Keywords : rapid, digital, seismic, surveys

Rapid Digital Seismic Surveys

The current high-speed seismic data acquisition system is no longer in use. Ifremer has chosen a system based on SERCEL digital technology to replace it, which is used with the SMT and HR acquisition systems.
This tool is deployed on the institute's various deep-sea vessels.

Acquisition System

This system includes seismic streamers, seismic acquisition electronics (SERCEL SN408 laboratory), two immersion sensors and on-board quality control/processing tools.

Main technical features:

  • streamers : 12.5 m traces, 16 hydrophones per trace ; 4 traces per 50 m active element; 1 x 150m ballasted head cable; 1 streamer reel with capacity for 300m of active sections,
  • SN408 HR acquisition laboratory: 24 bits, sampling from 0.25 to 4 ms, up to 12 auxiliary traces, not high voltage, real-time acquisition and quality control software,
  • offset for the implementation and quality control screens in the scientific command room
  • pressure gauges: 2 pressure gaugues at the top and bottom of the active section and accurate shot dating,
  • all acquisition electronics centralised in a 10 foot container;
  • interface with the ship's instruments. DGPS positioning, gyrocompass, probe.

Source Device

  • GI 105/105 and 45/45 type guns with special streamlining (traction speed of 10 knots)
  • Immersed in 6 metres of water at a surface speed of 10 knots
  • 140 bars' pressure
  • 2 x 300 m3/h compressors or 2 x 10 foot containers containers

Deployment

Examples of deployment in different oceanographic vessels:
  • RV Le Suroît, 1 streamer with 24 traces ; 2 GI sources, 1 'acquisition electronics' container ; 2 compressor containers and 1 workshop container
  • RV Thalassa, 1 streamer with 24 traces ; 2 GI sources ; 1 'acquisition electronics' container; 1 compressor container and 1 workshop container

Performance

  • Vessel speed 8-10 knots
  • Optimal immersion 6-7 m
    • Frequency: 50-55 Hz
    • Vertical resolution 5m ; horizontal resolution 25m
  • Shooting rate 5 to 10 seconds
  • Data volume 4-10 GB per 24 hours
  • Ground penetration: several hundred metres depending on the sediment type, source type, water depth, acquisition geometry, image processing quality, …
  • Simultaneous acquisitions possible: SMF bathymetry, sediment sounder