For any statistical model, many different realizations can be generated which all exhibit the same statistical properties. This trait is actually an advantage, since the uncertainties of the different scenarios can be studied by generating a large number of equally possible reservoir models. Obviously, their validity depends highly on the geological realism. Variogram Based For any two locations, the variogram as a function of distance relates to the statistical probability that the facies at these points differ. Any point of the reservoir gets a facies assigned such that the true facies is prescribed at known locations, e.g. along a borehole, while the statistics of the overall reservoir model approximates the chosen variogram.
Warm colors represent clean sands, while colder ones correspond to clays.
Object Based Using the object-based approach, the reservoir model is generated from objects that have some genetic significance rather than being built up one elementary pixel or voxel at a time as with the variogram approach. For each lithofacies, a geometric object is selected, e.g. a half-ellipsoid representing a river channel. A realization of the reservoir is generated by randomly placing these objects in the model until the prescribed overall proportions for the different lithofacies are attained. The geologic process response simulates the sedimentological processes which formed the reservoir in geologic time. Processes simulated include discharge of clastic sediments, transport, deposition, erosion, compaction, or subsidence.