Experiments on the role of water in petroleum formation
- Geological Survey, Denver, CO (United States)
Pyrolysis experiments were conducted on immature petroleum source rocks under various conditions to evaluate the role of water in petroleum formation. At temperatures less than 350{degrees}C for 72 h, the thermal decomposition of kerogen to bitumen was not significantly affected by the presence or absence of liquid water in contact with heated gravel-sized source rock. However, at 330 and 350{degrees}C for 72 h, the thermal decomposition of generated bitumen was significantly affected by the presence or absence of liquid water. Carbon-carbon bond cross linking resulting in the formation of an insoluble bitumen (i.e., pyrobitumen) is the dominant reaction pathway in the presence of liquid water. This difference in reaction pathways is explained by the availability of an exogeneous source of hydrogen, which reduces the rate of thermal decomposition, promotes thermal cracking, and inhibits carbon-carbon bond cross linking. The distribution of generated n-alkanes is characteristic of a free radical mechanism, with a broad carbon-number distribution (i.e., C{sub 5} to C{sub 35}) and only minor branched alkanes from known biological precursors (i.e., pristane and phytane). The generation of excess oxygen in the form of CO{sub 2} in hydrous experiments and the high degree of hydrocarbon deuteration in a D{sub 2}O experiment indicate that water dissolved in the bitumen is an exogeneous source of hydrogen. The overall geochemical implication of these results is that it is essential to consider the role of water in experimental studies designed to understand natural rates of petroleum generation, expulsion mechanisms of primary migration, thermal stability of crude oil, reaction kinetics of biomarker transformations, and thermal maturity indicators in sedimentary basins. 163 refs., 11 figs., 14 tabs.
- OSTI ID:
- 585477
- Journal Information:
- Geochimica et Cosmochimica Acta, Journal Name: Geochimica et Cosmochimica Acta Journal Issue: 17 Vol. 61; ISSN GCACAK; ISSN 0016-7037
- Country of Publication:
- United States
- Language:
- English
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