Page 171 - Principles of Applied Reservoir Simulation 2E

Chapter 16

Modeling Reservoir Architecture

Reservoir architecture is modeled by contouring and digitizing geologic
maps. The mapping/contouring process is the point where the geological and
geophysical interpretations have their greatest impact on the final representation
of the reservoir. This process has been discussed by several authors, including
Harpole [1985], Harris [1975], and Tearpock and Bischke [1991]. Methods for
numerically representing reservoir architecture are discussed in this chapter,

16.1 Mapping

The different parameters that must be digitized for use in a grid include
elevations or structure tops, permeability in three orthogonal directions, porosity,
gross thickness, net to gross thickness, and where appropriate, descriptions of
faults, fractures, and aquifers. The resulting maps are digitized by overlaying
a grid on the maps and reading a value for each gridblock. The digitizing process
is sketched in Figures 16-la through 16-Id.
The resolution of the model depends on the resolution of the grid. A fine
grid divides the reservoir into many small gridblocks. It gives the most accurate
numerical representation, but has the greatest computational expense. A coarse
grid has fewer gridblocks, but the coarse gridblocks must be larger than the fine
gridblocks to cover the same model volume. As a result, the coarse grid is less
expensive to run than a fine grid, but it is also less accurate numerically. The
loss of accuracy is most evident when a coarse grid is used to model the interface
between phases such a fluid contacts and displacement fronts. Thus, fine grid

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