Page 29 - Acquisition and Processing of Marine Seismic Data

20 1. INTRODUCTION

TABLE 1.6 Specifications of Conventional Single- and always some offset between the source and
Multichannel Seismic Systems Used to Obtain Relatively streamer because of the safety conditions, since
Deep Stratigraphy and Tectonic Setting the source energy may damage the streamer.
After each shot, the amplitudes of the reflected
signals received by the single-channel streamer
System Frequency Penetration Applications
(kHz) Depth (m)
are transmitted to the recorder. These ampli-
Single-channel 0.05–1 10–500 • Shallow
tudes are digitized at the recorder and plotted
seismics stratigraphy
side by side for each shot to constitute a zero-
• Gassy
sediments offset section (Fig. 1.13A). For single-channel
• Shallow acquisition, it is possible to obtain a preliminary
structural display of the subbottom stratigraphy during
setting
• Offshore the recording since plotting of the recorded
engineering traces is done in real time.
settlements Different seismic sources with different fre-
quency and amplitude characteristics can be
Multichannel 0.01–0.2 10–10,000 • Deep
seismics stratigraphy used for single-channel acquisition. Although
• Oil and gas a single air gun (mostly a GI gun) or a water
exploration gun can be deployed, the most common
• Shallow and single-channel seismic source is the sparker
deep array, which uses extremely high electric volt-
structural
setting age discharge to produce an impulsive source
signal in the water column (Section 2.1.3).

FIG. 1.13 Schematic illustration of (A) single- and (B) multichannel seismic data acquisition. Even though it is possible to
obtain subbottom reflector geometry during single-channel acquisition, multichannel seismic data require several additional
processing steps to obtain the subsurface geology; t(x) indicates the arrival time of each specific reflection event.