Usually, seismic data QC includes amplitude and frequency calculation for particular time windows per trace, and seismic processing geophysicist should evaluate the data. Therefore, evaluation consists of creating trace editing set (or library) for quantitative estimation as well as showing QC graphs, maps and schemes to clients. This chapter is spitted into two main parts:

1.Seismic data QC;

2.Trace editing.

SEISMIC DATA QC

Seismic data quality control is a special step in processing sequence where geophysicist should analyze new field seismic or legacy data sets. QC seismic attributes calculation is required for a current task. In g-Platform there are following modules for QC attributes calculation and visual estimation:

•QC Attributes;

•QC Attributes calculator;

•Seismic Instantaneous attributes;

•Signal to Noise ratio;

•Spectral Analysis.

The main module for QC is QC Attributes, so we are going to use it.

Create a new workflow 0020_Seismic_data_QC_and_trace_edtinig, open it.

QC Attributes module works with pre-stack and post-stack data sets. It is designed to display color maps of various calculated attributes, alongside a frequency spectrum. The attributes are calculated inside the area defined by the analysis window and inside the noise analysis window. In production seismic processing sequence it is usually when geophysicist should calculate and produce qualitative analysis of the following list of QC attributes: Signal Amplitude, Noise (microseism) Amplitude, Signal to Noise Ratio, Dominant Frequency, Spectrum Width.

Add all necessary modules for the first part. Connect input and output data items sequentially:

1. Read seismic traces

2. Select traces

3. Sort traces

4. QC Attributes

1) Read seismic traces. Load seismic traces from the previous step 0001_Geometry, because this data set has offset values which are required for window definition in QC attributes. Execute the module. There is no need to load seismic data into a RAM, because QC Attributes module is able to perform calculation without keeping the entire data set in memory. Define an input data file after geometry step:

Parameters:

2) Select traces. This module allows us to select traces that meets the given condition. Teapot 3D data set contains bad source gather (merged), therefore we need to remove it by using selection option. Connect an input DataItem (trace headers) and define selection condition:

Input data:

Parameters:

3) Sort traces. QC attributes module requires offset sorted data, so OFFSET is a secondary key in Sort traces module:

Input data:

Pay attention that you should select included traces after Select traces procedure:

Parameters:

4) QC Attributes. This module calculates many seismic attributes, so it is reasonable to choose only that we really need. Remove unnecessary picks in the check box list:

Input data:

Parameters:

Open vista windows for this module, look at gather and define windows for analysis by setting parameters in the module or use mouse for drawing qc windows:

and other parameters:

If we need to export QC attributes, use Save attributes to header parameter: add some traces headers -> click on Save attributes to headers function in the modules Action menu.

There is an option for hyperbolic window definition: change Window type parameter to a Hyperbolic one, adjust signal and noise window:

Also, there is an extra interactive option for defining window parameters: we can draw QC windows and its parameters will be updated automatically:

Make sure that you have selected appropriate domain: Prestack or Post stack. Execute the module and check results on the location map. Click on icon of the Location map window. Look at the View Properties window, here we can see all the attributes that were generated by QC attributes module. User should select/unselect the box to display the respective attribute maps.

We can choose any point from the location map by left mouse button (LMB) clicking on any source point and gather view will be updated immediately:

  Now we finished with attributes calculation and there is a last point: save pictures for presentation. Use the screenshot function/button :

         TRACE EDITING

This is an extra chapter, because we are going to test denoise modules for all kind of noise, so you can use trace editing in your current training project or not. Trace editing is also one of the key step in seismic data processing. It should be better to do at the initial stage (preferably). G-Platform provides manual and auto trace editing approaches. 

                      AUTO EDITING                      

Auto trace editing approach is one only method that is used in seismic processing today, because of huge amount of seismic traces in modern survey acquisitions, as well as shortage in processing time. QC attributes per trace is used for auto trace editing in g-Platform system. This module is based on QC Attributes module, because the basis is seismic attribute calculation and estimation. The QC attributes per trace module calculates necessary types of attributes per trace like RMS amplitudes, Mean amplitudes, Dominant frequency and other. User should analyze those values and create selection equation for auto trace editing. For example, we can remove zero traces or low amplitude traces, remove harsh/high amplitude noisy useless traces, sources, receivers  and so on. Many seismic attributes and complex user's equations will lead to a flexible and successful auto trace editing workflow. All seismic attributes are saved into trace headers on the output data set and we can use these trace headers for further selection equation via Select traces module. Therefore, we need to use both modules for auto trace editing:

1) QC Attributes (calculation);

2) Select traces (selection).

