11.3.2 Truncated Cell Grids

Although not as common as the three fundamental grid types, the petroleum industry also uses “truncated” cell grids. These grids are based upon a column-layer fundamental grid, but with the extension that cells can be split and truncated. These splits are used to describe complex juxtaposition and cell shapes at fault block boundaries. The resulting cell indexing is that of the underlying grid, plus additional unstructured cells.

• Truncated IJK Grids have 3+1 cell indices: NI, NJ, NK and #UnstructuredCells>0.

• Truncated Unstructured Column-layer Grids have 2+1 cell indices: #Columns, NK and #UnstructuredCells>0.

For each of the truncated grids, the cell count is increased by #UnstructuredCells compared to the base column-layer grid. When stored, these additional “truncation cells” are stored in a separate 1d patch array so that the multi-dimensional array structure of the column-layer grid is retained for rapid data access, at least for the majority of cells.