Organic matter accumulations in the Santonian-Campanian (Upper Cretaceous) lacustrine Nenjiang shale (K2n) in the Songliao Basin, NE China: Terrestrial responses to OAE3?
Wei LiuMu LiuT. YangXin LiuTheodore R. ThemKun WangCongsheng BianQi'an MengYongxin LiXu ZengWenzhi Zhao
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Source rocks consist of diverse lithofacies whose composition can vary according to the depositional environment and the provenance of the sediment composing the rock matrix. In general, the rock fabric is made up of very fine grained, laminated and non‐laminated intervals composed of authigenic, detrital and biogenic minerals, together with organic matter consisting of kerogen, bitumen and pyrobitumen. During burial, exposure to elevated temperatures and pressures transforms the kerogen in a source rock into hydrocarbons. This transformation is tracked according to different stages of maturity, and results in increases in both the porosity and aromaticity of the kerogen within the rock and the formation of pyrobitumen. Little is understood about how these changes affect the mechanical properties of the organic matter contained in the rock, or to what degree this also influences bulk rock mechanical moduli. Understanding this relationship is essential to determine the production potential of a “source rock reservoir”, i.e. an unconventional self‐sourced reservoir from which oil and gas can be recovered through hydraulic fracturing of the rock matrix. Direct measurement of the mechanical properties of organic matter in relation to its thermogenic transformation, however, is a challenge due to the small size of the materials composing the rock fabric, especially with source rocks that are finely laminated. To explore this relationship, the results of a non‐destructive, dual‐mode examination of source rock maturity and kerogen mechanical properties is presented using Raman spectroscopy and Atomic Force Microscopy (AFM), respectively. The analysed samples (n = 5) are a Silurian source rock from the Middle East. The results demonstrate the ability to measure both mechanical moduli and thermal maturity of organic components in intact source rock samples which range in maturity from the catagenesis through the metagenesis stages i.e %R o from 0.6 to 1.6. These techniques provide an opportunity to examine kerogen, bitumen and pyrobitumen properties at the micro‐ and nano‐scale using intact rock samples without disruption of the rock fabric, which readily occurs with conventional bulk core analysis techniques.
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AbstractPyrolysis of source rocks and kerogen isolated from the source rocks, which was collected from the Tertiary in Zhahaquan Depression, Qaidam Basin, China, was performed in a confined system. The kinetics for generation of crude oil from the source rocks and kerogen were studied and the kinetic parameters applied to modeling generation from the Tertiary source rocks on the basis of burial and thermal history of the Zhahaquan Depression. The results of kinetic modeling show that the source rocks entered the "oil window" a little earlier than the kerogen, however, it could be ignored in the geological time, which means that the catalytic role of the salts on the role of hydrocarbon generation control is weak. In addition, the elemental analysis data of kerogen shows that the high sulfur content, which might be the main reason of immature-low mature oil generation in Tertiary salinization Qaidam Basin.Keywords: pyrolysiskineticssource rockskerogenQaidam Basin Additional informationFundingThis work was supported by the Chinese Academic of Sciences Key Project (No. XDB03020405, XDA05120204), the National Science Foundation (41172169, 41272147, 40672123), and Western Light Joint Scholars Project.
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