Conditional simulation is a geos tat is tic al approach to generate multiple equiprobable distributions of a property with specified univariate and spatial attributes. These attributes are derived from sample data or inferred from external infor-mation. This paper evaluates the effectiveness of conditional simulation to describe distributions of porosity in a carbonate environment.

The reservoir studied produces from a dolomitized for-mation of complex lithology. The conditional simulation methods tested are the simulated annealing simulation (SAS) and the sequential indicator simulation (SIS). A validation procedure is introduced to compare observed and simulated porosity distributions and to quantify the quality of two- and three-dimensional conditional simulations. Results of three-dimensional validations indicate that SAS yields a good overall reproduction of observed porosity distributions. Comparisons of equiprobable two-dimensional distributions suggest that the quality of the porosity descriptions for SAS are slightly better than for SIS.

These results show that conditional simulation renders descriptions which capture variations of a property due to inherent geologic complexities. The major advantages of conditional simulation over traditional methods are: (l) it incorporates in a distribution of a property different degrees of variability for different directions, and (2) it accounts for uncertainties in the description.

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