Seismic Data Processing Using VISTA 2D 3D

VISTA® 2D/3D Seismic Data Processing

Geophysical Exploration & Development Corporation 1

1200, 815 – 8th Avenue SW, Calgary, AB T2P 3P2 Canada Tel: +1 (403) 262-5780 Fax: +1 (403) 262-8632 E-mail: [email protected]

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VISTA® 2D/3D Seismic Data Processing

Version 10 Course Notes

February 2011 - Houston

2 www.GEDCO.com VISTA® 2D/3D Seismic Data Processing

VISTA® 2D/3D Seismic Data Processing www.GEDCO.com 3

Contents:

Contents Contents: .....................................................................................................................................3 Introduction: ...............................................................................................................................5 A 2D Land Straight: ............................................................................................................7

A1. Create a project: .........................................................................................................7 A2. Geometry setup: ....................................................................................................... 11 A3. Sorts: ....................................................................................................................... 19 A4. LMO velocity definition: ......................................................................................... 29 A5. First breaks: ............................................................................................................. 33 A6. Time gates: .............................................................................................................. 41 A7. Signal analysis: ........................................................................................................ 45 A8. Header window: ....................................................................................................... 51 A9. Trace statistics: ........................................................................................................ 55 A10. Header Mapping: ..................................................................................................... 63 A11. Attribute window: .................................................................................................... 67 A12. Create a flow: .......................................................................................................... 69 A13. Mute function: ......................................................................................................... 73 A14. Refraction and elevation statics: ............................................................................... 75 A15. Apply the statics to the headers: ............................................................................... 85 A16. Scaling:.................................................................................................................... 87 A17. Surface consistent Deconvolution: ........................................................................... 90 A18. Attenuation of surface noise (ground roll): ............................................................... 95 A19. Time Variant Spectral Balancing: .......................................................................... 101 A20. Velocity analysis: .................................................................................................. 103 A21. Brute stack: ............................................................................................................ 109 A22. Plot parameters: ..................................................................................................... 111 A23. Residual statics: ..................................................................................................... 115 A24. Second Velocity Analysis: ..................................................................................... 117 A25. Stack after two passes of residual statics: ............................................................... 119 A26. Common receiver stack:......................................................................................... 123 A27. Trim Statics: .......................................................................................................... 125 A28. Attenuation of random noise: ................................................................................. 129 A29. Poststack migration: ............................................................................................... 131 A30. Prestack migration (PSTM):................................................................................... 133


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Introduction:

First developed in Canada in 1985, VISTA® is among the industry’s fastest selling 2D/3D Seismic Data Processing software package. VISTA® which was the market’s first PC-based seismic data processing software is also available for the LINUX environment.

It delivers proven algorithms for optimal quality control of seismic data in the field or the office.

VISTA® provides robust algorithms for Land, Marine and VSP processing and offers intuitive flows for complete seismic data processing. By taking advantage of VISTA®’s flexibility, reliability, and ease of use, processors increase their efficiency while maximizing the dependability of their results. VISTA® is available in four modules, 2D/3D Field QC, 2D/3D Field Processing, and 2D/3D Full Processing, and VSP.


A 2D Land Straight:

A1. Create a project:

A1.1 Inside your ‘Work Directory’ ……. create a folder and call it ExerciseA. Open Vista and create a new project 2D Land Straight Line inside the ExerciseA folder.Copy the file SHOT20.SGY from the vista ‘2D Land straight Line’ Tutorial directory to the ExerciseA directory (By default you can find this file in a directory such as: C:\ProgramData\Vista10\Tutorials\2D Land Straight Line). Or contact [email protected] for other ways to get the files needed for the exercises of this course.


The Project Data List window will pop up after clicking OK. This window contains the current

list of seismic datasets in Vista format. It will initially be empty until you import SEGY/SEGD/SEG2 files to the project or create data through a flow command.

A1.2 Create a new seismic dataset in the project, click on the new 2D seismic Data icon ( )

A1.3 Import a seismic dataset in SEGY format into the NEW 2-D DATA object. Click on ,

hold down, and then select .


Find the file SHOT20.sgy and open it. Take a look at the different tabs to control the

input in the Input SEG-Y Seismic Data File(s) dialogue. Click OK. The Transfer Header Info Seismic window will pop up when the input s done. It contains the range values for all the headers in the Vista file, these headers are defined by the project dictionary.

A1.4 A1.4 Close this window. To get this window back open it by clicking on , in the seismic object in the Project Data List window.


A2. Geometry setup:

A2.1 Click on in the SHOT20 dataset to open the Geometry window.

(The Project Data List window can be started from the main menu: Project/Project Data List).

Alternatively the Geometry window can be found in the main menu: Interactive/Geometry Window Display.

Hit Load to load the information from the headers of the dataset to the Geometry Window

After the loading process is done the shot spreadsheet will be displayed. The number between

brackets in the first column is the number of traces of the shot. Take a moment to get

familiar with the different columns of this spreadsheet. Then click on to see the


receiver spreadsheet.

In the receiver spreadsheet the number between brackets in the first column is the distance between the current station and the next one. (To come back to the shots spreadsheet

click on ). The next section (A2.2) presents the different options to edit these spreadsheets. Now, to set up the geometry you need to go through the following steps

1. Define the nominal geometry parameters, click on


2. Define the bin grid

3. Calculate fold and offset, click on .

Now the geometry is setup. Use the icons to create the following figures


To finish the process, save the geometry to the trace headers. Left click on , hold down

and then select the second subicon , write binning info to headers.

A window with a list of all the headers that will be overwritten with the information existing in the geometry window will pop up. (The other subicons can be used to save the geometry into external files in different formats, save the geometry in at least one of them, for example the SPS format). Click OK. To return to the previous view of the Geometry window click on

the upper left icon . Close the geometry window, click on the discard button, the geometry information will be discarded from the geometry window but it was saved to the headers, so it can be reloaded from the headers if necessary.


