Creating 2D Stratigraphic Thickness (Isopach) Maps

RockWorks | Borehole Manager | Stratigraphy | Stratigraphic Thickness | 2-Dimensional (Isopach)

Use this program to:

• Read a listing of stratigraphic contacts from the Borehole Manager database.
• Interpolate a grid model representing the top or base of the selected top formation, across the project area.
• Interpolate a grid model representing the top or base of the selected lower formation, across the project area.
• Subtract the lower surface from the upper, creating a thickness grid model.
• Create a (flat) contour map representing the isopach grid model, with a variety of map layers.
• Plot the map in RockPlot2D.

Feature Level: RockWorks Standard and higher

Menu Options
Step-by-Step Instructions

Menu Options

• Superface/Subface Options: Expand this as necessary to specify the formation(s) whose thickness is to be modeled. 
  • Unit Top:  Click on the formation name to the right to select the stratigraphic unit whose top or base is to represent the upper surface of the isopach model. 
    • Top of Unit: Click this radio button if the upper surface of the isopach model is to be the top of the selected formation.
    • Base of Unit: Click this button if the upper surface of the isopach model is to be the base of the selected formation.
       
  • Unit Base: Click on the formation name to the right to select the unit whose top or base is to represent the lower surface of the isopach model. 
    You can specify different formations for the top and the base, and the entire thickness between will be computed. The formation names that are listed here are read from the current Stratigraphy Types Table. 
    • Top of Unit: Click this radio button if the lower surface of the isopach model is to be the top of the selected formation.
    • Base of Unit: Click this button if the lower surface of the isopach model is to be the base of the selected formation.
       
  • Truncate Base: Check this box to constrain the lower surface from extending above the upper one, which can happen in areas with low control.
    The isopach is generated by subtracting the lower surface elevations from the upper.  If the surfaces cross, a negative thickness value will result, which (for obvious reasons) doesn't make much sense.  This base truncation option tells the program to compare the surfaces before subtraction and truncate base grid elevations where they exceed the upper.  The subtraction operation would then generate a thickness value of zero (pinched out) in those areas.
     
• Gridding Options: Click on the Options button to the right to establish the gridding method (aka algorithm), the grid dimensions, and other gridding options.  These will be used as the program "grids" or models the surface elevations and base elevations of the selected formation(s), and stores the difference in a thickness grid. 
  • Algorithms: Select a gridding method from the list on the left, and establish the method-specific Options in the middle pane.
  • Grid Dimensions:  Specify how the grid dimensions are to be established, using the settings on the right side of the dialog box.  Unless there's a specific reason to do otherwise, you should probably leave the grid dimensions set to the current project dimensions.
  • Additional options: Establish the other general gridding options (declustering, logarithmic, high fidelity, etc.).
     
• Save Grid Model: Insert a check here if you wish to save the thickness grid model that will be illustrated in the map.  You might, for example, wish to use the RockWorks Utilities "Grid" menu tools to edit the model.  Expand this item to assign the grid file name, such as "morrison-thickness.RwGrd". 
   
• Diagram Options: Establish the 2-D mapping options. To activate a layer insert a mark in its check-box. To access the layer's settings expand the item by clicking on its "+" button. You may include any/all of the layers to illustrate the isopach. 
  • Background Image: Insert a check in this check-box to include a raster image behind the line contours.
    • Expand this heading to establish the bitmap settings. (Note that this layer will be hidden if Colored Intervals are selected, above.) More. 
  • Contour Lines: Insert a check in this box to illustrate the isopach with line contours.
    • Expand this heading to click on the Options button establish the contour settings. More.  
  • Colored Intervals: Insert a check in this box to illustrate the thickness values with color-filled contour intervals.
    • Expand this heading to click on the Options button to establish the color contour settings. More.  
  • Fault Polylines: This option should not be activated for isopach maps.
  • Labeled Cells: Insert a check in this box to display on the map the actual node values stored in the thickness grid model.
    • Expand this heading to access the Options button where you can establish this layer’s settings. More.  
  • Borehole Locations:  Check this box to include a map layer with the borehole locations noted with symbols, plus a variety of labeling options. 
    • Expand this heading to click on the Options button where you can select symbol and label settings.  More.
  • Border: Insert a check in this check-box to annotate the map borders with axis titles and/or coordinate labels.
    • Expand this heading to click on the Options button where you can establish the border annotation settings. More.  
      
      

Step-by-Step Summary

Follow these steps to create a 2-dimensional (flat) contour map that represents the thickness of a single stratigraphic unit or adjacent units.

1. Access the RockWorks Borehole Manager program tab. 
2. Enter/import your data into the Borehole Manager database. This tool specifically reads location, orientation (if any), and stratigraphy data.
3. Select the Stratigraphy | Stratigraphic Thickness | 2-Dimensional (Isopach) menu option. 
4. Enter the requested menu settings, described above.
5. Click the Process button when the gridding and mapping settings are established to your satisfaction. 
6. If you have activated the gridding Dimensions / Confirm Dimensions option, the program will display a summary window with the grid boundary coordinates and node spacing.  Adjust these items if necessary and click OK.  More. 
7. If you have activated the Confirm Intervals setting for the Contour Lines, the program will display a summary window with default contour intervals.  Adjust these items if necessary and click OK.  More. 
8. If you have activated the Confirm Intervals setting for the Colored Intervals, the program will display a summary window with default color-contour intervals.  Adjust this item if necessary and click OK.  More. 

The program will read the depth intervals for the selected stratigraphic unit(s) as listed in the project's Stratigraphy tab. It will internally translate depths to elevations based on the boreholes' surface and downhole surveys. It will create two background grid models, of the top-formation's upper or lower elevations and of the base-formation’s upper or lower elevations, using the selected gridding method. It will then subtract the elevations in the lower-grid from those in the upper-grid, thus creating a thickness model. If you have requested, the model will be stored under the specified name on disk. From this model it will create a 2-dimensional map with the selected layers.  The map will be displayed in a RockPlot2D tab in the Options window.

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

 Back to Stratigraphy Menu Summary

RockWare home page