Geochemical and biological marker assessment of depositional environments using Brazilian offshore oils |
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| Institution: | 2. Novosibirsk State University, ul. Pirogova 2, Novosibirsk, 630090, Russia;3. Institute of Oil and Gas Problems, ul. Oktyabr’skaya 1, Yakutsk, 677890, Russia;1. Department of Civil Engineering, Auburn University, Auburn 36849, AL, USA;2. Department of Science and Technology, Bryant University, Smithfield 02917, RI, USA;3. Department of Civil, Construction and Environmental Engineering, The University of Alabama, Tuscaloosa 35487, AL, USA;1. School of Geosciences in China University of Petroleum, Qingdao 266580, China;2. Laboratory for Marine Mineral Resources, Qingdao National Laboratory for Marine Science and Technology, Qingdao 266580, China;3. Research Institute of Petroleum Exploration and Development, Xinjiang Petroleum Administration Bureau, Karamay 841000, China |
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| Abstract: | A combined geochemical and molecular characterization of a wide selection of oils from the major Brazilian offshore basins has been undertaken. The elemental (sulphur, nickel and vanadium) and bulk (oAPI and δ13C) properties of each sample been considered, together with its molecular composition determined using liquid and gas chromatography, and quantitative biological marker investigations using gas chromatography-mass spectrometry for alkanes.The results reveal significant differences in the chemical features of the various oils which enable them to be divided into five groups. The distinction of the groups appears to reflect differences in the depositional environment of the source rocks of the oils. Each group is correlated tentatively with source rocks laid down in a specific depositional regime, namely lacustrine freshwater, lacustrine saline water, marine evaporitic, marine carbonate or marine deltaic. The diagnostic features that allow this classification are: the relative abundance and carbon number distributions of n-alkanes; pristane/phytane ratios; sulphur, nickel and vanadium contents; carbon isotope data; the absolute concentrations of hopanes and steranes, and their abundance relative to 4-methylsteranes and, also the occurrence and abundance of several specific biological markers, including 18α(H)-oleanane, gammacerane, β-carotane, tricyclic terpanes, higher acyclic isoprenoids, 28, 30-bisnorhopane and 25, 28, 30-trisnorhopane. This investigation shows the value of a combined geochemical and molecular approach in the assessment of the palaeoenvironment of deposition of the source rocks which gave rise to the oils. |
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