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3-D Tomographic Amplitude Inversion for Compensating Transmission Losses in the Overburden
Abstract
A tomographic inversion approach using prestack depth migrated common image gathers is utilized to compensate reflection data for amplitude loss caused by transmission anomalies in the overburden. The approach has the advantage of estimating transmission losses from anywhere within the overburden using the actual seismic raypaths. Examples show that the method can mitigate amplitude attenuation caused by transmission anomalies and should be considered as one of the processes for amplitude preserving processing that is important for AVO analysis when transmission anomalies are present.
... Our method accommodates an effective Q field which is a function of t, x and y. Strategies for estimation of the Q field include the long established spectral ratio method and the more recently developed approach of Q tomography (Xin et al. 2008). The inversion problem can be solved, for example, by the method of Iteratively Reweighted Least Squares (Trad et al. 2003). ...
Following our previous work on Amplitude Tomography that deals with amplitudes alone, we extend our effort to include the compensation of bandwidth and phase of seismic signals that are distorted by seismic attenuation. Our new approach involves utilizing tomographic inversion for estimating the quality factor (Q) from prestack depth migrated common image gathers. By filtering the seismic data into different frequency bands and measuring the effect of attenuation on amplitudes in each band, the frequency dependent effect, which was ignored in our previous work, of attenuation is fully taken into account, allowing Q to be estimated from our tomographic method. By using the estimated Q volume in one of the migration methods that incorporates Q in the traveltime computation, we demonstrate, through examples, that our workflow provides an optimal compensation solution that resolves amplitude and bandwidth distortions due to seismic attenuation.
In this paper, we propose a new Q tomographic inversion approach using centroid frequency shift information. An adaptive correction is applied to the observed centroid frequency to account for any deviation from the explicit relationship through tabulating the absorption effect for different accumulated dissipation time. These adaptively corrected centroid frequency shift data will then be fed to reconstruct the attenuation distribution tomographically. We will demonstrate how our approach can accurately estimate Q model and can be included in the Q compensation process to fully account for attenuation and dispersion.
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