Transcript SEG 3-D Elastic Salt Model

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
3-D SEG
Acoustic
Salt
Model
snap shot at
781 ms
snap shot at
1450 ms
source
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, 40401
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
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 0.008 s, with 625 samples per trace
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
Marmousi II 2-D Elastic Model (University of Houston)
Low p-wave
velocity
simulating
hydrocarbons
to give AVO
response
Vp
Flat spot
on target
Vs
AVO
modeling
requires
Vp, Vs, and
Density
Density
Synthetic
data have
80 Hz
bandwidth
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
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
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
Sediment structures are related to salt tectonics
Allochthonous Salt
Autochthonous Salt
Salt
Salt
Autochthonous salt weld
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?