A2.2 Exercise (Edit the geometry spreadsheets)

This exercise is to get familiar with the editing tools of the Geometry Window. The exercise consists on creating the geometry of a prototype seismic line. The line is made up of 10 shots and 20 receivers with a station interval of 20 m. The spread is symmetrical and the shot stations are located on the middle points between receivers. Create a new 2D seismic object in the Project Data List. Change the name of the NEW2-D DATA to Flatland

Left click on the icon of the Flatland dataset. Click on cancel in the dialog that pops up. The empty shot spreadsheet will be displayed.

Click on , hold and select the first subicon ( ) to append one row.


Modify the DEF INCR row and the first raw of the spreadsheet with the values shown in the next figure

Left click on , hold down and select the second subicon ( ) to append nine rows.

Go to the receiver spreadsheet, by clicking on

Modify the DEF INCR row and the first raw of the spreadsheet with the values shown in the next figure


Click on , hold down and select the second subicon ( ) to append 19 rows.

There are options to select a range of cells and perform mathematical operations on them using the mathematical tools associated to the icons

Feel free to experiment with these options. Use the shift and ctrl keys and left click to select cells. Repeat the steps a, b, and c of the previous section (A2.1) to set up the geometry. Plot the stacking chart, the fold diagram and the surface view of the line


Save the geometry as SPS files, by left clicking on , holding down and selecting the SPS icon. Notice that this time does not make sense to save the geometry to the headers because the geometry work has been done on an empty dataset.


A3. Sorts:

A3.1 In the Project Data List window click on in the SHOT20 dataset to open the Seismic Window Display. It can also be opened from the main menu: Interactive/ Seismic Window Display.

The first 240 traces of the dataset will be displayed. The traces are displayed in the same sequence as they are stored in the file. Use the bottom scrollbar to go through the rest of the dataset. Notice that the top scrollbar is inactive at this point. Type ‘d’ on the keyboard. The dead traces will be displayed.

Type the ‘a’ key of the keyboard. An AGC will be applied to the display.


Sort the data in different ways using the icon of the vertical toolbar. Click on , hold

down and select the subicon to sort your data into shot order. Only the first shot gather of the line will be displayed. Use the top scrollbar to go through the rest of the shot gathers. Notice that the bottom scrollbar is inactive now; it would be active just if the number of traces in the gather were greater than 240, which is the maximum number of traces that can be displayed in the seismic window by default. In section A16 it is shown how to change plot parameters.

At the lower right corner of the display the note: is displayed. Double click on this note to open a list of shot gathers with some useful information.


Select a shot from the list to be displayed. Double click on number 10 for example:

This is shot number 10, located at the station 162, recorded in FFID 10 with 120 traces. Observe the ground roll present in this gather. Type the ‘f’ key to apply a filter. Type ‘f’ again to take the filter out.

Click again on in the vertical toolbar, hold down and select the subicon to sort the dataset into receiver order. Again use the top scrollbar and the note at the bottom of the display to surf through the receiver gathers of the line. Find out quickly how many receiver gathers are

there in the line!. Repeat the process with the subicon for CMP order.


Click on in the vertical toolbar, hold down and select the subicon. The list of all the existing sorts for this dataset will be shown using this option.


By default Vista creates these 4 sorts for any new 2D unstacked dataset. Use the last sort subicon

to create a new sort that is not in the list, .

Create for example Channel sort. Use the scrolling list of header words at the rigth of the Main sort and Secondary Sort Keys to change the dialog as follows


. Click OK, the data in the window is sorting and the channel 1 gather is now displayed. How many gathers were created in this sort? How many traces per gather? Locate channel 77, type ‘Shift+D’ to change the display type to Variable Density, use ‘Shift+V’ to come back to Variable Area+Wiggle, try also ‘Shift+A’, ‘Shift+W’, ‘Shift+E’ and ‘Shift+I’.


Go back to the sort subicon

Notice that the channel sort has been appended to the list of existing sorts of this dataset.


The existing sorts of any dataset can be modified in the Project Data List. Go to the Project Data List (minimize the seismic window to find it behind, or go to the main menu: Project/Project Data List).

In the lower panel of this window there is useful information about the highlighted dataset (in blue). The first tab corresponds to the sorts defined for the current dataset. To modify a particular sort double click on the SORT# cell of the sort. For example, to modify the Channel sort, close the seismic window and then double click on the ‘5’ cell


To update any change in the parameters definition of the sort use the icon to create or

recreate all the selected (red highlighted) sorts of the list. The icons can be used to add and delete sorts.

Finally the default list of sorts can be modified in the main menu: Project/Sort Defaults. The sorts defined at this location will be created for any new dataset added to the Vista project.


A4. LMO velocity definition:

A4.1 Open the seismic window display of the SHOT20 dataset. (By left clicking on its icon in the Project Data List or from the main menu: Interactive/Seismic Window Display).

Sort by shot and then apply offset mode display by left clicking on the icon in the vertical tool bar. Select shot 12, using the top scrollbar or from the shots list. Type ‘a’ on your keyboard to apply AGC to the display.

Zoom in on the time axis between 0 and 800 ms.

Click on the icon in the vertical toolbar to change the Display mode to Offset


Left click on the icon in the vertical tool bar, to start to pick a LMO velocity. On the right side of the spread define a LMO velocity by picking a few points on the first breaks (minimum 2) that best define the slope of the first breaks, double click to finish. In this example is easy to see one break in the slope of the first breaks (3 points is optimum, pick them on the right side of the spread). After clicking on OK an LMO function for this dataset will be defined. This is a short line and there are no important surface velocity variations, so this LMO velocity function is representative of the whole line. In cases where there are significant surface variations it might be necessary to pick LMO velocity functions in a few shots along the line that represent the range of variations along the survey. Vista will interpolate the LMO velocity function for the whole survey.

