Import and Digitize from a Bitmap Using Petrel Often a map with culture lines, contours or well spots is provided in paper form and must be entered into the computer. Many companies or groups within companies no longer have easy access to digitizing tablets but do have access to scanners. Petrel allows scanned images to be imported and registered to a coordinate system. Once registered, lines, points and values from those images can be digitized in Petrel. This Tips and Tricks paper describes steps used to prepare a map for scanning, how to import and register the scanned map in Petrel, and how to digitize information from that map.
Import Image
The starting point for this process is a piece of paper with a map on it that must be scanned and then imported into Petrel. The map must be properly prepared before scanning.
Prepare Map for Scanning
Ultimately the scanned image must be registered to a coordinate system. This requires that registration marks exist on the map before it is scanned. If these marks are not on the map, then place ticks in the lower left and upper right corners, along with coordinates corresponding to those locations. It is best to use locations with simple round numbers (usually ending in one or a few zeros).
To help orient the image once it is scanned, place either a horizontal or vertical line on the map having the same Y or X coordinate along its entire length.
Figure: Map before (left) and after (right) preparation for scanning. Note that the points to use for registration are indicated. No horizontal or vertical line was drawn as they already existed.
The map can be scanned by any tool as long as that tool maintains the image’s aspect ratio and collects enough detail to be useful. After scanning, the image should be rotated so that the X‐axis is horizontal and the Y‐axis is vertical. Although ways may exist to import and rotate a scanned map in Petrel, the authors have found it easiest to start with an image that is properly orientated before being imported into Petrel. A screen capture tool such as Snagit (A mark of TechSmith Corporation) or a graphic editing tool such as Adobe Photoshop (A mark of Adobe Incorporated) can be used to rotate and crop the image if needed. The image should be saved in one of the image formats accepted by Petrel (BMP, JPG, TIFF, GIF or PNG).
Figure: Scanned image before rotation to vertical (left) and after rotation and cropping (right), ready for import to Petrel.
Import
The prepared image is imported into Petrel using Import on selection:
1. Create a folder, 2. Right click on the folder 3. Select Import on selection 4. Use the Bitmap Image format 5. Select the file 6. Click Open to import 7. The file is placed in the folder
Figure: Import (on selection) picked by right clicking (top left), the import dialog with the Bitmap Image format selected (right) and the Input tab folder after importing (bottom).
Register Image
The image must be assigned a coordinate system. To do this, the coordinates you placed on the image are used. Fine tuning will then be needed to move these coordinates to the position of the ticks you placed on the image.
Assign Coordinates
To assign coordinates to the image, double click on the imported file and go to the Settings tab. Check the box in front of Located in world. Make sure the Orthonormal radio button is pressed. Enter the coordinates for the four corners you know (XMIN, YMIN, XMAX, YMAX) and a value of zero for the Z. Note: the coordinates will probably not be in the correct position since they will be linked to the absolute corners or the image and not the ticks you placed on the image. You will move the coordinates to the correct spot in the next step. Click OK when done.
Figure: Settings dialog of the imported image where coordinates are assigned (left) and with Orthonormal coordinates assigned (right).
Tune Coordinates
The X and Y coordinates are not correct, only close. You will need to adjust all four coordinates to move the X‐Y values from the corners of the image to the ticks that truly represent the coordinates. If coordiantes are positive it is best to adjust the Xmin and Ymin locations first and the Xmax and Ymax locations second. If the coordinates are negative then the opposite is true (maxes first then the mins). The following steps walk you through the tuning process. Note that a map window is used for this work. This allows the displayed coordinate axis to be adjusted in terms of annotation size, orientation, and posting rate.
1. Open a Map Window
2. Display the image in the window
3. Display the Axis on the window and adjust as needed
4. Zoom in on the lower left corner
5. Open Settings dialog for the image and go to the Settings tab
6. Adjust the Xmin coordinate until the axis label and the marked position on the map are in the correct position.
7. Repeat the process for the Ymin coordinate
8. Move to the upper right corner of the map and repeat for Xmax and Ymax.
9. Recheck all coordinates in case another round of tuning is required.
Figure: Image displayed in a Map Window with the coordinate axis added. The desired coordinates (Xmin=249200, Ymin=1877600, Xmax=2497600, and Ymax=1883200) are currently positioned at the corners of the image and must be relocated to the tick locations.
