The main objective of reservoir characterization is to describe the features which influence the amount, position, accessibility, and flow of fluids through a reservoir. These features will be: The structural aspects (depth to the reservoir boundaries and inter-reservoir surfaces), faults (both seismically identifiable and sub-seismic faults), flow-units or facies bodies (position, orientation and size), and the spatial distribution of the relevant petrophysical parameters (permeability, porosity, saturations, …) within each flow-unit. Although some "hard" data from seismic and wells will be available, there is a definite stochastic element in all these features. Stochastic techniques are thus required to model them properly.

The paper reviews a number of techniques available for stochastic modeling of the above features: (marked point processes, Markov fields, truncated Gaussian fields and indicator kriging for modeling discrete events (flow-units, faults, barriers); Gaussian fields and indicator kriging for modeling property values (depths, fault transmissibility, petrophysical variables)). The different techniques can be mixed or combined to give a complete stochastic model of every relevant aspect of the reservoir. Several examples from the North Sea will be presented.

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