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 C15+ and the amounts of hydrocarbon and non-hydrocarbon gases. Such results may be attributed to water-organic 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 δD values of hydrocarbon gases generated in both hydrous pyrolysis experiments are much lower than those in anhydrous pyrolysis. What is more, δD 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-C4/n-C4 ratios for gas products in hydrous pyrolysis implied the carbocation mechanism for water-kerogen reactions.
Highlights
IntroductionExperimental and field studies have demonstrated that the presence of water, minerals and catalytically active transition metal elements in sedimentary basins can influence petroleum generation and accumulation (Goldstein 1983; Huizinga et al 1987a, b; Pan et al 2009, 2010; Tannenbaum and Kaplan 1985a, b; Mango 1992; Mango and Joe 1997)
Organic and inorganic compounds coexist in most geological environments
We compared the chemical and isotopic compositions of thermogenic gas and oil generated during pyrolysis of Type-II kerogen with variation of EasyRo%, an index reflecting maturity, from 0.6% to 2.5%
Summary
Experimental and field studies have demonstrated that the presence of water, minerals and catalytically active transition metal elements in sedimentary basins can influence petroleum generation and accumulation (Goldstein 1983; Huizinga et al 1987a, b; Pan et al 2009, 2010; Tannenbaum and Kaplan 1985a, b; Mango 1992; Mango and Joe 1997). The classical hydrous pyrolysis system described by Lewan et al had verified that many organic reactions cannot occur without water (Mayer 1994), which plays an essential role in the process of petroleum generation, such as influencing the stability of crude oil and the secondary cracking of long-chain hydrocarbons (Lewan 1993, 1997).
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