Petrological and geochemical characterization of hydrogen-rich cody matter in the agur 1 drillhole, Negev, Israel

S. Feinstein, P. W. Brooks, T. Gentzis, Z. Aizenshtat, J. Slager

Research output: Contribution to journalArticlepeer-review

2 Scopus citations

Abstract

Five samples from Cretaceous and Jurassic organic-rich shale and coal layers in clastic intervals in the Agur 1 borehole (Negev, southern Israel) were analyzed in order to determine their genetic history, as well as their potential as a source for oil and gas. Analyses of the samples included elemental composition, various pyrolysis experiments and pyrolysis gas chromatography, organic solvent extraction, open-column liquid chromatographic fractionation, saturate fraction gas chromatography and combined gas chromatography-mass spectrometry, and detailed organic petrography using reflected white and fluorescent light microscopy. The results obtained suggest that the Cretaceous sample has a “normal” coaly composition and low maturation in the lignite range whereas the Jurassic samples have unique maceral and geochemical characteristics that reveal evolution through two major stages. In the first stage, terrestrially derived organic material was accumulated under partially oxidizing conditions forming coaly deposits. Primarily terrestrial origin and oxidizing conditions are indicated, for example, by the constituent macerals, abundance of reaction rims (mainly on vitrinite and resinite macerals), abundance of alkylbenzenes, ratio of pristane to phytane, and distribution of n-al-kane, sterance, and triterpane in the solvent extract of the samples. However, pulses of faster subsidence have resulted information of deeper lagoons. Consequently, coaly materials from the surrounding highs were eroded, transported, and redeposited within nearby lagoons. The transportation and redeposition were involved with selective removal of some of the humic substances, progressive bacterial degradation of some plant lipids, and further diagenesis under reducing conditions. The later modification resulted in enrichment of exinite, mainly bituminite, abundance offluo-rescent vitrinite (including particles with reaction rims), and the relatively high hydrogen content indicated by the elemental and RockEval analyses. These effects are particularly pronounced in the organic-rich shale and less in the coal. Abundance of microlayering texture in the organic materials suggests that deposition during the later phase took place in shallow water in a low energy environment. The later modification under reducing conditions resulted in a relatively high hydrogen content in contrast to what is commonly anticipated for terrestrial materials that were deposited originally in oxidizing conditions. RockEval pyrolysis S2 indicates that the studied samples have the potential to generate hydrocarbons. However, vitrinite reflectance, UV-fluorescence, Tmar, and sterane and triterpane isomerization ratios indicate an immature to marginally mature level, suggesting that the samples studied did not reach the major phase of oil generation. In addition, because of the unique composition of the organic materials, the major products anticipated upon generation are gas, aromatics, and oxygen-rich compounds.

Original languageEnglish
Pages (from-to)389-405
Number of pages17
JournalEnergy Sources
Volume13
Issue number3
DOIs
StatePublished - 1 Jan 1991
Externally publishedYes

Keywords

  • Biornarkers
  • Coal
  • Israel
  • Petrology
  • Rockeval

ASJC Scopus subject areas

  • Chemical Engineering (all)
  • Fuel Technology
  • Energy Engineering and Power Technology

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