Adding External Surfaces to a Borehole-Based Stratigraphy Model

RockWorks contains a number of tools which allow you to create a stratigraphy model from borehole data, then introduce additional surfaces to the model based on surveys or proposed excavations. This example is based on an inquiry from a customer who is modeling an existing fill site, in which there are borings surrounding the fill, but none inside. They have surface models of the fill base and fill top which they want to add to the borehole-based stratigraphy model, constraining those borehole surfaces with the fill surfaces.

Step 1: Create the RockWorks project and enter the borehole-based data

Create a new project in RockWorks, and import your borehole data (File | Import menu). Or, create the borehole records manually (Edit | New Borehole) and enter the stratigraphy data into the borehole manager: depth to formation top, depth to formation base, and formation name for each recorded unit in the borehole. The formation names are defined in the Stratigraphy Types table.

Here’s a Striplogs | 3D | Multiple Logs view of these stratigraphy logs.

strat_logs

Step 2: Establish the Output Dimensions

Once the borehole location and stratigraphy data have been entered, click the Scan Boreholes button at the bottom of the program window to automatically determine the coordinate extents for the project. (You can also just type these in, if you prefer.) Be sure to check the node spacing along the X and Y axes – this will determine how coarse or fine your grid models will be. (We generally recommend a node spacing that’s no greater than half the average distance between the boreholes.)  Here is how the Output Dimensions might look:

output_dims

Step 3: Create a Stratigraphy Model of the borehole-based data

Use the Borehole Manager | Stratigraphy | Model menu option to create surface models (aka “grid models” or “grids”) for the top and base of each stratigraphy formation and display them in the 3D plotting window. This project-wide and interactive view of the model allows you to drill down into the model to see how well the surfaces match the borehole data (be sure to turn on the Plot Logs option to display your stratigraphy logs in the 3D display). You can zoom into the display, rotate it, etc.

original_model

If you are not satisfied with the way the model looks, how it honors the log data, etc., you can adjust the gridding method and other model settings and click Process again to regenerate the grid models and the 3D scene.

Note: the automatic naming scheme for these grids is “formation_top.rwgrd” and “formation_base.rwgrd” for each formation name in your project.  You’ll see these grid names in the Project Manager / Grid Models heading.

Step 4: Create/Import the Fill Grid Models

Once you have a good model of the borehole data, the next step is to create or import the grids representing the fill. If you have XYZ points for the ground and base elevations of the fill, you can enter/import those data into the Utilities datasheet and use the Utilities | Map | Grid-Based Map menu to create the surface models.

Or, if you have existing grids from another software program, you can use the Utilities | Grid | Import menu to convert them into a RockWorks “.rwgrd” format. If necessary, use the Utilities | Grid | Math | Resample menu to resample these imported grids to match the extents and node spacing of your project’s Output Dimensions. It’s important that all of the grids to be incorporated into the final stratigraphic model have the same dimensions.

Important: Name these grid models using the RockWorks naming convention: “Fill_top.rwgrd” and “Fill_base.rwgrd”

Here’s an example of how these surfaces might look in the 3D viewer:

waste_3d

Step 5: Display the stratigraphy grids and fill base grid in cross section

This step will let you visualize the stratigraphic layers which will need to be constrained by the fill grids. Jump back to the Borehole Manager and use the Stratigraphy | Section menu to create a cross section diagram through the middle of the fill area.

BE SURE to turn Interpolate Surfaces OFF– you’ve already created a good stratigraphic model so you don’t need to keep recreating the grids.
BE SURE to turn Plot Surface Profile ON, choosing the Fill_base.rwgrd as the grid model to be displayed with the profile line.

Use the Section Selection Map tab to draw a cross-section trace through the middle of the fill area. In the resulting cross section, make note of the stratigraphic layers which are impacted by the fill and those which are not.

section1

Repeat if you like, for another cross-section trace.

section2

Step 6: Constrain the stratigraphy grids with the fill base

Jump back to the Utilities program tab. Use the Grid | Filters | Limit program to impose a “high-stop” filter on the top grid of your first formation, based on the Fill_Base.rwgrd file. Set the Truncation Type to “Grid A Node = Grid B Node”.

grid_limit_settings

This means that any nodes in this grid surface that stick up above the Fill_base grid are to be assigned the elevation of the Fill_base grid. You can set the output name to the original grid name. Do this for each formation_top and formation_base grid that is impacted by the fill layer.

Tip: Use an RCL script to automate this! Here’s an example.

rcl

(RCL scripts require Level 5 licensing in RockWorks16.)

Step 7: Add the Fill layer to your Stratigraphy Types table

Use the Project Manager to access the Project Tables / Types Tables / Stratigraphy Types, and add a new formation, “Fill”, with a color of your choice, as the first unit in the project. Even though you don’t have any fill layers in your boreholes, this now tricks RockWorks into incorporating the Fill top and base grids into the model.

strat_types

Step 8: Recreate your cross section with the Fill grids and the filtered grids

Use Stratigraphy | Section to recreate the cross section from Step 5 being VERY SURE that Interpolate Surfaces is OFF. This assures that RockWorks will read the existing (filtered) grid models for all of the formations in the Stratigraphy Types table.

section1_BYou can create other Stratigraphy menu diagram with these same surfaces.

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