热释烃成因机理初探

Genetic mechanism of pyrolytically desorbed hydrocarbon

在油气化探技术研究中,热释烃测试数据具有烯烃含量比同碳数烷烃高、异构烷烃含量比同碳数正构烷烃高的反常特征,且这种特征随着热释温度的升高而更加明显。然而油气源及地表样品中的酸解烃、顶空间轻烃、游离烃、水溶烃都不具有这样的特征。有学者从不同角度对热释烃的反常特征加以解释,但都没有考虑样品所含有机质在真空和加热状态下会不会裂解、重排而生成烯烃的问题。依据3个地区地表土壤样品热释温度实验,根据其热释烃与有机碳相关性研究,并分别结合树叶有机质、土壤有机质热生烃实验结果,推断土壤样品中的热释烃成因机理为化学吸附轻烃的解吸叠加有机质的热裂解。热释温度160℃以下的热释烃主要为化学吸附轻烃的解吸,而热释温度160℃以上的热释烃主要为土壤中的有机质在真空条件下的热裂解。地热田的热作用可以促进围岩中有机质成烃,在一定程度上使有机质含量降低、轻烃含量增加,可据此进一步研究热释烃的地热指示意义。

In the geochemical exploration for oil and gas,the test data of pyrolytically desorbed hydrocarbons have the abnormal characteristics that the relative content of olefins is higher than that of alkanes with the same carbon number,and the relative content of isoparaffins is higher than that of normal alkanes with the same carbon number,and this feature becomes more obvious with the increase of temperature of pyrolytical desorption.On the other hand,the acid hydrolyzed hydrocarbons,headspace light hydrocarbons,free hydrocarbons,and water-soluble hydrocarbons in oil and gas sources and surface samples do not have such feature.The abnormal characteristics of pyrolytically desorbed hydrocarbons have been previously explained from different aspects,but whether the organic matters contained in the samples will crack and rearrange to generate olefins under vacuum and heating conditions has not been considered.Some experiments of pyrolytical desorption temperature of surface soil samples from three regions were carried out.The correlation between pyrolytically desorbed hydrocarbons and organic carbon was discussed.Combined with the pyrolytical desorption experiments of organic matter in leaf and soil,it was inferred that the pyrolytically desorbed hydrocarbons in soil samples mainly came from the desorption of chemically adsorbed light hydrocarbons(below 160℃)and the thermal cracking of organic matter(above 160℃).The thermal action of geothermal field can promote the hydrocarbon generation of organic matter in surrounding rocks,and to a certain extent,reduce the content of organic matter and increase the content of light hydrocarbons,which can be used for further study of geothermal indicating significances of pyrolytically desorbed hydrocarbons.