attribute such as the permeability the permeability values evolve continuously from one point of the space to another in parallel a discrete realization can describe the spatial distribution of facies the various facies are identified by an indicator for example 1 for the reservoir facies and 2 for the non reservoir facies when switching from the reservoir facies to the non reservoir facies we have a discontinuity we directly shift from 1 to 2 it is also possible to extend the scope of the invention to a complex model comprising facies populated by a continuously varying attribute the first stage of the method according to the invention consists by statistical analysis in determining a random function characterizing the reference realization this analysis comprises for example an analysis of the mean of the variance and of the covariance function c of the random function within the scope of a particular embodiment of the method we choose to determine a random function characterizing the reference realization freed of the non stationary effect we therefore first identify a non stationary tendency if it exists for a continuous realization the non stationarity is assumed to be translated by a mean that varies in space for a facies realization it involves a variation of the facies proportions in space first let there be a continuous reference realization we assume that it is equivalent to the sum of two terms a mean non stationary and thus variable in space of low frequency and a perturbation stationary that can be characterized by a random function the two terms are separated from a filtering procedure the mean is extracted by.