Single Vessel Configurations
The most common approach to marine seismic acquisition is to use a single vessel towing a wide spread of many streamers and one, two or more source arrays.
The streamer and source configuration will determine data quality, illumination, and acquisition efficiency. The number of streamers, their length and separation, as well as the number and positioning of sources, have to be selected based on the geophysical and geological objectives.
Narrow azimuth and multi azimuth surveys are commonly acquired with a single vessel. These can use two or more sources. Note however that MAZ surveys can be constructed by adding new azimuths on top of existing datasets.
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.
- Provides better crossline common mid-point (CMP) sampling, for a given streamer separation, provides images with an improved spatial resolution
- Permits wider streamer separation and overall spread width with no reduction in crossline sampling
- Enables a reduction in deployed streamer equipment (without changing spread width or crossline sampling)
Adjust the parameters with our Acquisition Calculator to find the optimal configuration to solve your imaging challenge. Calculate illumination with various streamer and source configurations. Tailor the acquisition geometry and figure out the compromises for efficiency versus sampling.
The 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.
Of course, a trade-off is required. 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 has extensive experience with simultaneous and overlap shooting and has patented a variety of techniques to enable optimal source deblending in data processing.
In conventional, narrow-azimuth 3D marine surveys, a single vessel tows a streamer spread and the subsurface geology is illuminated from the acquisition direction. The multi-azimuth (MAZ) method also uses a single vessel but acquires data over a survey area in two or more directions.
In areas with complex geology, adding more azimuths can positively affect the subsurface image. The benefits of additional azimuths extend beyond illumination to include better signal-to-noise ratio and improved spatial sampling.
A standard MAZ survey comprises two or three survey azimuths. This may involve acquiring new data to complement a legacy survey.
Where the subsurface above the target area is complex, data quality and resolution may be improved by illuminating the area of interest from several different orientations. This can be achieved by repeating the acquisition from several sail-line directions using a technique called multi-azimuth acquisition (MAZ).