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The AAPG/Datapages Combined Publications Database

GCAGS Transactions

Abstract


Gulf Coast Association of Geological Societies Transactions
Vol. 46 (1996), Pages 474-474

Abstract: Advanced Surface Geochemical Interpretation With Case Studies

James M. Fausnaugh

ABSTRACT

A combination of statistics and compositional analysis is currently being used to test the validity of surface hydrocarbon anomalies. Once the hydrocarbon anomaly is detected a rigorous compositional analysis is undertaken to ascertain its source. Some of the techniques under investigation are Factor Analysis, Discriminant Analysis, diagnostic hydrocarbon ratios, and Pixler Plots.

Factor Analysis and Discriminant Analysis are used to detect any underlying structural relationships between variables. These statistical methods simplify the interpretation by reducing the number of variables to be used in the interpretation. The resulting factors are reclassified as a function of hydrocarbon composition. The extraction of various compositional structures can show the difference between reservoir and non-reservoir hydrocarbons. Compositional grouping based on molecular weight forms the bases of the interpretation. If thermogenic hydrocarbons are present, methane, ethane, and propane form one group while the heavier hydrocarbons form a separate distinct group. Non-reservoir hydrocarbons are comingled and do not exhibit specific relationships.

Hydrocarbon ratios have been used for many years to characterize reservoir attributes. Statistically processing the raw data prior to determining the ratios can yield information not readily apparent when using simple ratios.

Pixler plots show the relationship of methane to ethane, propane, butane, and pentane respectively. When plotted in graph form, these relationships, for any particular sample, may be representative of a producing or non-producing area or an oil bearing or gas bearing area. A more generalized compositional analysis is obtained by determining the slope and intercept of the line drawn through the coordinates of these ratios for each sample, which can then be plotted in map view.

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ACKNOWLEDGMENTS AND ASSOCIATED FOOTNOTES

Gallagher Research and Development Company, Lakewood, CO

Copyright © 1999 by The Gulf Coast Association of Geological Societies