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Adding map data to borehole model


Ian Madin
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I am trying to combine borehole stratigraphic data with geologic map data. From what I have been able to gather, this is done by creating psuedo boreholes at locations where the map provides stratigraphic data. To convert my contacts, I first converted the polylines to vertex points, then gave each point a collar elevation equal to the ground surface elevation, and then added two stratigraphic intervals. One interval extends from -10 ft to 0 and has the overlying unit, the other goes from 0 to 10 ft and has the underlying unit. Is this the right approach? Is there a simpler way to do it?

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I think this is a good approach.  Depending on whether you need to model other units as well, you may want to add additional contacts to the database, both above and below ground (perhaps using an average thickness value for each unit).

 

When creating the Stratigraphy model, be sure to use a "Constraining Surface" such as a DEM or grid that is based on borehole elevations.

 

Feel free to send us your project if you are having a problem creating a model that reflects these superficial contacts.

 

Best Regards,

Alison

 

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Thanks. I am using Rockworks for the first time, and really appreciate the advice.  I am making a fairly detailed and accurate geologic map on a lidar base, so I will have plenty of contacts on multiple horizons to include. I assume there is no way to include strike and dip data directly. I was planning on using the lidar as a topographic surface, but Rockworks choked on a 600,000 cell USGS DEM so I can't imagine how it would handle 1m lidar.

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You will definitely need to resample the DEM or LIDAR surface to match your project dimensions.  This can be done through the Grid|Math|Resample program under the Utilities.

 

In most cases, you can import the DEM as an ArcASCII file (or some other format), but you may not be able to display it.  You just need the RwGrd file to be created so that the resample tool can be used to bring it down to a resolution more appropriate for geologic modeling.

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Also, there are fields for strike and dip in the Stratigraphy table.  Use the Tab Manager tool to enable the fields.

 

image.png

 

If you populate these fields, then you would want to use the Dip interpolation algorithm during model creation:

 

image.png

 

Unfortunately, other interpolation algorithms don't take strike/dip into account, so you really just need to experiment to see if this approach works for you.  Limiting the number of points or applying a cutoff distance seems to help create more realistic surfaces.

 

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I am thinking that it will work better with a smaller number of higher quality points, and including structural data with them. If I put in points along a contact, and constrain the model with the ground surface, will I run into problems if there are small differences in the collar elevation and interpolated ground surface? I m worried that the model might truncate the interval of the borehole that includes the contact, and therefore not see the contact. Or does it build the model first and then clip to the ground surface?

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