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Using Didger to Digitize a Paper Well Log and Export as LAS

Introduction

If you have a paper well log and you would like to recreate the log digitally (e.g., in Strater or in another well log or borehole plotting software) or need the information in LAS format, you can use Didger 3. Didger can digitize well log curves from either a paper log on a digitizing tablet or from a scanned image, resample the curves to a specified interval, and export to an LAS file.

 

Digitizing From a Tablet

If you have a digitizing tablet, you can put the paper well log on the tablet and begin the digitizing process:

  1. Secure your paper well log to the digitizing tablet so that it doesn't move throughout the calibrating and digitizing process.
  2. Start the Calibration Wizard by going to Digitize | Tablet Calibration.
  3. In the Initial Calibration Settings dialog, select Cartesian Coordinates for the well log (since well logs are not projected).
  4. Select the X Axis Type and Y Axis Type to be either Linear or Logarithmic as appropriate.
  5. Leave the Calibration Units set to <unspecified>.
  6. Click the Next button to move to the Create Calibration Points dialog box.
  7. Select the first row and enter the World X and World Y coordinates for your first calibration point.
  8. Click on that location on the log on the tablet. Once a point is calibrated, the Tablet X and Tablet Yfields for that row are filled in. Try to be as precise as possible when clicking on the calibration points, as the resulting data is only as good as your calibration. If you make a mistake, you can select the row again and then redigitize the calibration point.

    Click on the tablet
    Didger records the tablet X/Y

    Click on the location of the calibration point on the tablet and the
    Tablet X and Tablet Y fields will automatically be filled in.

  9. Click the Add Point button at least twice and enter the World X and World Y values for the additional calibration points. Calibrate them on the tablet.

    Three calibration points

    Enter in the coordinates for the additional calibration points
    and calibrate them on the tablet.

  10. Click Next to move to the RMS Calibration Settings dialog box. This shows you the RMS error, which is a measure of the error in calibrating the points. The RMS error is only displayed when you calibrate using 4 or more points. Because I'm using Cartesian Coordinates, the RMS error is reported in the same units as my calibration points. If this value is too high, click Back and recalibrate the points using more care and confirm that the World X and World Y coordinates are correct for each point.
  11. Click the Next button to move to the Calibration Settings dialog box. Accept these default values for now.
  12. Click Next to move to the Specify Project Limits and Scale dialog box. These values can be changed later, if necessary, so just accept the default values for now.
  13. Click Finish to end the calibration process. The calibration points are shown in the plot window using the calibration marker. You can change the properties of the calibration marker by going toDigitize | Calibration Marker and choosing a new symbol shape, size, or color.
  14. Once the calibration is finished, go to Digitize | Polyline and then digitize the well log on the tablet using the tablet puck or stylus.

    Digitize the log
    The line appears in Didger

    Use the Digitize | Polylines command and trace the log on the tablet
    using the puck or stylus. The digitized log will be transferred
    to the Didger project window as you digitize.

  15. Once the log is digitized, select the digitized polyline on the screen and go to Tools | Resample Polylines.
  16. Choose to resample along the Y axis, and choose the starting, ending, and increment values. Uncheck the check box next to Create New Line and click OK and the line will be resampled. You can see in the Coordinate Manager that the coordinate values are resampled to the specified interval.

    Resample the polyline

    Choose to resample along the Y axis and specify the
    starting, ending, and increment value.



    Note the coordinates

    Once the polyline is resampled, you can see
    the coordinates in the Coordinate Manager
    showing the Y value incremented
    by the specified value.

  17. Once the polyline is resampled, go to File | Export LAS File and export the polyline to an LAS file. You have the option of including Well Info and Curve Info in the LAS Export Options dialog box.

    Exporting as LAS

    You have the option of entering Well Info and Curve Info
    when exporting a resampled polyline to an LAS file.

