Print this pageThree-dimensional digital modeling can substantially improve reservoir characterization. The 3D workstation is the only effective way of observing the spatial relationships of all of the reservoir attributes, from geologic facies to porosity and permeability. No other technology allows a researcher to visualize potential fluid pathways by delineating the lateral and vertical continuity of higher permeability beds. This same 3-D model can be used by a geologist to determine which wells have penetrated high permeability beds and whether these beds have been perforated in the well.
The modeling software cannot be used as a black box into which data are dumped and from which the relationship of different reservoir attributes such as facies and porosity become readily apparent. A critical step is normalizing the data. Wireline logs such as gamma ray and spontaneous potential curves do not have an absolute scale and must be normalized to each other. Calibration errors in the density and neutron logs should be corrected. Incorrect wireline logs or core data typically show up as stripes or hot spots in a 3-D model.
The stratigraphic framework must be well understood before modeling can begin. With contour mapping of reservoir attributes in two dimensions, errors such as the crossing of stratigraphic horizons are not always obvious; but in three dimensions interpretation errors produce an impossible geologic model of the subsurface. With 3-D visualization, the geologist is forced to use an iterative approach to mapping, whereby errors are found and corrected. Two-dimensional mapping by itself is no longer adequate for characterizing a subsurface reservoir.
AAPG Search and Discovery Article #90926©1999 AAPG Eastern Section Meeting, Indianapolis, Indiana