| OpendTect User Documentation version 4.2 |
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Table of Contents
7.1. Create Seismic Output
7.2. Create Grid Output
7.3. Madagascar
7.4. Generic Mapping Tools (GMT)
7.5. Batch Processing
In this module any (attribute) volume can be calculated and saved to disk. This includes 2D attributes, but the output is a new volume in the selected Line Set. The volume output module can also be run in batch mode.
With this module attribute-, neural network-, or filtered data cubes can be created among others.
A lineset attribute can be created through the following procedure: Processing > Create Volume output > Attribute > 2D
A window pops up as shown below:
First, Select the output quantity.
Note that only attributes from the current attribute set can be selected in the "Select quantity to output" window. To output an attribute that is not specified in the current set, you must select the attribute set in the attribute module.
Optionally, a trace or individual line selection can be specified.
Optionally, the output can be scaled with a Shift and a Factor. The output will be calculated with:
output = Factor * input + Shift
Null traces can be discarded.
First, Select the output quantity. Optionally, a sub-volume can be specified, or when calculating 2D data, a trace or individual line selection.
Note that only attributes from the current attribute set can be selected in the "Select output quantity" window. To output an attribute that is not specified in the current attribute set, you must change the current attribute set (select the attribute module to do so).
Optionally, the output can be scaled with a Shift and a Factor. The output will be calculated with:
output = Factor * input + Shift
Null traces can be discarded.
OpendTect batch jobs for 3D volumes can be processed on a single- or multiple machines. One line only 2D jobs are always processed on a single machine. 2D jobs with multiple lines from the line set are automatically sent to the multi-machine processing mode.
For more information look at batch processing.
Storage:
OpendTect can store data internally in 8-, 16-, 32-, and 64-bit seismic data formats. 8-bit signed has a data range between -127 and +127. 8-bit unsigned ranges between 0 and 255. Similarly, 16-bit signed ranges between -32767 and +32767 (unsigned 0 - 65535). The data is stored in the same byte-format as the input by default (Storage is set to 0 - auto).
Adjust z range to survey range: With this option, the user can adjust his/her new scaled seismic to the survey range.
Optimize horizontal slice access: For better performance when loading time slices, set this option to 'Yes'. This compromises some speed in loading crosslines, but it loads time slices significantly faster.
Multi-components cubes for some attributes (e.g Spectral Decomposition, Steering attributes) can be created.
Create first your attribute in the attribute engine.
Create the volume output: Go to Processing > Create volume output > Attribute > 2D/3D, fill in the dialog, and press Proceed.
In case the attribute allows multiple-component output, specify the wanted components.
How to display the Multi Component Volumes?
Whenever the user will display a multi-component attribute volume on an inline/crossline, the component selection dialog box (below) will pop up. In this dialog a user may select one or more outputs to be displayed on the same section.
Once several components are selected and displayed for an element (e.g. an inline), the user only needs to place the mouse in the scene, and use the keyboard's PAGE-UP/PAGE-DOWN keys to view the next/previous slice in real-time.
for more detail.
To display any component of the cube, right-click on attribute in the tree > Select Attribute > Store Cubes
In case it contains more than one component, an extra dialog will appear (see image below) to allow the user to choose which one to display.
The user can also display more than one component as multi-texture.
Use the pageUp & pageDown to display all selected components.(here 5,15,30hz)
-->
The volume-builder window can be launched from Processing > Create Volume Output > Volume Builder. The following window will pop-up. The window is used to create the output volume that has been defined in a volume builder setup. Optionally, if the initial volume builder setup is not defined, press the Edit button to define the setup. Write an appropriate Output Cube name. In next step press proceed to launch a batch processing window.
Processing > Create Seismic Output > Time - Depth Conversion
Time-depth conversion is done by applying Dix's equation, based on a interval- or RMS velocity volume. Provide a velocity and input volume, and set the direction of the conversion.
This tool can be used to convert interval velocity volumes to RMS velocity volumes and vice versa. The conversion will be applied using Dix's formula. Please note that for this reason it can only be applied in the time domain.
Pre-stack processing can be applied using a number of methods. In addition to importing, this is the only module where pre-stack data can be output based on another pre-stack datastore in OpendTect.
Open the Pre-stack processing window: Processing > Create Volume Output > Pre-Stack Processing
The processing can be done by a number of sequential steps.
The following sections will describe the processing done by each step.
Mute functions may be applied to Prestack gathers. This window allows for setting the mute definition, as well as specifying settings such as:
- Mute type: Top or tail
- Taper length (in samples)
Automatic Gain Control is one of the processing methods available for Prestack gathers. It will adjust the amplitude level using a sliding window of defined size (window width). Optionally, part of the lowest energy may be discarded from the amplitude level computation (in percent of the amplitude distribution).
