P and S Wave Velocity Determination

There are three general methods that can be used to determine formation velocities from full waveform logs. The first approach is to make use of the data from the entire waveform. This type of velocity analysis is performed either in the frequency domain (I.e. f-k analysis or the two station method) or in the time domain (I.e. velocity spectral analysis). The second approach is to identify the P wave pulses on individual traces and to determine delay times between traces. In conventional acoustic logging this technique has been used successfully to determine the compressional wave velocities. The third approach' is to use the phase velocity of the gUided waves (Pseudo-Rayleigh) to determine the shear velocity. Each of these approaches have certain advantages and limitations depending on the tool characteristics (number of records, frequency response), formation properties (high or low shear velocity), and computation times required. The etIect of these parameters upon each method of velocity determination is presented.