11.12.3.1 Special Consideration: Column Edge

The only indexable element where the commonality in indexing between the IJK grid and the unstructured column-layer grid is not obvious is the column edge.

• For the unstructured column-layer grid, the indexing of the shared column edges is explicit.

• For the IJK grid, the indexing is implicit and first follows the I column edges (NIL x NJ) and then the J column edges (NI x NJL). The I faces and J faces do not appear as explicit indexable elements but are instead part of the range of elements of the faces. The edge and face indices correspond to the enumeration of shared edges and faces. This ordering is a RESQML choice. The column edge indexing needs to be defined to support face indexing.

There are a number of “object1 per object2” indexable element kinds for IJK grids, which may be used in favor of “object1” indices when the latter are more complicated. For example, for an IJK grid, there are 6 “faces per cell”: 0=top, 1=bottom, 2-5 are side faces following the IJ circular node ordering, described previously. This is a very simple enumeration, versus the “faces” indexing, which depends on the grid faulting and column edge enumeration. Faces per cell indices appear in the grid connections representation and the blocked wellbore representation.