1. SEG 3-D Elastic Salt Model
Biondo Biondi, Bee Bednar, Arthur Chang leading SEG committee work
John Anderson is XOM contact
Meeting to discuss desirable features
Thursday, June 23, 2005, GW3-933
9:00 am to 10:30 am
Computational effort will take a long time
Current task is to define a suitable model

2. snap shot at 781 ms source snap shot at 1450 ms 3-D SEG Acoustic
Salt Model
snap shot at 781 ms
source
snap shot at 1450 ms

3. Acoustic (18 Hz peak) SEG Salt model (2 data sets)
45 shot data set
5 lines
9 shots/line
201 by 201 receiver grid per shot (40 m spacing, wide azimuth, source at center of grid, receivers/shot)
ideal for shot record migration
4800 shot data(C3-NA)
50 lines, 160 m cross-line spacing
96 shots / line, 80 m shot spacing
8 cables, 40 m group interval within a cable
68 receivers / cable
544 receivers / shot
simulates marine acquisition

4. Single raw 3-D shot record (8 streamers, C3-NA)
Numerical dispersion
Original SEG SALT model data
Each streamer has 68 receivers 40 m apart. The entire survey is 50 lines with 96 shots per line. Time sample rate is s, with 625 samples per trace 1

5. Computational Size of Problem
For 3-D acoustic SEG Salt model
Using model parameters for data without dispersion
441 shot wide-azimuth data set
21 lines of 21 shots each, receivers at every grid point
650 GB if SEGY, 400 CPU days on old hardware
Aimed at ideal conditions for shot migration
For 3-D elastic model (similar to acoustic model)
scale compute time by roughly 144
Vs = 0.5 Vp requires finer grid by factor of 2
Computation time scale factor is 16=24
3 components x 3 terms = factor of 9
Data set volume grows by factor of 3
Doubling bandwidth requires factor of 16=24

6. Marmousi II 2-D Elastic Model (University of Houston)Vp
Low p-wave velocity simulating hydrocarbons to give AVO response
Flat spot on target Vs
AVO modeling requires Vp, Vs, and Density
Density
Synthetic data have 80 Hz bandwidth

7. SEG 3-D Elastic Salt Model
Key desirable features:
(1) smooth and rugose (both deep notches and chirp signal) Top of Salt (TOS) components
(2) shallow salt with impedance match to give large P-S conversions
(3) deeper salt matched for P-P
(4) multiple salt bodies, one obscuring portions of the other
(5) compaction model for subsalt region honoring differences between salt and sediment overburdens

8. SEG 3-D Elastic Salt Model
Key desirable features:
(6) overpressure zone for part of subsalt zone
(7) sediment profile with some AVO target anomalies
(8) reservoir zones with compartmentalization
(9) variations in the Base Of Salt (BOS) (steep ramp to flat, gentle ramp to flat)
(10) subsalt sediments that truncate steeply against the BOS

9. SEG 3-D Elastic Salt Model
Key desirable features:
(11) realistic salt tectonics including faulting and structures in the sediments corresponding to deep salt withdrawal and slip interfaces
(12) deep carbonate with rift faults near bottom of section.
(13) components for calibrating image quality
deep horizontal reflector at bottom
isolated point diffractors

10. Sediment structures are related to salt tectonics
Allochthonous Salt
Autochthonous Salt

12. Salt
Salt
Autochthonous salt weld

14. Realistic Plan
Begin with a fully elastic model, progress as compute capacity grows
Acoustic model data set
Elastic multicomponent data set
Anisotropic multicomponent data set
Begin collecting data over subsets of the model
Subsets of the model could target different geologic objectives
Over time merge surveys to cover entire model
Surface, OBC, and VSP data
Both absorbing and reflecting surface boundary conditions
Zones of very dense sampling
Could we have an equivalent physical model done at Delft or University of Houston or elsewhere?
Can we get elastic physical models?