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TRANSCRIPT
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COMMONWEALTH OF AUSTRALIA
DEPARTMENT OF NATIONAL DEVELOPMENT
BUREAU OF MINERAL RESOURCESGEOLOGY AND GEOPHYSICS
012233
SOME OBSERVATIONS ON THE USE OFTHE -VIBRCSEIS - METHOD
F J MOSS
ECONOMIC COMMISSION FOR ASIA AND THE FAR EASTCOMMITTEE ON INDUSTRY AND NATURAL RESOURCES
Symposium on the Development of Petroleum Resources of Asia and the Far East
Third Session: 10th-20th November 1965
TOKYO, JAPAN
SOME OBSERVATIONS ON THE USE OF ME "VIBROSEIS" *METHOD
by
F. J. Moss
* Trademark of Continental Oil Co.
SUMMARY
INTRODUCTION
THE "VIBROSEIS" MErHOD
Principles of the method
Field techniques
Variable parameters
CONTENTS
Comparison of various characteristics of "Vibroseis"
and shot-hole methods.
TEST AREAS AND ASSOCIATED PROBLEMS
EXPERIMENTAL PROCEDURE
RESULTS
-Built-up-area project
Hawkesbury Sandstone project
Volcanics project
Gambier Limestone project
Sand-cover project
Effect of changing particular parameters
CON,CLUSIONS
COMMENTS
J
Page No.
1
2
2
2
4
6
8
10
11
11
12
13
13
14
15
16
18
Plate 1.
Plate 2.
Plate 3.
Plate 4.
Plate 5.
Plate 6.
Plate 7.
Plate 8.
ILLUSTRATIONS "'
"Vibroseis" system.
Sketch map of S.E. Australia - location of "Vibroseis" projects.
Section - Built-up-area project.
Comparison sections ~Hawkesbury Sandstone project.
Comparison sections - Volcanics projecto
Comparison sections - Gambier Limestone.Project.
Comparison sections - Sand-cover project.
Parameter comparisons.
i
SUMMARY
The Commonwealth of Australia, Bureau of Mineral Resources
employed a contractor from May to October 1964 to demonstrate the
effectiveness of the "Vibroseis" method of seismic exploration in areas
4
where conventional shot—hole methods were impractical or where they had
previously experienced difficulties in obtaining good quality re lections.,
The test areas chosen were in the Sydney and Otway Basins and
included the built—up area of the City of Maitland; areas of outcrop of
the Hawkesbury Sandstone Formation; areas of volcanics cover; an area
of cavernous Gambier Limestone outcrops; and sand covered areas. ) These
areas have problems mainly of drilling and energy transmission.
The experimental procedure consisted of recording noise tests
and testing by varying"Vibroseis" parameters, one at a time, to 'arrive
at the best recording technique with the facilities available to the
contractor; production tests were done with the best recording technique
for each area. The parameters of the "Vibroseis" method and some
characteristics which contribute to its flexibility are discussed and
compared with the parameters and some characteristics of shot—hole
methods.4
The method proved successful in the built—up area where
reflections were obtained to 1.1 seconds. It was not always possible
to use the best recording technique found because of restrictions to the
positioning of vibrators and geophones. On Hawkesbury Sandstone outcrops
the method was successful in obtaining fair quality reflection information
to 2 seconds. Fair quality shallow reflections were obtained in the
volcanias, Gambter Ltmsztone and sand—covered areas, but difficulties
were found in obtaining continuous deep reflections in these area'S.
The tests demonstrated the flexibility of the "Vibrosei6"
method whereby the parameters could be rapidly changed for carrying
out a series of experiments to arrive at "optimum" techniques. Fair
quality reflections were obtained in the test areas, which were
previously designated as poor reflection areas.
1.
INTRODUCTION
The "Vibroseis" method of seismic exploration, which uses as
an energy source, a signal of relatively long duration with a smciOthly
varying frequency, was described by Crawford, Doty and Lee in "Geophysics"
'Vol XXV, No. 1. The method was introduced into Australia early in 1963
In Vol. 1, Part 2ca of the "Proceedings of the Second SyMposium",
O'Donnell referred to the use of vibrators as new sources of energy in
seismic exploration work. In the section on "Petroleum Exploration
Techniques and Methods" in the "Report of the Second Symposium"
recommendation was made suggesting the use of contractors to stimulate
new advances in the industry and to show the applicability of new methods
for adaptation to areas with unusual terrain and particular seismic
problems.
