Let’s take a look at an example of using spectral shaping.
I am going to take some offset gathers and convert them into Angle stacks of Near-Mid and Far.
I open the angle stacks process,
select the gather volume as input, choose the velocity model and specify the angle range 5-13 degrees.
I repeat this for the mid range 10-22 degrees,
and again for mid range 20-32,
and finally the fars, 30-40 degrees, leaving me with 4 angle stack volumes of Near, Mid, Mid and Far.
Looking at each plot it is clear that frequency is decreasing with offset.
To confirm this statistically I can use the spectral analysis plot.
For this I need a polygon in a seismically quiet area away from AVA anomalies,
and I also need the seismic volume which can be dragged into the plot.
Here is the spectra analysis for the near angle stack,
I can adjust the display parameters to make it more visible.
I can also display the mid, further mid and the far angle stacks confirming the visual observation that frequency is decreasing with increasing offset.
The angle stacks in this example have low noise content and hence we are going to match the mids and fars to the near stack.
Going back to just the near stack, I can use spectral shaping to flatten off and boost the signal.
I select the spectral shaping process.
I select the near stack input. This creates a volume which I can drag into the spectral analysis to observe real time edits.
I can also display the volume in the seismic section to see the trace changes.
Back to the process, I can edit individual frequency – gain pairs to adjust to a flat spectrum.
The final spectrum looks nice and flat.
I can set up similar processes for each of the Near, mid, mid and far stacks that were generated.
Displaying the results, I can see that the frequency spectra all match statistically.
I can visually QC results in the section view by now displaying the spectrally shaped near-mid, mid and far stacks.
The result is a much improved view with similar frequency content.
This seismic data is now ready to be used in AVA analysis.
If you have questions, or would like to know more, visit our website at www.dug.com
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