3-D tomographic Q inversion for compensating attenuation anomalies

Abstract

The propagation of seismic wave through viscoacoustic media is affected by the attenuation that is caused by the quality factor Q, resulting in significant loss of signal strength and bandwidth. Gas trapped in sediment is an example of such media. Seismic images of geological structures underneath shallow gas often suffer from resolution degradation and the effect of amplitude dimming, making the identification and interpretation of the structures difficult. This in turn affects the ability to accurately predict the reservoir properties. Thus, there is a need to compensate the attenuation anomalies due to Q. In this paper, we present a workflow of Q estimation and compensation that is based on our previous work on amplitude tomography. Our new approach involves utilizing tomographic inversion for estimating Q from prestack depth migrated common image gathers that fully honours the wavepaths. 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 amplitude tomography work, of attenuation is fully taken into account, thereby 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 realdata examples, that our workflow provides an optimal compensation solution that resolves amplitude, phase and bandwidth distortions due to seismic attenuation.