Modelling 3D seismic wavefields through complex seabottom topography offshore NW Australia

Abstract

SUMMARY Seafloor canyons and complex seafloor topography pose significant challenges when analysing seismic data from the North West shelf off the Western Australian coast. Several prolific gas fields in this area lie beneath the continental shelf break, which contains large canyons that cause significant seismic amplitude distortion and complex wavefield behaviour (e.g. scattering and wavefield multi-pathing), and lead to irregular and poor illumination, unreliable AVO analysis, and difficulties in velocity model building. To illustrate these issues we present 3D elastic finite-difference simulation results from a model of a region of the North West Shelf in Western Australia. Using a high-performance computing cluster we model elastic wavefields through complex seabottom topography. We simulate plane-wave propagation through a bathymetric model to generate a pseudo stack. We observe many expected complex effects including wavefield (de)focusing, diffractions and triplications. We also measure wavefield amplitude variations of a factor of four over scale lengths of a few hundred metres; this is sufficient to cause significant imaging issues. By accurately modelling full 3D wavefield effects we can now generate data to benchmark existing algorithms and develop new techniques/algorithms for handling complex bathymetry.