1. Tutorial 3 Refractor assignment, Analysis, Modeling and Statics

2. Refractor assignment, analysis and modeling
are all accessed under the Model menu.

3. Refractors are assigned under Branch Assignment

4. This is a base map of your bin fold coverage
If you want to show sources and detectors on the map, check these then “Reload plot.”
This is a base map of your bin fold coverage

5. Click on base map to see picks centered on the closest bin
Here are the picks centered on the base map position
plotted by offset vs time

6. Currently we are assigning picks to the first refractor
By dragging the line you have done 3 things:
You have set a first refractor offset range
You have estimated a refractor velocity
You have estimated a delay time
To set refractor branch information drag a best-fit line over the range of picks you want to assign to the first refractor

7. These values are provided here and can be edited
The zero offset intercept estimates 2x the delay time
The slope of the line estimates the refractor velocity
Refractor offset distance is shown by the red zone

8. Another way to use the Branch Assignment window
As before the offsets, velocity and delay time appear here and are editable
Click on “Apply LMO correction to picks
Now move the slider
Drag the line again to specify the offset range for First refractor
Another way to use the Branch Assignment window

9. The base map provides a map of the branch parameters
To accept all these branch assignment parameters, you must push “OK – apply changes” button

10. After accepting your new branch assignment field, you will be asked if you want to interpolate the delay times and velocities to the source and detectors
If you push “Yes,” this will initialize the source and detector databases with these delay times and refractor velocities. If you already have a refractor solution from previous session, these new values will replace the old solution.
You will have one more chance to change your mind.

11. If you said “Yes” to interpolating the delay times and velocities to the source and detector tables, you will next see this “process” window.

12. Applying analyses to traces
Next, you will see how to apply a delay-time and refractor-velocity solution to the traces
The following two slides show the program options that you can use to help QC delay time and refractor velocities

13. From a conventional pick window …
Push the “M” toggle button
Under Options/Display under “Background color options,”
Click on “Use the branch numbers (if assigned)”

14. Eliminate the traces that don’t belong to the refractor – Push ‘X’ toggle button
Push “T” toggle button to limit the time window

15. Applying the branch assignment derived delay times and refractor velocities
Recall that above we assigned branch offsets in the Branch Assignment window
Recall that by assigning branch offsets, we also determined a crude delay time field and a refractor velocity field
Now we will apply those fields to our traces, using the technique we just described
Note that we have also turned off the refractor background color to simplify the display

16. A perfect refraction solution (refractor velocities and delay times) would flatten the refractor to zero time.
This shot is pretty good, meaning the refractor velocity and delay times for this source and its detectors are probably close to correct

17. This source did not respond as well
This source did not respond as well. The simple delay times interpolated from the branch assignment are not correct in detail.
This does not mean that this source has a problem. It just means that the delay time and refractor velocity field are not accurate for this location.
The flatness should improve when we actually compute refractor velocities and delay times from the picks themselves … in the next step.

18. Let’s see how the delay-time and velocity solution we picked in branch assignment looks in another window.

19. Inline-crossline azimuth-limited common-offset pick window
We will look at the solution applied to the traces that fall within a narrow offset range and a narrow azimuth range
We will look at these limited traces across an entire prospect

20. This cross line shows significant residual shape.
Here is the common-offset window with the branch-derived velocity and delay times applied.
As with the source record display, flattened traces imply a good solution.
In general, refracted arrivals along this inline and crossline line up pretty well on zero.
This cross line shows significant residual shape.

