Variograms and Structural Analysis

This chapter describes how to calculate experimental variograms for the facies and how to fit models to them. As the codes chosen to represent the facies are purely conventional and have no physical meaning (except for their ordering), the only representative numbers we can use to compute experimental variograms are the facies indicators. (The relationship between the facies indicators and the underlying gaussian values is not one-to-one, so we cannot back transform the indicator values to get the values of the gaussians). There is a theoretical relation linking the variograms of the underlying gaussians and those of the indicators. Rather than invert it, we use an indirect iterative procedure to fit a variogram model. But first, we show how to calculate the experimental variograms for the facies indicators.