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The AAPG/Datapages Combined Publications Database
The use of fabric elements to classify specific shale lithotypes tentatively permits rapid qualitative evaluation of productive potential and interpretation of general depositional environments without recourse to detailed chemical and mineralogic characterization.
To evaluate the usefulness of subjective lithotype classification, 169 samples from the Lincoln 1637 cored well, classified into the four shale lithotypes of E. B. Nuhfer and R. J. Vinopal, were examined through parametric and nonparametric statistical tests performed on petrophysical and compositional data derived from the same samples. The lithotypes consisted of: (1) sharply-banded shale, (2) thinly laminated shale, (3) lenticularly laminated shale, and (4) nonbanded shale. Analytic parameters considered were: bulk density, matrix density, porosity, log density, sonic travel time, resistivity, gamma-ray log response, silt (by thin-section point counts), quartz, illite, pyrite, and 14 angstrom clays quantified relatively by X-ray diffraction, total sulfur by rapid LECO method, organ c matter by loss-on-ignition between 100 and 550°C, and an additional loss-on-ignition between 550 and 1,000°C. The data were first tested for normality by means of Kolmogorov-Smirnov and Shapiro-Wilkes tests and then for significant differences between lithotypes by means of both the analysis of variance and the nonparametric analog, the Kruskal-Wallis test.
The test results show that significant differences do exist between the specific lithotypes, and therefore, that classification by fabric elements does reflect real differences in rock properties. Fabric-element classification must precede more destructive physical and analytic tests so that this valuable information is not lost and so that later test results can be related back to specific rock types.
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