A Super Gather may be used to laterally stack the traces in order to increase signal-to-noise ratio of Pre-stack gathers. The stack is controlled by an inline/crossline stepout, and the Shape (Cross or Rectangle). The computation is similar to a (non-steered) volume statistics attribute with a zero time-gate.
This processing method computes and applies a mute function based on a constant incidence angle. See the processing method documentation. The only difference is that this method reads the offset range from the input prestack datastore, such that the user does not need to specify it.
The application of the computed mute function is strictly identical to the application of a stored mute function.
An advanced ray-tracer is available if the VMB plugin is installed:
Note that the options "Project incoming wave" and "Select spreading geometry" do not influence the output of the ray-tracing.
This processing method applies a normal moveout correction based on both a correction velocity volume as well as on the migration velocity volume. A hyperbolic moveout is applied (non-hyperbolic moveout will be implemented later). The migration velocity must be linked to the prestack seismic in the velocity model building window. Then RMO's are picked on the prestack gather and gridded into the correction velocity volume, or the correction velocity volume originates from a tomographic update of the migration velocities.
This module creates angle-based Z-Offset functions from velocity volumes. The primary input is a velocity model that provides the time-depth relation. The option "Block" can be used to reduce the processing time by extracting linear time-depth trends from the velocity model.
Vertical 1D ray-tracing is performed assuming a fully flat, isotropic earth model, and the source and receiver depth can be set.
The offset range must be provided since the angle mute computer is not aware of any prestack datastore. It does not necessarily need to match your prestack data anyway. The output function will have one point at the start and stop of the Z range, and one point at each offset specified by the offset range parameters.
The main output parameter is the angle a which the mute function must be performed. By default the functions will be computed on a relaxed grid, every 20th time the inline/crossline stepout. This can be changed by selecting other "Volume subselection" parameters. In general it is not necessary to decrease that stepout. Note that this processing is not yet a batch process.
An advanced ray-tracer is available if the VMB plugin is installed:
Note that the options "Project incoming wave" and "Select spreading geometry" do not influence the output of the ray-tracing.
Bayesian classifications are used to link several attributes based on one or several Probability Density Functions.
First, one or several PDF(s) need to be provided:
The user can then decide to normalize the PDF based on a priori weights per PDF. Optionally the a priori weights can be provided by attribute volumes which will vary at every sample location.
The processing will be based on (inverted) stored volumes that should correspond to the variables used for generating the PDF. Please note that OpendTect cannot make this check.
The Bayesian classification volume will generate two volumes:
- A probability volume "P:PDF name"
- A determination strength volume, mainly for QC.
Create a seismic output between two horizons. Select the quantity to output from the list of stored data or attributes. Specify the horizons that form the upper and lower boundary of the output volume. Optionally, an Extra Z interval can be added. The first field specifies the top of the time window, relative to the upper horizon, and the second field specifies the bottom of the time window, relative to the lower horizon. Subsequently, a sub-area can be specified.
The Value outside the computed area is the undefined value. The standard undefined value in OpendTect is 1e30, but the user can specify any value.
Optionally, an interpolation of the surface can be made. The interpolation can be full or partial. In the second case, only the gaps smaller than the number you specify are filled. You can choose adding a fixed Z interval length to the leading horizon when the second surface is missing or in case of conflict during the interpolation.
The calculation parameter file can be given any name (a default name is provided) so you can re-start the calculation process easily, should anything go wrong during the calculation. Pressing Proceed takes you to the next step, where you choose on which available machine you want to run the calculation process. More information on this window is provided in single machine batch processing.
Create a seismic output in a time interval relative to a single horizon. Select the quantity to output from the list of stored data or attributes. Specify the horizon and the Z range around this horizon. Optionally, a sub-area can be specified.
The Value outside the computed area is the undefined value. The standard undefined value in OpendTect is 1e30, but the user can specify any value.
Optionally, an interpolation of the surface can be made. The interpolation can be full or partial.
A calculation parameter file is automatically created with a default name in the Store Processing Specification field. This file allows you to re-start the calculation process easily, should anything go wrong during the calculation. Pressing Proceed takes you to the next step, where you choose on which available machine(s) you want to run the calculation process. More information on this window is provided in multi-machine batch processing.
A processing flow that has been saved can be re-started with this functionality. The parameter file that has been saved is opened and can be run again in single machine or multi-machine mode. Select the appropriate parameter file with the Select button.
