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The AAPG/Datapages Combined Publications Database

Pacific Section of AAPG

Abstract


Environmental Concerns in the Petroleum Industry, 1989
Pages 159-181

Forensic Geochemistry in Characterization of Petroleum Contaminants in Soil and Water

I.R. Kaplan

Abstract

When crude or refined oil products enter soil, groundwater or an aqueous environment (river, lakes or ocean) they begin to be degraded by numerous microbiological or physical processes. The result of such changes is to alter the molecular composition of the product so that its source is unrecognizable. Numerous methods have been devised in the petroleum exploration industry to characterize source rock bitumens and reservoired hydrocarbons. A modification of these methods has been successfully applied to identify the source of the fugitive hydrocarbons.

The methods use different chemical classes for identification. For mildly altered products a detailed statistical comparison is made of the paraffinic or n-alkane distribution between C12-C35 for heavy products, C4-C7 for the gasoline range and C1-C5 for the gas range products. For highly altered products, a search is made for complex organic molecules which have undergone the least alteration. Among such groups are the long chain polycyclic aromatic hydrocarbons and the polyclic paraffinic hydrocarbons, frequently referred to as biomarks. The aromatic products often contain nitrogen or sulfur. The non-aromatic compounds have many isomeric forms which are characteristic of their sources. Elemental composition; especially sulfur, vanadium and nickel, for crude oil and lead or manganese for refined gasoline products can help identify sources. The isotopic ratio of 13C/12C and D/H have been shown to be very useful natural tracers for gasoline and heavy oil. The 34S/32S ratio may also be useful for heavy oils.


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