氧化作用对气态烃组成和碳同位素组成的影响  

Influence of oxidation by minerals on proportional and carbon isotopic compositions of gaseous hydrocarbons

作　　者：于林平[1] 潘长春[1] 刘金钟[1] 傅家谟[1] 

机构地区：[1]中国科学院广州地球化学研究所有机地球化学国家重点实验室,广东广州510640

出　　处：《地球化学》2005年第3期269-277,共9页Geochimica

基　　金：国家自然科学基金(40473033);中国科学院知识创新工程领域前沿项目(GIGCX-04-08)~~

摘　　要：通过加水模拟实验,揭示了气态烃在被矿物氧化过程中分子组成和碳同位素组成的变化。实验结果表明,随着反应时间的延长,气态烃、非烃(H2、CO2、H2S)组成及碳同位素组成发生了明显且很有规律的变化。气态烃碳数越高,氧化速率越快,碳同位素变化(增重)越大。当氧化剂为赤铁矿或赤铁矿+硫酸镁时,CH4含量没有明显降低,δ13C值增重1‰～2‰;C2H6含量最后(288h)降低了约20%,δ13C值增重约3‰;C3H8含量最后降低了约50%,δ13C值增重约5‰;iC4H10含量在72h时即降低了约80%,氧化速率远高于nC4H10。非烃CO2的含量增加了1.26～1.71倍。当氧化剂为硫酸镁时,CH4含量明显增高,最多时增加了34.7%,δ13C值增重约8‰;C2H6含量在72h时降低了约14%,在144h时降低了约85%,δ13C值增重约24‰;C3H8含量在72h时降低了约65%,在144h时降低了98%以上;iC4H10和nC4H10在72h时即降低了90%以上。非烃CO2含量最多增加了1.86倍,H2S最多增加了9.62倍。这些实验结果对认识天然气藏在矿物氧化过程中分子组成和碳同位素组成的变化具有重要意义。Oxidation experiments on gaseous hydrocarbons under hydrous condition are carried out to reveal the proportional and carbon isotopic fractionationsduring oxidation by minerals. With the oxidation time increasing, the proportional and carbon isotopic compositions of gaseous hydrocarbons and non-hydrocarbons (H2, CO2 and H2S) varied substantially and systematically. A general variation trend is that, with the carbon number increasing, the oxidation rate and the carbon isotopic fractionation extent increase. In the cases when Fe2O3 or Fe2O3+MgSO4 are used as the oxidants, with the oxidation time increasing, the variations for the gas components include that, (1) the amount of methane appears unchanged while its δ13C value increases 1‰～2‰; (2) the amount of ethane finally decreases about 20%and its δ13C value increases about 3‰at 288 h; (3) the amount of propane finally decreases about 50%and its δ13C value increases about 5‰at 288 h; (4) the amount of iC4H10 decreases about 80%at 72h, with an oxidation rate much rapider than that of nC4H10; and (5) the amount of CO2 increases by 1.26～1.71 times. In the cases when MgSO4 is used as the oxidant, the variations are as follows: (1) the amount of methane increases substantially, about 34.7%at the most, and its δ13C value increases about 8‰; (2) the amount of ethane decreases about 14%at 72 h, and about 85%at 144 h,and its δ13C value increases about 24‰; (3) the amount of propane decreasesabout 65%at 72 h, and more than 98%at 144 h; (4) the amounts of iC4H10 and nC4H10 decrease more than 90%at 72 h; and (5) both the amounts of CO2 and H2S increased substantially, about 1.86 and 9.62 times, respectively, at the most. The results of this study are significant for understanding molecular and carbon isotopic variations of gas components in natural reservoirs during oxidation by minerals.

关 键 词：气态烃氧化作用 赤铁矿 硫酸盐热化学还原作用 H2S 碳同位素 

分 类 号：P593[天文地球—地球化学] P597[天文地球—地质学]