Geological concepts invariably involve spatial relationships, so most exploration and reservoir analysis should be three dimensional. Significant benefits can be gained by working directly in three dimensions, rather than using a series of two-dimensional analyses to gain three-dimensional insights. These benefits include use of appropriate averaging, better analysis of reservoir continuity, ability to interface data with other programs, and increased geologist's productivity.

Because of spatial complexity and the need to process large amounts of geologic data, computer programs are used to map and model rock properties. The papers in this section deal with what we shall call 3-D geologic block models. In these models, we divide the geological volume to be studied into blocks, and use observed data to assign geological properties to the blocks to make a complete representation of the existing geology. The set of blocks with assigned geologic attributes thus constitute 3-D geologic block models.

Geological interpretation is important with 2-D computer mapping, and interpretation similarly should be used during the modeling process. The assignment of values to the model blocks should be made in a way that incorporates stratigraphic and structural information. This paper summarizes benefits of 3-D geologic block modeling over 2-D analyses, and then describes some current approaches to this type of modeling.