Depth Imaging with Amplitude Correction for Localized Absorption Anomalies. The North-West Australian Shelf Case Study

Seismic amplitudes within target intervals are often affected by localized absorption anomalies in the overburden. In the North-West Australian shelf and in many other regions, the majority of such anomalies are caused by gas trapped in shallow sediments. We apply amplitude tomography to build a high resolution 3D absorption model and to take this effect into account in geological settings typical for the North-West Australian shelf. Two approaches have been developed recently to correct for absorption in depth imaging – the first uses frequency independent models and the second based on Q- compensation with the linear frequency dependent assumption. We show how both techniques correct seismic amplitudes but their results are not frequency balanced. In order to achieve a better fit with the real seismic data, we propose and apply a mixed absorption model that combines frequency independent amplitude correction with the linear Q-compensation and reflects the presence of different effects responsible for seismic energy attenuation in real geological media. Pre-stack depth migration with this model corrects for the overburden effects and produces seismic data with spatially balanced amplitude and spectral characteristics.