by scaling the bandwidth BW to a specified fraction of f.sub.c ; BW=f.sub.c /Q. Similarly, the window length T.s…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.