Dual versus Triple Source

Most marine seismic surveys use a dual-source setup, however, triple-source can provide better spatial crossline sampling for high-resolution imaging, or greater streamer separation and thus greater acquisition efficiency. The method is usually combined with continuous recording and overlapping shot records.

Most seismic surveys deploy a dual-source set-up. However, it is possible to maintain crossline CMP bin spacing with larger streamer separations by introducing a third firing array. This configuration increases operational efficiency.

  • Better crossline CMP sampling, for a given streamer separation, provides images with improved spatial resolution
  • Permits wider streamer separation and overall spread width with no reduction in crossline sampling
  • Enables reduction in deployed streamer equipment for same streamer spread width and same crossline sampling 

 

The table below shows alternative options, with two or three source arrays, to achieve a given spatial sampling in the crossline direction.  

Crossline
bin width (m)

Sources

Streamer separation (m)

12.5

dual

50

12.5

triple

75

18.75

dual

75

18.75

triple

112.5

25

dual

100

25

triple

150

  

comparison of crossline bin width and illumination using dual and triple source configurationsThe illustration shows the source-streamer ray path contributions to each subline (i.e. CMP location) for dual-source shooting with 100 m streamer separation vs. triple-source shooting with 150 m streamer separation. In both scenarios, source separation is 50 m and crossline bin width (subline separation) is 25 m. The black diamonds represent the streamers and the blue rectangles represent sources. The crossline subsurface illumination is illustrated by the horizontal illumination bar at the bottom.

 

Deblending Overlapping Shot Records

To achieve the same in-line CMP fold, the shot interval for triple-source must be decreased by 33% compared to a dual-source acquisition. This means a part of each shot record may include energy from the next shot. 

PGS pioneered the commercial use of triple-source shooting in the early-1990 and has extensive experience with simultaneous and overlap shooting. We have patented a variety of techniques to enable optimal source blending in acquisition and deblending in data processing.