Description

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.

Input data

SEG-Y data handle

Link to input seismic dataset

Sorted headers(of seismic data)

Link to sorted headers of the input seismic traces

Vrms model

Velocity model used for migration corresponding to 100%

Parameters

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 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.

Aperture

Migration aperture

Use full CMP aperture

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

Stretch muting for migration operator

Stretching factor

Factor for managing the mute zone

Replacement velocity

Replacement velocity used to account for topography. Required parameter

Antialiasing coefficient

Anti-aliasing filter coefficient. Increasing the coefficient produces astronger filter (low frequency for far offsets)

Max freq for RHO

Maximum frequency of the output seismic data

Max Angle Aperture

Maximum angle aperture of the migration operator

Cmp interval along inline

Bin size along the inline direction

Cmp interval along crossline

Bin size along the xline direction

SEG-Y read parameters

Parameters for optimization disk operations for SSD drives

Decimation factor

Factor for data decimation with preservation of offset-azimuth distribution

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3D

Storage file 3D

3D storage file for calculated database

Input data BinGrid

BinGrid of input data

Velocity data BinGrid

BinGrid of velocity model

2D

Storage file 2D

2D storage file for calculated database

Arbitrary line (2D)

Arbitrary line for output geometry

VelFactor

Velocity factors to be used during migrations. 100% corresponds to input velocity model

Min Velocity factor

Minimum velocity factor in percentage from input model, normalized to 1

Max Velocity factor

Maximum velocity factor in percentage from input model, normalized to 1

Velocity factor step

Step in percentage between calculated velocities models

Calculation area

First inline number(-1 no limit)

First inline to be calculated

Default: -1

Last inline number(-1 no limit)

Last inline to be calculated

Default: -1

First crossline number(-1 no limit)

First xline to be calculated

Default: -1

Last crossline number(-1 no limit)

Last xline to be calculated

Default: -1

Calculation rule

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 along inline number

Step between calculated inlines

Default: 1

Step along crossline number

Step between calculated xlines

Default: 1

Settings

Execute on

Distribution options

Distributed execution

Bulk size

Number of threads

References

Schneider, W. A., 1978, Integral formulation for migration in two and three dimensions: Geophysics, 43, 49-76.