Estimating Seismic Attenuation (Q) by an Analytical Signal Method

The analytical signal method for seismic attenuation (Q) estimation is reviewed and investigated using a 1D surface data model and field VSP data. The error in Q-factor recovery from modelled data using the analytical signal method is better than 7 percent over a range of Q-factors from 25 to 100. The method is applied to the enhanced downgoing P-wave of an offset VSP-survey from Ross Lake, Saskatchewan. The logarithm of the instantaneousamplitude ratio versus time-increment plot (an internal step in the method) is surprisingly smooth when compared to log spectral ratios of the same data. The depth average of Q is 34 for clastic rocks of the Ross Lake area. This compares to a Q range of 37 to 41 obtained from the drift correction method over a similar depth range in previous work, which is somewhat lower than a Q of 67 obtained from the spectral ratio method. Errors in Q-estimation by the analytical signal method appear to be caused by insufficient moveout compensation.