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对一个低熟Ⅱ型干酪根分别开展了有、无四氧化三铁(Fe_3O_4)条件下的有水热解实验,旨在探讨含铁矿物对有机质生烃及同位素分馏的影响。气体产物的定量结果表明,Fe_3O_4的加入一定程度上降低了烃类气体、H_2和H_2S产率,对CO_2产率影响不大。稳定碳同位素的分析结果表明,相同热演化程度下。干酪根有水和水+Fe_3O_4条件下热解生成甲烷的碳同位素比值差异不大,但后者生成的乙烷和丙烷的碳同位素值明显偏高。同时,Fe_3O_4的加入明显抑制了气态烃中D的富集。在水+Fe_3O_4条件下,甲烷氢同位素值的偏低幅度可达5‰~50‰,乙烷可达24‰~40‰。2种热解体系固体残余物碳同位素无明显差异,水+Fe_3O_4体系中,固体有机质的氢同位素值低于有水体系。同时,Fe_3O_4的加入抑制了有水热解过程中干酪根H/C的降低。表明有水和水+Fe_3O_4热解体系中水—有机质的反应机制有一定的差别,前者为正离子反应,后者由于Fe_3O_4的存在这一反应受到了抑制,造成气体产率偏低,并存在H_2的间接加氢作用。
A pyrolysis experiment was carried out on a low-maturity type II kerogen with and without Fe 3 O 4. The aim was to investigate the effect of iron-bearing minerals on hydrocarbon generation and isotopic fractionation of organic matter. Quantitative analysis of gas products showed that the addition of Fe 3 O 4 reduced the yield of hydrocarbon gases, H 2 and H 2 S to a certain extent, and had little effect on the yield of CO 2. The results of stable carbon isotope analysis show that under the same degree of thermal evolution. There was no significant difference in the carbon isotope ratio of methane generated by pyrolysis in kerogen with water and water + Fe_3O_4, but the carbon isotope values of ethane and propane generated by the latter were obviously higher. Meanwhile, the addition of Fe 3 O 4 significantly inhibits the enrichment of D in gaseous hydrocarbons. Under the condition of water + Fe_3O_4, the hydrogen isotope value of methane can be as low as 5 ‰ ~ 50 ‰ and that of ethane up to 24 ‰ ~ 40 ‰. There was no significant difference in carbon isotope between two pyrolysis system solid residues. In the water + Fe_3O_4 system, the hydrogen isotope value of solid organic matter was lower than that of the aqueous system. At the same time, the addition of Fe 3 O 4 inhibited the reduction of kerogen H / C during hydrothermal pyrolysis. The results show that there is a certain difference in the reaction mechanism of water and organic matter in water and water + Fe_3O_4 pyrolysis system. The former is a positive ion reaction and the latter is suppressed due to the presence of Fe_3O_4, resulting in low gas yield and existence H 2 indirect hydrogenation.