Page 150 - Acquisition and Processing of Marine Seismic Data

2.6 QC IN DATA ACQUISITION 141

TABLE 2.15 Example Definitions or Characteristics of TABLE 2.16 Example Definitions or Characteristics of
Dead and Noisy Traces Typically Encountered During the Bad Records and Misfires Typically Encountered During
Acquisition the Acquisition
Dead • If trace polarity is reversed or partly Bad • If seismic data or positioning information is
traces reversed records lost for any reason
• If trace has continuous spikes or spike-like • If acquisition/source/recording/streamer/
noise navigation parameters do not meet the
• If trace amplitude is significantly low specifications
compared to an adjacent group (weak trace) • If source misfires/auto-fires, or if there is no
• If trace amplitude is significantly high fire
compared to an adjacent group (wild trace) • If source separations do not meet the
• If trace amplitude range is over the dynamic specifications
range (saturation) • If source and/or streamer positioning is
• If RMS noise limits exceed the specifications outside the specified criteria
• If trace does not pass from daily tests • If the shot is recorded during air leaks
• If trace sensitivity is not within the range of • If extended header or navigation header of
manufacturer’s specifications the shot is not correctly recorded
• If shot numbers or file numbers on digital
Noisy • If trace has a noticeable noise over the records do not correspond to shot numbers
traces source signal on data sheet
• If trace has a noticeable noise under strong • If unrecoverable errors or a complete loss of
weather or terrestrial conditions (storms, magnetic tape recording occur
thunders, waves, tides, earthquake, etc.) • If number of dead traces in a shot exceeds
• If trace has strong seismic interference noise 5% of the total number of channels
• If trace has a noticeable noise from man- • If more than 5 consecutive channels are
made sources (shipping, fisheries, vessel’s defined as bad traces
machinery, etc.) • If total number of dead and noisy traces
• If trace has noise at a specific frequency
exceeds 10% of total number of channels
Misfires • If an auto firing of any gun within the array
occurs
The following additional processing steps can
• If the performance of a string is below the
also be applied to seismic data onboard if specif- drop-out specifications
ically requested by the client to obtain a fully • If source depth/separation/configuration is
migrated 3D seismic data at the end of the different from specifications
survey: • If one or more guns has timing errors more
than 1ms
• Linear noise attenuation • If air pressure of an air gun drops below 90%
• Q compensation of the normal pressure level
• If source signature does not meet the
• Velocity analysis (typically at
specifications
1.0 km 1.0 km grid) • If total source volume does not meet the
• Radon multiple attenuation specifications
• Binning and trace interpolation • If signature recording of near-field
• 3D stack (typically 12.5 m 25 m grid) hydrophone is lost
• If shooting time of a record is not clearly
• Post stack Kirchhoff time migration
indicated
The purpose of the onboard processing is actu-
ally not to eliminate noise embedded in the data Auxiliary channel data (up to 60 channels) which
but to analyze the data during the recording and record the system time breaks and signatures of
to document the possible issues for a comprehen- each air gun from their individual near-field
sive processing in the processing center. hydrophones mounted on the gun strings are