Thursday, January 3, 2013

Prepare SPS for onland seismic data acquition

INTRODUCTION
More often the seismic data is processed by people who are not involved in the acquisition of data. So there is need to exchange data about the position coordinates of source, receiver and their relation. Not only the position coordinates but also other details like drilled depth and uphole time to mention a few have also be to exchanged. Different systems are used for acquisition and processing having their own file formats. So there was a need for industry standard to exchange these data. So in 1993 Society of Exploration Geophysicist (SEG) adopted the SPS standards used by Shell as Industry standard. The original specifications can be downloaded from the link given in references.

SPS standard consist of four simple text files as follows:
  1. Receiver file - R file
  2. Source file    - S file
  3. Relation file  - X file
  4. Comment file - Optional
which are formatted to avoid confusion. These standard is used to 3D seismic data acquisition and can be used for other geometries also.

Preparation of SPS
Though there are many ways of preparing SPS an easy way to prepare is by using spreadsheet like excel or calc. Let us have a simple geometry and prepare SPS for it manually.

Geometry:
To keep the manual work less let us consider a simple END ON  geometry with following details
Receiver lines - 5
Number of receiver per line - 20
Receiver line interval - 280 m
Interval between two receivers - 80m
Interval between two shots - 80m
Number of Shots per line - 5
Number of shot lines - 2
Shot line interval in 320 m
The unit template is as in the figure below
Fig 1. Unit Template
Let us do a in-line swath rollover towards the right side. Since the Shot line interval is 280 m we have to place one more Shot line parallel to existing shot line which is 280 m away and we have to add 4 new receivers in the each line (Hint: 320/80).

So now let us prepare the SPS for a total number of 10 shots.

R file
Receiver file contains the information about the receivers (or stations) type of reciever (geophone, hydrophone).
Fig 2. R and S file format
The figure shows the information put in each field. Each field has particular number of columns. By default the columns are right justified.  Some columns are left justified which are mentioned and we have to modify it.

Now let us start preparing R file using excel sheet. Open an excel sheet (any spreadsheet) and follow the steps below.

1. Column width adjustment - The column width for the first column as given in the table in 1. . So we have to adjust the column width of each column in the excel sheet upto O column. Now go to the first column. Right click on A and select column width. A dialogue box appears enter 1. Now right click on B and select the column width. Enter 16 in the dialogue box. Repeat it for all the columns till O. Select the column B and align text left. This is the only column which is left aligned in R file. Select the columns K L M and right click format cells. Select number and decimal place 1. Now the excel sheet is ready as below.
Fig 3. Formatted excel sheet
2. The bottom leftmost geophone is the first geophone. Let the first receiver line be 101 with starting picket 101. Let the next receiver be 103, 105 and so on. The next receiver line be 108, 115, etc. Let the easting and northing of geophone (101,101) be for example (100000, 2000000)

3. Now let us enter the information of first geophone in the excel sheet. In the cell A1 type R as per the format given in Fig 2. In the B1 we have to enter the line number of first geophone (101) then picket number in C1. In D1 enter the point code as 1. In E1 enter the reciever code for E1 for geophone. In K L M enter easting, northing, elevation. Other cells can be filled with relevant information. If they are not know they can be left.
Fig 4. R excel
4. Repeat step three for all the geophones, i.e., 120 geophones (5 x 24). So you will be having 120 rows.

5. Now save it as Formatted text (space delimited) with extension (*.prn). Click ok and ok. Now the saved file is a simple text file which can be opened with any text editor. So your R file is ready

S file
Source file like receiver contains information about the source points like its position coordinates, type of source, etc as given in Fig 2. Another excel sheet can be prepared in the way as prepared for R file. All relevant information shall be entered for each shot point and saved as *.prn file format. For this geometry with two shot lines there will be 10 rows because of 10 shots. The prepared S file is as follows.
Fig 5. S excel
X file
Relation file contains data about how source and receiver are related to each other. In simple terms it shows what receivers are  active while a particular source point is activated.
Fig 6. X file format
The figure shows the information put in each field. Prepare another excel sheet as we prepared for R and S file. The fields are different from R and S file. Prepare and format (right and left alignment) the excel sheet and given in the figure above.

