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.

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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.

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