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Managing Seismic Interference -Snorre 4D case studyR. Laurain*, S. Eidsvig*, D. Fischer*, A. Smith*** Statoil, ** WesternGeco
Classification: Internal 2012-09-03
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Content
• Introduction
• Interference sources
• Interference QC and removal
• Interference examples
• Statistics
• Conclusions
Classification: Internal 2012-09-032
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Introduction
• 2011 experience
− Encouraging experience in PL303 (Lupin)
− Decision to continue to assess SI in 2012
• In 2012, most activity in Tampen area
− Seismic and production related
− Fishing activity
• Three surveys in Tampen area were operated by Statoil
− Good control over time sharing
− Cooperation with other players in the area when possible
Classification: Internal 2012-09-033
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Introduction
• Plan for seismic interference handling
− Interference QC plan made in co-operation with WesternGeco who did both acquisition and processing
− WesternGeco onboard processing and onshore support
− Statoil geophysicists ready to perform QC with short turn around
− No line should be interrupted due to SI. Acceptance stage after processing
• Snorre 4D
− OBC survey less sensitive to SI (Kvitebjørn, Gullfaks)
− Snorre 4D was most critical to be able to finish in time
− High quality 4D acquisition
− Large area, long survey duration and possible conflict with fishery
Classification: Internal 2012-09-034
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Interference sources
• Installation activity (e.g. pile driving, drilling, …)
• Seismic activity
− Statoil: Snorre 4D, Gullfaks OBS and Kvitebjørn OBS
− TGS MC 3D
− PGS 3D
− Others?
• Fishing activity
− Mackerel fishing started end July
Classification: Internal 2012-09-035
20 km
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Interference removal
• Final 4D processing sequence was run up to interference removal Seismic
− Navigation/ seismic merge; 4ms resampling
− Deterministic zerophase designature; CMS deconvolution
− Swell noise attenuation ( 3 passes ); SINE – seismic interference elimination
• Interference Noise Elimination (SINE)
− A multidomain 3D spatial filter was designed in the τ-ρ domain to scan for SI noise on consecutive shots along the line, based on amplitude and frequency attributes. SI noise is separated and transformed back to the x-t domain where it is subtracted from the original data set. Process has been applied to all acquired lines.
− SEG San Antonio 2011 Annual Meeting / Margaret C. Yu, WesternGeco
Classification: Internal 2012-09-036
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Interference QC
• Interference was QCed onboard with the following product for each sequence:
− Every 3rd trace in every shot displayed before/after SI removal and difference
− Brute stack before/after SI removal and difference
− RMS SVT display of each trace for each sequence
− SOL/EOL Noise
− Background noise each streamer, each trace
− Near trace display
− Full 4D global QC: 4D difference cubes + 4D attributes maps – updated on weekly basis
• Onshore
− Initial SI testing, onboard testing support & final parameters approval
Classification: Internal 2012-09-037
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Interference from other than seismic sources
Classification: Internal 2012-09-038
SEQ. 17
SEQ. 18
Input After interference removal Difference
Weak high frequentnoise
Noise bursts
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Shots Before SINE: Seq 182 ssl03
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Shots After SINE: Seq 182 ssl03
Residual SI left
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Shots Difference: Seq 182 ssl03
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Stack Before SINE: Seq 182 ssl03
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Stack After SINE: Seq 182 ssl03
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Stack Difference: Seq 182 ssl03
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Seismic interference Seq 110Gullfaks OBS
Classification: Internal 2012-09-0315
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Seismic interference from ahead Seq 195
Classification: Internal 2012-09-0316
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Seismic interference from ahead Seq. 201Kvitebjørn OBS
Classification: Internal 2012-09-0317
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Statistics
• 307 sequences shot, 69 reshoot (22 %)
• 49 sequences identified as affected by seismicinterference
− Statoil threshold is 18 microbar− 39 SOL/EOL noise over 25 microbar − 5 out of 49 sequences reshot because of SI− 15 to 26 out of 49 sequences would have been
reshot with conventional QC
• Survey completed 14 days ahead of schedule and below budget
Classification: Internal 2012-09-0318
Repeatibility Swell SI Steering Source Form. Inj. Nav TOTAL# sequences 37 18 5 3 3 2 1 69
% of 307 sequences 12,1 5,9 1,6 1 1 0,7 0,3 22,6
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Conclusions
• Snorre 4D acquisition shows that large part of SI noise can be handled in processing
• Onboard processing capability made it possible to quickly and reliabily perform acceptance QC
• Close cooperation between asset, processing, acquisition, client rep, onshore processing center was essential for the success of the operation
Classification: Internal 2012-09-0319
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The way forward? (1)
• Great time saving can be achieve if all players (contractors, oil companies) cooperate
− Try as early as possible to clarify the seismic activity in the area
− Optimize the shooting patterns and identify the most critical situations related to SI
− Share knowledge of SI handling with all staff involved (client rep, onboard processing, QC geophysicists)
− Common Seismic Interference removal tool in the industry?
Classification: Internal 2012-09-0320
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The way forward? (2)
• Soft start
− Ramping up deteriorates the data quality of the other players in the area
• Induces lost revenues and production time for those involved in the timeshare
− Use a 40 cu.in mitigation gun instead
− Example: 2 hour line in timeshare
• 12 softstarts per 24 hours
• 12x20 min = 4 hours lost production every day
Classification: Internal 2012-09-0321
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Acknowledgements
• Partners− Centrica Resources (Norge) AS, Core Energy AS, ExxonMobil E&P Norway AS,
Idemitsu Petroleum Norge AS, Petoro AS, RWE Dea Norge AS, Statoil Petroleum AS, Total E&P Norge AS
• Onboard / onshore processing − M/V WesternGeco Amundsen; Onboard Processing Team− WesternGeco Stavanger Data Processing Center
• Client representatives− Keith Mackie, Mark Maynard, Peter Allan (GeoGuide Consultants Ltd)
• Randi Kristin Tønnessen, Marit Bø Reitan and Kristian Stormark (Snorre asset), Daniel Fischer (SIP), Thor Evert Paulsen (GOP), Leif Fenstad (GOP)
Classification: Internal 2012-09-0322
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Managing Seismic Interference - Snorre 4D case study
R. Laurain*, S. Eidsvig*, D. Fischer*, A. Smith*** Statoil, ** WesternGeco
www.statoil.com
Classification: Internal 2012-09-0323