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| TOMO3D
v1.2 is a 3D nonlinear refraction travel-time tomography software
product developed by GeoTomo LLC. Applications include imaging
near-surface velocity structures and making refraction statics
corrections in complex geological areas. TOMO3D has been
successfully applied to real data sets from the oil and gas as well
as the environmental and engineering industries. Customers include
Unocal, Schlumberger Geco-Prakla, and Exxon. |
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INTRODUCTION TO TOMO3D - A COMPLETE TOOL FOR 3D TOMOGRAPHY
TOMO3D v1.2 includes six major modules.
The combination of TOMO3D and TOMO+ is a complete 2D and 3D
tomography package from picking travel times, velocity analysis,
tomographic imaging, to statics interpretation. TOMO3D v1.2 has
capabilities for obtaining both tomographic and delay-time solutions
for statics interpretation. It can be applied to solve both 3D
marine refraction imaging and land imaging problems. |
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- GEOMETRY
ANALYSIS
There are more than 30 functions
in this module! Display 3D travel times, perform 3D geometry
coordinates transformation, analyze time picks, identify and
remove bad picks, automatically pick velocites from shot-offset
data, and many more ...
- MODEL
ANALYSIS
View 3D velocity models, and more than 15
functions! Extract or place back a small model section, create a
topography file from survey geometry, convert a 3D depth-velocity
model to a time-velocity model and more ...
- 3D
RAYTRACING
Perform 3D refraction
travel-time and raypath calculation for a given velocity model and
survey geometry. It can help you to design 3D seismic survey, and
also provide syhthetic data for tomography experiments.
- 3D
TOMOGRAPHY
There are three refraction tomography
approaches that you can choose: grid-based tomography,
interface-based tomography, and joint grid- and interface-based
tomography for your need. This module outputs updated velocity
models iteratively, outputs final tomography predicted travel
times, reports inversion progress and performance parameters.
- QC CONTROL
Analyze the convergence of
tomographic inversion, and help you understand misfit residuals in
several ways, identify inconsistent picks and geometry errors, and
relocate the shots with large misfits by inverting their positions
with the tomographic velocity solution.
- REFRACTION
STATICS
Calculate refraction statics from an input
velocity model and a survey geometry file, or from depth-velocity
parameters inferred from delay times. It can display statics
times in 1D/2D, output statics times in various formats.
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 GEOMETRY
ANALYSIS - Front Interface
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You may apply any of the
funtionality to process your time picks at any time. Each of them
is an independent process. When you select a data set to view, you
are able to control the data with a shot geometry display for any
process as shown in the following. The blue
shows the current active shot, the green
shows those with delay times picked, while the
red shows those untouched.
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GEOMETRY ANALYSIS -
Rapid Processing
With travel-time working window, you are able to do a few things: (1)
check picking quality and any processing result from using functions
in the front interface; (2) manually or automatically pick refraction
turning points for deriving simple statics solution directly or
building a realistic 3D starting model for tomography; (3) use overlay
function to compare fit between data and tomography predicted times.
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MODEL ANALYSIS MODULE - All About Velocities
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| View 3D Velocity
Model
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RAYTRACING MODULE - In and Out
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TOMOGRAPHY MODULE - Three Choices
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Performing 3D Tomographic Inversion - It cannot
be easier ! |
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You provide input and output files. You may choose to extend the model
laterally along the side raypaths near the model boundaries, or fix
the near-boundary velocities if this model will be placed back to a
large model. You may choose to downward extend the highest velocity
along the deep refractor or just leave it as it is. You may choose a
constant smoothing parameter or a linearly varying parameter. Or you
do not need to choose anything, just let the program figure it out ...
There are three different tomography approaches that you can choose.
The tomography approach inverting interfaces simply assumes that the
shallow Earth consists of a few layers with arbitrary interfaces and
constant velocities, while full grid-based tomography does not.
It all depends on data! |
| If you find that the data suggests sharp
interfaces and simple layer velocities, use the
interface tomography. If it shows evidence of both sharp
interfaces and variable velocities, you need to apply the
joint interface- and grid-based tomography.
You also have a choice of tomography without any assumption of the
Earth structure- full grid-based tomography.
Making assumption is not always right, but making no assumption is not
always easy either. All we need to do is to be flexible. |
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QC
CONTROL View inversion convergence rate,
look into misfit for each shot, relocate shot positions using
nonlinear inversion schemes if shot locations are suspected wrong from
misfit analysis. This shot relocation program provides a rapid
geometry solution with the tomographic velocity input. Instead of
using a direct-wave arrival and a simple near-surface velocity to
infer shot location, this module actually uses any first arrivals
including refractions, and derives shot locations in an arbitrary 3D
velocity model. |
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 REFRACTION
STATICS
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A 3D
Case History --Land 3D data,
10,207 Shots, 5,103,500 Traces
This large 3D survey was performed over a complicated near-surface
velocity structure. Because of the near-surface complexity, 3D seismic
data processing for imaging deep reflectors encounters significant
difficulties. Conventional refraction statics interpretation methods
failed because of assuming simplified velocity structures. 3D
refraction tomography is a powerful tool for solving the problem in
this situation. TOMO3D was successfully applied to reconstruct the
near-surface velocity structures for this case.
The above images show the near-surface velocity
distribution at four depths. Downward direction is the positive
increase. The surface is at a depth of about 2500 feet above the sea
level. The velocity images clearly show NW-SE structural trend. A
high-velocity intrusion occurs in the central area. A major fault
appears at the NE corner. The high-velocity sediment dips down from NE
to SW.
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