Creating Stereonet Maps from Fracture Data

RockWorks | Borehole Manager | Fractures | Stereonet Map
 

This program is used to plot a map with stereonets of downhole fractures centered over each borehole location. The above collage shows how fractures are displayed within a 3-dimensional striplog diagram versus a stereonet map. 

These options are very similar to those in the Planes | Stereonet option in the RockWorks Utilities, with the following exceptions:

• The program assumes that the downhole fracture data represent planes.
• The program assumes that the downhole fracture data is recorded in dip-direction parlance. This limitation is designed to maintain compatibility with the other programs that read the downhole fracture data (e.g. striplogs and fracture modeling).
• The Symbols option allows the user to either set uniform symbols (i.e. all the same), or symbols that are defined within the borehole location tab.
• The Labels option will automatically assign the borehole title as the point label. Many other additional options are included, including the automatic-offset capability.

See also: Single Stereonets

Feature Level: RockWorks Standard and higher

Menu Options
Step-by-Step Summary

Menu Options 

Stereonet Options (See the Details topic for more information about these stereonet-specific settings)

• Projection: Determines how points are to be projected on the stereonet plot, as an equal angle or Wulff projection, or as an equal area or Schmidt projection. A lower hemisphere projection is used for both types.
  ! Note Stereonet contours (activated below) are based on point distributions within a Schmidt projection (equal area) diagram.  If you plot points on a Wulff stereonet AND include contours, you may note that the point densities and contours might not correspond.
• Symbols: Insert a check here to activate the plotting of symbols on the stereonet. The symbols will represent the point of intersection of the poles to the planes. Expand this item to access the symbol settings. 
  • Size: Defined as percent of diagram size.
  • Type
    • Uniform: Choose this option if all of the symbols are to be the same.  Expand this heading to select the symbol style.
    • Use Borehole Symbol: Choose this option if the symbol listed in each borehole's Location tab should be used in the stereonet plot.
• Labels: Insert a check here to turn on the plotting of labels for each point in the stereonet. Expand this item to access the label settings. Note that the label text will be limited to the borehole ID.
• Contours: Insert a check in this check-box to activate the plotting of line contours on the diagram to represent point density. Expand this item to access the contouring settings. If you request contours, they will be drawn based on a program-computed grid model; be sure you establish the Gridding Options (see below). 

• Colored Intervals: Insert a check in this check-box to activate the plotting of color-filled intervals to represent point density on the diagram. Expand this item to access the colorfill settings. As with the line contours, above, the color intervals will be drawn based on a program-computed grid model.
• Great Circles: Use this check-box and it settings to activate the plotting of planar data as great circles. (If the source data are Lineations, this option will be ignored.) Expand this item to select the line styles.

• Mean Lineation Vector: To activate the plotting of the mean lineation vector, insert a check in this box. Expand this to select a symbol to represent it on the plot, and the label
• Best Fit Circle: Insert a check in this box to activate the plotting of the program-computed best-fit great circle on the stereonet. Expand this item to select its line style and color.
• Title: Check this to activate the plotting of a title on each stereonet, and expand this to enter the text, color, size, and position.
• Statistics: Check this item to plot a statistical legend for the data. Expand this item to select text size and color. (See the Statistical Summary.)  For stereonet maps, this is probably best left disabled since it will be scaled so small that it will be difficult to read.  (More.)
• Background: Expand this heading to turn on and off a variety of reference lines, ticks, and labels.  (More.)
• The Gridding Options and Density Units items in the Stereonet Options window are used to establish how the point densities are to be computed if either line or color-filled contours have been requested on the stereonet plot. The program uses a process of "gridding" to compute point densities, in a manner similar to the gridding process for creating maps. The methods used to extrapolate the grid node values in a stereonet differ from the methods used in mapping, however. To access these settings, expand the Gridding Options item.  For "basic" gridding, you might select the Step Function method, with density units in Percent. See Stereonet Gridding Options for a lengthy explanation.
  ! Note Stereonet contours are based on point distributions within a Schmidt projection (equal area) diagram.  If you plot points on a Wulff stereonet AND include contours, you may note that the point densities and contours might not correspond.
• Minimum Fractures: The "Minimum Fractures" setting defines how the program will handle boreholes that either contain no fractures or not enough fractures to generate a contoured net. Specifically:
  • A setting of 0 will plot the radial/concentric background grids for all boreholes, even if they have no fracture data.
  • A setting of 1 will omit nets for boreholes that don't have at least one fracture. If a borehole contains less than three fractures, the radial/concentric background grid will be plotted along with symbols depicting the projected fracture points.
  • A setting of 3 will only plot the contourable nets.
• Stereonet Dimensions: Use these settings to define the size of the stereonets, as a percent of the project size.  (Default = 10)  The program creates stereonet maps by rescaling individual diagrams and centering them on the borehole collar locations. Since the diagrams are typically circular (assuming that the statistical legend has been disabled), the x and y dimensions should be set to the same value.  If your diagrams contain additional information (e.g. titles, color legends, statistical summaries, etc.), you will need to experiment with x/y settings that produce circular diagrams.
• Border: Check this to include border annotations of the map coordinates.  Expand this heading to access the border settings.  (More.)

   

Step-by-Step Summary

1. Access the RockWorks Borehole Manager program tab.
2. Enter/import your fracture data.
3. Enable the boreholes whose fracture data is to be represented in the map.
4. Select the Fractures | Stereonet Map menu option.
5. Enter the requested menu settings, described above.
6. Click the Process button to proceed.

For each borehole, the program will generate a stereonet diagram that depicts the 3D orientations of the fractures. It will build a map of these diagrams, placing the stereonet center at the borehole location.  The completed map will be displayed in a RockPlot2D tab in the Options window.

7. You can adjust any of the options along the left and click the Process button to regenerate the map.
   ! Each time you click the Process button, the existing display will be replaced. 
    
8. View / save / manipulate / print / export the map in the RockPlot2D window.
   
   

 Back to Fracture Menu Summary 

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