Let me explain the important columns to be entered for the X file.
A - enter X
B - Enter the number of the tape to be used for recording (optional)
F - Shot line number
G - Shot point number
 I  - starting channel number ( Channel number is a continuous number from 1 to 100 in this survey. Because there are 100 channels active for each shot)
J  - Ending channel number
K - Channel increment(How many channels increased in each step)
L - Receiver line number
M - Starting receiver number
N  - Ending receiver number.
The final layout appears as below

Since there is Receiver line number in column L We have to prepare the row information for every line in a shot. In this example. There are 5 receiver lines in a shot. So we have to  prepare 50 rows ( 10shots x 5 receiver lines)

The x file is prepared as follows.
Fig 7 X excel file
Save the excel sheet as prn file. 

Now the sps is prepared and final geometry looks like as below.
Fig 8. Geometry
Comment record (optional)



Revision history

1.Rev1.0
2.Rev2.1

The procedure explained above is for the SPS Rev1.0 . The columns are slightly different in SPS Rev 2.1. The difference between the two formats can seen from the following figures.
Fig 9 SPS 2.1 R and S file format

Fig 10 SPS 2.1 X format

Terms used:


1.Unit Template is the smallest shooting pattern which gets repeated in certain directions.
In the Unit template all the shots have same set of active receivers.


23 comments:

  1. I think some correction is there in this lines in the SLI."Let us do a in-line swath rollover towards the right side. Since the Shot line interval is 280 m we have to place one more Shot line parallel to existing shot line which is 280 m away and we have to add 4 new receivers in the each line (Hint: 320/80)."

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    Replies
    1. Actually the Shot line interval is 320m and not 280m. And what you said is right the number of receivers between two shot lines is 4 receivers in each line which is the same as shown in fig8.

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  2. Replies
    1. This comment has been removed by the author.

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    2. F stands for Floating point, '4' indicates column width 4, "." indicates "." (decimal) can be used in the format and "1" after the "." indicates only one column after decimal. For example if a particular field is defined as F4.1 the possibilities are
      9
      99
      999
      9999
      .9
      9.9
      99.9

      but the following are not acceptable
      9.99 (there are two digits after decimal)

      But again the possible combinations are restricted by the "minimum and maximum values" defined for each field. This is done to avoid errors creeping into the data.

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  3. Informative and Nice Work Balaji

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  4. Very informative. Will refer my students and younger staff to this.

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  5. Nice post, Balaji.
    Generating R and S files can be relatively straightforward, X however is usually not so much and could even be extremely tedious as potential gaps in the R lines need to be taken in account.
    Short of having access to expensive software such as Omni and the likes, would you know of any (free) software/script/algorithm that could do this efficiently given the R, S and the patch characteristics?

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    Replies
    1. Thanks Yannick.
      Though as you said it is many times tedious to create x file manually I personally do it manually.
      Some times I use software such as MESA or Geoland by using R, S and patch characteristics. I have not come across any free software which can do this kind of function efficiently.

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  6. Informative, thank you for information

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  7. Could anyone point me in the direction of some example SPS files?

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  8. any one can help: to generate an XPS, when there is an absent or omit of receiver stations in some receiver lines.
    my shell program cant take in count this case.

    thank you.

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  9. please can anyone help with loading of SPS file on MESA 10.4 or any tutorial/training manual.......
    mide.oyeniyi@gmail.com

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  10. Olumide (Layout+receiver+import file( you must have configuration file) then follow the procedure if you MESA 10.4 just simply click on help u can get ur desire manual.

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  11. pls how I identify wrong SPS file

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  12. pls how can I identify wrong SPS file

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