OMNI 3D® Workshop Tutorial:
3D Ray Tracing and Analysis (May 2009)
This tutorial builds upon the skills learned in the tutorials “Building a 3D Model” and
“Interpreted Surfaces in 3D Models”. The object of this exercise is to ray trace a 3D
model and calculate a target analysis.
Set parameters as described or shown in pictures of
dialogs. As you work, use OMNI 3D’s Popup Help to see
explanations of all available parameters. Hover your
cursor over a parameter or click the question mark in the
upper right of a dialog and then click the parameter for
Popup Help.
Working with this Tutorial
If you are new to OMNI 3D, please see the “Basic Land”
tutorial before you use this tutorial. In this advanced
tutorial it is assumed that you can:
Start OMNI 3D
Create a project
Find and use menus in the Project Tree
Use Pop-Up Help in OMNI 3D’s menus and dialogs
Use right-click menus in the View tabs
Adjust the 3D View display
No License? No Problem!
You are invited to learn more about
OMNI 3D® by reviewing tutorials
and examining Tutorial Solution
projects.
To create your own project you
must have an OMNI 3D® license.
To obtain a trial license go to the
Help Menu and see: Help Contents
-> Getting Started -> License.
This tutorial applies to the tutorial solution project titled “3D Ray Tracing Example”.
You may compare your results to the solution project. Go to Help | Load Tutorial
Solutions and open the 3D Ray Model folder. The folder contains both the input data for
this exercise and the completed solution project.
To complete this set of exercises you will need these input files:
...\Tutorial\3D Ray Model\3D Ray Tracing Example-Data\3D Model 2.odb
...\
...\My 3D RM2.r3d
...\
...\Topography_250m_grid.xyz
To open the solution project, double-click the file named:
...\Tutorial\3D Ray Model\3D Ray Tracing Example.odb
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Exercise 3 - 3D Ray Analysis Setup
1.
On Main Menu:
File
Open
Open dialog
Look in directory used for
3D Model exercises
File name: = 3D Model 2.odb
Click Open button
2. On Main Menu:
File Save As…
Save As dialog
Save in directory used for
3D Model exercises
File name: = 3D Ray Tracing
Click Save button
Copy Analyses = Yes
In this exercise, we will use the model
created in the tutorial “Interpreted Surfaces
in 3D Models” for our analyses and 3D Ray
Tracing. Open your 3D Model 2 project and
save it as “3D Ray Tracing”. (If you haven’t
completed it, open 3D Model 2
Exercise.odb)
The illustration below shows the My 3D
RM2 model after the fault has been toggled
off and the horizons have been recalculated.
[3. If needed only
Under 3D Ray Models
MY 3D RM2
X Fault
Left click Blue horizon name to highlight
Hold down Shift key and left click Yellow
Right-click Blue horizon name
Select: Set to be NOT ‘Affected by Fault’]
The following adjustments have also been made in the 3D View.
1. Drag and drop model name into 3D View to display.
2. Ctrl + “z” key and drag up to expand the depth axis
3. Ctrl left-click and drag to rotate and tip model display.
4. Ambient Light = 20%
5. Force Axes Behind Object.
6. Click and drag up to zoom the entire model.
(See Building a 3D Model Tutorial for details.)
OMNI 3D computes a number of analyses based on 3D ray paths. We can also examine
specific ray paths to better understand analysis results. OMNI 3D computes “exploding”
horizons and fold illumination for 3D horizon surfaces. Fold illumination may be created
based on actual survey layout and synthetic seismic traces can be generated on your
survey and the 3D model.
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Exercise 3 – Maximum Frequency
(Under 3D Ray Models
MY 3D RM2 )
Analyses Create New Analysis
3D Ray Model Analysis dialog
Workshop Module
Maximum Frequency
Click Next button
3D Ray Model – Select Horizon dialog
Select Horizon = Yellow
Click Next button
Bin Grid – Definition dialog
Click Next button
Bin Grid – Select Partial Bin Coverage dialog
Click Next button
Maximum Frequency Analysis –
Calculation Method dialog
Sample Interval
Sample Interval = .004
Use this Dip Angle
Maximum Dip Angle
3D Ray Model Analyses
You may create Maximum Frequency,
Maximum Offset, Resolution, Migration
Aperture, and Attenuation analyses for your
model surfaces.
