Assigning faults

With the Assign Data step (model > Fault Stability > Assign Data) of the Discrete Analysis workflow you assign faults to your Fault Stability Model. You can assign faults from one of the following data folders: Surface Set, Seismic Interpretation, Fault Model, Structural Model and 3D Mesh Structural Model. You can only assign faults when they have a tri-mesh representation.

You cannot mix and match data sources; once you assigned faults to a fault stability model from a data source (e.g., from Surface Set A), you cannot assign faults from a different data source (e.g., Surface Set B). Selecting faults from a different source will reset the fault stability model and remove any previously assigned faults (and corresponding properties). If you intend to use faults from different sources it is recommended to store them in a new surface set and assign from there.

In case your faults do not have the necessary tri-mesh representations yet, here are some examples of how to create them:

  1. When a 3D mesh or 3D grid is available, you can extract tri-mesh surfaces for the faults directly from the volume. In the JewelExplorer, go to the faults under your 3D mesh or 3D grid, right click to open the context menu, and select Create > Create Tri-Mesh. Once these tri-meshes are created, they can be assigned to a Surface Set and then used in a Fault Stability Model.
    • If the 3D mesh contains geomechanics simulation results (i.e., 4D geomechanics), while exporting to tri-mesh you can also select 3D mesh properties to be exported as well. Nodal properties will end up as nodal properties on the exported tri-mesh, while element properties will be represented as triangle properties on the exported tri-mesh.
    • When stresses and pressures are exported in this way, the Fault Stability Model can later use these tri-mesh properties directly by selecting Source Type as Faults in Fault Stability Model on the Map Stresses form. This approach prevents using a mapping step that can introduce additional interpolation and artifacts.
  2. Fault polyline sets (or point sets) in your Surface Set can be triangulated as part of the Surface Sets workflow step Triangulate Faults (prepare > Surfaces > Triangulate Faults)
  3. Faults in a Seismic Interpretation with a point set or polyline set representation can be triangulated with the Triangulate tool of the Surfaces strip (prepare > Post-Processing Tools > Polyline Set Tools > Triangulate)

The tri-mesh resolution of your fault tri-meshes directly impacts the shape and orientation of the fault surface, as well as the level of detail on which the fault stability calculations will be performed. Before assigning your faults, make sure that the size of the fault surface triangles is suitable for the Discrete Analysis workflow. This means the triangles need to be evenly distributed over the fault surface and fine enough to provide sufficient detail in the final results. If you need to refine your tri-meshes, you can do this with the Refine Tri-Meshes form in the Tools section of the Fault Stability strip.

Important   If you refine a tri-mesh, any properties generated during the Discrete Analysis workflow will be removed. If you want to refine a tri-mesh, do this before the Assign Data step or directly after it, when no properties are generated yet.
When stress and pressure properties are already available on the tri-meshes to be assigned, typically when the tri-meshes were exported from 3D mesh with properties, it is best not to refine. Refinement (or coarsening) would not only remove the properties, but would also create a deviation from the original simulation results and resolution.

The Fault Stability Model can operate in two modes:

  • Node storage mode  All input data is stored on the nodes of the assigned tri-meshes, and all calculations are performed on the nodes.
  • Triangle storage mode  All input data is stored on the triangles of the assigned tri-meshes, and calculations are performed on the triangles.

Node storage mode also supports mapping data (on the Map Stresses form), for example, from 3D grid and 3D mesh volumes with properties to the tri-mesh nodes. In triangle storage mode, data cannot be mapped to the tri-meshes in this workflow but is assumed to be already available on the tri-meshes assigned to the Fault Stability Model.

Node storage mode is the default mode for the Fault Stability Model, but in some cases (e.g., using a 4D geomechanics simulation on a 3D mesh and depending on the simulator), calculating fault stability on triangles can be a closer representation of the element simulation results in the 3D mesh.

To assign faults to your fault stability model

  1. Open the Assign Data form and under Model, select the fault stability model to which you want to assign faults.
  2. From the Source drop-down list, select the folder that contains the faults you want to assign. Faults must be tri-meshes and stored in a Surface Set, Seismic Interpretation, Fault Model, Structural Model or 3D Mesh Structural Model to be available for selection.
  3. In the Faults table, select the faults you want to assign to your fault stability model by checking the corresponding checkboxes.
  4. Choose whether to apply the fault stability discrete analysis to node or triangle properties on the assigned tri-meshes. Note that this selection will also influence the options on the Map Stresses form.
    • For nodes, all Source Type options are available, including mapping from 3D mesh or 3D grid volumes.
    • For triangles, only the Faults in Fault Stability Mode option is available, meaning the assigned tri-mesh faults must already contain suitable stress and pressure properties.
  5. Click Apply to assign the faults and keep the Assign Data form open, or click OK to assign the faults and move to the next step, Set Frictional Parameters. The faults will be added as tri-meshes to the fault stability model in the JewelExplorer, with the auto-generated properties 'Dip' and 'Dip azimuth' for nodal mode, or 'Dip triangle' and 'Dip azimuth triangle' for triangle mode. These properties will be used as input to the fault stability calculation at the end of the workflow.
    6. Important   Assigning faults to a fault stability model will remove all previously assigned faults, even when the same faults are being re-assigned.