Figure: Dialog for the image file with Settings tab displayed and ready to begin adjusting the coordinates to properly locate the image (left) and after adjustment (right).
Figure: Map Window showing the lower left corner of the image before tuning coordinates (left) and after tuning (right).
Figure: Map Window showing the upper right corner of the image before tuning coordinates (left) and after tuning (right).
Digitize the data
In this example contours, polygons, and points are digitized. Usually these are the file types created from a bitmap. Although digitizing these features is fairly simple, the steps used to create each are presented. Although the fault block in this example is bounded on the east and west by faults and by a pinch‐out to the south, a single polygon will be used to define the entire area of interest. This will allow the contours to be digitized past the faults, the grid to be built beyond the faults, and the polygon used to constrain volume calculations to exactly the fault block as well as used to blank the grid for display purposes. A separate Polygon file will also be digitized for display purposes. The wells will be digitized as points and the name added as an attribute.
Digitize Polygons
Two polygons are created, one representing the faults for use in displays and the other a polygon for use in blanking and volume calculation.
Faults
Use the following steps to digitize the faults:
1. Open a 2D window
2. Make the Make/edit Polygons process active
3. Click on the Start new set of polygons icon and digitize the first fault
Figure: Digitized polygon for use in volume calculation and blanking the grid.
Digitize Contours
The Make/edit Polygons process is used to digitize contours. First the contours are created as polygons and then the lines are assigned the proper Z‐value. Usually the contours will be gridded. If the contours represent only one fault block bounded by a polygon, then it is useful to extend the contours beyond the polygon that defines the edge of the block. This will allow the gridding process to build a better grid up to the edge of the fault block.
The steps used to create the file are:
1. Make the Make/edit Polygons process active
2. Click on the Start new set of polygons icon to start a new polygon (contour) file
3. Digitize the desired contour
4. Click on the Start new polygon on active set of polygons to digitize each additional contour
5. Raise the polygons up 5 units (Calculations Z=Z+5) to see what you have done
6. Click on the Pops up Z‐Value selector icon to make the numeric bar active
7. Click on the Select and edit line icon and then click on a line to be assigned a contour level
8. Enter the value for the contour line in the Z= area of the numeric bar
9. Click on the = sign button of the numeric bar to assign the value to the highlighted line (points)
10. Repeat steps 8 and 9 for each contour (You can check the spreadsheet to make sure the values are changing)
11. Rename the contour file to be meaningful (e.g., Contours).
Figure: Digitized contours ready for gridding. Note that the contours are extended past the fault block boundary and that a ‐20 was added to the south and a 20 to the north. These provide control for the gridding process.
Digitize points
Use the following steps to digitize the points.
1. Make the Make/edit Polygons process active
2. Click on the Make/edit points icon to digitized points
3. Click on the Start new set of points icon to start digitizing
4. Digitize each point
5. Rename the points file to be meaningful (e.g., wells)
6. Right click on the file and select Insert new attribute
Figure: Add new attribute to points dialog with type String selected.
Figure: Points converted to tops and displayed with well symbols adjusted.
Use the Files
Build the Grid
The grid is allowed to extend past the polygon with a fairly fine grid increment. Techniques described in the Tips and Tricks Contour Gridding were used to build the grid. A second copy of the grid is made and that copy is blanked outside the polygon. The un‐blanked grid is used for volume calculation and the blanked grid is used for contour display.
Figure: Initial grid projecting past the volumetrics polgon (left) and clipped to the volumetrics polygon (right).
Calculate Volumes
Volumes are calculated using the grid that extends past the polygon. Both grids are used to show the difference.
Figure: 2D Grid volumes generated using the operation (left) and showing that the extended grid (top right) carries the volumes up to the polygon while the display grid does not (bottom right) and has less volumes. Note the grid used was very fine with 500 by 700 nodes so the two volumes are very close.
Make Display
The display should be made using the blanked grid, the fault polygons, and with the wells posted.
Figure: Original bitmap (left) and digitized map (right).
