Primary cracking of algal and landplant kerogens: Kinetic models of isotope variations in methane, ethane and propane
Primary cracking of algal and landplant kerogens: Kinetic models of isotope variations in methane, ethane and propane
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DOI：
10.1016/0009-2541(95)00120-4
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发表时间：
1995-12
期刊：
影响因子：
3.9
通讯作者：
U. Berner;E. Faber;G. Scheeder;Dieter Panten
中科院分区：
文献类型：
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作者：
U. Berner;E. Faber;G. Scheeder;Dieter Panten
富含藻类的干酪根和木质岩的样品进行了开放式热解，模拟了在(测量)的成熟度范围0.3-5.4%的镜质组反射率范围内的一次裂解(温度：20-810°C，升温速度：5°C/分钟，氦流量：21毫升/分钟)。分析了热解过程中收集的气体的分子组成和甲烷、乙烷、丙烷的碳同位素比值。随着富藻干酪根成熟度的提高，产出的轻烃碳同位素比值增大。然而，来自木质岩的甲烷的碳同位素值随着成熟度的增加而显著反转，这表明生成甲烷的前体存在同位素不均一性。库克石甲烷的氢同位素值在−2 11~−84‰之间变化，而木质岩甲烷的氢同位素比值从−314增大到−16 4‰。利用热解实验数据建立了生烃动力学模型，并与瑞利蒸馏模型相结合，描述了有机质和轻烃之间的同位素分馏。干酪根与单个气体组分之间的碳同位素分馏系数高的是库克石(αCH4-Kuk=1.017，αC2-Kuk=1.009，αC3-Kuk=1.005)，低的是木质岩(αCH4-XYL=1.0042，αC2-XYL=1.003，αC3-XYL=1.001)。库克石的氢同位素分馏系数较低，而木质岩的氢同位素分馏系数较高(αCH4-KuK=1.1，αCH4-XYL=1.2)。天然气生成和同位素模型与热干酪根蚀变动力学模型相结合。计算结果与美国特拉华州和瓦勒维德盆地自然样品的测量数据进行了比较。
Samples of an algae-rich kerogen and a xylite were subjected to an open-system pyrolysis that allows a simulation of primary cracking (temperatures: 20 to 810°C, heating rate: 5°C/min, helium flow: 21 ml/min) within the (measured) maturity range 0.3 to 5.4% vitrinite reflectance. Gases collected during pyrolysis were analyzed for their molecular composition and the carbon isotope ratios of methane, ethane and propane. With increasing maturity of the algae-rich kerogen, we observe an increase of the carbon isotope ratios of produced light hydrocarbons. Carbon isotope values of methane derived from xylite, however, show significant inversions with increasing maturity, that indicate an isotopic inhomogeneity of the precursors from which methane is generated. Hydrogen isotope values of methane from Kukersite vary between −211 and −84‰, whereas, hydrogen isotope ratios of methane from xylite increase from −314 to −164‰. The data of the pyrolysis experiments have been used to develop kinetic models of hydrocarbon generation that are combined with Rayleigh-distillation models to describe the isotope fractionation between organic matter and light hydrocarbons. Carbon isotope fractionation factors between kerogens and individual gas components are high for Kukersite (αCH4-Kuk= 1.017, αC2-Kuk= 1.009, αC3-Kuk= 1.005) and low for xylite (αCH4-Xyl= 1.0042, αC2-Xyl= 1.003, αC3-Xyl= 1.001). Hydrogen isotope fractionation factors are lower for Kukersite and higher for xylite (αCH4-Kuk= 1.1, αCH4-Xyl= 1.2). Gas generation and isotope models are combined with kinetic models of thermal kerogen alteration. The results of the calculations are compared to measured data of natural samples from the Delaware and Val Verde basins (U.S.A.).