In accordance with its policies for accelerated oil search,
the Commonwealth of Australia Bureau of Mineral Resources employed a
contractor, from May to October 1964, to demonstrate the applicability
of the "Vibroseis" method by conducting experimental surveys in several
areas chosen because of their specific seismic problems. The test areas
selected lie within the Otway and Sydney Basins. The objective of the
surveys was to show if reasonable quality results could be achieved in
the problem areas by making use of the inherent flexibility of the;
"Vibroseis" method. A further objective litaa.to assess the costs of
Published by permission of Director, ThWe -ati of Mineral Resources Geologyand Geophysics.
2.
"Vibroseis" operations as compared with those of shot hole methods..
THE "VIBROSEIS" METHOD
Principles of 'the method
Plate 1 sholOthe "Vibroseis" system.
The method uses vibrators operating at the surface of the
ground as contolled energy sources, as an alternatWe to explosives in
shot holes. A signal of continuously varying frequencies, called a sweep,
is injected into the ground over a period of 7 seconds by the vibrators,
which are activated by servo—controlled hydraulic rams that follow a
signal transmitted by radio from the recording truck.
The maximum bandwidth of this signal is 10 c/s to 120 c/s.
However, generally, an input with a range of about two octaves is chosen.
The bandwidth is selected to contain frequencies that form the spectrum
of a normal reflection pulse; no energy is wasted by injecting frequencies
which it is known the earth will not efficiently transmit.
The signal picked up by the geophone is recorded on magnetic
tape. By a process of continuous correlation of this magnetic tape
against the recorded input signal, a record similar to a conventional
shot—hole record is obtained, i.e. the final result is the same as if •
all frequencies had been injected into the ground simultaneously.
Field techniques
• The field procedures are extremely flexible l mainly owing. to
the fact that no predetermined drilling programme is required. The
vibrators are extremely mobile but there are limits to their positioning
as they .require relatively flat surfaces for good vibrator—to—ground
3.
coupling. The recording techniques used depend on desired spatial noise
filtering penetration required, and degree of compositing.
In the standard in—line method, geophones are laid out in groups
at locations along the spreads as in normal shot—hole seismic operations
and vibrators operate at the conventional shot—point positions. In poor
reflection areas where a high effort involving large numbers of geophones
and vibrations is required, this may be tedious. However, in good
reflection areas where a low effort is required, this method gives the
highest production rates.
The transposed method was used more generally in the experi-
mental surveys. With this method the geophones are grouped in two nests,
one at either end of the spread, and the vibrators operate between the
nests at the positions normally occupied by the geophones in shot—hole
methods.'
Both these methods allow the use of large geophone and/or
vibration patterns for cancellation of noise and for the compositing of
large numbers of independent ray paths. However, the transposed method
is more felxible to use and a greater degree of compositing and speed of
operation can be more readily attained by using this method in poor
reflection areas. An additional advantage of this method is that
recordings made on each trace are made at different times from those made
on adjacent traces. This tends to increase the random nature of the
noise between final traces.
4.
The "Vibroseis" method is particularly well suited to the use of
a "rollalong' common depth point (C.D.P.) method using standard in—line
geophone spreads. Recordings at different offset distances, from the sarrie
subsurface point, are stacked. This increasssthe relative amplitudes of
signal to background noise and also produces cancellation of any multiple,
reflections recorded.
Variable Parameters
The flexibility of the "Vibroseis" method is due mainly to the
ease in which most parameters can be varied. The main parameters are as
follows:
Sweep frequency range Several sweep frequency ranges are
available and a choice is made to suit the particular area and
the problem being investigated.
No. of vibrations (sweeps). The results of numbers of sweeps can
be added because of the relatively uniform duplication of the
enei-from successive transmissions. The time independence of
recordings aids noise cancellation when sweeps are added. The
number of sweeps used is varied normally in steps from 5, 10, 20,
40 to 80 sweeps. The theoretical signal—to—background noise ratio
improves as the square root of the number of sweeps.
Vibrator thrust This can be varied, but the energy from-A-i-
vibrator must not exceed the elastic limits of the surface
formations. A maximum vibrator thrust of 10,000 lb is normally
applied and no damage is caused to surfaces on which the vibrators
operate.
5.
