Estimating frequency-dependent attenuation quality factors in pre-stack surface seismic data

Estimation of a power-law frequency-dependent seismic quality factor is introduced into the pre-stack Q inversion (PSQI) method for estimating seismic attenuation from prestack data. The adapted method is tested with synthetic data, and found to estimate successfully the frequency dependence of the attenuation quality factor, within errors. Notably, though, if low frequencies (<20Hz) are excluded from the inversion, then frequency dependent estimates become inaccurate. The adapted PSQI method is applied to a CDP supergather over a North Sea oil field, and a slight frequency dependence on the attenuation quality factors is found, with a mean frequency exponent of 0.03±0.10. A previous study, based on available well log data, has found that the scattering attenuation quality factor value, in the range of 2.28s TWT and 2.68s TWT, shows a negative dependency on frequency, and can therefore account for much of the frequency dependence seen in the surface seismic results in this region.