Written by Thomas Proença, Geoscientist, Brazil
A common issue observed in sub-salt imaging is migration artifacts such as "smiles" (Figure 1). Migration smiles occur when the velocity survey used in the depth correction contains imperfections. When re-processing is not an option, a specific data conditioning workflow can be applied within GeoTeric with the aim of removing/reducing migration noise and increasing the signal to noise ratio in the data; thus making it clearer and easier to interpret.
|Figure 1 - Migration smiles|
Noise Attenuation Workflow
The first step to removing the migration smiles is to create smooth steering volumes, with the aim of reducing the contamination of the steering dip and azimuth. This is done by applying a grid oriented smoothing filter of the original seismic data. Migration smiles are the most problematic part in the Z direction of the seismic data, using a large filter in X and Y directions will attenuate its vertical response. A typical filter size for this process is 9x9x5.
The smoothing attribute can be found at:
Reveal tab > Processes and Workflows > Processes > Attributes > Stratigraphic attributes
After the original data has been smoothed, the steering volumes can now be calculated. The recommended filter size for dip and azimuth is above 15 (note that if the bin sizes are different between the X, Y and Z directions, the filter size for the steering volumes should be adjusted to compensate for the difference and make them square).
Once the steering volumes are generated, they are used along with the original seismic data as inputs to the SO Noise filter found under the Processes and Workflow menu. The recommended filter size for this process is between 5 and 9. If the data is extremely noise to get better result the SO Noise filter can be run twice.
|Figure 2 - Original (left) x attenuated (right)|