Automatic time picking and velocity determination on full waveform sonic well logs

Lejia (Lilly) Han, Joe Wong, John C. Bancroft, Robert R. Stewart

Full waveform sonic logging is used to determine formation interval velocities within a well bore. In order to obtain P-wave velocities, we must perform time-picking on the first arrivals on the recorded sonic seismograms. A typical full waveform log from a well consists of thousands to tens of thousands of seismograms, and manual time-picking is not practical. We have developed and evaluated new methods of automatic picking of first arrivals by computer. We used MATLAB for coding the software for these methods. Techniques employed within the automatic time-picking algorithms include energy ratio calculation, noise reduction, deconvolution, wavelet approximation, and median filtering. The time picks resulting from these methods are much more accurate than those obtained from a commercial software package. Our automatic time picks compare very favorably with manual time picks, even over noisy data segments. We show P-wave velocity results from a full waveform log using a monopole source, and S-wave velocity results from a log using a dipole source.