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TRANSCRIPT
G. Willoughby, N. Macdonald, A. Darling and T. Hiller
February 2012 1
Applying Novel Sub-Bottom Boomer Technology to the
Submerged Wellington Fault.
Presentation 2-3, Shallow Survey 2012, Wellington, New Zealand.
2
Presentation Outline
February 2012
• S-Boom Background
• Technology Innovations
• Survey Methodology
• Results
• Conclusions
• Applications
3
Introduction
February 2012
• In late 2010 Applied Acoustics released a novel 3-plate boomer sub-bottom profiling system, the S-Boom.
• On 6 - 9 December 2010 this system was used to survey the Shallow Survey 2012 Common Data Set area.
• Objectives:
– Test the performance of the new technology compared with previous surveys and older systems.
– Provide new images of the Wellington Fault.
4
S-Boom development
February 2012
• In March 2010 survey company customers of Applied Acoustics identified a gap in their survey capabilities.
• The requirements were mainly driven by the rapidly growing offshore renewable energy industry, especially wind turbine installations.
• System requirements:
– The high resolution of a boomer system (~25cm)
– Deeper penetration than current boomer systems (100m)
– Portable for deployment on vessels of opportunity
– Flexible for operation in deep and shallow water
5
Development Timeline:
February 2012
Applied Acoustics has a 20-year history of rapidly delivering highly technical acoustic solutions to the offshore industries. This helped drive the rapid development of the S-Boom:
• March 2010 – requirements identified
• Technology development based on existing experience with successful SBP products and high energy power supplies.
• September 2010 - first system trials of S-Boom
• November 2010 - first S-Boom delivery
• December 2010 - Wellington Survey
• 2011/2012 uptake by major survey companies including repeat orders
6
Key S-Boom Innovations
February 2012
• 3-plate surface-tow boomer system: allowing higher source levels, with beamforming to improve source directivity.
• Single power source: High recharge compact PSU providing highly synchronised and repeatable pulses to the three plates.
• Separate supply to each plate: via HV cable with 3 pairs.
7
Beampattern Video
February 2012
8
S-Boom Beamforming
February 2012
Single plate source:
±30 degree beam S-Boom 3-plate source: 3x AA202 transducers
± 30 degree across-track, ±15 degree fore-aft
Directivity Improvement of 6dB over single boomer plate
Source Level: 223 dB re 1 μPa @ 1m
9
CSP-S 1250 Energy Source
February 2012
• Used experience from developing high power 6kJ and 12kJ sparker systems
• 3200 J/s peak recharge rate
• 3 pulse per second at 1000J/pulse
• Single source single phase supply
• 12U transit case
• Adjustable for higher rep rates at lower powers for faster survey
Supplies the 3 plates separately via 3-pair HV cable allowing better synchronisation and control (1, 2, or 3-plate operation).
10
CSP-S 1250 Pulse Shape
February 2012
• 300-500µs pulse giving 25cm resolution
• Power in the 100Hz-5kHz band with peak at ~1kHz
• Clean and repeatable pulse shape
• Highly synchronised between the 3 plates (<2microseconds)
11
Cat-300 Surface Tow Mount
February 2012
New Cat-300 catamaran towbody: improved tow performance • Pitch and yaw stability improvements • Up to sea state 4 – 5 depending on vessel safe working practices.
12
The Wellington Fault
February 2012
• An active fault on a tectonic plate boundary
• A major topographic feature in the city
• Submerged section runs along northwest edge of Wellington Harbour, trending northeast past Kaiwharawhara
• Previously surveyed in 1980’s and 1990’s (Lewis and Mitchell, 1986)
• More details in NIWA’s presentation.
Path of Wellington Fault looking southwest
towards the ferry terminal (photo: D.L. Homer).
13
Wellington Harbour Line Plan
February 2012
• 4 Days data collection 6-9 Dec 2011
• 35 lines collected around the harbour
• Mainly over the Wellington Fault (survey tracks shown as red)
• Other lines collected shown in white.
• Also collected S-Boom, single plate and squid comparison lines (lines 31,32,33).
• 12 selected lines are available as CODA .COD files in the Common Data Set.
Profiles from Lines 3, 13, 31, 32 and 33 above are
shown in this presentation and the accompanying
paper.
14
NIWA’s Survey Vessel: the RV Ikatere
February 2012
Photo: NIWA
RV Ikatere: 13.9m Aluminium catamaran
powered by twin Hamilton jet units.
