Flexures of 3D grid layers around fault model inconsistencies

In some cases, you may encounter unwanted flexures in constructed surfaces or 3D grids after performing the Structural Modeling and/or 3D Gridding workflows. See image below, where a k-layer is ‘smeared’ along the fault where is should have been properly offset. These flexures can have multiple causes, see section 'Cause' below.

Potential flaws or issues can be located more easily in the QC grid than on the constructed surfaces.

Artifact in the k-layering of a 3D grid. Here the k-layer should be properly offset by the fault, instead, the layer is turned into a flexure. This artifact may be related to inconsistencies in the fault model    click to enlarge

Where encountered

  • model > 3D Structure > Construct Surfaces / Fault Cutoff Line Edits
  • model > 3D Grid > Create Jewel Grid

Cause

Local flexures are mostly attributed to two different causes:

  1. Not covered in this section: inconsistencies in the geometry of other surfaces (i.e. non-fault model surfaces) particularly due to poor horizon clean-up, see:
  2. Covered in this section: inconsistencies in the assigned fault model

In case the flexures are caused by inconsistencies in the fault model, this often means the fault model is not completely watertight along sections where it should be. The following images show examples of the consequences for gridding and how the artifact cascades from the structural model to the 3D grid with k-layers.

Detailed view of the faults contained in the QC grid of a structural model. By giving the faults individual colors (via Autocreate Colors on the Faults context menu), you can see the inconsistency more easily. Here the green fault is extended through a small gap, beyond the blue fault. This artifact may not yet cause problems in the 3D structural model, but when this artifact is carried along into the 3D grid, the internal k-layering is affected (see next image)    click to enlarge

Same location as previous image, but after gridding has been performed (the faults that are displayed, are the faults contained in the 3D grid, rendered using color coding for ZoneID). It is clearly visible that the k-layers of the grid are distorted by the artifacts in the fault (see previous image)    click to enlarge

How to fix the issue

The flexures discussed in this topic are a different manifestation of the same issues (i.e. fault model inconsistencies) which are described in Holes in constructed surfaces or 3D grids. Refer to the paragraph 'How to fix the issue' in that section for the steps to take to solve the issues.

Result

After using the various options to clean-up the faults as described in Holes in constructed surfaces or 3D grids (paragraph ‘How to fix the issue’), fault intersections should be watertight where required. As a result, there should be no flexures anymore in the produced grid. Additional QC steps can be found in paragraph ‘Optional: method to verify fault model compatibility before building the full structural model’ in the same section.

Important   If you edited your faults in the fault model, you have to reassign it to the 3D structural model and perform Construct Surfaces again to include the edits in the 3D structural model. If you edited your faults in the 3D structural model (not recommended), you can directly perform Construct Surfaces, but beware that the fault model (that was used to create the 3D structural model) will be out of sync. Note that the 3D grid will always use the latest surfaces from the assigned 3D structural model.