No. of vibrators The number can be varied since vibrators are
synchronised. Three are normally used on a party with another
vibrator available as a spare. The theoretical signal—to—background
noise ratio is improved proportionally to the number of vibrators
used.
Vibration patterns These may be transposed to occupy the positions
of geophone patterns in shot—hole methods. The length and width of
the patterns and spacing of vibration points within the patterns are
determined from the spatial noise filtering and random noise
cancellation requirements, the objectives of the survey, the number
of vibrato's used, and sweeps required.
No, of geolihcnes^2000 geophones were available on the experimental
party. For the transposed method large numbers of geophons(up to
800) are laid in individual groups.
Geo hone pattern^The characteristics of the patterns are determined
by the same principles that define the vibration patterns.
Offset distance "Vibroseis" work requires the vibrators to be
offset from the nearest geophones since recordings are made without
automatic volume control and with gains set for 100% magnetic tape
modulation on the highest amplitude event recorded; this may be
refracted energy (as in the first breaks), coherent noise, or a
reflection event. If no offset is used the relative amplitudes of
noise interference from the vibrator and later reflection events are
likely to exceed the dynamic range of the recording instruments (aboui
45 db.). A short offset distance is necessary (to avoid refraction
6.
paths) for obtaining shallow reflection information and a long offset
distance may be necessary to reduce the relative amplitudes of the
refracted or coherent noise energy, which decays with distance from
the source, and the later reflection events. Offset distances of 1,
2, and 3 spread lengths are normally used for systematic continuous
recording.
Electrical filters on playbacks^Normal electrical filtering can be
applied. to the correlated magnetic tapes. Filtering is varied to give
a final record with limited frequency pass band as is done with the
processing of shot—hole recordings. However the correlation process
normally also performs this function.
Automatic volume control (A.V.C.) on playback This is applied to the
correlated magnetic tapes. A.V.C. is varied to give uniform signal
level as with playbacks from shot —hole recordings.
Comparison of various characteristics of "Vibroseis" and shot—hole methods
The following table compares these two seismic exploration
methods.
7.
"Vibroseis",method
Sweep frequency range
Sweep
No0 of sweeps
Vibration patterns
No, of geophones ma4800 fortransposed recording
Geophone pattern
Amplifier record filters - set' at limitsof the sweep frequency range.
Cross correlation - sharp cut offfiltering dependent on sweep frequencyrange
Offset distance - min.geophone-to-vibrator offset is dictated byinstrument limitations and objectives.
Electrical playback filters - as forrecord filters.
A.V.C. on playback
Easy transposition of vibrationpoints and geophones
Rapid variation of vibration point andgeophone arrays between experiments.
Weathering information not generallyavailable.
No damage to ground surfaces
C.F. Explosion
No0 of shots and/or size of charge
Shot-hole patterns
Depth of shot
No0 of geophones max.approx.98 per trace
As for "Vibroseis" in-line recording
Amplifier record filters - set as wide aspossible at limits of seismic pulsespectrum
A.V.C. and/or programmed gain on record.
Offset distance - no limit for geophone -to-shot offsets but not normally required.
Electrical playback filters narrower limitsthan for recording.
A.V.C. - rate dependent on reflectionresolution.
Difficult transposition of shots andgeophones.
Slow variation of arrays betweenexperiments
Weathering information generally available
Damage to surfaces with drilling and shots
Shot-hole Method
8.
The "Vibroseis" method has clear advantages by:
i. l'imi ting the sweep frequency range to contain frequend~s-, which
contribute to reflection resolution.
-.2,. Jl4sing the cross-correlation process to provide a sharp cut-off filter
3. ..l#3ing the correlation process to discriminate against random noise.
4. the ability to employ high multiplicity of vibration points
and geophones for relatively low cost.
The "Vibroseis" method has some disadvantages by:
1. having no counterpart to varying depth of shot
2. requiring the use of an offset distance to record the signal
within the dynamic range of the "Vibroseis" system (45 d.b.);
in shot-hole methods A.V.C. or programmed gain on record is used
for this purpose. For the "Vibroseis" recordings without A.V.C.
it is necessary to ensure that the highest amplitude Signal does
not saturate the tape and cause distortion since this would
affect other signals that it overlaps in the correlation:process.
