热模拟实验甲烷碳同位素演化特征——兼析实验与自然条件下δC-R关系的差异

Evolution characteristics of methane stable carbon isotope in thermal simulation experiment:Discussion of δC-R relationship under experimental and natural conditions

薛罗 徐思煌 袁彩萍 刘晓霞 李松峰

Xue Luo Xu Sihuang Yuan Caiping Liu Xiaoxia Li Songfeng

中国地质大学(武汉)构造与油气资源教育部重点实验室, 武汉, 430074

Key Laboratory of Tectonics and Petroleum Resources of Ministry of Education, China University of Geosciences, Wuhan, Hubei 430074, China

对珠一坳陷古近系5个泥岩样品进行了热模拟实验,测定了热模拟甲烷碳稳定同位素值。研究发现,热模拟条件下甲烷碳稳定同位素在Ro为1.2%～1.3%之前是随着Ro的增大而减小,之后是随着Ro的增大而增大。用甲烷的碳同位素动力学模型来分析这种"先减小后增大"的规律,认为这是由13C甲烷(重甲烷)与12C甲烷(轻甲烷)的活化能差异造成的。对比发现,实验条件下与自然条件下甲烷碳稳定同位素与成熟度的关系有明显的差异性,认为这是由"成烃后作用"造成的,其中大规模气体运移将导致碳同位素分馏效果弱化。这对于气田的勘探有较好的指导意义,甲烷碳同位素重,说明气源岩成熟度高、运移体积规模大、大气藏勘探前景较好。

By means of thermal simulation experiment,5 mudstone samples from Palaeogene of the Zhu Ⅰ Depre-ssion have been tested.The studies of methane stable carbon isotope have shown that when Ro is below 1.2%-1.3%,methane stable carbon isotope decreases as Ro increases.When Ro is over 1.2%-1.3%,methane stable carbon isotope increases as Ro increases.The changing principle may be explained by the differences of activation energy between 13C methane(heavy methane)and 12C methane(light methane).Under experimental and natural conditions,the relationship between methane stable carbon isotope and Ro are different,which might be the results of "effects after hydrocarbon generation".Due to the effects,massive gas migration leads to the weaken-ing of carbon isotope fractionation.The studies may guide gas field exploration.Heavy methane carbon isotope indicates high-mature gas source rocks,large-scale migration and good prospects for gas exploration.

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https://doi.org/10.11781/sysydz201206617