A New Three-Dimensional Computer Modeling System for Geology

Donald C. Swanson

Three-dimensional computer modeling of geological volumes can lead to better reservoir description and more successful prospecting in high-density data areas. One method of 3-D modeling is the distribution of attributes to small incremental sub-volumes or cells. In the past, some incremental systems used horizontal layers or cells each of which were of equal size, shape, and had a uniform vertical dimension. Such systems have inherent difficulties in modeling strata which have a depositional slope and/or structural dip. A smoothly modeled boundary between strata and critical surfaces such as unconformities or fault planes are also difficult with such systems.

New incremental cellular modeling systems divide volumes into stratigraphic sequences or structural blocks which are bounded by surfaces such as unconformities, diastems, surfaces of intrusive bodies, or fault planes. Cells with variable vertical dimensions are placed within the sequences and/or blocks so that layers are parallel to depositional surfaces or time lines. The cells' layers then reflect various stratigraphic patterns such as onlap, offlap, truncation, or proportional thickness variation.

Accurate modeling of proportional thickness variation is only possible where the vertical cell dimensions may have unlimited variation. Cells in the new systems may have some or all vertical dimensions zero which allows smooth, more accurate boundaries in the model.

The new incremental cellular systems also extrapolate and interpolate from and between data points along each unique cell layer only. This distributes critical data within the model so that lateral and vertical variations are closely analogous to variation of natural properties in nature. In order to solve problems in the distribution of qualities and quantities to cells, rule-based systems are also used by the new modeling program.

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.