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A study of maturation and chemical correlation of petroleum from the Carnarvon basin of Western Australia

Woodhouse, Garry (1979) A study of maturation and chemical correlation of petroleum from the Carnarvon basin of Western Australia. PhD thesis, Murdoch University.

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A new parameter which is a quantitative and sensitive indicator of the level of thermal maturity of organic matter contained in sediments was established. This parameter, termed the PAP value, is a measure of the percentage of aromatic protons in the aromatic fraction of sediment extracts. A regular increase in the PAP value with increased sediment temperature was observed for sedimentary sequences from a range of geographical locations along the Western Australian coastline. Pyrolysis of immature organic matter for increasing times at 300°C showed that the parameter is largely time and temperature dependent. Application of the new maturity indicator for comparing the levels of thermal maturity of crude oils and source rock extracts is discussed.

A chemical correlation study was carried out between Windalia oil, which is a commercial accumulation located in a reservoir of Cretaceous age at Barrow Island, Western Australia, and the hydrocarbons extracted from 37 Cretaceous sediment samples. The sediment samples were recovered from different stratigraphic levels in seven wells on and around Barrow Island. The formations most likely to contain the source beds for Windalia oil were assessed. Parameters used were (i) carbon isotope ratios, (ii) pristane/phytane ratios, (iii) a series of isoprenoid to n-alkane ratios, (iv) composition of the saturated fraction, (v) n-alkane distributions, and (vi) carbon preference indexes. A new correlation parameter, namely the ratio of (pristane plus n-heptadecane) to (phytane plus n-octadecane), is proposed. The influence of thermal maturation on several of the correlation parameters was investigated by pyrolising source rocks at 300°C for varying times. The changes observed in these experiments were used to infer the effects which thermal maturation processes have on these correlation parameters. The possibility that Windalia oil has been bacterially altered is discussed.

A series of pyrolysis experiments was carried out to assess the influence of processes other than temperature on maturation. The effect of variables related to the inorganic sediment matrix including (i) properties of the surface-active minerals, (ii) proton availability, (iii) concentration of elemental sulphur, and (iv) water content are reported. The influence of the composition of the soluble organic matter on maturation was also investigated. The effect of each variable on the rate of maturation during pyrolysis was monitored by measuring the rate of change of the PAP value. Proton availability and the concentration of nitrogen, sulphur and oxygen containing compounds in the soluble organic matter were observed to have the greatest influence on maturation. The implications of these results for natural geological systems is discussed.

A mechanism for the formation of Windalia oil is proposed. This mechanism accounts for the unusual combination of chemical and physical characteristics of this crude oil.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): School of Mathematical and Physical Sciences
Notes: Note to the author: If you would like to make your thesis openly available on Murdoch University Library's Research Repository, please contact: Thank you.
Supervisor(s): Alexander, Robert, Davidson, Lawrence and Giles, Dion
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