Base of borehole in Stratigraphy model

[TimR]

Hi,

I am working on a model where there are 3 basic strata, we'll call them A, B and C; these are in a consistent order with A at the top and C at the bottom.

Some of the shallower boreholes stop in stratum B, so we don't know at what depth stratum C comes in. However, Rockworks seems to assume that in this case the interface between B and C is the base of the borehole, which is clearly incorrect (it could be at least 10m deeper); obviously this has a major effect on the model and any subsequent sections. Is there an option to tell the software to ignore the base of a borehole and just work out the models for the base of B and top of C from boreholes where the interface is actually present, but making sure that the interfaces pass below the bare of boreholes where the interface has not been reached.

 

As an aside I have had a few times when the modelling has ignored a borehole's data and worked out interfaces that do not agree with the borehole (which we know to be correct); surely, it shouldn't be possible for this to happen?

 

Any advice gratefully received,

Thanks,

Tim

[Alison]

Tim,

 

For boreholes that don't fully intersect a unit, I would recommend that you leave the depth of the lowest unit  (for example, the base of Unit "B") blank in the database table.  As long as you have that contact defined in deeper surrounding boreholes, the program should use the surrounding contacts during grid interpolation.  Here is an example of how this looks in a shallower borehole in our Sample project.

 

 

There are some model settings that you may have adjusted that could affect how this works (under the Strat Rules tab in the various Stratigraphy modeling/diagram windows).  Also, if the base of Unit B has a highly variable elevation, then you could run into problems where the program plots the contact above the base of the borehole.  In this case, we usually recommend that you add a contact point below the base of the borehole (this is pretty rare).

 

If you continue to run into problems, we would be happy to take a look at your project.  You can back up your project or database through the File menu in the Borehole Manager, and send us the ZIP file created during the backup process.  Please send it to tech@rockware.com.

 

Best Regards,

Alison

 

 

 

[JoshZA]

Does the same logic apply to the top intersection, say A-Horizon, such that you make it blank and 1.5m?  I have a similar 3 strat problem with incomplete units throughout.

 

I'm having a lot of trouble trying to get a strat model from stratigraphy all dipping about 15 degress in the same direction and almost the same dip as the slope.

 

Is there a preferred modelling method for modelling stratigraphy that is inclined as even with kriging I seem to get the search going horizontally.

 

Thanks,

 

Josh

[Alison]

Josh,

 

Yes, you could do the same thing with a top contacts (leave them blank if the upper portion of the unit has been eroded away).

 

Also, you may want to look into use the "Dip" gridding algorithm, which would allow you to specify a bedding orientation at contacts where this is known.  You would need to populate the Dip and Dip Direction fields in the Stratigraphy Table in the Borehole Manager, which are hidden by default.

 

Here are some steps to use to show these in the interface:

 

1.  In the Stratigraphy table, click the Tab Manager button.  The Tab Manager window should open up.

2.  Make sure that Stratigraphy is selected and click "Edit Fields".

3.  Click on the Top and Base Dip Direction and Dip Angle fields, and click OK (and then OK to close the Tab Manager).

 

 

If you have a constant Dip Direction (which 90 degrees to Strike) and Dip Angle for all of the units in the model, I would populate these fields for all of the populated contacts.  You should leave non-intersected contacts at the top and base of each borehole blank, without a depth or orientation information.

 

When creating the Stratigraphy model, you should use the "Dip" algorithm, rather than Kriging or Inverse Distance.  You might need to experiment with limiting the number of points used during the interpolation.  The more points you use, the smoother the surfaces.

 

 

Please feel free to send us your data if you are having a hard time with this project.  We'd be happy to take a look and provide additional advice!  You can send a backup of your project to tech@rockware.com.

 

Best Regards,

Alison