Click on the upper left icon to quit the LMO picking mode. As a result of picking and LMO velocity function Vista compute theoretical first breaks (TFB) for each trace. Type the ‘t’ key to display them.


To change the appearance of the TFB right click on the seismic traces and selecting the Theoretical First Break Display option.

For example change the color of the break to green and the size to 5 Right click on the shot numbers on the top annotation and select the option Display shot position. You will see a red flag at the source location.


Hit the ‘l’ key to apply LMO to the data based on the LMO velocity just defined.

Go shot by shot checking the geometry with respect to errors in the source coordinates using this method. Sort the data in receiver order to check the receiver locations. There are more ways to check the consistency of the geometry in Vista. In later exercises some of them will be illustrated.


A5. First breaks:

A5.1 In the Seismic Window Display of the SHOT20 dataset, sort by shot and then left click on

the icon in the horizontal tool bar. Hit the “t” key to hide the theoretical first breaks if they are currently displayed. Go to one of the shots in the middle of the line. Zoom in vertically to see the first 800 ms of data.

Left click on the icon to define options for the picking process. Try first without using LMO function. In this case, the Search window starts at zero and goes until the size of the window. Use a Search window of 800 ms, to include the FB for all the traces. Try a sliding window of 40, this parameter needs to be tested and depends on the frequency content and signal to noise ratio of the data. The amplitude of the RMS is computed inside this window, the window moves one sample at a time, and the ratio between the RMS values of two consecutive windows is taken, the FB is picked from the graph of this ratio.


With the parameter values shown in the last figure pick the FB of the current record by left

clicking on the icon.

These parameters seem very good for the record except for the short offsets. Use them to pick all the records by left clicking on the icon.


Use the Display tab of the Options dialog to change the appearance of the FB.

Now correct the short offset FB. Left click on icon, go to the Offset range tab and set up the dialog as shown in the next figure


Now go to the FBP options tab and change the SEARCH window to 100.

Click OK. Left click again on the icon to test the parameters on the short offset FB of the current record. Then correct the rest of the records using the icon.

To QC the FB left click on the icon to create and XT plot


Each panel corresponds to an XT plot of the FB for a shot. As there are 20 shots in the line there are 20 panels. The color of the panel represents the standard deviation of the picks. This plot is a powerful geometry QC tool, if the FB were picked without LMO function, because the horizontal axis contains the geometry and the vertical axis the first arrival times picked from the data. Any relevant geometry error will be detected in this plot, as well as any gather with lower signal to noise ratio. A receiver domain version of this XT plot can be created by left clicking on the icon in this window.

As there are many receiver gathers is better to zoom in on the horizontal axis to see just a few panels at a time. Use the scrollbar to go through the panels.

Now go back to the shot domain XT plot, click on , and tile vertically the windows using the main menu: Window/Tile vertically to get the following display


Minimize (or close) the extra viewed windows and then repeat the vertical tiling Windows/Tile vertically, if there are more windows open than the two of the previous figure. Right click on any of the panels and select the first option Broadcast Record

Immediately the same shot will be shown in the seismic display. To make some manual adjustments to any of the picks, use the Based on search type option, as shown in the next figure,

and then click on the icon. Click on the traces to define the new position of the pick, and use shift+left click to delete picks. The pick will still be forced to be at the closest peak, to get more freedom to locate the pcik turn off the ‘Use Search Mode on Manual Pick’ option.


Now pick the FB using the LMO function. To do this first delete the current FBs. Left click on to delete the FB for all the traces in the dataset.

Then go back to the options dialogue (click on ), turn on the Use LMO function when Auto-picking option and go back to the Sliding Win/Treshold option for FB Pick Method. Also go to the Offset Range tab and uncheck the option Limit FB Pick by Offset. In the next figure both tabs of the dialogue with the correct parameters are shown.

Click OK and test the parameters picking the FB first for the current record, , then pick the

breaks for all the records . Notice that at using the LMO function to guide the search, the search window needed is shorter because is measured around the theoretical FB. Generally is easier to pick the FB using the LMO option as long as the LMO function is correctly defined (the theoretical FB are close enough to the real FB), the Search Window is long enough, and especially, there are no relevant geometry problems. To finish this exercise display the FB and the TFB simultaneously on one shot. Type ‘b’ and ‘t’ to turn off and on the real and theoretical FB respectively, in the display. Then plot the XT plots both in the shot and receiver domain


Close the XT windows and Use the icon in the Seismic Window Display to return to the main tool bar.


A6. Time gates:

A6.1 Time gates are used in Vista for multiple purposes, for example for amplitude statistical analysis, scaling and deconvolution. For these tasks usually it is necessary a time gate containing the best reflection signal of the data. To prepare the data for picking the time gates open the seismic window display of the SHOT20 dataset. Sort by shot and then

apply offset mode display by left clicking on the icon in the vertical tool bar. Select shot 12 (or any shot with enough live traces in both sides of the spread), using the top scrollbar or from the shots list. Hit ‘a’ to apply AGC and ‘f’ to apply and Ormsby filter.

To create the gate use the Define (Pick) Time-Gates icon, . Define the upper and the lower limits of the time gate. Use the keys ‘b’ and/or ‘t’ to turn the FB off if they are on the display.

To define the top limit, left click on .

Then define the top limit below the refractions and above the best reflection events that can be detected. Left click on a few locations to define control points, usually three points are enough.


Then quit the picking mode by left clicking on the upper left corner icon , and repeat the process to pick the bottom limit selecting the icon .

