Genetic mechanism of pyrolytically desorbed hydrocarbon

Abstract

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.

Keywords

• pyrolytically desorbed hydrocarbons
• genetic mechanism
• olefins
• organic matter
• thermal cracking