5 UI S1 Marine 2D Seismic Acq Lecture Notes 5 14 Mar2014.pdf

8/9/2019 5 UI S1 Marine 2D Seismic Acq Lecture Notes 5 14 Mar2014.pdf

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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.

15 16


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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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5 UI S1 Marine 2D Seismic Acq Lecture Notes 5 14 Mar2014.pdf