Quit the picking mode and save the time gates into a file with a name such as ‘signal’ using the

icon. Use the icon to return to the main tool bar.

Create a new time gate with only top limit defined: Click on to delete the current window.

Define the top window as in the previous time gates, the top limit should be immediately after the refractions, the purpose of this window is to use it later in a processing step in which and AGC function will be applied internally. This top defines the time at which the AGC function will start to be applied to avoid a shadow effect due to the high amplitudes of the refractions.


Save the gate with the name TVSB.


A7. Signal analysis:

A7.1 There are many tools in Vista to apply signal analysis on the data. Some of them can be

accessed by clicking on the Seismic Analysis Window icon, , in the Seismic Window Display. Take a look to the list of functions to perform signal analysis.

Select from the list Frequency Analysis Window, and then left click on . Hit OK in the phase spectrum. Left click on the icon to see the spectra of all the traces. Right click on the amplitude spectrum graph and select the Db spectrum graph display option

Experiment with some options from the right click menu to change the appearance of the display. Then close this window and try the Amp. Spectrum Create (plot) option of the functions list.

Click on to see the amplitude spectra of all the traces presented as a spectra gather Now change the plotting parameters as follows. Right click on the traces and select Display Options/Display Type/Variable Density (or ‘Shift+d’) then right click again and apply Display


Options/Plot scale type/Mean scale. Now left click on the to add the color bar (or type ’c’ in the keyboard). Then right click on the color bar and select Display Mode/Db display.

Display the data in the FK domain and use this display to design an FK filter. Close the amplitude spectrum display (discard it) and go back to the Seismic display. Select from the list FK-spectrum Design window and hit


To design a FK filter, left click on the FK Pie rejection icon, , or on the other selection icons according to the necessities . To mark a rejection zone left click, hold, drag and release. Do it just at one side of the FK spectrum, then quit the picking mode ( ). Now right click on the spectrum and select the option Mirror defined rejection zones to create a symmetric filter (or repeat the selection process on the other side if a symmetrical filter is not the best option for the data) .


Click on the icon, to see the Seismic data with applied F-K filter in the right panel.

.

Click on the icon to see the rejected noise in the right panel

Experiment with the other FK filter design tools and the different displays available in the

toolbar. Save the designed filter as a file using the icon , name it ground_roll_rejection, to be used later in the processing flows. Create a Signal to Noise ratio (S/N) display. Use the option Copy analysis window to create a copy of the data currently displayed in the window.


The S/N will be computed for all the dataset and in a long line is better to run it on a small

portion of the dataset. Hit to create a copy of the data shown in the screen. In the copy just

created, left click on , select Signal/Noise 2D analysis calculation and left click on

again. You will see the S/N in the background in colors. Add the color bar ( ). Close the window (discard).


A8. Header window:

A8.1 To open the header window click on the icon in the Project Data List. Or from the main menu: Interactive/Header View/Edit Window Display. Or from the right click menu in the Seismic Display WindowThe next figure sketches the 3 mentioned ways to open the Header window of the SHOT20 dataset.

Once in the header window learn to navigate quickly the list of headers

There are 2 shortcuts to find a header word in the long list. First way: click on the displayed header word to highlight it as in the next figure

Then use the initial letter of the searched header word to type the following letters until get the desired header word.


Second way: select a subset of headers to get a shorter list. Left click on , the icon just to the left of the list. Hold and select one of the subicons, then search in the shorter list. For example,

select the time header words, .

Take a look to the other subgroups and get familiar with them. To return to the general list use

the first subicon . Add the OFFSET header word to the spreadsheet. Select OFFSET_SH_REC in the list, by

hitting ‘o; in the general list, or selecting it from the sublist. Then click on .

Plot the offset: highlight the column by clicking on its label. Then left click on the second icon in

the vertical tool bar, .

Double click inside the graph to get a view of the offset for all the traces in the file. Close this graph window and add the Data_Firstbreak header word to the spreadsheet.


Now plot both items using the 3 icons (one at the time) encircled in the previous figure to get the 3 following graphs.

To delete a column from the spreadsheet right click on the column label and select the delete option form the menu. Or left click, hold down and draw it towards the right. There are many more options in the header window that will be illustrated in upcoming exercises.


A9. Trace statistics:

9.1 In the Header window click on ,

Then select the first icon . A dialog to compute amplitude statistics for every trace will pop up. Click on the SET button to select the signal time gate created in section 6.

Go back to the main vertical tool bar, by clicking on . Cross plot DATA_RMSAMPLITUDE Vs. Offset.


Repeat the process to crossplot DATA_MAXFREQ and DATA_EXPAMPDECAY vs. OFFSET and get the following 3 graphs.

In the left panel DATA_RMSAMPLITUDE vs. OFFSET are plotted. DATA_RMSAMPLITUDE is proportional to the energy of the trace, so it decreases exponentially with offset as can be observed in the graph. In the middle panel DATA_MAXFREQ vs. OFFSET are plotted. DATA_MAXFREQ is the frequency corresponding to the maximum amplitude in the amplitude spectrum. Traces with strong noise which frequency content is located at either high or low ranges of frequency can be detected easily. Also traces with monochromatic noise with a known frequency value as the one introduced by the interference of the power lines can be detected. In its graph there are a few traces with very high maximum frequency which means the presence of high frequency noise; also there are a few traces with maximum frequency of 60 Hz which most probably indicates the presence of power lines noise.


In the right panel DATA_EXPAMPDECAY vs. OFFSET are plotted. DATA_EXPAMPDECAY is a measure of the attenuation in the trace. It is defined as the exponent of the exponential function that best fit the absolutes values of the amplitudes in the trace. One of its multiple applications is spikes detection.

