Pre-stack depth migration for improved imaging under seafloor canyons: 2D case study of Browse Basin, Australia*
Helen Debenham 1 2 4 Shane Westlake 31 Fugro Seismic Imaging, 69 Outram St, West Perth, WA 6005, Australia.
2 Current address: ION-GXTechnology, 578 Murray St, West Perth, WA 6005, Australia.
3 Finder Exploration, 9 Richardson St, West Perth, WA 6005, Australia.
4 Corresponding author. Email: helen.debenham@iongeo.com
Exploration Geophysics 45(3) 216-222 https://doi.org/10.1071/EG12085
Submitted: 21 December 2012 Accepted: 30 April 2013 Published: 7 June 2013
Abstract
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.
Key words: Australia, Browse Basin, canyon, channel, modelling, pre-stack depth migration (PSDM).
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