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University of Wollongong (1985)

The relationship between coals and dispersed organic matter in associated sediments in four basins in central Australia

Smyth, Michelle

Titre : The relationship between coals and dispersed organic matter in associated sediments in four basins in central Australia

Auteur : Smyth, Michelle

Université de soutenance : University of Wollongong

Grade : Doctor of Philosophy (PhD) 1985

Résumé
The major oil and gas fields in Australia produce from coal measure sediments, in contrast to the giant oil fields of the Northern Hemisphere which are associated with the marine rocks. The organic matter in the Australian fields is present both as coal seams and fragments of coaly material dispersed through the adjacent sediments. The purpose of this study is to determine whether the organic matter in the coal seams and as dispersed fragments is the same, different or systematically related. The type of organic matter in each may indicate that one is better, or the same, as a source for hydrocarbons.
The sedimentary sequences examined are those of the Permian- Triassic Cooper Basin, the Permian Pedirka Basin, the Triassic Simpson Desert Basin, and the Jurassic-Cretaceous Eromanga Basin, all of which are located in central Australia. In addition, the relationship of organic matter type to the depositional environment for the Permian sequence in the Cooper Basin was investigated. AH of the studies were carried out using reflected and transmitted light microscopic techniques for analyses of the organic matter.
Relationships have been found between the maceral types of the dispersed organic matter (DOM) and the maceral and microlithotypecompositions of the associated coals. Exinite (sporinite) DOM correlates with vitrinite and sporinite in the associated coals in the Cooper and Eromanga Basins, Exinite (cutinite) DOM correlates negatively with cutinite in the coal in the Simpson Desert Basin, Sporinite DOM correlates with vitrite plus clarite and intermediate, microlithotypes (duroclarite, clarodurite and vitrinertite) in the coals of the Cooper Basin. Vitrinite DOM correlates with vitrinite and the intermediate microlithotypes in associated coal in the Cooper Basin, and with resinite in the coal of the Eromanga Basin, Inertinite DOM, mostly inertodetrinite, correlates with inertodetrinite and durite plus inertite in the associated coals in the Cooper Basin. The microlithotype compositions of coals formed in association with a large lake environment are distinctly different from the microlithotype compositions of coals formed on the lower coastal plain and in areasdominated by coal swamps in the Permian of the Cooper Basin, Channel belt coals are also distinct in type from those of the lower coastal plain, upper coastal plain and areas dominated by coal swamps. Lower coastal plain coals can be differentiated from upper coastal plain coals on the basis of their microlithotype compositions. Those coals with the highest vitrite plus clarite contents have formed in channel belts and associated with large lakes. Coals with the highest durite plus inertite contents have formed in the areas dominated by coal swamps. Given that exinite is the coal maceral richest in hydrogen, and therefore the best material for generating hydrocarbons, the best source rocks in the Permian of the Cooper Basin are those which have formed in the large lake and channel belt environments. If inertinite has the least potential as a source for hydrocarbons, then the sequences in areas dominated by coal swamps have the lowest potential as source rocks for hydrocarbons.

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