TEST AREAS & ASSOCIATED PROBLEMS
The project areas are shown in Plate 2. The areas, with particular
problems sele~ted to test the flexibility of the "Vibroseis" method, were as
follows:
Built-up-area project. Fair quality seismic information had 'been
recorded, using shot-hole methods on the east and west outskitts of
the city of Maitland. It was considered that a test of "Vibroseis"
recordings through this built-up area would illustrate the applicability
9.
of the method in an area where shot—hole methods could not be ilsed.
#Hawkesbury Sandstone project.^The hard, somewhat quartzitic,
Triassic Hawkesbury Sandstone, which covers large areaiof the Sydney
Basin, transmits seismic energy poorly.
A
Drilling is difficult and expensive. Access is poor and seismic
traverse generally follow roads that run along the rugged Hawkesbury
Sandstone 'ridges. Power lines also follow these roads and give
troublesome 50 c/s. interference. The weathering on the highly eroded
surface is extremely variable.
Volcanics project.^Extensive volcanic activity during the Quiternary
period partly covered the eastern part of the Otway Basin with'basalt,
tuff, and other volcanic residue. This cover, which varies not only
in its composition but also in its thickness and depth, consti .iutes
an energy transmission problem for seismic exploration. Otherproblems
associated with the voicanics are an erratic weathering tone; probable
variations' in velocity distribution in the section due tO basalt layers;
general low average velocities in the section, which result in large
dynamic corrections and limits the lengths of geophone and source
patterns that can be used; and in some places hard drilling, Which
often makes Shot—hole drilling difficult.
Gambier Limestone project. A large part of the western part Of the
Otway Basin is covered by the cavernous Tertiary Gambier Limestone,
which is up to 500 ft thick in some areas. This limestone constitutes
1 0.
an energy transmission problem as well as having associated drilling
problems with circulation losses, and often slow drilling rates due
to hard flintstone bands in the formation.
Sand-cover project Other areas in the western part of the 0tWay
Basin are covered by a sand sheet or sand dunes. These areas Of
loose sand' are troublesome for shot-hole seismic work because of
absorption of the seismic energy and difficult drilling.
EXPERIMENTAL PROCEDURE
The selection of areas in which to test the applicability of the
method was based on knowledge of surface geology, information from wells
drilled, and previous geophysical surveys including aeromagnetic, gravity,
and seismic. The results of previous seismic experimental work wee
studied.
Noise tests were initially recorded as a guide to further experi-
mentation. These were recorded using an in-line method with ohe
-, -- vihrator, a 10 - 120 c/s sweep and a normal recording distance out to-
approx. 4000 ft with geophonesat 20t 5 intervals. The number Of sweeps
was increased with distance from the source. The results were
illustrated in graphs of Time v Distance. Amplitude v Wave NuMber
and Frequency v Wave Number.
InillartEmling parameters were selected from previous knowledge of
recording conditions and from the interpretation of the noise 'tests
for choosing offset distance, spatial filtering requirements, and sweep
spectrum.
1 1,
ILTerimentation proceeded with recordings made generally over several
spreads with the initial technique selected. Parameters Were then
changed.one at a time in order to assess the effectiveness of the-^-^-^-
changes. Record^
were generally repeated using the different
techniques in order to assess revised techniques over more than one
spread, The technique found to be best in a particular area was in
most cases tried in another area with a similar problem. Up to :- six
weeks was spent on each problem.
RESULTS
Parts only of some cross-sections recorded along the .experimental
traverses are included as illustrations (Plates 3-7) of the results of the
"Vibroseis" tests. The recording techniques are noted in the plates.
Built -up -ArEl_moi2It
• After initial testing using standard in-line recording with
•vibrator• force-levels at 25% maximum, a high-effort transposed-recording
technique was adopted for the test. Vibrators with maximum force-level
operated on -the bitumen roadways" and geophones were laid in nests as
far from the roadways and power lines as possible in order to. reduce
extraneous noise due to traffic and 50 c/s interference. Traffic Was very
heavy.
• A. high-amplitude l high velocity, near surface refractionwave
masked the reflections down to 005 second and limited the recording level
for later reflection events, which are evident in Plate 3 at times of approx.
0.7 and 1.1 seconds.
12.
\0
The me~hod has been demonstrated to operate successfully in a
highly populated, built-up area without interfering with traffic. However,
it may not be possible to attain an optimum recording technique in all
built-up areas owing mainly to limitations on the offset distance and
pat terri': lengths of vibrations and geophones that can be used.