The list of trace headers and their equivalents of calculated attributes:

•   MAXIMUM_AMPLITUDE: Maximum amplitudes;

•   MINIMUM_AMPLITUDE: Minimum amplitudes;

•   MAXIMUM_ABS_AMPLITUDE: Maximum abs amplitudes;

•   MINIMUM_ABS_AMPLITUDE: Minimum abs amplitudes;

•   RMS_AMPLITUDE: RMS amplitudes;

•   AMPLITUDE_ARITHMETICAL_MEAN_ABS_VALUE: Amplitudes arithmetical mean abs value;

•   STANDARD_DEVIATION: Amplitudes standard deviation;

•   DOMINANT_FREQUENCY: Dominant frequency (RMS);

•   FREQUENCY_RANGE: Spectrum width;

•   MEAN_FREQUENCY: Mean frequency;

•   SIGNAL_NOISE: Signal/Noise RMS;

•   SIGNAL_NOISE_AMPLITUDE: Signal/Noise amplitudes.

The example of the workflow for auto trace editing:

Parameters for QC attributes per trace module:

Execute the module and open all vista groups:

Analyze high values for further removing:

After execution we have output trace header vector as result with new headers (attributes) that were chosen for calculation. So, the next step is using those headers for selection creation.

Add Select traces module and define and necessary parameters as shown below:

Lets select bad traces which have harsh RMS amplitude values. For selection you can use free-expression (example below) or expression by table.

Define selection expression as shown below and execute the module:

Check statistics in the Information tab. So, 798 traces were selected as bad traces and we can look at them:

Use Seismic loop for checking bad traces. Get the output trace headers vector from the Select traces module and use location map and gather view from Seismic loop for analyzing bad traces as shown below::

If we satisfied there is a last step: write good traces into file. Use seismic loop also, you just need to change the expression in Select traces module for selection good traces:

Check the output trace statistic again:

Execute Seismic loop for the entire data (press button from upper menu):

You can create two gather views: before and after auto trace editing, by using two Seismic loop modules:

Notice that you can create complex expression by merging several selections:

                    MANUAL EDITING                  

There are two modules for manual editing: Kill empty traces and Geometry application module. In Geometry application module there are three main functions that we need:

1. Trace killing/Dead traces

2. Polarity reversal

3. Auxiliary trace marking

Trace removing: In order to perform this task, the user should make sure that the geometry is already assigned to the input gather. Once it is confirmed, within the Geometry application, go to the Gather source view window and click on Control item  for options. Select Dead traces source option as shown below and follow the steps as described. 

1. Add the trace header TRACE_TYPE. Prior to the trace kill,  TRACE_TYPE of the seismic data is 1 however after marking the trace as dead/kill, TRACE_TYPE changes from 1 to 2 which eventually updates the trace header information. 

2. To kill/dead any trace in the current shot gather, the user should hold LMB or MB1 and drag the mouse to select N number of traces and release it. It will draw a horizontal line as shown below. Upon releasing the mouse, it will mark these traces as Dead by color code Black (By default) and update the from 1 to 2. 

3. To edit more traces, the user should go to next shot and continue the same procedure to kill/dead the traces. 

4. To reverse the trace kill/dead, the user should hold and drag RMB/MB3 to overwrite the updated trace headers information i.e. TRACE_TYPE from 2 to 1. 

 Please make a note of it that upon marking the traces for killing/dead, DO NOT execute the Geometry application module again. It will overwrite your current changes and put them back to the original trace headers information. It is applicable to all trace editing i.e. trace killing, trace reversal and auxiliary traces. 

Polarity reversal: To reverse the polarity of any particular trace can be done similarly like the trace kill. Instead of choosing Dead traces source, the user should select Inverted trace source. Prior to the trace reversal, it is advised to change the trace display from Variable Density to Wiggle and Zoom the shot gather to a certain extent to observe the changes.

Similar to the trace kill/dead, the user should follow the same procedural steps to mark the traces for trace reversal. Selected traces are marked as YELLOW (by default) in color. 

If you have any questions, please send an e-mail to: support@geomage.com