Diagenesis of ammonium during hydrocarbon maturation and migration, Wilcox Group, Louisiana, U.S.A.

L. B. Williams, B. R. Wilcoxon, R. E. Ferrell, R. Sassen

Research output: Contribution to journalArticle

63 Scopus citations

Abstract

As organic matter matures, N is released in the reduced form as NH4+ and substitutes for K+ in clay minerals. As oil forms, an abundance of N is generated, coincident with the formation of authigenic illite. This study suggests that NH4+ released from organic matter during maturation migrates through sandstones together with the pore fluids and volatile phases generated from the migrating crude oil. This causes anomalously high NH4+ substitution in authigenic illites. Fixed-NH4 concentrations in illite are a product of both hydrocarbon maturation and migration. Concentrations of fixed-NH4 from organic-rich mudstones in two Wilcox Group oil fields show a general increase with depth, coincident with increasing organic maturation. Reservoir sandstones containing crude oils have fixed-NH4 concentrations as much as two times those of the mudstones, when values are normalized to the quantity of clay minerals. Fixed-NH4 concentrations in the gaseous portion of the reservoir are three times as high. Two out of five sandstones from a dry hole adjacent to a producing oil field contain anomalously high (>2σ above mean) concentrations of fixed-NH4 with respect to total organic centent. This, together with a high Production Index and Hydrogen Index in those units, suggests that migrating hydrocarbons may have influenced the fixed-NH4 concentrations.

Original languageEnglish (US)
Pages (from-to)123-134
Number of pages12
JournalApplied Geochemistry
Volume7
Issue number2
DOIs
StatePublished - Mar 1992
Externally publishedYes

ASJC Scopus subject areas

  • Environmental Chemistry
  • Pollution
  • Geochemistry and Petrology

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