15
Equipment Deployed
February 2012
Equipment Model
SBP source: S-Boom system: 3 x AA202 Boomer Plates CAT 300 Surface tow catamaran towbody HV3000 Power Cable
Power Source: Model CSP-S 1250 Seismic Power Supply
Hydrophone: Model AH150/20
Data Collection: Coda DA2000
Other Equipment: Model CSP-D 2400 Seismic Power Supply
Squid 500 Sound Source
Geometrics Geo-Eel 8 Channel Streamer Hydrophone
Geometrics Geode Data logger
16
Equipment Layout:
February 2012
• Cat-300 with S-Boom source towed to port
• Receive array to starboard
17
Equipment on the vessel
February 2012
• PSU and data collection installed in vessel cabin. • S-Boom data acquisition and on-line QC: CODA DA2000 system. • All data processing for this presentation was in CODA software.
18 February 2012
Survey results 1 : Line 3 – the Wellington Fault
19
Survey results 1 – the Wellington Fault
February 2012fa
Profile from line 3 showing 80ms, 200m long line over the Wellington Fault (arrowed). Line runs northwest towards the shore. Geophysical interpretation is provided in NIWA’s presentation.
20 February 2012
Survey results 2 : Line 13 – Somes Island
February 2012 21
Survey results 2 – Somes Island
Profile from line 13 showing 200ms, 800m line to the south of Somes Island, showing deeper penetration in parts of the survey. Line runs west-east. Data processed in CODA.
22 February 2012
Survey results 3 – Comparison Lines Lines 31, 32 and 33
23
Comparison with Single Plate Data
February 2012
Line 31: S-Boom Line 32: Single-plate boomer
• First 80ms of ~1000m long lines heading inshore (east-west)
• Some blanking seen in both traces, similar to previous surveys
• No difference in resolution of shallow layers
• Better resolution of deeper horizons with S-Boom
• Some improvement in horizons near blanked regions with S-Boom
24
Comparison with Squid 500 Data
February 2012
Line 31: S-Boom Line 33: Squid 500
• S-Boom gives similar penetration in this environment
• S-Boom shows better resolution of fine and shallow horizons
25
Comments on the Seismic Environment
February 2012
• The blanking layers seen in previous surveys (Lewis and Mitchell 1986) was also seen with all 3 systems here.
• Attributed to a gas or fluid masking layer.
• Present in sections of most survey lines. A difficult acoustic environment for sub-bottom work.
• There was possibly some evidence of improved data from the S-Boom around the masked areas.
S-Boom (left) vs single plate data over
a blanking patch
26
North Sea Trials Results
February 2012
S-Boom data from a more benign acoustic environment: The North Sea off Great Yarmouth, UK, showing more than 200ms penetration in a sand and limestone.
250ms →
27
Technology Conclusions: Capabilities
February 2012
• The 3-plate arrangement provides improved source levels giving improved penetration compared with single plate source.
• The high energy source gave reliable and repeatable pulse shapes.
• Synchronised pulses give similar resolution to single plate boomer.
• Source Level: 223 dB re 1 μPa @ 1m
• Repeat rate: 3 pulses per second at 1000 J/pulse
• Penetration: >200m
• Resolution: 25cm
• Water depths: 2m – 1000m
• System is easily transported and deployed on vessels of opportunity.
28
Conclusions
February 2012
• The S-Boom penetration and resolution in Wellington Harbour and the North Sea match with design expectations.
• 3-plate arrangement provided improved source levels giving improved penetration compared with a single plate source.
• The strong synchronisation of the drive pulses resulted in a similar vertical resolution to a single plate boomer.
• Data over the fault rupture zone shows the S-Boom system can improve geohazard investigations.
29
Applications of the S-Boom Technology
February 2012
S-Boom is the only commercial SBP system with 3 plates driven by a single synchronised source.
It is anticipated that the S-Boom technology will find applications in:
• Renewable energy installations, especially wind farms in North Sea and Northern Europe
• Geohazard surveys (faults and slope stability)
• Offshore construction
• Cable route surveys
• General geophysical site surveys
30
Acknowledgements
February 2012
The authors would like to acknowledge the assistance and contribution of NIWA staff during the duration of the trials, the crew and officers of the NIWA Survey Vessel Ikatere, and CODA for use of the DA2000 acquisition system and processing software.
September 2010 31
• Tel: +44 1493 440355
• Fax: + 44 1493 440720
• Mob: +44 7799 773139
Gavin Willoughby
Tel: +44 1493 440355
Fax: +44 1493 440720
Mob: +44 7799 773139