Separated wavefield imaging (SWIM) is an innovative imaging technology that uses up- and down-going wavefields, recorded by GeoStreamer dual hydrophone and motion sensors. It delivers high-resolution images of the subsurface not achievable with traditional reflection seismic imaging.
The fundamental concept is based on using each receiver as a virtual source, expanding the angular diversity and subsurface coverage, particularly for shallow reflectors. By effectively turning the streamer spread into a (virtual)-source-and-receiver array, PGS reduces the source sampling in the crossline direction from the distance between sail lines to that between streamers.
SWIM uses virtual sources (VS) and delivers extra illumination (EI) and denser sampling (DS).
- Virtual sources - Utilizing sea-surface reflections and making each receiver a virtual source results in the survey area having increased source sampling and improved angular diversity and illumination.
- Extra illumination - Sea-surface reflections add additional information about subsurface reflectivity, to enable high-resolution imaging that is unachievable with traditional reflection seismic.
- Denser sampling - Extended angular illumination of each point in the subsurface and information from acute, near angles can significantly improve shallow target AVA analysis.
Improved Angular Diversity
While imaging with primaries is controlled by the source illumination and therefore the shot density, the inclusion of sea-surface reflections provides illumination across the area covered by all receivers.
SWIM provides extended angular illumination of each single point in the subsurface (as illustrated above). The improved angular diversity enabled by SWIM aids shallow target AVA analysis, by improving the statistical reliability of gradient and intercept volumes.
Using primary reflections only results in uncertainty in gradient and intercept due to the lack of near-angle information.
SWIM provides essential angle information, especially for near-angles, allowing for accurate AVA analysis away from well data.
Key SWIM Benefits
- Permits cost-effective wide-tow acquisition in shallow water
- Allows accurate imaging of the overburden without sail-line illumination footprint
- Increases data density by complementing traditional primary imaging
- Improves illumination to a depth equal to the width of the streamer spread
- Provides high-resolution images suitable for shallow hazard work to mitigate drilling risks
- Enables the CWI workflow, to enhance imaging of deeper targets as shallow model and imaging uncertainty is removed
- Allows direct estimation of a reflectivity cube for 3D wavefield modeling SRME
- Enhances sample density on gathers by increasing angular diversity improving interpretation of complex structure QC and AVA analysis