Transcript Extended Diffraction-Slice Theorem for Wavepath Traveltime

Applications of Time-Domain
Multiscale Waveform Tomography
to Marine and Land Data
C. Boonyasiriwat1, J. Sheng3, P. Valasek2, P.
Routh2, B. Macy2, W. Cao1, and G.T. Schuster1
1
Department of Geology and Geophysics, University of Utah
2 Seismic Technology Development, ConocoPhillips
3 Formerly University of Utah, Currently at Nexus Geoscience
Outline
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Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
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Waveform Tomography
• Wave-equation based model building technique.
True Vp Velocity of Marmousi II Model
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Depth (km)
4500
4
1000
Reconstructed Vp Velocity Model
0
Depth (km)
4500
4
0
Horizontal Position (km)
Boonyasiriwat et al., 2008
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1000
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Problem and Solution
Problem:
Find a velocity model from seismic data that
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minimizes the data residual Pobs  Pcalc
Proposed Solution:
- Use a gradient-based method
- Use a multiscale method in X-T domain
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Waveform Tomography
True
Velocity
Observed Wavefield
Initial
Velocity
P
Calculated Wavefield P calc
obs
Wavefield Residual
P
obs
P
calc
Velocity Update
Iterate until wavefield
residual is small
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Outline
•
•
•
•
Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
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Why Use Multiscale?
Coarse Scale
Misfit function ( f )
Low Frequency
High Frequency
Fine Scale
Model parameter (m)
Image from Bunks et al. (1995)
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Multiscale Waveform Tomography
1. Collect data d(x,t)
syn.
2. Generate synthetic data d(x,t) by FD method
3. Adjust v(x,z) until ||d(x,t)-d(x,t)syn.|| 2 minimized by CG.
4. To prevent getting stuck in local minima:
a). Invert early arrivals initially
mute
b). Use multiscale: low freq.
high freq.
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Outline
•
•
•
•
Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
8
Processing Workflow
Pre-Processing of Data
Estimating Source Wavelet
Generating Initial Model
Multiscale Waveform Tomography
Validating Velocity Tomograms
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Processing Workflow
Pre-Processing of Data
Estimating Source Wavelet
3D-to-2D conversion
Attenuation compensation
Random noise removal
Generating Initial Model
Multiscale Waveform Tomography
Validating Velocity Tomograms
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Processing Workflow
Pre-Processing of Data
Estimating Source Wavelet
Generating Initial Model
Generate a stacked section
Pick the water-bottom
Stack along the water-bottom
Multiscale Waveform Tomography
Validating Velocity Tomograms
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Processing Workflow
Pre-Processing of Data
Traveltime picking
Estimating Source Wavelet
Generating Initial Model
Initial model: RMS velocity
Refraction traveltime inversion
Multiscale Waveform Tomography
Validating Velocity Tomograms
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Processing Workflow
Pre-Processing of Data
Estimating Source Wavelet
Generating Initial Model
Low-pass filtering
Multiscale Waveform Tomography
Inversion from low- to
high-frequency bands
Validating Velocity Tomograms
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Processing Workflow
Pre-Processing of Data
Estimating Source Wavelet
Generating Initial Model
Multiscale Waveform Tomography
Migration images
Validating Velocity Tomograms
Common image gathers
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Outline
•
•
•
•
Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
10
Gulf of Mexico Data
480 Hydrophones
515 Shots
a) Virtu
b) Original CSG 1
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0.5
0.5
12.5 m
dt = 2 ms
Tmax = 10 s
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Time (s)
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1.5
1.5
2
2
2.5
2.5
3
1
2
1.5
Offset (km)
2.5
3
1
1.5
Offs
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Low-pass Filtering
(b) 5-Hz CSG
(c) 10-Hz CSG
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0
0.5
0.5
0.5
1
1
1
1.5
1.5
1.5
2
2.5
Time (s)
0
Time (s)
Time (s)
(a) Original CSG
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2.5
2
2.5
3
3
3
3.5
3.5
3.5
4
0
2
4
Offset (km)
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0
2
4
Offset (km)
4
0
2
4
Offset (km)
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Reconstructed Velocity
Velocity (m/s)
Velocity (m/s)
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Kirchhoff Migration Images
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Kirchhoff Migration Images
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Comparing CIGs
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Comparing CIGs
CIG from Traveltime Tomogram
CIG from Waveform Tomogram
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Comparing CIGs
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Comparing CIGs
CIG from Traveltime Tomogram
CIG from Waveform Tomogram
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Comparing CIGs
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Comparing CIGs
CIG from Traveltime Tomogram
CIG from Waveform Tomogram
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Outline
•
•
•
•
Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
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Saudi Arabia Land Survey
1.6 km
Y-Coord. (km)
100 m
0 km
0 0
X-Coord. (km)
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1. 1279 CSGs, 240 traces/gather
2. 30 m station interval,
max. offset = 3.6km
3. Line Length = 46 km
4. Pick 246,000 traveltimes
5. Traveltime tomography -> V(x,y,z)
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-3.6
Offset (km)
3.6
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Brute Stack Section
0
2.0
3920
CDP
5070
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Traveltime Tomostatics + Stacking
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2.0
3920
CDP
5070
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Waveform Tomostatics + Stacking
0
2.0
3920
CDP
5070
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Outline
•
•
•
•
Introduction
Time-domain multiscale waveform tomography
Processing workflow
Field data results:
• Gulf of Mexico
• Saudi Arabia
• Summary
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Summary
Acoustic waveform inversion was successfully applied to
both marine and land datasets, and can provide accurate
velocity subsurface structures.
Issues:
• Cost > 100 iterations: How to reduce cost?
• Acoustic vs. Elastic: How far can we go with acoustic?
• Anisotropy needed?
• Source wavelet important: Source-independent inversion.
• Missing low frequencies: Better initial model via
reflection tomography.
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Acknowledgment
We would like to thank
• UTAM sponsors for financial support.
• Amarada Hess and Saudi Aramco for providing
us the datasets.
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