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Abstract: Use of NSO Compounds in Reservoir Heterogeneity Studies

Caroline Magnier, Alain Yves Huc

One aspect of reservoir geochemistry is to account for the composition variation of light hydrocarbons as it is prone to exhibit heterogeneities within a petroleum field. However there are specific cases in which such an approach cannot be directly applied due to lack of light hydrocarbons in the samples. In such instances, reservoir geochemistry analysis rely on the higher molecular weight compounds, and for example use the information contained in the NSO's. The latter have been known to contain genetic information useful in studies of oil/source rock correlations (Behar and Pelet 1985).

We propose an extent of this approach for reservoir geochemistry purposes which utilizes the information associated to NSO's. Such information can be obtained in two ways, by chemical or thermal degradation of the heavy fractions. Fingerprints of the released compounds can then be compared. NSO compounds of heavy sulfur rich oils which exhibited geochemical heterogeneities (biomarker based analyses) were chemically degraded. The released saturates (C15+) clearly confirmed two populations of hydrocarbons with the presence of biomarkers associated to specific depositional environments. NSO's were also thermally degraded by closed system pyrolysis. Important compositional differences appeared in the light hydrocarbons enabling the same characterization of two hydrocarbon populations.

If we assume that NSO compound properties are related to genetic causes and are likely to be least sensitive to contain alteration processes (biodegradation, waterwashing, etc...), the combined study of free LHC and those generated by pyrolysis of asphaltenes is a potential tool to be used in reservoir studies.

AAPG Search and Discovery Article #90956©1995 AAPG International Convention and Exposition Meeting, Nice, France