Permeability estimation in three dimensions commonly suffers from inadequate horizontal data sampling. Thus, modeling the variogram in the horizontal plane and determining anisotropy ratios in the vertical direction is associated with substantial uncertainty. This uncertainty about spatial correlation of permeability is transferred into uncertainty in reservoir performance forecasting. Analog information, such as data borrowed from more extensively sampled fields or horizontal correlation measures derived from geologic process modeling, may be used to narrow this uncertainty. We present a compilation of published results of horizontal and vertical variograms of petrophysical parameters. A stepwise procedure describing a process to establish horizontal variograms for numerical geological modeling is developed based on the distinction between three different types of anisotropy. We also emphasize the challenge of meaningful combining data of varying volume support and the need for modeling decisions.

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