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rudyabo

Stratigraphic Modeling, Interpolation extend

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Dear Rockworks technical team,

 

I'm going to use Rockworks 17 to construct 3D stratigraphic model determined generally by 3 main layers from the top to base as follows:

Quaternary/ alluvium 

Neogene/ Limestone 

Paleogene/ Clayey Limestone

Grid and model dimensions are: 100 x 100 x 5

The Quaternary sediments fill the depressions of the model.

 

Modeling option:

-Inverse Distance was selected as interpolation algorithm with additional options, including Decluster (Average), Smooth (2x2), Faulted (2D Fault).

-Modeling Sequence Base-to-Top (Onlap)

-Constraining Surface: Truncate Units above ground surface/ Replace top surface with ground surface

-Hide thin Zones: 0.005

 

Problem:

After successful running the interpolation, the Quaternary sediment extends over the whole region despite no Quaternary deposits are recorded in the boreholes.

I tried to increase the model resolution, playing with cutoff value, using different interpolation algorithms.. but nothing is changed. (Please have a look on the screenshot)

 

any suggestions to bypass this issue?

 

thanks,

Rudy

 

1504536368_tmp_Rockworks.jpg

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Hi Rudy,

 

In areas of no data, RockWorks uses the data from other areas to estimate what the top and base of a unit are when gridding. You can constrain the interpolation by specifying a maximum distance to allow the program to search for nearby data, or add points with the same top and base of the unit (zero thickness) where the unit is absent. Polygons and faults can also be used to constrain a unit.

 

For display purposes, you can increase the Hide Thin Zone value to a larger value, such as 1.0m or ft.

 

You may want to grid the Quaternary separately, then add it to the model by changing the name to use the Stratigraphy model naming convention: <unit>_top.RwGrd, <unit>_base.RwGrd.

 

Regards,

Tom B

RockWare Inc

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Hi Tom,

 

thank you so much for your quick response.

I would try the second option which seems more reasonable (giving zero thicknesses). Unfortunately, polygon clipping option requires a lot of post-processing and time for smoothing grids.

I think the most challenging issue in Rockworks is how to replicate complex stratigraphic succession. So it would be so appreciated when Rockware put Stratigraphic package on the subsequent development plan.

I'll tell you about the results.

 

Thanks :)

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Dear Tom,

 

Unfortunately, results of zero-thickness option didn't provide good results (almost no changes).

I  increased the cutoff to 1, 20% maximum interpolation distance. The interpolation continues trends for the Quaternary deposits!

For each borehole I inserted new stratigraphic formation belongs to the Quaternary as follows:

          Depth to Top               Depth to Base           Formation 

1        0                                  0                               Quaternary

2        0                                  50                             Neogene

3        50                                100                           Aquitanian 

4        100                               200                          Paleogene 

 

The depths measured from the elevation.

 

please any advice?

 

thanks,

Rudy

 

 

1_1.gif

2_2.gif

2.gif

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I'm wondering if the difference between the borehole Z elevation and the DEM could cause such problem! 

By the way, how to snap them to the topographic surface?

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Hi Rudy,

 

  • 20% may be too high a number for the maximum distance. Try 5% or 10%.
  • You may want to try another gridding method. Triangulation will result in angular surfaces, but it is automatically truncated to the boundaries of the "convex hull" surrounding the data points.
  • There is something unusual going on in the SE corner, where the Quaternary and Aquitanian (gray and yellow) stick out of the brown Paleogene. It may be that the upper units are not constrained by the underlying Paleogene because it is not interpolated in that corner.
  • To change the borehole elevations to match a DEM, choose the Borehole Manager Edit | Adjust Elevations Based on Grid Model.

If you are unable to resolve the Stratigraphy model problems, back up the project with the File | Backup Project menu command to create a ZIP file. Add the RwGrd files to the ZIP, and send it to [email protected] or upload to http://rockware.com/upload

 

Regards,

Tom B

 

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Hi Tom,

 

Thanks for your support. In the southeastern corner, the yellow Neogene deposits pinched out of the Paleogene formation once I activate the maximum interpolation distance to 20%. However, I tired with 5 and 10%, but the result was a clustered small circles surrounding boreholes.

I'll try to snap all boreholes to the surface grid elevation and see if it can solve the problem.

I will send you a copy if it doesn't work.

 

Sincerely,

Rudy

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Dear Tom,

 

No changes after snapping wells to surface topography, I uploaded a backup of the project as requested (File name: Backup_Rudy.rar).

I also enclosed the shape files represent the real Quaternary and Neogene boundaries.    

 

Best Regards,

Rudy

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Hi Rudy,

 

The top of the Quaternary is raised above the base by the option under Stratigraphic Modeling Options | Constraining Surface | Replace Top Surface with Ground Surface. The base of the Quaternary is not pulled up, resulting in a net thickness to this unit.

 

To make the model match the Quaternary SHP file, add points along the polygon or use polygon clipping.

2017-09-08_11-20-56-305.png

 

Many of the boreholes omit missing formations rather than including them at the proper depth with zero thickness, causing the model to be unconstrained for the missing formations in certain areas.  The Top Down modeling order works well for all formations based on an west to east cross section. Create additional cross-sections to test this setting throughout the model.

2017-09-08_13-23-29-590.png

 

Regards,

Tom B

RockWare Inc

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Dear Tom,

thank you so much for your help.

I've just few questions:

 

1. Should I deactivate the option/ replace top suface with ground surface?

2. Do you construct the Quaternary top and bottom based on boreholes elevation?

3. Could you please provide me with the your modified version of the project for comparison purpose.

please accept my sincere appreciation.

Rudy

 

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Hi Rudy,

 

1. Deactivate the option to replace the top surface with the ground surface to prevent the Quaternary_Top from being pulled away from the base.

2. The elevations of the Quaternary top and base are based on the borehole elevation minus the depth to the top and base of the Quaternary.

3. There is a consulting charge of $150/hr to provide files, but support (without files) is included for free with your license. 

 

Regards,

Tom B

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Dear Tom,

thanks for your support.

I finished the model yesterday and I pleased to share you the result I don't know why There was a problem processing the uploaded file. Please contact us for assistance "

Actually, I based on the tools: Raster calculation, Polygon clip, and substitute surface (for the Neogene and Paleogene).

 

Regards,

Rudy

 

 

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Hi Rudy,

 

I'm glad to hear you were able to create a model that you liked.

 

Regards,

Tom B

RockWare Inc

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Hi Rudy,

 

I don't know of any size limitations to image uploads. Send your screenshot to [email protected], and we'll pursue the issue further.

 

Regards,

Tom B

RockWare Inc

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