Page 91 - Acquisition and Processing of Marine Seismic Data

82 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.38 Example of conventional 3D source and streamer layouts. (A) Dual source (A and B) and a single streamer (S1),
(B) single source (A) and two streamers (S1 and S2), (C) dual source and two streamers, (D) dual source with four streamers.
Dashed lines correspond to CMP lines associated with specific source-streamer pairs.

tectonism, as is the case in the Gulf of Mexico. acquire data with a superior resolution mainly
The common purpose is to obtain seismic data incorporating the marine seismic products of
with improved S/N ratio, greater bandwidth Sercel.
and better resolution to obtain a more reliable
illumination and mapping of the target. For 2.3.1 Acquisition Patterns
instance, Western Geco employs the Q-Marine
acquisition system in towed streamer acquisi- In a conventional 3D survey, seismic data is
tions, which utilizes point-receivers to record acquired along several parallel preplot lines
the data using calibrated receivers and a cali- with the same azimuth over predetermined tar-
brated seismic source. The Q-Marine system get zones determined from vintage seismic data
also uses fully braced acoustic positioning for of previous 2D surveys. The typical sail line
better streamer steering. PGS employs GeoStrea- spacing for 3D surveys changes between 400
mer and GeoSource technology in their fleet to and 800 m depending on the number of
eliminate the ghost and acquire higher resolu- streamers deployed and the separation between
tion data along with steerable seismic source the streamers. The acquisition template for 3D
arrays for a better repeatability of 4D time-lapse surveys is termed a racetrack pattern, which sig-
seismic surveys. CGG Veritas utilizes BroadSeis nificantly reduces the dead times required for
and BroadSource technology to completely line changes during the turns, where the vessel
remove the source and receiver ghosts, to skips over several parallel sail lines when it