The traces which statistics are far from the main trend or present unexpected values should be investigated. Go back to the DATA_MAXFREQ graph, use the selection tools in the vertical tool bar of the window and select the dots with MAXFREQ greater than 60


Then click on to broadcast the trace information associated to the selected dots.

Right click inside the graph and select Seismic Window Display;

In the Seismic Display click on to receive the previously broadcasted information.


You should see just the traces in the line contaminated with very high frequency noise.

Click on in the vertical tool bar, then click on a trace to create a graph of the trace (Hold down and draw the mouse over the desired traces for multiple traces selection). In this window click on to plot the frequency spectra.


Right click on the spectrum to change the amplitude scale to dB. Use the scrollbar to go through the traces and their spectra if there were selected more than one trace. The blue lines correspond to the average trace and spectra.

Close the windows, go back to the MAXFREQ crossplot. Kill the selected traces by click the icon encircled in the following figure


To hide the dots corresponding to the traces just killed, right click and make sure that the option Ignore Dead Traces is checked.

Repeat the previous process to the traces with MAX_FREQ very close to 60 Hz. Delete the

previous selection clicking on .


A10. Header Mapping:

A10.1 In this exercise mathematical operations to create new headers based on the existing ones will be used. Store the result in the Vista user header words. To illustrate the process, the absolute value of the difference between the theoretical and the real first break will be computed and the result stored in the VWUSER1 header.

In the Header Window, left click on , the vertical toolbar will change, select the icon from the new vertical toolbar

Find the VMUSER_1 in the header list and add it to the spreadsheet, . Click on the checkbox,

, to open the dialogue to edit the formula


Click on ITEM and find the FIRST_BREAK header word from the list, check the option Assign Item.

Click OK. Again left click on ITEM, and this time find the header word THEORETICAL_FIRST_BREAK, but now check the option Subtract Item.

Click OK. To finish find Absolute Value from the list of OPERATIONS and click on OPERATION. Left click OK to finish defining the equation.


Use the VWUSER_2 header word to do the same exercise with a different method. Add VWUSER_2 to the spreadsheet. Click on the checkbox, . This time click on EQUATION to open the User Defined Header Equation dialog. In this dialog type the equation as shown in the next figure (the functions and header words can be added using the list and insert buttons, but the parenthesis and minus sign have to be typed). This dialog is case sensitive.

Close the dialogs. Save this definition to an external file, use . In this way the formula can be edited and can be also used in other Vista projects.


Some comments can be added, then use the icon to quit this window. Click on SAVE and APPLY in the dialogs that will pop up. Finally plot VWUSER_1 vs OFFSET and VWUSER_2 vs OFFSET.

Exercise: to practice header mapping compute the absolute offset (from the source and receiver coordinates) and store it in the VWUSER_3, plot it and compare it with the AOFFSET_SH_REC header values.


A11. Attribute window:

A11.1 Attribute window can be opened from many places in Windows, for example: left clicking

on , in the Project Data List; or from the main menu: Interactive/Attribute Window Display; or from the right click menu in the Seismic Window Display.

Open the Attribute Window for the SHOT20 Dataset. This window has many utilities. A few of them will be introduced in this section. In later exercises more applications will be presented. Right click inside the window and turn Display Bins off. Right click again and select Display Parameters/Shot Display parameters to open a dialog for the shot parameters. Change Draw symbol to 60, uncheck the Draw Lines box. Repeat for receivers display parameters.

In the attribute window, statistics of any header word can be plotted on the surface view of the survey for shot, receiver and CMP gathers. Select VWUSER_1 from the header list, remember that in the previous section the difference between the theoretical and the real FB in VWUSER_1

was stored in this header. Select Mean from the statistics variables list. Click on to calculate and plot. By default this is done in the source domain.

To create the plot in the receiver domain, click on to go to the receiver domain and then to calculate and replot. To create the plot in the CMP domain click on to go to the CMP domain,

to calculate and replot. The plots in the 3 domains are shown next.


These plots can be used for QC. For example the Mean value of the FBs difference in the receiver domain can be a good indicator of a problem in the receiver; this could be a geometry error, or a technical acquisition problem, such as noise or bad coupling. Similarly for a shot gather. For CMP gathers might be an indicator of what to expect about the quality of the stack at each CMP location. Right click inside the attribute window and select Attribute window Display Mode/Attribute+Seismic Vertical Window. To broadcast a shot into the seismic window use ‘Shift+left click’. You can broadcast a receiver gather into an independent Seismic window: right click in the attribute window and select Geometry Window/Broadcast Mode/Receiver Station and then Shift+Click again. Similarly for broadcasting a CMP gather.

Use ‘shift+left click’ on the attribute window to broadcast instantaneously the desired shot.


A12. Create a flow:

A12.1 Close all the windows (Main menu: Window/close all). Create a new flow window, in the Main Menu: Flows/ New flow. There are two ways to add commands to the window. By dragging them from the Vista Flow Command Window or by right click inside the command window to select Create Flow Command and getting the desired command from the list and sublists. You can open the Vista Flow Command Window from the Main Menu: Flows/Vista Flow Command Window.

Add the Input, Output and Filter panel test commands to the Job Flow Window. The Filter panel test can be found in the FILTERING group. Click, hold and drag on a command to move it around the window. The next step is to feed each command with the desired parameters. Double left click on the input command, select the SHOT20 dataset and OK. Then left double click on the filter panel test and add three new panels as shown in the following figure (right). To edit the information of one panel just left double click and modify the frequency values. OK.

Double click on the output command and give a name to the file such us ‘filter_test’. Click on and add links to the command in the logic sequence. . To create a link click in the first icon, hold and drag until around the midpoint of the second icon, release. Activate for execution the commands. You can do it one at the time by right clicking on each command and selecting Mark for execution. Or all at the same time by right clicking on an empty point of the window and selecting SET ALL EXECUTE ON.


