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Description
This module performs 2D/3D time migration of seismic traces before stack. The algorithm is a Kirchhoff integral trace migration where each sample is considered the top of coherent events of a diffracted wave followed by stacking the samples. In other words, Kirchhoff migration estimates diffracted amplitudes by correlating the input seismic data using a calculated model of the diffraction as it would appear if the image point consisted of a diffraction event. All dip and diffraction events are migrated into their real location. Diffraction waves are described by RMS velocities. The migration process is run in offset classes (user-defined parameters) and requires regularized input seismic data (that can be produced using the “Regularization” module). Gaps in the offset classes can cause migration operator artifacts. This module reads input seismic data directly from disk and it is unnecessary to load it to RAM.
Input seismic data are CMP gathers.
Output data are common image gather - CIG.
Execution options: standalone (1 computer execution) and remote (parallel/cluster execution).
Input data
SEG-Y data handle
Sorted headers of input data
Link to sorted headers of the input seismic traces
Vrms model
Link to sorted headers of the input velocity traces
Output geometry
Link to virtual trace headers which has geometry information for outputseismic traces migrated
By default the module defines output geometry from “Sorted headers of input data”
Input VTI model
Output file name
Full path and filename of output SEGY file
Dimension
Choose the dimension from the drop down menu.
V0 Map
Parameters
CIG/CAG
Choose the appropriate output gather type. Depending on the user preference, the final output gather will be either CIG or CAG.
Use variable offset model
If the offset is irregular, then the user can check this option.
Offset classes
Define the offset classes by clicking on the icon.
Migrate by pickets
This option is useful if it is a straight line where the source and receivers are falling on the same line.
Minimum offset CIG
Minimum offset for the common image gather
Maximum offset CIG
Maximum offset for the common image gather
Offset increment of CIG
Offset increment for the common image gather. Parameters Max offset and offset step can be used to limit the offset range of the input data. Cases where the Offset step of CIGis larger than the Max offset CIGwill produce only 1 offset class with the input data range equal to the Offset step of CIG. In cases where the Offset step of CIGis smaller than the Max offset CIG, the offset of the input data will be equal to the Max offset CIGplus the Offset step of CIG.
Examples:
Min offset CIG
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Max offset CIG
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Offset step of CIG
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Result
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0
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1000
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2000
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Produces a migrated stack section for data up to 2000m
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0
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2000
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1000
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Produces a CIG with 2 offset classes: 0 and 2000, the max offset used in migration will be 3000m
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Aperture
Migration aperture
Aperture type
Choose the aperture type. i.e. Constant or Time variant
Time-aperture factors
If the aperture type is Time Variant then the user should provide the values here.
Side aperture
Distance (meters) from the survey edge. Aperture value will be linearly increased (from 0 to maximum) in this offset range from the edge. Use this parameter to minimized migration operator artifacts along the survey edge
Use stretching factor
Stretching muting for migration operator
Stretching factor
Factor for managing the mute zone
Replacement velocity
Replacement velocity used to account for topography. Required parameter
Anti-aliasing coefficient
Anti-aliasing filter coefficient. Increasing the coefficient produces a stronger filter (low frequency for far offsets)
Max frequency
Maximum frequency of the output seismic data
Max angle aperture
Maximum angle aperture of the migration operator
Use Regularization Weights
By default No. Choose the available options from drop down menu.
Velocity factor
Velocity multiplier. By default 1 is used. (100% velocity field used)
Use Vrms map
By default FALSE.
Cmp interval along inline
Bin size along the inline direction. Meters
Cmp interval along crossline
Bin size along the crossline direction. Meters
Decimation factor
Define the decimation factor. It is 1 by default i.e. no decimation.
VTI
By default FALSE. If user provides the VTI model in the Input data tab, then it should be checked.
Boost-factor
Define the value to increase the performance run time so that it will take less time to finish the migration without compromising the quality of the final output.
Normalization by fold
Choose the normalization type from the drop down menu. By default None.
Normalization by VRMS
Advanced
3D grid define
Switch on this option for grid definition. Simplifies search for seismic data within the aperture range. By default the module defines it automatically
Input data bin grid
Link to virtual trace headers which have geometry information for the input seismic traces
Migrate all trace_types traces
By default FALSE. If user checks this option, it will migrate all the trace types.
Settings
SegyReadParams
Execute on
Choose the available options i.e CPU or GPU
Distribution options
Distributed execution
In case the job needs to be executed in parallel/cluster mode, the user should check this box.
Bulk size
How to calculate “Bulk Size” parameter within migration module
GRT- is parameter of GPU RAM TOTAL
For example, if RAM value is 11.2 GB, we will use only 10GB as 1GB of RAM is used by others processes
GRA– is parameter for GPU RAM AVAILABLE
For example, if RAM is 10 GB, the parameter value will be calculated as following:
10 * 1024 * 1024 * 1024 = 10737418240 (size in bytes)
Data parameters:
NS– indicates number of samples (for example, 2000 samples)
MinOFF– indicates the minimum offset of CIG (for example, 0m)
MaxOFF– indicates the maximum offset of CIG (for example, 10000m)
StepOFF– indicates the CIG offset step (for example, 200m)
TCIG– indicates the number of traces in one CIG, this parameter is calculated as following:
TCIG = (MaxOFF – MinOFF) / StepOFF, for example (10000-0)/200=50
CIG_B– indicates the size (in bytes) of a single CIG, this parameter is calculated as following:
TCIG * NS * 4, for example 50*2000*4=400000bytes
MAXIMUM BULK SIZE– is an optimal parameter for PSTM calculation, this parameter is calculated as following:
MAXIMUM BULK SIZE = GRA / CIG_B,for example 10737418240/400000=26843.5456 – this number indicates the maximum bulk size.
Please note, from common practice, it’s better to round this number down, use 26000
Comments
Input seismic data must be regularized and without gaps in the offset classes. You can use the “Regularization” module to do this. The input velocities should be smoothed.
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