Effects of U-ore on the chemical and isotopic composition of products of hydrous pyrolysis of organic matter

Abstract

In order to investigate the impact of U-ore on organic matter maturation and isotopic fractionation, we designed hydrous pyrolysis experiments on Type-II kerogen samples, supposing that the water and water-mineral interaction play a role. U-ore was set as the variable for comparison. Meanwhile, anhydrous pyrolysis under the same conditions was carried out as the control experiments. The determination of liquid products indicates that the presence of water and minerals obviously enhanced the yields of C 15? and the amounts of hydrocarbon and nonhydrocarbon gases. Such results may be attributed to waterorganic matter reaction in the high-temperature system, which can provide additional hydrogen and oxygen for the generation of gas and liquid products from organic matter. It is found that dD values of hydrocarbon gases generated in both hydrous pyrolysis experiments are much lower than those in anhydrous pyrolysis. What is more, dD values are lower in the hydrous pyrolysis with uranium ore. Therefore, we can infer that water-derived hydrogen played a significant role during the kerogen thermal evolution and the hydrocarbon generation in our experiments. Isotopic exchange was facilitated by the reversible equilibration between reaction intermediaries with hydrogen under hydrothermal conditions with uranium ore. Carbon isotopic fractionations of hydrocarbon gases were somehow affected by the presence of water and the uranium ore. The increased level of i-C 4 /n-C 4 ratios for gas products in hydrous pyrolysis implied the carbocation mechanism for water-kerogen reactions.

Genesis and Geological Significance of Siderite in the First Member of the Nantun Formation of Dongming Sag, Hailar Basin

“…The formation of diagenetic siderite mainly reflects the active iron cycle process between water and sediments but cannot directly reflect the atmospheric CO 2 concentration [4,18,19]. In continental petroliferous sedimentary basins, carbonate minerals such as calcite and dolomite have a greater impact on the hydrocarbon generation of source rocks [27][28][29][30][31].…”

Carbon and hydrogen isotope fractionation for methane from non-isothermal pyrolysis of oil in anhydrous and hydrothermal conditions

“…On consideration of the additional hydrogen source from water, Seewald (2003) implied a greater gas potential in sedimentary basins. However, most hydrous pyrolysis of organic matters did not generate higher yields of hydrocarbon gases compared with anhydrous pyrolysis (Cai et al., 2017; Gao et al., 2014; Lewan et al., 1997). Although water–hydrocarbon reactions were observed at elevated temperature (Helgeson et al., 1993; Leif and Simoneit, 2000; Seewald, 2001), the effect of water on the generation of oil cracking gas (secondary gas) remains controversial (He et al., 2011, 2018a; Hesp and Rigby, 1973; Shuai et al., 2012).…”