The flow is ready to be executed. However it will apply the process on the entire dataset. For tests normally only some data samples are necessary. Select a shot by left clicking on the input command and selecting Data Input Control/ Data Header Selection. This will open a window to define the selections.

To select a shot, left click on , then . Select shot 173 as shown in the next figure

Close the selection window, clicking on OK. Save, , and run the flow using . Use the top scrollbar to go through the filtered data, or use the list that you get by double clicking on the note at the lower left corner of the shot


An alternative data selection method is through the seismic attribute window. Right click on the input command and open the Seismic Attribute Display.

Zoom in around one of the shots. Click on to expand the Selection Toolbar. Then click on to Select shots, hold and pick Select one shot, . Click on the desired shot, you should see a

change in the shot symbol.


Click on to broadcast the information of the shot. Close the attribute window. Right click on the input command, select Data Input Control/RECEIVE Data/Header Selections. This will delete any previous selection and set the new ones.

After executing the flow a new icon, , will be active in the Project Data List The flow used to generate a Vista file will be kept associated to the dataset. You can use the icon in the Project Data List to open the associated flow.


A13. Mute function:

A13.1 Different kind of mute functions are applied in the seismic processing flow. In this section a mute function will be designed to mute the refraction events. This kind of mute is usually applied before Time Variant Scaling and also during Prestack Time Migration. To design the mute function, open the Seismic Window Display of the data that will be muted, sort by shot and apply offset mode display, as in the design of the time gates

Click on to design a top mute.

Define the top function as follows; use only either the positive or the negative range of offsets.


To redefine the mute just repick a new mute function. Click on to quit the picking mode and save it the mute as a file with the name ‘scale.mut’. This file will be used later in some flows to process the data.


A14. Refraction and elevation statics:

A14.1 Click on the refraction statics icon, , of the 20SHOTS dataset to open the refraction statics window (or from the main menu: Statics->Elevation/Refraction Statics). This step needs the First Break in the Headers that were picked above in section A5.

Use the following parameters


Click OK. At this point the Elevation statics referred to the fixed datum are calculated: DATA_SURFACETO_FIXEDDATUM_SRC, DATA_SURFACETO_FIXEDDATUM_RCV, and DATA_SURFACETO_FIXEDDATUM_TOTAL.

Click on to add a new control point

Use the horizontal axis to zoom in on the first 500 m at the East end of the line. To create a control point click on the line, on the desired center of the circle, hold down, drag and release the right button of the mouse. The circle should contain a few shots inside (between 2 and 4).

Click on the icon in the right vertical toolbar, then drag a line on the first visible slope of the first break line (near offset side)


Click on , to change to layer 2, and draw a line on the far offset visible layer in the first breaks (far offset slope)

Generate automatically one control point per shot: click on and use the following parameters


Take a look at the solution using the right click menu options (examine all the results available at the menus Geometry Display Mode, Shot Display and Receiver Display.


The control points can be redefined or deleted, if one of the control points is changed click on

to update the solution. Save the solution to the headers.

Take a look to the model of the near surface layer created with this static solution: click on


Notice that only the elevation statics with reference to a fixed datum where calculated.

Elevations statics with respect to a floating datum can be computed also clicking on .

Compute Short Wave refraction statics. Click on and use the following parameters.


Use to display the calculated statics as a graph. Select the statics that will be displayed from the right click menu.


Click on , hold down and select the subicon to save the statics to the headers.


A15. Apply the statics to the headers:

A15.1 From the main menu use Job Flow/Open Flow File to open Flow A_elev_ref_statics_apply.flw

Take a look at the parameters of each command, double click on an icon to see its parameter dialogue. In particular confirm that the input file is shot20 by clicking OK in the Input icon parameters dialogue.

Click on to run the flow. Compare the input with the output:


A closer look to the strong reflections in this shot allows to observe the differences and the benefits of the statics easier.


A16. Scaling:

2 Different ways to scale the data are shown in this section. To scale in the time direction the first one uses Exponential Time Power and the second one Time Variant Scaling. To scale in the offset direction in both cases the same Scaling command is used. A16.1 Scaling with Exponential Time Power

Open the flow Scaling_with_exp_time_pwr.flw from the Flows/Optional/Scaling folder. The parameters for ExpTPow and Scale are shown in the following figure. The window used in the Scale command was designed above in the section A6 of this manual. To check the selection of the Shot 185 (or change the selected shot, or delete the selection, review section A12).

A16.2 Scaling with Time Variant Scaling

To scale with the Time Variant Scaling command a mute function as the defined in section A13 of this manual should be used. The key point of this method of scaling is to define a set of time windows, generally overlapping. The size of the window usually increases with time among other reasons due to the frequency losses that the data suffers due to absorption. Open the flow Scaling_with_tvscale.flw from the Flows/Optional/Scaling folder. The parameters for the MuteTrc and TVScale icons are shown next. The Scale icon uses the same parameter as in A16.1.


Confirm that the input file is Raw+Statics, the same shot 185 as in the previous flow has been

selected. Click on to run the flow. Compare the scaled shots (from the 2 methods) with the raw+statics.


A17. Surface consistent Deconvolution:

This processing step calculates the spectra of each source and receiver wavelet. Later on, in Flow C, a deconvolution operator is built, by convolving the wavelets computed in this flow, and applied to the data. Open Flow B_SC Dec_Calc.flw. Follow the instructions in the notes inside the flow window. Notice that this flow does not need an output. The autocorrelation length should be appropriate for the frequency of the data and longer or equal than the operator that will be applied later in SCDECON APPLY in Flow C. Select a range of offsets and a Design Window with a good signal to noise ratio.