Hawkesbury Sands tone pro,i ec t
The results of a noise test indicated a high-velocity, high
amplitude, first-break interference event. Good quality shailow
reflections down to 1.0 second were obtained using 600-feet-iong vibrator
and geophone patterns with a minimum one-spread offset and a 10-40 cc/s
sweep. Deeper reflections do,m to 2 seconds were obtained, wi th r~sul ting
deterioration of the quality of the shallow information, by increa~ing
the pattern lengths to 1000 ft so that spatial filtering effects r~duced
the amplitudes of the first-break event relative to the reflectiontevents.
It was necessary to increase the number of sweeps and:'to use a: minimum two
spread offset. Comparisons with these recording techniques are shbwn in
Plate 4.
The use of a 10-40 cis sweep in "Vibroseis" recordings. on
Hawkesbury Sandstone cover is considered to be a major factor in the
attainment of good quality reflections. I
It eliminates the- generation. of
high frequency noise and the correlation process eliminates 50 cis high
line pick-up. The test indicates that "Vibroseis" recording techniques
can be successfully applied on the hard Hawkesbury Sandstone Formation.
1 3.
Volcanics Project
Transposed recordings were made along the complete traverses and
parts of the traverses were re—recorded using in—line and C.D,P. methods.
Experimentation showed that the technique yielding the best result 6 varied
along the traverse; this was probably due to extreme variations in the
surface and subsurface conditions. Fair quality reflections were 4
recorded over most of the traverse using transposed methods. Thiswas
-considered to be the result of effective compositing over 12,001Dspparate
ray paths for each trace. A comparison of ten—fold C.D.P. recording and
transposed recording is shown in Plate 5. The slower Ca.P. recording,
one mile per day compared with Imost two miles per day for transposed
recording, was successful in improving the reflection quality. The
improvement wais probably due to the vertical stacking.
Gambier Limestone project
The noise tests indicated high—amplitude interference
.events - with velocities of 2500, 3300, and 7200 ft/ s. Fair quality
reflection information was recorded at 0.8 to 1.0 second on the initial
experimental Work with a low—effort transposed method; no deep
reflections were obtained and shallower poor quality events were obscured
by the noise interference. After considerable experimentation, a •
1 4.
transposed recording technique was developed using a minimum three—
spread offset, 20 sweer per trace, and a diamond shaped geophone
pattern. The effective pattern length of vibrator and geophcine
patterns was 200 ft.^All efforts made with transposed techniques.
were unsuccessful in substantially reducing the amplitude of the
noise interference; however, some success was achieved with ten-
fold C.D.P. recording as shown in Plate 6. The C.D.P. section
shows better continuity than the transposed section but the quality
of deeper reflection events was not improved, this was probably
due to the reduction of ray paths composited with the particular
C.D.P. technique used.
It would appear that the quality of "Vibroseis" recordina
is limited in this area by the high—amplitude interference waves. This
noise problem would probably be less acute for shot—hole methods aiere
the charges can be placed below the weathering layer.
Sand—cover project
The section shown for Traverse 1 in Plate 7 was recorded in an
area of fair quality reflections off the sand cover. Apart from a noise
• test, only limited experimenta.tion vias carried out along Traverse 2 on the ~.
sand cover to ,the north of Traverse 10 The lengths of geophone an~ ,
~ ~
vibrator patterns represented a compromise for obtaining both shallow and .
deep reflectio'ns down to about 2 secpnds.
The 'test showed that fair quality reflection information: could
be readily obtained on the sand cover using "Vibroseis" techniques'by
increasing the number of sweeps and the offset distance (Plate' 7).'
Effect of changing particular parameters
Records shown in Plate 8 have been selected to demonstrate the
effects of changing particular recording parameters.
The transposed in-line compartson shows two recordings made on
the same profile in approximately the same recording time. The tr~nsposed
recording .has a higher signal-to-background-noise ratio maintY because of
increase -in 'the number of ray paths composi-ted per trace.
The sweep frequency comparison indicates that the 10-40 ~/s : .
sweep is superior to the 20-5Q cis sweep for recording on Hawkesbury
Sandstone. Reflection events are discernible to 2.5 seconds on the 10-40
cis sweep record compared with 0 .. 9 second on the 20-57 cis sweep record.
The number of sweeps comparison shows that although shaliow '
reflections can be recorded to 0.7 second with 5 sweeps per trace, i effective
" penetration to 2.5 seconds can be obtained with 10 sweeps per trace.