Maximum Frequency Analysis Example
Use specifications listed in the Exercise 3 –
Maximum Frequency parameter box. The
maximum un-aliased frequency that can be
obtained from a surface is computed based on
depth, velocity, dip and sampling. The only
one of these factors we can fully control is
sampling – specifically, the bin size (spatial
sampling) and sample interval (time).
By default OMNI 3D uses the bin grid of
your 3D model for computations. You can
modify the bin size used for the Maximum
Frequency calculation on the Bin Grid –
Definition page of the wizard.
Since our model is small, we will compute the
entire surface. If it were very large we would
limit the area of our computation to a specific
Edit View
area of interest or a representative portion of
the model. Perhaps an analysis of just a
quarter of the model would allow us to quantify our parameter selection. In that case, we
would specify a subset of the model in terms of bin grid location. In other words, define
the first In-line or X-line (Min) by number and a count of bins to include. (Note that the
first In-line or X-line number of the grid is zero.)
Click Finish button
The Sample Interval and the dynamic range of our recording equipment will also limit
the frequencies we can attain. Smaller sample rates will also increase computation time.
The computation can be based on either Maximum Dip Angle or Apparent Dip Angle.
The Apparent Dip Angle option computes the dip as “seen” by lines of stations (or grid
nodes) as they cross the structure.
Go to the Edit View to see the maximum un-aliased frequency after migration. Rightclick on the analysis file name and select Style. On the Bin Display tab select Unmig-InLine. You will notice that the frequencies are slightly higher before migration. (You may
need to rescale the display. Right-click in the color scale and select Set Levels from
Data.)
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Also, you can display statistics for
both the In-Line and X-Line
calculations. Since the bins in this
example are symmetrical there will
be no difference in the values for
In-Line and X-Line.
Go to the 3D View. In the Project
Tree, click on the analysis file
name and drag and drop into the
display space. Select Mig-InLine
on Model.
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3D Ray Display
In order to understand the exploration target better, we can generate and view sets of ray
paths. All of the options described work similarly. You will set up a shot and theoretical
receiver locations for ray tracing. Rays between a single shot and a single receiver may
be generated using Trace a Shot/Receiver. Trace a Surface Line will allow you to
examine rays for a shot taken at one end of a line of receivers placed at the surface. In
Trace a VSP a series of receivers is placed below the surface in a vertical line. Rays may
be viewed in the Edit and 3D Views.
To begin, we will toggle the Analyses display off. Next, to make it easier to see the rays,
make the horizons transparent. When we created the horizons (in Exercise 2) we set all of
the horizons to Reflect rays, with the exception of Topo (the surface horizon). To
confirm that these settings are still in effect we will select the Blue, Green, and Yellow
horizons and Set to Reflect.
Exercise 3 - 3D Ray Display Setup
1. Under
3D Ray Models
MY 3D_RM2
X Analyses
Topo Transparent
(Use slider to set transparency to ~65%)
Click OK button
Blue Transparent
(Use slider to set transparency to ~75%)
Click OK button
You can select all three horizons at once and
make a batch change as described in the
parameter box step 2. Alternatively you can
simply right click each horizon to see if there
is a check mark next to Reflects. If it is
checked, the horizon will reflect rays. If it
does not have a check mark next to it, click to
toggle the setting.
Green Transparent
(Use slider to set transparency to ~75%)
Click OK button
Yellow Transparent
(Use slider to set transparency to ~75%)
Click OK button
2. Under 3D Ray Models
MY 3D_RM2
Left click Blue horizon name to highlight
Hold down Shift key and left click Yellow
Right-click Blue horizon name
Select: Set to Reflect
3D View
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Ray Trace Surface Line Example
Right-click on the name of the model and select Rays | Trace a Surface Line. OMNI 3D
will open the 3D Ray Model – Trace a Surface Line wizard and switch the main display
to Edit View. The surface line will be described by a click at a shot location and a second
click to define the end of the surface line. Receivers are placed between the shot and the
last point on the line at the station Interval you specify. The Depth of the shot can also
be specified. Note that a value of “0” will place the shot on the surface of the shallowest
horizon in the model. A value of “100” would place the shot at 100 m below the surface.
