fracture combine command


fracture combine keyword ... <range>

Primary keywords:

angle    collapse    distance    merge

Simplify fractures. Fractures are sorted by decreasing size and, starting with the largest fracture (termed the reference fracture), the algorithm determines smaller fractures in which the following 2 criteria are met:

  • The difference between the reference fracture and fracture orientations is smaller than a given angle (provided by the angle keyword).
  • The distance between fractures (as determined by the distance between the smallest fracture center and the largest fracture plane) is less than a specified distance (provided by the distance keyword).


  • Using the merge keyword can significantly change the fracture density. Use this keyword with caution.
  • All intersections are deleted when the fracture combine command is used.

When these criteria are met, smaller fractures are rotated to have the same orientation as the reference fracture. The algorithm continues by switching the reference fracture to the next largest fracture that has not been previously rotated. If the merge keyword is given, the fractures that are coplanar are translated onto the reference fracture plane if they would overlap. If a fracture falls completely within a larger fracture, it is removed; otherwise, the surface of the largest fracture is increased so that it is equal to the sum of the surface of the two merged fractures.

angle f

Angle criterion for fracture proximity identification with f ≥ 0.


Collapse rotated fractures onto the reference fracture plane. Fractures are not merged by default.

merge-convex <iterations i > (3D ONLY)

Merge the collapsed fractures into planar convex fractures. This operation happens after all fractures have been collapsed. Collapsed fractures that are within the distance specified with the distance keyword are removed and the convex hull of these fractures is created. This is an iterative operation that, by default, continues until no fractures can be merged unless the iterations keyword is given.

distance f

Distance criterion for fracture proximity identification with f ≥ 0.


Merge fractures that would overlap the reference fractures if they were collapsed onto the reference fracture plane. If a fracture falls completely within a larger fracture, it is removed.

Usage Example

The following example illustrates how the fracture combine command can be used to reduce the number of fractures in a fracture set with close orientations (3D). After having generated a DFN, it proceeds in two steps:

  • first, fractures with the closest orientation (solid angle between them smaller than 20°) are merged;
  • second, fractures with a more flexible orientation criterion (solid angle between them smaller than 50°) are projected on the same plane but not merged.

The initial DFN is thus “simplified,” and there are no small angles between fractures, which can help for further mesh.

The example in 3D:

model new
model random 10000
model domain extent -5 5 -5 5 -5 5 
;Create a template
fracture template create 'example' orientation fisher 50 150 10
;Generate fractures using the template
fracture generate template 'example' fracture-count 400
;Combine fractures based on angle and distance, merging 
fracture combine angle 20 distance 0.5 merge
;Combine fractures based on angle and distance, collapse
fracture combine angle 50 distance 0.5 collapse
program return