Imaging with Separated Wavefields
SWIM® is a depth-imaging technology that uses both up- and downgoing wavefields available from GeoStreamer® recording to expand coverage and enhance subsurface illumination.
It has traditionally been very difficult to estimate near surface velocities accurately in areas of shallow water, due to the poor angle illumination provided by the primary arrivals within the required angle mute zone. This has made it difficult to produce a sufficiently good quality image of the water bottom and underlying geology.
The more frequent use of wide tow acquisition to increase project efficiency has made crossline footprint artifacts a more common occurrence in near-surface images, making shallow hazard analysis very difficult.
With SWIM each receiver can also function as a virtual source, expanding the coverage and enhancing subsurface illumination, particularly for shallow reflectors. By turning the streamer spread into a set of (virtual) sources as well as a receiver array, the survey area benefits from increased spatial sampling and an improved distribution of offsets and azimuths.
This improves the source sampling by reducing the sampling interval in the cross-line direction from the distance between sail lines to that between streamers, mitigating wide-tow sail line artifacts.
Three depth slices in water depth of 70 m offshore Malaysia. SWIM images at the bottom, benefit from the additional illumination provided by sea surface reflections. These show seamless and complete images of the complex shallow channel systems with no sail line imprint.