Hydrocarbon Generation Potential And Molecular Evolution Characteristics Of The Terrestrial Shallow Sediments

The classical theory of late thermal degradation of kerogen has played a great guiding role in oil and gas exploration,but there is still a lack of research on hydrocarbon generation potential and product characteristics before organic is converted into kerogen.This paper selects the Quaternary strata of Shaobo Lake in Yangzhou City,Jiangsu Province.The 32 samples are selected to carry out the TOC,Rock-Eval and maceral analysis.The results show that the average abundance of the organic matter is 0.51% and the type of organic matter is type III.On this basis,the samples with TOC values of 1.23%(1.42?1.48 m),1.65%(1.56?1.62 m)and 0.86%(150.59?150.69 m)are selected for carring out the low-temperature hydrous pyrolysis,gas chromatography-mass spectrometry(GC-MS),GC and high resolution MS analysis.The results show that the main product in the low maturation stage is pyrolysis oil and the highest yield is 23 mg/g TOC,and the highest hydrocarbon gas yield is 32 ml HC/g TOC.At the maturity stage,the product is dominated by hydrocarbon gas,and the hightest yield is 176 ml HC/g TOC and the yield of pyrolysis oil is 18 mg HC/g TOC.As the thermal evolution maturity increase,the oil content gradually increases and the methane gas gradually enriches.At the mature stage,the component of the pyrolysis oil is similar to the kerogen thermal degraduation crude oil.Bulk Geochemical data and biomarker compositons indicated that the pyrolysis oil is mainly derived from plankton and bacterial.Heteroatom compounds in non-hydrocarbon fractions are dominated by oxygenate compounds,which are different from those in terrestrial crude oil.In general,terrestrial shallow type III organic matter can generate oil and gas,and the product properties are gradually similar to terrestrial crude oil during the thermal evolution.