Post on 14-Feb-2016
description
22.04.23 1
Using Dual Azimuth Acquisition to Illuminate
Beneath Salt Domes
Fiona Dewey 1
Julia Bernard 2
1 Wintershall Noordzee BV2 Now with Wintershall Erdoelwerke A.G.
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Agenda
The Problem Acquisition Time Processing Depth Migration ResultsConclusions Acknowledgements
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The ProblemPoor Imaging Below Salt Structures
W E
??
1990 Acquisition with (1999) PrSDM processing
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The Problem
Many gas discoveries close to salt features.
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The Solution
New AcquisitionDetermine best acquisition direction for
illuminationOptimize streamer length
Improved Processing TechniquesImproved noise suppressionPrestack Depth migration taking
anisotropy into account
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Dip vs Strike Acquisition
Industry rules:
Dip Shooting
Better imaging below complex overburden
Strike shooting
Better at imaging salt flanks
Multiple energy more coherent
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Illumination Study
Study Objectives:
Map illumination for different acquisition directions
Investigate effect of increasing cable length
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Illumination Study
Conclusions:
Illumination patchy under salt ridge
N-S acquisition provides additional illumination under salt flanks
Optimal cable length 5000-6000 m
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Acquisition Parameters Comparison1990 Acquisition
2003 Acquisition
Streamer length 3000m 5100m
Navigation Syledis DGPS
Configuration 2 Vessels4 Sources4 Streamers
1 Vessel2 Sources6 Streamers
Near Trace offset 117m 110m
Fold of Coverage 20 68
CDP trace spacing 75m 37.5m
CDP spacing In line Cross line
12.5m25m
6.25m25m
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2003 Acquisition Program
Main acquisition direction W-E (556 km²)
Two additional swaths N-S (196 +185 km²)
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Hide
Vessel Position Tracks
Shooting pattern optimised to reduce waiting on tides and maximise feather matching
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Conclusions
Illumination differences seen on sides and under salt structures
Away from salt illumination differences are small
In less complex areas summation of PrSTM data sets gives improved signal to noise
Depth migration moves steep dips to similar locations
Anisotropy parameters defined for each orientation
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Summary
Orthogonal acquisition combined with long streamers has illuminated previously hidden parts of the subsurface
Challenges still remain in processing to define one unique velocity field that will account for the differences in anisotropy of the two acquisition directions
Does the imaging improvements justify the extra cost ??
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Working Together
Contractor
Illumination study Concept systems
Acquisition PGS
Time processing Veritas DGC
Depth migration WesternGeco
Acquisition and processing QC
Monarch Technical Services
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Acknowledgement
Wintershall Noordzee BV
Energie Beheer Nederland BV
Petro-Canada