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Marine 2D Reflection Seismic
Acquisition
Lecture Notes 514 March 2014
EquipmentSources, Receivers, Recording Instruments
Marine LayoutSource/Receiver Arrays, Positioning
Modern Marine 2D SeismicReflection Profiling Process
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Equipment
Sources, Receivers, Recording Instruments
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Air gun
An air gun is used for marine reflection and refraction surveys. It consists of one
or more pneumatic chambers that are pressurized with compressed air at
pressures from 14 to 21 MPa (2,000 to 3,000 psi). The air gun array is submerged
below the water surface, and is towed behind a ship. When the air gun is fired, a
solenoid is triggered, which releases air into a fire chamber which in turn causes a
piston to move, thereby allowing the air to escape the main chamber and to
produce a pulse of acoustic energy. Air gun arrays are built up of up to 48
ndividual air guns with different size chambers, the aim being to create the
optimum initial shock wave with minimum reverberation of the bubble after the first
shot.
Gun arrays can be fired in flip-flop mode; typically this would be 48 guns per
source, which would be selected and fired alternately. Large chambers (i.e.,
greater than 1.15 L or 70 cu in) tend to give low frequency signals, and the small
chambers (less than 70 cubic inches) give higher frequency signals. The air gun is
made from the highest grades of corrosion resistant stainless steel.
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Airgun
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Airgun Sub-Array Configuration
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Airgun
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Airgun
Airgun Compressor
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Airgun
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Airgun
Sercel G. Gun II Airgun
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Airgun Sub-Array Configuration
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Airgun Source Signature with Source Ghost
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Airgun Source Signature
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Receivers- Hydrophones
A hydrophone converts mechanical energy into electrical
energy. The conversion of energy can be based on the
property of materials such as “piezo-electricity”.
Piezo-electricity is the electricity or electrical polarity resulting
from the application of mechanical pressure on a dielectriccrystal.
The application of mechanical stress produces in certain
dielectric crystals and electric polarization (electrical dipole
moment per cubic centimeter) which is proportional to this
stress, and finally if the crystal is isolated, this polarizationproduces a voltage across the crystal.
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Hydrophone
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Hydrophone
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Hydrophone
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Hydro-Geophone
We will not discuss much on this!
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Sercel Seal Recording
Navigation Equip
Recording Equipment
(Older System)
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Sercel SeaPro Real-time SP Gathers
(Older System)
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Sercel SeaPro Real-time CDP Gathers
(Older System)
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Cable ~4500m 360 channel at 12.25m
Streamers can be oil filled, foam filled
or solid.
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Frequency spectra comparison of conventionalhydrophone-only streamer (black) and GeoStreamer (red)
data using a log frequency scale.
Hydrophone-Streamer
http://www.google.com/url?sa=i&rct=j&q=&esrc=s&frm=1&source=images&cd=&cad=rja&uact=8&docid=dtsjrb9Lf3qURM&tbnid=Kh2xMNgqRs8EyM:&ved=0CAYQjRw&url=http://www.pgs.com/en/Geophysical-Services/Seismic-Techniques/Sub-Salt/&ei=JbMfU_mUMsTYrQefo4H4AQ&bvm=bv.62788935,d.bmk&psig=AFQjCNGjn0w3i9hrFhAyWL6BtxBykAd0DQ&ust=1394671080054916
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Marine LayoutSource/Receiver Arrays, Positioning
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Source Array
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Sercel Streamer/Receiver Array
Hydrophone Spacing per SSAS
and Xmax per No. of SSAS
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Sercel Streamer Components
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Sercel Streamer Components
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Acoustic Positioning and Streamer Control
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ECOS (Integrated navigation system)
Depth controllers handling (depth, heading)
Vessel navigation (GPS / DGPS)
Tail buoy navigation (RGPS)
Layout visualization
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Streamer Control Unit
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Streamer Control Unit
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Vessel
Streamer
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2D Marine Seismic Acquisition
Process
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2D Seismic Streamer Array
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Streamer
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Streamer “Birds” for Depth Control
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Streamer depth controller
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Tail Buoy - GPS/Radar Transponder
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Streamer Maintenance and Repair Boat
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Streamer Maintenance and Repair Boat
Getting on Streamer at front end.
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Barnacles on Cable - Must Be Cleaned
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Modern Marine 2D Seismic
Reflection Profiling Process
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Recording Process
http://localhost/var/www/apps/conversion/tmp/scratch_2//upload.wikimedia.org/wikipedia/commons/e/ee/Source_Receivers_single_fold-3_Fold.jpghttp://localhost/var/www/apps/conversion/tmp/scratch_2//upload.wikimedia.org/wikipedia/commons/1/1f/Single_End_Spread_&_Split_Stread.jpg
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L= Marine record with hard water bottom and refraction A. Gather has
primarily linear guided waves at B, C and D. Reflection at E is weak.
R= Wave packet A is mostly guided waves. Direct arrival at B. Reflectionwith reverberation at E with long period multiples at M1-M4.
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L= Marine record with cable geometry change noted at first break A.
Dispersive energy at B. C and D have different move-out. C is multiple.
R= Marine airgun record with high velocity reflections A and B having littlemove-out. Guided wave at C result from strong water bottom refractor C.
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