Geologists often face challenges when modeling faulted deposits, as workflows in many software packages are often manual, time consuming and costly. In Minex, there are two main methods for modeling a fault, 2D and 3D faulting. Typically 2D faulting is applied when little or no information is known about the fault and the fault is assumed to be dipping vertically.
2D faulting is also preferred when modeling needs to be completed quickly. In contrast, 3D faulting is favored when detailed information is known about the fault, such as dip and throw.
An example of a 2D fault model is shown below:
A summary of how to apply this functionality in your daily work is provided below.
Firstly, ensure that:
• GEOVIA Minex 6.5.1 software is installed and running
• The Minex borehole database file (*.b31), geometry file (*.GM3) and parameter file (*.mpf) must be open
• Created DDNames / grid folders. For example NT.grd
• Completed Seam Splitting and/or Father/Son operations (if applicable)
• Completed Set Missing Seam process
• Generated and validated preliminary structural grids
- Create fault trace: String > Create
The first step in 2D faulting is to create a string that defines the fault trace. Remember that a 2D Fault is a vertically dipping fault plane, therefore it is best to digitize the fault trace in Plan View.
There are two String types to model a 2D fault, either, Fault WT (With Throw) or Fault NT (No Throw).
If you choose NT, the software will automatically calculate the throw of the faults for you from the seam intervals either side of the fault plane. With WT, the elevation of the fault trace will be the throw of the fault. For example, if the Z elevation of the string is 10m, then the throw of the fault will be 10m. The option to create each string type each is shown below:
- After digitizing the fault trace, it is advisable to annotate the string with Direction Arrows. This is because the string direction can help control which side of the fault is up-thrown or down-thrown. Typically, the left-hand side of the fault trace is the down-thrown side. The below example demonstrates a graben.
- Create Faulted Grids: SeamModel > Multi-Seam Multi-Variable Gridding
In the below form:
• Select an Output grid folder (e.g. NT).
• Select Seam Variables (e.g. BASERL and TOPRL).
• Select a Grid parameter (e.g. STR) for each Seam Variable. If one doesn’t exist save a parameter in the Grid Compute function.
• Select Seams (e.g. A1, A2, B etc).
• Tick Access Geometry and select the fault geometry by clicking
4. In the following form select the Group, Map, Ident and Class of your fault strings:
In the form above, save a parameter called *SF and *SR, if gridding BASERL and TOPRL. These parameters will ensure all seams in stratigraphic sequence are faulted by the 2D fault strings. Please see the Minex help for more advanced parameter options.
5. Select *SF and *SR in Multi-Seam Multi-Variable gridding and click Update List. This will provide a preview of the grids to be created in the Output window. Then click OK, to confirm and proceed with gridding.
6. The resultant seam floors and roofs should be faulted when displayed:
7. Lastly, to achieve a valid seam model the standard grid modelling process should be completed, typically this involves the following functions:
- SeamModel > Seam Model Operations > Arithmetic > Seam Thickness
- SeamModel > Seam Model Operations > Arithmetic > Interburden Thickness
- SeamModel > Seam Model Operations > Model Build or Strata Build
- SeamModel > Seam Grid Statistics
The model is now complete and ready for additional tasks, such as resource reporting.
Check out our other Minex how-to posts here. For more information on coal seam splitting, check out our post on Using Minex to Better Understand Coal Deposits.
