3D Spread Control
Various techniques to efficiently control lateral position and depth of the streamer spread are available to help improve 4D repeatability. Such techniques may also minimize infill and optimize the streamer depth profile. This in turn increases data quality as well as reducing the total survey turnaround time.
Better streamer control can improve survey turnaround time by:
- Minimizing infill in 3D surveys
- Increasing repeatability in 4D surveys
- Optimizing the streamer depth profile and increasing vessel speed
Acoustic network and deflector positioning
Streamer Depth Control
PGS developed the Streamer Depth Controller (SDC) buoy to accurately control the depth of the streamer front end, which is used during deep-towing with GeoStreamer®. The SDC is standard equipment on all PGS vessels.
Each buoy is connected to the front end of a streamer by a radio controlled winch. The buoys and winches are managed from the instrument room onboard the seismic vessel, from where it is possible to control the depth of the streamer, and monitor technical information about the buoy such as humidity and voltage. The powerful and durable electric winch is powered by a battery connected to an underwater generator, allowing the unit to be towed without maintenance for several months at the time.
The SDC can raise the front of the streamers to the surface during deployment and for maintenance. This simplifies workboat access to the in-sea equipment.
The slim eBird® design allows effective lateral steering and depth control of seismic streamers with minimal additional acoustic noise. The uniform three wing solution also provides full roll control capabilities. Feather correction of 2˚ to 3˚can be achieved, and the system quickly responds to depth or lateral corrections.
The eBird has a body and three detachable wings. The snap-on/snap-off mechanism makes attachment and removal of wings easy both during streamer deployment and retrieval, and workboat maintenance. All wearing parts like motors, gears and batteries are located in the wings. The SmartWing® concept makes it possible to maintain a very slim body, minimizing turbulence and acoustic noise.
PGS vessels equipped with eBirds and GeoStreamer use a full acoustic network for positioning, thus reducing compass dependency.
Streamer and Deflector Positioning
Streamer spread positioning can be challenging in areas where fresh and salt water layers meet. To tackle the problem PGS has installed acoustic and GNSS (Global Navigation Satellite System) units on its deflectors, with specially developed heavy duty generators and associated electronics to power the equipment. These systems are mounted on our deflectors as standard.
Deflector with positioning equipment
Traditionally, the acoustic streamer network was tied to the GNSS position of the vessel and of the sources. In areas where acoustic ranging is difficult, it was previously necessary to deploy positioning units on front floats, closer to the streamer spread.
Today, widening streamer spreads are increasing the distance from the vessel and the source to the outer streamers. Deflector positions system are very useful, as they provide a position fix at the outer extent of the spread.
PGS deflector positioning:
- Improves positioning geometry for wider spreads
- Fixes the outer perimeter of the spread to the GNSS position on the deflectors
- Simplifies the staggering of streamers
- Eliminates the need for front buoys and reduces workboat operations
- Accurate deflector position increases safety, particularly during turns and close passes
This robust solution includes backup units for the GNSS, acoustic units and dedicated generators on the deflectors to increase operating time.