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3-D
Geologic Visualization for Subsurface Reservoir
Characterization
Three-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