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

Heterogeneous reservoirs lead to serious discontinuities in production from well to well, whether caused by sedimentological or structural factors. Geostatistical methods, such as ordinary kriging, are useful both for assessing degree of heterogeneity and for drawing maps of production and initial potential. Because of small-scale spatial variability in production from heterogeneous reservoirs, conventional contour maps suffer from numerous closed contours and ill-defined trends, whereas maps of kriged estimates suffer from a lack of fine details because of the smoothing property of kriging. Indicator kriging uses multiple transforms based on selected cutoffs to model spatial variability. For each indicator variable, the practitioner computes variograms, fits a model, and computes kriged estimates representing the probability of exceeding the cutoff. Applied to cumulative production and initial potential of oil from wells in a Lower Mississippian sandstone in West Virginia, indicator kriging with three cutoffs showed the presence of distinct north-south trends and a major east-west discontinuity in production and potential. These trends could be related to similar anisotropies in the presence of interbedded shales and high-density zones within the reservoir, north-south oriented basement faults, and an east-west structural discontinuity.