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Migration velocity analyses
This module performs 3D time migration of seismic traces before stack with different percentages of the velocity model. The number of PreSTM results calculated with different velocity models gives possibility to build an optimal migration velocity model. 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.
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.
Link to input seismic dataset
Link to sorted headers of the input seismic traces
Velocity model used for migration corresponding to 100%
Minimum offset for the common image gather
Maximum offset for the common image gather
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 CIG will 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 CIG plus the Offset step of CIG.
Migration 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.
Stretch muting for migration operator
Factor for managing the mute zone
Replacement velocity used to account for topography. Required parameter
Anti-aliasing filter coefficient. Increasing the coefficient produces astronger filter (low frequency for far offsets)
Maximum frequency of the output seismic data
Maximum angle aperture of the migration operator
Bin size along the inline direction
Bin size along the xline direction
Parameters for optimization disk operations for SSD drives
Factor for data decimation with preservation of offset-azimuth distribution
3D storage file for calculated database
BinGrid of input data
BinGrid of velocity model
2D storage file for calculated database
Arbitrary line for output geometry
Velocity factors to be used during migrations. 100% corresponds to input velocity model
Minimum velocity factor in percentage from input model, normalized to 1
Maximum velocity factor in percentage from input model, normalized to 1
Step in percentage between calculated velocities models
First inline to be calculated
Default: -1
Last inline to be calculated
Default: -1
First xline to be calculated
Default: -1
Last xline to be calculated
Default: -1
How calculation will be performed in case calculation steps bigger than 1. Logical AND calculation performed along inlines and crosslines with determined steps. Logical OR calculation performed in interception points with determined steps.
Default: logical AND
Step between calculated inlines
Default: 1
Step between calculated xlines
Default: 1