Alpha Seismic Compressors – Offshore rentals. Air source ...
Offshore Seismic Exploration Presented to: BC Seafood ... · Offshore Seismic Exploration Presented...
Transcript of Offshore Seismic Exploration Presented to: BC Seafood ... · Offshore Seismic Exploration Presented...
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Offshore Seismic ExplorationPresented to:
BC Seafood Alliance February 17, 2004
Doug BogstieMarketing ManagerWesternGeco
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GECO DIAMOND
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Marine Acquisition System
Sea bed
Boat
Cable with hydrophones
Sea Surface
Source
Sedimentary Layers
Incidentwaves Reflected
waves
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MARINE ACQUISITION
Sea bottom
Subsurface interface
Common Shot gather
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MARINE ACQUISITION
Sea bottom
Subsurface interface
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MARINE ACQUISITION
Common Mid Point (CMP) gather
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COMMON MID POINT GATHER
Common Mid Point (CMP) gather
“Primary” reflections
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COMMON SHOT GATHER
1.0
2.0
3.0
4.0
5.0
6.0
7.0
8.0
Two-
Way
Tim
e, s
econ
dsOffset
Direct Arrival
Sea bottom reflection
Swell noise
Sea bottom multiple
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2D vs 3D Marine Seismic
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Aerial View of Seismic Vessel in Operation
~ 100 m ~ 20m x 20m~ 200 m
~ 600 m
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VESSEL “FOOTPRINT” CONCEPT
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Constituents of Seismic Data
SchlumbergerGeco-PraklaSmall Throws
Thin Beds
Steep DipsLateral Variation
Fresnel Zone
Surface Waves
Interbed Multiples
Losses
Surface Ghosts
Receiver Array
Scattering
Reverberations
Source Array
uneven seabed
overburden
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STANDARD SEISMIC DATA 3D PROCESSING
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Dual source
300% door20 m 2200 litre float
10.5 m Tow Point to CoS9m
12 m
100 m190 m185 m
185 m 10.5 m Tow Point to CoS190 m100 m
250 m 12 m
9m
20 m300% door
2200 litre float
120 m
6 m
6 m6 m
6 m
6 m
6 m
250 m
.
Vessel
= CoS
= SPU
Sub-array
Array
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3397 Airgun Array Output(6 Meter Tow Depth)
0 100 200 300 400 500Time (msec)
55
33
11
-11
-33
-55
Aco
ustic
Pre
ssur
eB
ar-M
eter
s
Tow Depth = 6 mPeak Amp = 50.9 Bar-m
Am
plitu
de S
pect
rum
dB re
1µP
a/H
z at
1m198.8
186.8
174.8
162.8
150.8
210.8
Frequency (hz)0 50 100 150 200
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Peak to Peak pressure in the horizontal plane at 10m depth, far field.
10 m
500 m radius
Center of source
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Peak to Peak pressure in the vertical plane
500 m radius
Center of source
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Nessie 4 Streamer•High vessel efficiency through minimal technical down-time•High strength for increased streamer lengths•Contains foam and ISOPAR M
Cross-section cartoon of streamer:
Kevlar stress members
Hydrophones and wires
Polyurethane jacket
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Monowing Towing Technology
0.0020.0040.0060.0080.00
100.00120.00140.00
0 5 10 15
Std. Deflectors Monow ings.
Monowings
Total Drag (t) for N Streamers (6000 m, ∆ y = 100 m)
Conventional Towing
Number of streamers
Typical Pulling Limitation
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3D Seismic Surveys: Shot Zamboni or Race Track Style
At Least As Long As The Streamer:In The GoM, At Least 6 Km.
Turns Take At Least 2.5 Hours
Area To Be Surveyed
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Horizontal & vertical streamer steering
Q Fin
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Streamer Steering
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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Acoustic Testing from Mackenzie River 2002 Project
• The Objectives
• Record seismic source levels• Record ambient and back
ground noise• Record sound attenuation
over distance
Graphic
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Positioning of the cages
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Caged Fish Assessment Result
• Test located in backwaters at Norman Wells• Sound level was 220 db at 2 m from airguns• 4 fish out of 196 died (no large fish mortalities)• Examinations show that these fish did not die from exposure
to airguns, but died as a result of handling induced stress.
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Presentation Outline
•Seismic Acquisition Fundamentals
•Acquisition Footprint
•Seismic Data
•Marine Seismic Source
•Streamers
•Mackenzie River 2002 Test
•Mitigation Measures
•Questions
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WesternGeco Mitigation Measures
•Ramped Start-up•Source Shutdown•Documentation & Reporting•Trained Mammal Observers•Passive Acoustic Monitoring
Bottlenose Whales
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Questions
MV Geco SnapperBeaufort Sea 2001-2002