Page 93 - Acquisition and Processing of Marine Seismic Data

84 2. MARINE SEISMIC DATA ACQUISITION

FIG. 2.40 Typical acquisition patterns for conventional 3D surveys. (A) Racetrack and (B) antiparallel survey patterns.

it is always preferred to shoot along the long sail 2.3.2 Streamer Steering
lines. If the survey area is rectangular, then it is
3D towed seismic acquisition simply requires
more feasible to collect the data along the sail
lines lying parallel to the longer borderline of several streamers to be deployed and towed by
the survey area. the vessel in parallel. Typically, the lateral sepa-
Line naming of the seismic profiles is usually ration between the streamers is 100 m even
in the following format: though it is 50 m for high-resolution 3D surveys.
AABBYY-LLLLCSSSS In 2D acquisition, only the depth of the streamer
is an issue and we deploy bird units at regular
AA: Client code intervals of approximately 300 m along the
BB: Survey area code streamer to maintain the streamer depth along
YY: Year of acquisition the sail lines. In 3D surveys, specific steering
LLLL: Line number equipment is also required to maintain both ver-
C: Code for line type tical and lateral positions of several streamers.
P: Prime line Operation of these steering units is controlled
R: Reshoot line by an integrated navigation system, which auto-
F: Infill line matically controls the wings of the devices, and
T: Test line required streamer separation is obtained and
SSSS: Line sequence number maintained in minutes following the activation
of the streamer steering system. The steering
The sequence number starts from 0001 and
regularly increases for each line with respect system usually fails to keep the streamers
to the acquisition order of the seismic lines. straight behind the vessel in the case of strong