 | MULTIPLE ATTENUATION (ITERATION 2) |
| MULTIPLE ATTENUATION (ITERATION 2) |
|
<< Click to Display Table of Contents >> Navigation: Tutorials > Seismic Processing 2D LAND >
|
The second iteration of multiple attenuation should after migration step. g-Platform provides several radon modules and we are going to use Radon multiple attenuation (high resolution Radon).
Keep in mind that you have several radon modules with a bit different functionality and results:
•Radon multiple attenuation: vista views: input, output, difference gathers, user-defined time curves on gather;
•Radon - TauP - High resolution: vista views: input, output, difference gathers, Tau-P domain, interactive curve on gather;
•Radon - TauP: vista views: input, output, difference gathers, Tau-P domain, interactive curve on gather;
•Radon multiple attenuation by velocity: vista views: input, output, difference, NMO-corrected gathers, interactive velocity spectrum for constrain-polygon picking;
•Radon - by picking: vista views: input, output, difference gathers, interactive Tau-P domain for constrain-polygon picking.
If you are not happy with one result, try another module or mix them, create a complex workflow.
Create a new workflow 0500_Multiple_attenuation_(iteration_2):
Add all necessary modules to the workflow:
1. Read seismic traces - load traces after migration
2. Sort traces - sort traces by CMP
3. Seismic loop - process every sorted gather in a loop (one by one)
4. Radon multiple attenuation - remove multiples
5. Save seismic by gather - save seismic traces
1) Read seismic traces. Load seismic data set after migration 0480_Trim.
Parameters:
2) Sort traces. Sorting by CDP - offset:
Parameters:
Execute those modules.
3) Seismic loop. Put two modules inside: Radon multiple attenuation and Save seismic by gather.
4) Radon multiple attenuation.
This module transforms seismic traces into Tau/P (intercept time and slowness dt/dx = p) domain where we can easily separate multiples and primaries. Such separation allows to attenuate energy of multiple waves before reverse transformation into time domain (T-X). Basic idea is separation primaries and multiples by their velocity (moveout). Input traces are decomposed so hyperbolic events map to elliptical curves in Tau-P domain.
Input seismic gather must be sorted by Common Middle Point (CMP) - Offsets and the primaries should be flattened by applying Normal Move Out (stack velocity) correction before Radon transform. In this case the primary energy will be near P=0, which produces difference in moveout makes it possible to flatten the primary reflections while leaving the multiples under-corrected with a moveout approximately parabolic.
Slowness = 1 / Velocity
Model of CMP gather: 1) Time domain (T-X): Primaries+Multiples;
2) Tap-P domain: Primaries+Multiples:
3) Time domain (T-X): Primaries.
The module performs a model of primary and multiple events. This computation is based on data decomposition into user-defined parabolas and calculated by high-resolution algorithm, de-aliased least-squares method in the frequency space domain for every frequency of the pass-band which is defined by frequency min (Hz) and frequency max (Hz) parameters. Events corresponding to parabolas with a bigger curvature are considered as multiples. Events corresponding to parabolas smaller than this constrain are primary events. The area limits between primaries and multiples is user defined parametrization.
Parameters:
Minimum p-value for transform data from t-x into tau-p domain.
Middle p-value for transform data from t-x into tau-p domain.
This parameter is start for modeling multiple waves.
Maximum p-value for transform data from t-x into tau-p domain.
(Choose this parameter with care because run time for this process increases with the square of the number of P-values).
Amount of modeling waves.
Should be approximately equal signal response time interval.
Taper zone between P min/mid/max-values.
Taper zone between start time - filtered - end time.
Time varying reference offset for multiple modeling.
Time– time.
Reference offset– reference offset.
Minimum frequency for filtering
Maximum frequency for filtering
Pre-whitening factor for stabilizing tau-p to t-x transformation.
Apply automatic gain control pre radon filtering and remove after radon filtering.
Window for automatic gain control.
Execute the module and open all vista windows:
6) Save seismic by gather. Define an output file 0500_Demultiple2 name. Turn off difference calculations execute calculations for the entire data set.
Next step >>> Additional denoise.
If you have any questions, please send an e-mail to: support@geomage.com