After running the flow, inspect the computed spectra of the wavelets. Notice that the output files are in the frequency domain. Where is the number of traces in each file coming from?


Open the Shot and Receiver Component files and try to understand them. The spectra of the shots are shown in the following figure: (to change to DB scale, add the colorbar to the display, type ‘c’, and use the right click menu on the color bar as shown next)

Open and run Flow C_Decapply.flw. The input, the mute and the scales parameters are exactly the same as in the previous flow

Compare the input (before SCDECON) with the output (after SCDECON)


A17.1 Autocorrelation

Some users find useful to plot the autocorrelation of the raw data to make a decision about the deconvolution operator length. Open the Autocorrelation flow from the Flows/Optional/Deconvolution Folder.

The output of this flow is the autocorrelation graph shown next.


A17.2 Deconvolution panels

The Decon Panel Test icon is a good tool to test deconvolution parameters. Open the Decon_panel_test flow from the Flows/Optional/Deconvolution Folder.

The output of the flow is sorted, so the user can use the top scroll bar to go through the deconvolved shot with different parameters. Double click on the note at the bottom left corner of the gather to open the list of gathers.


A18. Attenuation of surface noise (ground roll):

There are many ways in Vista to attenuate surface noise. In the Flows/Optional/Surface_noise folder the user will find flow examples to attenuate surface noise, using FK, FK-FX, Tau-Pi, and radial transform. A18.1 FK Filtering

The filter must have been previously designed, as in section A7. Open the FK_filtering flow from the o Flows/Optional/Surface_noise folder. The FK filter attenuates well the surface noise but it smears some high amplitude noise especially when the number of samples in the offset domain is low as in this example (120 channels). Notice the way that the flow is set up


A18.2 FK-FX

An alternative to FK filter is FK-FX filter. FX-FK filter is applied to remove or isolate linear noise. A kind of pie-shape operator is designed in FK domain within the range of apparent velocities, and temporal and spatial frequency ranges of the noise. The operator is then converted in FX domain and applied to the data using the exact shot/receiver coordinates. The level of noise removal is controlled by the length of the applied operator. Its application in FX domain allows handling any irregular geometry, including 3D. Open an run flow file Fk_Fx_filter_apply.flw from the Flows/Optional/Surface_Noise_Attenuation folder. Follow the instructions in the note inside the flow.


A18.3 Tau-Pi

Filtering in the Tau-Pi domain is another alternative to attenuate linear noise. The Tau-Pi transform is one of the variants of the Radon transform in which the integration paths are straight lines. The Tau coordinate is related to the intercept of the line with the T time and the Pi to the slope of the line. In the example shown in this tutorial the surface noise is attenuated just by taking the forward and inverse transform in cascade. The filtering can be strengthened by applying an additional filtering operation in the Tau-Pi domain such as a muting, a bandpass filter or a smoothing.


A18.4 Radial Transform

The radial transform is a mapping of the data from the Offset-Time (X-T) domain to a Velocity-Time domain. To create the transform, the samples along a line of constant velocity are extracted from the X-T gather and plotted vertically as a single trace in the radial domain. Create a plot of the Radial Transform of a shot. Open and run the flow Flows/Optional/Linear_noise_attenuation/RT_plot.flw


Open and run the flow Flows/Optional/Linear_noise_attenuation/RT_noise_attenuation.flw


A19. Time Variant Spectral Balancing:

A19.1 This is a complementary step for the surface consistent deconvolution, it compensates for absorption. Open and run Flow D_RT_TVSB.flw. The input of this flow is DCON Shots. Previous to the application of the TVSB icon, the surface noise is attenuated through filtering in the radial transform domain. In the previous section 4 different methods to attenuate noise were tested, and all of them work fine on this data. Arbitrarily one of the methods was selected to continue the tutorial. The user interested in any of the other methods should check the flows illustrated in the previous section.


A20. Velocity analysis:

A20.1 To run the following flow, the statics computed in section A15 should have been saved in the headers of the input file (Input in VelZone). The true surface NMO method is used in the flow and it needs the refraction and elevation statics referred to a fixed datum applied to the data and save to the headers, otherwise the results will be wrong. The input file that will be used in this example is Shots+Statics+Dcon+RT+TVSB which has the required statics applied to the data and save to the headers since previous steps.

Open Flow E_Velanbrute.flw. With the parameter window of each command open, type F1 to open its help page. To verify that the correct file is input, double click on the Vel Zone command, select the Shots+Statics+Dcon+RT+TVSB dataset, click OK. To check the CMP locations selected for Velocity analysis (or change the locations), right click on VelZone, select Data Input Control/Data Header Selection and notice the CMP locations where the velocity analysis will be performed (edit them if the user consider it necessary).


Execute the flow, . Go to the Main menu, Velocity/Interactive Velocity Analysis, and select the three output files of the previous flow.


Left click on to start to pick velocities. It can be done on the semblance panel and/or on the

CVS panel (right). Click on in the vertical tool bar to turn on the Interval velocities.

Play with the icons of the vertical toolbar, also explore the right click menus and the options

dialogue (clicking on ). Go to the remaining CMP locations (using the top scrollbar) and save the velocities into a file with a name such as brute_vel. Display the velocity file that will be

applied for NMO correction in the next exercise, .

Close the Velocity Display file.


Pick a NMO stretch mute function: right click on the gather panel and select Gather Parameters/Gather Mute Pick

Pick the mute function on the gather

Save the mute function to a file: right click on the gather and select Gather Parameters/Save Mute File


A21. Brute stack:

A21.1 Open and run Flow F_Brute Stack.flw.


To change the plot parameters see the following section.


A22. Plot parameters:

A22.1 The appearance of the seismic display can be controlled using the uppermost icon in the vertical tool bar.

