No abstract

Surface related multiple elimination (SRME) method is known to have difficulties in attenuating shallow water multiples. Particularly, for water-layer related multiples in very shallow water environments such as seabeach-shallow water areas because the primary water-bottom reflection that is required by SRME for predicting the multiples is not recorded due to near offset gap. Thus, predictive deconvolution in either x-t or tau-p domain is often used in processing workflow to suppress this kind of multiples in these situations. However, deconvolution also attenuates primary events that have a periodicity which is close to that of the water-layer. In this case study, we present a two-step processing workflow for removing free-surface multiples. Firstly, we use a multi-channel prediction filter estimated from the multiples for attenuating water-layer related multiples. Secondly, we apply SRME for suppressing other surface multiples generated by sub-surfaces underneath the water-bottom. We demonstrate that this workflow provides an optimal suppression of free-surface multiples on marine data that have been recorded in the Bohai Sea offshore eastern China.

No abstract

The presence of gas, both as shallow pockets and as commercial reservoirs, has long been recognized as a significant problem in imaging seismic data. In this paper we describe how we successfully applied Q tomography and Q-PSDM technology to compensate the phase, frequency and amplitude loss due to shallow absorption, thus improving structure imaging and potentially accurate AVO/DHI analysis underneath shallow gas.

No abstract

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.

No 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, such as shallow gas, 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.