Geologists working on resource model generation may find the Seam Washout Grid function in GEOVIA Minex™ helpful. Often, coal seams will be washed out, either by rivers or streams, or burnt out by fires, affecting the continuity of the deposit. This also affects the tonnages and volumes reported.
By using the Seam Washout Grid function, users can generate more accurate results by identifying the areas where one or more seams are washed out or burnt.
Minex generates a grid with value of 1 or value of 0 to identify these areas, where value of 0 indicates washout zone. These areas are determined by the presence or an absence of seam picks in boreholes with a defined valid distance in the input dialog.
To compute washout grids follow the steps below:
1. Create the seam washout grid by selecting Seam Model in the main menu. Select Compute Seam Washout Grid to open up the below dialog box.
2. You can select TOPS or any other grid which has desired extents as the reference grid
3. As a prerequisite, you will need to model the seam floor grids for all the seams you require washout grids for.
4. Under ‘Select Seams’, select seams to be processed.
5. Under Input Parameters, enter a valid distance from boreholes. This refers to the radius of the washout circle around each washout borehole. All mesh points within this circle are assigned a value of 0.
6. Under Input Parameters, enter a valid maximum distance from borehole. Note that for each valid seam pick, a box (for which the length and height are located at maximum distance from the borehole) will be placed over the grid. Normally these boxes overlap. A value of 1 is assigned to all mesh points inside this box.
7. Select the Borehole Seam Data. If you have a split borehole database, you should use both ‘Inp’ and ‘Est’.
8. Under Output Parameters – DD Name, define the grid suffix (e.g. MK) and select a DD name where the output grids need to be saved.
9. Click OK to generate washout grids.
The image below shows the initial model prior to executing the Seam Washout Grid function. Note the interpreted seams are indicated in pink.
The following diagram and steps explain how the washout grid is generated.
For those boreholes that do not contain any input seam pick data – estimated (E) or Interpolated (I) – and are between collar and total depth, the mask grid values are set to 0 (washout). This is indicated by the red line in the above diagram.
Minex will also check the barren holes in each seam floor grid to determine if they intersect the borehole between the collar and total depth elevations. If it intersects, the mask grid values around are set to 0 value. This value estimates where the seam would have been located prior to washout or burnout.
For all other cases, the mask grid values are set to 1 (indicating existence of seam grid). This is indicated by the green line in the above diagram.
The image below illustrates the final model. Note the washed or burnt out areas identified in the model.
As this process generates grids for each seam, it is easily validated and modified to suit the geologist’s interpretation and may subsequently be used to set the seam thickness grids to represent the burnt zone or washout zone.
Want to learn more? Check out some of the other geology features in Minex.
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Ajay Reddy
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