 

Digitizing From a Scanned Image

If you do not have a digitizing tablet but you have a scanner, you can scan in the paper well log and use the bitmap image in Didger. This process takes a few more steps than digitizing it from a digitizing tablet:

  1. Scan the paper well log and save the scanned image as a bitmap file (BMP, TIF, JPG, GIF, etc.).
  2. Open Didger.
  3. Go to File | Import Bitmap | Into Raster Project.
  4. The Import Raster File dialog box opens. Select your bitmap image and click Open.
  5. Click OK in the Bitmap Import Options dialog box.
  6. Click OK in the second Bitmap Import Options dialog box to import the bitmap.
  7. Once the bitmap is imported, go to Image | Calibrate Image.
  8. In the Initial Calibration Settings dialog, select Cartesian Coordinates for the well log (since well logs are not projected).
  9. Select the X Axis Type and Y Axis Type to be either Linear or Logarithmic as appropriate.
  10. Leave the Calibration Units set to <unspecified>.
  11. Click the Next button to move to the Raster Calibration dialog to enter the coordinates for the calibration points.
  12. Select the first row and enter the World X and World Y coordinates for one of your calibration points.
  13. Move your mouse to the location on the well log image and click the left mouse button. This will enter coordinates under the Source X and Source Y columns and place a calibration marker at the location you clicked on the image. Try to be as precise as possible when clicking on the calibration points, as your resulting data is only as good as your calibration. If you need to zoom in to digitize a calibration point accurately, hold down the SHIFT key on your keyboard and click on the image. Hold down the CTRL key while clicking to zoom out. You can also use the scroll bars to move around the image while zoomed in.

    Calibrating the first point

    Enter in the calibration coordinates in the World X and World Y
    columns and then click on that location on the image.

  14. Click the Add Point button at least twice and enter the World X and World Y values for the additional calibration points. Calibrate them on the screen. If you make a mistake, you can click the row number and then redigitize the calibration point.

    Three points calibrated

    Click the Add Point button to add calibration points. Enter their coordinates in the
    World X and World Y columns and then digitize them on the image.

  15. Click the Next button to move to the RMS Calibration Settings dialog box. This shows you the RMS error, which is a measure of the error in calibrating the points. The RMS error is only displayed when you calibrate using 4 or more points. Because I'm using Cartesian Coordinates, the RMS error is reported in the same units as my calibration points. If this value is too high, clickBack and recalibrate the points using more care and confirm that the World X and World Ycoordinates are correct for each point.
  16. Click the Next button to move to the Calibration Settings dialog box. Accept these default values for now.
  17. Click the Finish button and the calibration points are shown in the plot window using the calibration marker. You can change the properties of the calibration marker by going to Digitize | Calibration Marker and choosing a new symbol shape, size, or color
  18. Now that the image is calibrated, you can digitize the well log using the commands under theDigitize menu. First, you might consider zooming in to the log to help accuracy. To zoom in, use the View | Zoom | In option and click on the image where you want to zoom.
  19. If the well log is a simple line, you will then use Digitize | Polyline to digitize the log.

    Digitize the log

    Digitize the well log by going to Digitize | Polyline and then tracing over
    the log with the mouse while holding the left button down.

  20. Go to File | Save and save your project for future use.
  21. Go to File | Export and export the polyline to a vector file format (e.g., Golden Software Interchange, *.GSI).
  22. Go to File | New | Import Vector and import the vector file back into Didger.
  23. Once the polyline is imported into a vector project, select the polyline and go to Tools | Resample Polylines.
  24. Choose to resample along the Y axis, and choose the starting, ending, and increment values. Uncheck the check box next to Create New Line, click OK, and the line will be resampled. You can see in the Coordinate Manager that the coordinate values are resampled to the specified interval.

    Resample the polyline

    Choose to resample along the Y axis and specify the
    starting, ending, and increment value.



    Note the coordinates

    Once the polyline is resampled, you can see
    the coordinates in the Coordinate Manager
    showing the Y value incremented
    by the specified value.

  25. Once the polyline is resampled, go to File | Export LAS File and export the polyline to an LAS file. You have the option of including Well Info and Curve Info in the LAS Export Options dialog box.

    Exporting as LAS

    You have the option of entering Well Info and Curve Info
    when exporting a resampled polyline to an LAS file.

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