The offset comparison show high-amplitude good quality shallo'w
events to 0.8 second and poor quality events deeper, with a one-spread
16.
offset. The shallow events deteriorate, whereas the deeper events are
enhanced using the three-spread offset.
The pattern length comparison illustrates the use of 400-,ft ..7long
vibrator and geophone patterns to suppress the high-amplitude first break
arrivals. The recording tape was 100% modulated on these arrivals when
200-ft-long patterns were used and the later poorer quality reflection
events, are of too low level to be clearly seen.
CONCLUSIONS
The flexibility of the "Vibrosies" method was illustrated by the
recording of fair quality seismic information in previously designated
poor pr no-reflection areas with unusual terrain.
Results were obtained in the built-up area with no resul'ting
damage to roadways, water mains, houses, etc. However, the use of an
optimum recording technique was not always possible owing to limitations
imposed by the positions of houses, road intersections, water main,
railway lines, etc.
The test on the Hawkesbury Sandstone indicated that the 6Vibroseis"
method was Capable of solving this areals problems; this was manly due to
the selection of a particular controlled sweep. The best methods
obtaining shallow and deep reflections differed.
The best recording technique was found to vary along the'Volcanics
traverses. Variations of technique were readily accomplished by "Vibroseis"
methods since no predetermined extensive drilling programme was required.
17.
C.D.P. recording techniques were used to improve the results in areas where
poor quality results were obtained using transposed techniques; the
"Vibroseis" is very adaptable to the use of C.D.P. methods. The high
multiplicity of ray paths per trace inherent with "Vibroseis" recording
techniques probably contributed largely to the success of the methods in
this area.
High—energy noise, generated in the surface layers in the
, Gambier. LimPstnne area by the "Vibroseis" methodT limited the effeCtive-
ness of the method for obtaining good quality deep reflections. This
noise was attenuated by C.D.P. recording, which improved the quality of
the seismic data.
Penetration for recording deep reflections was achieved in
the sand—cover area. However, a compromise of pattern length and Offset
distance was necessary for recording shallow and deep reflections.
The quality of results was generally not adversely affecled by
the assumption of uniform weathering layer thicknesses and velocities in
the problem areas. This was probably due to the averaging of the effects
of weathering Variations by ground mixing and compositing. Some
inconvenience was experienced in the delay necessary for 'correlation of
the field,:ecordings whereby the results of the experimental work could
not be examined until some hours later; for production recording these
delays are not important.
18.
COMMENTS
The ,"Vibroseis" method, by virtue of its flexibility for
rapidly carrying out a range of experiments, is able to approach an
"optimum" technique much more quickly than shot-hole methods. Shoe-
hole methods, although they may employ different parameters from tflose
of the "Vibroseis" method, are able to take advantage of experience
gained when following a "Vibroseis" survey and may thus produce better
records than a survey preceding the "Vibroseis". This has, in fact,
proved to be the case in a current survey covering the Volcanics arid
Gambier Limestone areas mentioned above.
Since the "Vibroseis" test survey, further "Vibroseis" wrirk
has been carried out on Hawkesbury Sandstone in a built-up area on the
outskirts of Sydney. Techniques adopted for the built-up area and'
Hawkesbury Sandstone projects in the test survey were combined for'
this survey. Other surveys have been carried out in the Gippsland
Basin where C.D.P. methods were used to tackle a problem of multiple
reflectionsl and in the Officer Basin where cartage of explosives,
drilling water, etc. are problems, associated with the remoteness of
the area.
'., I '
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PLATE
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RECORDING UNIT
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• RECORDING METHODSWEEP FREQUENCYNo. OF SWEEPSOFFSET DISTANCEVIBRATOR PATTERN LENGTHGEOPHONE PAT TE RN(360 Geo)
2.0
HORIZONTAL SCALE
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RECORDING ME1 HODSWEEP FREOUENCYNo. OF SWEEPSOFFSET DISTANCEVIBRATOR PATTERN LENGTHGEOPHONE PATTERN
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TRAVERSE 2 TRANSPOSED
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RECORDING METHODSWEEP FREQUENCYNo. OF SWEEPSOFFSET DISTANCEVIBRATOR PATTERN LENGTHGEOPHONE PATTERN
TRAVERSE I
COMPARISON SECTIONS- SAND COVER PROJECTTRAVERSE 2
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