Spatial Statistics of Permeability Data from Carbonate Outcrops of West Texas and New Mexico: Implications for Improved Reservo

Abstract
This report presents a statistical analysis of outcrop-permeability data for quantifying spatial patterns of petrophysical heterogeneity in carbonates that are difficult or impossible to observe in the subsurface. In the study, workers made permeability measurements using plug samples and mechanical field permeameters (MFP) from Permian and Cretaceous shallow-water platform carbonate outcrops in West Texas and New Mexico. The report includes a detailed discussion of factors affecting the accuracy of the measurements and the portability of resulting spatial statistics to subsurface studies. The permeability data from these carbonate outcrops vary by two to five orders of magnitude, much of the variation occurring within distances of a few feet or less in single rock-fabric units. This short-range variability, present in every outcrop, composes most of the overall variance in each case. It has weak spatial correlation that can be modeled by using semivariograms having asymptotic power-law behavior at small lags. Avariety of longer range features were also observed, including (1) vertical trends within grainstone bodies, (2) vertical average permeability contrasts between grainstone bodies, (3) 140- to 180-ft lateral periodicities within high-frequency cycles, and (4) lateral trends at scales ranging from several hundred to several thousand feet in high-frequency cycles. The longer range features, composing a smaller fraction of the overall variability, may require careful analysis to detect. They can, however, have a significant effect on fluid displacement, and special attention should be given to modeling them in reservoir-performance predictions.
Authors
James W. Jennings, Jr.
Citation

Jennings, J. W., Jr., 2000, Spatial Statistics of Permeability Data from Carbonate Outcrops of West Texas and New Mexico: Implications for Improved Reservoir Modeling: The University of Texas at Austin, Bureau of Economic Geology, Report of Investigations No. 258, 50 p.

Code
RI258
ISSN
2475-367X
Number
258
Number of figures
31
Number of pages
50
Publisher
The University of Texas at Austin, Bureau of Economic Geology
Series
Report of Investigation
Year
2000