Play with the annotations. Go to the annotations tab, BOTTOM Axis tab, add the fold header as a Graph annotation as in the next figure.

Open the SHOT20 dataset, go back to the Seismic Data Plot Parameter dialog ( ) again to the annotation tab. Double click on TEXT: SHOT POINT_NO, check User Defined Annotate increment interval 100, check Annotation Control Header, select Offset from the header list.


Now repeat the same process for TEXT:CHANEL_NO and TEXT:OFFSET_SH_REC

Go back to the Seismic Data Plot Parameter dialog ( ).Take a look at the Process tab. This tab can be used to quickly test some processing parameters on a gather (without changing the dataset, only affecting the display). The filter and AGC parameters defined here are the ones applied when typing the hotkeys ‘a’ and ‘f’. To finish this exercise left click on WRITE PARMS to save all the parameters defined in this dialog to a file that can be read later using the option READ PARMS.


When closing the Seismic Window Display and open a new one the display will get back to the default parameters. To make the plot parameters modifications permanent for the current project open a similar dialog from the main menu in Project /Plotting Defaults/Unstacked Data Options. After changing the Project default plotting parameters save the project in File/Save Project.


A23. Residual statics:

A23.1 Open Flow G_Stkpower1.flw. Make sure that the path of the output file is the one in which the ASCII file containing the statics should be saved.

Use the No model Building option in the Model tab. In the other tabs use the parameters shown next.

After the execution of the previous flow open the file Flow H_Stack with first pass residual.flw,


A24. Second Velocity Analysis:

A24.1 Open and run Flow I_Velan after Stkpowr1.flw.

Repeat the velocity picking as in section A20.

Save the velocity file as vel2.vel


A25. Stack after two passes of residual statics:

A25.1 Open and run Flow J_Stkpower2.flw

The output of the previous flow is an ASCII file. After executing the previous flow, open and run Flow J_Stkpower2.flw.


Left click on the seismic compare icon . This tool allows comparing the current dataset with

all the comparable datasets (same number of traces and samples). Click on and select from the list the desired dataset to compare it with the current in a ‘movie’ mode.

Play with the icons inside the rectangle in the next figure.


A26. Common receiver stack:

A26.1 Open and run Flow L_CR_Stack with second pass residual.flw.

This flow is similar to the flow to create a CMP stack. There are 2 differences: the data is sorted by Field Station Number (receiver gathers), and a RecvStk icon is used instead of a CMPStk icon. This flow is run as a quality control for example to assess statics corrections and polarity errors. Notice the statics problems remaining at the right edge of the section, however is very difficult to deal with them due to the low RECEIVER and CMP fold in this area of the data, also the elevations for the receivers are not available at this side of the line and the value of the last shot elevation is used for a considerable number of stations.


A27. Trim Statics:

A27.1 Open and run Flow M_trimpsmprep.flw.

The stacked output of this flow will be used for migration (previous random noise attenuation). The unstacked output will be used for pre-stack migration velocity and aperture angle analysis.


Trim statics are tiny. It can be appreciated at a microscopic scale. They should increase the sharpness and the continuity of the events. Finally in the main menu go to Statics/Auto-Statics 2-D Surface Con and Select the correlations file created by the Mcorr icon.


In the statics window click on to calculate the statics.


Click on to saves the statics into a file. This file will be used later to apply the trim statics to the shots before the final migration


A28. Attenuation of random noise:

A28.1 Two different options to attenuate random noise on stack data are illustrated in this section: FX prediction filtering and 4D-DEC.

Open and run Flow N_Stack+FXpred.flw


Open and run Flow O_Stack+4D-DEC_Random_noise_attenuation.flw


A29. Poststack migration:

Open and run Flow P_FD Migration.flw.


A30. Prestack migration (PSTM):

A30.1 Apply PSTM to a single trace: open and run Flow Q1_PSTM_single_trace.flw

A29.1 Create the migrated sections for velocity analysis: open and run Flow Q2_PSTM_velocity

analysis.flw. Observe that this flow uses variable strings. To turn on and off the Variable

string panel click on in the vertical toolbar of the flow window. Several commands have the option to use variable strings. To activate the variables strings of a particular icon turn select the option Variable String ON from the right click menu (see next figure). To open the variable strings dialogue select Variable String Defn, from the right click menu.


A29.2 PSTM velocity analysis. The previous flow outputs a set of files migrated at different

percentage of the best existing velocity. To pick PSTM migration velocities go to the main menu and select Velocity/PSTM Migration/Velocity Analysis, select the files generated by the previous flow.


Type F1 (with the Migration Imaging Velocity Analysis Window active) to get help about the picking functions of this window). Save the picked velocities as Vel3_PSTM.vel


A29.3 PSTM Angle Analysis. Open and run Flow Q3_PSTM_angle analysis.flw. The angle analysis is similar to the previous migration velocity analysis. This flow creates the files that will be used in next step to pick the angles.

A29.4 Migration Aperture Angle Analysis.

From the main menu select Velocity/PSTM Migration/Angle Analysis


In the Migration Imaging Angle Analysis Window, click on in the vertical toolbar to create automaticly control points at the locations shown in next figure.

Click OK. Then click on to go to the panel mode and pick angles functions. Type F1 to get help, this window is the same used to pick migration velocities in the previous step, so the help page will be the same. A29.5 Create input file for final migration

Open and run Flow Q5_Final_PSTM.flw. The program THOR is a powerful noise attenuator, it removes spikes, and in general high amplitude noise. Also the trim statics are applied to the data

A29.6 Run final migration

Open and run Flow Q5_Final_PSTM.flw .


A29.7 Clean the final migration.

Open and run Flow Q6_Clean_Final_PSTM.flw

Seismic Data Processing Using VISTA 2D 3D

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