Subsurface Illumination with SWIM
SWIM uses sea-surface reflections that contain valuable subsurface information to deliver high-resolution images that are unachievable with traditional reflection seismic imaging.
With SWIM, each receiver is used as a virtual source, reducing the source line spacing to be the same as the streamer spacing. The resulting equivalent survey area has increased source sampling resulting in improved subsurface illumination and angular diversity.
SWIM enables the design and use of cost effective acquisition geometries such as super-wide tow. In shallow water, gaps in near-surface coverage can be filled successfully by SWIM and the acquisition footprint reduced.
Improved illumination provides a continuous seismic dataset unaffected by source illumination issues. In deep water acquisitions, SWIM can augment angular diversity mitigating the limiting effects of long inline offsets on super-wide tow acquisitions.
Turning the receiver spread into virtual sources (VS) and receiver arrays reduces source sampling in the crossline direction from the distance between sail lines to that between streamers. Using SWIM in shallow water fills in gaps in near-surface coverage successfully reducing the acquisition footprint (AF).
The images above show a comparison of subsurface illumination from a single shot within 2D images using 6 km streamer length.
In both images, the gray-scale stacks are derived from shot profile migrations of all shots. On the left: amplitudes contributed by migrating the primary reflections from a single shot gather. On the right: amplitudes contributed by migrating the same shot with PGS' SWIM algorithm.
Note the profoundly greater spatial extent of illumination from a single shot provided by SWIM in comparison to primary reflections. The lateral extent of the illumination is limited only by the areal distribution of streamers associated with each shot.