Page 143 - Acquisition and Processing of Marine Seismic Data

134 2. MARINE SEISMIC DATA ACQUISITION

2.6.1 Preacquisition Instrument Tests parameters for the source, navigation devices,
recording system and survey geometry are com-
Several tests and calibrations are performed plete and properly set. An example checklist for
before the survey to ensure that all mobilized source, streamer, navigation devices, and
equipment is functioning properly. These tests recording system is shown in Table 2.10.
are termed start-up tests and include testing
Preacquisition implementations may also
and calibration of navigation units, seismic
include the acquisition of a test line close to
recorder and streamer, and air gun array. Some the study area just before the survey is initiated
of the instrument tests are repeated regularly in to ensure that all the equipment deployed is
a daily or monthly basis, depending on the operational in a predefined manner, if requested
requirements of the survey and client demands. by the client. Usually, one or more noise records
An instrument mobilization checklist for is collected before start-of-line (SOL) and after
streamers and recording system as well as seis- end-of-line (EOL) for each survey profile, to
mic source is prepared by the chief observer and understand the ambient noise level in the
approved by the party manager before each sur-
survey area.
vey. These checklists are used to assure that the

TABLE 2.10 An Example Parameter Checklist for the Mobilized Instruments (Streamers, Recording System and
Seismic Source) Controlled Before the Survey
☑
Parameter Planned Configured
Streamers Number of streamers 6 6 □
Total length of active channels 8000 m 8000 m □
Streamer depth 8 m 8 m □
Streamer separation 100 m 100 m □
Total number of channels per streamer 640 640 □
Group interval 12.5 m 12.5 m □
Number of depth leveler bird per streamer 10 10 □
Number of compass bird per streamer 16 16 □
Number of steering devices per streamer 16 16 □
Total number of acoustics per streamer 14 14 □
Total number of velocimeters for spread 2 2 □
Minimum offset 120 m 120 m □
Recording system Record length 10 s 10 s □
Sample rate 2 ms 2 ms □
Shot interval 25 m 25 m □
Data format SegD 8036 SegD 8036 □
Array forming N/A N/A □
Continued