Ex. PGS 1043
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`sezszvuc DATA ACQUI-_91TION
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`_included several technical innovations that furthered the development of
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`seismic data acquisition equipment and theinterpretation of seismic data.
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`Beginning in the early 1930s seismic exploration activity in the United
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`States surged for 20 years as related technology was being developed and
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`refined (Figure 2). For the next 20 years, seismic activity, as measured by the
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`U.S. crew count, declined. During this period, however, the so~called digital
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`revolution ushered in what some historians now are calling the Information
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`Age. This had a tremendous impact on the seismic exploration industry. The
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`ability to record digitized seismic data on magnetic tape, then process that
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`data in a computer, not only greatly improved the productivity of seismic
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`crews but also greatly improved the fidelity with which the processed data
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`imaged earth structure. Modern seismic data acquisition as we know it could
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`not have evolved without the digital computer.
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`During the past 20 years, the degree of seismic exploration activity has
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`become related to the price of a barrel of oil, both in the United States
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`(Figure 3) and worldwide. In 1990, US$2.195 billion was spent worldwide in
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`geophysical exploration activity (Goodfellow, 1991). More than 96% of this
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`(US$2.110 billion) was spent on petroleum exploration.
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`Despite the recent decline in the seismic crew count, innovation has con-
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`tinued. The late 1970s saw the development of the 3-D seismic survey, in
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`which the data imaged not just a vertical cross-section of earth but an entire
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`volume of earth. The technology improved during the 19803, leading to more
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`Crew Count
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`70?)
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`TOTAL LAND AND MARINE CREWS
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`MARINE ONLY o
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`1960
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`Fig. 2. U.S. seismic crew count (Goodfellow, 1991).
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`SEISMIC DATA ACQlIlSITI(§
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`- the advent of the IBM personal computer (PC). The PC reduced the cost-
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`" =._processing but was frequently too slow or had inadequate software to per
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`form much more than the simplest of input/ output functions. UND(-base
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`_ workstations were then developed to be more powerful than the PCs. Today,_.,.,
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`' "many field crews have data processing workstations to provide quick-look’?
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`general data processing support during field acquisition.
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`Interactive field computers are considered necessary during land crew:
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`' startup when test lines and source tests need to be evaluated. Processing costs
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`and time at the computer center can be saved using a field computer system"
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`that can demultiplex field records. Three~dimensional data acquisition, both‘
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`land and marine, would be almost impossible today without some form of‘
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`field computing-—even if it were only to locate the position of common mid-
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`points during the recording operations—to ensure that the fold of coverage is .
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`adequate and within specified tolerances.
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`Field computers have blossomed on marine vessels during the upsurge in
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`3-D data recording. When four streamers are collecting data from four source
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`arrays, the amount of positioning information for recording increases sub-
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`stantially. Networked workstations are becoming the norm for recording and
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`processing the navigation sensor data in near real time. For example, a
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`streamer's depth, feathering angle, and x,y location can be updated every sec-
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`ond using ship-monitoring computers. The collected data also can be
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`inspected to ensure that the quality of recording is acceptable.
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`Many recording systems have computers able to perform on-line phone
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`tests and analyses as well as cable tests prior to each shot. This is useful in
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`checking receiver integrity before recording commences. A number of instru-
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`ments are able to perform limited signal processing as a quick-look data pro-
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`cessing package. The advantage of having a system that can do some form of
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`field processing is that interpretation of field stacks may identify interesting
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`formations that could be further delineated by a modified program. One
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`quick-look approach in marine 3-D recording is to bin short offset traces in a
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`low fold 3-D volume, which may be rapidly processed and provide an early
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`indication of data quality as well as profiles and time slices through the 3-D
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`volume.
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`Exercise 4.1
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`1)
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`If two seismic lines (which tie at their respective centers) were
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`recorded by different source, receivers, and instruments, what tests
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`would be needed on the field-acquisition system to ensure that the
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`data phase ties in data processing would be made correctly?
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`EX. PGS 1043
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`Ex. PGS 1043