Stratigraphy Modeling Options

Menu Options

• Modeling Sequence: These options tell the program whether to build formations as entered, or with bottom-up or top-down rules.
  
  
  • None: Selecting this tells RockWorks to interpolate the stratigraphic surfaces based on the borehole data (with any other applicable data-filling rules appllied). The program makes no consideration about overlying or underlying units, so missing data can result in gaps between units or crossing units.

  

  • Onlap: This option "fixes" models in which portions of an upper unit extend below the base of a lower unit. In order for this program to work correctly, the sequence of formations within the Stratigraphy Types Table must be listed from top to bottom (i.e. the younger formations at the top and the lower formations at the base.  It's also necessary to have good base surfaces, upon which you can layer the upper surfaces.

  

  • Underlap: This option is the opposite of Onlap. It gives priority to upper surfaces. Starting from the highest unit and proceeding downward, if a unit extends above the overlying unit, it will be truncated along the base of the overlying unit. As above, it is important that you have your formations ordered correctly in the Stratigraphy Types Table, and you have a good upper surface from which to work downward.

  

If you are dealing with non-sequential stratigraphic units (which is NOT what the Stratigraphic capabilities within RockWorks were designed for!), such as dikes, it may still possible to model the geology by disabling the Onlap feature and plotting the model as a voxels-only diagram:

• Constraining Surface: Insert a check here if you want the stratigraphy model to be filtered with a surface, typically representing the ground surface. You can also request that the uppermost interpolated surface be replaced with this constraining surface.
  ! This model must have the same dimensions and node spacing as is represented in the stratigraphy model surfaces.  If you need to resample the ground surface grid, refer to the Utilities | Grid | Math | Resample option.
  • Ground Surface Grid Model:  Click here to browse for the name of the grid model to be used to truncate the stratigraphy model and (optionally) to replace the uppermost stratigraphic unit's top surface.
    • Truncate Units Above Ground Surface: This option will filter the surfaces above the ground surface, setting those nodes to the null value.  In the example below, in which the ground surface grid model represents an excavation pit, this would result in the "post-excavation stratigraphic model" or pit model.
    • Truncate Units Below Ground Surface: This option will null-out the stratigraphic model below the ground surface grid.  In the pit example below, this could be used to isolate the materials to be removed from the site.  At the bottom of the graphic below, you'll see the volume report for these removed materials.

    

    • Replace Topmost Surface with Ground Surface Grid Model:  Check this option if the constraining surface is to be used as the uppermost stratigraphic surface. This can prevent gaps between the uppermost surface (which is modeled from boreholes) and the constraining ground surface (which is typically more accurate).
       
• Polygon Filter: Activate this option if you want to clip the stratigraphic surfaces with a user-defined polygon.
  • Polygon Table: Click the Edit button to select the name of the table, in the project database, that contains the polygon vertex coordinates.
  • Filter Type: Expand this heading to define how the surfaces are to be filtered:
    • Interior: The portions (nodes) of the stratigraphic surfaces that lie inside the polygon boundary will be set to null.  (e.g. a pit)
    • Exterior: The portions (nodes) of the stratigraphic surfaces that lie outside of the polygon boundary will be set to null.  (e.g. a lease boundary)

    

  • Note that the stratigraphic model polygon filtering works with interior filtering with both complex and concave polygons.

• Baseplate: Insert a check in the Baseplate option if you want the base of the lowest formation to be extended down to a set elevation. This is helpful for data sets missing depth-to-base values in the lowest formation (boreholes never reach the bottom).
  • Stratigraphic Unit: Click on this button to select from the stratigraphy types the name of the formation to be extended to the baseplate elevation declared below.
  • Elevation: Click on this item to type in the elevation to assign as the base of the unit selected above.  NOTE that you must enter the baseplate ELEVATION not depth.

See also: Stratigraphy Rules

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