| 氏名 |
Yessalina Svetlana
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| 論文題目 |
Origin and Timing of Expulsion of Hydrocarbons from theYufutsu Oil and Gas Deposits, Southern Hokkaido, Japan
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| 論文要旨 |
Seven petroleum samples from onshore and offshore wells, Akebono and
Yufutsu oil and gas deposits located in the Yufutsu area, southern
part of Hokkaido, have been analyzed to reveal the source organic
matter and the timing of expulsion. The crude oils mainly originated
from terrestrial source rocks, based on the presence of wide variety
of higher plant biomarkers. The source organic matter of either
gymnosperm and angiosperm origin is supposed to be a major contributor
of these hydrocarbons. Analyzed saturated fraction showed low
abundance of oleanane. However, detailed analysis of the aromatic
fraction, revealed occurrence of numerous aromatic triterepnoids of
angiosperm origin. Formation of these biomarkers is generally accepted
to take place in more oxic depositional environment of terrestrial
realm as opposed to the marine one. Detection of these biomarkers in
oils is of particular interest, as they have been rarely reported to
occur in crude oils. Furthermore it have to be mentioned that the
whole assemblage of these unique biomarkers in the Yufutsu oil and gas
deposits was found to be identical to that reported in the study of
Indonesian oils, which have been proposed to derive from source rocks
dominated by angiosperm plant material. These biomarkers are of
especial importance as they allowed to elucidate not only the source
organic matter type, but also the age and the source rocks
depositional environment. This further supports an idea that these
Paleogene- reservoired oils have been produced from the coal-bearing
sequences of Eocene age deposited in fluvial-deltaic environment. The
results of maturity determination based on aromatic hydrocarbons show
that investigated crude oils expelled from the source rocks in the
late stage of catagenesis, corresponding to vitrinite reflectance in
the range from 0.9 to 1.3 % Rc. Considering the temperature increasing
rate of the source rocks in Hokkaido Eocene sedimentary basin
temperature at the time of expulsion was estimated to be about 135 to
165 C.
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