Exercise 3 – Trace Surface Line
Under 3D Ray Models
MY 3D_RM2 Rays Trace a Surface Line
3D Ray Model – Trace a Surface Line wizard
Multiple reflections per trace
Shot and First Receiver
Depth = 0
Last Receiver
Interval = 60
In Edit View:
Define shot location and receiver line.
Left-click in center of model
Drag to Eastern corner of model.
Release mouse button.
Click Apply Button
(Do not Exit wizard)
3D View
The ray tracing algorithm will search for a
reflection point on each horizon that
satisfies each receiver. When Multiple
reflections per trace is checked, ray tracing
will search for additional reflection points.
Leave Multiple Reflections per trace
unchecked.
Click at the center of the model and drag to
the eastern corner before releasing the
mouse button. Return to the 3D View to see
the rays better.
While working in the 3D View you may
change settings in the Trace a Surface Line
wizard and click Apply to update the view.
For an example, specify Multiple
reflections per trace.
Multiple reflections per trace
Click Apply Button
Click Exit Button
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Single Reflection Solution
Multiple reflections per Trace
When you close the wizard, the traces will remain on the screen until you recalculate the
model or perform another ray trace function. Right-click on 3D Rays under the model
name and select Remove 3D Rays to clear the rays. Note that the appearance of the rays
is controlled by 3D Rays Style found on the same sub-menu. This includes the ability to
manually remove rays from the display for specific receivers.
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Exploding Horizon Example
The Exploding Horizon function finds the reflection points on an illuminated horizon
which would be generated if energy were to explode from the surface of another horizon.
The energy may be down going energy or up going energy.
Exercise 3 – Exploding Horizon
1. Under
3D Ray Models
MY 3D_RM2 Rays Exploding Horizon
3D Ray Model – Exploding Horizon wizard
Multiple reflections per trace
Exploding Horizon = Green
Illuminated Horizon = Yellow
Ray Spacing
Model Inline = 60
Model Xline = 60
The Multiple reflections per trace
setting will take some time for an entire
model surface. Just how long the
computations take will depend upon the
speed of your computer. If you have a
fast processor and plenty of RAM you
should be able to compute the
illumination in 15 or 20 min. In these
examples we are not computing
Multiple reflections per trace but feel
free to do so if you have the time.
Click Apply Button
(Do not Exit wizard)
3D View
Green Source - Yellow Illuminated
(Edit View)
Multiple reflections per trace
Exploding Horizon = Blue
Illuminated Horizon = Yellow
Ray Spacing
Model Inline = 120
Model Xline = 120
Click Apply Button
Click Exit Button
Blue Source - Yellow Illuminated
(3D View)
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Exercise 3 – Setup of Survey
for Analysis
X 3D Ray Models
Survey Analysis with 3D Ray Tracing
First, to simplify our view, we will toggle off
the display of 3D Ray Models. If Survey
South Outcrop is inactive, toggle it on.
Surveys
Survey South Outcrop
(Under Surveys)
Survey South Outcrop Attributes---------Set from XYZ file
Stations – Choose Attribute dialog
Shots
Choose Attribute = Elevation
Click Next button
Stations – Choose Attribute dialog
Receivers
Choose Attribute = Elevation
Click Next button
Stations – Interpolate Attributes
from Points dialog
Click Load button
Open dialog
Look in: 3D Ray Tracing
Example-Data
File name: =
Topography_250m_grid
Click Open button
Click Finish button
Illumination of Fold
In this portion of the exercise we will create
an illumination map for the Blue horizon.
This map will be calculated using source
locations and receiver locations from a
survey layout. We will need station
elevations for ray tracing. These can be
imported from an XYZ file.
Use the settings supplied in the parameter
boxes to create an illumination map.
Examine the results in the Edit and 3D
Views.
To display the analysis in the 3D View,
click on the newly created analysis and drag
in into the view area.
