In the Browse Basin, as in many areas of the world, complex seafloor topography can cause problems with seismic imaging. This is related to complex ray paths, and sharp lateral changes in velocity. This paper compares ways in which 2D Kirchhoff imaging can be improved below seafloor canyons, using both time and depth domain processing.In the time domain, to improve on standard pre-stack time migration (PSTM) we apply removable seafloor static time shifts in order to reduce the push down effect under seafloor canyons before migration. This allows for better event continuity in the seismic imaging. However this approach does not fully solve the problem, still giving sub-optimal imaging, leaving amplitude shadows and structural distortion. Only depth domain processing with a migration algorithm that honours the paths of the seismic energy as well as a detailed velocity model can provide improved imaging under these seafloor canyons, and give confidence in the structural components of the exploration targets in this area. We therefore performed depth velocity model building followed by pre-stack depth migration (PSDM), the result of which provided a step change improvement in the imaging, and provided new insights into the area.

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Onshore 3D seismic data is often acquired with rich azimuth coverage by utilising orthogonal shooting (or cross-spread) layouts. This means that azimuthal anisotropy, if present, can be readily observed and its effects on the data can be quantified and accounted for as part of the processing and imaging flow. In this example from the Canning Basin, the data appeared initially to be exhibiting the effects of azimuthal anisotropy. However, with careful handling and honouring of the azimuths of the acquired data during the PreSDM velocity model building, it was possible to correct for most of the variation simply with a laterally variable velocity model, without the need to invoke the presence of azimuthal anisotropy.

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