Anyone who has done exploration or reservoir studies involving large numbers of logs, cores, or seismic data is aware of the great amount of manual labor required to reduce the data, to draw structure and thickness contour maps, and to make lithologic cross sections. While computers are commonly used to draw contour maps, lithologic cross sections and 3-dimensional interpretations are still made by hand. Computer programs have been developed that build and use 3-dimensional models. These programs use data from wells or shotpoints to interpolate the geologic properties in 3 dimensions between control points much as a geologist would construct cross sections (i.e., by correlating between stratigraphic horizons). Modeling may be done at any scale, from large basins to indivi ual reservoirs, and with an appropriate amount of incorporated detail. After the model is constructed, it is available for calculations and displays. Cross sections can be constructed showing the geographic extent of the rock properties. Similarly, facies maps can be drawn to depict geology at specified depths or along geologic time surfaces. Information in the model can also be used to construct contour maps such as net pay thickness or average porosity, and to compute volumes.

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