Molecular, Carbon And Hydrogen Isotopic Composition Of Organic Matter From Salt Lake Depositional Environment And Hydrocarbon-generation Characterization Of Sulfur-rich Kerogen

Many oil and gas are closely related to salt lake sedimentary basin in China, such as Jianghan Tertiary sedimentary basin. The geochemical characteristics of organic matter may be diverse at different sedimentary stage in salt lake deposition. A geological section in Xiaoban depression, Jianghan basin was selected in this paper to study the variation in biomarkers, carbon and hydrogen isotope composition, the pyrolysates of kerogen by Py-GC -MS. And also study on the pyrolysis mechanism of sulfur-rich kerogen by a closed system pyrolysis using kerogen with the addition of sulfur was carried out in this paper.1) The characteristics of biomarkers show different organic sources at different deposition stage. Alga was the mainly input of the source rocks during the carbonate depositional stage. High abundances of phytane, gammacerane, C35homohopane, dibenzothiophene, sulfur containing compounds, aryl isoprenoids, C40 isorenieratane and sulfur containing C40 isorenieratane in the samples in carbonate depositional stage indicate that source rocks were formed under anoxic depositional environment with stratified water column. Higher relative abundances of C21+ isoprenoids and squelane, triaromatic-sterane, benzohopane indicate more input of halophilic bacteria in chloride stage. Low content of sulfur containing compounds and the detection of dibenzofuran in the samples in chloride depositional stage show that source rocks were formed under relative oxic condition.2) 13C is richer in the source rocks deposited in the carbonate depositional stage than that in the chloride depositional stage, showing that different organic source input in different depositional stage or it is the increase of salinity that lead to the rich of 13C in the chloride stage. The hydrogen isotopes of the individual compounds show source rocks in Qianjiang formation, Xiaoban depression was deposited in salt lake sedimentary environment. Hydrogen isotopes show little difference among the samples from different depths which was interpreted as â‘  the hydrogen composition is mainly controlled by the big sedimentary environment. No obvious difference of the hydrogen composition was found in the source rocks deposited in different stage. â‘¡ source rocks in Xiaoban depression were perhaps deposited in deep-water saline lake environment during Eq3-Eq4 formation, not shallow-water environment because in the shallow-water deposition environment the evaporation of water will make D enriched in the organic matter.3) The pyrolysates of kerogen show source rocks were mainly derived from plankton, also including some bacteria and terrestrial soure input in Qianjiang formation, Xiaoban depression, Jianghan basin and were source from the stratified water column, anoxicdepositional environment. The depositional environment became more reducing from, from the carbonate to chloride depositional stage.4) A closed system pyrolysis was performed on Maoming oil shales kerogen(Type I ), compared to this kerogen with addition of sulfur ether and this kerogen with addition of sulphur. The results suggest that the existence of sulfur:(l) makes the kerogen generate more hydrocarbon yields;(2) makes the temperature of the maximum generation of heavy hydrocarbon (the Cis+ fraction) and the aromatics fraction lower;(3) accelerates the aromatization process. The pyrolysates of the kerogen with the addition of sulfur are similar to the heating products of the sulfur-rich kerogen in the literatures. It seems that the sulfur catalysis is also an important factor that makes the sulfur-rich kerogen generate low mature oil at earlier diagensis, except for the weakness of the C-S and S-S bonds. It does not show obvious carbon isotope fraction of gas and n-alkane in the presence of sulfur.