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Abstract


 
Chapter from: CA 3: Stochastic Modeling and Geostatistics 
Edited by 
Jeffrey M. Yarus and Richard L. Chambers

Author:
Ricardo A. Olea

Methodology and Concepts


Published 1994 as part of Computer Applications 3
Copyright © 1994 The American Association of Petroleum Geologists.  All Rights Reserved.
Chapter 4

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Fundamentals of Semivariogram
Estimation, Modeling, and Usage
Ricardo A. Olea
Kansas Geological Survey
Lawrence, Kansas, U.S.A.

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ABSTRACT

The semivariogram is a measure of the rate of change with distance for attributes that vary in space. Semivariogram analysis is helpful in comparing such attributes and in designing their adequate sampling. In addition, the semivariogram is required in almost any geostatistical procedure for prediction away from control points.

Correct semivariogram estimation requires a thorough assessment of the sampling, variations in the mean, or geometry of the volume that may be associated to a measurement, and a sensitivity analysis of the semivariogram to variations in the azimuth. In the simplest case, the semivariogram is a scalar function of lag. Depending on the application, one may need to estimate the parameters for linear combinations of admissible semivariogram models, which is customarily done as a curve fitting to a tabulation by lag of estimated semivariogram values.

Numerical examples illustrate every stage in estimating and modeling a semivariogram.

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