磁铁矿对有机质生烃及同位素分馏的影响  

The effect of magnetite on the products and isotopic fractions of gaseous hydrocarbons

作　　者：蔡郁文[1,2,3] 张水昌[2,3] 何坤[2,3] 米敬奎[2,3] 张文龙[2,3] 王晓梅[2,3] 王华建[2,3] 吴朝东[1] 

机构地区：[1]北京大学地球科学与空间科学学院,北京100871 [2]中国石油勘探开发研究院,北京100083 [3]中国石油天然气股份有限公司油气地球化学重点实验室,北京100083

出　　处：《天然气地球科学》2017年第2期331-340,共10页Natural Gas Geoscience

基　　金：国家油气专项"高过成熟阶段天然气生成机理与源灶有效性评价"(编号:2016ZX05007001);中国石油天然气股份有限公司"深层油气勘探开发理论认识与技术集成"项目(编号:2014D-3209)联合资助

摘　　要：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。In this paper,the influences of iron-bearing minerals on gas generation and isotopic fractionation of organic matters was studied by hydrous pyrolysis of a type-II kerogen of low maturity in the presence or absence of Fe3 O4.Quantitative determination of the gas products generated during the experiments indica- ted that the addition of Fe2O4 would lower the yields of gaseous hydrocarbons, H2 and H2 S,whereas exerting little influence on the yields of CO2.Carbon isotopic analysis revealed that when Fe3O4 is added to the reaction system,the carbon isotope of methane was not significantly affected, however, the isotopic values of both ethane and propone showed increase to different degrees.In contrast,the hydrogen isotopic values of the gaseous products in the presence of iron-bearing mineral were more depleted, and the reduction of methane and the ethane were 5‰-50‰ and 24‰-40‰, respectively. Likewise, the isotopic analysis of the residues showed similar trends with the gas products, which is the lighter hydrogen isotope values in the experiments with Fe304 ,and there are no obvious differences of carbon isotope with or without Fe2O4.Ad- ditionally, H/C elemental ratios of the residues decreased at a slower rate and exhibited higher values in the cases of iron-bearing mineral added experiments.The above results indicated that different reaction systems are of different reacting mechanisms.When Fe2O4 is absent,the reaction system operates in the cationic reacting mode. However, when Fe3O4 is added to the reaction system, cationic reactions were inhibited, thus resulting in the reduction of gas generation,and there exists indirect hydrogenation controlled by the pres- ence of hydrogen.

关 键 词：气态烃 四氧化三铁(Fe3O4) 有水热解 碳同位素组成 氢同位素组成 

分 类 号：TE122.113[石油与天然气工程—油气勘探]