Exercise 3 – Create Illumination Map
(Under Surveys
Survey South Outcrop
Scripts)
Pattern 6X56 Create New Analysis
Bin Analysis – Create a New Analysis dialog
3D Workshop Module
IlluminationRay-traced fold over a complex model
Click OK button
Target Analysis – Calculation Method dialog
Calculation Detail
Fold AND Points
Calculation Method
Ray 3DModel (3D multiple horizon)
Click Next button
3D Ray Model – Input File dialog
3D Ray Model File name
Click Browse button
Open dialog
Look in: 3D Ray Tracing-files
File name: = My 3D_RM2.r3d
Click Open button
Click Next button
3D Ray Model – Select Horizon dialog
Select Reflecting Horizon = Blue
Click Next button
Script – Other Scripts to Combine dialog
Click Next button
Bin Grid – Definition dialog
Click Next button
Bin Grid – Select Partial Bin Coverage dialog
Click Next button
Flex Bin – Modes dialog
Click Next button
Analysis – Calculation Schedule dialog
When to calculate
Immediate mode. Calculate now.
Click Finish button
3D View
You will notice that some areas of the
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illumination map have empty bins. These are areas where there are no reflections due to
steep dip. If the analysis calculation had been allowed to search for Multiple Reflections
per trace the coverage would have been more complete. However the full calculation
would have taken hours.
The quick calculation gives us a good first look for survey evaluation. This evaluation
shows us that we will need to decrease line and station intervals to properly sample this
flank of this structure. Longer offsets may also be required. The next step would be to
modify the survey design and rerun the analysis. Multi-reflection ray tracing can be
applied to the survey after parameters have been refined.
Dip of Blue Horizon
Fold Illumination - Blue Horizon
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Contribution of Individual Shots to Illumination
We can select specific shots and examine their contribution to the illumination of the
target. The Bin Data – Select Rays wizard displays rays for an individual shot, receiver,
or bin.
Exercise 3 – Create Illumination Map
(Under:
Surveys
Survey South Outcrop
Scripts
Pattern 6X56)
Pattern 6X56 – TRGT001 Select Stns/Bins for Rays
Bin Data – Select Rays dialog
Mouse Select Mode
Select Individual Shots
Click on a shot near area of missing coverage
Edit View
Select a shot near an area of the map where
coverage is poor. Select several shots. Rays
remain on the screen until you click Clear
all Selections. Go to the 3D View to better
understand the relationship between the
Blue horizon’s structure and the
illumination coverage.
Select Shot
3D View
Display in 3D
Rotated Image
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Exercise 3 – Create Synthetic Seismic
(Under Surveys
Survey South Outcrop
Scripts)
Pattern 6X56 Create New Analysis
Bin Analysis – Create a New Analysis dialog
3D Workshop Module
Synthetic - SEGY over a complex model
Click OK button
Target Analysis – Calculation Method dialog
Choose Model Type to Ray-Trace
3D Ray Model (3D multiple horizon)
Click Next button
3D Ray Model – Input File dialog
3D Ray Model File Name
Click Browse button
Open dialog
Look in: 3D Ray Tracing-files
File name: = My 3D_RM2.r3d
Click Open button
Click Next button
3D Ray Model – Ray Trace Parameters dialog
Ray Tracing Mode
P-Wave
2 Reflections
Intensive Search
Top Reflection Horizon = Blue
Bottom Reflecting Horizon = Yellow
Click Next button
Synthetic Seismic Data
Use the parameters listed in the box titled
“Exercise 3 – Create Synthetic Seismic”.
We are using defaults for many of the
settings, but as you page through the
dialogs, notice that there are a large number
of options.
You may work with P- or S-waves and add
linear events to simulate noise. Ricker,
Ormsby and user defined wavelets may be
used.
When the calculation is complete switch to
the Chart View. Click on the new analysis
file and drag it into the Chart View. Rightclick in the chart display and select Full
View. Click and drag in the Trace axis to
zoom in on a few traces.
Right-click in the Chart View and select
Patten 6x56-SYNT-001 - Synthetic Style...
to modify display settings.
Trace Select – Offset/Azimuth dialog
Click Next button
Segy File – Output Description dialog
Trace Parameters
Trace Legth (sec) = 2.500
Sample Rate (sec) = 0.002
AGC
Apply AGC
Length (sec) = 0.400
Click Next button
Wavelet Page
Wavelet
Ricker
Rick Frequency = 30
Click Next button
Trace Noise dialog
Click Next button
Analysis – Calculation Schedule
When to calculate
Immediate mode. Calcualate now.
Click Finish button
Chart View
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