21. Click on RVC for a conventional least-squares solution
Compute conventional refractor velocities and delay times by going to Model/RVC delay time/velocity computation sequence

22. This runs your data through a standard sequence of steps shown here

23. Analysis QC At this point You have picked refracted arrivals
You have assigned your picks to refractors
You have computed refractor velocities and delay times
You have also estimated source and detector geometry errors
This is automatically performed as part of the standard sequence
It estimates source and detector mispositions

24. At this point in the tutorial you will examine your velocity and delay time fields

25. Click on Model/3D (and 2D) model building window

26. In this window, the surface elevations, weathering velocity and weathering thickness are accessed through “weathering layer”

27. Refractor delay times, refractor velocities and elevation of the refractors are accessed via “First refractor,” “Second refractor,” etc.
Note: Some versions of Seismic Studio require you to click on “Weathering layer definition” before you can examine refractor parameters

28. This window can be used to construct simple refractor-based earth models.

29. In this case, we will use the default constant weathering velocity of 2000.

30. The result is this “First refractor elevation” surface.
To smooth the refractor elevations (and cause the weathering velocity to be modified) click on “Modify attribute”
Note: Modify attribute will modify the attribute that is currently being displayed.

31. Specify the smoothing radius here.

32. To compute statics, click here
The weathering velocity is no longer constant 2000.
This now displays the smoothed first refractor elevation.
If you change your mind, you can undo the modification here.

33. Statics in Seismic Studio
Seismic Studio computes an individual static value at each source and detector location.
Statics are calculated as the sum of vertical times through each model layer, then to an intermediate datum, then to a final datum.
Both the intermediate datum and final datum are optional.

34. Statics in Seismic Studio
Surface
Weathering velocity … set in model building, typically varies spatially
Refractor
Refractor velocity …varies spatially
Intermediate
Datum
Replacement velocity … constant, user-specified
Final
Datum
For this model, at any station location,
the static will be the sum of 3 times.

35. Statics in Seismic Studio
Surface T1
T1 = layer-thickness / weathering-velocity T2
T2 = refractor-to-intermediate datum thickness / refractor-velocity T3
T3 = intermediate-to-final datum thickness / replacement-velocity
For this model, at any station location,
the static will be the sum of 3 times.

36. Statics in Seismic Studio
Surface
As mentioned above, both the intermediate datum and final datum are optional T1
T1 = layer-thickness / weathering-velocity T2
T2 = refractor-to-final datum thickness / replacement-velocity
If no intermediate datum is requested, for example, then the static would be the sum of two times

37. Accessing the Statics Wizard
Each of Seismic Studio’s model building windows has a “Compute statics” button.

38. This is the first page of the Statics Wizard
If you want either an intermediate datum or a final datum, check them here.
Click “Next >>”

39. If you requested an intermediate datum, you design it here
The wizard shows you some model statistics to help you
For this model, we choose an flat intermediate datum of -100 to be just beneath the refractor
Click “Next >>”

40. If you requested an final datum, you design it here
Again, the wizard shows you some model statistics to help you
Final datum elevation and replacement velocity are often specified by the project client
Click “Next >>”

41. Otherwise, you can ignore this page.
If your data have uphole information associated, then this page provides several options.
Otherwise, you can ignore this page.
Click “Finish”

42. In the “3D (and 2D) model building window,” click “Plot statics” to see the statics you just computed.

43. What to do with the statics
You can see some stacks of the traces with statics applied
You can export the statics for use by other processing systems

44. To Stack traces in Seismic Studio click on “Stacks”

45. Slice Stacking in Seimic Studio
Will be presented in a special tutorial

46. Exporting statics
Statics are computed for each source and detector in the survey
There are several options for exporting the statics for use by processing systems
This tutorial will show you one option:
Export source/detector tables

47. Click on Export/Export source/detector tables

48. We will create a format called “demo statics”
This window is actually a general purpose database exporting facility

49. First, we will define which source parameters we want to output with the statics

50. Don’t forget the statics!
Add whatever identifiers you want
Don’t forget the statics!

51. If the source parameters are completed, do similar for the detector parameters

52. Once we have defined the formats, we must name the output files for each table

53. Type in a file name that makes sense
Don’t forget to check here
Push “Save”

54. Do the same for the detector statics file
Push “OK” to create the files

55. Sample source statics page

56. Conclusions
This tutorial shows you a standard analysis/modeling path through Seismic Studio
On simple data, this may be an adequate template
For more difficult data, more advanced procedures may be required
Advanced procedures can be learned via a Renegade training class