Separating overlapping seismic shots to remove incoherent noise
What is Deblending?
Deblending is the process of separating overlapping seismic shots that were fired close in time during simultaneous-source acquisition.
In blended acquisition:
•Two or more shot records overlap in time
•They interfere with each other
•Raw gathers contain blended noise and cross-talk
Deblending removes this interference to recover clean, unblended shot gathers.
Why blended acquisition is used?
•Higher productivity
•Denser source sampling
•Lower cost
•Better illumination
Why deblending is needed?
•To remove cross-talk between overlapping shots
•To recover individual source wavefields
•Required before imaging, velocity analysis, AVO, inversion
Simultaneous sources produce incoherent noise, while true reflections are coherent.
Therefore:
•If we enforce coherency across offsets/inlines, reflections remain
•If we enforce incoherency, blended interference is removed
This is done using:
•Iterative subtraction
•Sparse inversion
•Median filtering
•f-x domain coherency constraints
•Moveout (velocity) constraints
•Time-variant muting
Input DataItem
Input gather - connect/reference to the Output gather that needs to be deblended/separated from the incoherent noise.
Sweep collection - provide the sweeps information. This is applicable for LAND seismic data which is recorded by vibroseis. Seismic operators stores the sweep information in the trace headers. connect/reference to the corresponding trace headers where the sweep information is stored.
Use time-variant delending - this option enables the time-variant deblending approach. Blending is not uniform, due to that time-variant deblending helps in attenuating the incoherent noise and brings stability and reduces artifacts to the result. By default, TRUE (Checked).
Cross-correlation time - cross-correlation helps in detecting the coherent and incoherent noise based on the cross correlation time window. The smaller the cross-correlation time, the finer the details.
V0 - specify the reference velocity value. This value is used to guide coherency. Reflections consistent with V0 are preserved and considered as true signal and the others are considered as incoherent and attenuated.
Deblending degree - specify the deblending degree value. This value can be treated as an iteration number where it controls the aggressiveness of the attenuation. Higher the degree value, aggressive separation/attenuation that may lead to primary damage.
Window - this is time-spatial window is used to apply the deblending operator. Larger window size smooths the result and less accurate. Smaller window size may give better results however that may create artifacts.
F1 - provide the lower frequency to be considered while performing the deblending. Lower frequency is hard to deblend.
F2 - provide the higher frequency to be considered while performing the deblending. Incoherent noise commonly higher frequency and it is easier to separate.
Auto-connection - By default, TRUE(Checked).It will automatically connects to the next module. To avoid auto-connect, the user should uncheck this option.
Bad data values option { Fix, Notify, Continue } - This is applicable whenever there is a bad value or NaN (Not a Number) in the data. By default, Notify. While testing, it is good to opt as Notify option. Once we understand the root cause of it, the user can either choose the option Fix or Continue. In this way, the job won't stop/fail during the production.
Notify - It will notify the issue if there are any bad values or NaN. This will halt the workflow execution.
Fix - It will fix the bad values and continue executing the workflow.
Continue - This option will continue the execution of the workflow however if there are any bad values or NaN, it won't fix it.
Number of threads - One less than total no of nodes/threads to execute a job in multi-thread mode. Limit number of threads on main machine.
Skip - By default, FALSE(Unchecked). This option helps to bypass the module from the workflow.
Output DataItem
Output gather - generates the output gather after deblending. This is free from any incoherent noise.
GGatherItemOutFiltered - generates the filtered output gather
There is no information available for this module so the user can ignore it.
There are no action items available for this module.
YouTube video lesson, click here to open [VIDEO IN PROCESS...]
Yilmaz. O., 1987, Seismic data processing: Society of Exploration Geophysicist
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