Hydrocarbon Formation Mechanism In The Earth's Interior

Wansheng Xiao ( Mineralogy ) Directed by Prof. Huifen Zhang and Prof. Kenan WengAlthough the fact that hydrocarbon exists in the Earth's interior has widely been accepted, various kinds of standpoints still exist on its formation mechanism. On the basis of up-to-date achievements on the nature and behavior of supercritical water, this thesis combines the research of hydrocarbon formation mechanism in deep Earth with the study of mantle C-O-H fluids, and puts forward a new hypothesis that carbon-containing materials react with water to form hydrocarbon in deep earth. The author highlights the point that higher pressure and the existence of water are favorable for the formation and preservation of hydrocarbon. To verify this new mechanism, experimental research has been carried out on the reactions of carbon-containing materials with water to form hydrocarbon under mantle conditions with the pressure and temperature up to these in 200 km depth using diamond anvil cell (DAC). In the experimental process, changes in the samples were observed and photographically recorded using microscope, fluorescence spectrum, Raman spectrum and infrared absorption spectrum of the reacting systems were also determined in situ under high pressure. The results show that CH4-dominated hydrocarbons were produced along with CC>2 and sometimes, with other gases. In order to analyze the compositions of the trace gases produced in the experiments, this thesis designed a special sampling method for the DAC apparatus so that the gas samples could be measured using chromatography. All experimental results ofcarbon-containing materials-FkO systems at high pressure and temperature indicate that H2O participates in the hydrocarbon formation reactions, which provides hydrogen to form hydrocarbons and provides oxygen for CCh. Besides providing hydrogen resource to form hydrocarbons, H2O lowers the activation energy in the hydrocarbon formation reactions and plays a key role to destroy carbon rings, Si-C, and other covalent bonds in graphite (also aromatic hydrocarbons), moissanite and other minerals. Thermodynamic calculation results of some hydrocarbon formation reactions suggest that, higher pressure is favorable for the stability of hydrocarbon, and CO2 coexists stably with CRt under high-pressure conditions. Most of these calculation results are in agreement with the experimental results, but it can't explain the experimental results of calcite reacting with water to form hydrocarbons. This new kind of hydrocarbon formation mechanism of carbon-containing materials reacting with water or water-containing minerals under the Earth's mantle conditions can also improve our understanding of some phenomena in deep Earth, and provides a new path or idea to the exploration of some significant Earth scientific problems, such as the genesis of volcano, earthquake and other geological catastrophes.