Description

Stereo tomography is based on Ray tracing. The basis of the Stereo Tomography concept is to recognize any locally coherent events characterized by their travel times and local slopes (two slopes) in the prestack data to provide some information about velocity model. (Stereo tomography: Past, present and future - Gilles Lambaré). The locally coherent events can be interpreted as pairs of ray segments and provide the velocity information independently.

How it works?

A stereo tomographic dataset consists of locally coherent events parametrized by source & receiver positions, travel time and slopes of the events in the common shot and receiver domain.

This module is used to generate the updated velocity models. We generate the Tomo items from the PSDM Imaging module. Within the PSDM imaging module, we have "Create tomo parameters" action items and it will create the Tomo item for Stereo Tomography as an input.

Input

Tomo Item full

Fixed constraints horizons - This is optional

Fixed constraints polygons - This is optional

Output

Updated depth velocity model. By using Save seismic by gather module, the user can save the final updated velocity model for next iteration or can be used as a final velocity model.

In the "create tomo params" of PSDM Imaging module, the user should provide the First Step X(meter), Step Y(meter) & Depth (meter). This is important and the size shouldn't be big number otherwise it will thrown error of "Bad allocation" while running the Stereo tomography.

Connect/reference the Tomo item to PSDM Imaging -> Tomo item

Connect/reference Initial velocity or Stack (for Geometry) to Read seismic traces (here the user can read either velocity model or stack for geometry purpose)

Connect/reference Trace headers to Read seismic traces where the velocity/stack is read.

Input data

Tomo item full

Connect/reference the Tomo item full to PSDM Imaging -> Tomo item full

Fixed constraints horizons

In case the user wants to use the horizons as fixed constraints then connect/reference the horizons from the PSDM Imaging module to Output horizons

Fixed constraints polygons

If the user wants to use the polygons, then connect/reference the polygons from PSDM Imaging module to Output polygons.

Parameters

Tomo file name

Use side constraint

Use Init Velocity

By default TRUE  however if the user check this option as TRUE then the user can ignore the InitialVelocityMin and V0(Velocity) & InitialVelocityMax(Velocity). It is always better to use this option as checked.

Use gather constraints

Layer constraint

Layer from

Here the user can select the layers from the available drop down menu.

Layer to

Similarly the user can select the layer from the drop down menu for the bottom layer.

Use layer constraint

If the user wants to use these layers as constraints in stereo tomography then it should be checked.

Salts collection

Datum

Define the datum value.

Velocity from topo to datum(0 - don't fille)

Global iteration count

Define total number of iterations to be carried out. By default 3

Time step

Localization iteration count

Joint inversion iteration count

Define the inversion iteration count. By default 5.

Regularization weight

Outliers threshold

Outliers start

Maximum depth

InitialVelocityMin and V0

Provide the initial velocity value. This will be the starting gradient value

InitialVelocityMax

Provide the maximum velocity value. This will be the maximum gradient value.

InitStepX

This is the initial step in X direction which considers the pickets in the X direction. By default 1200

InitStepY

This is the initial step in Y direction which considers Depth in the Y direction.By default 400.

Adding bound size(samples)

OutputDZ

Calc Alter cost

Sealing Factor

By default 0.5. This value defines the InitStepX & InitStepY values in the subsequent velocity iterations.

We have 3 global iterations and 5 joint inversion iterations. So in total we'll have 15 iterations. Now these 15 iterations are generated initially with 1200 & 400 as the Initial Step X & Y parameters. So we will have

Iteration1-1200-400

Iteration2-1200-400

Iteration3-1200-400

Iteration4-1200-400

Iteration5-1200-400

Now with the sealing factor of 0.5, Step X 1200 becomes 600 and Step Y 400 becomes 200

Iteration6-600-200

Iteration7-600-200

Iteration10-600-200

Similarly Step X 600 becomes 300 and Step Y 200 becomes 100.

Iteration11-300-100

Iteration15-300-100

Smooth Model Factor

LSQR parameters

Conlim

Percitnlim

Min vertical shift

Max vertical shift

Create sub models

Path for Depth Models

Provide the path for output depth velocity models

Tomo item read params

Maximum points

Here the user can limit the total number of tomo item points to read. In case there are too many tomo item points and we need to limit then this where the user can limit it.

Min angle

Max angle

Leave/Remove event

Factor